CN104405377B - Method and device for accurately simulating core under-pressure placing displacement in laboratories - Google Patents

Abstract

A method and device for accurately simulating rock core displacement under pressure in a laboratory. The main purpose is to solve the problem that the porosity of the core is easy to change during the deformation process when simulating the core displacement in the laboratory, which leads to the inaccurate data obtained. The method is summarized as follows: Calculate the reasonable displacement pressure required for displacement through empirical formulas, calculate the ring pressure and displacement pressure required to maintain porosity according to the porosity change formula, so as to keep the core porosity unchanged, And keep the ring pressure changing with the displacement pressure during the core displacement process, so that the pressure difference remains unchanged. A device with an adjustable temperature electric heating core holder is designed, and a back pressure valve is added at the outlet end of the core holder to keep a certain pressure in the holder. According to the empirical formula, a reasonable displacement pressure is obtained, and then The pressure difference between the ring pressure of the holder and the displacement pressure is kept constant through the ring pressure system to ensure that the porosity of the core remains unchanged during the deformation process.

Description

Method and device for accurately simulating rock core displacement under pressure in the laboratory

technical field

The invention relates to a method and a device for placing and displacing rock cores under pressure in a laboratory, in particular to a method and a device for performing more accurate simulation experiments on formation cores in oil field development and production.

Background technique

In reservoir development engineering, testing and displacement experiments on cores are generally carried out in laboratories. However, after a long period of practical application, it was found that the existing test flooding method has the following problems: the test flooding method commonly used in the laboratory is only to inject water and saturated oil under pressure at one end of the test core, heat it and place it, and then Go straight to the test experiment. As a result: 1. There is no pressurization during the heating and placement of the core to be tested; 2. Only applying high pressure to one end of the core to be tested may cause the core pore structure to be damaged or fractured; 3. The constant temperature box currently used in the laboratory High temperature cannot be realized, so it is difficult to simulate formation temperature. The above three factors lead to large errors in the data of the core test and displacement experiments obtained in the laboratory experiments.

Contents of the invention

In order to solve the technical problems mentioned in the background technology, the present invention provides a method and a device for simulating rock core displacement under pressure in a laboratory. By using the method and device, the porosity of the rock core can be kept constant during the flooding process, thereby ensuring the authenticity and reliability of the obtained data.

The technical solution of the present invention is: the device for accurately simulating the displacement of rock cores under pressure in the laboratory consists of a first constant pressure and constant speed pump, a second constant pressure and constant speed pump, a first piston container, a second piston The container is composed of a flow meter, an electric heating core holder, a first pressure sensor and a second pressure sensor with a pressure display gauge, a back pressure valve and a measuring cylinder.

Wherein, the back pressure valve has a valve seat, a back pressure container chamber, a liquid inlet, a liquid outlet, a piston, a spring, and a spring adjustment knob, and the liquid inlet and the liquid outlet are located on two sides of the liquid flow channel in the back pressure container chamber. At the end, the spring pushes the piston to move upward along the inner cavity of the back pressure container cavity, and the spring adjustment knob is used to adjust the elastic force of the spring.

The electric heating core holder has an inner cavity that can close the core, and the inner cavity is covered with a rubber sleeve resistant to high temperature and high pressure. The clamper liquid flow input pipe and the clamper liquid flow output pipe that are connected to the inner cavity; the outer wall of the annular cylinder and the inner wall of the annular cylinder that are sealed are fixed between the two threaded connection ends; the inner wall of the annular cylinder The first ring space is formed between the rubber sleeve and the second ring space is formed between the outer wall of the annular cylinder and the inner wall of the annular cylinder. An electric heater is built in the second ring space, and the temperature adjustment device of the electric heater is located at Outside the outer wall of the annular cylinder; through the outer wall of the annular cylinder and the inner wall of the annular cylinder after sealing treatment, a ring pressure introduction pipe is fixed, and the opening of the ring pressure introduction pipe is located in the space of the first ring sleeve.

The pump outlet end of the first constant pressure and constant speed pump is connected to the piston driving force inlet port of the first piston container and the second piston container in parallel through the pipeline; the two content output ports of the first piston container and the second piston container are respectively After being controlled on and off by the first valve and the second valve, it flows into the holder liquid flow input pipe of the electric heating core holder through the pipeline. Before the pipeline enters the holder liquid flow input pipe, a flow rate is connected to the pipeline meter and third valve;

The pump outlet end of the second constant pressure constant speed pump is connected with the ring pressure introduction pipe on the electric heating core holder through the pipeline, before the pipeline enters the ring pressure introduction pipe, the first pressure sensor and the first pressure sensor are connected on the pipeline. The fourth valve: the holder liquid flow output pipe of the electric heating core holder is connected with the liquid inlet on the back pressure valve through the pipeline, before the pipeline enters the liquid inlet, the pipeline is connected with the first Two pressure sensors and a fifth valve; the liquid outlet on the back pressure valve is connected with the measuring cylinder.

A method for accurately simulating the displacement of rock cores under pressure in a laboratory using the device described in claim 1, the method is composed of the following steps:

The first step is to close all valves in the device described in claim 1, and check the tightness of the device;

The second step is to adjust the temperature of the electrically heated core holder described in claim 1 to be close to the formation temperature, monitor its temperature change through a temperature sensor, and keep its temperature near the formation temperature;

In the third step, a certain amount of water and oil are respectively filled into the first piston container A and the second piston container B in the device described in claim 1, so that the oil and water are respectively filled with the first valve, the second valve and the second valve. The pipeline between the three valves;

In the fourth step, the interval of the displacement pressure gradient is obtained through the relationship between the displacement pressure gradient and the flow rate:

(1)

In the formula: ——seepage velocity, cm/s; ——displacement pressure gradient, Mpa/cm; ——starting pressure gradient, Mpa/cm; a, b, c——quadratic polynomial coefficients, mainly related to fluidity, which can be obtained by fitting core pressure difference-flow velocity experimental data;

The reasonable displacement pressure is: (2), where —core length, in m;

In the fifth step, in order to keep the porosity of the rock unchanged, the reasonable ring pressure P c during the displacement experiment is determined according to the porosity change formula in the elastic deformation of the rock:

(3)

The above formula is the porosity change formula in the rock elastic deformation process;

From this formula, it can be seen that the absolute change of porosity is related to the porosity itself, the effective pore compressibility coefficient and the net confining pressure ( Pc - P );

If the net confining pressure remains constant, the porosity will also remain unchanged; otherwise, the porosity will change; therefore, the displacement pressure P is obtained through calculation. Within its reasonable range, as it increases continuously, the ring pressure P c is also constantly changing, so that the core can be tested under reasonable pressure displacement conditions;

In the formula: Vp—apparent volume of rock, m3; Vb—pore volume, m3; Cbp—pseudo-apparent volume compressibility, 1/Mpa; Cbc—apparent volume compressibility, 1/Mpa; Cpp—effective pore compressibility , 1/Mpa; Cr—volume compressibility coefficient of rock skeleton particles, 1/Mpa; Pc—overburden pressure (ring pressure), Mpa; P—fluid pressure (displacement pressure), Mpa;

The sixth step is to conduct a saturated oil experiment on the core located in the electrically heated core holder (6) in the device described in claim 1, open the fourth valve and the first valve, and start the second constant pressure and constant speed pump to the electric Heating the first ring space in the core holder to add ring pressure;

The seventh step, according to the values obtained in the fourth and fifth steps, determine the net confining pressure value to ensure that the core porosity does not change when the displacement experiment is carried out ;

In the eighth step, start the first constant pressure and constant speed pump in the device described in claim 1, adjust the pressure to the middle value P _of the displacement pressure value P obtained in the fourth step, and open the second valve corresponding to the second piston container ;

The ninth step is to open the back pressure valve in the device described in claim 1, adjust the spring adjustment knob, so that the back pressure value in the back pressure valve is equal to the displacement pressure P obtained _in the eighth step, and start to saturate oil experiment;

The tenth step, after the saturation is completed, the device described in claim 1 is not disassembled, the first constant pressure constant speed pump (1) and the valve of the piston container B are closed, the third valve and the fifth valve are closed, and the pressure is placed for 24 hours ;

In the eleventh step, start the constant speed and constant pressure pump in the device described in claim 1, open the valve of the first piston container, open the valve 4 and the valve 11, and start the oil displacement experiment; when the oil displacement experiment starts, the displacement The pressure P is taken as the middle value P _, and the back pressure valve is also adjusted to P. At this time _, the pressure sensor detects the displacement pressure change. By comparing with the pressure detected by the ring pressure sensor, in order to keep the net confining pressure unchanged, Manually start the constant speed and constant pressure pump to pressurize, and the ring pressure Pc is _in Pc; from the formula (3): if the difference between the ring pressure and the displacement pressure is kept constant, the porosity of the core can be guaranteed to remain unchanged;

Therefore, if the value of the displacement pressure P is adjusted to the P _end , and the back pressure valve is adjusted to the P _end , the ring pressure is also continuously adjusted to the Pc _end . At this time, turn off the heater to ensure that the core test is carried out under the conditions of close to the real formation temperature and pressure; when the discharged liquid is all water, the oil displacement test is completed;

In the twelfth step, according to the cyclic operation of the eleventh step, adjust the displacement pressure P, the ring pressure Pc and the pressure value of the back pressure valve several times, and conduct the test;

The thirteenth step, according to the measurement results of the flow meter and the measurement cylinder, calculate the test data of each displacement pressure P: parameters such as core oil saturation, porosity, permeability, etc., find the average value.

The present invention has the following beneficial effects: the reasonable displacement pressure required for core displacement can be obtained by calculating the relationship between displacement pressure gradient and flow velocity; The internal pressure and ring pressure of the holder are stable; according to the relationship between the porosity of the core and the net confining pressure, the stress on the core is kept constant; the temperature of the electric heating core holder is adjusted to be close to the formation temperature, so that the whole core is at a high temperature close to the formation High pressure real environment. The flow meter is used to accurately measure the amount of passing fluid, and accurately calculate the physical parameters of the core. Applying this method can reduce the displacement error during core displacement, make the experimental environment closer to the actual formation conditions, and obtain more accurate experimental data.

Description of drawings:

Fig. 1 is a schematic diagram of the overall structure of the present invention.

Fig. 2 is the structure diagram after the electric heating core holder of the present invention is connected with the second constant pressure and constant speed pump;

Fig. 3 is a schematic structural view of the back pressure valve of the present invention;

Fig. 4 is a schematic structural view of the electric heating core holder of the present invention.

detailed description:

The present invention will be further described below in conjunction with accompanying drawing:

As shown in Figure 1, this kind of device for accurately simulating the displacement of rock cores under pressure in the laboratory consists of a first constant pressure and constant speed pump 1, a second constant pressure and constant speed pump 9, a first piston container A, a second Two piston containers B, a flow meter 5, an electric heating core holder 6, a first pressure sensor 8 and a second pressure sensor 10 with a pressure display gauge, a back pressure valve and a measuring cylinder 17 are composed.

Wherein, the structure of the back pressure valve as shown in Figure 3, has a valve seat 12 and a back pressure container cavity 13, a liquid inlet 18, a liquid outlet 19, a piston 22, a spring 23 and a spring adjustment knob 20, and the liquid inlet 18 and liquid outlet 19 are located at both ends of the liquid flow channel in the back pressure container cavity 13, the spring 23 pushes the piston 22 to move upward along the inner cavity of the back pressure container cavity 13, and the spring adjustment knob 20 is used to adjust the elastic force of the spring 23. In actual implementation, the ZZY type self-operated pressure regulating valve of Shanghai Yuhu Company can be used. No external energy is needed, and the energy of the regulated medium itself is used as the power source to introduce the actuator to control the position of the valve core, changing the pressure difference and flow at both ends, so that the valve Stable pressure before or after the valve. The self-operated pressure regulating valve has the advantages of sensitive action, good sealing, and small fluctuation of the pressure set point. The self-operated pressure regulating valve is widely used in the automatic control of gas, liquid and medium pressure stabilization or pressure relief.

The structure of the electric heating core holder 6 is as shown in Figure 4. It has an inner cavity that can close the rock core 31. The inner cavity is covered with a rubber sleeve 29 resistant to high temperature and high pressure. The two ends of the inner cavity are provided with sealing plugs. The threaded connection end of the clamper is closed, and the holder liquid flow input pipe 33 and the holder liquid flow output pipe 21 that are connected with the inner cavity are drawn out respectively; a sealed annular ring is fixed between the two threaded connection ends. The outer wall 27 of the cylinder and the inner wall 32 of the annular cylinder; the first annulus space 30 is formed between the inner wall 32 of the annular cylinder and the rubber sleeve 29, and the second annulus space 28 is formed between the outer wall 27 of the annular cylinder and the inner wall 32 of the annular cylinder , an electric heater 26 is built in the second ring sleeve space 28, and the temperature regulating device 25 of the electric heater 26 is located outside the outer wall 27 of the annular cylinder; after being sealed, it penetrates the outer wall 27 of the annular cylinder and the inner wall 32 of the annular cylinder, A ring pressure introduction pipe 24 is fixed, and the opening of the ring pressure introduction pipe 24 is located in the first ring sleeve space 30 .

The pump outlet end of the first constant pressure and constant speed pump 1 is connected to the piston driving force inlet port of the first piston container A and the second piston container B in parallel through the pipeline; The output end of the content is controlled on and off by the first valve 2 and the second valve 3 respectively, and then flows into the holder liquid flow input pipe 33 of the electric heating core holder 6 through the pipeline, and enters the holder liquid flow in the pipeline Before the input pipe 33, a flow meter 5 and a third valve 4 are connected to the pipeline.

As shown in Figure 2, the pump outlet end of the second constant pressure and constant speed pump 9 is connected with the ring pressure introduction pipe 24 on the electric heating core holder 6 through the pipeline, before the pipeline enters the ring pressure introduction pipe 24 , the pipeline is connected with a first pressure sensor 8 and a fourth valve 7;

The holder liquid flow output pipe 21 of the electric heating core holder 6 is connected with the liquid inlet 18 on the back pressure valve through the pipeline, and before the pipeline enters the liquid inlet 18, the pipeline is connected with the first Two pressure sensors 10 and a fifth valve 11;

The liquid outlet 19 on the back pressure valve is connected with the measuring cylinder 17 .

The method for accurately simulating the displacement of the core under pressure in the laboratory by using the device is composed of the following steps:

The first step is to close all valves in the device and check the tightness of the device;

In the second step, adjust the temperature of the electrically heated core holder 6 to be close to the formation temperature, monitor its temperature change through a temperature sensor, and keep its temperature near the formation temperature;

In the third step, a certain amount of water and oil are respectively loaded into the first piston container A and the second piston container B, so that the oil and water are filled with the space between the first valve 2, the second valve 3 and the third valve 4 respectively. pipeline;

The fourth step is to use the relationship between displacement pressure gradient and flow rate, that is, formula (1):

(1)

In the formula: ——seepage velocity, cm/s; —displacement pressure gradient, Mpa/cm; a, b, c—quadratic polynomial coefficients, mainly related to mobility, obtained by fitting core pressure difference-velocity experimental data. According to the core pressure difference-velocity experimental data fitting quadratic polynomial coefficients, the statistics of quadratic polynomial coefficients are shown in Table 1:

Table 1

Through the relationship between the displacement pressure gradient and the threshold pressure, that is, formula (2):

(2)

In the formula: ——Start-up pressure gradient, Mpa/cm;

Combining formula (1) and formula (2), we get

(3)

Solving formula (3), we get

(4)

So the displacement pressure gradient interval is

(5)

So the reasonable displacement pressure is: (6), where —core length, in m;

In the fifth step, in order to ensure that the porosity of the core remains unchanged, according to the porosity change formula in rock elastic deformation:

(7)

but (8)

again (9)

(10)

Substituting (8) and (9) into (7) to get

(11)

According to the relationship between the four compression coefficients of Cbc, Cbp, Cpc, and Cpp, formula (11) can be sorted into

(12)

The above formula is the porosity change formula in the rock elastic deformation process. It can be seen from this formula that the absolute change in porosity is related to the porosity itself, the effective pore compressibility and the net confining pressure (Pc-P). If the net confining pressure is kept constant, the porosity will also remain unchanged; otherwise, the porosity will change. Therefore, the displacement pressure P in the fifth step is brought into (12) to calculate the reasonable ring pressure Pc interval. In the formula: Vp—apparent volume of rock, m3; Vb—pore volume, m3; Cbp—pseudo-apparent volume compressibility, 1/Mpa; Cbc—apparent volume compressibility, 1/Mpa; Cpp—effective pore compressibility , 1/Mpa; Cr—volume compressibility coefficient of rock skeleton particles, 1/Mpa; Pc—overburden pressure (ring pressure), Mpa; P—fluid pressure (displacement pressure), Mpa.

The sixth step is to conduct saturated oil experiment on the core (31) located in the electric heating core holder (6), open the fourth valve (7) and the first valve (2), and start the second constant pressure and constant speed pump ( 9) Add ring pressure to the first ring space (30) in the electrically heated core holder (6);

The seventh step, according to the values obtained in the fourth and fifth steps, determine the net confining pressure value to ensure that the core porosity does not change when the displacement experiment is carried out .

In the eighth step, start the first constant pressure and constant speed pump (1), adjust the pressure to the middle value P _of the displacement pressure value P obtained in the fourth step, and open the second valve (3) corresponding to the second piston container (B) );

In the ninth step, open the back pressure valve, adjust the spring adjustment knob (20), so that the back pressure value in the back pressure valve is equal to the displacement pressure P obtained _in the eighth step, and start the saturated oil experiment;

The tenth step, after the saturation is completed, the whole device is not disassembled, close the valve 3 of the constant speed and constant pressure pump 1 and the piston container B, close the valve 4 and valve 11, and place it under pressure for 24 hours;

In the eleventh step, start the constant speed and constant pressure pump 1, open the valve 2 of the piston container A, open the valve 4 and the valve 11, and start the oil displacement experiment. When the oil displacement experiment starts, the displacement pressure P takes the middle value P _, and the back pressure valve is also adjusted to P. At this time _, the pressure sensor detects the displacement pressure change, and compares it with the pressure detected by the ring pressure sensor. , in order to keep the net confining pressure unchanged, the constant-speed constant-pressure pump is manually started to pressurize, and the ring pressure Pc is _in Pc; from the formula (12): if the difference between the ring pressure and the displacement pressure is kept constant, then It can ensure that the porosity of the core remains unchanged. Therefore, if the value of the displacement pressure P is adjusted to the P _end , and the back pressure valve is adjusted to the P _end , the ring pressure is also continuously adjusted to the Pc _end . Turn off the heater at this time to ensure that the core experiment is carried out under conditions close to the real formation temperature and pressure. When the discharged liquid is all water, the oil displacement experiment is completed.

The twelfth step, according to the cyclical operation of the eleventh step, adjust the displacement pressure P, the ring pressure Pc, and the pressure value of the back pressure valve several times, and carry out the test.

The thirteenth step, according to the measurement results of the flowmeter and the measurement cylinder, calculate the test data of each displacement pressure P: parameters such as core oil saturation, porosity, permeability, etc., calculate the average value.

Provide experimental example below according to above-mentioned embodiment scheme:

Connect the experimental device according to the above steps, artificial homogeneity, 2.5cm×2.5cm×50cm, effective permeability 500mD. , to measure the porosity and permeability data of the core.

The first step is to close all valves in the device described in claim 1, and check the tightness of the device;

The second step is to adjust the temperature of the electrically heated core holder 6 to be close to the formation temperature, monitor its temperature change through a temperature sensor, and keep its temperature close to the formation temperature;

The third step is to put a certain amount of water and oil into the first piston container A and the second piston container B respectively, so that the oil and water fill the space between the first valve 2, the second valve 3 and the third valve 4 respectively. pipeline;

The fourth step is to use the relationship between displacement pressure gradient and flow rate, that is, formula (1):

(1)

In the formula: ——seepage velocity, cm/s; —displacement pressure gradient, Mpa/cm; a, b, c—quadratic polynomial coefficients, mainly related to mobility, obtained by fitting core pressure difference-velocity experimental data. According to the core pressure difference-velocity experimental data fitting quadratic polynomial coefficients, the statistical table of quadratic polynomial coefficients is obtained as follows:

Through the relationship between the displacement pressure gradient and the threshold pressure, that is, formula (2):

(2)

In the formula: ——Start-up pressure gradient, Mpa/cm;

Combining formula (1) and formula (2), we get

(3)

Solving formula (3), we get

(4)

So the displacement pressure gradient interval is

(5)

So the reasonable displacement pressure is: (6), where —core length, in m;

So the reasonable displacement pressure is ; where —core length, m.

In the fifth step, in order to ensure that the rock porosity remains unchanged, according to the porosity change formula in rock elastic deformation:

(7)

but (8)

again (9)

(10)

Substituting (8) and (9) into (7) to get

(11)

According to the relationship between the four compression coefficients of Cbc, Cbp, Cpc, and Cpp, formula (11) can be sorted into

(12)

The core volume calculated by the above steps is , driving pressure , then the reasonable ring pressure can be calculated . It can be seen from the above formula that the absolute change of porosity is related to the porosity itself, the effective void compressibility coefficient and the net confining pressure (Pc-P). If the net confining pressure is kept constant, the porosity will also remain unchanged; otherwise, the porosity will change. Therefore, the displacement pressure is calculated by , within its reasonable range; ring pressure , so that the core can be tested under reasonable pressure displacement conditions.

In the seventh step, according to the values obtained in the fifth and sixth steps, it is determined that the net confining pressure value for ensuring that the core porosity does not change during the displacement experiment is 4.8Mpa.

In the eighth step, start the first constant pressure and constant speed pump 1, adjust the pressure to within the range of the displacement pressure value P obtained in the fifth step, and open the second valve 3 corresponding to the second piston container B;

In the ninth step, open the back pressure valve, adjust the spring adjustment knob 20, so that the back pressure in the back pressure valve is equal to the net confining pressure obtained in the seventh step, and start the saturated oil experiment;

The tenth step, after the saturation is completed, the whole device is not disassembled, close the valve 3 of the constant speed and constant pressure pump 1 and the piston container B, close the valve 4 and valve 11, and place it under pressure for 24 hours. At this time, the core pressure value and the calculated pressure value consistent;

In the eleventh step, start the constant speed and constant pressure pump 1, open the valve 2 of the piston container A, open the valve 4 and the valve 11, and start the oil displacement experiment. When the oil displacement experiment starts, the displacement pressure P takes an intermediate value , the back pressure valve is also adjusted to , at this time, the pressure sensor detects the change of displacement pressure. By comparing with the pressure detected by the ring pressure sensor, in order to keep the net confining pressure unchanged, the constant speed and constant pressure pump is manually started to increase the pressure. The ring pressure Pc is ; According to the formula (12): if the difference between the annular pressure and the displacement pressure is kept constant, the porosity of the core can be guaranteed to be constant. Therefore, the value of adjusting the displacement pressure P is , the back pressure valve is adjusted to , the ring pressure is constantly adjusted to . Turn off the heater at this time to ensure that the core experiment is carried out under conditions close to the real formation temperature and pressure. When the discharged liquid is all water, the oil displacement experiment is completed.

In the twelfth step, follow the cyclic operation of the eleventh step, adjust the displacement pressure P, the ring pressure Pc, and the pressure value of the back pressure valve several times, and carry out the test.

In the thirteenth step, parameters such as core permeability and porosity are calculated according to the measurement results of the flow meter and the measuring cylinder. In order to measure more accurate porosity and permeability data, several sets of experiments were done according to the above-mentioned experimental procedures and operation methods, and the data of the average permeability of 0.0051um ² and porosity of 0.15 were obtained. While the permeability measured by other indoor experiments is 0.0045um ² , the porosity is 0.13, and the error is 11.76%, 13.33%. The experimental data obtained by this experimental method and device are more accurate and reliable.

Claims (1)

1. A method for accurately simulating rock core displacement under pressure in a laboratory, the method consists of the following steps: The first step is to close all the valves in the pressure-placed displacement device of the simulated core, and check the tightness of the device; The second step is to adjust the temperature of the electrically heated core holder (6) in the displacement device under pressure for the simulated core to be close to the formation temperature, monitor its temperature change through a temperature sensor, and keep its temperature near the formation temperature; In the third step, a certain amount of water and oil are respectively filled into the first piston container (A) and the second piston container (B) in the simulated rock core displacement device under pressure, so that the oil and water are respectively filled with the first valve ( 2), the pipeline between the second valve (3) and the third valve (4); In the fourth step, the interval of the displacement pressure gradient is obtained through the relationship between the displacement pressure gradient and the flow rate: $\frac{\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\sqrt{{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}<span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; \&rsqb;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \&le;</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; +</span>\sqrt{{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}<span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; \&rsqb;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ In the formula: K-core permeability, 10 ^-3 μm ² ; μ-fluid viscosity, mpa s; △p-displacement pressure gradient, Mpa/cm; G-threshold pressure gradient, Mpa/cm; a, b, c-quadratic polynomial coefficient, mainly related to fluidity, can be obtained by fitting core pressure difference-velocity experimental data; Reasonable displacement pressure is: p=△p·l(2), where l-core length, unit m; In the fifth step, in order to ensure that the rock porosity remains unchanged, the reasonable ring pressure Pc for the displacement experiment is determined according to the porosity change formula in rock elastic deformation: The above formula is the porosity change formula in the rock elastic deformation process; From this formula, it can be seen that the absolute variation of porosity is related to porosity itself, effective pore compressibility and net confining pressure (Pc-P); If the net confining pressure remains constant, the porosity will also remain unchanged; otherwise, the porosity will change; therefore, the displacement pressure P is obtained through calculation. Within its reasonable range, as it continues to increase, the ring pressure Pc will also increase. Constantly changing, so that the core can be tested under reasonable pressure displacement conditions; In the formula: Cpp—effective pore compressibility, 1/Mpa; Cr—volume compressibility of rock skeleton particles, 1/Mpa; Pc—overburden pressure, Mpa; P—fluid pressure, Mpa; In the sixth step, the saturated oil experiment is carried out on the rock core (31) located in the electrically heated core holder (6) of the simulated rock core displacement device under pressure, and the fourth valve (7) and the first valve (2) are opened, Start the second constant pressure and constant speed pump (9) to add ring pressure to the first ring space (30) in the electric heating core holder (6); In the seventh step, according to the values obtained in the fourth and fifth steps, determine the net confining pressure value (p _c -p) that ensures that the core porosity does not change when the displacement experiment is carried out; In the eighth step, start the simulated rock core under pressure and place the first constant pressure constant speed pump (1) in the displacement device, adjust the pressure to the middle value P _of the displacement pressure value P obtained in the fourth step, and open the second piston container ( B) the corresponding second valve (3); In the ninth step, open the back pressure valve in the displacement device under pressure of the simulated rock core, adjust the spring adjustment knob (20), so that the back pressure value in the back pressure valve is equal to the displacement pressure P obtained in the eighth step _, start the saturated oil experiment; In the tenth step, after the saturation is completed, the whole simulated rock core is placed under pressure and the displacement device is not disassembled, and the first constant pressure and constant speed pump (1) and the valve of the piston container B are closed, and the third valve (4) and the fifth valve ( 11), placed under pressure for 24 hours; In the eleventh step, start the first constant-pressure and constant-speed pump in the pressure-placed displacement device of the simulated rock core, open the valve of the first piston container (A), open the third valve (4) and the fifth valve (11), Start the oil displacement experiment; when the oil displacement experiment starts, the displacement pressure P is the middle value P _, and the back pressure valve is also adjusted to P _, at this time, the pressure sensor detects the displacement pressure change, and the displacement pressure is detected by the ring pressure sensor. In order to keep the net confining pressure unchanged, the second constant pressure and constant speed pump is manually started to increase the pressure, and the ring pressure Pc is _in Pc; from the formula (3): if the ring pressure and the displacement pressure are always kept The difference between the two values remains unchanged, which can ensure that the porosity of the core remains unchanged; Therefore, adjust the value of the displacement pressure P to the P _end , adjust the back pressure valve to the P _end , and then adjust the ring pressure to the Pc _end continuously. At this time, turn off the heater to ensure that the core test is close to the real formation temperature and pressure. Carry out; when the discharged liquid is all water, the oil displacement experiment is completed; In the twelfth step, according to the cyclic operation of the eleventh step, adjust the displacement pressure P, the ring pressure Pc and the pressure value of the back pressure valve several times, and carry out the test; In the thirteenth step, according to the measurement results of the flowmeter and the measuring cylinder, calculate the test data of each displacement pressure P, including the core oil saturation, porosity and permeability parameters, and calculate the average value.