CN104563927B - A kind of wellbore stability method and experimental facilities being applicable under balance pressure drilling - Google Patents

Abstract

The invention relates to a well wall stabilization method and an experimental device suitable for underbalanced drilling. The method includes the following steps: (1) determining the formation water activity of the shale; (2) determining the pore pressure of the formation to be drilled; (3) calculating the formation temperature; (4) measuring the formation membrane efficiency by using a membrane efficiency testing experimental device; (5) ) Determine the drilling fluid density according to the drilling fluid column pressure and the well depth; (6) If the drilling fluid density is determined, determine the difference between the drilling fluid column pressure and the formation pressure as the underpressure value. According to the principle of total potential energy balance, use The chemical potential difference is obtained from the underpressure value, and then the drilling fluid activity is determined according to the chemical potential difference and the formation water activity; (7) The drilling fluid density or activity is adjusted according to the determination result to maintain the stability of the borehole wall. Beneficial effects: fully consider the role of chemical potential, accurately give the drilling fluid density when maintaining the balance of the total potential energy of the formation, effectively prevent the drilling fluid filtrate from invading the formation, improve the stability of the well wall, and enhance the performance of the underbalanced drilling technology. App promotion.

Description

A Wellbore Stabilization Method and Experimental Device Applicable to Underbalanced Drilling

technical field

The invention relates to an oil field drilling method, in particular to a well wall stabilization method and an experimental device suitable for underbalanced drilling.

Background technique

Underbalanced drilling refers to the drilling technology in which the circulating pressure of the drilling fluid (including liquid column pressure and circulating back pressure) is lower than the pore pressure of the formation during the drilling process, so that the formation fluid enters the wellbore in a controlled manner and circulates it to the surface. The use of underbalanced drilling technology can increase the mechanical penetration rate, prolong the life of the drill bit, reduce or eliminate leakage and differential pressure sticking, improve drilling efficiency, and reduce the direct cost of drilling; it can also discover new production layers, reduce oil and gas layer soaking time, reduce or Eliminate the invasion and damage of drilling fluid to the formation, so as to effectively protect the oil and gas layers and increase the cumulative production of the reservoir.

Therefore, underbalanced drilling technology has been widely used at home and abroad. Since 2007, the number of underbalanced drilling wells completed in the United States has been more than 12,000 per year, accounting for about 26% of the total number of wells drilled each year. It has become the preferred technology for opening reservoirs; , China has completed 1017 underbalanced wells, and the application effect is remarkable; however, the wellbore stability of underbalanced drilling has not been effectively solved, and has become the main obstacle restricting the development of underbalanced drilling technology.

Wellbore instability in underbalanced drilling mostly occurs in shale intervals. After the shale formation is opened, pressure transmission and material exchange will occur after the drilling fluid contacts the formation, resulting in formation pressure changes and rock strength reduction, leading to wellbore instability. Formation pressure transfer and material exchange are mainly controlled by two factors: (1) the hydraulic potential difference between the drilling fluid column pressure and the formation pore pressure; (2) the chemical potential difference between the drilling fluid filtrate and the formation fluid. At present, the drilling fluid density of underbalanced drilling is designed according to the formation collapse pressure, formation pore pressure and the pressure bearing capacity of the equipment. Formation pore pressure, without considering the influence of chemical potential on formation pressure transfer and material exchange, resulting in drilling filtrate intrusion into formation under the action of chemical potential, resulting in downhole complex situations such as borehole wall collapse and pipe sticking. Therefore, only by keeping the hydraulic potential difference and chemical potential difference between the drilling fluid and the formation fluid balanced at the same time, that is, the total potential energy balance, can the drilling fluid filtrate be prevented from invading the formation, reducing the strength of the formation, causing complex accidents and polluting the formation.

In summary, the traditional underbalanced drilling fluid density design method is not applicable, and a simple and practical underbalanced drilling borehole stability design method based on the total potential energy balance theory is very important for underbalanced drilling borehole stability.

The semi-permeable membrane membrane efficiency tester announced by the utility model patent of China Patent Application No. 200720187488.9 and the shale membrane efficiency tester announced by the utility model patent of 200420089356.9 all adopt the conductivity of the semi-permeable membrane liquid in the equilibrium state with the known Conductivity comparison, an indirect measurement method converted into semi-permeable membrane membrane efficiency, only considers the changes in the properties of the semi-permeable membrane fluid in equilibrium, ignoring the influence of shale properties and pore structure on osmotic pressure and membrane efficiency; Chinese patent The utility model patent application number 200620034702.2 discloses a drilling fluid semipermeable membrane measurement device that can only be tested at room temperature, and cannot measure the membrane efficiency at the actual formation temperature. The flow of drilling fluid in the wellbore; the development of the shale film efficiency tester, oil drilling and production technology, 2010, No. 11, author, Zhang Yan, Xiang Xingjin, Yan Jienian, Wu Bin, Zhao Lei; The film formation efficiency of different drilling fluid systems can only be analyzed qualitatively, and the measurement results of shale film efficiency cannot be given quantitatively. Shale Hydration-Mechanics Coupling Simulation Experimental Device and New Pressure Transfer Experimental Technology, and Journal of Petroleum, Volume 26, Issue 6, November 2005 Xu Jiafang, Qiu Zhengsong, Lu Kaihe Mud Shale Membrane Efficiency Test Device and Testing Technology Although Lu Kaihe, Qiu Zhengsong, and Xu Jiafang directly measured the osmotic pressure and membrane efficiency, they can only use regular standard cores to carry out experiments, and cannot use irregular cores and dropped blocks to carry out experiments. And the experimental device is complicated and inconvenient for on-site operation and use.

Contents of the invention

The purpose of the present invention is to aim at the above-mentioned defects existing in the prior art, and to provide a wellbore stabilization method and an experimental device suitable for underbalanced drilling. application promotion.

A borehole stabilization method suitable for underbalanced drilling, comprising the following steps:

(1) Determining the formation water activity of mud shale by means of isothermal adsorption test collection;

(2) Determine the pore pressure of the formation to be drilled according to the logging data of the adjacent well and the formation pressure test data;

(3) Determine the formation temperature based on the formation temperature data of logging while drilling, or calculate the formation temperature according to the geothermal gradient in the region;

(4) Measuring formation membrane efficiency by using a membrane efficiency testing experimental device; the membrane efficiency testing experimental device includes a servo-controlled injection pump (1), a constant temperature box (7), a core holder (8), a computer data acquisition system ( 19), the back pressure regulator (21), the liquid storage tank (28), the core holder (8) is placed in the constant temperature box (7), and the servo-controlled injection pump (1) is used to realize the drilling fluid for the lower end of the core Provide pressure and circulating pressure for the drilling fluid at the upper end of the core, the back pressure regulator (21) is used to keep the flow pressure of the drilling fluid at the upper end of the core holder (8) constant; the computer data acquisition system (19) is used for real-time acquisition and recording Pressure and temperature in the constant temperature box (7); the core holder (8) includes the upper end cover of the core holder (29), the lower end cover of the core holder (30), epoxy resin (9) and sealing ring (31), the rock core (10) is clamped between the upper end cover (29) of the core holder and the lower end cover (30) of the core holder, and the epoxy resin (9) wraps around the core to form a regular sample;

(5) If it is determined to use a certain drilling fluid, use a hygrometer to measure the activity of the drilling fluid to be used, determine the chemical potential difference between the drilling fluid and the formation fluid, and then use the chemical potential difference and formation fluid according to the principle of total potential energy balance. The pore pressure determines the drilling fluid column pressure, and the drilling fluid density is determined according to the drilling fluid column pressure and well depth;

(6) If the drilling fluid density is determined, determine the difference between the drilling fluid column pressure and the formation pressure as the underpressure value. According to the principle of total potential energy balance, use the underpressure value to obtain the chemical potential difference, and then according to the chemical potential difference and Formation water activity determines drilling fluid activity;

(7) Adjust the drilling fluid density or activity according to the determined results to keep the wellbore stable.

The specific method in the above step (1) is:

(a) Weigh several shale samples of weight (W _I );

(b) Place the shale samples in an oven at 200°F for 24 hours, then measure the weight (W _d ) of each dry shale sample;

(c) Then the original water content of each shale sample is:

(1)

(d) Place the dried shale samples in desiccators with different activities;

(e) Measure the weight of each sample every day until the weight no longer increases, and record the weight ;

(f) Draw the isotherm adsorption curve according to the adsorption amount of shale and the humidity of the dryer where the shale is placed;

(g) Determine the original formation water activity a _shale using the original formation water content.

The servo-controlled injection pump (1) in the membrane efficiency test experimental device in the above step (4) is connected to the lower end of the core holder (8) through the lower end of the thermostat box (7) through the first high-pressure pipeline (2) , the first valve (3) and the first pressure sensor (5) are set on the first high-pressure pipeline (2); the servo-controlled injection pump (1) is used to provide pressure to the drilling fluid at the lower end of the core and to provide the drilling fluid at the upper end of the core Provide circulating pressure; the first valve (3) is used to control the entry and exit of drilling fluid at the lower end of the core holder (8); the first pressure sensor (5) is used to indicate and record the drilling fluid pressure at the lower end of the core holder (8); The second valve (4) is externally connected between the first valve (3) and the first pressure sensor (5), and the second valve (4) is used to vent or adjust the drilling fluid pressure on the lower end surface of the core holder (8); (7) Used to provide and maintain the temperature required by the core holder (8) during the membrane efficiency test.

The experimental device in the wellbore stabilization method suitable for underbalanced drilling mentioned in the present invention includes a servo-controlled injection pump (1), a constant temperature box (7), a core holder (8), and a computer data acquisition system (19) , a back pressure regulator (21), a liquid storage tank (28), a core holder (8) placed in a constant temperature box (7), and a servo-controlled injection pump (1) is used to provide pressure to the drilling fluid at the lower end of the core and provide circulating pressure for the drilling fluid at the upper end of the core, and the back pressure regulator (21) is used to keep the flow pressure of the drilling fluid at the upper end of the core holder (8) constant; the computer data acquisition system (19) is used for real-time acquisition and recording of pressure and The temperature in the constant temperature box (7); the core holder (8) includes the upper end cover of the core holder (29), the lower end cover of the core holder (30), epoxy resin (9) and sealing ring (31 ), the core (10) is clamped between the upper end cover (29) of the core holder and the lower end cover (30) of the core holder, and the epoxy resin (9) wraps the surrounding of the core to form a regular sample.

The above-mentioned servo-controlled injection pump (1) is connected to one end of the second high-pressure pipeline (11), and the other end of the second high-pressure pipeline (11) passes through the upper end of the thermostat box (7) and the inlet of the upper end of the core holder (8) connection, the second high-pressure pipeline (11) is provided with a third valve (12) and a second pressure sensor (13), the third valve (12) is used to control the inflow of drilling fluid at the upper end of the core holder (8), and the second The pressure sensor (13) is used to indicate and record the drilling fluid pressure at the entrance of the upper end of the core holder (8);

One end of the third high-pressure pipeline (15) is connected to the back pressure regulator (21), and the other end passes through the upper end of the constant temperature box (7) to connect with the upper end outlet of the core holder (8). The third high-pressure pipeline (15) There is a fourth valve (20) and a third pressure sensor (16); the fourth valve (20) is used to control the outflow of drilling fluid at the upper end of the core holder (8), and the third pressure sensor (16) is used to indicate and Record the drilling fluid pressure at the outlet of the upper end of the core holder (8), the back pressure regulator (21) is used to keep the flow pressure of the drilling fluid at the upper end of the core holder (8) constant, and the fourth high-pressure pipeline (22) connects the fifth valve (23) Connected between the fourth valve (20) and the back pressure regulator (21), the fifth valve (23) is used to vent and replace the circulating drilling fluid on the upper end surface of the core holder (8);

One end of the fifth high-pressure pipeline (27) is connected to the back pressure regulator (21), and the other end is connected to the upper end of the liquid storage tank (28). The fifth high-pressure pipeline (27) is provided with a fourth pressure sensor (25) and The sixth valve (26); the fourth pressure sensor (25) is used to indicate and record the drilling fluid pressure at the outlet of the back pressure regulator (21), and the sixth valve (26) is used to control the outlet of the back pressure regulator (21) The outflow of drilling fluid at the place, the fluid storage tank (28) is used to collect the drilling fluid that circulates out;

The computer data collection system (19) passes through the first data collection line (6), the second data collection line (14), the third data collection line (17), the fourth data collection line (18) and the fifth data collection line respectively. The acquisition line (24) is connected to the first pressure sensor (5), the second pressure sensor (13), the third pressure sensor (16), the incubator 7 and the fourth pressure sensor (25), and is used for the computer data acquisition system (19). The pressures of the first pressure sensor (5), the second pressure sensor (13), the third pressure sensor (16) and the fourth pressure sensor (25) and the temperature in the thermostat (7) are collected and recorded in real time.

The above-mentioned core holder (8) includes an upper end cover (29) of the core holder, a lower end cover (30) of the core holder, epoxy resin (9) and a sealing ring (31), and the core (10) is clamped on the core Between the upper end cover (29) of the holder and the lower end cover (30) of the core holder, the epoxy resin (9) wraps around the core to form a regular sample, and fixes the core while preventing the drilling fluid from seeping out from the side; and There is a sealing ring (31) on the bottom surface of the upper end cover (29) of the rock core holder and the top surface of the lower end cover (30) of the rock core holder respectively, and the sealing ring (31) is used to seal the rock core and prevent liquid from top and bottom. connected;

The lower end surface of the upper end cover (29) of the above-mentioned core holder and the upper end surface of the lower end cover (30) of the core holder are respectively provided with grooves to facilitate the flow of drilling fluid; the second high-pressure pipeline (11) and the third high-pressure The pipelines (15) are respectively connected to the upper end cover (29) of the core holder, and the second high-pressure pipeline (2) is connected to the lower end cover (30) of the core holder.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The role of chemical potential is fully considered, and the drilling fluid density when maintaining the balance of the total formation potential energy is accurately given, which effectively prevents the drilling fluid filtrate from invading the formation, improves the stability of the wellbore wall, and enhances the performance of underbalanced drilling technology. application promotion;

(2) When determining the underpressure value, the well wall can be kept stable by adjusting the drilling fluid activity, which not only improves the ROP, prolongs the life of the drill bit, but also improves the drilling efficiency and ensures rapid and safe drilling;

(3) The method provided by the present invention is simple and convenient, has strong operability, good application effect, has broad promotion prospects, and has strong guiding significance for on-site drilling construction;

(4) The epoxy resin is used to seal the core in this membrane efficiency tester, which overcomes the disadvantages of not being able to measure irregular cores or dropped blocks in previous studies, solves the difficulty of obtaining test cores, and realizes the use of downhole dropped blocks to test Formation film efficiency at different depths improves the application range of underbalanced drilling technology and is more instructive for field applications;

(5) The constant temperature box is added to the membrane efficiency tester, which realizes the membrane efficiency test experiment under high temperature conditions, and overcomes the disadvantages of temperature fluctuations that cause errors in test results.

Description of drawings

Fig. 1 is the flow chart of the novel underbalanced drilling borehole stability calculation method proposed by the present invention;

Fig. 2 is the experimental device schematic diagram of testing mud shale film efficiency of the present invention;

Fig. 3 is the schematic diagram of the core holder in the constant temperature box;

Fig. 4 is a sectional view of the bottom end surface of the upper end cover of the core holder;

Fig. 5 is a sectional view of the upper end face of the lower end cover of the core holder;

Fig. 6 is isotherm adsorption curve figure;

Figure 7 is the pressure profile of the overlying strata

Fig. 8 is a trend line diagram of formation normal pressure;

Above: servo control injection pump (1), first high pressure pipeline (2), first valve (3), second valve (4), first pressure sensor (5), first data acquisition line (6) , constant temperature box (7), rock core holder (8), epoxy resin (9), rock core (10), second high-pressure pipeline (11), third valve (12), second pressure sensor (13), The second data collection line (14), the third high pressure pipeline (15), the third pressure sensor (16), the third data collection line (17), the fourth data collection line (18), the computer data collection system (19) , the fourth valve (20), the back pressure regulator (21), the fourth high pressure pipeline (22), the fifth valve (23), the fifth data collection line (24), the fourth pressure sensor (25), the sixth Valve (26), fifth high-pressure pipeline (27), liquid storage tank (28), upper end cover of rock core holder (29), lower end cover of rock core holder (30), sealing ring (31).

detailed description

The new wellbore stabilization technology for underbalanced drilling proposed by the present invention is described as follows in conjunction with the accompanying drawings and examples.

To achieve the above object, the present invention adopts the following technical solutions:

1. The water activity of the shale formation was collected by isothermal adsorption test. The specific experimental method is as follows:

(1) Weigh several shale samples with a weight of (W _I );

(2) Place the shale samples in an oven at 200°F for 24 hours, then measure the weight (W _d ) of each dry shale sample;

(3) The original water content of each shale sample is:

(1)

(4) Place the dried shale samples in desiccators with different activities;

(5) Measure the weight of each sample every day until the weight does not increase, record the weight .

(6) Draw the isothermal adsorption curve according to the adsorption capacity of shale and the humidity of the dryer where the shale is placed.

(7) Use the original formation water content to determine the original formation activity a _shale , as shown in the above figure, the original formation water activity is determined to be 0.915 according to the original formation shale water content.

2. Determine the pore pressure of the formation to be drilled according to the logging data of the adjacent well and the formation pressure test data;

(1) Calculate the overburden pressure s _v by using the formation density logging data.

(2)

In the formula: is the overlying pressure gradient at a certain depth, g/cm ³ ; s _v is the overlying rock pressure, MPa; is the average density of the upper layer without logging data, g/cm ³ ; is the thickness of the upper layer without logging data, m; is the density scatter data at a certain depth, g/cm ³ ; is the depth interval, ; H is well depth, m. The pressure profile of the overlying strata in the figure below can be obtained by calculation based on the logging data.

(2) Use the acoustic transit time logging data of 3-5 adjacent wells to establish the normal compaction trend line of the formation in this area, and determine the coefficients A and B in the following formula.

(3)

In the formula is the formation acoustic time difference at depth h, μs/m; h is vertical depth, m; A and B are normal trend line coefficients. The established pressure trend line is shown in the figure below.

(3) Calculate the formation index c from the following formula according to the pressure of the overlying strata and the actual oil test data.

(4)

Among them, s _v is the overburden pressure, MPa; P _n is the normal formation pressure, MPa; P _p is the actual formation pressure, MPa; D t _n is the acoustic time difference on the normal trend line of predicted depth, μs/m; D t _s is the actual acoustic time difference of the predicted depth formation, μs/m;

(4) Calculating the formation pore pressure using Eaton's formula:

(5)

Among them, c is the area index, P _p is the predicted actual formation pressure, MPa;

3. The formation temperature can be determined according to the formation temperature data of logging while drilling, or the formation temperature can be calculated by the following formula according to the regional geothermal gradient.

In the formula is the absolute temperature gradient of the formation; is the average surface temperature, °C; is the regional geothermal gradient, ℃/100m; H is the formation depth, m.

4. Use the membrane efficiency testing experimental device to measure the formation membrane efficiency, the specific method is as follows;

As shown in Figure 2, the membrane efficiency test experimental device includes: servo control injection pump 1, constant temperature box 7, rock core holder 8, computer data acquisition system 19, back pressure regulator 21, liquid storage tank 28, rock core holder The device 8 is placed in the incubator 7.

The servo-controlled injection pump 1 passes through the lower end of the thermostat 7 through the first high-pressure pipeline 2 and is connected to the lower end of the core holder 8. The first high-pressure pipeline 2 is provided with a first valve 3 and a first pressure sensor 5; the servo control The injection pump 1 is used to provide pressure to the drilling fluid at the lower end of the core and to provide circulating pressure for the drilling fluid at the upper end of the core; the first valve 3 is used to control the entry and exit of the drilling fluid at the lower end of the core holder 8; the first pressure sensor 5 is used to indicate And record the drilling fluid pressure at the lower end of the core holder 8; a second valve 4 is externally connected between the first valve 3 and the first pressure sensor 5, and the second valve 4 is used to vent or adjust the drilling fluid pressure at the lower end of the core holder 8 ; The thermostat 7 is used to provide and maintain the temperature required by the core holder 8 during the membrane efficiency test.

One end of the second high-pressure pipeline 11 is connected with the servo control injection pump 1, and the other end passes through the upper end of the thermostat 7 and is connected with the upper end inlet of the core holder 8. The second high-pressure pipeline 11 is provided with a third valve 12 and a second valve. The pressure sensor 13 and the third valve 12 are used to control the inflow of drilling fluid at the upper end of the core holder 8 , and the second pressure sensor 13 is used to indicate and record the drilling fluid pressure at the inlet of the upper end of the core holder 8 .

One end of the third high-pressure pipeline 15 is connected with the back pressure regulator 21, and the other end passes through the upper end of the thermostat 7 and is connected with the upper end outlet of the core holder 8. The third high-pressure pipeline 15 is provided with a fourth valve 20 and a third valve. Pressure sensor 16; the fourth valve 20 is used to control the outflow of the drilling fluid at the upper end of the core holder 8, the third pressure sensor 16 is used to indicate and record the drilling fluid pressure at the outlet at the upper end of the core holder 8, and the back pressure regulator 21 is used for Keep the flow pressure of the drilling fluid at the upper end of the core holder 8 constant. The fourth high-pressure pipeline 22 connects the fifth valve 23 between the fourth valve 20 and the back pressure regulator 21 , and the fifth valve 23 is used for emptying and replacing the circulating drilling fluid on the upper end surface of the core holder 8 .

One end of the fifth high-pressure pipeline 27 is connected to the back pressure regulator 21, and the other end is connected to the upper end of the liquid storage tank 28. The fifth high-pressure pipeline 27 is provided with a fourth pressure sensor 25 and a sixth valve 26; the fourth pressure sensor 25 Used to indicate and record the drilling fluid pressure at the outlet of the back pressure regulator 21, the sixth valve 26 is used to control the outflow of drilling fluid at the outlet of the back pressure regulator 21, and the liquid storage tank 28 is used to collect the circulating drilling fluid.

Described computer data acquisition system 19 connects the first pressure sensor 5, the 2nd data acquisition line 14, the 3rd data acquisition line 17, the 4th data acquisition line 18 and the 5th data acquisition line 24 respectively by the first data acquisition line 6, Second pressure sensor 13, the 3rd pressure sensor 16, incubator 7 and the 4th pressure sensor 25, computer data acquisition system 19 is used for collecting and recording the first pressure sensor 5, the second pressure sensor 13, the 3rd pressure sensor 16 in real time , the pressure of the fourth pressure sensor 25 and the temperature in the thermostat 7.

As shown in Figure 3, described rock core holder 8 comprises: rock core holder upper end cover 29, rock core holder lower end cover 30, epoxy resin 9 and sealing ring 31, rock core 10 is clamped on the rock core holder upper end Between the cover 29 and the lower end cover 30 of the core holder, the epoxy resin 9 wraps around the core to form a regular sample, and fixes the core while preventing drilling fluid from seeping out from the side; the upper end cover 29 of the core holder in contact with the core There is a sealing ring 31 on the bottom surface and the top surface of the lower end cover 30 of the core holder respectively, and the sealing ring 31 is used to seal the rock core and prevent the communication of the top and bottom liquids. As shown in Figure 3 and Figure 4, the lower end surface of the upper end cover 29 of the core holder and the upper end surface of the lower end cover 30 of the core holder are respectively provided with grooves to facilitate the flow of drilling fluid; the second high-pressure pipeline 11 and the third The high-pressure pipeline 15 is respectively connected with the upper end cover 29 of the core holder, and the second high-pressure pipeline 2 is connected with the lower end cover 30 of the core holder.

As shown in Figure 4, there are grooves on the section of the bottom end surface of the upper end cover 29 of the core holder to facilitate the flow of drilling fluid on the end surface of the core inlet;

As shown in Figure 5, there are grooves on the upper end surface section of the lower end cover 30 of the core holder to facilitate the flow of drilling fluid on the end surface of the core outlet;

Wherein, the method for simulating the membrane efficiency test experiment uses the above-mentioned experimental device, and the specific experimental steps are as follows:

(1), prepare drilling fluid, formation fluid and rock core to be tested;

(2), the rock core 10 to be tested is placed in the epoxy resin 9, and the standard sample required for the test is made, the standard sample to be tested is installed on the rock core holder 8, and placed in the thermostat 7, adjusted The temperature in the incubator 7 is the set temperature;

(3), core saturation stage

① Fill up the formation fluid in the servo-controlled injection pump 1; open the first valve 3 and keep the other valves closed, and use the servo-controlled injection pump 1 to gradually inject the formation fluid into the bottom of the core holder 8 and increase the pressure until the first valve 3 is closed. The pressure value displayed by the pressure sensor 5 reaches the set value, and the first valve 3 is closed after stabilization;

② Open the third valve 12, the fourth valve 20 and the fifth valve 23, the first valve 3, the second valve 4 and the sixth valve 26 are all in the closed state; use the servo control injection pump 1 to gradually feed the top of the core holder 8 Formation fluid is injected, and the top of the formation fluid core holder 8 circulates. When the formation fluid flows out at the outlet of the fifth valve 23, the fifth valve 23 is closed, the back pressure regulator 21 is adjusted, and the sixth valve 26 is opened. The injection pump 1 and the back pressure regulator 21 control the circulating flow pressure at the top of the core holder 8 to be greater than the pressure at the bottom by 0.5 MPa, and keep it constant.

3. Utilize the computer data acquisition system 19 to collect and record the first pressure sensor 5, the second pressure sensor 13, the third pressure sensor 16 and the fourth pressure sensor 25 pressure data, observe the second pressure sensor 13 and the third pressure sensor 16, if If there is a large difference, it means that the pores are blocked, and the experiment fails. If the pressures are equal, the experiment is normal; at this time, observe the pressure data of the first pressure sensor 5, and when the pressures of the first pressure sensor 5 and the third pressure sensor 16 are equal, Then the core saturation stage is completed.

(4) Membrane efficiency test stage

① After the core saturation stage is completed, replace the fluid in the servo-controlled injection pump 1 with the designed drilling fluid;

② The maximum pressure difference recorded by the third pressure sensor 16 and the first pressure sensor 5 is the actual expansion pressure s _measured .

(5), after the test experiment is completed, open the second valve 4, the fourth valve 20, the fifth valve 23 and the sixth valve 26, close the first valve 3 and the third valve 12; the pressure is released, the fluid is released, and then taken out Core, the experiment is over.

(6) Calculation of membrane efficiency.

First calculate the theoretical osmotic pressure according to the following formula;

is the gas constant, 8.314J/(mol*K), is the absolute temperature, K, is the partial molar volume of water L/mol, is the bottom fluid activity, is the top circulating fluid activity.

Calculate the membrane efficiency by using Equation 7 again

5. If it is determined to use a certain drilling fluid, use a hygrometer to measure the activity of the drilling fluid to be used to determine the chemical potential difference between the drilling fluid and the formation fluid. Based on the principle of total potential energy balance, use the chemical potential difference and formation pores The pressure determines the drilling fluid column pressure, and the drilling fluid density is determined according to the drilling fluid column pressure and well depth;

6. If the underpressure value (the difference between the drilling fluid column pressure and the formation pressure) is determined, according to the principle of total potential energy balance, use the underpressure value to determine the chemical potential difference, and then determine the drilling pressure according to the chemical potential difference and formation water activity. Liquid activity.

7. Adjust the drilling fluid density or activity according to the determined results to keep the wellbore stable.

Among them, the total potential energy calculation formula is as follows:

① When the drilling fluid activity is known, the calculation method is as follows:

Among them, the formula for calculating the chemical potential difference between drilling fluid and formation fluid is as follows:

In the formula, is the chemical potential of pure water, is the gas constant, is the absolute temperature, is the partial molar volume of water, is the drilling filtrate activity, is the water activity of the shale formation.

Substituting Equation (9) into Equation (8), the wellbore fluid column pressure at the balance of total potential energy can be obtained as:

In the formula, is the formation water pore pressure, is the wellbore fluid column pressure, is the membrane efficiency.

Among them, the calculation formula of drilling fluid equivalent density is as follows:

In the formula, is equivalent density of drilling fluid, and H is vertical depth.

②The undervoltage value is known, and the calculation method is as follows:

Put formula (9) into formula (8) to get

In the formula, is the undervoltage value.

Among them, the calculation formula of drilling fluid activity is as follows:

Claims (7)

1. A well wall stabilization method applicable to underbalanced drilling is characterized in that it comprises the following steps: (1) Determining the formation water activity of mud shale by means of isothermal adsorption test collection; (2) Determine the pore pressure of the formation to be drilled according to the logging data of the adjacent well and the formation pressure test data; (3) Determine the formation temperature based on the formation temperature data of logging while drilling, or calculate the formation temperature according to the geothermal gradient in the region; (4) Measuring formation membrane efficiency by using a membrane efficiency testing experimental device; the membrane efficiency testing experimental device includes a servo-controlled injection pump (1), a constant temperature box (7), a core holder (8), a computer data acquisition system ( 19), the back pressure regulator (21), the liquid storage tank (28), the core holder (8) is placed in the constant temperature box (7), and the servo-controlled injection pump (1) is used to realize the drilling fluid for the lower end of the core Provide pressure and provide circulation pressure to the drilling fluid at the upper end of the core, the back pressure regulator (21) is used to keep the flow pressure of the drilling fluid at the upper end of the core holder (8) constant; the computer data acquisition system (19) is used for real-time acquisition and Record the pressure and the temperature in the constant temperature box (7); the core holder (8) includes the upper end cover of the core holder (29), the lower end cover of the core holder (30), epoxy resin (9) and sealing ring (31), the rock core (10) is clamped between the upper end cover (29) of the core holder and the lower end cover (30) of the core holder, and the epoxy resin (9) wraps around the core to form a regular sample; (5) If it is determined to use a certain drilling fluid, use a hygrometer to measure the activity of the drilling fluid to be used, determine the chemical potential difference between the drilling fluid and the formation fluid, and then use the chemical potential difference and formation fluid according to the principle of total potential energy balance. The pore pressure determines the drilling fluid column pressure, and the drilling fluid density is determined according to the drilling fluid column pressure and well depth; (6) If the drilling fluid density is determined, determine the difference between the drilling fluid column pressure and the formation pressure as the underpressure value. According to the principle of total potential energy balance, use the underpressure value to obtain the chemical potential difference, and then according to the chemical potential difference and Formation water activity determines drilling fluid activity; (7) Adjust the drilling fluid density or activity according to the determined results to keep the wellbore stable. 2. The borehole stabilization method suitable for underbalanced drilling according to claim 1, characterized in that: the specific method in the step (1) is: (a) Weigh several shale samples of weight (W _i ); (b) Place the shale samples in an oven at 200°F for 24 hours, then measure the weight (W _d ) of each dry shale sample; (c) Then the original water content of each shale sample is: (d) Place the dried shale samples in desiccators with different activities; (e) Measure the weight of each sample every day until the weight no longer increases, and record the weight ; (f) Draw the isotherm adsorption curve according to the adsorption amount of shale and the humidity of the dryer where the shale is placed; (g) Use the original water content to determine the original formation water activity a _shale . 3. The wellbore stabilization method suitable for underbalanced drilling according to claim 1, characterized in that: the servo-controlled injection pump (1) in the membrane efficiency testing experimental device in the step (4) passes through the first The high-pressure pipeline (2) passes through the lower end of the constant temperature box (7) and is connected to the lower end of the core holder (8). The first high-pressure pipeline (2) is provided with a first valve (3) and a first pressure sensor (5); The servo-controlled injection pump (1) is used to provide pressure for the drilling fluid at the lower end of the core and to provide circulating pressure for the drilling fluid at the upper end of the core; the first valve (3) is used to control the entry and exit of the drilling fluid at the lower end of the core holder (8) ; The first pressure sensor (5) is used to indicate and record the drilling fluid pressure at the lower end of the core holder (8); the second valve (4) is externally connected between the first valve (3) and the first pressure sensor (5) , the second valve (4) is used to vent or adjust the drilling fluid pressure on the lower end surface of the core holder (8); temperature. 4. An experimental device for testing membrane efficiency applied to the wellbore stabilization method for underbalanced drilling according to any one of claims 1-3, characterized in that it includes a servo-controlled injection pump (1), a constant temperature Box (7), core holder (8), computer data acquisition system (19), back pressure regulator (21), liquid storage tank (28), and core holder (8) placed in the constant temperature box (7) Inside, the servo-controlled injection pump (1) is used to provide pressure for the drilling fluid at the lower end of the core and to provide circulating pressure for the drilling fluid at the upper end of the core, and the back pressure regulator (21) is used to maintain the drilling at the upper end of the core holder (8) The flow pressure of the liquid is constant; the computer data acquisition system (19) is used to collect and record the pressure and the temperature in the thermostatic box (7) in real time; the core holder (8) includes an upper end cover (29) of the core holder, Core holder lower end cover (30), epoxy resin (9) and sealing ring (31), the rock core (10) is clamped between the core holder upper end cover (29) and the rock core holder lower end cover (30) , the epoxy resin (9) wraps around the core to form a regular sample. 5. The membrane efficiency testing experimental device suitable for the wellbore stabilization method of underbalanced drilling according to claim 4, characterized in that: the servo-controlled injection pump (1) is connected to the second high-pressure pipeline (11) One end, the other end of the second high-pressure pipeline (11) passes through the upper end of the thermostat (7) and is connected to the upper inlet of the core holder (8), and the second high-pressure pipeline (11) is provided with a third valve (12) And the second pressure sensor (13), the third valve (12) is used to control the inflow of drilling fluid at the upper end of the core holder (8), and the second pressure sensor (13) is used to indicate and record the core holder (8) Drilling fluid pressure at the upper inlet; One end of the third high-pressure pipeline (15) is connected to the back pressure regulator (21), and the other end passes through the upper end of the constant temperature box (7) to connect with the upper end outlet of the core holder (8). The third high-pressure pipeline (15) There is a fourth valve (20) and a third pressure sensor (16); the fourth valve (20) is used to control the outflow of drilling fluid at the upper end of the core holder (8), and the third pressure sensor (16) is used to indicate and record the drilling fluid pressure at the outlet of the upper end of the core holder (8), the back pressure regulator (21) is used to keep the flow pressure of the drilling fluid at the upper end of the core holder (8) constant, and the fourth high-pressure pipeline (22) will The fifth valve (23) is connected between the fourth valve (20) and the back pressure regulator (21), and the fifth valve (23) is used for venting and replacing the circulating drilling fluid on the upper end surface of the core holder (8); One end of the fifth high-pressure pipeline (27) is connected to the back pressure regulator (21), and the other end is connected to the upper end of the liquid storage tank (28). The fifth high-pressure pipeline (27) is provided with a fourth pressure sensor (25) and The sixth valve (26); the fourth pressure sensor (25) is used to indicate and record the drilling fluid pressure at the outlet of the back pressure regulator (21), and the sixth valve (26) is used to control the outlet of the back pressure regulator (21) The outflow of drilling fluid at the place, the fluid storage tank (28) is used to collect the drilling fluid that circulates out; The computer data collection system (19) passes through the first data collection line (6), the second data collection line (14), the third data collection line (17), the fourth data collection line (18) and the fifth data collection line respectively. The acquisition line (24) is connected to the first pressure sensor (5), the second pressure sensor (13), the third pressure sensor (16), the incubator 7 and the fourth pressure sensor (25), and is used for the computer data acquisition system (19). The pressures of the first pressure sensor (5), the second pressure sensor (13), the third pressure sensor (16) and the fourth pressure sensor (25) and the temperature in the thermostat (7) are collected and recorded in real time. 6. The membrane efficiency testing experimental device suitable for wellbore stabilization methods in underbalanced drilling according to claim 4, characterized in that: the core holder (8) includes a core holder upper end cover (29 ), core holder lower end cover (30), epoxy resin (9) and sealing ring (31), the rock core (10) is clamped on the core holder upper end cover (29) and the rock core holder lower end cover (30) Between them, epoxy resin (9) wraps around the core to form a regular sample, fixes the core and prevents the drilling fluid from seeping out from the side; A sealing ring (31) is respectively arranged on the top surface of the lower end cover (30), and the sealing ring (31) is used to seal the rock core and prevent the communication of the top and bottom liquids. 7. The membrane efficiency testing experimental device suitable for wellbore stabilization method of underbalanced drilling according to claim 6, characterized in that: the lower end surface of the upper end cover (29) of the core holder and the core clamping The upper end surface of the lower end cover (30) of the device is respectively provided with grooves to facilitate the flow of drilling fluid; the second high-pressure pipeline (11) and the third high-pressure pipeline (15) are respectively connected with the upper end cover (29) of the core holder. Two high-pressure pipelines (2) are connected with the lower end cover (30) of the rock core holder.