RU2472925C1 - Stimulation method of formation fluid influx from well - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: method involves lowering of the tubing to the well; drop of pressure on productive formation with replacement of fluid column in the well with gas-liquid mixture by its supply with booster unit; provision of the required ratio of mixture components in order to achieve the specified value of pressure drop on productive formation. When formation pressure is equal to 0.5-0.7 of value of hydrostatic pressure of fluid column in the well, prior to lowering of tubing to the well there installed is a remote downhole pressure gauge on lower end of the tubing. After the tubing is lowered to the well, stimulation of formation fluid influx from the well is performed in two cycles. The first cycle involves replacement of fluid column in the well with gas-liquid mixture-foam with density that is lower than fluid density in the well, which is pumped via the tubing with the aeration degree providing the rise of bottomhole pressure in the well above formation pressure as per readings of remote downhole pressure gauge by 25-30%. As gas-liquid mixture there used is aerated mixture of water solution of surface active substance (SAS) and stabilising agent providing the foam stability and preservation of collecting properties of the formation at foam penetration into the bottom-hole zone. The second cycle of stimulation of formation fluid influx from the well involves replacement of foam obtained during the first cycle with the foam of lower density by its pumping to annular space of the well with increase in aeration degree. Besides, backpressure on productive formation is decreased, the value of which is controlled as per readings of remote downhole pressure gauge; foam is destructed when it leaves the well during stimulation process of formation fluid influx from the well by throttling for repeated use.EFFECT: improving well development efficiency.2 dwg

Description

The invention relates to the oil and gas industry and can be used in the development of wells with reservoir pressure in the range from 0.5 to 0.7 of the hydrostatic pressure of the liquid column in the well.

A known method of well development by creating a depression on the formation (patent RU No. 2272897, IPC 8 E21B 43/18; B 43/27, publ. 03/27/2006 in bull. No. 9), including replacing the fluid filling the well with a solution of surface active substance (surfactant) with its subsequent aeration by feeding a blowing agent in the form of ammonium carbonate into the well, while before feeding the blowing agents, the bottomhole zone is subjected to acid treatment with the acid being pushed into the formation, and aqueous solutions of sodium nitrate NaNO are additionally used as blowing agents ₂ and hydrochloric acid HCl; aqueous solutions of blowing agent reagents are injected in 0.5-2.0 m portions in the following sequence: ammonium carbonate, hydrochloric acid, sodium nitrite, and each subsequent solution has a density greater than the previous one; the volume of injected reagents is 0.3- 1.0 volume of the well, but not less than 1.1 of the internal volume of the pressure column, and is determined by the useful volume of the well, and the surfactant solution additionally contains hollow glass microspheres.

The disadvantages of this method are:

- firstly, the surfactant solution is aerated directly in the well by supplying gas-forming substances to the bottomhole zone of the well, and the sequence of chemical reactions and the temperature regime may change, which can lead to a change in the physical and chemical properties of the replacement fluid, including decomposition carbonated liquid for gas and water, which generally reduces the success of well development;

- secondly, the magnitude of the depression created on the bed is not regulated.

Also known is a method of inducing formation fluid inflow from a well (N. A. Sidorov. Drilling and operation of oil and gas wells. - M .: Nedra, 1982, pp. 270-271), which includes reducing pressure on the producing formation by supplying it with the surface of the gas or gas-liquid mixture and replacing the column of liquid in the well with a gas-liquid mixture, while the gas is supplied by a compressor.

The disadvantages of this method are:

- firstly, the need for a compressor - a source of neutral fire and explosion-proof high pressure gas in a well;

- secondly, the magnitude of the depression created on the formation is not controlled from the wellhead.

The closest in technical essence is the method of causing the flow of formation fluid from the well (patent RU No. 2263206, IPC 8 E21B 43/25, published on 10/27/2005 in Bulletin No. 30), including the descent of the tubing string (tubing) into the well, reducing the pressure on the reservoir by replacing the column of liquid in it with a gas-oil (gas-liquid) mixture by supplying the mixture with a booster unit with the selection of the components of the mixture from a working well or from a production collector, while the required ratio of the components of the mixture to achieve a given value s to reduce the pressure reservoir provide selection components of the mixture through the separator, the outputs of which are communicated to the collector of product collection.

The disadvantages of this method are:

- firstly, to give stability to the gas-liquid mixture (foam), it is necessary to add surface-active substances (surfactants) to it as a foaming agent, otherwise premature decomposition of the foam into components, loss of its calculated density and, as a consequence, reduction in call quality and efficiency, are possible formation fluid inflow from the well;

- secondly, it is practically impossible to select the required ratio of the components of the gas-liquid mixture (water and gas) to achieve a given depression on the formation without controlling the change in the bottomhole pressure during the process of causing the flow of formation fluid from the formation in the well;

- thirdly, when the inflow of formation fluid from the well is called by applying a gas-liquid mixture (foam) by a booster unit to the annular (annular) space, the liquid is displaced to the surface along the tubing string, repression is created on the formation, therefore, when developing wells in which the reservoir pressure is in the range from 0.5 to 0.7 of the hydrostatic pressure of the fluid column, as the foam column in the annular space approaches the lower end of the tubing string, a significant amount of well fluid penetrates the formation, which negatively affects the efficiency of the process of causing formation fluid inflow from the well and significantly reduces the productivity of the formation. On the contrary, if the call of formation fluid inflow from the well, the reservoir pressure in which is in the range from 0.5 to 0.7 of the hydrostatic pressure of the liquid column in the well, is carried out only by pumping the gas-liquid mixture into the tubing string, then at the initial moment of the call this requires higher pressures developed by the booster unit for displacing the well fluid from the annular space to the surface, due to the large difference in the cross sections of the annular and pipe spaces, therefore the process of reducing the density of the foam, i.e. increase the degree of aeration, is delayed, which in turn increases the duration of the process of calling the flow of formation fluid from the well;

- fourthly, the addition of only surfactants to the gas-liquid mixture as a foaming agent can lead to the absorption of foam by the formation, which will lead to a decrease in the natural permeability of the formation in the bottomhole zone;

fifthly, there is no possibility of destruction of the foam when it leaves the well in the process of causing the influx of formation fluid from the well for reuse.

The objective of the invention is to improve the quality and efficiency of the call of the influx of reservoir fluid from the reservoir by injection into the well of a gas-liquid mixture (foam), in which the reservoir pressure is in the range from 0.5 to 0.7 of the hydrostatic pressure of the liquid column in the well, due to elimination of premature inflow of formation fluid from the well and giving the gas-liquid mixture (foam) a stable state and stability with the possibility of reducing the foam absorption intensity by the productive area whether or not the foam is completely absorbed by the reservoir in order to preserve its natural permeability (reservoir properties), as well as the control of the bottomhole pressure during the flow inflow process, with the possibility of the foam breaking when it leaves the well during the process of stimulating the reservoir fluid inflow for reuse.

The problem is solved by the method of causing the flow of formation fluid from the well, including the descent of the tubing string into the well, reducing the pressure on the reservoir by replacing the column of liquid in the well with a gas-liquid mixture by feeding it with a booster unit, providing the required ratio of the components of the mixture to achieve the desired pressure drop on the reservoir .

What is new is that when the reservoir pressure is in the range of 0.5-0.7 of the hydrostatic pressure of the liquid column in the well, before the tubing string is lowered into the well, a remote depth gauge is installed on the lower end of the tubing string, after the tubing string is lowered into the well is charged with inflow of formation fluid from the well in two cycles; in the first cycle, the column of liquid in the well is replaced by a gas-liquid mixture with a foam density less than the density of the liquid in the well, which is pumped through the column A tubing with an aeration degree that ensures a bottomhole pressure in the well above the reservoir by 25-30% as indicated by a remote depth gauge, uses a carbonated mixture of an aqueous solution of a surfactant and stabilizer as a gas-liquid mixture, which ensures foam stability and preserves reservoir properties when foam penetrates the bottomhole zone, in the second cycle of calling the flow of formation fluid from the well, replace the foam obtained in the first cycle with a foam of lower density by pumping it into the annulus consistency of the well with the degree of aeration thus reduce the back pressure on the producing formation, the magnitude of which is monitored for indications of remote depth gauge destroys foam upon its exit from the borehole during the call formation fluid inflow from the well throttling for reuse.

Figure 1 shows a diagram of the replacement of fluid in a well by injecting a gas-liquid mixture (foam) through a tubing string.

Figure 2 shows a diagram of the call flow formation fluid from the well by pumping a gas-liquid mixture (foam) into the annulus of the well.

The proposed method is as follows.

If the value of reservoir pressure in the well is in the range from 0.5 to 0.7 of the hydrostatic pressure of the liquid column in the well, then the condition is met:

where P _PL - reservoir pressure in the well, MPa;

P _g - hydrostatic pressure of the liquid column in the well, MPa.

For example, at reservoir pressure P _PL = 9 MPa and hydrostatic pressure of a liquid column in a well with a height of H = 1700 m:

where ρ is the density of the fluid in the well, kg / m ³ , for example, the density of water is 1000 kg / m ³ ;

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

H - the height of the liquid column in the well from the top of the reservoir to the mouth, m

Then, substituting in the formula (2), we obtain:

P _g = 1000 kg / m ³ · 9.8 m / s ² · 1700 m = 17 MPa.

Substituting in the formula (1), we obtain:

9 MPa = (0.5-0.7) · 17 MPa = 8.5-11.9 MPa, which satisfies condition (1).

Before lowering the tubing string 1 (see Fig. 1) into the well 2, a remote depth gauge 3 (conventionally shown in Fig. 1) is installed on the lower end of the tubing string, while its readings are transmitted to a control station (not shown), which allows monitoring change in bottomhole pressure during the process of causing formation fluid inflow from formation 4. A tubing string 1 is lowered into well 2, while its lower end should be at a depth h 2-3 meters above the bottom of formation 4. A faceplate 5 is installed at the mouth of well 2 with a central gate valve 6.

The central valve 6 is connected with the discharge line 7 of the booster unit 8, for which, for example, a gas booster system of the UNG 8/15 brand is used. An annular valve 9 is tied up by a flow line 10 with a gutter vessel 11. A needle valve (not shown) is installed on the flow line 10 at the entrance to the gutter tank 11, which allows the foam to be destroyed during the process of inflowing formation fluid from the well for reuse.

Open the central 6 (see figure 1) and annular valve 9. For example, according to the testimony of the remote depth gauge 3 at the control station, the reservoir pressure value of the formation 4 is 9 MPa. At the wellhead 1, a gas-liquid mixture (foam) is prepared. The gas-liquid mixture is a carbonated mixture of an aqueous solution of a surface-active substance (surfactant), which is used as a foaming agent, and a stabilizer that imparts stability to the foam. Stability is the ability of a foam to maintain its original volume. The criterion for evaluating the foam stability index is the lifetime of a liquid film between gas bubbles.

As a foaming agent, a surfactant is used, for example, sulfanol (according to TU 6-01-862-73) in a concentration of 0.1-0.3% of the volume of fresh water or other surfactants, for example, OP-7; OP-10 (according to TU 8433-81) in a concentration of 0.3-0.6% of the volume of fresh water.

For foam stability, a stabilizer is added, consisting of 5-7% wt., Modified starch according to GOST 7698-93 and 0.18-0.3% wt., Sulfacell according to TU 6-55-221-1210-91. Practical experiments showed that the stability of the foam with the addition of a stabilizer increased 5-9 times.

A mixture of an aqueous solution of a surfactant and a stabilizer is prepared as follows. The volume of an aqueous surfactant solution for inducing formation fluid from a well is determined based on the foam multiplicity, which is 3.5-5 in the process of inducing formation fluid from a well, as well as from the required volume of a gas-liquid mixture V _g , consisting of the volume V _{1 of the} well for replacing the fluid in the well with a gas-liquid mixture (first cycle) and volume V _{2 of the} well for circulating the gas-liquid mixture (foam) in the process of causing the flow of formation fluid from the well (second cycle), i.e. Equal volumes of the two wells, namely: V ₁ = V _2, then V _r = 2 × V ₁ and at 3.5-5 multiplicity foam volume of aqueous surfactant solution is determined by the formula:

where V _in - the volume of an aqueous solution of a surfactant, m ³ ;

V _g - the required volume of the gas-liquid mixture, m ³ ;

3,5-5 - the multiplicity of the foam.

For example, when the height of the liquid column from the formation to the mouth: H = 1800 m and a casing string diameter of 168 × 9 mm, the volume V _{1 of the} well is determined by the formula

where V ₁ - one well volume, m ³ ;

π = 3.14;

d is the inner diameter of the casing of the well, m,

those.

d = 168 mm - (9 mm2) = 150 mm = 0.15 m.

H - the height of the liquid column from the mouth to the bottom, m

Then, substituting into formula (4): V ₁ = (3.14 + (0.15 m) ^2/4) * 1800m = 31.8 m ^3, and the required amount of liquid mixture to the entire process of the call inflow:

V _g = 2V ₁ = 2 · 31.8 m ³ = 63.6 m ³ .

We take the foam multiplicity equal to 4.

Then the required volume of an aqueous surfactant solution is determined by the formula (3):

V _in = V _r / (4) = 63.6 m ^3/4 = 15.9 m ³ take aqueous surfactant solution volume of 16 ^m3.

Next, prepare an aqueous solution of a surfactant.

First, in fresh water with a volume of 16 m ³ and density ρ = 1000 kg / m ³ , for example, sulfanol (according to TU 6-01-862-73) is added in a concentration of 0.1-0.3% of the volume of fresh water.

Then, in an aqueous surfactant solution (heated to 40-45 ° C), a stabilizer consisting of 5-7% wt., Modified starch and 0.18-0.3% wt. Is added with constant stirring. sulfacella. After complete dissolution of the stabilizer in an aqueous solution of a surfactant, a mixture of an aqueous solution of a surfactant and a stabilizer is obtained.

Fill the tank 12 of the booster unit 8 with a mixture of an aqueous solution of a surfactant and a stabilizer (see figure 1). As a gas that is safe under ignition conditions of a hydrocarbon medium, gas (for example, nitrogen) generated by the gas generator 13 of the booster unit 8 is used as a result of the combustion of fuel (gasoline, diesel fuel) in compressed air, i.e. burnout of oxygen.

Gas from the gas generator 13 is supplied to the booster (mixing) unit 14, where the continuous mixing (carbonation) gas mixture of aqueous surfactant and stabilizer solution to form a liquid mixture, e.g., density ρ = 800 kg / m ³ feed booster pump 15 from the tank 12 of the booster unit 8. The central valve 6 is opened and the gas-liquid mixture (foam) is fed into the tubing string 1 through the discharge line 7 by the booster unit 8, i.e. into the pipe space 16 of well 2 in order to replace the entire column of fluid in the well (well fluid), for example, with a density ρ = 1000 kg / m ³ with a foam density (ρ = 800 kg / m ³ ), less than the density of the liquid in the well (ρ = 1000 kg / m ³ ) with a degree of aeration, which provides an excess of bottomhole pressure in the well above the reservoir by 25-30%, which is controlled by the readings of a remote depth gauge. For example, as noted above, when reservoir pressure P _pl = 9 MPa bottomhole pressure (P _s) would be P _s = (25-30% / 100%) · P + P _{pl pl} = (0.25-0.3) 9 MPa + 9 MPa = 11.25-12 MPa. Thus, the bottomhole pressure is maintained within 11.25-12 MPa, with a flow rate of a mixture of an aqueous solution of a surfactant and a stabilizer equal to, for example, 8 l / s, injection of foam with a degree of aeration, for example, 20-40 m ³ / m ³ , (i.e. 20-40 m ^{3 of} air per 1 m ^{3 of an} aqueous surfactant solution), replace the entire column of fluid in the well (well fluid). At the moment the column reaches the bottom of the foam tubing 1 from the annulus 17 of the tubing 1 through the annular valve 9 and the flow line 10 into the groove tank 11, the outflow of the well fluid displaced by the foam begins. The injection of foam into the tube space 16 is continued until the well fluid is completely replaced with foam of volume V ₁ , i.e. before the appearance of foam in the gutter container 11 (determined by the appearance of the circulation of the foam).

On this, the first cycle of the call of formation fluid inflow from the well ends. Under such conditions, foam penetrates into the bottom-hole zone of formation 4, while a carbonated mixture of an aqueous surfactant solution and stabilizer is used as a gas-liquid mixture, which ensures foam stability and preserves reservoir properties when the foam penetrates into the bottom-hole zone. The addition of a stabilizer allows one to reduce the intensity of foam absorption by the reservoir or to prevent the absorption of foam by the reservoir, thereby preserving its natural permeability (reservoir properties).

Then, a second cycle of inducing formation fluid from the well is produced by supplying a gas-liquid mixture (foam) to the annulus 17 of well 2.

Before the start of the second cycle of the call of formation fluid inflow from the well, the equipment is re-lined at the wellhead 2 (see Fig. 2). To do this, the annular valve 9 of the well 2 is connected with the injection line 7 of the booster unit 8, for which, for example, a gas booster unit of the UNG 8/15 brand is used, and the central valve 6 with the trough capacity 11, and a needle valve is installed at the outlet from the well by throttling. (not shown) on the flow line 10 (see figure 2) at the entrance to the groove capacity 11.

Open the central 6 and annular 9 valves. For example, according to the testimony at the control station of the remote depth gauge 3, the value of the reservoir pressure of the formation 4 is 9 MPa. Foam is injected into the annulus 17 through the injection line 7 and the open annular valve 9, then in the well 2, the foam obtained during the first cycle with a density ρ = 800 kg / m ^{3 is} replaced with a foam of lower density, i.e. ρ = density of less than 800 kg / m ³ by gradually increasing the degree of aeration (20-40 m ³ / m ³ or higher), i.e. increase the supply of gas produced by the gas generator 13 to the booster device 14 of the booster unit 8, at a constant flow rate of a mixture of an aqueous solution of a surfactant and a stabilizer, for example, 8 l / s In this case, the circulation of the foam is continued by pumping the booster unit 8 along the injection line 7 into the annulus 17 and exiting into the chute 11 through the pipe space 16 of the tubing string 1 and flow line 10 until the specified pressure drop on the reservoir 4 is achieved by increasing the degree of aeration, for example, up to 120 m ³ / m ³ , i.e. to a density ρ = 120 kg / m ³ , while monitoring the readings of a remote depth gauge 3, the value of which should gradually decrease. For example, the value of the set value (allowable depression) of the pressure drop on the reservoir is 4 MPa (the set value of the pressure drop is determined by the geological service of the oil and gas company individually for each well, depending on the strength of the cement ring behind the casing string and other factors) (see Bulatov A. I. Well development: reference, allowance / A.I. Bulatov, Yu.D. Kagmar, P.P. Makarenko: under the editorship of R. Yaremiichuk - M .: Nedra-Business LLC, 1999. - 473 from).

Then the readings of the remote depth gauge 3 should not be lower than 9 MPa-4MPa = 5 MPa. Thus, gradually increasing the degree of aeration of the liquid (by increasing the volume of gas supplied by the gas generator 13 of the booster unit 11), the back pressure on the reservoir is reduced and, depending on the magnitude of the change in reservoir pressure, an acceptable depression on the reservoir 4 is achieved.

Upon reaching the set value of the bottomhole pressure of 4 MPa, the circulation of the foam continues, but the increase in the degree of aeration of the foam is stopped. Further, maintaining the achieved pressure by changing the injection pressure of the booster unit (back pressure at the wellhead), the foam is circulated, and the pressure is monitored according to the readings of the remote depth gauge 3. During the second cycle of the flow of formation fluid from the well when the foam leaves the well 2 the foam is destroyed by throttling a needle valve (not shown) installed on the flow line 10 at the entrance to the trough 11. After the foam is destroyed, an aqueous solution of surfactant Paet in channel capacity 11 for reuse.

The presence of inflow from the formation 4 is determined visually by the volumetric output of the formation fluid from the well into the trough 8 together with the foam. If there is a sufficient amount of formation fluid inflow from the well (determined by the geological service of the oil and gas company individually for each well, depending on the previous production rate during the operation of the well), the formation fluid inflow is stopped.

The tubing string is lifted 1, production equipment (not shown) is lowered into well 2 and put into operation.

Implementation of the proposed method will improve the quality and efficiency of the call of formation fluid inflow from the well, the reservoir pressure in which is in the range from 0.5 to 0.7 hydrostatic pressure of the liquid column in the well due to the fact that the formation fluid inflow from the well is called in two cycles, while in the first cycle of the call of formation fluid inflow from the well, foam is injected into the well to replace the column of well fluid in the pipe space, and in the second cycle, the call of inflow The formation fluid from the well is injected with foam into the annulus, which minimizes the flow of well fluid into the formation.

The use of a gas-liquid mixture as a foam consisting of an aqueous solution of a surfactant and a stabilizer allows you to maintain a predetermined density of the foam during the entire process of causing inflow from the well, and the presence of a stabilizer in the foam will allow you to preserve the natural permeability of the formation, reduce the negative impact of the borehole fluid on the formation while monitoring behind the change in bottomhole pressure during the inflow call by means of a remote depth gauge, and the destruction of the foam when it leaves the well during the call fluid inflow from the well throttling allows you to make its reuse.

Claims (1)

A method of inducing formation fluid inflow from a well, including lowering the tubing string into the well, reducing the pressure on the producing formation by replacing the column of liquid in the well with a gas-liquid mixture by feeding it with a booster unit, providing the required ratio of the components of the mixture to achieve a predetermined amount of pressure reduction on the producing formation, characterized in that when the value of reservoir pressure, which is in the range of 0.5-0.7 of the hydrostatic pressure of the liquid column in the well, before the descent of the tubing string into a remote depth gauge is installed on the lower end of the tubing string, after the tubing string is lowered into the well, the formation fluid is called in from the well in two cycles, in the first cycle, the column of fluid in the well is replaced by a gas-liquid mixture with a foam density less than the density of the liquid in the well, which is pumped along the tubing string with a degree of aeration, which ensures that the bottomhole pressure in the borehole is higher than the reservoir pressure according to the testimony of the remote depth gauge by 25-30%, as a gas-liquid one If a carbonated mixture of an aqueous solution of a surfactant and a stabilizer is used, which ensures the stability of the foam and preserves the reservoir properties of the formation when the foam penetrates into the bottomhole zone, in the second cycle of inducing formation fluid from the well, the foam obtained in the first cycle is replaced with foam of lower density by pumping it into the annulus of the well with an increase in the degree of aeration, while reducing the back pressure on the reservoir, the value of which is controlled by the testimony of the remote deep manoma tra, destroy the foam when it exits the well in the process of causing the influx of formation fluid from the well by throttling for reuse.

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