Huff and puff production experiment equipment and method based on the action of pressure-driven fracture propagation

Abstract

The present invention discloses a throughput production experimental device and method based on the effect of pressure-driven fracture expansion, which relates to the field of oil and gas production technology. The throughput production experimental device includes an experimental rock plate and a temperature-controlled box. The injection port of the experimental rock plate is connected to an intermediate container, and the discharge port is provided with a drain valve. The intermediate container is connected to a displacement pump. The fluid pressure in the experimental rock plate is monitored by a pressure detection device; the fracture pressure in the experimental rock plate is controlled by a pressure control device; the fluid percolation in the fractures within the reservoir rock sample is observed by an observation device; saturated formation water and formation crude oil are sequentially injected into the experimental rock plate by the displacement pump, and then a displacement fluid is injected and the pressure, flow rate, and fracture response of the injected fluid are monitored; the well is shut down and pressure changes are continuously monitored; after the shut down is completed, the drain valve is opened, and the oil and gas produced during the flowback process is recorded to calculate the recovery rate. The present invention can study the fluid percolation and the soaked well diffusion flowback laws under the dynamic expansion of pressure-driven fractures.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas production, and in particular to a throughput production experimental device and method based on the effect of pressure-driven crack expansion. Background Art

[0002] With the continuous advancement of oil and gas extraction technology, pressure flooding (i.e., injecting fluids to displace oil and gas) has become a key means of improving oil and gas recovery, particularly in the exploitation of unconventional oil and gas resources such as low-permeability reservoirs, tight oil formations, and shale gas. The core concept of pressure flooding is to increase reservoir pressure by injecting displacing agents such as gas and liquids, thereby promoting the flow of oil and gas to production wells and thus improving oil and gas recovery. In reservoirs rich in natural fractures, the dynamic expansion of pressure-driven fractures and the fluid seepage process are key factors in determining oil and gas recovery.

[0003] During pressure flooding, injected fluid not only fills the fracture system but also alters the fluid flow path as the fractures expand, affecting oil and gas distribution and recovery efficiency. Dynamic fracture expansion creates new fluid pathways and alters the existing seepage network structure. As fractures continue to expand, the path and intensity of fluid seepage significantly change, further impacting the pressure flooding effect. Furthermore, dynamic fracture expansion alters the interaction between rock and fluid, affecting displacement efficiency.

[0004] Well-sucking technology also plays a crucial role in the pressure-driven flooding process. This involves temporarily halting production operations in a production well during the flooding process, allowing the displacing fluid to maintain a certain pressure within the wellbore to enhance its penetration and expansion within the reservoir. Effective well-sucking can encourage the injected fluid to penetrate deeper into the reservoir and facilitate the flow of crude oil through expanded fracture channels. Well-sucking not only reduces injection pressure fluctuations but also increases fluid viscosity and retention time, thereby improving oil and gas recovery.

[0005] Fluid seepage during fracture expansion not only affects fluid distribution but is also closely related to the soaking effect during the expansion process. Soaking accelerates fluid flow during pressure drive and promotes the diffusion and flowback of injected fluids. Therefore, the key to this process lies in balancing the dynamic expansion of fractures with fluid accumulation during soaking, ensuring uniform fluid distribution and achieving optimal recovery. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a throughput mining experimental device and method based on the effect of pressure-driven fracture expansion.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] A throughput mining experimental device based on the action of pressure-driven crack expansion, the throughput mining experimental device includes an experimental rock plate for simulating reservoir rocks with cracks, the experimental rock plate is arranged in a temperature-controlled box, and the temperature-controlled box is connected to a temperature controller; the injection port of the experimental rock plate is connected to an intermediate container through an injection pipe, the top of the experimental rock plate is provided with a sampling tube, the side discharge port is provided with a discharge valve, the inlet of the intermediate container is connected to the outlet of the displacement pump, the experimental rock plate is connected to a pressure detection device for real-time monitoring of the pressure of the fluid in the reservoir rock sample in the experimental rock plate; the experimental rock plate is connected to a pressure control device for controlling the crack pressure in the reservoir rock sample in the experimental rock plate; the probe of the observation device extends to the top of the experimental rock plate for observing the fluid percolation in the cracks inside the reservoir rock sample.

[0009] Furthermore, the experimental rock plate includes a base, a rock matrix and a cover plate on its top. The annular area between the inner wall of the convex eaves around the base and the support frame is a confining pressure cavity. The base includes convex eaves around the base and a rectangular trough inside the base. A grid-shaped support frame is provided in the rectangular trough. The grid of the support frame is surrounded by frames with mutually interpenetrating guide grooves. The guide grooves in the frames are interpenetrating with the inner cavity of the grid and the cavity between the convex eaves and the support frame to simulate the crack morphology. The injection port and the drainage port are symmetrically arranged on the convex eaves on both sides.

[0010] The rock matrix includes a plurality of square reservoir rock samples, the number of which matches the number of grids in the support frame, and the plurality of reservoir rock samples can be placed one-to-one in the reservoir rock sample placement slots in the grids;

[0011] Back-pressure valves are installed at the four corners of the support frame. The bottom liquid outlet of the back-pressure valve is connected to the guide groove, and the top liquid inlet extends to the outside of the cover plate. The back-pressure valves on one side of the support frame are connected to the pressure control device.

[0012] A cover plate is provided on the top of the base and the rock matrix, and the four sides of the cover plate are connected to the four sides of the base by bolt pairs; a plurality of viewing windows are provided on the cover plate, a sampling tube is provided in the middle of the viewing window, and a back-pressure valve groove for installing a back-pressure valve is provided around the viewing window, the sampling end of the sampling tube extends to the outside of the cover plate, and the inlet end of the sampling tube extends to the top of the reservoir rock sample.

[0013] Furthermore, there are multiple drainage ports, which are arranged throughout the convex eaves around the base, and the drainage valve is arranged at the outlet end of the drainage port and on the outside of the convex eaves.

[0014] Furthermore, the guide groove is arranged in the middle of the frame of the grid, and two parallel upright ribs are provided on the top of the grid, and two parallel card grooves are correspondingly provided on the bottom surface of the cover plate, and the ribs can be placed in the card grooves; the ribs on the top of the grid around the support frame intersect with each other, and the intersection of the ribs of adjacent grids forms a back pressure valve installation groove, and the bottom of the back pressure valve installation groove is connected to the guide groove in the adjacent frame.

[0015] Furthermore, the back-pressure valve includes a quadrangular prism-shaped riser and a support at its bottom. The liquid outlet of the riser is connected to the inner cavity of the support. The support is provided with a guide channel connected to its inner cavity around it. The outlet of the guide channel is multiple and connected to the guide groove in the adjacent frame. The four opposite faces of the support are provided with bosses that can extend into the guide groove. The liquid inlet at the upper end of the inner cavity of the riser is set in the middle, and the liquid inlet extends to the outside of the cover plate. The top of the riser is provided with a disc-shaped pressure cover and multiple back-pressure valve fixing screws, and multiple back-pressure valve fixing screws are evenly distributed around the liquid inlet. The pressure cover is set on the top of the cover plate and is connected to the riser through the back-pressure valve fixing screws. The back-pressure valve can act as a bolt structure through a special snap-fit structure to ensure that the cover plate can withstand the pressure during the displacement process and is stably installed on the experimental rock plate.

[0016] Furthermore, the sampling tube includes a catheter and a sampling head on its top, the bottom of the catheter extends to the top of the rock matrix, the sampling head extends to the outside of the cover plate, the side of the sampling head is provided with a liquid inlet connected to the inner cavity of the catheter, the top sampling port of the sampling head is provided with a pluggable rod, the lower part of the rod is provided with a radial through hole, which can be rotated to block or penetrate the inner inlet of the liquid inlet; the side opening of the sampling head can be connected to a pressure detection device for real-time monitoring of the pressure in the rock matrix.

[0017] Furthermore, the base and the support frame are both made of high-pressure-resistant and corrosion-resistant metal materials, and the cover is made of acrylic material.

[0018] Furthermore, the displacement pump is a constant pressure and constant speed displacement pump, and there are multiple intermediate containers, which are respectively used to hold saturated formation water, formation crude oil and displacement fluid; the inlets of the multiple intermediate containers are respectively connected in parallel with the displacement pump, and the outlets are respectively connected in parallel with the injection pipe.

[0019] The present invention also provides a huff-and-puff mining experimental method based on pressure-driven fracture expansion, comprising the following steps:

[0020] Assembling the aforementioned throughput mining experimental equipment;

[0021] Set the initial fluid parameters according to the experimental requirements: injection rate, injection volume, and fracture opening pressure;

[0022] Start the pressure control device to inject water into the guide groove in the experimental rock plate and the annular area between the experimental rock plate and the base to form a confining pressure, and ensure that the confining pressure is always greater than the displacement pressure by 5 MPa;

[0023] Start the displacement pump and inject saturated formation water and formation crude oil into the experimental rock plate in sequence;

[0024] Start the displacement pump again to inject the displacement fluid into the experimental rock plate according to the set flow rate and injection volume, monitor the pressure, flow rate and fracture response of the injected fluid, and record the experimental data;

[0025] Stop when the injection of displacement fluid reaches the set injection volume;

[0026] Set the soaking time according to experimental requirements;

[0027] During the soaking period, continue to monitor pressure changes;

[0028] After the well is soaked, the oil and gas volume produced during the flowback process is recorded and the recovery factor is calculated; and the changes in recovery factor under different conditions are analyzed;

[0029] After the experiment, open the drain valve, release the confining pressure, and disassemble the device for cleaning and standby use.

[0030] Furthermore, based on multivariate nonlinear regression analysis, R 2 =0.96; the recovery factor calculation formula of the throughput mining experimental equipment is as follows:

[0031]

[0032] Where: v is the injection velocity of displacement fluid, m 3 / min;

[0033] Q——displacement fluid injection volume, m 3 ;

[0034] L——crack length, m;

[0035] C – conductivity, D·cm;

[0036] t——well stewing time, days;

[0037] P——flowback pressure, MPa.

[0038] Compared with the prior art, the present invention has the following technical advances:

[0039] The present invention uses an experimental rock plate to simulate a reservoir rock with cracks, places it in a temperature-controlled box and controls the temperature through a thermostat; injects fluid into the experimental rock plate through a displacement pump, uses a pressure detection device to monitor the pressure of the fluid in the reservoir rock sample in real time, and controls the crack pressure in the experimental rock plate through a pressure control device; observes the fluid percolation in the internal cracks of the reservoir rock sample through an observation device; through experiments, the production conditions under different injection speeds, injection volumes, crack opening pressures, crack morphologies, crack conductivity, well-sucking time, and backflow pressures can be analyzed, the distribution of injected fluids and reservoir fluids can be characterized, the percolation range can be clarified, the production capacity law can be given, the percolation conditions of the fluid around the fracture network during the entire life cycle can be revealed, and the oil production mechanism of pressure-diffusion-backflow can be implemented. Through the present invention, in-depth research can be conducted on the fluid percolation and well-sucking diffusion backflow under the dynamic expansion of pressure-driven cracks, thereby improving the recovery rate, better understanding the complexity of fluid percolation in the pressure-driven process, optimizing the pressure-driven operation, and thus providing theoretical support and technical guidance for the development of unconventional oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0041] In the attached figure:

[0042] Figure 1 Schematic diagram of the structure of the throughput mining experimental equipment in an embodiment of the present invention;

[0043] Figure 2 for Figure 1 Top view of the experimental rock plate;

[0044] Figure 3 for Figure 2 Axonometric drawing of the experimental rock slab without the cover plate;

[0045] Figure 4 is a top view of a cover plate according to an embodiment of the present invention;

[0046] Figure 5 for Figure 4 Schematic diagram of the bottom structure of the middle cover;

[0047] Figure 6 This is an axonometric view of a cover plate according to an embodiment of the present invention;

[0048] Figure 7 This is an axonometric view of the base in an embodiment of the present invention;

[0049] Figure 8 Schematic diagram of the structure of the rock matrix in an embodiment of the present invention;

[0050] Figure 9Schematic diagram of the structure of the back pressure valve in an embodiment of the present invention;

[0051] Figure 10 Schematic diagram of the structure of the sampling tube in an embodiment of the present invention;

[0052] Figure 11 Schematic diagram of the process of assembling the rock matrix in step 1 of the throughput mining experimental method according to an embodiment of the present invention;

[0053] Figure 12 This is a diagram of the state after the cover plate is assembled in step 1 of the huff-and-puff mining experimental method;

[0054] Figure 13 for Figure 12 Schematic diagram of the process of assembling the cover;

[0055] Figure 14 for Figure 12 Schematic diagram of the middle cover and the base after assembly;

[0056] Figure 15 for Figure 14 Structural diagram of the experimental rock slab after assembly;

[0057] Figure 16 for Figure 15 Schematic diagram of the structure of the middle discharge pressure relief valve;

[0058] Figure 17 for Figure 15 Schematic diagram of the structure of the middle bolt pair;

[0059] Figure 18 Schematic diagram of the coordination between the back pressure valve, the cover plate and the support frame in an embodiment of the present invention;

[0060] In the picture:

[0061] 1-Intermediate container; 2-Displacement pump; 3-Pressure detection device; 4-Pressure control device; 5-Thermostat; 6-Sampling tube; 7-Observation device; 8-Drain pressure relief valve; 9-Experimental rock plate; 10-Injection port; 11-Back pressure valve; 12-Temperature control box;

[0062] 13-base; 14-diversion groove; 15-rock matrix; 16-cover plate; 17-support frame; 18-back pressure valve groove; 19-viewing window; 20-convex eaves; 21-sampling tube groove; 22-clip;

[0063] 23-back pressure valve installation groove; 24-connecting port; 25-reservoir rock sample placement groove; 26-reservoir rock sample; 27-sampling point connection;

[0064] 28-rib; 29-slot; 30-vertical pipe; 31-support; 32-flow channel; 33-liquid inlet; 34-back pressure valve fixing screw; 35-conduit; 36-sampling head; 37-insert rod, 38-opening; 39-bolt pair; 40-connecting hole. DETAILED DESCRIPTION

[0065] The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0066] like Figure 1 As shown, a throughput mining experimental device based on the effect of pressure-driven crack expansion, the throughput mining experimental device includes an experimental rock plate 9 for simulating reservoir rocks with cracks, the experimental rock plate 9 is arranged in a temperature control box 12, and the temperature control box 12 is connected to a temperature controller 5; the injection port 10 of the experimental rock plate 9 is connected to the intermediate container 1 through an injection pipe, the top of the experimental rock plate 9 is provided with a sampling pipe 6, and the side drain port is provided with a drain valve 8 (as shown in FIG. Figure 16 As shown in the figure), the inlet of the intermediate container 1 is connected to the outlet of the displacement pump 2, and the experimental rock plate 9 is connected to the pressure detection device 3 for real-time monitoring of the pressure of the fluid in the reservoir rock sample 26 in the experimental rock plate 9; the experimental rock plate 9 is connected to the pressure control device 4 for controlling the fracture pressure in the reservoir rock sample in the experimental rock plate 9; the probe of the observation device 7 extends to the top of the experimental rock plate 9 for observing the fluid percolation in the internal fractures of the reservoir rock sample.

[0067] During fabrication, water was injected into the annular area between the rock matrix and the base sidewall of the experimental slab 9 via a pressure control device 4 to create a confining pressure that remained above the displacement pressure of 5 MPa. The displacement pump 2 was a constant-pressure, constant-speed displacement pump, achieving constant-speed, constant-pressure displacement of the experimental slab. Multiple intermediate containers 1 were provided, each containing saturated formation water, formation crude oil, and displacement fluid. The inlets of these containers 1 were connected in parallel to the displacement pumps 2, and their outlets were connected in parallel to the injection pipes. The displacement pumps were activated to sequentially inject saturated formation water and formation crude oil, followed by the displacement fluid (proppant or other fluid), and the fluid pressure, flow rate, and fracture response within the experimental slab were observed.

[0068] In addition, the pressure detection device 3 includes several pressure sensors. The pressure sensors and the pressure control device 4 are all controlled by a computer. The various pressure measurement points are connected by pipelines, and the pressure changes at each point are fed back to the computer terminal in real time. At the same time, the pressure of each back-pressure valve can be set through the computer terminal. The temperature control box adopts a constant temperature box, which performs macro-control according to the temperature required for the experiment. The observation device adopts a microscope, which is connected to the computer and can visually observe the fluid conditions in the experimental rock plate. The constant temperature box, microscope and pressure control device are all existing technologies and will not be described here.

[0069] As a preferred structure, Figure 2 、 Figure 3 、 Figure 12 、 15 As shown, the experimental rock plate 9 includes a base 13, a rock matrix 15 and a cover plate 16 on its top. The annular area between the inner wall of the convex eaves around the base and the support frame is a confined pressure cavity; the base 13 includes convex eaves 20 around the base and a rectangular trough inside the base. A grid-shaped support frame 17 is fixed in the rectangular trough. The grid of the support frame 17 is surrounded by frames with guide grooves 14 that are interconnected. The guide grooves 14 in the frames are connected to the inner cavity of the grid and the cavity between the convex eaves 20 and the support frame 17 to simulate the crack morphology. The injection port 10 and the drainage port are symmetrically arranged on the convex eaves 20 on both sides. There are multiple drainage ports, which are arranged through the convex eaves 20 around the base 13. The drainage valve 8 is arranged at the outlet end of the drainage port and on the outside of the convex eaves 20, as shown in FIG. Figure 1 Connecting holes 40 are correspondingly provided on the convex eaves of the cover plate and the base, and the bolts of the bolt pair 39 pass through the connecting holes and cooperate with the nuts to fix the cover plate on the base.

[0070] In a specific embodiment of the present invention, Figure 8 、 11 As shown, the rock matrix 15 includes a plurality of square reservoir rock samples 26. The number of square reservoir rock samples 26 matches the number of grids within the support frame. The plurality of reservoir rock samples 26 can be placed one-to-one in the reservoir rock sample placement slots 25 within the grid. Each square reservoir rock sample is provided with a sampling point 27 for analyzing the physical properties of the fluid at the sampling point.

[0071] In a specific embodiment of the present invention, Figure 7 、 11As shown in Figures 13 and 14, back-pressure valves 11 are installed at each of the four corners of the support frame 17. The bottom outlet of each back-pressure valve 11 is connected to the guide groove 14, and the top inlet extends to the top and outside of the cover plate 16. The back-pressure valves 11 on one side of the support frame 17 are all connected to the pressure control device 4. The pressure control device allows the back-pressure valve pressure to be freely set to simulate application scenarios with different fracture opening pressures. When the fluid displacement pressure is less than the back-pressure valve pressure, that is, insufficient to pass through the back-pressure valve, it will diffuse into the reservoir rock sample in the rock matrix through the side windows of the guide groove. The percolation of the fluid within the fracture grid during the pressure drive process can be observed through the visual window 19 on the cover plate. A back-pressure valve mounting slot 23 is provided at the intersection of the grid frame, and a communication port 24 is provided at the interface between the guide groove 14 and the rock matrix 15 within the frame. This allows the guide groove 14 and the rock matrix 15 to communicate, enabling the percolation process of the injected fluid.

[0072] In a specific embodiment of the present invention, Figure 4-6 As shown in Figures 17 and 17, a cover plate 16 is provided on the top of the base 13 and the rock matrix 15. The four sides of the cover plate 16 are connected to the four sides of the base 13 by bolt pairs 39. The cover plate 16 is provided with a plurality of viewing windows 19. The sampling tube groove 21 in the middle of the viewing window 19 is used to install the sampling tube 6. The back pressure valve groove 18 around the viewing window 19 is used to install the back pressure valve 11. The sampling end of the sampling tube 6 extends to the outside of the cover plate 16, and the inlet end of the sampling tube 6 extends to the top of the reservoir rock sample 26. Figure 2 、 18 As shown, the cover plate 16 is connected to the base 13 by bolt pairs 39 on all sides, and the bottom of the back pressure valve 11 cooperates with the support frame 17 to ensure that the cover plate 16 can withstand the pressure during the displacement process.

[0073] In a specific embodiment of the present invention, Figure 13 、 14 As shown, the guide groove 14 is arranged in the middle of the frame of the grid, and two parallel upright ribs 28 are provided on the top of the grid. Two parallel card grooves 29 are correspondingly provided on the bottom surface of the cover plate 16, and the ribs 28 can be placed in the card grooves 29; the ribs 28 on the top of the grid around the guide groove 17 intersect with each other, and the intersection of the ribs 28 of adjacent grids forms a back pressure valve installation groove 23, and the bottom of the back pressure valve installation groove 23 is connected to the guide groove 14 in the adjacent frame.

[0074] In a specific embodiment of the present invention, Figure 9 、 18As shown, the back-pressure valve 11 includes a quadrangular prism-shaped standpipe 30 and a support 31 at its bottom. The liquid outlet of the standpipe 30 is connected to the inner cavity of the support 31. The support 31 is provided with a guide channel 32 connected to its inner cavity around it. The guide channel 32 has multiple outlets and is connected to the guide groove 14 in the adjacent frame; the four opposite surfaces of the support 31 are provided with bosses that can extend into the guide groove 14, the liquid inlet 33 at the upper end of the inner cavity of the standpipe 30 is arranged in the middle, and the liquid inlet 33 extends to the outside of the cover plate 16, the top of the standpipe 30 is provided with a disc-shaped pressure cover and multiple back-pressure valve fixing screws 34, and multiple back-pressure valve fixing screws 34 are evenly distributed around the liquid inlet 33, the pressure cover is arranged on the top outer side of the cover plate, and is connected to the standpipe through the back-pressure valve fixing screws 34. This special snap-on structure at the upper and lower ends of the back-pressure valve can play the role of bolt tightening, realizing the connection between the cover plate and the support frame, ensuring that the upper cover plate can withstand the pressure during the displacement process and be stably installed on the experimental rock plate.

[0075] When designing specifically, Figure 10 As shown, the sampling tube 6 includes a conduit 35 and a sampling head 36 at its top. The bottom of the conduit 35 extends to the top of the rock matrix 15, and the sampling head 36 extends to the outside of the cover plate 16. A liquid inlet is provided on the side of the sampling head 36, communicating with the inner cavity of the conduit 35. A knob 37 is provided at the top of the sampling port of the sampling head 36 to control the opening and closing of the sampling port. The lower portion of the knob 37 has a radial through hole, which can be rotated to block or open the inner entrance of the liquid inlet. The side opening 38 of the sampling head 36 can be connected to the pressure detection device 3 for real-time monitoring of the pressure within the rock matrix 15. The opening and closing principle of the knob is similar to that of a faucet, and will not be further described here.

[0076] During specific production, the base 13 and the support frame 17 are both made of high-pressure and corrosion-resistant metal materials, which can withstand the pressure required for the experiment; the cover plate 16 is made of acrylic material, which can observe the flow state of the fluid in the guide groove.

[0077] The present invention also provides a throughput production experimental method based on pressure-driven fracture expansion, which is used to analyze production conditions under different injection rates, injection volumes, fracture opening pressures, fracture morphologies, fracture conductivity, soaking times, and flowback pressures, including the following steps:

[0078] Before the experiment begins, assemble the above-mentioned throughput mining experimental equipment, such as Figure 11-15 shown.

[0079] At the start of the experiment, different initial parameters, such as injection rate, injection volume, and fracture opening pressure, were set according to the experimental requirements. The temperature control box was set to the desired experimental temperature using a thermostat. A pressure control system was used to control the confining pressure, which was always set 5 MPa above the displacement pressure. A constant-pressure, constant-speed displacement pump was used to sequentially saturate the experimental rock slab with formation water and then formation crude oil.

[0080] Start the constant-pressure, constant-speed displacement pump and inject the displacement fluid at the set flow rate and injection volume. Use the pressure detection device to monitor the percolation of the reservoir rock sample, the pressure and flow of the injected fluid in the diversion channel, and the response of the fracture (i.e., the change in fluid pressure at the back-pressure valve) in real time, and record the experimental data.

[0081] The injection of displacement fluid stops when the set injection volume is reached; different soaking times can be set based on experimental requirements. Pressure changes are continuously monitored during the soaking period. Because this device is designed to simulate the expansion of a real fracture in the presence of proppant, the injected fluid maintains a certain pressure in the reservoir, encouraging the fracture system to maintain or further expand.

[0082] During the experiment, the rock matrix can be observed through a microscope, and the fluid in the diversion channel can be sampled through a sampling tube to analyze the physical properties of the fluid at the sampling point.

[0083] After the well was soaked, the drain valve was opened, the oil and gas volume produced during the flowback process was recorded, and the recovery factor was calculated. The recovery factor changes under different injection parameters (such as injection rate, volume, and pressure) were compared. This data analysis revealed the factors influencing the changes in proppant conductivity within the fractures. The proppant retention in the fractures was also determined based on the proppant recovery data, as shown in Table 1 below.

[0084]

[0085] Based on the multivariate nonlinear regression analysis, R 2 =0.96; the recovery factor η is calculated as follows:

[0086]

[0087] Where: v is the injection velocity of displacement fluid, m 3 / min;

[0088] Q——displacement fluid injection volume, m 3 ;

[0089] L——crack length, m;

[0090] C – conductivity, D·cm;

[0091] t——well stewing time, days;

[0092] P——flowback pressure, MPa.

[0093] In the present invention, the crack is characterized by a guide groove. The above-mentioned "crack length" refers to the length of the open guide groove. The back pressure valve is initially closed. When it is opened, the displacement liquid will enter the corresponding guide groove, which will increase the guide area and the length of the crack.

[0094] The above-mentioned conductivity is generally expressed by the product of the permeability Kf of the fracture support zone and the support slit width wf (Kf*wf). Among them, the support slit width is the width of the guide groove. The fracture support zone is the area of the formation fracture supported by the proppant in the formation, so the guide groove is used to simulate the formation fracture in the present invention. The opening pressure of each back pressure valve is set in the initial stage. When the pressure is reached, the back pressure valve will be flushed open, realizing the expansion of the fracture. Under different experimental conditions, all the back pressure valves opened during the pressurization process and all the guide groove areas with liquid flow constitute the fracture area of this group of experiments, which can be equivalent to the fracture support zone area of this group of experiments. Therefore, the permeability of the fracture support zone can be obtained by performing a permeability test using the above-mentioned throughput mining experimental equipment.

[0095] During the experiment, the present invention mainly adjusts different factors such as injection rate, injection volume, fracture opening pressure, fracture morphology, fracture conductivity, soaking time and backflow pressure to analyze and characterize the distribution of injected fluid and reservoir fluid, clarify the percolation range, reveal the production capacity law, and further explore the changing process of fluid percolation in the fracture network throughout its life cycle, and finally implement the pressure-diffusion-backflow oil production mechanism.

[0096] In summary, the present invention uses a guide trough that simulates the morphology of a real fracture as the main body, and the grid of the support frame is filled with reservoir rock samples. The outside can add annular pressure through a pressure control system. The grid frame is open on the side to allow the fluid in the guide trough to connect with the rock matrix. The reservoir rock samples in the grid are provided with sampling tubes, which can collect crude oil samples from different locations for physical property analysis. A back-pressure valve is provided at the junction of the grids. The back-pressure valve is adjusted by a pressure control device. When the fluid pressure in the guide trough is higher than the valve pressure, the back-pressure valve automatically opens and remains open, simulating the process of support by proppant after the fracture is opened. During the experiment, the percolation of the fluid in the reservoir rock sample can be observed in real time through a microscope.

[0097] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A throughput mining experimental device based on pressure-driven fracture expansion, characterized by: The throughput mining experimental equipment includes an experimental rock plate for simulating reservoir rocks with fractures, the experimental rock plate is arranged in a temperature-controlled box, and the temperature-controlled box is connected to a temperature controller; the injection port of the experimental rock plate is connected to an intermediate container via an injection pipe, the top of the experimental rock plate is provided with a sampling tube, and the side discharge port is provided with a discharge valve, the inlet of the intermediate container is connected to the outlet of the displacement pump, and the experimental rock plate is connected to a pressure detection device for real-time monitoring of the pressure of the fluid in the reservoir rock sample in the experimental rock plate; The experimental rock plate is connected to a pressure control device for controlling the fracture pressure in the reservoir rock sample in the experimental rock plate; the probe of the observation device extends above the experimental rock plate for observing the fluid percolation in the fractures inside the reservoir rock sample; The experimental rock plate includes a base, a rock matrix and a cover plate on top thereof. The annular area between the inner wall of the convex eaves of the base and the support frame is a confining pressure cavity. The base includes convex eaves on all sides and a rectangular trough inside thereof. A grid-shaped support frame is provided in the rectangular trough. The grid-shaped support frame has guide grooves that are interconnected within the frame around the support frame. The guide grooves in the frame are interconnected with the inner cavity of the grid and the cavity between the convex eaves and the support frame to simulate the crack morphology. The injection port and the drainage port are symmetrically arranged on the convex eaves on both sides. The guide groove is arranged in the middle of the frame of the grid, and two parallel upright ribs are provided on the top of the grid. Two parallel card slots are correspondingly provided on the bottom surface of the cover plate, and the ribs can be placed in the card slots; the ribs on the top of the grid around the support frame intersect with each other, and the intersection of the ribs of adjacent grids forms a back-pressure valve installation groove, and the bottom of the back-pressure valve installation groove is connected to the guide groove in the adjacent frame; The rock matrix includes a plurality of square reservoir rock samples, the number of which matches the number of grids in the support frame, and the plurality of reservoir rock samples can be placed one-to-one in the reservoir rock sample placement slots in the grids; Back-pressure valves are installed at the four corners of the support frame. The bottom liquid outlet of the back-pressure valve is connected to the guide groove, and the top liquid inlet extends to the outside of the top surface of the cover plate. The back-pressure valves on one side of the support frame are connected to the pressure control device. A cover plate is provided on the top of the base and the rock matrix, and the four sides of the cover plate are connected to the four sides of the base by bolt pairs; a plurality of viewing windows are provided on the cover plate, a sampling tube is provided in the middle of the viewing window, and a back-pressure valve groove for installing a back-pressure valve is provided around the viewing window, the sampling end of the sampling tube extends to the outside of the cover plate, and the inlet end of the sampling tube extends to the top of the reservoir rock sample.

2. The huff-and-puff mining experimental equipment based on pressure-driven fracture expansion according to claim 1, characterized in that: There are multiple drainage ports, which are arranged throughout the convex eaves around the base. The drainage valve is arranged at the outlet end of the drainage port and on the outer side of the convex eaves.

3. The throughput mining experimental equipment based on pressure-driven fracture expansion according to claim 1, characterized in that: The back-pressure valve includes a quadrangular prism-shaped standpipe and a support at its bottom. The liquid outlet of the standpipe is connected to the inner cavity of the support. The support is provided with a guide channel connected to its inner cavity around it. There are multiple outlets of the guide channel, which are connected to the guide groove in the adjacent frame. The four opposite surfaces of the support are provided with bosses that can extend into the guide groove. The liquid inlet at the upper end of the inner cavity of the standpipe is set in the middle, and the liquid inlet extends to the outside of the cover plate. The top of the standpipe is provided with a disc-shaped pressure cover and multiple back-pressure valve fixing screws, and the multiple back-pressure valve fixing screws are evenly distributed around the liquid inlet. The pressure cover is set on the top of the cover plate and is connected to the standpipe through the back-pressure valve fixing screws.

4. The huff-and-puff mining experimental equipment based on pressure-driven fracture expansion according to claim 1, characterized in that: The sampling tube includes a catheter and a sampling head at its top. The bottom of the catheter extends to the top of the rock matrix, and the sampling head extends to the outside of the cover plate. A liquid inlet communicating with the inner cavity of the catheter is provided on the side of the sampling head. A rotatable switch is provided at the top sampling port of the sampling head. A radial through hole is provided at the bottom of the switch, which can be rotated to block or penetrate the inner inlet of the liquid inlet. The side opening of the sampling head can be connected to a pressure detection device for real-time monitoring of the pressure in the rock matrix.

5. The throughput mining experimental equipment based on pressure-driven fracture expansion according to claim 1, characterized in that: The base and the support frame are both made of high-pressure-resistant and corrosion-resistant metal materials, and the cover is made of acrylic material.

6. The throughput mining experimental equipment based on pressure-driven fracture expansion according to claim 1, characterized in that: The displacement pump is a constant pressure and constant speed displacement pump, and there are multiple intermediate containers, which are respectively used to contain saturated formation water, formation crude oil and displacement fluid; the inlets of the multiple intermediate containers are respectively connected in parallel with the displacement pump, and the outlets are respectively connected in parallel with the injection pipe.

7. A method for huff-and-puff mining experiment based on pressure-driven fracture expansion, characterized in that: The following steps are involved: Assembling the throughput mining experimental equipment according to any one of claims 1 to 6; Set the initial fluid parameters according to the experimental requirements: injection rate, injection volume, and fracture opening pressure; Start the pressure control device to inject water into the guide groove in the experimental rock plate and the annular area between the experimental rock plate and the base to form a confining pressure, and ensure that the confining pressure is always greater than the displacement pressure by 5 MPa; Start the displacement pump and inject saturated formation water and formation crude oil into the experimental rock plate in sequence; Start the displacement pump again to inject the displacement fluid into the experimental rock plate according to the set flow rate and injection volume, monitor the pressure, flow rate and fracture response of the injected fluid, and record the experimental data; Stop when the injection of displacement fluid reaches the set injection volume; Set the soaking time according to experimental requirements; During the soaking period, continue to monitor pressure changes; After the well is soaked, the drainage valve is opened, the oil and gas volume produced during the flowback process is recorded, and the recovery factor is calculated; and the changes in the recovery factor under different conditions are analyzed; After the experiment, open the drain valve, release the confining pressure, and disassemble the device for cleaning and standby use.

8. The method of huff-and-puff mining experiment based on pressure-driven fracture expansion according to claim 7, characterized in that: Based on the multivariate nonlinear regression analysis, R 2 =0.96, the recovery factor calculation formula is as follows: ； Where: v ——displacement fluid injection velocity, m 3 / min; Q ——Displacement fluid injection volume, m 3 ; L ——crack length, m; C ——conductivity, D·cm; t ——Simmering time, days; P ——Flowback pressure, MPa.

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