RU2196869C2 - Method of producing gas-bearing formation drilling-in - Google Patents

Abstract

FIELD: drilling of gas wells with regulation of hydrostatic pressure in wellbore; applicable in drilling-in large-thickness overpressed formation. SUBSTANCE: method includes calculation of drilling mud minimal density in initial stage of drilling-in; determination of hydraulic losses in well annular space; building up of wellhead initial pressure to rated value; determination of gas-saturation permissible limits of drilling mud; drilling of the first interval and next interval of producing formation for controlled time with continuous monitoring of pressure in pipes and flow rate of drilling mud at well outlet. In the course of drilling of the first interval, when pressure in pipes remains invariable or reduces with simultaneous increase of drilling mud flow rate at well outlet, actual gas saturation of drilling mud is determined and compared with permissible limits, and if they equal each other, drilling of the first interval is continued by increasing wellhead pressure to maximum permissible value; and drilling is ended. When actual gas content in drilling mud exceeds the permissible limits, drilling is discontinued, formation fluid is washed out, maximum density of drilling mud is corrected, wellhead pressure is built up to maximum permissible value and drilling of formation is ended. When actual gas content in drilling mud does not attain limit value, drilling of the first and subsequent intervals is continued with initial wellhead pressure and with monitoring the pipe pressure. At the first interval, permissible limit pressure drop in pipes is determined, and, if actual pipe pressure drop is equal to permissible limits, drilling of next intervals is continued with increase of wellhead pressure to maximum permissible value, and drilling of formation is ended. In case of absence of gas inflow, i.e. at constant pressure in pipes and flow rate of drilling mud at well outlet, rated pressure differential is built up for tapped interval. Drilling is continued until increase of drilling mud flow rate at well outlet, and drilling program provided for drilling of the first interval and for the subsequent intervals is repeated with corresponding change of drilling parameters of the first interval with those of tapped interval. Drilling program is based on mathematical computations of actual data on drilling. EFFECT: improved quality and higher safety of formation drilling-in. 3 dwg, 1 ex

Description

 The invention relates to the mining industry, namely to drilling gas wells with the regulation of hydrostatic pressure in the wellbore, and can be used when opening formations of high power with abnormally high reservoir pressures (AAP).

Analysis of the current level of technology showed the following:
There is a known method of opening a productive gas-bearing formation by drilling under the conditions of AAP, according to which control the flow of gas into the well is carried out (see RF patent 2081993 from 07.22.93 according to class E 21 B 21/08, 47/00, published in OB 17, 1997). Control includes the creation of hydraulic pressure pulses at the bottom or wellhead and registration of pressure signals at the wellhead in pipes and annulus. The equilibrium state in the well is maintained by increasing the flow rate and / or density of the flushing fluid until the calculated difference in the arrival time of the pressure signals at the wellhead in a conventional flushing fluid and a gas-liquid mixture is achieved.

где ρ_o - минимальная плотность промывочной жидкости в начальный момент вскрытия, кг/м³;
g - ускорение свободного падения, м/с²;
Н_к - глубина залегания кровли продуктивного пласта, м;
Р_пл - проектная величина пластового давления, Па;
[Р_y] - технологически достаточное давление устьевого оборудования при бурении, согласно условию [P_y]≤Р_пл-P_min, Па,
где P_min - давление столба промывочной жидкости наименьшей плотности на глубине Н_к, обеспечивающей технологический эффект, Па;
S_заб - площадь забоя, м² ;
v_м - механическая скорость проходки, м/с;
m - коэффициент пористости породы;
z - коэффициент сжимаемости газа;
Р_o - атмосферное давление, Па;
Q - производительность насосов, м³/с.The disadvantage of this method is the poor penetration and a high probability of emergency situations. The low quality of the opening of the formation is caused by the deterioration of the reservoir properties of the bottomhole zone of the formation due to the penetration of the filtrate of the heavier flushing fluid in the process of regulating the bottomhole pressure, and emergency situations arise as a result of insufficiently operative measures to control the gas saturation of the flushing fluid (control at the mouth is fraught with the possibility of disturbing the equilibrium state in wellbore until the gas-liquid mixture exits) and downhole pressure control (increase in flow ode and / or wash fluid density);
as a prototype, we took a method of opening a productive gas-bearing formation by drilling (see RF patent 2148698 from 07.14.98, class E 21 B 21/08, published in OB 13, 2000). According to the method, the wellhead is sealed and at the initial opening moment, the minimum density of the flushing fluid is calculated by the formula

where ρ _o - the minimum density of the flushing fluid at the initial opening, kg / m ³ ;
g is the acceleration of gravity, m / s ² ;
N _to - the depth of the roof of the reservoir, m;
P _PL - design value of reservoir pressure, Pa;
[P _y ] - technologically sufficient pressure of the wellhead equipment during drilling, according to the condition [P _y ] ≤P _PL -P _min , Pa,
where P _min is the pressure column of the washing liquid of the lowest density at a depth of N _to provide a technological effect, Pa;
S _Zab - the area of the face, m ² ;
v _m - the mechanical speed of penetration, m / s;
m is the coefficient of porosity of the rock;
z is the gas compressibility coefficient;
P _o - atmospheric pressure, Pa;
Q - pump capacity, m ³ / s.

In addition, hydraulic losses are determined in the annular space of the well, and for drilling the first interval of the reservoir, the initial wellhead pressure is adjusted to a value determined by the formula
P _y1 = [P _y ] -P _kn , (2)
where P _y1 - pressure at the mouth at the initial opening, Pa;
P _KP - hydraulic pressure loss in the annular space, Pa.

где P_y1 - давление на устье для вскрываемого i-го интервала, где i=2,... ,n, Па;
h_j - вскрытый интервал бурения, где j=1,...,n, м.The drilling of both the first and subsequent intervals is carried out for the control time for the first interval, determined by the formula
t ₁ = (H _to • S _kp ) / Q, (3)
where t ₁ is the control drilling time of the first interval, s;
S _KP - the cross-sectional area of the annular space, m ² ,
at the same time, the pressure in the pipes is constantly monitored and, in the absence of gas inflow (constant pressure in the pipes), they create depression on the formation by successively lowering the wellhead pressure to a value determined by the dependence

where P _y1 is the pressure at the mouth for the opened i-th interval, where i = 2, ..., n, Pa;
h _j - open drilling interval, where j = 1, ..., n, m

In the event of a decrease in pressure in the pipes, the process of deepening and flushing the well is stopped. The well is “closed” and the actual reservoir pressure is determined by the pressure in the pipes and the minimum density of the flushing fluid is adjusted. The formation fluid is washed out and the depression in the formation roof is brought to a safe value by creating wellhead pressure, the value of which is determined by the formula
P _y = P _yi - (P _pl.f -P _pl ), (5)
where P _y is the pressure at the mouth to open the remaining part of the reservoir, ai = n-1, Pa;
R _pl.f - the actual reservoir pressure, Pa.

 Next, the pressure in the pipes is measured and this value is maintained during the subsequent drilling to the bottom of the formation, controlling wellhead pressure.

 The disadvantage of this method is the reduced quality of the formation and the likelihood of emergency situations. Poor reservoir penetration is caused by a lower degree of reservoir penetration in terms of depression power, which is determined by the absence of gas inflow by this method, while drilling in the depression in the case of safe (maximum permissible) gas inflow is not provided, as well as increased repression to the bottom of the reservoir as a result of minor depression on the roof. Possibility of emergency situations, i.e. opening safety is associated with limited control over gas inflow in one parameter - reducing the pressure in the pipes, which does not always pay off, especially when drilling deep wells, when intensive expansion of gas occurs in the upper part of the wellbore.

The technical result that can be obtained by carrying out the invention is as follows:
- improves the quality of the opening of the reservoir by increasing the degree of opening of the reservoir in capacity for depression, reducing repression on the bottom of the formation, which ensures maximum preservation of reservoir properties of the formation;
- increases the safety of drilling through the efficiency of detection at an early stage of gas inflow into the well.

где [a₁] - предельно допустимое газонасыщение промывочной жидкости, приведенное к нормальным условиям (н.у.);
а_{выб 1} - допустимое газонасыщение промывочной жидкости, соответствующее условию начала выброса и приведенное к н.у.;
а_{уст 1} - допустимое газосодержание промывочной жидкости, обеспечивающее устойчивость стенок скважины и приведенное к н.у.;
[Р_ymax] - максимально допустимое давление на устье скважины, определяемое технической характеристикой устьевого оборудования (вращающегося превентора, дросселя), Па;
P_з - давление в скважине на глубине залегания кровли продуктивного пласта, равное сумме гидростатического и гидродинамического давления в кольцевом пространстве на глубине залегания кровли пласта и давления на устье скважины, Па;
Т_о, Т_з - температура промывочной жидкости на устье и на забое соответственно, К;
z_o - коэффициент сжимаемости газа в нормальных условиях;
ΔР_max - максимально допустимая депрессия на стенки скважины в пределах 10-15% эффективных скелетных напряжений, т.е. разницы между горным и поровым давлением пород (Правила безопасности в нефтяной и газовой промышленности. Москва. 1998 г., п. 2.7.3.5), Па;
ρ_г - плотность газа при атмосферном давлении соответственно, кг/м³;
α_T - коэффициент растворимости газа при нормальных условиях и средней температуре промывочной жидкости, Па^-1;
причем наряду с отслеживанием давления в трубах дополнительно отслеживают расход промывочной жидкости на выходе из скважины и в процессе бурения первого интервала в случае постоянства или снижения давления в трубах при одновременном увеличении расхода промывочной жидкости на выходе из скважины определяют фактическое газонасыщение промывочной жидкости по формуле

при этом

P_з=P_у1+H_к•grP_с,
grP_c = gρ_o+P_кп/H_к,
ΔP_з = P_з-ΔP_т1;
ΔP² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{пл}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{з}}$ ,
P(h, t_б)=P_у1+h•grP_с-ΔP_т1•(1-h/t_бv_кп),
b=S_заб•v_м•m•z,
α_з = α_т•Q
где а_{ф 1} - фактическое газонасыщение промывочной жидкости, приведенное к н.у.;
V_н.у.(t_б) - объем газа в скважине, поступивший за счет переменной депрессии и с выбуренной породой за время бурения, приведенный к н. у., м³.The technical result is achieved using a known method, including sealing the wellhead and at the initial opening moment, calculating the minimum density of the flushing fluid according to formula (1), determining hydraulic losses in the annular space of the well, and for drilling the first interval of the reservoir, bringing the initial wellhead pressure to a value determined by the formula (2), drilling of both the first and subsequent intervals, for the control time for the first interval, determined by the formula (3), with a constant from by caking the pressure in the pipes and in the absence of gas inflow, creating a depression on the formation by successively lowering the wellhead pressure to a value determined by dependence (4), in which at the initial opening moment the maximum allowable gas saturation of the flushing fluid is additionally determined by the expression
[a ₁ ] = min {a _{choice 1} , a _{mouth 1} }, (6)
wherein

where [a ₁ ] is the maximum allowable gas saturation of the washing fluid, reduced to normal conditions (nos);
and _{choice 1} is the permissible gas saturation of the flushing fluid, corresponding to the condition for the onset of emission and reduced to nu .;
and _{mouth 1} - the permissible gas content of the flushing fluid, ensuring the stability of the walls of the well and reduced to NU .;
[P _ymax ] - the maximum allowable pressure at the wellhead, determined by the technical characteristics of the wellhead equipment (rotating preventer, throttle), Pa;
P _s - pressure in the well at the depth of the roof of the productive formation, equal to the sum of hydrostatic and hydrodynamic pressure in the annular space at the depth of the roof of the formation and pressure at the wellhead, Pa;
T _about , T _s - the temperature of the flushing fluid at the mouth and at the bottom, respectively, K;
z _o - gas compressibility coefficient under normal conditions;
ΔР _max - the maximum allowable depression on the well walls within 10-15% of the effective skeletal stresses, i.e. differences between rock and pore pressure of rocks (Safety rules in the oil and gas industry. Moscow. 1998, p. 2.7.3.5), Pa;
ρ _g - gas density at atmospheric pressure, respectively, kg / m ³ ;
α _T is the solubility coefficient of the gas under normal conditions and the average temperature of the washing liquid, Pa ^-1 ;
moreover, along with monitoring the pressure in the pipes, the flow rate of the flushing fluid at the exit from the well is additionally monitored, and during drilling of the first interval in case of constant or decreasing pressure in the pipes while increasing the flow rate of flushing fluid at the exit of the well, the actual gas saturation of the flushing fluid is determined by the formula

wherein

P _s = P _y1 + H _to • grP _s ,
grP _c = gρ _o + P _kp / H _k ,
ΔP _s = P _s -ΔP _t1 ;
ΔP ² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{pl}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{s}}$ ,
P (h, t _b ) = P _y1 + h • grP _s -ΔP _t1 • (1-h / t _b v _kp ),
b = S _zab • v _m • m • z,
α _s = α _t • Q
where a _{f 1} - the actual gas saturation of the washing fluid, reduced to NU .;
V _n.a. (t _b ) - the volume of gas in the well, received due to a variable depression and with cuttings during drilling, reduced to N. at., m ³ .

где P_y(t) - текущее создаваемое устьевое давление, Па;
t_п - время, в течение которого осуществляется повышение давления на устье, мин;
t - текущий момент времени повышения давления на устье, мин,
и при этом давлении завершают бурение до подошвы продуктивного газоносного пласта, при условии а_ф1 > [a₁] останавливают бурение, определяют фактическое пластовое давление, вымывают пластовый флюид, корректируют минимальную плотность промывочной жидкости по формуле

где ρ - откорректированная минимальная плотность промывочной жидкости, кг/м³,
доводят устьевое давление до максимально допустимого давления устьевого оборудования, и при этом давлении завершают бурение до подошвы продуктивного газоносного пласта, и при условии а_ф1 <[a₁] продолжают бурение как первого, так и последующих интервалов с начальным устьевым давлением и отслеживают давление в трубах, причем на первом интервале определяют предельно допустимое снижение давления в трубах по формуле

где [ΔP_{т 1}] - предельно допустимое снижение давления в трубах при бурении в начальных условиях, Па,
при условии ΔP_тф = [ΔP_{т 1}] продолжают бурение последующего интервала, повышая давление на устье до максимально допустимого давления устьевого оборудования по зависимости (12), и на этом устьевом давлении завершают бурение до подошвы продуктивного газоносного пласта, а в случае отсутствия притока газа, т. е. при постоянстве давления в трубах и неизменном расходе промывочной жидкости на выходе из скважины, создают расчетную величину депрессии по формуле (4) для вскрываемого интервала и проводят бурение до увеличения расхода промывочной жидкости на выходе из скважины и далее повторяют программу буровых работ, предусмотренную как для бурения первого, так и последующих интервалов, с соответствующей заменой параметров бурения первого интервала на параметры вскрываемого интервала.and _{pf 1} - a parameter characterizing the reservoir properties of the reservoir and gas inflow to the bottom of the well under specific technological conditions, m ³ / s ² , Pa;
t _b - drilling time, s;
v _CP - upward flow velocity, m / s;
ΔQ _f1 - the actual increase in the flow rate of flushing fluid at the exit from the well, m ³ / s;
Δt is the time interval during which there was an increase in the flow rate of flushing fluid, s;
gr P _c - gradient of the total pressure of the washing liquid in the annular space, Pa / m;
ΔР _T1 - the current decrease in pressure in the pipes, equal to the pressure difference in the pipes at the beginning of the formation drilling and the current moment, Pa;
P (h, t _b ) - pressure distribution in the well over the height of the gas-liquid mixture formed during drilling, Pa;
h is the current height of the gas-liquid mixture, m;
α _s - parameter characterizing the amount of dissolved gas, m ³ / (s • Pa);
b is a parameter characterizing the reservoir properties of the reservoir and gas inflow with cuttings, m ³ / s,
compare with the maximum allowable gas saturation of the flushing fluid and, provided _a1 = [a ₁ ], continue drilling the first interval, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment, depending
P _y (t) = [P _{y max} ] -ρ _o g (t _p -t) v _cp • 60, (12)
wherein

where P _y (t) is the current generated wellhead pressure, Pa;
t _p - the time during which the increase in pressure at the mouth, min;
t - current time point of pressure increase at the mouth, min,
and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, provided that _a1 > [a ₁ ], drilling is stopped, the actual formation pressure is determined, the formation fluid is washed out, and the minimum density of the flushing fluid is adjusted by the formula

where ρ is the adjusted minimum density of the washing liquid, kg / m ³ ,
bring the wellhead pressure to the maximum allowable pressure of the wellhead equipment, and at this pressure complete drilling to the bottom of the productive gas-bearing formation, and subject to _a1 <[a ₁ ] continue drilling both the first and subsequent intervals with the initial wellhead pressure and monitor the pressure in the pipes , and in the first interval determine the maximum allowable pressure drop in the pipes according to the formula

where [ΔP _{t 1} ] - the maximum allowable pressure drop in the pipes when drilling in the initial conditions, Pa,
provided ΔP _tf = [ΔP _{t 1} ] continue drilling the subsequent interval, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment according to dependence (12), and at this wellhead pressure complete drilling to the bottom of the productive gas-bearing formation, and in the absence of gas inflow , i.e., with constant pressure in the pipes and a constant flow rate of flushing fluid at the exit from the well, the calculated value of depression is created according to formula (4) for the opening interval and drilling is carried out until the flow rate of flushing fluid is increased ti output from the well and further drilling operations are repeated program provided for drilling the first and subsequent slots, with the corresponding change in drilling parameters for a first interval parameters reveals interval.

 The method is based on determining the maximum permissible gas saturation of the flushing fluid, depending on the specific geological and technical conditions of drilling the well.

Drilling a gas-bearing formation under conditions of pressure equilibrium in the well-formation system or depression creates prerequisites for gas inflow into the well, the intensity of which is mainly due to the magnitude of the depression on the formation roof. Under these conditions, the safety of the drilling process directly depends on the amount of incoming gas, i.e. gas saturation (the ratio of gas flow to flushing fluid flow) of flushing fluid, as well as methods for controlling pressure in the well, which allow maintaining a safe depression on the formation. In turn, a safe depression on the formation is predetermined by the condition for the stability of the walls of the well, the amount of incoming gas and pressure at the wellhead. In general, the condition
ΔP _max ≥ [ΔP] = f ([a], [P _{y max} ]), (15)
where [ΔP] is a safe depression on the reservoir, Pa.

 The gas entering the well, as it rises to the wellhead, expands, reducing the density of the drilling fluid, which leads to an increase in depression on the formation and a more intense flow of gas. The gas expansion energy, starting from a certain section of the wellbore, becomes sufficient to raise the flushing fluid in the annular space without the aid of pumps, which leads to a “discharge” of flushing fluid. The well thus begins to work like a gas lift. Therefore, gas saturation of the flushing fluid characterizes the safety of drilling. Known methods for determining the maximum allowable gas saturation of the flushing fluid, which ensures its safe (from the standpoint of preventing absorption, violation of the tightness of the casing and the destruction of the wellhead) removal from the well when killing manifestations. For safe drilling with a uniform gas inflow into the well, we propose to determine the maximum permissible gas saturation of the flushing fluid according to condition (15), i.e., the maximum permissible gas saturation of the flushing fluid satisfies the conditions of stability of the walls of the well and preventing the "discharge" of flushing fluid, ensuring safe drilling of the well.

The condition for the start of the “ejection” of washing liquid is a violation of the energy balance
A _p = A _p , (16)
where A _p is the work of gas expansion in a gas-liquid mixture, J;
A _p - work on lifting the washing fluid in the mixture, equal to the sum of the work on changing the potential energy of the mixture, overcoming hydraulic resistance and inertia, J.

 To determine the conditions for the occurrence of a “discharge” of washing liquid from a certain depth, it is quite sufficient to consider the dynamic equilibrium of the elementary volume in this section containing 1 kg of a gas-liquid mixture. In the overlying volumes of the gas-liquid mixture, these conditions will be especially true. Since the pressure at all points in the volume of 1 kg of the gas-liquid mixture will be practically the same during the expansion process, the principles of thermodynamics are applicable.

Based on the energy balance, for the selected elementary volume of a gas-liquid mixture, the equation of equilibrium of the acting forces is as follows:
dA _p / dh = dA _p / dh, (17)
where dA _p is the elementary work of expanding the gas contained in 1 kg of a gas-liquid mixture, J;
dA _p - elementary work on lifting the washing liquid contained in 1 kg of gas-liquid mixture, J;
dh - increment of the lifting height of 1 kg of gas-liquid mixture, m

где а - коэффициент газонасыщения промывочной жидкости и равен отношению расхода газа (в нормальных условиях) к расходу жидкости;
Р - давление в рассматриваемом сечение скважины, равное сумме гидростатического и гидродинамического давления в кольцевом пространстве на глубине рассматриваемого сечения, устьевого давления, Па.The elementary work of the gas contained in 1 kg of gas-liquid mixture during expansion is equal to

where a is the gas saturation coefficient of the washing liquid and is equal to the ratio of gas flow (under normal conditions) to liquid flow;
P is the pressure in the considered section of the well, equal to the sum of the hydrostatic and hydrodynamic pressure in the annular space at the depth of the section, wellhead pressure, Pa.

где I - гидродинамическая составляющая давления.The elementary work of lifting the liquid contained in 1 kg of a gas-liquid mixture can be determined by neglecting the forces of inertia due to their smallness, by the expression

where I is the hydrodynamic component of pressure.

где h_выб - глубина поперечного сечения, где нарушается энергетический баланс, м.After substituting the obtained expressions into condition (17) and integrating, taking into account the direction of the acting forces, within the indicated limits, we obtain the dependence of the depth of the cross section, where the energy balance is violated from the gas saturation of the washing liquid

where h _SEL - the depth of the cross-section where the energy balance is disturbed, m.

To prevent ejection from the depth h _sps energy necessary to compensate expansion of the gas released to the wellbore, through the creation of excess pressure at the wellhead. In the case when drilling is carried out with an initial wellhead pressure, the required additional pressure is equal to the difference between the maximum allowable pressure at the wellhead and the previously created wellhead pressure. Given these conditions, the gas saturation of the flushing fluid, which corresponds to the condition for the start of the ejection, is determined by the formula (7), which allows you to take into account specific technical ([P _ymax ]) and technological (P _s ) conditions.

где Т - текущая температура, К;
Р - текущее гидростатическое давление в кольцевом пространстве, Па.There is no doubt that a decrease in the density of the flushing fluid due to the inflow of gas into the well and its expansion as it rises along the wellbore reduces the bottomhole pressure, which leads to an increase in depression on the formation and a violation of the stability of the well walls. Therefore, the pressure created by the column of gas-liquid mixture should provide the maximum allowable depression on the well walls. The column pressure of the gas-liquid mixture is determined by integrating the equation
dP = ρ _rx gdh, (21)
with the substitution of the formula for the density of the gas-liquid mixture, which takes into account the presence of a solid phase and gas solubility

where T is the current temperature, K;
P - current hydrostatic pressure in the annular space, Pa.

где Р_гж - давление столба газожидкостной смеси на глубине Н_К, равное Р_пл - ΔР_mах, Па;
Р_y - избыточное устьевое давление на устье, равное [Р_ymах]-Р_y1, Па,
где [Р_ymах] - P_y1 - технический резерв устьевого давления, Па.Then

where P _gf is the column pressure of the gas-liquid mixture at a depth of H _To , equal to R _PL - ΔP _max , Pa;
P _y - excess wellhead pressure at the mouth equal to [P _ymax ] -P _y1 , Pa,
where [P _ymax ] - P _y1 - technical reserve of wellhead pressure, Pa.

 According to condition (15), substituting the value of the technical reserve of wellhead pressure and the pressure of the gas-liquid mixture into equation (23), the acceptable gas saturation of the washing liquid is determined by the formula (8).

 Thus, the maximum allowable gas saturation of the flushing fluid, which ensures safe drilling of the well, satisfying the condition of preventing the "ejection" of flushing fluid, the stability of the walls of the well and equal to the smaller of the permissible values, is determined by the expression (6).

 It is known that the main signs of gas inflow into the well are an increase in the flow rate of flushing fluid at the outlet of the well and a decrease in pressure in the pipes. The increase in the flow rate of flushing fluid at the outlet is directly proportional to the volume of gas distributed over the wellbore during the rise, and the decrease in pressure in the pipes reflects the change in the total pressure of the flushing fluid during circulation. The joint use of actual data of wellhead information allows one to determine the amount of incoming gas even before the gas-liquid mixture reaches the mouth, i.e. the actual gas saturation of the flushing fluid at the actual flow of flushing fluid at the exit of the well and the pressure in the pipes, which ensures prompt detection at an early stage of gas inflow.

где ΔР_т - текущее снижение давления в трубах, равное разнице давлений в трубах в начале бурения пласта и текущий момент, Па.The actual gas saturation of the wash fluid is determined by the formula (10), which was obtained as a result of analytical studies under the following assumptions:
- during the drilling process, gas enters the well as a result of exceeding the actual reservoir pressure above the bottomhole and together with the cuttings;
- with a decrease in bottomhole pressure (depression on the formation is variable), gas inflow from the formation increases;
- the gas entering the well rises to the wellhead with a moving flushing fluid (there is no gas movement relative to the solution) and changes its volume due to a decrease in temperature and pressure along the wellbore;
- takes into account the solubility of the gas in the washing liquid;
- technically, a constant predetermined wellhead pressure is provided, regardless of the flow rate of flushing fluid at the exit of the well;
- the dependence of the pressure change in the gas-liquid mixture of the annular space on the magnitude of the pressure drop in the pipes at a constant wellhead pressure in the form

where ΔР _t is the current decrease in pressure in the pipes, equal to the pressure difference in the pipes at the beginning of the formation drilling and the current moment, Pa.

при этом grP_c = gρ₀+P_кп/H_к, h_в=H_к-t_бv_кп,
где h_В - глубина верхней границы столба газожидкостной смеси, м.Under the assumptions made, the distribution of pressure in the well is determined as

in this case, grP _c = gρ ₀ + P _kp / H _k , h _c = H _k -t _b v _kp ,
where h _In - the depth of the upper boundary of the column of the gas-liquid mixture, m

 In FIG. 1 and 2 schematically show the location of the current depth relative to the upper boundary of the gas-liquid mixture, corresponding to the above conditions, respectively.

при этом

ΔP² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{пл}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{з}}$ ,
ΔP_з = P_з-ΔP_т1;
P_з=P_у1+H•grР_с,
f(ΔP_т) = ΔP_т1;
где dV'_o - объем газа, поступившего в скважину за элементарный отрезок времени за счет депрессии и приведенный к н.у., м³;
k - коэффициент проницаемости пласта, м²;
η - вязкость газа, Па•с;
R_k, r_с - соответственно радиусы контура питания и скважины, м;
- с выбуренной породой в ствол скважины поступает газ в объеме

где dV''_o - объем газа, поступившего в скважину за элементарный отрезок времени с выбуренной породой и приведенный к н.у., м³.The amount of gas delivered to the well in an elementary time interval is determined:
- due to depression, according to Darcy's law

wherein

ΔP ² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{pl}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{s}}$ ,
ΔP _s = P _s -ΔP _t1 ;
P _s = P _y1 + H • grP _s ,
f (ΔP _t ) = ΔP _t1 ;
where dV ' _o is the volume of gas supplied to the well for an elementary period of time due to depression and reduced to nu, m ³ ;
k is the permeability coefficient of the formation, m ² ;
η — gas viscosity, Pa • s;
R _k , r _s are respectively the radii of the power circuit and the well, m;
- with the cuttings in the borehole, gas is supplied in volume

where dV '' _o is the volume of gas supplied to the well for an elementary period of time with cuttings and reduced to n.o., m ³ .

где dV''_o - объем растворенного газа за элементарный отрезок времени и приведенный к н. у., м³.According to Henry's law, the volume of gas dissolved in a given volume of liquid at a given temperature is proportional to the current pressure. At the bottom, the gas dissolves over an elementary period of time in volume

where dV '' _o is the volume of dissolved gas for an elementary period of time and reduced to n. at., m ³ .

Рассматривая интервал газожидкостной смеси 0 ≤ h_ГЖ ≤ h_В, образованный за время бурения, находят элементарный объем газа на уровне текущей глубины h (фиг.1):

где dV_tб(h) - элементарный объем газа, поступивший на глубину h в момент бурения t_б, м³;
dV_o(t) - объем газа, поступившего на забой в момент времени t при изменившемся забойном давлении на величину снижения давления в трубах ΔP_T(t), м³.The total amount of free gas received at the bottom of the well for an elementary period of time at the time of drilling t _b is equal to the sum

Considering the interval of the gas-liquid mixture 0 ≤ h _GF ≤ h _B formed during drilling, find the elementary volume of gas at the level of the current depth h (figure 1):

where dV _tb (h) is the elementary volume of gas received at a depth h at the time of drilling t _b , m ³ ;
dV _o (t) is the volume of gas entering the face at time t with a changed bottomhole pressure by the amount of pressure decrease in the pipes ΔP _T (t), m ³ .

The volume of gas dV _o (t) received at the bottom of the well at the time of drilling t at a pressure of P _s -ΔP _T (t) is raised to the level h by the time t _b , with t <t _b . Therefore, the time of volume rise dV _o (t) from the bottom to the level h is determined by the difference t _b - t, i.e.

H _K -h = v _kn (t _b -t).

Подставляя в (32) t = t_б -(Н_к - h)/v_кп, dt = dh/v_кп, получим

Объем свободного газа в рабочих условиях за время бурения определяется численным интегрированием выражения

Аналогично определяют объем свободного газа в скважине в нормальных условиях к моменту бурения t_б по выражению (10).Given (30), the volume of free gas at level h at the time of drilling t _b is

Substituting in (32) t = t _b - (H _k - h) / v _kn , dt = dh / v _kn , we obtain

The volume of free gas under operating conditions during drilling is determined by numerical integration of the expression

Similarly, the volume of free gas in the well is determined under normal conditions at the time of drilling t _b by the expression (10).

где Q_вых - расход промывочной жидкости на выходе из скважины, м³/с.Given the accelerated nature of the flow of flushing fluid from the well, due to the flow and expansion of gas during drilling, we can write

where Q _o - flow rate of flushing fluid at the exit of the well, m ³ / s

Equating expressions (33) and (34), using the numerical integration, find the parameter "a _pf1 " by the formula (11).

Substituting the value of a _pf1 in the expression (10), determine the volume of gas under normal conditions. Using the obtained values, the actual gas saturation of the washing liquid is determined by the formula (9).

где Q_г(t_б) - расход газа, поступающего в скважину за счет переменной депрессии за время бурения и приведенного к нормальным условиям, м³/с.Determine the flow rate of gas entering the well as a result of inflow from the reservoir with a variable depression and reduced to normal conditions using the expression

where Q _g (t _b ) is the flow rate of gas entering the well due to a variable depression during drilling and reduced to normal conditions, m ³ / s.

где R(t_б) - параметр продуктивности вскрытого интервала газоносного пласта за время бурения, м³/с•Па;
ΔР - текущее значение депрессии, Па.Dividing expression (35) by the current value of depression, determine the productivity parameter of the open interval of the gas-bearing formation during drilling

where R (t _b ) is the productivity parameter of the open interval of the gas-bearing formation during drilling, m ³ / s • Pa;
ΔР - current value of depression, Pa.

[P_ymax]-P_y(t)≤[P_ymax]-P_y1, (40)
при этом h-h_п=t•v_кп,

где h - глубина, с которой необходимо повышать устьевое давление по мере подъема газожидкостной смеси к устью скважины, м;
h_п - текущая глубина скважины, h_п ≤ h, м.According to the definition, the maximum allowable gas saturation of the flushing liquid leads to a safe depression on the formation. Therefore, under the condition a _f1 - [a ₁ ], to ensure the safety of further drilling to the bottom of the formation, it is necessary to maintain a constant depression in the roof of the formation. The constancy of depression is achieved by increasing wellhead pressure as the gas-liquid mixture rises along the wellbore, thereby compensating for the decrease in bottomhole pressure as a result of gas expansion. Based on this condition and taking into account the pressure created by the gas-liquid mixture of the maximum allowable gas saturation, the following equations can be written to determine the dependence of the increase in pressure at the mouth during circulation:

[P _ymax ] -P _y (t) ≤ [P _ymax ] -P _y1 , (40)
moreover, hh _n = t • v _kn ,

where h is the depth with which it is necessary to increase wellhead pressure as the gas-liquid mixture rises to the wellhead, m;
h _p - current well depth, h _p ≤ h, m.

Solving equations (37), (38) and (39) taking into account condition (40) with respect to P _y (t), as well as for the convenience of practical use, setting the time parameter in minutes, determine the dependence of the increase in wellhead pressure to the maximum allowable wellhead pressure equipment (12).

Решая уравнения (41) и (42) относительно ρ_, определяют зависимость корректировки минимальной плотности промывочной жидкости (13). При фактическом пластовом давлении больше проектной величины потребуется утяжеление промывочной жидкости для обеспечения меньшей депрессии на кровлю пласта.Provided a _{f 1} > [a ₁ ] carry out the technological operations provided for in the liquidation of fluid manifestations, allowing the calculation to determine the actual reservoir pressure and productivity parameter of the opened interval of the gas-bearing formation. For further safe drilling to the bottom of the formation, it is advisable to ensure a constant depression in the roof of the formation by adjusting the density of the flushing fluid and creating the maximum allowable pressure at the mouth. Based on this condition and taking into account the actual reservoir pressure and the reservoir productivity parameter, the following equalities can be written (in hydrostatics) to determine the value of the adjusted density of the flushing fluid:

Solving equations (41) and (42) with respect to ρ _{, the} dependence of the correction of the minimum density of the washing liquid (13) is determined. With the actual reservoir pressure greater than the design value, a flushing fluid will be required to provide less depression on the formation roof.

Решая уравнения (43) и (44) относительно [ΔP_{т 1}], определяют величину предельно допустимого снижения давления в трубах при циркуляции промывочной жидкости по формуле (14).The condition a _f1 <[a ₁ ] indicates the admissibility of drilling under initial conditions. However, after the control time of drilling, when the upper boundary of the gas-liquid mixture reaches the wellhead, the determination of the actual gas saturation of the flushing fluid by increasing the flow rate of flushing fluid at the outlet using formula (10) becomes unreliable. At the same time, safe depression, according to the definition of the formation productivity parameter, corresponds to the maximum allowable pressure drop in the pipes

Solving equations (43) and (44) with respect to [ΔP _{t 1} ], the value of the maximum allowable pressure drop in the pipes during the circulation of the flushing fluid is determined by the formula (14).

With a change in bottomhole pressure, the pressure in the pipes changes according to the law of communicating vessels. When the actual pressure drop in the pipes reaches the maximum permissible value, i.e. when the condition ΔP _tf = [ΔP _t1 ] is fulfilled, the safety of further drilling to the bottom of the formation is ensured by maintaining constant depression in the roof of the formation by increasing pressure at the mouth during circulation to the maximum allowable pressure according to (12).

 The absence of fluid manifestations, along with other signs, indicates the equilibrium of the well-reservoir system. In order to reduce back pressure on the formation, wellhead pressure is reduced as the well deepens, providing a variable depression in the roof of the gas-bearing formation. The magnitude of the wellhead pressure decrease is equal to the increase in the hydrostatic pressure of the flushing fluid per drilled interval and determines the wellhead pressure for drilling the subsequent interval. The change in hydraulic pressure loss in the annular space as it deepens is taken small and not taken into account, because the hydraulic flushing program does not change. Thus, under the condition of constant pressure in the pipes and flow rate of flushing fluid at the well exit during drilling, a certain pattern of wellhead pressure decrease is observed as the well deepens according to expression (4).

- фактическое газосодержание промывочной жидкости по формуле

при этом

P_з=P_уi+H_к•grP_с,
grP_c=gρ_o+P_кп/H_к,
ΔP_з = P_з-ΔP_{т i};
ΔP² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{пл}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{з}}$ ;
P(h, t_б)=P_уi+h•grP_с-ΔP_тi•(1-h/t_бv_кп),
при условии а_{ф i} = [а_i] зависимость повышения давления на устье до максимально допустимого давления устьевого оборудования
P_y(t)=[P_ymax]-ρ_og(t_п-t)v_кп•60,
при этом

при условии а_{ф i} > [a_i] корректируют минимальную плотность промывочной жидкости по формуле

и при условии а_{ф i} <[а_i] определяют предельно допустимое снижение давления в трубах по формуле

при условии ΔP_тф = [ΔP_{т i}] повышают давление на устье до максимально допустимого давления устьевого оборудования по зависимости, указанной в условии а_{ф i} = [а_i].As a result of a variable depression, a gas inflow into the well occurs at the top of the formation. All theoretical conclusions made for drilling the first interval in the case of gas inflow into the well are also valid for drilling subsequent "ix" intervals in the conditions of gas inflow with the corresponding replacement of the parameters of the first interval with the "i", namely:
- determine the maximum allowable gas saturation of the washing fluid by the expression
[a _i ] = min {a _{select i} , a _{mouth i} },
wherein

- the actual gas content of the washing liquid according to the formula

wherein

P _s = P _уi + H _к • grP _s ,
grP _c = gρ _o + P _kp / H _k ,
ΔP _s = P _s -ΔP _{t i} ;
ΔP ² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{pl}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{s}}$ ;
P (h, t _b ) = P _уi + h • grP _s -ΔP _ti • (1-h / t _b v _кп ),
provided a _{f i} = [a _i ] the dependence of the increase in pressure at the mouth to the maximum allowable pressure of the wellhead equipment
P _y (t) = [P _ymax ] -ρ _o g (t _p -t) v _kn • 60,
wherein

subject to a _{f i} > [a _i ] adjust the minimum density of the washing liquid according to the formula

and subject to a _{f i} <[a _i ] determine the maximum allowable pressure drop in the pipes by the formula

under the condition ΔP _tf = [ΔP _{t i} ] increase the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment according to the dependence specified in the condition a _{f i} = [a _i ].

 When drilling the remainder of the formation to the sole, a constant safe depression in the roof of the formation is maintained by increasing wellhead pressure. Compliance with this condition as the well deepens upsets the pressure balance at the bottom, i.e. autopsy is conducted on repression. It should be noted that in this case, the degree of penetration of the reservoir in terms of capacity for depression increases, and the magnitude of the repression will be significantly less than the repression that occurs during traditional drilling at the same depth of the face.

 An analysis of the inventive step showed the following: it is known that the main signs of gas inflow into the well (i.e. gas saturation of the flushing fluid) is an increase in the flow rate of flushing fluid at the well exit (see New materials and fluids for drilling wells and hydraulic fracturing of productive formations. scientific works, VNIIKrneft, Krasnodar, 1990, p. 166) and pressure reduction in pipes (see p. 98114211/03 (015254) dated 07/14/98 according to class E 21 B 21/08, with the decision of FIPS on the grant of a patent dated December 23, 1999). Moreover, the dependence of the gas saturation of the flushing fluid on the pressure in the pipes and on the increase in the flow rate of flushing fluid at the exit from the well has not been studied by anyone and in the practice of opening a productive gas-bearing formation has not been used according to available sources of fame.

 It is known that in the process of opening a formation, the values of the maximum allowable gas saturation of the flushing fluid are known (see oil industry 5, 1998, p. 25. Causes of well discharges and the detection of oil and gas manifestations at an early stage of their occurrence. Authors: AV Mnatsakanov, R.V. Avetov et al .; Kuksov A.K., Babayan E.V., Shevtsov V.D. Prevention and liquidation of gas and oil and gas occurrences during drilling. - M .: Nedra, 1992, p. 102) or his , but for diffusion gas occurrences (see AS 1798475 dated June 5, 1990, according to class E 21 B 21/00, published in OB 8, 93).

 Also known is the measurement in the process of opening the formation of the flow rate and pressure of the incoming and outgoing gas (see A. Laktionov, Fundamentals of the theory and technique of drilling wells with bottom-hole cleaning by air or gas: M., Gostoptekhizdat, 1961, p. 209-215). Also known is a calculation method for determining the actual reservoir pressure from the pressure in the pipes during the elimination of gas occurrences during well construction (see Zubarev V.G. Prediction, prevention and elimination of manifestations in wells. M., VNIIOENG, 1979, p. 27; Temporary instruction on the prevention and liquidation of gas and oil manifestations during the construction of wells. M., RAO "Gazprom", approved on March 19, 1997, p. 21). According to the method, the circulation of the washing liquid is stopped, the mouth is sealed, the pressure in the pipes is measured and the actual reservoir pressure is calculated according to the known formula. The flushing of the gas entering the well is carried out as described in No. 4253530 dated 10.10.79, class. E 21 B 7/00, 21/08, publ. 03.03.81 g. Dresser Industries, Inc.

 Based on the foregoing, we have not identified technical solutions that are based on features that match the distinctive features of the claimed technical solution. Thus, the latter does not follow explicitly from the analyzed prior art, i.e. has an inventive step.

 In more detail, the essence of the proposed method is illustrated by the following example using a simulation of the drilling process.

Example. The reservoir is represented by sandstones of the Valanginian deposits, well R-110 Zapolyarnaya of the Urengoy gas condensate field. Use the Uralmash ZD-76 drilling rig. The wellhead is sealed with a rotary preventer PV S-1-280 x 7.5 MPa, at the outlet from the well, a Regan-5000 choke is installed, the circulation system also includes a DVS-II degasser
Initial data:
Design well depth N _p , m - 3440
Depth of the roof of the formation N, m - 3340
Formation pressure R _pl , MPa - 41.27
Avg. the outer diameter of the drill string d _N , m - 0,097
Avg. the inner diameter of the drill string d _In , m - 0,077
Avg. well diameter d _c , m - 0.154
The diameter of the bit d _d , m - 0,140
The porosity coefficient of the rock m _o - 0.3
The solubility coefficient of gas in NU α _T , 10 ^-6 • Pa ^-1 - 0.11
The compressibility coefficient of gas in NU z _o - 1
The gas compressibility coefficient z _cp is 1.04
Pump capacity Q, m ³ / s - 0.005
The speed of the upward flow of the solution v _CP , m / s - 0.44
Downhole temperature of the solution T _s , K - 413
The temperature of the solution at the mouth of T _y , K - 333
The average temperature of the solution T _cf , K - 373
The maximum allowable depression on the walls of the well ΔР _max , MPa - 2.0
Permissible operating pressure of the rotating preventer PVS-1-280 x 7 when drilling [P _{y max} ], MPa - 3.5
In static conditions, MPa - 7.0
Atmospheric pressure P _about , MPa - 0.1
Gas density in ns ρ _g , kg / m ³ - 0.7
A technical column is lowered to the top of the formation, drilling a cement cup is carried out on a working flushing fluid, followed by replacement with a lightweight one for opening the reservoir.

Вскрытие пласта проводят на промывочной жидкости следующего состава, мас.%:
Бентонитовая глина - 8
КССБ - 1
КМЦ - 0,2
Нефть - 2
Барит - 5
Вода - Остальное
обеспечивающую рассчитанное ρ_o. Перед началом бурения определяют гидравлические потери давления в кольцевом пространстве, которые равны Р_КП = 1,81 МПа, создают устьевое давление с помощью перекрытия дросселя, равное P_y1 = (3,5 - 1,81)10⁶ = 1,69 МПа. При этом давление в трубах равно сумме давления на преодоление гидравлических сопротивлений в циркуляционной системе Р_цс = 11 МПа и созданного устьевого давления Р_то = (11+1,69)10⁶ = 12,69 МПа.Determine the minimum density of the flushing fluid at the initial opening of the reservoir, taking into account the technological sufficiency of the allowable working pressure of the rotating preventer, because at P _min = 1000 • 9.81 • 3340 = 32.76 MPa the condition [P _y ] ≤ 41 is satisfied, 27-32.76-8.5 MPa and in our case [P _y ] = [P _{y max} ]

The autopsy is carried out on the washing fluid of the following composition, wt.%:
Bentonite clay - 8
KSSB - 1
CMC - 0.2
Oil - 2
Barite - 5
Water - Else
providing the calculated ρ _o . Before the start of drilling, hydraulic pressure losses in the annular space are determined, which are equal to P _KP = 1.81 MPa, create wellhead pressure using the throttle shutoff equal to P _y1 = (3.5 - 1.81) 10 ⁶ = 1.69 MPa. The pressure in the pipes is equal to the sum of the pressure to overcome the hydraulic resistance in the circulation system P _cs = 11 MPa and the wellhead pressure created P _then = (11 + 1.69) 10 ⁶ = 12.69 MPa.

Также перед началом бурения определяют предельно допустимое газонасыщение промывочной жидкости [a₁]. Для этого сначала определяют допустимое газонасыщение промывочной жидкости а_{выб 1}, соответствующее условию начала выброса по формуле

и допустимое газонасыщение промывочной жидкости а_уст1, исходя из условия устойчивости стенок скважины:

Далее из двух расчетных величин выбирают минимальное, таким образом, предельно допустимое газонасыщение промывочной жидкости равно 2,0 (что соответствует газосодержанию 67%).Calculate the control time for drilling the first interval according to the formula

Also, before the start of drilling, the maximum permissible gas saturation of the flushing fluid is determined [a ₁ ]. To do this, first determine the permissible gas saturation of the wash liquid and _{select 1} , corresponding to the condition for the start of the emission according to the formula

and permissible gas saturation of the flushing fluid a _set1 , based on the condition of stability of the walls of the well:

Next, from the two calculated values, choose the minimum, thus, the maximum allowable gas saturation of the washing liquid is 2.0 (which corresponds to a gas content of 67%).

 The first interval is drilled with a constant pressure at the wellhead of 1.69 MPa for a control time of 2 hours, while monitoring the pressure in the pipes and the flow rate of the flushing fluid at the well exit.

 1. Drilling of the first interval in the case of constant or reduced pressure in the pipes with a simultaneous increase in the flow rate of flushing fluid at the exit of the well.

1.1. Condition a _{f 1} - [a ₁ ].

Suppose that after one and a half hours of drilling at a mechanical speed of 1 m / h, an increase in the flow rate of flushing fluid at the well exit is recorded ΔQ _f1 = 0.0006 m ³ / s in five minutes (12% of the pump capacity), while the decrease in pressure in the pipes is ΔP _t1 = 0.4 MPa (pressure in pipes 12.29 MPa), which indicates the flow of gas into the well as a result of depression.

P_з=1,69•10⁶+3340•1,19•10⁴=41,3•10⁶ Па;
grP_c=1155•9,91+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з = (41,3-0,4)•10⁶ = 40,9•10⁶ Па;
ΔP² = (41,27•10⁶)²-(40,9•10⁶)² = 2,68•10¹³ Па;
P(h,t₆)=1,69•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Продолжают бурение первого интервала, повышая давление на устье до максимально допустимого давления устьевого оборудования по зависимости

P_y(t)=3,5•10⁶-1155•9,81•0,44•60•(6-t)=3,5•10⁶-0,299•10⁶•(6-t). Так, в первый момент повышают устьевое давление до величины 1,7 МПа, через 4 мин - 2,9 МПа, через 6 мин на устье создают давление 3,5 МПа, сохраняя на кровле продуктивного пласта постоянную безопасную депрессию [ΔP] - 41,27•10⁶ = (1,69 + 1,81 + 9,81 • 1,155 • 3,34 - 0,4)10⁶ = 0,33 МПа.The actual gas saturation of the flushing fluid a _{f 1 is} determined, having previously calculated the parameter a _{pf 1} and the volume of gas in the well, reduced to normal conditions (n.a.) using a PC (Excel-Office 97 software):
dh = 1m;

P _s = 1.69 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.3 • 10 ⁶ Pa;
grP _c = 1155 • 9,91 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.3-0.4) • 10 ⁶ = 40.9 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.9 • 10 ⁶ ) ² = 2.68 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.69 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Drilling of the first interval is continued, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment, depending

P _y (t) = 3.5 • 10 ⁶ -1155 • 9.81 • 0.44 • 60 • (6-t) = 3.5 • 10 ⁶ -0.299 • 10 ⁶ • (6-t). So, at the first moment, the wellhead pressure is increased to a value of 1.7 MPa, after 4 minutes - 2.9 MPa, after 6 minutes a pressure of 3.5 MPa is created on the wellhead, while maintaining a constant safe depression on the roof of the productive formation [ΔP] - 41, 27 • 10 ⁶ = (1.69 + 1.81 + 9.81 • 1.155 • 3.34 - 0.4) 10 ⁶ = 0.33 MPa.

что составляет 1,8% превышения над пластовым давлением.On depression, one interval was opened with a thickness of 2 m, i.e. the degree of opening of the reservoir in depression is k _B = 2/100 = 0.02 or 2%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 1.8% excess over reservoir pressure.

1.2. Condition a _{Φ 1} > [a ₁ ].

Assume that a half hour with a mechanical drilling speed of 1 m / hour washing liquid flow fixed gain at the output from the well ΔQ _F1 = 0.0007 m ³ / s for five minutes (14% pump performance), the pressure drop in the tubes was ΔP _t1 = 0.4 MPa (pressure in pipes 12.29 MPa), which indicates the influx of gas into the well as a result of depression.

P_з=1,69•10⁶+3340•1,19•10⁴=41,3•10⁶ Па;
grP_c=1155•9,91+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з=(41,3-0,4)•10⁶=40,9•10⁶ Па;
ΔP²=(41,27•10⁶)²-(40,9•10⁶)²=2,68•10¹³ Па;
P(h,t₆)=1,69•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Останавливают процесс углубления и промывки скважины. Скважину "закрывают" и по величине давления в трубах P_T= 4,17 МПа определяют фактическое пластовое давление по формуле
P_{пл ф}=P_т+ρg(H_к+v_мt_б)=4,17•10⁶+1155•9,81(3340+1,5)=42,03 МПа.The actual gas saturation of the flushing fluid a _{f 1 is} determined, having previously calculated the parameter a _{pf 1} and the volume of gas in the well, reduced to normal conditions (n.a.) using a PC (Excel-Office 97 software):
dh = 1m;

P _s = 1.69 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.3 • 10 ⁶ Pa;
grP _c = 1155 • 9,91 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.3-0.4) • 10 ⁶ = 40.9 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.9 • 10 ⁶ ) ² = 2.68 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.69 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Stop the process of deepening and flushing the well. The well is “closed” and the actual reservoir pressure is determined by the pressure in the pipes P _T = 4.17 MPa according to the formula
P _{pl f} = P _t + ρg (H _k + v _m t _b ) = 4.17 • 10 ⁶ + 1155 • 9.81 (3340 + 1.5) = 42.03 MPa.

добавляя барит до 3%. Возобновляют промывку скважины с прежней производительностью насосов и вымывают пачку газожидкостной смеси с одновременным доведением плотности до требуемой величины. Вымывание пачки ведут с поддержанием постоянного давления в трубах Р_т=12,29•10⁶ МПа, регулируя давление на дросселе. На кровле продуктивного пласта сохраняется постоянная безопасная депрессия

На депрессии вскрыт один интервал мощностью 2 м, т.е. степень вскрытия продуктивного пласта на депрессии составляет k_B = 2/100 = 0,02 или 2%. Доводят устьевое давление до максимально допустимого давления устьевого оборудования 3,5 МПа и при этом давлении завершают бурение до подошвы продуктивного газоносного пласта, где создается репрессия величиной

что составляет 3,2% превышения над пластовым давлением.Correct the minimum density of flushing fluid of the same composition

adding barite to 3%. The flushing of the well is resumed with the previous pump capacity and the pack of the gas-liquid mixture is washed out while the density is brought to the required value. Wash the packs while maintaining a constant pressure in the pipes P _t = 12.29 • 10 ⁶ MPa, adjusting the pressure on the throttle. Permanent safe depression remains on the roof of the reservoir

On depression, one interval was opened with a thickness of 2 m, i.e. the degree of opening of the reservoir in depression is k _B = 2/100 = 0.02 or 2%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 3.2% excess over reservoir pressure.

1.3. The condition a _{Φ 1} <[a ₁ ].

Suppose that after one and a half hours of drilling at a mechanical speed of 1 m / h, an increase in the flow rate of flushing fluid at the well exit ΔQ _f1 = 0,00035 m ³ / s in five minutes (9% of the pump capacity) is recorded, while the decrease in pressure in the pipes is ΔP _T1 = 0.4 MPa (pipe pressure 12.29 MPa), which indicates the flow of gas into the well as a result of depression.

P_з=1,69•10⁶+3340•1,19•10⁴=41,3•10⁶ Па;
grP_c=1155•9,91+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з=(41,3-0,4)•10⁶=40,9•10⁶ Па;
ΔP²=(41,27•10⁶)²-(40,9•10⁶)²=2,68•10¹³ Па;
P(h,t₆)=1,69•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Определяют предельно допустимое снижение давления в трубах

и удовлетворяет условию (41,27 - 41,3 + 0,92)•10⁶ = 0,89 МПа ≤ 2 МПа.The actual gas saturation of the flushing fluid a _{f 1 is} determined, having previously calculated the parameter a _{pf 1} and the volume of gas in the well, reduced to normal conditions (n.a.) using a PC (Excel-Office 97 software):
dh = 1 m

P _s = 1.69 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.3 • 10 ⁶ Pa;
grP _c = 1155 • 9,91 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.3-0.4) • 10 ⁶ = 40.9 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.9 • 10 ⁶ ) ² = 2.68 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.69 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Determine the maximum allowable pressure drop in the pipes

and satisfies the condition (41.27 - 41.3 + 0.92) • 10 ⁶ = 0.89 MPa ≤ 2 MPa.

P_y(t)=3,5•10⁶-1155•9,81•0,44•60•(6-t)=3,5•10⁶-0,299•10⁶•(6-t). Так, в первый момент повышают устьевое давление до величины 1,7 МПа, через 4 мин - 2,9 МПа, через 6 мин на устье создают давление 3,5 МПа, сохраняя на кровле продуктивного пласта постоянную безопасную депрессию
[ΔP] = 41,27•10⁶ = (1,69 + 1,81 + 9,81 - 1,155 • 3,34 - 0,92)10⁶ = 0,85 МПа.Drilling of the first interval is continued with an initial wellhead pressure of 1.69 MPa, monitoring the pressure in the pipes during the control time, after which a gas-liquid mixture leaves the wellhead. When drilling the second interval for 1 hour (total drilling time 3 hours) with an actual mechanical speed of 1 m / h, a gradual decrease in pressure in the pipes by ΔP _tf = 0.92 MPa is observed, i.e. the condition ΔP _tf = [ΔP _{t 1} ] is satisfied. Drilling of the second interval is continued, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment, depending

P _y (t) = 3.5 • 10 ⁶ -1155 • 9.81 • 0.44 • 60 • (6-t) = 3.5 • 10 ⁶ -0.299 • 10 ⁶ • (6-t). So, at the first moment, the wellhead pressure is increased to 1.7 MPa, after 4 minutes - 2.9 MPa, after 6 minutes a pressure of 3.5 MPa is created at the mouth, while maintaining a constant safe depression on the roof of the reservoir
[ΔP] = 41.27 • 10 ⁶ = (1.69 + 1.81 + 9.81 - 1.155 • 3.34 - 0.92) 10 ⁶ = 0.85 MPa.

что составляет 1,8% превышения над пластовым давлением.Two intervals with a thickness of 4 m, i.e. the degree of opening of the reservoir in depression is k _B = 4/100 = 0.04 or 4%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 1.8% excess over reservoir pressure.

 2. Drilling the first interval and subsequent ones in the absence of gas inflow, that is, with constant pressure in the pipes and a constant flow rate of flushing fluid at the exit of the well.

The first interval is drilled with constant pressure at the wellhead of 1.69 MPa for a control time of 2 hours, monitoring the pressure in the pipes and the flow rate of the flushing fluid at the well exit. When drilling during the control time with an actual mechanical speed of 2 m / h, the flow rate of the flushing fluid at the exit from the well and the pressure in the pipes were kept constant, which indicates the absence of gas inflow into the well. Create a depression on the reservoir by reducing the wellhead pressure at the wellhead to the value with which the second interval will be opened and equal to
R _y2 = 1.69 • 10 ⁶ -1155 • 9.81 • 2 • 2 = 1.64 MPa. In this case, the pressure in the pipes decreases to a value of P _t2 = 12.64 MPa.

и допустимое газонасыщение промывочной жидкости a_{уст 2}, исходя из условия устойчивости стенок скважины:

Далее из двух расчетных величин выбирают минимальное, таким образом, предельно допустимое газонасыщение промывочной жидкости равно 2,2 (что соответствует газосодержанию 69%).Determine the maximum allowable gas saturation of the washing fluid [a ₂ ]. To do this, first determine the permissible gas saturation of the wash liquid and _{select 2} , corresponding to the condition for the start of the emission according to the formula

and permissible gas saturation of the flushing fluid a _{mouth 2} , based on the condition of stability of the walls of the well:

Next, from the two calculated values, choose the minimum, thus, the maximum allowable gas saturation of the washing liquid is 2.2 (which corresponds to a gas content of 69%).

The second interval is drilled during the control time with a constant pressure at the mouth of 1.64 MPa, monitoring the flow rate of flushing fluid at the exit of the well and the pressure in the pipes. After this time, there is no increase in the flow rate of the flushing fluid and the pressure in the pipes remains equal to 12.64 MPa, the actual mechanical speed of penetration of the second interval is 3 m / h, there is no gas inflow into the well. Create a depression on the reservoir by reducing the wellhead pressure at the wellhead to the value with which the third interval will be opened and equal to
P _y3 = 1.69 • 10 ⁶ -1155 • 9.81 (2 • 2 + 3 • 2) = 1.58 MPa;
the pressure in the pipes - P _T3 = 12.58 MPa.

и допустимое газонасыщение промывочной жидкости а_{уст 3}, исходя из условия устойчивости стенок скважины:

Далее из двух расчетных величин выбирают минимальное, таким образом, предельно допустимое газонасыщение промывочной жидкости равно 2,4 (что соответствует газосодержанию 70%).Determine the maximum allowable gas saturation of the flushing fluid [a ₃ ]. To do this, first determine the permissible gas saturation of the wash liquid and _{select 3} , corresponding to the condition for the start of the emission according to the formula

and permissible gas saturation of the flushing fluid a _{mouth 3} , based on the condition of stability of the walls of the well:

Next, from the two calculated values, choose the minimum, thus, the maximum allowable gas saturation of the washing liquid is 2.4 (which corresponds to a gas content of 70%).

Drilling of the third interval with wellhead pressure of 1.58 MPa is carried out, observing the flow rate of flushing fluid at the exit of the well and the pressure in the pipes, during the control time equal to 2 hours. When drilling this interval with an actual mechanical penetration rate of 2.5 m / s, the flow rate of the flushing fluid and the pressure in the pipes are also kept constant, there is no gas inflow. Create a depression on the reservoir by reducing the wellhead pressure at the wellhead to the value with which the fourth interval will be opened and equal to
P _y4 = 1.69 • 10 ⁶ -1155-9.81 (2 • 2 + 3 • 2 + 2.5 • 2) = 1.52 MPa;
the pressure in the pipes - R _t4 = 12.52 MPa.

и допустимое газонасыщение промывочной жидкости а_{уст 4}, исходя из условия устойчивости стенок скважины:

Далее из двух расчетных величин выбирают минимальное, таким образом, предельно допустимое газонасыщение промывочной жидкости равно 2,5 (что соответствует газосодержанию 71%).Determine the maximum allowable gas saturation of the flushing fluid [a ₄ ]. To do this, first determine the permissible gas saturation of the wash liquid and _{select 4} , corresponding to the condition for the start of the emission according to the formula

and the permissible gas saturation of the flushing fluid a _{mouth 4} , based on the stability conditions of the walls of the well:

Next, from the two calculated values, choose the minimum, thus, the maximum allowable gas saturation of the washing liquid is 2.5 (which corresponds to a gas content of 71%).

Drilling of the fourth interval is also carried out for 2 hours with a mechanical speed of 3.5 m / s, changes in the flow rate of flushing fluid at the exit of the well and pressure reduction in the pipes are not observed, which indicates the equilibrium of the well-reservoir system. Create a depression on the reservoir by reducing the wellhead pressure at the wellhead to the value with which the fourth interval will be opened and equal to
P _y5 = 1.69 • 10 ⁶ -1155 • 9.81 (2 • 2 + 3 • 2 + 2.5 • 2 + 3.5 • 2) = 1.44 MPa;
the pressure in the pipes - R _t5 = 12.44 MPa.

и допустимое газонасыщение промывочной жидкости а_{уст 5}, исходя из условия устойчивости стенок скважины:

Далее из двух расчетных величин выбирают минимальное, таким образом, предельно допустимое газонасыщение промывочной жидкости равно 2,6 (что соответствует газосодержанию 72%).Determine the maximum allowable gas saturation of the flushing fluid [a ₅ ]. To do this, first determine the permissible gas saturation of the wash liquid and _{select 5} , corresponding to the condition for the start of the emission according to the formula

and permissible gas saturation of the flushing fluid a _{mouth 5} , based on the condition of stability of the walls of the well:

Next, from the two calculated values, choose the minimum, thus, the maximum allowable gas saturation of the washing liquid is 2.6 (which corresponds to a gas content of 72%).

2.1. The condition a _{Φ 5} = [a ₅ ].

Suppose that after an hour of drilling with a mechanical speed of 2.5 m / h, an increase in the flow rate of flushing fluid at the well exit ΔQ _f5 = 0.00075 m ³ / s in five minutes (15% of the pump capacity) is recorded, while the pressure in the pipes is reduced amounted to ΔР _t5 = 0.4 MPa (pressure in the pipes 12.29 MPa), which indicates the influx of gas into the well as a result of depression.

P_з=1,44•10⁶+3340•1,19•10⁴=41,19•10⁶ Па;
grP_c=1155•9,81+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з=(41,19-0,4)•10⁶=40,7•10⁶ Па;
ΔP²=(41,27•10⁶)²-(40,7•10⁶)²=4,72•10¹³ Па;
P(h,t₆)=1,44•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Продолжают бурение пятого интервала, повышая давление на устье до максимально допустимого давления устьевого оборудования по зависимости

P_y(t)=3,5•10⁶-1155•9,81•(7-t)•0,44•60=3,5•10⁶-0,299•10⁶•(7-t). Так, в первый момент повышают устьевое давление до величины 1,5 МПа, через 4 мин - 2,6 МПа, через 7 мин на устье создают давление 3,5 МПа, сохраняя на кровле продуктивного пласта постоянную безопасную депрессию
[ΔP]= 41,27•10⁶ - (1,44 + 1,81 + 9,81 • 1,155 • 3,34 - 0,4)•10⁶ = 0,58 МПа.The actual gas saturation of the flushing fluid a _{f 5 is} determined, having previously calculated the parameter a _{pf 5} and the volume of gas in the well, reduced to normal conditions (n.a.) using a PC (Excel-Office 97 software):
dh = 1 m;

P _s = 1.44 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.19 • 10 ⁶ Pa;
grP _c = 1155 • 9,81 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.19-0.4) • 10 ⁶ = 40.7 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.7 • 10 ⁶ ) ² = 4.72 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.44 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Drilling of the fifth interval is continued, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment, depending

P _y (t) = 3.5 • 10 ⁶ -1155 • 9.81 • (7-t) • 0.44 • 60 = 3.5 • 10 ⁶ -0.299 • 10 ⁶ • (7-t). So, at the first moment, the wellhead pressure is increased to a value of 1.5 MPa, after 4 minutes - 2.6 MPa, after 7 minutes a pressure of 3.5 MPa is created at the mouth, while maintaining a constant safe depression on the roof of the productive formation
[ΔP] = 41.27 • 10 ⁶ - (1.44 + 1.81 + 9.81 • 1.155 • 3.34 - 0.4) • 10 ⁶ = 0.58 MPa.

что составляет 1,4% превышения над пластовым давлением.Five intervals with a total thickness of 27 m, i.e. the degree of opening of the reservoir in the depression is k _B = 27/100 = 0.27 or 27%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 1.4% excess over reservoir pressure.

2.2. Condition af ₅ > (a ₅ ).

Suppose that after an hour of drilling at a mechanical speed of 2.5 m / h, an increase in the flow rate of flushing fluid at the well exit is _recorded ΔQ _f5 = 0,0008 m ³ / s in five minutes (16% of the pump capacity), while the pressure in the pipes is reduced amounted to ΔР _t5 = 0.4 MPa (pressure in the pipes 12.29 MPa), which indicates the influx of gas into the well as a result of depression.

P_з=1,44•10⁶+3340•1,19•10⁴=41,19•10⁶ Па;
grP_c=1155•9,81+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з=(41,19-0,4)•10⁶=40,7•10⁶ Па;
ΔP²=(41,27•10⁶)²-(40,7•10⁶)²=4,72•10¹³ Па;
P(h,t₆)=1,44•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Останавливают процесс углубления и промывки скважины. Скважину "закрывают" и по величине давления в трубах Р_т = 3,91 МПа определяют фактическое пластовое давление по формуле

Корректируют минимальную плотность промывочной жидкости того же состава

добавляя барит до 3%. Возобновляют промывку скважины с прежней производительностью насосов и вымывают пачку газожидкостной смеси с одновременным доведением плотности до требуемой величины. Вымывание пачки ведут с поддержанием постоянного давления в трубах Р_т=12,29•10⁶ МПа, регулируя давление дросселем. На кровле продуктивного пласта сохраняется постоянная безопасная депрессия

На депрессии вскрыто пять интервалов, общей мощностью 27 м, т.е. степень вскрытия продуктивного пласта на депрессии составляет k_В = 27/100 = 0,27 или 27%. Доводят устьевое давление до максимально допустимого давления устьевого оборудования 3,5 МПа и при этом давлении завершают бурение до подошвы продуктивного газоносного пласта, где создается репрессия величиной

что составляет 0,45% превышения над пластовым давлением.The actual gas saturation of the flushing fluid a _{f 5 is} determined, having previously calculated the parameter a _{pf 5} and the volume of gas in the well, reduced to normal conditions (n.a.) using a PC (Excel-Office 97 software):
dh = 1m;

P _s = 1.44 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.19 • 10 ⁶ Pa;
grP _c = 1155 • 9,81 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.19-0.4) • 10 ⁶ = 40.7 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.7 • 10 ⁶ ) ² = 4.72 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.44 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Stop the process of deepening and flushing the well. The well is “closed” and the actual reservoir pressure is determined by the pressure in the pipes R _t = 3.91 MPa according to the formula

Correct the minimum density of flushing fluid of the same composition

adding barite to 3%. The flushing of the well is resumed with the previous pump capacity and the pack of the gas-liquid mixture is washed out while the density is brought to the required value. Wash the packs with maintaining a constant pressure in the pipes P _t = 12.29 • 10 ⁶ MPa, adjusting the pressure with a throttle. Permanent safe depression remains on the roof of the reservoir

Five intervals with a total thickness of 27 m, i.e. the degree of opening of the reservoir in the depression is k _B = 27/100 = 0.27 or 27%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 0.45% excess over reservoir pressure.

2.3. The condition a _{Φ 5} <[a ₅ ].

Suppose that after an hour of drilling with a mechanical speed of 2.5 m / h, an increase in the flow rate of flushing fluid at the well exit ΔQ _f5 = 0.0006 m ³ / s in five minutes is recorded (12% of the pump capacity), while the pressure in the pipes is reduced amounted to ΔР _t5 = 0.4 MPa (pressure in the pipes 12.29 MPa), which indicates the influx of gas into the well as a result of depression.

P_з=1,44•10⁶+3340•1,19•10⁴=41,19•10⁶ Па;
grP_c=1155•9,81+1,81•10⁶/3340=1,19•10⁴ Па/м;
ΔP_з=(41,19-0,4)•10⁶=40,7•10⁶ Па;
ΔP²=(41,27•10⁶)²-(40,7•10⁶)²=4,72•10¹³ Па;
P(h,t₆)=1,44•10⁶+h•1,19•10⁴-0,4•10⁶•(1-h/5400•0,44) Па;
b=0,015•2,8•10^-4•0,3=1,28•10^-6 м³/с;

что соответствует условию в рассматриваемом случае. Определяют предельно допустимое снижение давления в трубах

и удовлетворяет условию (41,27 - 41,09 + 0,83)•10⁶ = 1,01 МПа ≤ 2 МПа.The actual gas saturation of the flushing fluid a _{f5 is determined} , preliminarily calculating the parameter a _{pf 5} and the volume of gas in the well, reduced to normal conditions ( _n.a. ) using a PC (Excel-Office 97 software):
dh = 1m

P _s = 1.44 • 10 ⁶ + 3340 • 1.19 • 10 ⁴ = 41.19 • 10 ⁶ Pa;
grP _c = 1155 • 9,81 + 1,81 • 10 ^6/3340 = 1,19 • 10 ⁴ Pa / m;
ΔP _s = (41.19-0.4) • 10 ⁶ = 40.7 • 10 ⁶ Pa;
ΔP ² = (41.27 • 10 ⁶ ) ² - (40.7 • 10 ⁶ ) ² = 4.72 • 10 ¹³ Pa;
P (h, t ₆ ) = 1.44 • 10 ⁶ + h • 1.19 • 10 ⁴ -0.4 • 10 ⁶ • (1-h / 5400 • 0.44) Pa;
b = 0.015 • 2.8 • 10 ^-4 • 0.3 = 1.28 • 10 ^-6 m ³ / s;

which corresponds to the condition in the case under consideration. Determine the maximum allowable pressure drop in the pipes

and satisfies the condition (41.27 - 41.09 + 0.83) • 10 ⁶ = 1.01 MPa ≤ 2 MPa.

P_y(t)=3,5•10⁶-1155•9,81•0,44•60•(7-t)=3,5•10⁶-0,299•10⁶•(7-t). Так, в первый момент повышают устьевое давление до величины 1,5 МПа, через 4 мин - 2,6 МПа, через 7 мин на устье создают давление 3,5 МПа, сохраняя на кровле продуктивного пласта постоянную безопасную депрессию
[ΔP]=41,27•10⁶-(1,44+1,81+ 9,81•1,155•3,34-0,83)•10⁶=1,01 МПа.Drilling of the fifth interval with wellhead pressure of 1.44 MPa is continued, monitoring the pressure in the pipes for a control time, after which a gas-liquid mixture leaves the wellhead. Carry out the drilling of the sixth interval during the control time with wellhead pressure of 1.44 MPa, monitoring the pressure in the pipes. When drilling the sixth interval for 1 hour (total drilling time is 7 hours) with an actual mechanical speed of 2.5 m / h, a gradual decrease in pressure in the pipes by ΔP _tf = 0.83 MPa is observed, i.e. the condition ΔP _tf = [ΔP _t5 ] is satisfied. Drilling of the sixth interval is continued, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment, depending

P _y (t) = 3.5 • 10 ⁶ -1155 • 9.81 • 0.44 • 60 • (7-t) = 3.5 • 10 ⁶ -0.299 • 10 ⁶ • (7-t). So, at the first moment, the wellhead pressure is increased to a value of 1.5 MPa, after 4 minutes - 2.6 MPa, after 7 minutes a pressure of 3.5 MPa is created at the mouth, while maintaining a constant safe depression on the roof of the productive formation
[ΔP] = 41.27 • 10 ⁶ - (1.44 + 1.81 + 9.81 • 1.155 • 3.34-0.83) • 10 ⁶ = 1.01 MPa.

что составляет 1,4% превышения над пластовым давлением.Six intervals with a total thickness of 29.5 m, i.e. the degree of opening of the reservoir in the depression is k _B = 29.5 / 100 ≈ 0.30 or 30%. The wellhead pressure is adjusted to the maximum allowable pressure of the wellhead equipment of 3.5 MPa, and at this pressure, drilling is completed to the bottom of the productive gas-bearing formation, where repression of

which is 1.4% excess over reservoir pressure.

 Figure 3 presents graphs of the dependence of changes in pressure at the mouth from the opening depth of the productive gas-bearing formation and the pressure distribution in the annular space of the well at the completion of the opening of the formation according to the claimed technology (see section of the example - line 1) and the prototype (see line 2).

On the abscissa axis (pressures), the values of the pressures at the wellhead [P _ymax ], P _y1 , P _yi , P _y5 , P _y and reservoir P _pl , P _{plf are marked} . On the ordinate axis (depths), the values of the depths of the roof H _K , the soles H _{p of the} reservoir and drilling intervals h ₁ - h ₅ are marked (moreover, starting from the 2nd, the interval planned for opening should be considered i-hole, and all drilled - j-tovs).

 Line 1 characterizes the pressure distribution in the annular space of the well filled with flushing fluid of adjusted density and maximum allowable gas saturation, taking into account hydraulic pressure losses and wellhead pressure equal to the maximum allowable pressure of wellhead equipment.

Line 2 characterizes the pressure distribution in the annular space of the well filled with flushing fluid of adjusted density, taking into account hydraulic pressure losses and estimated wellhead pressure P _y .

Compared with the prototype (see Fig. 3), it is obvious that the quality of the opening of the formation is improved by increasing the degree of opening of the formation by depression power: k _in = 27%, and in the prototype k _B = 24%, as well as a decrease in repression to the bottom of the formation ΔР _p = 0.19 MPa, and according to the prototype ΔP _p = 0.36 MPa, and improving the safety of the process due to the speed of detection at an early stage of gas inflow into the well by analyzing the actual data of wellhead information.

 The productive formation was opened from the roof in a depression to a depth caused by gas saturation of the flushing fluid, and the rest to the bottom of the formation was repressed while maintaining a safe depression in the roof. As a result, the effect of flushing fluid on the bottom-hole zone of the formation is insignificant, which allows maximum preservation of the natural permeability of the formation and improves the quality of opening. The use of wellhead pressure to control the bottomhole provides quickness and ease of implementation, since it does not require significant additional costs for preparing a weighted solution and changing the hydraulic program for flushing the well. The inventive technology allows to determine the actual reservoir pressure, the composition of the reservoir fluid and the productivity parameter (reservoir properties) of the reservoir directly during drilling, which ensures the reliability of the pressure acting on the reservoir and helps to reduce the likelihood of emergency situations.

 The technology includes traditional drilling equipment and tools, in addition to which a commercially available wellhead equipment is required: a rotating preventer, a throttle with a variable flow area, a degasser. The method is expediently applied when opening gas reservoirs in unstable hydrodynamic equilibrium with a well, i.e. jointly open, without lowering an additional technical column, the developing and absorbing layers (for example, at the fields of Tyumenburgaz enterprises).

Claims (1)

A method for drilling a productive gas-bearing formation by drilling, including sealing the wellhead and at the initial opening moment, calculating the minimum density of the flushing fluid, determining hydraulic losses in the annular space of the well, and for drilling the first interval of the producing formation, bringing the initial wellhead pressure to a value determined by the formula
P _y1 = [P _y ] - P _cells ,
where P _y1 - pressure at the mouth at the initial opening, Pa;
[R _y ] - technologically sufficient pressure wellhead equipment when drilling, according to the condition
[P _y ] ≤ P _pl - P _min , Pa,
where R _PL - design value of reservoir pressure, Pa;
P _min - the pressure column of the washing liquid of the lowest density at a depth of N _to provide a technological effect, Pa;
N _to - the depth of the roof of the reservoir, m;
P _KP - hydraulic pressure loss in the annular space, Pa,
drilling of both the first and subsequent intervals, for the control time for the first interval, determined by the formula
t ₁ = (Н _к • S _кп ) / Q,
where t ₁ is the control drilling time of the first interval, s;
S _KP - the cross-sectional area of the annular space, m ² ;
Q - pump capacity, m ³ / s,
with constant monitoring of the pressure in the pipes and in the absence of gas inflow, the creation of depression on the reservoir by successively lowering the wellhead pressure to a value determined by the dependence

where Р _уi is the pressure at the mouth for the opened i-th interval, Pa, i = 2,. . . , n;
h _j - open drilling interval, m, j = 1,. . . , n;
ρ _o - the minimum density of the washing fluid at the initial opening, kg / m ³ ;
g is the acceleration of gravity, m / s ² ,
characterized in that at the initial moment of opening, the maximum allowable gas saturation of the washing liquid is additionally determined by the expression
[a ₁ ] = min {a _choice1 , and _mouth1 },
wherein

where [a ₁ ] is the maximum allowable gas saturation of the flushing fluid, reduced to normal conditions (n.a.);
and _vyb1 - permissible gas saturation of the flushing fluid, corresponding to the condition of the beginning of the discharge and reduced to N. at. ;
and _ust1 - the permissible gas content of the flushing fluid, ensuring the stability of the walls of the well and reduced to N. at. ;
[P _{at max} ] - the maximum allowable pressure at the wellhead, determined by the technical characteristics of the wellhead equipment (rotating preventer, throttle), Pa;
P _s - pressure in the well at the depth of the roof of the reservoir, equal to the sum of hydrostatic and hydrodynamic pressure in the annular space at the depth of the roof of the formation and pressure at the wellhead, Pa;
T _about , T _s - the temperature of the flushing fluid at the mouth and at the bottom, respectively, K;
ΔР _max - the maximum allowable depression on the borehole walls, within 10-15% of the effective skeletal stresses, i.e. the difference between rock and pore rock pressure (Safety rules in the oil and gas industry. - M., 1998, p. 2.7. 3.5), Pa;
ρ _g - gas density in n at. kg / m ³ ;
α _t is the solubility coefficient of the gas under normal conditions and the average temperature of the washing liquid, Pa ^-1 ;
P _about - atmospheric pressure, Pa;
z _o , z is the gas compressibility coefficient under normal conditions and averaged, respectively,
moreover, along with monitoring the pressure in the pipes, the flow rate of the flushing fluid at the exit from the well is additionally monitored, and during drilling of the first interval in case of constant or decreasing pressure in the pipes while increasing the flow of flushing fluid at the exit of the well, the actual gas saturation of the flushing fluid is determined by the formula

wherein

P _s = P _y1 + H _to • gr P _s ;
grP _c = gρ _o + P _kp / H _k ,
ΔP _s = P _s -ΔP _t1 ,
ΔP ² = P $\genfrac{}{}{0ex}{}{\text{2}}{\text{pl}}$ -ΔP $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ;
P (h, t _b ) = P _y1 + h • grP _s - ΔP _t1 • (1-h / t _b v _kp );
b = S _zab • v _m • m • z;
α _s = α _T • Q,
where a _f1 - the actual gas saturation of the flushing fluid, in n. at. ;
V _n.a. (t _b ) - the volume of gas in the well, received due to variable depression and with cuttings during drilling, to n at. , m ³ ;
and _pf1 is a parameter characterizing the reservoir properties of the reservoir and gas inflow to the bottom of the well under specific technological conditions, m ³ / s ² , Pa;
t _b - drilling time, s;
v _CP - upward flow velocity, m / s;
ΔQ _f1 - the actual increase in the flow rate of flushing fluid at the exit from the well, m ³ / s;
Δt is the time interval during which there was an increase in the flow rate of flushing fluid, s;
gr P _c - gradient of the total pressure of the flushing fluid in the annular space, Pa / m;
ΔP _t1 - the current decrease in pressure in the pipes, equal to the difference in pressure in the pipes at the beginning of drilling the formation and at the current moment, Pa;
P (h, t _b ) - pressure distribution in the well over the height of the gas-liquid mixture formed during drilling, Pa;
h is the current height of the gas-liquid mixture, m;
S _Zab - cross-sectional area of the face, m ² ;
v _m - mechanical drilling speed, m / s;
m is the coefficient of porosity;
α _З - parameter characterizing the amount of dissolved gas, m ³ / (s • Pa);
b is a parameter characterizing the reservoir properties of the reservoir and gas inflow with cuttings, m ³ / s,
is compared with the maximum permissible gas saturation of the washing liquid and under the condition _F1 = [a _1] continue drilling a first interval, increasing the pressure at the wellhead to wellhead maximum pressures depending on
P _y (t) = [P _{y max} ] - ρ _o g • v _kp • 60 • (t _p -t),
wherein

where P _y (t) is the current generated wellhead pressure, Pa;
t _p - the time during which the increase in pressure at the mouth, min;
t - current time point of pressure increase at the mouth, min,
and thus complete the drilling pressure to half productive gas reservoir provided and _F1> [a _1] Drilling is stopped, determine the actual formation pressure, the formation fluid is eluted, adjusted minimum density flushing fluid according to the formula

where ρ is the adjusted minimum density of the washing liquid, kg / m ³ ;
R _{pl f} - the actual reservoir pressure, Pa,
bring the wellhead pressure to the maximum allowable pressure of the wellhead equipment and at this pressure complete the drilling to the bottom of the productive gas-bearing formation and provided that _a1 <[a ₁ ] continue drilling both the first and subsequent intervals with the initial wellhead pressure and monitor the pressure in the pipes, and on the first interval determine the maximum allowable pressure drop in the pipes according to the formula

where [ΔP _t1 ] - the maximum allowable pressure drop in the pipes when drilling in the initial conditions, Pa,
and under the condition ΔP _tf = [ΔP _t1 ] continue drilling the subsequent interval, increasing the pressure at the wellhead to the maximum allowable pressure of the wellhead equipment according to the condition specified in condition a _ф1 = [a ₁ ], and at this wellhead pressure complete drilling to the bottom of the productive gas-bearing formation, and in the absence of gas influx, i.e., with constant pressure in the pipes and a constant flow rate of flushing fluid at the exit from the well, create the estimated value of depression for the opening interval and drill until the flow rate increases myvochnoy fluid output from the well and further drilling operations are repeated program provided for drilling the first and subsequent intervals with the corresponding change in drilling parameters for a first interval parameters reveals interval.

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