RU2649204C1 - Method for drilling-in at controlled drawdown - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to oil and gas industry, and in particular to drilling of oil wells. Method comprises lowering a drill pipe string with a drilling bit into the well, a wellhead banding, flushing a borehole, and feeding washing liquid to the drilling bit when drilling, carrying out of researches on establishment of drilling modes, establishment of an optimum charge of a washing liquid according to the schedule. For the plotting of the data from neighboring wells, the average productivity coefficient is determined, and dependence of the wellhead pressure on the bottom-hole pressure on several modes of the same wells is established. Optimum drilling mode is selected according to the graphs of these dependencies at the point of intersection of the flow characteristic of the reservoir with the flow characteristic of the well, and drilling is performed by controlling the wellhead pressure such that the well rate is 30÷50 % of the maximum well rate of neighboring wells.

EFFECT: quality of drilling-in is increased, the bottom hole colmatation is prevented, its initial permeability is maintained.

1 cl, 2 dwg

Description

The invention relates to the field of oil and gas industry and, in particular, to the drilling of oil wells.

A known method of drilling a gas-bearing formation (Patent RU 2148698, ЕВВ 21/08, published on 06/20/05), including calculating the minimum density of the flushing fluid at the initial opening moment and conducting the autopsy of the reservoir on the flushing fluid, ensuring a minimum design density.

The disadvantage of this method is the inability to quickly respond to changes in reservoir pressure by adjusting the bottomhole, because changing the density of the flushing fluid is time-consuming, and excessive weighting of the drilling fluid can lead to an emergency.

A known method of drilling a well in a depression (Patent RU 2287660, ЕВВ 21/14, published on November 20, 2006), including the use of aerated flushing fluid, drilling a predetermined interval without extracting the drill string, flushing the well in aeration mode with the drill string pacing before building it, gas injection and adding oil to the pipe space, sealing the annulus.

The closest in technical essence is the method of opening the reservoir for depression (RF patent No. 2199646, IPC 21B 21/00, 08/20/03). The wellbore is washed, aerated flushing fluid is fed to the bit while drilling. In the wellbore, studies are underway to establish depression drilling regimes. Autonomous and cable gauges measure pressure in all modes. Set the pressure loss in the interval from the installation of the pressure gauge to the wellhead. According to changes in the bottomhole pressure from the flow rate of the washing liquid and the gaseous agent, a graph of the obtained dependence is built. According to the schedule, the required mode of fluid supply and agent is established.

The disadvantage of this method is the high accident rate in case of non-compliance with the calculated value of depression, the difficulty of implementing the method due to the difficulty of ensuring the necessary properties of the washing liquid at a depth. When implementing the method, part of the cuttings inevitably falls into the bottomhole formation zone and creates a mating effect.

The objective of the method of opening a productive formation in depression is to improve the quality of opening of productive layers due to the ability to control the depression and flow rate with which the formation produces.

The technical result of the invention is to prevent mudding of the bottomhole zone and preservation of its initial permeability.

The technical result is achieved by the fact that in the method of opening a productive formation in a controlled depression, which includes lowering drill pipe string with a bit, tying the wellhead, flushing the wellbore and supplying drilling fluid with drilling bit, conducting research to establish drilling modes, establishing the optimal the flow rate of flushing fluid according to the schedule, while to build a schedule according to the data of neighboring wells, the average productivity coefficient is determined, the dependence of pressure from bottomhole in several modes for the same wells, the optimal drilling mode is selected according to the schedule of this dependence at the point of intersection of the flow rate of the formation with the flow rate of the well, and drilling is carried out by controlling wellhead pressure, so that the well production is 30 ÷ 50% from the largest flow rate of neighboring wells.

In FIG. 1 shows a diagram of the circulation of the drilling fluid during the opening of the reservoir in a controlled depression. Drilling fluid through the drill string 1 is fed into the well with a depth of N (m). In this case, the bottomhole pressure (at the exit from bit 2) is P ₁ (MPa), the pressure at the wellhead is P ₂ (MPa), the flow rate of the drilling fluid at the well inlet is Q ₀ (m ³ / s). Casing pipes were lowered into the well 3. Wellhead pressure adjustment can be carried out by adjusting the nozzle 4. The pump supply is chosen so as to ensure rock removal from the bottom of the well. The hydraulic resistances in the circulation system are proportional to the squared flow rate.

To solve the problem of opening a reservoir, we introduce the following assumptions that characterize the entire well-reservoir system. We assume that the casing is lowered to the top of the reservoir, the composition and properties of the drilling fluid are selected in accordance with geological conditions, the hydraulic resistances are calculated according to well-known formulas or determined by special experiments before the formation is opened, and the properties of the formation fluids are known. It is necessary to determine the discharge characteristics “formation-face” and “face-fitting”, ie:

where q is the production rate, m ³ / s;

P ₁ - bottomhole pressure, MPa;

P ₂ - pressure on the casing fitting, MPa.

To determine the discharge characteristics of the “face-bottom” in accordance with the Dupuis law, you can write:

where R _PL and P ₁ - reservoir and bottomhole pressure, respectively, MPa;

q - formation flow rate, m ³ / s;

.A is the coefficient of productivity,

.

Consumption characteristics "face-fitting" (Fig. 1) are determined:

where: P ₁ - bottomhole pressure, MPa

λ is the coefficient of hydraulic resistance in the casing;

ρ is the density of the solution, kg / m ³ ;

N - well depth, m;

g is the acceleration of gravity, m / s ² ;

Q is the flow rate of the drilling fluid at the exit from the well, m ³ / s.

Drilling fluid consumption at the exit from the well:

where: q - formation flow rate, m ³ / s;

Q ₀ - the flow rate of the drilling fluid at the entrance to the well, m ³ / s

When constructing the “face-choke” discharge characteristics, the intersection point of the “face-union” and “reservoir-face” discharge characteristics (point M) is obtained. At point M, the wellhead and bottomhole pressures are selected and drilling is carried out, controlling the depression so that the production rate of the wells is 30-50% of the production rate of neighboring wells.

The implementation of the method is illustrated by an example.

. Глубина разбуриваемой скважины Н=1200 м, плотность раствора ρ=1000 кг/м³, пластовое давление Р_пл=20 МПа. Применяя формулу (2), строим расходную характеристику «пласт-забой» по уравнению Р₁=20-16667q. Эта характеристика представлена на фиг. 2 зависимостью I.The Vatinskoye field is being drilled. The reservoir is opened by well No. 729/88. According to the study of neighboring wells, the productivity coefficient is

. The depth of the drilled well N = 1200 m, the density of the solution ρ = 1000 kg / m ³ , reservoir pressure R _PL = 20 MPa. Using the formula (2), we construct the flow characteristic “formation-face” according to the equation P ₁ = 20-16667q. This characteristic is shown in FIG. 2 dependence I.

When determining the pressure loss λQ ² H, it is necessary to determine Q ₀ , since Q is determined by the formula (4). In accordance with the recommendations, the upward velocity ν for the removal of cuttings should be about 2 m / s. Determine Q ₀ according to the following formula:

where ν is the velocity of the upward flow, m / s;

r _c - well radius, m

.Then

.

To determine the flow characteristics of the “bottom-fitting" in the equation (3) we substitute the numerical values.

In the formula (3): ρ⋅g⋅Н = 1000⋅9.8⋅1200 = 11.76 MPa.

The value of Q is represented by the formula (4) as the sum of the flow rate at the entrance to the well Q ₀ and the flow rate q:

и величиной q² можно пренебречь. Следовательно:The flow rate of the formation is much less than the flow rate at the entrance to the well (q << Q ₀ ), therefore

and q ² can be neglected. Hence:

We determine: Q ² = (0.0628) ² + 2⋅0.0628⋅q.

, следовательно: λ⋅Q²⋅Н=0,0421⋅[(0,0628)²+2⋅0,0628⋅q]⋅1200=0,2+6,3⋅q [МПа], причем наибольший средний дебит соседних скважин q=0÷0,0012 м³/с. Окончательно получаем:In the formula (3), the value of the hydraulic resistance coefficient is adopted for rough pipes:

therefore: λ⋅Q ² ⋅Н = 0.0421⋅ [(0.0628) ² + 2⋅0.0628⋅q] ⋅1200 = 0.2 + 6.3⋅q [MPa], with the highest average flow rate neighboring wells q = 0 ÷ 0.0012 m ³ / s. Finally we get:

Now, given the values of P ₁ , from the relation (8) we determine the discharge characteristics “bottom-fitting” at q = 0.0012 l / s. With P ₁ = 17.5 MPa, from (7) we obtain P ₂ = 5.5 MPa, with P ₁ = 15 MPa, P ₂ = 3.0 MPa, etc. These characteristics are shown in FIG. 2 as dependencies II.

The intersection points of the flow-face-and-face-discharge flow characteristics of FIG. 2 are modes of stable well operation. Approximately in the area of formation flow rate (0.4-0.5) ⋅ 10 ^-3 m ³ / s, which will be 30-50% of the production rate of neighboring wells, we got a certain point M. At point M, the bottomhole pressure P ₁ and P ₂ = 5 MPa, the flow rate of the solution at the exit from the well is 63.2 l / s.

If the flow rate at the exit from the well is shifted to point B, it is necessary to open the nozzle so that the bottomhole pressure decreases and the flow rate increases to 0.4⋅10 ^-3 m ³ / s (Q change from 63 to 63.2 l / s). If the point moves toward C, then the nozzle at the wellhead must be covered so that the wellhead P ₂ grows to 5 MPa. To implement the method, it is necessary to equip the wellhead with a flow meter, a manometer and an adjustable fitting.

Claims (1)

A method of opening a productive formation in a controlled depression, including lowering drill pipe with a bit into the well, tying the wellhead, flushing the wellbore and feeding the bit when drilling drilling fluid, conducting studies to establish drilling modes, setting the optimal flow rate of drilling fluid according to a schedule that differs the fact that to plot using the data from neighboring wells, the average productivity coefficient is determined, the wellhead pressure depends on the bottomhole pressure several modes for the same wells, and the optimal drilling mode is selected according to the graphs of these dependencies at the point of intersection of the reservoir flow rate with the flow rate of the well, and drilling is carried out by controlling wellhead pressure so that the flow rate of the well is 30 ÷ 50% of the largest flow rate of neighboring wells .

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