Multi-turn pressing-braising injection-production oil displacement system and method for simulating gas-water alternation

Abstract

The invention relates to the technical field of unconventional oil and gas development, in particular to a system and a method for simulating gas-water alternation multi-turn pressing-braising injection and production oil displacement. According to the scheme, a pressing fracture network and a matrix reservoir are equivalently simulated, and pressing-braising injection and production of well soaking time are reasonably considered, so that the result is more accurate, and the oil displacement efficiency is improved. After the fracture core clamping unit and the matrix core clamping unit are exchanged in the forward direction and the reverse direction, a compact core is rapidly saturated, the oil reservoir initialization time is shortened, the influence of multiple fracture parameters on oil displacement in the three stages of pressing, braising and mining can be considered without repeatedly disassembling and assembling the core clamping unit, the fracture form is changed by replacing the fracture forming core, and the oil displacement efficiency is improved. The influence rule of a water-gas composite medium on the oil well pressing-braising-production capacity under different storage and seepage modes can be researched, the different storage and seepage modes comprise a multi-stage fracture-matrix reservoir, a large fracture-matrix reservoir, a micro-fracture-matrix reservoir and an original matrix reservoir, and independence and integrity of a fracture core and a matrix core are ensured; the experiment time is greatly shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas development, and in particular to a system and method for simulating gas-water alternating multiple rounds of pressure-stem injection-production oil recovery. Background Art

[0002] The isolated wells in the three types of reservoirs in the oil reservoir have no injection-production system or the injection-production relationship is imperfect, which leads to difficulties in the formation energy supply, difficulty in well network deployment, and high production costs. Due to the limitation of gas sources and the influence of gas channeling, the feasibility of large-scale gas injection and huff-and-puff is low. At the same time, the efficiency of conventional water injection for oil recovery is low, and the scope of pressure-driven water injection technology is limited. Therefore, the feasibility of multiple rounds of pressure-driven injection and recovery by alternating gas and water is discussed. Considering that multi-scale fractures are often developed in the near-wellbore area of ​​tight reservoirs, different injection media have different seepage characteristics, and each medium plays a different role. Therefore, it is urgent to carry out physical simulation research on core flooding with multiple rounds of alternating injection of water-gas composite media.

[0003] The existing pressure-drive experimental methods are mainly based on single specific core displacement experiments, ignoring the differences between fluid seepage along fractures to matrix and matrix seepage to fractures (positive and negative pressure drive) during the throughput stage. At the same time, it is difficult to consider the impact of water-gas composite media under different storage and permeability modes on the pressure-simmering-production capacity of oil wells. In addition, during the soaking stage under real formation conditions, the soaking time will also have a significant impact on the oil-gas-water three-phase flow and pressure diffusion in the fracture-matrix coupled reservoir, thereby reducing the recovery factor. Summary of the invention

[0004] The purpose of the present invention is to provide a system and method for simulating multiple rounds of pressure-simmering injection and production oil recovery by alternating gas and water, so as to solve the problem that the pressure-drive experimental method in the prior art is mainly based on a single specific core displacement experiment, ignoring the differences in fluid seepage along the fracture to the matrix and matrix to the fracture during the throughput stage, and it is difficult to consider the influence of water-gas composite media under different storage and permeability modes on the pressure-simmering-production capacity of the oil well. In addition, in the well-simmering stage under real formation conditions, the well-simmering time will also have a great influence on the oil-gas-water three-phase flow and pressure diffusion in the fracture-matrix coupled reservoir, thereby reducing the recovery rate.

[0005] To achieve the above-mentioned purpose, the present invention provides a simulated gas-water alternating multiple rounds of pressure-stew injection-production oil recovery system, the simulated gas-water alternating multiple rounds of pressure-stew injection-production oil recovery system comprising a vacuum pump, a five-way valve, a constant temperature box, a first high-pressure displacement pump, a second high-pressure displacement pump, a sample preparation unit, an inlet pressure gauge, a fracture core clamping unit, an intermediate pressure gauge, a matrix core clamping unit, an outlet pressure gauge and a metering unit, the vacuum pump is arranged on one side of the sample preparation unit and is connected to the e-port of the five-way valve, the first high-pressure displacement pump is arranged below the sample preparation unit and is connected to the sample preparation unit through a first valve, the second high-pressure displacement pump is arranged above the sample preparation unit and is connected to the sample preparation unit through a second valve, the inlet pressure gauge is connected to the sample preparation unit, and the intermediate pressure gauge is connected to the matrix core clamping unit, and the outlet pressure gauge is connected to the sample preparation unit. The inlet pressure gauge is connected to the c port of the five-way valve, the fracture core clamping unit is arranged on the side of the inlet pressure gauge away from the five-way valve, the intermediate pressure gauge is arranged on the side of the fracture core clamping unit away from the inlet pressure gauge, the matrix core clamping unit is arranged on the side of the intermediate pressure gauge away from the fracture core clamping unit, the metering unit is arranged on the side of the matrix core clamping unit away from the intermediate pressure gauge through the three-way valve, the outlet pressure gauge is arranged on the three-way valve, the sample preparation unit, the inlet pressure gauge, the fracture core clamping unit, the intermediate pressure gauge, the matrix core clamping unit and the outlet pressure gauge are all located in the constant temperature box, and the metering unit is located outside the constant temperature box.

[0006] Wherein, the sampling unit includes a formation water sampler, a formation crude oil sampler and a carbon dioxide sampler, the formation water sampler, the formation crude oil sampler and the carbon dioxide sampler are respectively connected to the a port, b port and d port of the five-way valve, and are all located in the constant temperature box, the first high-pressure displacement pump is connected to the formation water sampler and the formation crude oil sampler through the first valve, and the second high-pressure displacement pump is connected to the carbon dioxide sampler through the second valve.

[0007] Wherein, the fracture core clamping unit includes a first core clamp and a first confining pressure pump, the inlet pressure gauge and the intermediate pressure gauge are respectively connected to both sides of the first core clamp, the first confining pressure pump is connected to the first core clamp, and the first core clamp and the first confining pressure pump are both located in the constant temperature box.

[0008] Wherein, the matrix core clamping unit includes a second core clamp and a second confining pressure pump, the intermediate pressure gauge and the outlet pressure gauge are respectively connected to both sides of the second core clamp, the second confining pressure pump is connected to the second core clamp, and the second core clamp and the second confining pressure pump are both located in the constant temperature box.

[0009] Wherein, the metering unit includes an oil-water separation device and a gas meter, one side of the oil-water separation device is connected to the second core clamp through the three-way valve, and the other side of the oil-water separation device is connected to the gas meter, the outlet pressure gauge is installed on the three-way valve, and the oil-water separation device and the gas meter are both located outside the constant temperature box.

[0010] The present invention also provides a simulated gas-water alternating multiple rounds of pressure-stem injection recovery method, which is applied to the simulated gas-water alternating multiple rounds of pressure-stem injection recovery system as described above, and comprises the following steps:

[0011] S1: Check the sealing performance of the simulated gas-water alternating multiple rounds of pressure-injection-production flooding system, select the fracture core A and the matrix core B, and record the length L of the core A 1 and permeability K 1 and the length L of core B 2 and permeability K 2 , put the washed core A and core B into a thermostatic box, bake at 105°C for 4 hours, reduce the temperature to the formation temperature of 75°C and continue to bake for 4 hours, then put the dried core A and core B into the fracture core clamping unit and the matrix core clamping unit respectively, the thermostatic box simulates the formation temperature of 75°C, and the confining pressure is set to 60MPa;

[0012] S2: The core saturated formation water is displaced with formation crude oil at a constant speed until only oil but no water comes out of the core holder outlet, and the positions of the fracture core clamping unit and the matrix core clamping unit are swapped, and the core saturated formation water is displaced with formation crude oil at a constant speed until only oil but no water comes out of the core holder outlet;

[0013] S3: Close the c port of the five-way valve, open the three-way valve, simulate the flow of matrix crude oil to the fracture end, until the pressure at the outlet end drops to 10MPa, close the three-way valve, record the oil production, water production and gas production respectively, and calculate the gas-oil ratio, water content and recovery degree of depletion development;

[0014] S4: The positions of the fracture core clamping unit and the matrix core clamping unit are swapped, and the second high-pressure displacement pump is set to push the carbon dioxide in the sample preparation unit at a constant speed until the outlet pressure reaches the carbon dioxide miscible pressure of 21 MPa, and the d port and c port of the five-way valve are closed to simulate the carbon dioxide soaking stage, and the reading P of the inlet pressure gauge is recorded. 1 and the outlet pressure gauge reading P 3 , the shut-in time of the gas injection miscible phase is determined by using the shut-in limit calculation model;

[0015] S5: Open the a port and c port of the five-way valve, and set the injection pressure of the first high-pressure displacement pump to the core fracture pressure Pf , push the injection water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30MPa, close the a port and c port of the five-way valve, simulate the water injection well soaking stage, and record the reading P of the inlet pressure gauge 1-1 and the outlet pressure gauge reading P 3-1 , the well shut-in time in the pressure drive water injection stage is determined using the well shut-in limit calculation model;

[0016] S6: swapping the positions of the fracture core clamping unit and the matrix core clamping unit, opening the three-way valve until the pressure at the outlet drops to 10 MPa, closing the three-way valve, recording the oil production, water production and gas production respectively, and calculating the gas-oil ratio, water content and recovery degree of the first cycle of gas-water alternating pressure-injection recovery;

[0017] S7: Repeat steps S4 to S6 to a preset number of times, and respectively calculate the gas-oil ratio, water content and recovery degree of multiple rounds of pressure-injection recovery.

[0018] Wherein, in step S1, the fractured core is prepared by gradually adjusting the axial pressure through a triaxial testing instrument until fractures are formed in the core.

[0019] Among them, in step S4 and step S5, the soaking stage is used to simulate the imbibition process of crude oil in the matrix, and in the soaking stage, the pressure propagates from the fracture to the matrix boundary. The soaking time is the seepage time of the injection end fluid along the fracture to reach the matrix boundary. The soaking limit calculation model is derived based on the Darcy formula:

[0020]

[0021] Among them, t is the limit time of soaking well, s; L 1 is the length of the fractured core, cm; L 2 is the length of the matrix core, cm; K m is the average matrix permeability, mD; μ is the fluid viscosity, mPa·s; △P is the pressure difference between the core inlet and outlet, MPa.

[0022] The present invention provides a simulated gas-water alternating multi-round pressure-stew injection-production oil displacement system and method, comprising a vacuum pump, a five-way valve, a thermostatic box, a first high-pressure displacement pump, a second high-pressure displacement pump, a sample preparation unit, an inlet pressure gauge, a fracture core clamping unit, an intermediate pressure gauge, a matrix core clamping unit, an outlet pressure gauge and a metering unit. Compared with a single-tube long core displacement device, the fracture core clamping unit and the matrix core clamping unit are connected in series to simulate the equivalent of a fracture network and a matrix reservoir. The fracture core clamping unit and the matrix core clamping unit are reversed to achieve rapid Saturated tight core shortens reservoir initialization time. During the experiment, there is no need to repeatedly disassemble and assemble the core holder, so the influence of fracture parameters such as fracture length and conductivity on oil displacement in the three stages of pressure-simmering-production can be considered. By changing the fracture morphology of the fracture core, the influence of water-gas composite media under different storage and permeability modes on the pressure-simmering-production capacity of the oil well can be studied, including multi-stage fracture-matrix reservoirs, large fracture-matrix reservoirs, micro-fracture-matrix reservoirs and original matrix reservoirs, which ensures the independence and integrity of fracture cores and matrix cores and greatly shortens the experimental time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a structural schematic diagram of the injection phase of a simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system provided by the present invention.

[0025] Figure 2 It is a structural schematic diagram of the production phase of the simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system provided by the present invention.

[0026] Figure 3 It is an equivalent schematic diagram of the fracture core-matrix core series simulation of the fracture-matrix coupled reservoir provided by the present invention.

[0027] Figure 4 This is a production flow chart of simulating multiple rounds of gas-water alternating pressure-steeping injection and oil recovery provided by the present invention.

[0028] Figure 5 It is a schematic diagram of the results of numerical simulation of single-cycle pressure-simmering injection-production oil recovery of a single well model provided by the present invention.

[0029] Figure 6 It is a curve diagram of daily oil production changing with time in a single round of pressure-stewing injection-production oil recovery process provided by the present invention.

[0030] Figure 7 It is a curve diagram of the change of water content over time in a single round of pressure-steeping injection and recovery oil recovery process provided by the present invention.

[0031] Figure 8 A curve diagram showing the variation of bottom hole flow pressure with time during a single round of pressure-injection recovery provided by the present invention.

[0032] 1-vacuum pump, 2-first high-pressure displacement pump, 3-second high-pressure displacement pump, 4-formation water sampler, 5-formation crude oil sampler, 6-carbon dioxide sampler, 7-constant temperature box, 8-fracture core clamping unit, 9-matrix core clamping unit, 10-first core clamp, 11-second core clamp, 12-first confining pressure pump, 13-second confining pressure pump, 14-oil-water separation device, 15-gas meter, 16-five-way valve, 17-three-way valve, 18-inlet pressure gauge, 19-intermediate pressure gauge, 20-outlet pressure gauge, 21-first valve, 22-second valve. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0034] See also Figure 1The present invention provides a simulated gas-water alternating multiple rounds of pressure-stew injection-production oil recovery system, the simulated gas-water alternating multiple rounds of pressure-stew injection-production oil recovery system comprises a vacuum pump 1, a five-way valve 16, a constant temperature box 7, a first high-pressure displacement pump 2, a second high-pressure displacement pump 3, a sample preparation unit, an inlet pressure gauge 18, a fracture core clamping unit 8, an intermediate pressure gauge 19, a matrix core clamping unit 9, an outlet pressure gauge 20 and a metering unit, the vacuum pump 1 is arranged on one side of the sample preparation unit and is connected to the e port of the five-way valve 16, the first high-pressure displacement pump 2 is arranged below the sample preparation unit and is connected to the sample preparation unit through a first valve 21, the second high-pressure displacement pump 3 is arranged above the sample preparation unit and is connected to the sample preparation unit through a second valve 22, the inlet pressure gauge 18 is connected to the inlet pressure gauge 18 and the metering unit. The fracture core clamping unit 8 is connected to the port of the five-way valve 16c, the fracture core clamping unit 8 is arranged on the side of the inlet pressure gauge 18 away from the five-way valve 16, the intermediate pressure gauge 19 is arranged on the side of the fracture core clamping unit 8 away from the inlet pressure gauge 18, the matrix core clamping unit 9 is arranged on the side of the intermediate pressure gauge 19 away from the fracture core clamping unit 8, the metering unit is arranged on the side of the matrix core clamping unit 9 away from the intermediate pressure gauge 19 through the three-way valve 17, the outlet pressure gauge 20 is arranged on the three-way valve 17, the sample preparation unit, the inlet pressure gauge 18, the fracture core clamping unit 8, the intermediate pressure gauge 19, the matrix core clamping unit 9 and the outlet pressure gauge 20 are all located in the constant temperature box 7, and the metering unit is located outside the constant temperature box 7.

[0035] In this embodiment, compared with the single-tube long core displacement device, the fracture core clamping unit 8 and the matrix core clamping unit 9 are connected in series to simulate the equivalent fracturing network and the matrix reservoir. The fracture core clamping unit 8 and the matrix core clamping unit 9 are reversed to achieve rapid saturation of the dense core, shortening the reservoir initialization time. During the experiment, there is no need to repeatedly disassemble and assemble the core clamp, so the influence of fracture parameters such as fracture length and conductivity on the three stages of oil displacement can be considered. By changing the fracture morphology by replacing the fracture core, the influence of water-gas composite media under different storage and permeability modes on the pressure-simmering-production capacity of the oil well can be studied, including multi-stage fracture-matrix reservoirs, large fracture-matrix reservoirs, micro-fracture-matrix reservoirs and original matrix reservoirs, ensuring the independence and integrity of the fracture core and the matrix core, and greatly shortening the experimental time.

[0036] Furthermore, the sampling unit includes a formation water sampler 4, a formation crude oil sampler 5 and a carbon dioxide sampler 6, the formation water sampler 4, the formation crude oil sampler 5 and the carbon dioxide sampler 6 are respectively connected to the a port, b port and d port of the five-way valve 16, and are all located in the constant temperature box 7, the first high-pressure displacement pump 2 is connected to the formation water sampler 4 and the formation crude oil sampler 5 through the first valve 21, and the second high-pressure displacement pump 3 is connected to the carbon dioxide sampler 6 through the second valve 22.

[0037] In this embodiment, formation water sampling is completed by setting the formation water sampler 4, formation crude oil sampling is completed by setting the formation crude oil sampler 5, and carbon dioxide sampling is completed by setting the carbon dioxide sampler 6.

[0038] Furthermore, the fracture core clamping unit 8 includes a first core clamp 10 and a first confining pressure pump 12, the inlet pressure gauge 18 and the intermediate pressure gauge 19 are respectively connected to the two sides of the first core clamp 10, the first confining pressure pump 12 is connected to the first core clamp 10, and the first core clamp 10 and the first confining pressure pump 12 are both located in the constant temperature box 7.

[0039] Furthermore, the matrix core clamping unit 9 includes a second core clamp 11 and a second confining pressure pump 14, the intermediate pressure gauge 19 and the outlet pressure gauge 20 are respectively connected to the two sides of the second core clamp 11, the second confining pressure pump 14 is connected to the second core clamp 11, and the second core clamp 11 and the second confining pressure pump 14 are both located in the constant temperature box 7.

[0040] Furthermore, the metering unit includes an oil-water separation device 14 and a gas meter 15, one side of the oil-water separation device 14 is connected to the second core clamp 11 through the three-way valve 17, and the other side of the oil-water separation device 14 is connected to the gas meter 15, the outlet pressure gauge 20 is installed on the three-way valve 17, and the oil-water separation device 14 and the gas meter 15 are both located outside the constant temperature box 7.

[0041] In this embodiment, by providing the oil-water separator 14 and the gas meter 15 , the oil production, water production and gas production can be recorded respectively.

[0042] See also Figures 1 to 4 The present invention also provides a simulated gas-water alternating multiple rounds of pressure-stewing injection-production oil recovery method, which is applied to the simulated gas-water alternating multiple rounds of pressure-stewing injection-production oil recovery system as described above, and comprises the following steps:

[0043] S1: Check the sealing performance of the simulated gas-water alternating multiple rounds of pressure-injection-production flooding system, select the fracture core A and the matrix core B, and record the length L of the core A 1 and permeability K 1 and the length L of core B 2 and permeability K 2 , put the cleaned core A and core B into a thermostat 7, bake at 105°C for 4 hours, lower the temperature to the formation temperature of 75°C and continue baking for 4 hours, then put the dried core A and core B into the fracture core clamping unit 8 and the matrix core clamping unit 9 respectively, the thermostat 7 simulates the formation temperature of 75°C, and the confining pressure is set to 60MPa;

[0044] S2: The core saturated formation water is displaced with formation crude oil at a constant rate until only oil but no water comes out of the core clamp outlet, and the positions of the fracture core clamp unit 8 and the matrix core clamp unit 9 are swapped ( Figure 2 ), displacing the core with formation crude oil at a constant rate until only oil but no water comes out of the core holder outlet;

[0045] S3: Close the port c of the five-way valve 16, open the three-way valve 17, simulate the flow of matrix crude oil to the fracture end, until the pressure at the outlet end drops to 10 MPa, close the three-way valve 17, record the oil production, water production and gas production respectively, and calculate the gas-oil ratio, water content and recovery degree of depletion development;

[0046] S4: Swap the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 ( Figure 1 ), set the second high-pressure displacement pump 3 to push the carbon dioxide in the sample preparation unit at a constant speed until the outlet pressure reaches the carbon dioxide mixed phase pressure of 21 MPa, close the d port and c port of the five-way valve 16, simulate the carbon dioxide soaking stage, and record the reading P of the inlet pressure gauge 18 1 and the indication P of the outlet pressure gauge 20 3 , the shut-in time of the gas injection miscible phase is determined by using the shut-in limit calculation model;

[0047] S5: Open the port a and the port c of the five-way valve 16, and set the injection pressure of the first high-pressure displacement pump 2 to the core fracture pressure P f , push the injection water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30MPa, close the port a and port c of the five-way valve 16, simulate the injection water soaking stage, and record the reading P of the inlet pressure gauge 18 1-1 and the indication P of the outlet pressure gauge 20 3-1 , the well shut-in time in the pressure drive water injection stage is determined using the well shut-in limit calculation model;

[0048] S6: Swap the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 ( Figure 2 ), open the three-way valve 17 until the outlet pressure drops to 10MPa, close the three-way valve 17, record the oil production, water production and gas production respectively, and calculate the gas-oil ratio, water content and recovery degree of the first cycle of gas-water alternation pressure-injection recovery;

[0049] S7: Repeat steps S4 to S6 to a preset number of times, and respectively calculate the gas-oil ratio, water content and recovery degree of multiple rounds of pressure-injection recovery.

[0050] In this embodiment, compared with the single-tube long core displacement device, the fracture network and matrix reservoir are simulated equivalently by connecting the fracture unit and the matrix unit in series, and the device is reversed to achieve rapid saturation of the tight core, shortening the reservoir initialization time. During the experiment, there is no need to repeatedly disassemble and assemble the core clamp, and the influence of fracture parameters such as fracture length and conductivity on the three stages of oil displacement of pressure-simmering-production can be considered, ensuring the independence and integrity of the fracture core and the matrix core, greatly shortening the experimental time, and for the multi-scale fractures formed after the tight oil reservoir is fracturing, the experimental device is based on the core fracture pretreatment, and the fracture morphology is changed by replacing the fracture unit fracture core, which can study the influence of different injection media under different storage and permeability modes on the pressure-simmering-production capacity of oil wells, including multi-stage fracture-matrix reservoirs, large fracture-matrix reservoirs, micro-fracture-matrix reservoirs and original matrix reservoirs. Based on this, the experimental device can also determine the gas-water and oil-water relative permeabilities of the core under different storage and permeability modes, clarify the relationship between the two-phase flow range of the fracture-matrix coupled reservoir and the fracture parameters, and at the same time, after the water-gas alternating pressure-steeping injection-production oil recovery experiment is completed, by loading and unloading the series-connected fracture units and matrix units, the permeabilities of the fractured cores and matrix cores are measured in turn, and the changes in the core permeabilities before and after pressure-steeping injection-production are compared. The influence of multiple rounds of carbonized water injection and production on the permeability of the core can be analyzed, and the mechanism of carbonized water dissolution and mineral pore throat blockage before and after injection and production can be preliminarily clarified.

[0051] Among them, in step S1, the sealing performance of the simulated gas-water alternating multiple rounds of pressure-stew injection-production oil recovery system is checked, and the pressure of the device is kept constant at 30MPa. If the system pressure change is less than 0.5% within 12 hours, it means that the sealing performance of the device is good. The constant pressure for checking the sealing performance of the device is the original formation pressure of the reservoir. The fractured core is gradually adjusted by the triaxial test instrument until the core has cracks, and the fracture pressure of the core at this time is recorded as P f After washing and drying the core, the core is placed in the fracture core clamping unit 8 and the matrix core clamping unit 9 respectively, and the equivalent fracture network-original matrix coupling reservoir is connected in series. The equivalent schematic diagram is shown in Figure 3The simulated temperature of the thermostatic box 7 is the original formation temperature of the reservoir, and the device confining pressure in step S1 is greater than the core fracture pressure.

[0052] In step S2, core A and core B are saturated with formation water and then displaced with formation crude oil at a constant rate of 0.1 mL / min until only oil but no water comes out of the outlet of the matrix core clamping unit 9, and the positions of the fracture unit and the matrix unit are swapped ( Figure 2 ), displace the fracture core with formation crude oil at a constant rate of 0.1 mL / min until only oil but no water comes out of the outlet of the fracture core clamping unit 8, and record the core saturated crude oil volume V.

[0053] Among them, in step S3, the c port of the five-way valve 16 is closed, and the three-way valve 17 is opened until the outlet pressure drops to 10MPa, and the three-way valve 17 is closed, and the oil production V is recorded respectively. o , water production V w And the gas production V g , calculate the recovery degree R in the depletion stage w , calculation model of recovery degree in depletion stage:

[0054]

[0055] In the formula, R w V is the moisture content in the exhaustion stage, in %; o is the oil production in the depletion stage, in mL; V is the saturated crude oil volume in the core rapid saturation stage, in mL.

[0056] Wherein, in step S4, the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 are swapped ( Figure 1 ), set the second high-pressure displacement pump 3 to pump the carbon dioxide in the sample preparation unit at a constant speed of 0.3 mL / min until the outlet pressure reaches the carbon dioxide mixed phase pressure of 21 MPa, close the d port and c port of the five-way valve 16, simulate the carbon dioxide well soaking stage, and record the reading P of the inlet pressure gauge 18 1 and the indication P of the outlet pressure gauge 20 3 The shut-in time in the gas injection miscible phase is determined using the shut-in limit calculation model.

[0057] The simulated production process is shown in Figure 4 (a) and Figure 4(b) The injected gas diffuses rapidly along the direction of the volumetric fracture, displacing the crude oil around the well, but the affected area is limited, and the injected gas only exists around the fracture. After the well is shut in, the carbon dioxide dissolves in the crude oil, giving full play to the role of expanding the volume of the crude oil and reducing its viscosity. As the mass transfer capacity of the oil and gas components is enhanced and the fluidity of the crude oil increases, the affected area of ​​the injected gas-crude oil composite system in the shut-in stage is larger than that in the gas injection mixed phase stage.

[0058] The well-sucking limit is calculated as follows:

[0059]

[0060] Where, t is the limit time of gas injection miscible phase well blocking, s; L 1 is the length of the fractured core, cm; L 2 is the length of the matrix core, cm; K m is the average permeability of the matrix, mD; μ 1 For CO 2 Viscosity, mPa·s; P 1 is the inlet pressure, MPa; P 3 is the outlet pressure, MPa.

[0061] Specifically, the soaking stage is used to simulate the imbibition process of crude oil in the matrix. If the soaking time is too long, the injection pressure will diffuse, increase the use cost of the injection medium, and affect the throughput effect; while if the soaking time is too short, it will affect the mass transfer of oil and gas components and the effect of carbonized water throughput, and reduce the crude oil recovery rate. In the soaking stage, the crude oil imbibition rate tends to be flat as the soaking time increases, and the oil-water imbibition replacement in the matrix reaches a relatively stable state. At this time, the soaking effect is the best, which is the ideal soaking time. The best oil production can be obtained by opening the well for production. Therefore, it is particularly important to determine the soaking limit time during the experiment. In addition, since gas has better fluidity than water, carbon dioxide is injected in the early stage of pressure-driven water injection to achieve miscible drive, and the gas can reach the matrix pores along the cracks. In addition, in the soaking stage, CO 2 The effects of gas injection, solubilization and expansion, and extraction of crude oil can effectively capture the remaining oil in the small pores of the matrix.

[0062] In step S5, the a port and c port of the five-way valve 16 are opened, and the injection pressure of the first high-pressure displacement pump 2 is set to the core fracture pressure P f , push the injection water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30MPa, close the port a and port c of the five-way valve 16, simulate the injection water soaking stage, and record the reading P of the inlet pressure gauge 18 1-1 and the indication P of the outlet pressure gauge 20 3-1 , the shut-in time in the pressure-driven water injection stage is determined using the shut-in limit calculation model.

[0063] The simulated production process is shown in Figure 4 (c) and Figure 4 (d) Water is injected under rock fracture pressure, and intricate micro-cracks are formed around the original main fractures around the well. The pressure difference formed by pressure-driven water injection causes the injected gas-crude oil composite system to further diffuse, and the affected range is significantly increased; in the well-sealing stage, the oil-gas-water three-phase mass transfer occurs, and the formation energy is effectively supplemented. In addition, the undissolved carbon dioxide forms carbonated water with the injected water, which increases the porosity and permeability of the seepage channel, which is beneficial to the migration of reservoir fluids.

[0064] The soaking limit is calculated as follows:

[0065]

[0066] Where, t is the limit time of well soaking for pressure-driven water injection, s; L 1 is the length of the fractured core, cm; L 2 is the length of the matrix core, cm; K m is the average permeability of the matrix, mD; μ 2 is the viscosity of injected water, mPa·s; P 1-1 is the inlet pressure, MPa; P 3-1 is the outlet pressure, MPa.

[0067] Specifically, pressure-driven water injection injects a large amount of water in a short period of time at a high injection pressure to further increase the formation pore pressure to drive the front CO 2 The gas continues to flow deep into the matrix, and at the same time forms a large number of micro-cracks near the wellbore, increasing the permeability around the injection well. As the soaking time increases, the injection-production pressure difference between the inlet pressure and the outlet pressure gradually decreases, and CO 2 After contacting with water, carbonated water is gradually formed. The density of carbonated water increases and the mobility ratio with crude oil decreases, which is beneficial to improve the rapid fingering phenomenon of single gas injection medium. 2 -Under water-rock interaction, the oil-water interfacial tension decreases, the amount of crude oil attached to the rock surface decreases, and at the same time, calcium carbonate is dissolved to increase the permeability of fractures and matrix.

[0068] Among them, in step S6, the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 are swapped, the three-way valve 17 is opened until the outlet pressure drops to 10 MPa, the three-way valve 17 is closed, and the oil production V o1 , water production V w1 And the gas production V g1 , calculate the gas-oil ratio GOR of the first cycle of water-gas alternation pressure-simmering injection and production oil recovery stage 1 , moisture content f w1 , recovery degree R w1 .

[0069] The simulated production process is shown in Figure 4 (e) After the four steps of gas injection-well shut-in-pressure water injection-well shut-in, the reservoir formation has sufficient energy. After the well is opened, the carbonated water preferentially swallows and exhales the crude oil in the fractures around the well and the large pores of the reservoir. Under the action of the injection-production pressure difference, the carbon dioxide flows from the deep reservoir along the high permeability channel to the wellbore in a directional manner, and continues to push the remaining carbonated water in the reservoir to accelerate the efficiency of oil washing around the well. At the same time, the carbon dioxide will displace the remaining oil in the micro-fractures and small pores, giving full play to the oil recovery potential of the water-gas composite medium.

[0070] Calculation model of gas-oil ratio in the pressure-simmering injection-production flooding stage:

[0071]

[0072] In the formula, GOR 1 The gas-oil ratio in the flooding stage, unit: m 3 / m 3 ; V o1 V is the oil production in the flooding stage, in mL; w1 is the water production in the flooding stage, in mL; the gas production V g1 It is the gas production in the flooding stage, unit is mL.

[0073] Furthermore, the water content calculation model of the pressure-simmering injection-production oil recovery stage is:

[0074]

[0075] In the formula, f w1 V is the water content in the flooding stage, unit: %; o1 V is the oil production in the flooding stage, in mL; w1 It is the water production in the flooding stage, unit is mL.

[0076] Furthermore, the calculation model of the recovery degree in the pressure-simmering injection-production flooding stage is:

[0077]

[0078] In the formula, R w1 V is the water content in the flooding stage, unit: %; o1 is the oil production in the flooding stage, in mL; V is the saturated crude oil volume in the core rapid saturation stage, in mL.

[0079] Specifically, in step S6, as the number of cyclic injection and production rounds increases, the water cut gradually increases, and the water cut increase rate shows a trend of slow increase in water cut in the early stage - accelerated increase in water cut in the middle stage - slow increase in water cut in the later stage. In the low water cut or high water cut stage (water cut is lower than 30% or higher than 90%), the water cut in the reservoir increases slowly, and the water cut increase rate is lower than 2%; in the medium-high water cut stage (water cut is between 30% and 90%), the water cut in the reservoir increases rapidly, and the water cut increase rate is about 5%.

[0080] See also Figures 5 to 8 The present invention also provides a numerical simulation of water-gas alternating pressure injection and production oil displacement in a simulated fracture-matrix coupling reservoir:

[0081] Considering that the isolated wells of the three types of reservoirs have no injection-production system or the injection-production relationship is imperfect, the numerical simulation takes a single well model with a single round of pressure-simmering injection-production as an example, and sets the model size to 50×50×5, the plane grid is 10m×10m, and the vertical grid is 0.5m. The reservoir permeability is 0.1mD, the porosity is 9%, the main fracture permeability is 3000mD, and when the formation pressure reaches the fracture pressure, several micro-fractures are randomly generated around the well and the micro-fracture permeability is 300mD. Two sets of phase permeability curves are used for fractures and matrix in the model.

[0082] The model scheme sets the gas injection volume of the injection well at the mixed phase stage to 3000m 3 / d, the bottom hole pressure is 60MPa (formation fracture pressure 58MPa), the gas injection time is 60 days, and after 3 days of shut-in, it is switched to pressure drive water injection, and the water injection volume of the injection well is 10m 3 / d, water injection time is 30 days, well is shut down for 2 days and then well is opened for production for 90 days, oil production of production well is 8m 3 / d, and the minimum bottom hole pressure is 10MPa.

[0083] Specifically, the numerical simulation of single-well model single-cycle water-gas alternating pressure injection and production oil recovery can be divided into the following aspects:

[0084] S101 gas injection mixed phase stage: the bottom flow pressure of the injection well gradually increases with the increase of carbon dioxide injection volume. When the reservoir pressure reaches the fracture pressure of 58MPa, several microcracks are randomly generated around the well. Figure 8 It can be seen from the pressure change in the gas injection mixed phase area that when the pressure reaches the limiting flow pressure, the bottom hole flow pressure remains unchanged at 60MPa. Figure 5 a It can be seen that the reservoir pressure around the well increases from the original formation pressure of 30MPa to 40MPa.

[0085] S102 Well shut-in stage: After the gas injection is completed, the well is shut down, and the oil and gas system undergoes a violent physical and chemical reaction, causing the volume of crude oil to expand. Figure 5 b shows that the pressure around the well expands outward in a small range, and the pressure field is more uniform. Figure 8It can be seen from the pressure change in the wellbore area after gas injection that after the wellbore is completed, the bottom hole flowing pressure drops from 60MPa to 58MPa due to pressure diffusion.

[0086] S103 pressure-driven water injection stage: After the well is shut down, the injection well is converted into a water injection well. As the pressure-driven water injection volume increases, carbon dioxide is forced to flow into the deep reservoir and small pores in the matrix. Figure 5 The pressure field of c and Figure 8 It can be seen from the pressure curve of pressure-driven water injection that the pressure loss caused by well soaking was recovered in a short time, the reservoir pressure was stabilized at 60MPa for a long time, and the formation energy was further replenished.

[0087] S104 Well shut-in stage: After the pressure drive water injection is completed, the well is shut down. Figure 5 It can be seen from the pressure field of d that the reservoir pressure around the well remains basically unchanged, and the bottom flow pressure of the injection well decreases by about 1MPa. Figure 8 The pressure change in the wellbore area after pressure-driven water injection shows that the pressure diffusion effect of wellbore in pressure-driven water injection is weaker than that in gas injection. This is because carbon dioxide has better fluidity than water, and carbonated water has greater seepage resistance in tight reservoirs. Therefore, the reservoir pressure loss is small during the wellbore stage.

[0088] S105 Pressure injection and production flooding stage: At the beginning of well production, the water content reaches 90% ( Figure 7 ), the daily oil production was stable for 0.9 days and then from 8m 3 / d drops rapidly to 0.3m 3 / d( Figure 6 ), the reservoir pressure dropped from 58.9MPa to 12.5MPa ( Figure 8 ), this process is mainly based on carbonation water drive; as the pressure difference between the bottom hole and the reservoir increases, carbon dioxide carries the crude oil to the bottom hole quickly, and the bottom hole flow pressure of the injection well increases by about 4MPa and maintains for a long time ( Figure 8 ), the water content of the oil well quickly dropped to 5% ( Figure 7 ), daily oil production is stable at 8m 3 / d( Figure 6 ).from Figure 5 From the pressure field, it can be seen that after 30 days of production, the bottom hole pressure remains at around 12MPa, indicating that carbon dioxide huff and puff effectively maintains the formation pressure. Figure 5 It can be seen from the pressure field that after 90 days of production, the bottom hole pressure dropped from 60MPa to 10MPa, and the pressure around the well dropped from 48MPa to 22MPa. The water-gas composite medium pressure injection and recovery oil recovery technology effectively supplements the formation energy, expands the oil sweeping area, and improves the oil washing efficiency.

[0089] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A simulated gas-water alternating multi-round pressure-steeping injection-production oil recovery system, characterized in that: The invention comprises a vacuum pump, a five-way valve, a thermostatic box, a first high-pressure displacement pump, a second high-pressure displacement pump, a sample preparation unit, an inlet pressure gauge, a fracture core clamping unit, an intermediate pressure gauge, a matrix core clamping unit, an outlet pressure gauge and a metering unit, wherein the vacuum pump is arranged at one side of the sample preparation unit and connected to the e port of the five-way valve, the first high-pressure displacement pump is arranged below the sample preparation unit and connected to the sample preparation unit through a first valve, the second high-pressure displacement pump is arranged above the sample preparation unit and connected to the sample preparation unit through a second valve, the inlet pressure gauge is connected to the inlet pressure gauge and the c port of the five-way valve, the fracture core clamping unit The inlet pressure gauge is arranged on a side away from the five-way valve, the intermediate pressure gauge is arranged on a side away from the inlet pressure gauge of the fracture core clamping unit, the matrix core clamping unit is arranged on a side away from the intermediate pressure gauge of the fracture core clamping unit, the metering unit is arranged on a side away from the intermediate pressure gauge of the fracture core clamping unit through a three-way valve, the outlet pressure gauge is arranged on the three-way valve, the sample preparation unit, the inlet pressure gauge, the fracture core clamping unit, the intermediate pressure gauge, the matrix core clamping unit and the outlet pressure gauge are all located in the constant temperature box, and the metering unit is located outside the constant temperature box.

2. The simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system as claimed in claim 1, characterized in that: The sampling unit includes a formation water sampler, a formation crude oil sampler and a carbon dioxide sampler. The formation water sampler, the formation crude oil sampler and the carbon dioxide sampler are respectively connected to the a port, the b port and the d port of the five-way valve, and are all located in the constant temperature box. The first high-pressure displacement pump is connected to the formation water sampler and the formation crude oil sampler through the first valve, and the second high-pressure displacement pump is connected to the carbon dioxide sampler through the second valve.

3. The simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system as claimed in claim 2, characterized in that: The fracture core clamping unit includes a first core clamp and a first confining pressure pump, the inlet pressure gauge and the intermediate pressure gauge are respectively connected to both sides of the first core clamp, the first confining pressure pump is connected to the first core clamp, and the first core clamp and the first confining pressure pump are both located in the constant temperature box.

4. The simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system as claimed in claim 3, characterized in that: The matrix core clamping unit includes a second core clamp and a second confining pressure pump, the intermediate pressure gauge and the outlet pressure gauge are respectively connected to both sides of the second core clamp, the second confining pressure pump is connected to the second core clamp, and the second core clamp and the second confining pressure pump are both located in the constant temperature box.

5. The simulated gas-water alternating multiple rounds of pressure-steeping injection-production oil recovery system as claimed in claim 4, characterized in that: The metering unit includes an oil-water separation device and a gas meter. One side of the oil-water separation device is connected to the second core clamp through the three-way valve, and the other side of the oil-water separation device is connected to the gas meter. The outlet pressure gauge is installed on the three-way valve. The oil-water separation device and the gas meter are both located outside the constant temperature box.

6. A simulated gas-water alternating multiple rounds of pressure-stew injection recovery method, applied to the simulated gas-water alternating multiple rounds of pressure-stew injection recovery system as claimed in claim 1, characterized in that: The steps include: S1: Check the sealing of the simulated gas-water alternating multiple rounds of pressure-injection-production flooding system, select the fracture core A and the matrix core B, record the length L1 and permeability K1 of the core A and the length L2 and permeability K2 of the core B, put the cleaned core A and core B into a constant temperature box, bake at 105°C for 4 hours, reduce the temperature to the formation temperature of 75°C and continue to bake for 4 hours, then put the dried core A and core B into the fracture core clamping unit and the matrix core clamping unit respectively, the constant temperature box simulates the formation temperature of 75°C, and the confining pressure is set to 60MPa; S2: The core saturated formation water is displaced with formation crude oil at a constant speed until only oil but no water comes out of the core holder outlet, and the positions of the fracture core clamping unit and the matrix core clamping unit are swapped, and the core saturated formation water is displaced with formation crude oil at a constant speed until only oil but no water comes out of the core holder outlet; S3: Close the c port of the five-way valve, open the three-way valve, simulate the flow of matrix crude oil to the fracture end, until the pressure at the outlet end drops to 10MPa, close the three-way valve, record the oil production, water production and gas production respectively, and calculate the gas-oil ratio, water content and recovery degree of depletion development; S4: swapping the positions of the fracture core clamping unit and the matrix core clamping unit, setting the second high-pressure displacement pump to push the carbon dioxide in the sample preparation unit at a constant speed until the outlet pressure reaches the carbon dioxide miscible pressure of 21 MPa, closing the d port and the c port of the five-way valve, simulating the carbon dioxide soaking stage, recording the reading P1 of the inlet pressure gauge and the reading P3 of the outlet pressure gauge, and determining the soaking time of the gas injection miscible stage using the soaking limit calculation model; S5: Open the a port and c port of the five-way valve, and set the injection pressure of the first high-pressure displacement pump to the core fracture pressure P f , push the injection water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30MPa, close the a port and c port of the five-way valve, simulate the water injection well soaking stage, and record the reading P of the inlet pressure gauge 1-1 and the outlet pressure gauge reading P 3-1 , the well shut-in time in the pressure drive water injection stage is determined using the well shut-in limit calculation model; S6: swapping the positions of the fracture core clamping unit and the matrix core clamping unit, opening the three-way valve until the pressure at the outlet drops to 10 MPa, closing the three-way valve, recording the oil production, water production and gas production respectively, and calculating the gas-oil ratio, water content and recovery degree of the first cycle of gas-water alternating pressure-injection recovery; S7: Repeat steps S4 to S6 to a preset number of times, and calculate the gas-oil ratio, water content and recovery degree of multiple rounds of pressure-injection recovery.

7. The method for simulating multiple rounds of gas-water alternating pressure-simmering injection and recovery according to claim 6, characterized in that: In step S1, the fractured core is fractured by gradually adjusting the axial pressure through a triaxial testing instrument until fractures are generated in the core.

8. The method for simulating multiple rounds of gas-water alternating pressure-simmering injection and recovery according to claim 7, characterized in that: In step S4 and step S5, the soaking stage is used to simulate the imbibition process of crude oil in the matrix, and in the soaking stage, the pressure propagates from the fracture to the matrix boundary. The soaking time is the seepage time of the injection end fluid along the fracture to reach the matrix boundary. The soaking limit calculation model is derived based on the Darcy formula: Where, t is the soaking limit time, s; L1 is the length of the fracture core, cm; L2 is the length of the matrix core, cm; K m is the average matrix permeability, mD; μ is the fluid viscosity, mPa·s; △P is the pressure difference between the core inlet and outlet, MPa.

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