Huff and puff mining experimental equipment and method based on pressure-driving crack propagation effect

Abstract

The invention discloses a huff-puff mining experimental device and method based on the pressure flooding crack propagation effect, and relates to the technical field of oil and gas exploiting.The huff-puff mining experimental device comprises an experimental rock plate and a temperature control box, an injection port of the experimental rock plate is connected with an intermediate container, a liquid outlet is provided with a liquid drainage valve, and the intermediate container is connected with a displacement pump; monitoring the fluid pressure in the experimental rock plate through a pressure detection device; the crack pressure in the experimental rock plate is controlled through a pressure control device; observing the fluid percolation condition in the internal crack of the reservoir rock sample by using an observation device; sequentially injecting saturated formation water and formation crude oil into the experimental rock plate through a displacement pump, then injecting displacement fluid, and monitoring the pressure and flow of the injected fluid and the response condition of the crack; soaking the well and continuously monitoring the pressure change; and after the soaking is finished, opening the drain valve, recording the oil gas quantity produced in the flowback process, and calculating the recovery ratio. According to the invention, fluid seepage and soaking diffusion flowback laws under dynamic expansion of the pressure-driven fracture can be studied.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploitation, and particularly relates to a huff and puff exploitation experimental device and method based on the expansion of pressure-driven fractures. Background Art

[0002] With the continuous development of oil and gas exploitation technologies, especially in the exploitation of unconventional oil and gas resources such as low-permeability reservoirs, tight oil formations, and shale gas, pressure drive (i.e., injecting fluids to displace oil and gas) has become one of the important means to improve the recovery rate. The core idea of pressure drive technology is to increase the reservoir pressure by injecting displacement agents such as gases and liquids, and push the oil and gas to flow to the production well, thereby improving the oil and gas recovery rate. Especially in some reservoirs with abundant natural fractures, the dynamic expansion of pressure-driven fractures and the fluid seepage process become the key factors determining the recovery rate.

[0003] During the pressure drive process, the injected fluid not only fills the fracture system, but also under the action of fracture expansion, the flow path of the fluid will change, thus affecting the distribution of oil and gas and the recovery efficiency. The dynamic expansion of fractures will form new fluid channels and change the original seepage network structure. As the fractures continue to expand, the flow path and intensity of fluid seepage will change significantly, thereby affecting the pressure drive effect. In addition, the dynamic expansion of fractures will also cause changes in the interaction between rocks and fluids, affecting the displacement efficiency.

[0004] The soaking well technology also plays an important role in the pressure drive process. Soaking well means that during the pressure drive process, the oil production operation of the production well is temporarily stopped, allowing the displacement fluid to maintain a certain pressure in the well to enhance the penetration and expansion of the fluid in the reservoir. Through reasonable soaking well operations, the injected fluid can be promoted to penetrate deeper into the reservoir and help the crude oil flow through the expanded fracture channels. Soaking well can not only reduce the fluctuation of injection pressure, but also increase the viscosity of the liquid, increase the residence time of the fluid, thereby improving the oil and gas recovery rate.

[0005] The fluid seepage under the action of fracture expansion not only affects the distribution of the fluid, but is also closely related to the soaking well effect during the expansion process. Soaking well operations can accelerate the liquid flow during the pressure drive process and promote the diffusion and backflow of the injected fluid. Therefore, the key to this process lies in how to balance the dynamic expansion of fractures and the fluid accumulation during the soaking well process, ensure the uniform distribution of the fluid, and achieve the optimal recovery rate. Summary of the Invention

[0006] To solve the above problems, the present invention provides a huff and puff exploitation experimental device and method based on the expansion of pressure-driven fractures.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows: A huff and puff production experiment device based on the action of pressure-driven fracture propagation. The huff and puff production experiment device includes an experimental rock plate for simulating reservoir rock with fractures. The experimental rock plate is arranged in a temperature control box body, and the temperature control box body is connected to a temperature controller. The injection port of the experimental rock plate is connected to an intermediate container through a liquid injection pipe. A sampling pipe is arranged at the top of the experimental rock plate, and a drain valve is arranged at the side drain port. The inlet of the intermediate container is connected to the outlet of a 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 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 filtration situation in the internal fractures of the reservoir rock sample.

[0008] Further, 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 an confining pressure chamber. The base includes convex eaves around and a rectangular sink inside. A grid-shaped support frame is arranged in the rectangular sink. The grid four-side frames of the support frame are provided with mutually connected diversion channels. The diversion channels in the frames are communicated with the grid inner cavity and the cavity between the convex eaves and the support frame for simulating the fracture morphology. The injection port and the drain port are symmetrically arranged on the opposite convex eaves on both sides. The rock matrix includes several reservoir rock samples in the shape of square grids. The number of reservoir rock samples in the square grids matches the number of grids in the support frame. Several reservoir rock samples can be correspondingly placed in the reservoir rock sample placement slots in the grids one by one. Back pressure valves are installed at the four corners of the grid of the support frame. The bottom liquid outlet of the back pressure valve is communicated with the diversion channel, and the top liquid inlet extends outside the cover plate. The back pressure valves on one side of the support frame are all connected to the pressure control device. A cover plate is arranged on the top of the base and the rock matrix. The four sides of the cover plate are connected to the four sides of the base through bolt pairs. The cover plate is provided with several visual windows. A sampling pipe is arranged in the middle of the visual window. A back pressure valve groove for installing a back pressure valve is arranged around the visual window. The sampling end of the sampling pipe extends outside the cover plate, and the inlet end of the sampling pipe extends to the top of the reservoir rock sample.

[0009] Further, the drain ports are multiple and penetrate through the convex eaves around the base. The drain valve is arranged at the outlet end of the drain port and on the outside of the convex eaves.

[0010] Furthermore, the diversion channels are arranged in the middle of the borders of the grids. There are two upright ribs arranged side by side at the top of the grids. Corresponding to these, there are two slots arranged side by side on the bottom surface of the cover plate, and the ribs can be placed in the slots. The ribs at the top of the grids around the periphery of the support frame cross each other, and the cross - over parts of the ribs of adjacent grids form back - pressure valve installation grooves, and the bottoms of the back - pressure valve installation grooves are communicated with the diversion channels in the adjacent borders.

[0011] Furthermore, the back - pressure valve includes a square - prism - shaped riser pipe and a support at its bottom. The liquid outlet of the riser pipe is communicated with the inner cavity of the support. There are diversion channels communicated with the inner cavity around the support. The outlets of the diversion channels are multiple and are communicated with the diversion channels in the adjacent borders. There are bosses on four opposite surfaces of the support that can extend into the diversion channels. The upper - end liquid inlet of the inner cavity of the riser pipe is arranged in the middle and the liquid inlet extends to the outside of the cover plate. There is a disc - shaped gland and multiple back - pressure valve fixing screws at the top of the riser pipe, and the multiple back - pressure valve fixing screws are evenly distributed around the liquid inlet. The gland is arranged on the top of the cover plate and is connected to the riser pipe through the back - pressure valve fixing screws. The back - pressure valve can act as a bolt structure through a special snap - fit structure, ensuring that the cover plate can withstand the pressure during the displacement process and is stably installed on the experimental rock slab.

[0012] Furthermore, the sampling tube includes a conduit and a sampling head at its top. The bottom of the conduit extends to the top of the rock matrix, and the sampling head extends to the outside of the cover plate. There is a liquid inlet on the side of the sampling head that is communicated with the inner cavity of the conduit. There is a pluggable rod at the sampling port at the top of the sampling head. There are radial through - holes in the lower part of the rod, and by rotating, the inner inlet of the liquid inlet can be blocked or penetrated. 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.

[0013] Furthermore, both the base and the support frame are made of high - pressure - and corrosion - resistant metal materials, and the cover plate is made of acrylic material.

[0014] Furthermore, the displacement pump is a constant - pressure and constant - speed displacement pump. 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 pipes.

[0015] The present invention also provides a huff - and - puff production experiment method based on the action of pressure - driven fracture propagation, including the following steps: Assemble the above - mentioned huff - and - puff production experiment equipment; Set the initial parameters of the fluid according to the experimental requirements: injection speed, injection volume, fracture opening pressure; Start the pressure control device to inject water into the diversion channels in the experimental rock slab and the annular area between the experimental rock slab and the base to form confining pressure, and ensure that the confining pressure is always greater than the displacement pressure by 5 MPa; Start the displacement pump to sequentially inject saturated formation water and formation crude oil into the experimental rock slab; Start the displacement pump again to inject displacement fluid into the experimental rock slab according to the set flow rate and injection volume, and monitor the pressure, flow rate of the injected fluid and the response of the fracture, and record the experimental data; Stop when the injected displacement fluid reaches the set injection volume; Set the soaking time according to the experimental requirements; During the soaking period, continue to monitor the pressure change; After the soaking is over, record the amount of oil and gas produced during the flowback process, calculate the recovery rate; and analyze the change of the recovery rate under different conditions; After the experiment is over, open the drain valve, release the confining pressure, and disassemble and clean the device for standby.

[0016] Further, based on multiple nonlinear regression analysis, R 2 = 0.96; The calculation formula for the recovery rate of the huff and puff production experimental equipment is as follows:

[0017] In the formula: v——Displacement fluid injection rate, m 3 / min; Q——Displacement fluid injection volume, m 3 ; L——Fracture length, m; C——Conductivity, D·cm; t——Soaking time, days; P——Flowback pressure, MPa.

[0018] Compared with the prior art, the technical progress achieved by the present invention is as follows: The present invention uses experimental rock slabs to simulate reservoir rocks with fractures, places them in a temperature-controlled box body and controls the temperature through a thermostat; injects fluids into the experimental rock slabs through a displacement pump, uses a pressure detection device to monitor the pressure of the fluids in the reservoir rock samples in the experimental rock slabs in real time, and controls the fracture pressure in the experimental rock slabs through a pressure control device; observes the fluid filtration situation in the fractures inside the reservoir rock samples through an observation device; through experiments, the production situations under different injection speeds, injection volumes, fracture opening pressures, fracture morphologies, fracture conductivity, soaking time, and backflow pressures can be analyzed, the distributions of the injected fluids and reservoir fluids can be characterized, the filtration range can be clarified, the productivity law can be given, the fluid filtration situation around the fracture network during the entire life cycle can be revealed, and the oil production mechanism of injection-diffusion-backflow can be implemented. Through the present invention, the fluid seepage and soaking diffusion backflow under the dynamic expansion of pressure-driven fractures can be deeply studied, thereby improving the recovery rate, better understanding the complexity of fluid seepage during the pressure-driven process, optimizing the pressure-driven operation, and providing theoretical support and technical guidance for the development of unconventional oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0020] In the drawings: Figure 1 is a schematic structural diagram of the huff and puff production experimental equipment in the embodiment of the present invention; Figure 2 is Figure 1 a top view of the experimental rock slab in Figure 3 is Figure 2 an axonometric view of the experimental rock slab in after removing the cover plate; Figure 4 is a top view of the cover plate in the embodiment of the present invention; Figure 5 is Figure 4 a schematic bottom surface structure diagram of the cover plate in ; Figure 6 is an axonometric view of the cover plate in the embodiment of the present invention; Figure 7 is an axonometric view of the base in the embodiment of the present invention; Figure 8 is a schematic structural diagram of the rock matrix in the embodiment of the present invention; Figure 9 is a schematic structural diagram of the back pressure valve in the embodiment of the present invention; Figure 10 is a schematic structural diagram of the sampling tube in the embodiment of the present invention; Figure 11It is a schematic diagram of the process of assembling the rock matrix in step 1 of the throughput mining experimental method in an embodiment of the present invention; Figure 12 This is a state diagram after the cover plate is assembled in step 1 of the huff-and-puff mining experimental method; Figure 13 for Figure 12 Schematic diagram of the process of assembling the cover; Figure 14 for Figure 12 Schematic diagram of the cooperation between the middle cover and the base after assembly; Figure 15 for Figure 14 Structural diagram of the experimental rock slab after assembly; Figure 16 for Figure 15 Schematic diagram of the structure of the middle discharge pressure relief valve; Figure 17 for Figure 15 Structural diagram of the middle bolt pair; Figure 18 This is a schematic diagram of the cooperation between the back pressure valve, the cover plate and the support frame in an embodiment of the present invention; In the figure: 1-intermediate container; 2-displacement pump; 3-pressure detection device; 4-pressure control device; 5-temperature controller; 6-sampling tube; 7-observation device; 8-drainage pressure relief valve; 9-experimental rock plate; 10-injection port; 11-back pressure valve; 12-temperature control box; 13-base; 14-diversion groove; 15-rock matrix; 16-cover plate; 17-support frame; 18-back pressure valve groove; 19-visible window; 20-convex eaves; 21-sampling tube groove; 22-buckle; 23-back pressure valve installation groove; 24-connection port; 25-reservoir rock sample placement groove; 26-reservoir rock sample; 27-sampling point connection; 28-rib plate; 29-slot; 30-vertical pipe; 31-support; 32-flow guide 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

[0021] The following specific embodiments may 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 in conjunction with the accompanying drawings.

[0022] like Figure 1As shown in the figure, a huff and puff production experimental device based on the action of pressure-driven fracture propagation, the huff and puff production experimental device includes an experimental rock plate 9 for simulating reservoir rock with fractures, 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 an intermediate container 1 through a liquid injection pipe, a sampling pipe 6 is arranged at the top of the experimental rock plate 9, and a drain valve 8 is arranged at the side drain port (as Figure 16 shown), the inlet of the intermediate container 1 is connected to the outlet of a displacement pump 2, and the experimental rock plate 9 is connected to a 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 a 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 above the experimental rock plate 9 for observing the fluid filtration situation in the internal fractures of the reservoir rock sample.

[0023] During specific production, water is injected into the annular area between the rock matrix of the experimental rock plate 9 and the side wall of the base through the pressure control device 4 to form confining pressure and ensure that the confining pressure is always greater than the displacement pressure by 5 MPa. The displacement pump 2 is a constant pressure and constant speed displacement pump to achieve constant speed and constant pressure displacement of the experimental rock plate; there are multiple intermediate containers 1, which are respectively used to contain saturated formation water, formation crude oil and displacement fluid. The inlets of the multiple intermediate containers 1 are respectively connected in parallel with the displacement pump 2, and the outlets are respectively connected in parallel with the liquid injection pipe. Start the displacement pump to inject saturated formation water and formation crude oil in sequence, and then inject displacement fluid (proppant or other fluid), and observe the response of the fluid pressure, flow rate and fractures in the experimental rock plate.

[0024] In addition, the pressure detection device 3 includes several pressure sensors. The pressure sensors and the pressure control device 4 are both controlled by a computer. Each pressure measurement point is connected through pipelines, and the pressure change conditions of 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 uses a constant temperature box for macroscopic regulation according to the temperature required for the experiment. The observation device uses a microscope, and the microscope is connected to the computer to directly observe the fluid situation in the experimental rock plate. The constant temperature box, microscope and pressure control device are all prior arts and will not be elaborated here.

[0025] As a preferred structure, as Figure 2 、 Figure 3 、 Figure 12 、 15As shown, the experimental rock slab 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 protruding eaves around the base and the support frame is the confining pressure chamber; the base 13 includes protruding eaves 20 around its perimeter and a rectangular sunken groove inside. A grid-shaped support frame 17 is fixed in the rectangular sunken groove. A mutually connected flow guiding groove 14 is provided in the grid four-side frame of the support frame 17. The flow guiding groove 14 inside the frame is communicated with the grid inner cavity and the cavity between the protruding eaves 20 and the support frame 17, for simulating the crack morphology; the injection port 10 and the drainage port are symmetrically arranged on the opposite protruding eaves 20 on both sides. Among them, the drainage port is multiple and penetrates through the protruding eaves 20 around the base 13. The drainage valve 8 is arranged at the outlet end of the drainage port and on the outer side of the protruding eaves 20, as Figure 1 shown. Corresponding connection holes 40 are provided on the cover plate and the protruding eaves of the base. The bolt of the bolt pair 39 passes through the connection hole and cooperates with the nut to fix the cover plate on the base.

[0026] In a specific embodiment of the present invention, as Figure 8 , 11 shown, the rock matrix 15 includes several reservoir rock samples 26 in the shape of square grids. The number of reservoir rock samples 26 in the square grids matches the number of grids in the support frame. Several reservoir rock samples 26 can be correspondingly placed in the reservoir rock sample placement grooves 25 in the grids one by one. Sampling points 27 are provided on each reservoir rock sample in the square grid to analyze the fluid physical property parameters at the sampling points.

[0027] In a specific embodiment of the present invention, as Figure 7 , 11 , 13 shown, backpressure valves 11 are installed at the four corners of the grid of the support frame 17. The bottom liquid outlet of the backpressure valve 11 is communicated with the flow guiding groove 14, and the top liquid inlet extends to the outside of the top of the cover plate 16; the backpressure valves 11 on one side of the support frame 17 are all connected to the pressure control device 4. The pressure of the backpressure valve can be freely set through the pressure control device to simulate the application scenarios of different crack opening pressures. When the fluid displacement pressure is less than the backpressure valve pressure and is not sufficient to pass through the backpressure valve, it will diffuse into the reservoir rock samples of the rock matrix through the side window of the flow guiding groove. The percolation situation of the fluid in the crack grid during the pressure displacement process can be observed through the viewing window 19 on the cover plate. Among them, a backpressure valve installation groove 23 is provided at the junction of the grid frame, and a communication port 24 is provided at the contact surface between the flow guiding groove 14 in the frame and the rock matrix 15, which can communicate the flow guiding groove 14 with the rock matrix 15 to realize the injection fluid percolation process.

[0028] In a specific embodiment of the present invention, as Figures 4 - 6, as shown in Fig. 17, a cover plate 16 is provided on the top of the base 13 and the rock matrix 15, and the four sides of the cover plate 16 are connected to the four sides of the base 13 through bolt pairs 39; several visual windows 19 are provided on the cover plate 16, a sampling tube groove 21 is installed in the middle of the visual window 19 to install a sampling tube 6, and a back pressure valve groove 18 around the visual window 19 is installed with a 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. As Figure 2 , 18 shown, the four sides of the cover plate 16 are connected to the base 13 through bolt pairs 39 and, at the same time, through the cooperation of the lower part of the back pressure valve 11 and the support frame 17, it is ensured that the cover plate 16 can withstand the pressure during the displacement process.

[0029] In a specific embodiment of the present invention, as Figure 13 , 14 shown, the diversion groove 14 is arranged in the middle of the border of the grid. Two parallel and upright rib plates 28 are provided on the top of the grid, and two parallel card slots 29 are correspondingly provided on the bottom surface of the cover plate 16. The rib plates 28 can be placed in the card slots 29; the rib plates 28 at the top of the four sides of the grid of the diversion groove 17 intersect with each other, and the intersecting parts of the rib plates 28 of adjacent grids form a back pressure valve installation groove 23, and the bottom of the back pressure valve installation groove 23 communicates with the diversion groove 14 in the adjacent border.

[0030] In a specific embodiment of the present invention, as Figure 9 , 18 shown, the back pressure valve 11 includes a quadrangular prism-shaped riser 30 and a support 31 at its bottom. The liquid outlet of the riser 30 communicates with the inner cavity of the support 31. Diversion channels 32 communicating with its inner cavity are provided around the support 31. The outlets of the diversion channels 32 are multiple and communicate with the diversion groove 14 in the adjacent border; convex platforms that can extend into the diversion groove 14 are provided on four opposite surfaces of the support 31. The upper liquid inlet 33 of the inner cavity of the riser 30 is arranged in the middle and the liquid inlet 33 extends to the outside of the cover plate 16. A disc-shaped gland and multiple back pressure valve fixing screws 34 are provided at the top of the riser 30, and the multiple back pressure valve fixing screws 34 are evenly distributed around the liquid inlet 33. The gland is arranged on the outer side of the top of the cover plate and is connected to the riser through the back pressure valve fixing screws 34. Through this special snap structure at both ends of the back pressure valve, the function of bolt fastening can be achieved, 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 is stably installed on the experimental rock plate.

[0031] During the specific design, as Figure 10As 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 communicating with the inner cavity of the conduit 35 is provided on the side of the sampling head 36. A knob 37 capable of controlling the opening and closing of the sampling port is provided at the sampling port at the top of the sampling head 36. A radial through-hole is provided at the lower part of the knob 37, and the inner inlet of the liquid inlet can be blocked or penetrated by rotation. 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 in the rock matrix 15. The principle of the switch of the knob is the same as that of the faucet, which will not be elaborated here.

[0032] During specific production, the base 13 and the support frame 17 are both made of high-pressure and corrosion-resistant metal materials and can withstand the pressure required for the experiment. The cover plate 16 is made of acrylic material and can observe the flow state of the fluid in the diversion groove.

[0033] The present invention also provides a huff and puff production experiment method based on the action of pressure-driven fracture propagation for analyzing the production conditions under different injection rates, injection volumes, fracture opening pressures, fracture morphologies, fracture conductivity, soaking time, and backflow pressures, including the following steps: Before the experiment starts, assemble the above-mentioned huff and puff production experiment equipment as Figures 11 - 15 shown.

[0034] At the start of the experiment, set initial parameters such as different injection rates, injection volumes, and fracture opening pressures according to the experimental requirements. Set the temperature control box to the required temperature of the experiment through the temperature controller. Inject confining pressure using the pressure control system and set the confining pressure to always be 5 MPa greater than the displacement pressure. Use the constant pressure and constant speed displacement pump to saturate the formation water and formation crude oil into the experimental rock slab in sequence.

[0035] Start the constant pressure and constant speed displacement pump and inject the displacement fluid according to the set flow rate and injection volume. Real-time monitor the filtration situation of the reservoir rock sample fluid, the pressure, flow rate of the fluid injected into the diversion groove, and the response situation of the fracture (i.e., the change of the fluid pressure at the backpressure valve) through the pressure detection device, and record the experimental data.

[0036] Stop when the injected displacement fluid reaches the set injection volume; set different soaking times according to the experimental requirements. During the soaking period, continue to monitor the pressure change. Since this device aims to simulate the expansion of real fractures in the case of proppants, the injected fluid will maintain a certain pressure in the reservoir and promote the maintenance or further expansion of the fracture system.

[0037] During the experiment, the inside of the rock matrix can be observed through a microscope, and at the same time, the fluid in the diversion groove can be sampled through the sampling tube to analyze the physical property parameters of the fluid at the sampling point.

[0038] After the shut-in well operation is completed, open the drain valve, record the amount of oil and gas produced during the flowback process, and calculate the recovery rate. According to different injection parameters (such as velocity, volume, pressure, etc.), compare the changes in the recovery rate under different conditions. By organizing the data, the influencing factors for the change in the conductivity of the proppant in the fracture can be obtained, and the retention situation of the proppant in the fracture can be obtained from the production of the proppant as shown in Table 1 below.

[0039]

[0040] Based on the multiple nonlinear regression analysis, R 2 = 0.96; the calculation formula for the recovery rate η is as follows:

[0041] In the formula: v —— injection velocity of the displacement fluid, m 3 / min; Q —— injection volume of the displacement fluid, m 3 ; L —— fracture length, m; C —— conductivity, D·cm; t —— shut-in well time, days; P —— flowback pressure, MPa.

[0042] In the present invention, the fracture is characterized by the flow guide groove. The above-mentioned "fracture length" refers to the length of the opened flow guide groove. The backpressure valve is initially in the closed state. When it is opened, the displacement liquid will enter the corresponding flow guide groove, increasing the flow guide area and the fracture length.

[0043] The above-mentioned conductivity is generally expressed by the product (Kf * wf) of the permeability Kf of the fracture support zone and the support fracture width wf. Among them, the support fracture width is the width of the flow guide groove. The fracture support zone is the area of the formation fracture supported by the proppant in the formation. Therefore, in the present invention, the flow guide groove is used to simulate the formation fracture. The opening pressure of each backpressure valve is set in the initial stage. When the pressure reaches, the backpressure valve will be flushed open, realizing the fracture expansion. Under different experimental conditions, all the opened backpressure valves and all the flow guide groove areas with liquid flow during the pressurization process form 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 conducting a permeability test using the above-mentioned huff and puff production experimental equipment.

[0044] During the experiment of the present invention, by mainly adjusting factors such as different injection rates, injection volumes, fracture opening pressures, fracture morphologies, fracture conductivity, shut-in time, and backflow pressure, etc., the distribution of injected fluid and reservoir fluid is analyzed and characterized, the filtration range is clarified, the productivity law is revealed, and further the change process of fluid filtration in the fracture network during the whole life cycle is explored. Finally, the oil production mechanism of injection-diffusion-backflow is implemented.

[0045] In summary, the present invention uses a flow guiding groove that simulates the real fracture morphology as the main body. The inside of the grid of the support frame is filled with reservoir rock samples, and the confining pressure can be added through the pressure control system on the outside. There are openings on the side of the grid border so that the fluid in the flow guiding groove can be connected to the rock matrix. Sampling tubes are provided in the reservoir rock samples in the grid to collect crude oil samples at different positions for physical property analysis. A backpressure valve is equipped at the grid junction, and the backpressure valve is adjusted by the pressure control device. When the fluid pressure in the flow guiding groove is higher than the valve pressure, the backpressure valve automatically opens and remains open continuously, simulating the process of being supported by proppants after the fracture opens. During the experiment, the filtration situation of the fluid in the reservoir rock samples can be observed in real time through a microscope.

[0046] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. An experimental device for huff and puff production under the action of pressure-driven fracture propagation, characterized in that: The cyclic steam stimulation experimental equipment includes an experimental rock plate for simulating reservoir rock with fractures. The experimental rock plate is arranged in a temperature control box body, and the temperature control box body is connected to a temperature controller. The injection port of the experimental rock plate is connected to an intermediate container through a liquid injection pipe. A sampling pipe is arranged at the top of the experimental rock plate, and a drain valve is arranged at the side drain port. The inlet of the intermediate container is connected to the outlet of a 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 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 filtration situation in the internal fractures of the reservoir rock sample.

2. The huff and puff production experimental equipment based on the pressure-driven fracture propagation according to claim 1, wherein: 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 surrounding eaves of the base and the support frame is a confining pressure chamber. The base includes surrounding eaves and a rectangular sink inside. A grid-shaped support frame is arranged in the rectangular sink. Flow guiding grooves are arranged in the four surrounding frames of the grid of the support frame and are mutually connected. The flow guiding grooves in the frame are connected to the inner cavity of the grid and the cavity between the eaves and the support frame, for simulating the fracture morphology. The injection port and the drain port are symmetrically arranged on the two opposite eaves. The rock matrix includes several reservoir rock samples in the shape of square grids. The number of reservoir rock samples in the square grids matches the number of grids in the support frame. Several reservoir rock samples can be correspondingly placed in the reservoir rock sample placement grooves in the grids one by one. Back pressure valves are installed at the four corners of the grid of the support frame. The bottom liquid outlet of the back pressure valve is connected to the flow guiding 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 all connected to the pressure control device. A cover plate is arranged on the top of the base and the rock matrix. The four sides of the cover plate are connected to the four sides of the base through bolt pairs. Several visual windows are arranged on the cover plate. A sampling pipe is arranged in the middle of the visual window. Back pressure valve grooves for installing back pressure valves are arranged around the visual window. The sampling end of the sampling pipe extends to the outside of the cover plate, and the inlet end of the sampling pipe extends to the top of the reservoir rock sample.

3. The throughput mining experimental equipment based on the action of pressure-driven fracture propagation according to claim 2, characterized in that: There are multiple drain ports, which penetrate through the surrounding eaves of the base. The drain valve is arranged at the outlet end of the drain port and on the outside of the eaves.

4. The huff and puff production experimental equipment based on the pressure-driven fracture propagation according to claim 3, wherein: The flow guiding grooves are arranged in the middle of the frames of the grid. Two parallel upright rib plates are arranged at the top of the grid. Two parallel card slots are correspondingly arranged on the bottom surface of the cover plate. The rib plates can be placed in the card slots. The rib plates at the top of the four surrounding grids of the support frame intersect with each other. The intersecting parts of the rib plates of adjacent grids form back pressure valve installation grooves, and the bottom of the back pressure valve installation grooves is communicated with the flow guiding grooves in the adjacent frames.

5. The throughput mining experimental equipment based on the pressure-driven fracture propagation according to claim 4, characterized in that: The backpressure valve includes a riser pipe in the shape of a quadrangular prism and a support at its bottom. The liquid outlet of the riser pipe communicates with the inner cavity of the support. The periphery of the support is provided with diversion channels communicating with its inner cavity. The outlets of the diversion channels are multiple and communicate with the diversion grooves within adjacent frames. On each of the four opposite faces of the support, there are bosses that can extend into the diversion grooves. The upper liquid inlet of the inner cavity of the riser pipe is arranged in the middle and extends outside the cover plate. At the top of the riser pipe, there is a disc-shaped gland and multiple backpressure valve fixing screws, and the multiple backpressure valve fixing screws are evenly distributed around the liquid inlet. The gland is arranged on the top of the cover plate and is connected to the riser pipe through the backpressure valve fixing screws.

6. The huff and puff production experiment device based on the action of pressure-driven fracture propagation according to claim 2, wherein: The sampling tube includes a conduit and a sampling head at its top. The bottom of the conduit extends to the top of the rock matrix. The sampling head extends outside the cover plate. The side of the sampling head is provided with a liquid inlet communicating with the inner cavity of the conduit. The sampling port at the top of the sampling head is provided with a rotatable switch. The lower part of the switch is provided with a radial through-hole, and the inner inlet of the liquid inlet can be blocked or penetrated by rotation. The side opening of the sampling head can be connected to a pressure detection device for real-time monitoring of the pressure within the rock matrix.

7. The huff and puff production experiment equipment based on the pressure-driven fracture propagation according to claim 2, wherein: Both the base and the support frame are made of high-pressure and corrosion-resistant metal materials, and the cover plate is made of acrylic material.

8. The throughput mining experimental equipment based on the pressure-driven fracture propagation according to claim 1, characterized in that: The displacement pump is a constant-pressure and constant-speed displacement pump. 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.

9. An experimental method for huff and puff production based on the action of pressure-driven fracture propagation, characterized in that, It includes the following steps: Assemble the huff and puff production experiment equipment as described in any one of claims 1-8; Set the initial parameters of the fluid according to the experimental requirements: injection rate, injection volume, fracture opening pressure; Start the pressure control device to inject water into the diversion grooves within 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 to sequentially inject saturated formation water and formation crude oil into the experimental rock plate; Start the displacement pump again to inject the displacement fluid into the experimental rock plate according to the set flow rate and injection volume, and monitor the pressure, flow rate of the injected fluid, and the response of the fracture, and record the experimental data; Stop when the injected displacement fluid reaches the set injection volume; Set the soaking time according to the experimental requirements; During the soaking period, continue to monitor the pressure change; After the soaking is over, open the drain valve, record the amount of oil and gas produced during the backflow process, calculate the recovery rate, and analyze the change of the recovery rate under different conditions; After the experiment is over, open the drain valve, release the confining pressure, and disassemble and clean the device for standby.

10. A method for huff and puff production experiment based on the propagation of pressure-driven fractures according to claim 9, characterized in that, Based on multiple nonlinear regression analysis, R 2 = 0.96, and the oil recovery calculation formula is as follows: ； where: v——injection rate of displacement fluid, m 3 / min; Q—the injection volume of the displacement fluid, m 3 ; L - fracture length, m; C - conductivity, D·cm; t - soaking time, days; P - backflow pressure, MPa.

Images