An integrated pressure-soaking-permeation-drainage experimental device and method for actual temperature and pressure conditions of shale reservoirs

Abstract

The present invention belongs to the field of shale reservoir development in the technology of oil and gas reservoir development, and discloses a pressure-soaking-infiltration-drainage integrated experimental device and method under the actual temperature and pressure conditions of a shale reservoir. The device includes: a power system, a fluid supply system, a reservoir simulation system, a temperature control system, and an electronic metering system; the power system is used to provide pressure to the fluid supply system; the fluid supply system is used to supply fluid to the reservoir simulation system, wherein the fluid is oil during the saturated oil process or fracturing fluid during the displacement process; the reservoir simulation system is used to simulate the integrated process of fracturing-soaking-infiltration-flowback under the actual temperature and pressure conditions of the target shale reservoir; the temperature control system is used to simulate the actual temperature of the shale reservoir; the electronic metering system is used to measure the oil saturation in the produced fluid. This device is resistant to high temperature and high pressure, can simulate the actual reservoir environment of ultra-high temperature and high pressure in the shale reservoir, and can realize the integrated process of fracturing-soaking-infiltration-flowback considering the actual formation pressure of the shale.

Description

Technical Field

[0001] The present invention belongs to the field of shale reservoir development in oil and gas reservoir development technology, and particularly relates to a pressure-soaking-infiltration-drainage integrated experimental device and method under the actual temperature and pressure conditions of a shale reservoir. Background Art

[0002] China's shale oil reservoirs are rich in reserves and have great development potential. Shale reservoirs have the characteristics of extremely low porosity and permeability, and a large number of micro-nano pore throats are developed, and the natural productivity is extremely low. At present, large-scale volume fracturing technology must be used for the development of shale oil reservoirs to obtain commercial productivity. Mainly by adding oil displacement agents to the fracturing fluid, the oil displacement agents are sent into the reservoir matrix during fracturing, and the shale oil in the reservoir matrix is displaced into the fractures through the imbibition effect of the fracturing fluid during the shut-in period, thereby greatly improving the shale oil recovery rate. Therefore, it is of great significance to establish an experimental device for simulating the integrated development process of fracturing-shut-in-imbibition-flowback under the actual temperature and pressure conditions of shale oil reservoirs for the further development of shale oil reservoirs.

[0003] At present, in the laboratory simulation of the fracturing development process of shale oil reservoirs, the fluid pressure in the core is often not considered, and the shale recovery evaluation experiment is carried out on the core without internal fluid pressure. However, in the actual fracturing development process of shale reservoirs, there is extremely high fluid pressure in the reservoir matrix. After the fracturing fluid is injected, the formation pressure is supplemented, the matrix rock is compressed, and the pore throat size is improved; in addition, during the flowback process, the formation pressure decreases, the matrix rock expands, and the pore throat size shrinks. This pressure change process has a great impact on the flow ability of shale oil and seriously affects the shale oil recovery rate. To solve the above problems, the present invention provides a pressure-soaking-infiltration-drainage integrated experimental device and method under the actual temperature and pressure conditions of a shale reservoir. Summary of the Invention

[0004] To overcome the problem that the existing laboratories cannot simulate the integrated process of fracturing-shut-in-imbibition-flowback under the actual formation fluid pressure of shale reservoirs, the present invention provides a pressure-soaking-infiltration-drainage integrated experimental device and method under the actual temperature and pressure conditions of a shale reservoir. The experimental device is resistant to high temperature and high pressure, has a prefabricated fracture in the core (simulating the shale reservoir after fracturing), and there is fluid pressure in the core (simulating the actual fluid pressure of the shale formation). Then, the fracturing fluid injection process is carried out. After the injection is completed, the shut-in and imbibition are started, and finally the fracturing fluid flowback process is simulated, solving the problem of the integrated process of fracturing-shut-in-imbibition-flowback that cannot be simulated under the formation fluid pressure.

[0005] To achieve the above object, the present invention provides the following solution:

[0006] A pressure-soaking-infiltration-drainage integrated experimental device under the actual temperature and pressure conditions of a shale reservoir, the device includes: a power system, a fluid supply system, a reservoir simulation system, a temperature control system, and an electronic metering system;

[0007] The power system is connected to the fluid supply system, the fluid supply system is connected to the reservoir simulation system, the fluid supply system and the reservoir simulation system are placed inside the temperature control system, and the reservoir simulation system is connected to the electronic metering system;

[0008] The power system is used to provide pressure to the fluid supply system;

[0009] The fluid supply system is used to supply fluid to the reservoir simulation system, wherein the fluid is oil in the saturated oil process or fracturing fluid in the displacement process;

[0010] The reservoir simulation system is used to simulate the integrated process of fracturing - soaking - imbibition - flowback under the actual temperature and pressure conditions of the target shale oil reservoir;

[0011] The temperature control system is used to simulate the actual temperature of the shale reservoir;

[0012] The electronic metering system is used to measure the oil saturation in the produced fluid.

[0013] Preferably, the power system includes: a double - cylinder constant - speed and constant - pressure pump, which provides power, i.e., pressure, to the fluid supply system under constant - speed or constant - pressure conditions.

[0014] Preferably, the fluid supply system includes: a first high - temperature and high - pressure double - way valve, a second high - temperature and high - pressure double - way valve, and a high - temperature and high - pressure intermediate container;

[0015] The first high - temperature and high - pressure double - way valve controls the power system to provide power to the high - temperature and high - pressure intermediate container, and the second high - temperature and high - pressure double - way valve controls the outflow of the fluid in the high - temperature and high - pressure intermediate container.

[0016] Preferably, the reservoir simulation system includes: a third high - temperature and high - pressure double - way valve, a first high - temperature and high - pressure back - pressure valve, a fourth high - temperature and high - pressure double - way valve, a high - temperature and high - pressure core holder, a shale core, a fifth high - temperature and high - pressure double - way valve, a second high - temperature and high - pressure back - pressure valve, and a produced - fluid collection device;

[0017] The third high - temperature and high - pressure double - way valve and the fourth high - temperature and high - pressure double - way valve control whether the fluid can flow to the high - temperature and high - pressure core holder, and the first high - temperature and high - pressure back - pressure valve and the second high - temperature and high - pressure back - pressure valve control the pressure of the fluid flowing into and out of the high - temperature and high - pressure core holder, thereby controlling the fluid pressure inside the shale core;

[0018] The left end of the first high - temperature and high - pressure back - pressure valve is connected to the fluid supply system, and the right end is connected to the left end of the high - temperature and high - pressure core holder, simulating the fracturing - fluid injection process in the actual development process of the shale oil reservoir;

[0019] The right end of the high-temperature and high-pressure core holder is connected to the fifth high-temperature and high-pressure two-way valve, and the fifth high-temperature and high-pressure two-way valve is connected to the second high-temperature and high-pressure backpressure valve to simulate the formation fluid pressure of the actual shale oil reservoir.

[0020] Preferably, the temperature control system includes a constant temperature box, and the temperature control system ensures that the temperatures of the fluid supply system and the reservoir simulation system are the same as the actual temperature of the shale oil reservoir.

[0021] Preferably, the electronic metering system includes an infrared laser instrument, a data automatic reading device, and a data visualization device. The electronic metering system is connected to the produced fluid collection device in the reservoir simulation system to measure the oil saturation in the produced fluid.

[0022] The present invention also provides a pressure-soaking-infiltration-drainage integrated experimental method under the actual temperature and pressure conditions of a shale reservoir, which is realized by using the pressure-soaking-infiltration-drainage integrated experimental device under the actual temperature and pressure conditions of the shale reservoir, and includes the following steps:

[0023] S1. Place the shale core saturated with shale oil into the high-temperature and high-pressure core holder. Fill the high-temperature and high-pressure intermediate container of the fluid supply system with shale oil, and set the pressures of the first high-temperature and high-pressure backpressure valve and the second high-temperature and high-pressure backpressure valve to the actual formation pressure of the shale reservoir.

[0024] S2. Open the first high-temperature and high-pressure two-way valve, the second high-temperature and high-pressure two-way valve, the third high-temperature and high-pressure two-way valve, the fourth high-temperature and high-pressure two-way valve, and the fifth high-temperature and high-pressure two-way valve. Start the double-cylinder constant-speed and constant-pressure pump of the power system, and start the oil saturation process in a constant-speed injection manner. The injection speed of the double-cylinder constant-speed and constant-pressure pump is the preset experimental speed until the pressure in the shale core reaches the actual formation pressure of the shale reservoir. Then close the third high-temperature and high-pressure two-way valve, the fourth high-temperature and high-pressure two-way valve, the fifth high-temperature and high-pressure two-way valve, and the double-cylinder constant-speed and constant-pressure pump.

[0025] S3. Adjust the pressure of the first high-temperature and high-pressure backpressure valve to the actual fluid pressure in the fracture after fracturing of the shale oil reservoir to simulate the process of fracturing fluid entering the reservoir matrix during the actual fracturing process of the shale reservoir, and fill the high-temperature and high-pressure intermediate container of the fluid supply system with the actual fracturing fluid used on site.

[0026] S4. Open the third high-temperature and high-pressure two-way valve and the fourth high-temperature and high-pressure two-way valve. Start the double-cylinder constant-speed and constant-pressure pump of the power system, and inject the fracturing fluid in the high-temperature and high-pressure intermediate container into the shale core at the actual fluid pressure in the fracture after fracturing of the shale oil reservoir in a constant-pressure injection manner until the injection volume of the fracturing fluid reaches the preset experimental injection volume. Then close the third high-temperature and high-pressure two-way valve, the fourth high-temperature and high-pressure two-way valve, and the double-cylinder constant-speed and constant-pressure pump, and start the soaking and imbibition process according to the preset soaking time of the experiment.

[0027] S5. After the shut-in well operation is completed, adjust the pressure of the first high-temperature and high-pressure back-pressure valve to the actual bottom-hole flowing pressure after the shut-in of the actual backflow during the fracturing development of the shale reservoir. Connect the third high-temperature and high-pressure two-way valve to the produced fluid collection device, open the third high-temperature and high-pressure two-way valve and the fourth high-temperature and high-pressure two-way valve, and simulate the process of fracturing fluid backflow until the pressure in the core drops to the preset pressure and the oil production no longer changes, then the experiment ends;

[0028] S6. Collect the data recorded by the data visualization device in the electronic metering system, calculate the recovery rate and draw the corresponding recovery rate curve.

[0029] Preferably, in S3, adjust the pressure of the first high-temperature and high-pressure back-pressure valve to the actual fluid pressure in the fracture during the fracturing of the shale reservoir, and simulate the process of fracturing fluid entering the reservoir matrix during the actual fracturing process of the shale reservoir, including:

[0030]

[0031] where p z is the injection pressure, MPa; p 0 is the surface injection pressure of the fracturing fluid during the actual on-site construction, MPa; is the density of the injected fracturing fluid, kg / m 3 ; g is the acceleration of gravity, m / s 2 ; p my is the frictional resistance along the way, MPa; p mj is the local frictional resistance, MPa; p ms is the perforation frictional resistance, MPa.

[0032] Preferably, in S6, calculating the recovery rate includes:

[0033] EOR = Vo / Vz

[0034] where EOR is the recovery rate, %; Vo is the volume of shale oil in the backflow fluid, mL; Vz is the volume of oil saturated in the core, mL.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] On the one hand, the present invention can simulate the reservoir environment of the actual formation temperature and formation pressure in the shale reservoir, solve the problem that the traditional experimental device cannot simulate the actual formation pressure, and is equipped with an electronic metering system to solve the problems of low accuracy and large reading errors of the traditional produced fluid collection device; on the other hand, the experimental device is easy to operate and can fully simulate the whole process of fracturing - soaking - imbibition - flowback in the actual development of shale, and can accurately predict the production degree of the shale core after fracturing, providing data support for the feasibility of fracturing and developing shale reservoirs, and solving the problem of the integrated process of fracturing - soaking - imbibition - flowback under the actual formation temperature and pressure in the laboratory. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 It is a schematic structural diagram of the experimental device of the present invention;

[0039] Figure 2 It is a schematic structural diagram of the shale core;

[0040] Figure 3 It is a curve of the shale oil recovery rate varying with the volume of the flowback fluid in Embodiment 1 of the present invention.

[0041] In the figure, a - power system, b - fluid supply system, c - reservoir simulation system, d - temperature control system, e - electronic metering system, 1 - double - cylinder constant - speed and constant - pressure pump, 2 - first high - temperature and high - pressure two - way valve, 3 - high - temperature and high - pressure intermediate container, 4 - second high - temperature and high - pressure two - way valve, 5 - third high - temperature and high - pressure two - way valve, 6 - first high - temperature and high - pressure back - pressure valve, 7 - fourth high - temperature and high - pressure two - way valve, 8 - high - temperature and high - pressure core holder, 9 - shale core, 10 - fifth high - temperature and high - pressure two - way valve, 11 - second high - temperature and high - pressure back - pressure valve, 12 - produced fluid collection device, 13 - infrared laser instrument, 14 - data automatic reading device, 15 - data visualization device, 16 - constant - temperature box, 17 - preset fracture, 18 - steel wire mesh. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0043] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] Example 1

[0045] As Figure 1 shown, the embodiment of the present invention provides an integrated pressure-soaking-infiltration-production experimental device for the actual temperature and pressure conditions of a shale reservoir. The device includes: a power system a, a fluid supply system b, a reservoir simulation system c, a temperature control system d, and an electronic metering system e;

[0046] The power system a is connected to the fluid supply system b, the fluid supply system b is connected to the reservoir simulation system c, the fluid supply system b and the reservoir simulation system c are placed inside the temperature control system d, and the reservoir simulation system c is connected to the electronic metering system e;

[0047] The power system a is used to provide pressure to the fluid supply system b;

[0048] The fluid supply system b is used to supply fluid to the reservoir simulation system c, where the fluid is oil during the saturated oil process or fracturing fluid during the displacement process;

[0049] The reservoir simulation system c is used to simulate the integrated process of fracturing-soaking-infiltration-production under the actual temperature and pressure conditions of the target shale oil reservoir;

[0050] The temperature control system d is used to simulate the actual temperature of the shale reservoir;

[0051] The electronic metering system e is used to measure the oil saturation in the produced fluid.

[0052] In this embodiment, the power system a includes: a double-cylinder constant-speed and constant-pressure pump 1, which provides power, i.e., pressure, to the fluid supply system under constant-speed or constant-pressure conditions.

[0053] In this embodiment, the fluid supply system b includes: a first high-temperature and high-pressure double-pass valve 2, a second high-temperature and high-pressure double-pass valve 4, and a high-temperature and high-pressure intermediate container 3;

[0054] The first high-temperature and high-pressure double-pass valve 2 controls the power system a to provide power to the high-temperature and high-pressure intermediate container 3, and the second high-temperature and high-pressure double-pass valve 4 controls the outflow of the fluid in the high-temperature and high-pressure intermediate container 3.

[0055] In this embodiment, the reservoir simulation system c includes: a third high-temperature and high-pressure double-pass valve 5, a first high-temperature and high-pressure back-pressure valve 6, a fourth high-temperature and high-pressure double-pass valve 7, a high-temperature and high-pressure core holder 8, a shale core 9, a fifth high-temperature and high-pressure double-pass valve 10, a second high-temperature and high-pressure back-pressure valve 11, and a produced fluid collection device 12;

[0056] The third high-temperature and high-pressure two-way valve 5 and the fourth high-temperature and high-pressure two-way valve 7 control whether the fluid can flow to the high-temperature and high-pressure core holder 8. The first high-temperature and high-pressure backpressure valve 6 and the second high-temperature and high-pressure backpressure valve 11 control the pressure of the fluid flowing into and out of the high-temperature and high-pressure core holder 8, thereby controlling the fluid pressure in the shale core 9.

[0057] The left end of the first high-temperature and high-pressure backpressure valve 6 is connected to the fluid supply system b, and the right end is connected to the left end of the high-temperature and high-pressure core holder 8, simulating the fracturing fluid injection process in the actual development process of the shale oil reservoir. Among them, simulating the fracturing fluid injection process in the actual development process of the shale oil reservoir means that the fracturing fluid is injected into the shale core 9 from the high-temperature and high-pressure intermediate container 3 in the fluid supply system.

[0058] The right end of the high-temperature and high-pressure core holder 8 is connected to the fifth high-temperature and high-pressure two-way valve 10, and the fifth high-temperature and high-pressure two-way valve 10 is connected to the second high-temperature and high-pressure backpressure valve 11, simulating the actual formation fluid pressure of the shale oil reservoir. Among them, simulating the actual formation fluid pressure of the shale oil reservoir includes: during the oil saturation process, the fluid pressure in the shale core 9 is controlled by setting the pressures of the first high-temperature and high-pressure backpressure valve 6 and the second high-temperature and high-pressure backpressure valve 11. During the oil saturation process, by setting the pressures of the first high-temperature and high-pressure backpressure valve 6 and the second high-temperature and high-pressure backpressure valve 11 to the actual fluid pressure in the rock reservoir (actual monitoring data from oil fields and mines), and then starting the oil saturation until a continuous and stable oil flow appears in the produced fluid collection device 12, it is considered that the fluid pressure in the shale core 9 reaches the formation fluid pressure of the shale oil reservoir.

[0059] As Figure 2 shown, the shale core 9 is first prefabricated with a core fracture 17 and then filled with sand (the sand of the mesh size used in the actual fracturing process of the shale oil reservoir). After filling with sand, a steel wire mesh 18 with a mesh size smaller than the used sand is used to wrap the fracture surface, which can simulate the reservoir after shale fracturing, that is, the prefabricated fracture shale core is used to simulate the reservoir after shale fracturing.

[0060] By setting the pressure of the first high-temperature and high-pressure backpressure valve 6 (the backpressure valve pressure can be directly set), the pressure Pz of the fluid entering the shale core 9 can be controlled, and the process of the fracturing fluid entering the reservoir matrix from the fracture during the actual shale fracturing process can be simulated.

[0061] The second high-temperature and high-pressure backpressure valve 11 can control the fluid pressure in the shale core 9, and can simulate the actual formation pressure conditions of the shale oil reservoir, that is, during the oil saturation process, by setting the pressure of the second high-temperature and high-pressure backpressure valve 11 (the backpressure valve pressure can be directly set) to control the fluid outflow pressure in the core, the fluid pressure in the core can be controlled.

[0062] Specifically, a shale core sample is installed in the high-temperature and high-pressure core holder 8 within the reservoir simulation system c (the core is pre-fractured and then filled with sand to simulate the reservoir after fracturing; and there is fluid pressure inside the core, which can simulate the real formation pressure environment within the shale reservoir). Both the left and right ends are connected to the first high-temperature and high-pressure backpressure valve 6 to simulate the integrated process of fracturing - shut-in - imbibition - flowback under the actual temperature and pressure conditions of the target shale oil reservoir.

[0063] The integrated process of fracturing - shut-in - imbibition - flowback under the actual temperature and pressure conditions of the target shale oil reservoir includes:

[0064] Using the core after pre-fracturing to simulate the reservoir after shale fracturing, after the core is saturated with oil and the injection of the fracturing fluid is completed, the valve is closed to simulate the shut-in process. During the shut-in process, the fracturing fluid displaces the crude oil in the core into the fractures through imbibition. After reaching the preset shut-in time, the valve is opened to start the flowback process.

[0065] Specifically, using the pre-fractured shale core 9 to simulate the fractured reservoir after shale oil reservoir fracturing, during the process of saturating the shale core 9 with oil, the fluid pressure inside the saturated shale core 9 is made consistent with the actual fluid pressure of the shale reservoir by controlling the pressures of the first high-temperature and high-pressure backpressure valve 6 and the second high-temperature and high-pressure backpressure valve 11; then, by controlling the pressure of the first high-temperature and high-pressure backpressure valve 6, the pressure when the fracturing fluid in the high-temperature and high-pressure intermediate container 3 is injected into the shale core 9 is made consistent with the pressure when the fracturing fluid flows from the fractures to the matrix after shale oil reservoir fracturing. After the injection of the fracturing fluid is completed, the fourth high-temperature and high-pressure two-way valve 7 and the fifth high-temperature and high-pressure two-way valve 10 are closed to simulate the shut-in process after shale oil reservoir fracturing. During the shut-in process, controlled by capillary force, the fracturing fluid can displace the crude oil in the core matrix into the fractures through imbibition. After reaching the preset shut-in time, the pressure of the first high-temperature and high-pressure backpressure valve 6 is adjusted to be consistent with the liquid production pressure of the production well in the field to simulate the flowback process after shale oil reservoir fracturing.

[0066] In this embodiment, the temperature control system d includes a constant temperature box 16, and the temperature control system b ensures that the temperatures of the fluid supply system b and the reservoir simulation system c are the same as the actual temperature of the shale oil reservoir.

[0067] In this embodiment, the electronic metering system e includes an infrared laser instrument 13, a data automatic reading device 14, and a data visualization device 15. The electronic metering system e is connected to the produced fluid collection device 12 in the reservoir simulation system c to measure the oil saturation in the produced fluid, that is, to read the oil volume in the produced fluid through infrared rays.

[0068] This experimental device is resistant to high temperature and high pressure, can simulate the actual reservoir environment of ultra-high temperature and high pressure in the shale reservoir, can realize the integrated process of fracturing - shut-in - imbibition - flowback considering the actual formation pressure of the shale, and solves the problem that the real formation fluid pressure of the shale reservoir cannot be simulated in the laboratory.

[0069] Example 2

[0070] The embodiment of the present invention provides a pressure-soaking-infiltration-drainage integrated experimental method for the actual temperature and pressure conditions of a shale reservoir, which is realized by using the pressure-soaking-infiltration-drainage integrated experimental device for the actual temperature and pressure conditions of the shale reservoir described in Example 1, and includes the following steps:

[0071] S1. Place the shale core 9 saturated with shale oil into the high-temperature and high-pressure core holder 8. Fill the high-temperature and high-pressure intermediate container 3 of the fluid supply system b with shale oil, and set the pressures of the first high-temperature and high-pressure backpressure valve 6 and the second high-temperature and high-pressure backpressure valve 11 to the actual formation pressure of the shale reservoir;

[0072] S2. Open the first high-temperature and high-pressure two-way valve 2, the second high-temperature and high-pressure two-way valve 4, the third high-temperature and high-pressure two-way valve 5, the fourth high-temperature and high-pressure two-way valve 7 and the fifth high-temperature and high-pressure two-way valve 10. Start the double-cylinder constant-speed and constant-pressure pump 1 of the power system a, and adopt the constant-speed injection method. The injection speed of the double-cylinder constant-speed and constant-pressure pump 1 is the preset experimental speed until the pressure in the shale core reaches the actual formation pressure of the shale reservoir. Then close the third high-temperature and high-pressure two-way valve 5, the fourth high-temperature and high-pressure two-way valve 7, the fifth high-temperature and high-pressure two-way valve 10 and the double-cylinder constant-speed and constant-pressure pump 1;

[0073] S3. Adjust the pressure of the first high-temperature and high-pressure backpressure valve 6 to the actual fluid pressure in the fracture after fracturing of the shale reservoir to simulate the process of fracturing fluid entering the reservoir matrix during the actual fracturing process of the shale reservoir, and fill the high-temperature and high-pressure intermediate container 3 of the fluid supply system b with the actual fracturing fluid used on site;

[0074] S4. Open the third high-temperature and high-pressure two-way valve 5 and the fourth high-temperature and high-pressure two-way valve 7. Start the double-cylinder constant-speed and constant-pressure pump 1 of the power system a, and adopt the constant-pressure injection method to inject the fracturing fluid in the high-temperature and high-pressure intermediate container 3 into the shale core 9 at the actual fluid pressure in the fracture after fracturing of the shale reservoir until the injection volume of the fracturing fluid reaches the preset experimental injection volume. Then close the third high-temperature and high-pressure two-way valve 5, the fourth high-temperature and high-pressure two-way valve 7 and the double-cylinder constant-speed and constant-pressure pump 1, and start the soaking and imbibition process according to the preset soaking time;

[0075] S5. After the soaking is over, adjust the pressure of the first high-temperature and high-pressure backpressure valve 6 to the actual bottom-hole flowing pressure after the actual backflow shut-in of the shale reservoir after fracturing development, connect the third high-temperature and high-pressure two-way valve 5 to the produced fluid collection device 12, open the third high-temperature and high-pressure two-way valve 5 and the fourth high-temperature and high-pressure two-way valve 7 to simulate the backflow process of the fracturing fluid until the pressure in the core drops to the preset pressure and the oil production no longer changes, and the experiment ends;

[0076] S6. Collect the data recorded by the data visualization device 15 in the electronic metering system e, calculate the recovery rate, and draw the corresponding recovery rate curve.

[0077] In this embodiment, in S3, the pressure of the first high-temperature and high-pressure backpressure valve 6 is adjusted to the actual fluid pressure in the fracture after shale reservoir fracturing, and the process of fracturing fluid entering the reservoir matrix during the actual fracturing process of the shale reservoir is simulated, including:

[0078]

[0079] where p z is the injection pressure, MPa; p 0 is the surface injection pressure of the fracturing fluid during actual on-site construction, MPa; is the density of the injected fracturing fluid, kg / m 3 ; g is the acceleration of gravity, m / s 2 ; p my is the frictional resistance along the way, MPa; p mj is the local frictional resistance, MPa; p ms is the perforation frictional resistance, MPa.

[0080] In this embodiment, in S4, start the soaking and imbibition process according to the preset soaking time of the experiment, including: after the soaking starts, the fracturing fluid displaces the shale oil through imbibition, and the imbibition process occurs during the soaking process (the oil-water saturation distribution field is redistributed under the action of imbibition during the soaking process).

[0081] During the actual fracturing process of the reservoir, after the fracturing fluid is injected into the reservoir, the production well will be closed for the soaking process, so that the fracturing fluid flows from the fracture to the matrix, and the crude oil at the far end of the matrix is displaced through imbibition. During the experiment, after the fracturing fluid is injected into the core, the actual soaking process is simulated by closing the fourth high-temperature and high-pressure two-way valve 7 and the fifth high-temperature and high-pressure two-way valve 10.

[0082] In this embodiment, in S5, simulate the fracturing fluid backflow process, including: after the soaking process ends, connect the high-temperature and high-pressure two-way valve 5 with the produced fluid collection device, and open the third high-temperature and high-pressure two-way valve 5 and the fourth high-temperature and high-pressure two-way valve 7. Due to the fluid pressure in the core, the valve is connected to the atmospheric pressure, and the fluid in the core flows out from the valve under the action of the pressure difference.

[0083] In this embodiment, in S6, calculate the recovery rate, including:

[0084] EOR = Vo / Vz

[0085] where EOR is the recovery rate, %; Vo is the volume of shale oil in the backflow fluid, mL; Vz is the volume of oil-saturated core, mL.

[0086] Embodiment Three

[0087] Using the integrated pressure-soaking-permeation-drainage experimental device and method for the actual temperature and pressure conditions of shale reservoirs provided in Embodiment 1 and Embodiment 2 of the present invention, the fracturing development effect of shale cores in Z Oilfield is evaluated.

[0088] 1. Experimental materials

[0089] The experimental water is simulated formation water with a salinity of 12497 mg / L; the fracturing fluid is the actual fracturing fluid provided by Z Oilfield, containing a chemical oil displacement agent (mass fraction 0.35%), and the oil-water interfacial tension is 0.0023 mN / m; the experimental oil is simulated oil, which is a mixture of dehydrated and degassed crude oil from Z Oilfield and aviation kerosene, with a viscosity of 4.158 mPa·s (134.2 °C); the experimental core is a natural shale core sample from the reservoir in Z Block, with the geometric dimensions of the core appearance: length 10.0 cm, diameter 2.5 cm, and permeability 0.238 mD.

[0090] 2. Experimental equipment

[0091] The main equipment includes: a - power system, b - fluid supply system, c - reservoir simulation system, d - temperature control system, e - electronic metering system, 1 - double-cylinder constant-speed and constant-pressure pump, 2 - first high-temperature and high-pressure double-pass valve, 3 - high-temperature and high-pressure intermediate container, 4 - second high-temperature and high-pressure double-pass valve, 5 - third high-temperature and high-pressure double-pass valve, 6 - first high-temperature and high-pressure back-pressure valve, 7 - fourth high-temperature and high-pressure double-pass valve, 8 - high-temperature and high-pressure core holder, 9 - shale core, 10 - fifth high-temperature and high-pressure double-pass valve, 11 - second high-temperature and high-pressure back-pressure valve, 12 - produced fluid collection device, 13 - infrared laser instrument, 14 - data automatic reading device, 15 - data visualization device, 16 - constant temperature box. All connecting lines in systems a, b, c, and d are high-temperature and high-pressure conduits, and the connecting lines in system e are data transmission lines. The flow schematic diagram of the experimental device is shown in Figure 1 .

[0092] 3. Experimental method

[0093] S1. Place the shale core saturated with shale oil into the high-temperature and high-pressure core holder 8. Fill the high-temperature and high-pressure intermediate container in the fluid supply system with shale oil, and set the pressures of the first high-temperature and high-pressure back-pressure valve 6 and the second high-temperature and high-pressure back-pressure valve 11 to the actual formation pressure of the shale reservoir (the actual formation pressure of the reservoir in Z Block is 62.99 MPa).

[0094] S2. Open the first, second, third, fourth, and fifth high-temperature and high-pressure two-way valves, start the double-cylinder constant-speed and constant-pressure pump of the power system, and start the saturation oil process in a constant-speed injection manner. The injection speed of the double-cylinder constant-speed and constant-pressure pump is the experimentally preset speed (0.01 ml / min) until the pressure in the shale core reaches the actual formation pressure of the shale reservoir (62.99 MPa). Then close the third, fourth, and fifth high-temperature and high-pressure two-way valves and the double-cylinder constant-speed and constant-pressure pump.

[0095] S3. Adjust the pressure of the first high-temperature and high-pressure back-pressure valve 6 to 87.4 MPa ( ), which is used to simulate the process of fracturing fluid entering the reservoir matrix during the actual fracturing process of the shale reservoir, and fill the high-temperature and high-pressure intermediate container of the fluid supply system with the actual fracturing fluid used on site.

[0096]

[0097] p z is the injection pressure, MPa; p 0 is the surface injection pressure of the fracturing fluid during actual on-site construction; is the density of the injected fracturing fluid, kg / m 3 ; g is the acceleration of gravity, m / s 2 ; p my is the frictional resistance along the way, Pa; p mj is the local frictional resistance, Pa; p ms is the perforation frictional resistance, Pa.

[0098] S4. Open the third and fourth high-temperature and high-pressure two-way valves, start the double-cylinder constant-speed and constant-pressure pump of the power system, and use the constant-pressure injection method to inject the fracturing fluid in the high-temperature and high-pressure intermediate container 3 into the shale core at the actual fluid pressure in the fracture after fracturing of the shale reservoir until the injected volume of the fracturing fluid reaches the experimentally preset injected volume (0.3 PV, the pore volume of the core is 4.54 ml, 0.3 PV = 4.45 * 0.3 = 1.362 ml). Then close the third and fourth high-temperature and high-pressure two-way valves and the double-cylinder constant-speed and constant-pressure pump, and start the soaking and imbibition process according to the experimentally preset soaking time (1 h).

[0099] S5. After the soaking is over, adjust the pressure of the first high-temperature and high-pressure back-pressure valve 6 to the actual bottom-hole flowing pressure after the actual flowback and shut-in of the shale reservoir after fracturing development (the bottom-hole flowing pressure after fracturing flowback in Block Z is 30 MPa), connect the third high-temperature and high-pressure two-way valve to the produced fluid collection device, open the third and fourth high-temperature and high-pressure two-way valves, simulate the process of fracturing fluid flowback until the pressure in the core drops to the preset pressure (30 MPa) and the oil production no longer changes, and the experiment ends.

[0100] S6. Collect the data recorded by the data visualization device in the electronic metering system, calculate the recovery rate and draw the corresponding recovery rate curve.

[0101] 4. Experimental results

[0102] The curve of shale oil recovery rate changing with the volume of the produced fluid is as Figure 3 shown. It can be seen from the figure that the recovery rate first rises rapidly and then slowly with the increase of the volume of the produced fluid, and finally tends to be stable. The final shale recovery rate is 16.32%.

[0103] EOR = Vo / Vz = 0.862 / 5.28 = 16.32%

[0104] EOR is the recovery rate, %; Vo is the volume of shale oil in the produced fluid, mL; Vz is the volume of oil saturated in the core, mL.

[0105] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A pressure-simmering-permeation-drainage integrated experimental method under actual temperature and pressure conditions of shale reservoirs, characterized in that: The experiment was realized by using a pressure-stem-permeation-drainage integrated experimental device under the actual temperature and pressure conditions of shale reservoirs. The device comprises: a power system (a), a fluid supply system (b), a reservoir simulation system (c), a temperature control system (d), and an electronic metering system (e); The power system (a) is connected to the fluid supply system (b), the fluid supply system (b) is connected to the reservoir simulation system (c), the fluid supply system (b) and the reservoir simulation system (c) are placed in the temperature control system (d), and the reservoir simulation system (c) is connected to the electronic metering system (e); The power system (a) is used to provide pressure to the fluid supply system (b); The fluid supply system (b) is used to supply fluid to the reservoir simulation system (c), wherein the fluid is oil in the oil saturation process or fracturing fluid in the displacement process; The reservoir simulation system (c) is used to simulate the integrated process of fracturing-well soaking-imbibition-flowback under the actual temperature and pressure conditions of the target shale oil reservoir; The temperature control system (d) is used to simulate the actual temperature of the shale reservoir; The electronic metering system (e) is used to measure the oil saturation in the produced fluid; The reservoir simulation system (c) comprises: a third high temperature and high pressure two-way valve (5), a first high temperature and high pressure back pressure valve (6), a fourth high temperature and high pressure two-way valve (7), a high temperature and high pressure core holder (8), a shale core (9), a fifth high temperature and high pressure two-way valve (10), a second high temperature and high pressure back pressure valve (11) and a produced fluid collection device (12); The third high temperature and high pressure two-way valve (5) and the fourth high temperature and high pressure two-way valve (7) control whether the fluid can flow to the high temperature and high pressure core holder (8), and the first high temperature and high pressure back pressure valve (6) and the second high temperature and high pressure back pressure valve (11) control the pressure of the fluid flowing into and out of the high temperature and high pressure core holder (8), thereby controlling the fluid pressure in the shale core (9); The left end of the first high temperature and high pressure back pressure valve (6) is connected to the fluid supply system (b), and the right end is connected to the left end of the high temperature and high pressure core holder (8), so as to simulate the fracturing fluid injection process in the actual development process of shale oil reservoirs; The right end of the high temperature and high pressure core holder (8) is connected to the fifth high temperature and high pressure two-way valve (10), and the fifth high temperature and high pressure two-way valve (10) is connected to the second high temperature and high pressure back pressure valve (11) to simulate the actual shale reservoir formation fluid pressure; The following steps are involved: S1. A shale core (9) saturated with shale oil is placed in a high temperature and high pressure core holder (8), a high temperature and high pressure intermediate container (3) of a fluid supply system (b) is filled with shale oil, and the pressures of the first high temperature and high pressure back pressure valve (6) and the second high temperature and high pressure back pressure valve (11) are both set to the actual formation pressure of the shale reservoir; S2, opening the first high temperature and high pressure two-way valve (2), the second high temperature and high pressure two-way valve (4), the third high temperature and high pressure two-way valve (5), the fourth high temperature and high pressure two-way valve (7) and the fifth high temperature and high pressure two-way valve (10), starting the double-cylinder constant speed and constant pressure pump (1) of the power system (a), and starting the oil saturation process by means of constant speed injection, the injection speed of the double-cylinder constant speed and constant pressure pump (1) being the experimental preset speed, until the pressure in the shale core reaches the actual formation pressure of the shale reservoir, and closing the third high temperature and high pressure two-way valve (5), the fourth high temperature and high pressure two-way valve (7) and the fifth high temperature and high pressure two-way valve (10) and the double-cylinder constant speed and constant pressure pump (1); S3, adjusting the pressure of the first high temperature and high pressure back pressure valve (6) to the actual fluid pressure in the fracture of the shale oil reservoir after fracturing, so as to simulate the process of fracturing fluid entering the reservoir matrix during the actual fracturing of the shale reservoir, and filling the high temperature and high pressure intermediate container (3) of the fluid supply system (b) with the fracturing fluid actually used on site; S4, opening the third high temperature and high pressure two-way valve (5) and the fourth high temperature and high pressure two-way valve (7), starting the double-cylinder constant speed and constant pressure pump (1) of the power system (a), and injecting the fracturing fluid in the high temperature and high pressure intermediate container (3) into the shale core (9) by means of constant pressure injection at the actual fluid pressure in the fracture after fracturing the shale oil reservoir, until the injection volume of the fracturing fluid reaches the injection volume preset in the experiment, closing the third high temperature and high pressure two-way valve (5), the fourth high temperature and high pressure two-way valve (7) and the double-cylinder constant speed and constant pressure pump (1), and starting the well soaking and absorption process according to the well soaking time preset in the experiment; S5, after the well is shut down, the pressure of the first high temperature and high pressure back pressure valve (6) is adjusted to the actual bottom hole flow pressure after the well is shut down after the shale oil reservoir is fracturing and developed, and the third high temperature and high pressure two-way valve (5) is connected to the produced fluid collection device (12), and the third high temperature and high pressure two-way valve (5) and the fourth high temperature and high pressure two-way valve (7) are opened to simulate the fracturing fluid backflow process until the pressure in the core drops to the preset pressure and the oil production no longer changes, and the experiment ends; S6. Collect the data recorded by the data visualization device (15) in the electronic metering system (e), calculate the recovery factor and draw a corresponding recovery factor curve.

2. The method according to claim 1, characterized in that The power system (a) comprises: a double-cylinder constant speed and constant pressure pump (1) which provides power, i.e. pressure, to the fluid supply system under constant speed or constant pressure conditions.

3. The method according to claim 1, characterized in that The fluid supply system (b) comprises: a first high temperature and high pressure resistant two-way valve (2), a second high temperature and high pressure resistant two-way valve (4) and a high temperature and high pressure resistant intermediate container (3); The first high temperature and high pressure resistant two-way valve (2) controls the power system (a) to provide power to the high temperature and high pressure resistant intermediate container (3), and the second high temperature and high pressure resistant two-way valve (4) controls the outflow of fluid in the high temperature and high pressure resistant intermediate container (3).

4. The method according to claim 1, characterized in that: The temperature control system (d) comprises a constant temperature box (16), and the temperature control system (d) ensures that the temperature of the fluid supply system (b) and the reservoir simulation system (c) is the same as the actual temperature of the shale oil reservoir.

5. The method according to claim 1, characterized in that The electronic metering system (e) comprises an infrared laser instrument (13), an automatic data reading device (14) and a data visualization device (15). The electronic metering system (e) is connected to a produced fluid collection device (12) in a reservoir simulation system (c) to measure the oil saturation in the produced fluid.

6. The method according to claim 1, characterized in that In S3, the pressure of the first high temperature and high pressure back pressure valve (6) is adjusted to the actual fluid pressure in the fracture of the shale oil reservoir after fracturing, simulating the process of fracturing fluid entering the reservoir matrix during the actual fracturing of the shale reservoir, including: Among them, p z is the injection pressure, MPa; p0 is the ground injection pressure of the fracturing fluid during actual construction on site, MPa; is the density of the injected fracturing fluid, kg / m 3 ; g is the acceleration due to gravity, m / s 2 ;p my is the friction along the way, MPa; p mj is the local friction, MPa; p ms is the perforation friction, MPa.

7. The method according to claim 1, characterized in that In S6, calculating the recovery factor includes: EOR=Vo / Vz Wherein, EOR is the recovery factor, %; Vo is the volume of shale oil in the flowback fluid, mL; Vz is the core saturated oil volume, mL.

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