Analog gas-water alternating multi-cycle pressure-braising injection and flooding system and method

Abstract

The present invention relates to the technical field of unconventional oil and gas development, and specifically to a system and method for simulating multiple rounds of gas-water alternating pressure-stealing injection-production recovery. This scheme equivalently simulates a fracturing network and a matrix reservoir, and reasonably considers the pressure-stealing injection-production during the well-stealing time, resulting in more accurate results. The fracture core clamping unit and the matrix core clamping unit are swapped in the forward and reverse directions to achieve rapid saturation of the dense core, shortening the reservoir initialization time. The core clamping unit does not need to be repeatedly disassembled and assembled, so the effects of multiple fracture parameters on the three-stage pressure-stealing recovery recovery can be considered. By changing the fracture morphology through replacing the fractured core, the influence of water-gas composite media under different storage and permeability modes on the pressure-stealing recovery capacity of the oil well can be studied. The different storage and permeability modes include multi-stage fracture-matrix reservoirs, large fracture-matrix reservoirs, micro-fracture-matrix reservoirs, and original matrix reservoirs. This ensures the independence and integrity of the fracture core and the matrix core, greatly shortening the experimental time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of unconventional oil and gas development, and particularly relates to a simulation gas-water alternating multi-cycle pressure-steaming injection-production system and method. BACKGROUND

[0002] The isolated well point of the three types of reservoirs has no injection-production system or imperfect injection-production relationship, and has problems of difficult formation energy supply, difficult well pattern deployment, and high production cost. Due to the limitation of gas source and gas channeling, it is less feasible to carry out large-scale gas injection huff and puff, and the oil displacement efficiency of conventional water injection is low, and the swept range of the pressure drive water injection process is limited. Therefore, the feasibility of gas-water alternating multi-cycle pressure-steaming injection-production is discussed. Considering that the near-wellbore zone of the tight reservoir often develops multi-scale fractures, different injection media have different seepage characteristics, and each medium plays a different role, therefore, it is urgent to carry out core displacement physical simulation research on multi-cycle alternating injection of water-gas composite medium.

[0003] The existing pressure drive experiment method mainly takes single specific core displacement experiment as the main, ignores the difference of fluid seepage along the fracture to the matrix and matrix to the fracture in the huff and puff stage (forward and reverse pressure drive), and it is difficult to consider the influence of water-gas composite medium under different storage and seepage modes on the pressure-steaming-production capacity of the oil well, in addition, in the steaming well stage under the real formation condition, the steaming well time will also have a great influence on the oil-gas-water three-phase flow and pressure diffusion in the fracture-matrix coupled reservoir, therefore, the recovery efficiency will be reduced. SUMMARY

[0004] The present application aims to provide a simulation gas-water alternating multi-cycle pressure-steaming injection-production system and method, which solves the problem that the existing pressure drive experiment method mainly takes single specific core displacement experiment as the main, ignores the difference of fluid seepage along the fracture to the matrix and matrix to the fracture in the huff and puff stage (forward and reverse pressure drive), and it is difficult to consider the influence of water-gas composite medium under different storage and seepage modes on the pressure-steaming-production capacity of the oil well, in addition, in the steaming well stage under the real formation condition, the steaming well time will also have a great influence on the oil-gas-water three-phase flow and pressure diffusion in the fracture-matrix coupled reservoir, therefore, the recovery efficiency will be reduced.

[0005] In order to achieve the above object, the application provides a simulated gas-water alternating multi-cycle pressure-braising injection and oil displacement system, which comprises 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 connected with the e port of the five-way valve, the first high-pressure displacement pump is arranged below the sample preparation unit and connected with the sample preparation unit through a first valve, the second high-pressure displacement pump is arranged above the sample preparation unit and connected with the sample preparation unit through a second valve, the inlet pressure gauge is connected with 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 a three-way valve, the three-way valve is provided with the outlet pressure gauge, 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] The sample preparation unit comprises a formation water sample preparation device, a formation crude oil sample preparation device and a carbon dioxide sample preparation device, the formation water sample preparation device, the formation crude oil sample preparation device and the carbon dioxide sample preparation device are respectively connected with the a port, the b port and the d port of the five-way valve and all located in the constant temperature box, the first high-pressure displacement pump is connected with the formation water sample preparation device and the formation crude oil sample preparation device through the first valve, and the second high-pressure displacement pump is connected with the carbon dioxide sample preparation device through the second valve.

[0007] The fracture core clamping unit comprises a first core holder and a first confining pressure pump, the inlet pressure gauge and the intermediate pressure gauge are respectively connected on the two sides of the first core holder, the first confining pressure pump is connected with the first core holder, and the first core holder and the first confining pressure pump are both located in the constant temperature box.

[0008] The matrix core clamping unit comprises a second core holder and a second confining pressure pump, the intermediate pressure gauge and the outlet pressure gauge are respectively connected on the two sides of the second core holder, the second confining pressure pump is connected with the second core holder, and the second core holder and the second confining pressure pump are both located in the constant temperature box.

[0009] The metering unit comprises an oil-water separation device and a gas meter, one side of the oil-water separation device is connected with the second core holder through the three-way valve, the other side of the oil-water separation device is connected with 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 located outside the thermostat.

[0010] The application also provides a simulation gas-water alternating multi-round pressure-brewing injection production oil method, which is applied to the simulation gas-water alternating multi-round pressure-brewing injection production oil system and comprises the following steps.

[0011] S1: checking the sealing property of the simulation gas-water alternating multi-round pressure-brewing injection production oil system, selecting a fracture core A and a matrix core B, recording the length L1 and the permeability K1 of the core A and the length L2 and the permeability K2 of the core B, placing the washed core A and the core B into a thermostat, baking at 105 DEG C for 4 hours, reducing the temperature to 75 DEG C, and continuing to bake for 4 hours, then placing the baked core A and the core B into the fracture core clamping unit and the matrix core clamping unit respectively, and setting the thermostat to simulate the formation temperature of 75 DEG C and the confining pressure of 60 MPa.

[0012] S2: saturating the core with formation water at a constant speed until only oil is discharged at the outlet end of the core holder, adjusting the positions of the fracture core clamping unit and the matrix core clamping unit, and displacing the core with formation oil at a constant speed until only oil is discharged at the outlet end of the core holder.

[0013] S3: closing the c port of the five-way valve and opening the three-way valve, simulating the flow of matrix oil to the fracture end until the outlet end pressure is reduced to 10 MPa, closing the three-way valve, and recording the oil production, water production and gas production respectively, and calculating the gas-oil ratio, water cut and recovery degree of the depletion development.

[0014] S4: adjusting 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 is 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 brewing stage, recording the readings P1 of the inlet pressure gauge and the readings P3 of the outlet pressure gauge, and determining the brewing time of the gas injection miscible phase by using the brewing limit calculation model.

[0015] S5: opening the a port and the c port of the five-way valve, setting the first high-pressure displacement pump to inject the core rupture pressure P fPush the formation water in the sample unit at a set speed until the outlet pressure is the original formation pressure 30 MPa, close the a port and the c port of the five-way valve, simulate the huff and puff stage of the formation water, and record the reading P of the inlet pressure gauge 1-1 and the reading P of the outlet pressure gauge 3-1 Determine the huff and puff time of the water injection stage by using a huff and puff limit calculation model.

[0016] S6: Switch the positions of the fracture core clamping unit and the matrix core clamping unit, open the three-way valve until the outlet end pressure drops to 10 MPa, close the three-way valve, and record the oil production, water production, and gas production, respectively, and calculate the gas-oil ratio, water cut, and recovery efficiency of the gas-water alternating first cycle pressure-huff and soak injection and production.

[0017] S7: Repeat steps S4-S6 to a preset number of times, and calculate the gas-oil ratio, water cut, and recovery efficiency of the multiple cycles of pressure-huff and soak injection and production.

[0018] In step S1, the fracture core is obtained by gradually adjusting the axial pressure of the triaxial tester until the core produces a fracture.

[0019] In steps S4 and S5, the huff and puff stage is used to simulate the imbibition process of crude oil in the matrix, and in the huff and puff stage, the pressure propagates from the fracture to the matrix boundary, the huff and puff time is the seepage time of the injected fluid along the fracture to the matrix boundary, and a huff and puff limit calculation model is derived based on Darcy's formula:

[0020]

[0021] where t is the huff and puff 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 permeability of the matrix, mD; is the fluid viscosity, mPa·s; and ΔP is the pressure difference between the inlet and outlet of the core, MPa.

[0022] The simulation gas-water alternating multi-round pressure-steaming injection production oil displacement system and method of the present application comprises 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 distribution 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. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is the structure diagram of the injection stage of the simulation gas-water alternating multi-round pressure-steaming injection production oil displacement system provided by the present application.

[0025] Figure 2 is the structure diagram of the production stage of the simulation gas-water alternating multi-round pressure-steaming injection production oil displacement system provided by the present application.

[0026] Figure 3 is the equivalent schematic diagram of the fracture-matrix coupled reservoir simulated by the fracture core-matrix core series connection provided by the present application.

[0027] Figure 4 is the production flow chart of the simulation gas-water alternating multi-round pressure-steaming injection production oil displacement provided by the present application.

[0028] Figure 5 is the result schematic diagram of the single well model single-round pressure-steaming injection production oil displacement numerical simulation provided by the present application.

[0029] Figure 6 is the curve diagram of the daily oil production in the single-round pressure-steaming injection production oil displacement process provided by the present application.

[0030] Figure 7 is a graph of water cut versus time in a single round of the pressure-simmer injection oil recovery process provided by the present invention.

[0031] Figure 8 is a graph of bottom hole flowing pressure versus time in a single round of the pressure-simmer injection oil recovery process provided by the present invention.

[0032] 1 - vacuum pump, 2 - first high pressure displacement pump, 3 - second high pressure displacement pump, 4 - formation water proportioner, 5 - formation crude oil proportioner, 6 - carbon dioxide proportioner, 7 - thermostat, 8 - fracture core holder unit, 9 - matrix core holder unit, 10 - first core holder, 11 - second core holder, 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 like reference numerals used throughout refer to the same or like elements or elements having the same or similar function. The embodiments described below by reference to the drawings are exemplary and are intended to be illustrative of the present invention, and are not to be construed as limiting the present invention.

[0034] Referring to Figure 1The application provides a simulated gas-water alternating multi-cycle pressure-steaming injection and oil displacement system, which comprises a vacuum pump 1, a five-way valve 16, a thermostat 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 with an 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 with 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 with the sample preparation unit through a second valve 22, the inlet pressure gauge 18 is connected with a c port of the five-way valve 16, the fracture core clamping unit 8 is arranged on one side of the inlet pressure gauge 18 away from the five-way valve 16, the intermediate pressure gauge 19 is arranged on one side of the fracture core clamping unit 8 away from the inlet pressure gauge 18, the matrix core clamping unit 9 is arranged on one side of the intermediate pressure gauge 19 away from the fracture core clamping unit 8, the metering unit is arranged on one side of the matrix core clamping unit 9 away from the intermediate pressure gauge 19 through a three-way valve 17, the three-way valve 17 is provided with the outlet pressure gauge 20, and 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 located in the thermostat 7.

[0035] In the embodiment, compared with a single pipe long core displacement device, by connecting the fracture core clamping unit 8 and the matrix core clamping unit 9 in series, the fracture core clamping unit 8 and the matrix core clamping unit 9 are equivalent to simulate a fractured fracture network and a matrix reservoir, and the fracture core clamping unit 8 and the matrix core clamping unit 9 are reversed to realize a fast saturated dense core, shorten the initialization time of the oil reservoir, and do not need to repeatedly disassemble the core clamping device during the experiment, so that the influence of the fracture length, the flow conductivity and other fracture parameters on the oil displacement in the three stages of pressure-steaming-production can be considered, the fracture shape can be changed by replacing the fracture core, the influence law of a water-gas composite medium on the pressure-steaming-production capacity of an oil well under different reservoir-permeability modes can be researched, including a multi-stage fracture-matrix reservoir, a large fracture-matrix reservoir, a micro fracture-matrix reservoir and an original matrix reservoir, and the independence and integrity of the fracture core and the matrix core are ensured, and the experimental time is greatly shortened.

[0036] Further, the sample preparation unit comprises a formation water sample preparation device 4, a formation oil sample preparation device 5 and a carbon dioxide sample preparation device 6, which are connected with the five-way valve 16a ports b and d respectively and are located in the thermostat 7, the first high-pressure displacement pump 2 is connected with the formation water sample preparation device 4 and the formation oil sample preparation device 5 through the first valve 21, and the second high-pressure displacement pump 3 is connected with the carbon dioxide sample preparation device 6 through the second valve 22.

[0037] In the embodiment, the formation water sample preparation is completed through the formation water sample preparation device 4, the formation oil sample preparation is completed through the formation oil sample preparation device 5, and the carbon dioxide sample preparation is completed through the carbon dioxide sample preparation device 6.

[0038] Further, the fracture core clamping unit 8 comprises a first core clamping device 10 and a first confining pressure pump 12, the inlet pressure gauge 18 and the intermediate pressure gauge 19 are connected on the two sides of the first core clamping device 10 respectively, the first confining pressure pump 12 is connected with the first core clamping device 10, and the first core clamping device 10 and the first confining pressure pump 12 are located in the thermostat 7.

[0039] Further, the matrix core clamping unit 9 comprises a second core clamping device 11 and a second confining pressure pump 14, the intermediate pressure gauge 19 and the outlet pressure gauge 20 are connected on the two sides of the second core clamping device 11 respectively, the second confining pressure pump 14 is connected with the second core clamping device 11, and the second core clamping device 11 and the second confining pressure pump 14 are located in the thermostat 7.

[0040] Further, the metering unit comprises an oil-water separation device 14 and a gas meter 15, one side of the oil-water separation device 14 is connected with the second core clamping device 11 through the three-way valve 17, the other side of the oil-water separation device 14 is connected with 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 located outside the thermostat 7.

[0041] In the embodiment, the oil production, water production and gas production can be recorded respectively through the oil-water separation device 14 and the gas meter 15.

[0042] Please refer to Figures 1 to 4 The application also provides a simulation gas-water alternating multi-round pressure-brewing injection and displacement oil method, which is applied to the simulation gas-water alternating multi-round pressure-brewing injection and displacement oil system and comprises the following steps.

[0043] S1: check the sealing of the simulated gas-water alternating multi-cycle pressure-steaming injection and displacement oil recovery system, select fracture core A and matrix core B, record the length L1 and permeability K1 of core A and the length L2 and permeability K2 of core B, put the washed core A and core B into the thermostat 7, bake at 105℃ for 4 hours, reduce the temperature to formation temperature 75℃ and continue to bake 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℃, and the confining pressure is set to 60MPa;

[0044] S2: core saturated with formation water is displaced by formation crude oil at a constant speed until only oil but no water comes out of the core holder outlet end, the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 are exchanged Figure 2 , and the formation crude oil is displaced at a constant speed until only oil but no water comes out of the core holder outlet end;

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

[0046] S4: exchange 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 is the carbon dioxide miscible pressure 21MPa, close the d port and c port of the five-way valve 16, simulate the carbon dioxide steaming stage, record the reading P1 of the inlet pressure gauge 18 and the reading P3 of the outlet pressure gauge 20, and determine the steaming time of the gas injection miscible phase by using the steaming limit calculation model;

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

[0048] S6: exchange 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 10 MPa, close the three-way valve 17, and record the oil production, water production and gas production, respectively, and calculate the gas-oil ratio, water cut and recovery efficiency of the first cycle of gas-water alternating pressure-steaming injection and production;

[0049] S7: Repeat steps S4-S6 to a predetermined number of times, and calculate the gas-oil ratio, water cut and recovery efficiency of multiple cycles of pressure-steaming injection and production.

[0050] In this embodiment, compared with a single pipe long core displacement device, the fractured fracture network and matrix reservoir are simulated by connecting the fracture unit and the matrix unit, and the device realizes fast saturation of dense cores after forward and reverse adjustment, shortening the initialization time of the reservoir. During the experiment, the influence of fracture length, conductivity and other fracture parameters on the oil displacement in the three stages of pressure-steaming-production can be considered without repeatedly disassembling the core holder, 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 fracturing of the tight oil reservoir, after the core fracturing pretreatment, the experimental device can change the fracture morphology by replacing the fracture unit of the fractured core, and can study the influence law of different injection media on the production capacity of the oil well under different storage and permeation modes, including multi-stage fracture-matrix reservoir, large fracture-matrix reservoir, micro-fracture-matrix reservoir and original matrix reservoir. Based on this, the experimental device can also measure the core gas-water, oil-water relative permeability under different storage and permeation modes, and determine the relationship between the two-phase flow range of the fracture-matrix coupled reservoir and the fracture parameters. At the same time, after the water-gas alternating pressure-steaming injection and production experiment is completed, the fracture unit and the matrix unit are connected and disconnected in turn to measure the permeability of the fractured core and the matrix core, and the change of the core permeability before and after the pressure-steaming injection and production is compared, which can analyze the influence law of multiple injection and production of carbonized water on the permeability of the core, and preliminarily determine the carbonized water dissolution and mineral pore throat plugging mechanism before and after injection and production.

[0051] In step S1, the sealing of the simulated gas-water alternating multiple cycles of pressure-steaming injection and production system is checked, the device pressure is kept constant at 30 MPa, and if the system pressure changes less than 0.5% within 12h, it indicates that the device sealing is good, the constant pressure for checking the sealing of the device is the original formation pressure of the reservoir, and the fractured core is obtained by gradually adjusting the axial pressure of the triaxial tester until the core produces a fracture, and the core fracture pressure at this time is P f After the core is washed and dried, it is respectively placed in the fracture core clamping unit 8 and the matrix core clamping unit 9, and the equivalent fractured fracture network-original matrix coupled reservoir is connected in series, and the equivalent schematic diagram is shown in Figure 3 The constant temperature box 7 simulates the temperature of the original formation temperature of the reservoir, and the confining pressure of the device in step S1 is greater than the core fracture pressure.

[0052] Wherein, in step S2, after saturating the core A and the core B with formation water, the formation crude oil is used to displace at a constant speed of 0.1 mL / min until only oil is discharged at the outlet end of the matrix core clamping unit 9, the positions of the fracture unit and the matrix unit are exchanged Figure 2 , the formation crude oil is used to displace at a constant speed of 0.1 mL / min until only oil is discharged at the outlet end of the fracture core clamping unit 8, and the saturated crude oil volume V of the core is recorded.

[0053] Wherein, 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 end pressure is reduced to 10 MPa, the three-way valve 17 is closed, and the oil production V o , the water production V w , and the gas production V g are recorded respectively, the recovery degree R w of the depletion stage is calculated, and the recovery degree calculation model of the depletion stage is as follows:

[0054]

[0055] In the formula, R w is the water cut of the depletion stage, the unit is %, V o is the oil production of the depletion stage, the unit is mL, and V is the saturated crude oil volume of the core in the rapid saturation stage, the unit is mL.

[0056] Wherein, in step S4, the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 are exchanged Figure 1 , the second high-pressure displacement pump 3 is set to displace carbon dioxide in the sample preparation unit at a constant speed of 0.3 mL / min, until the outlet pressure is the carbon dioxide miscible pressure 21 MPa, the d port and the c port of the five-way valve 16 are closed, the carbon dioxide soaking stage is simulated, the readings P1 of the inlet pressure gauge 18 and the readings P3 of the outlet pressure gauge 20 are recorded, and the soaking time of the gas injection miscible phase is determined by using the soaking limit calculation model.

[0057] The simulated production process is shown in (a) of Figure 4 and (b) of Figure 4 The injected gas rapidly spreads along the direction of the volumetric fracture, displaces the crude oil around the well, but the swept range is limited, and the injected gas exists only around the fracture; after the well is closed, the carbon dioxide is dissolved with the crude oil, fully plays the role of expanding the crude oil volume and reducing the crude oil viscosity, with the mass transfer capacity of the oil and gas components being strengthened, the flowability of the crude oil is increased, and the swept range of the injected gas-crude oil composite system in the soaking stage is larger than that in the gas injection miscible phase.

[0058] Wherein, the soaking limit is calculated as follows:

[0059]

[0060] Where, t is the limit time of gas injection miscible phase soaking, 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; is the viscosity of CO2, mPa·s; P1 is the inlet pressure, MPa; P3 is the outlet pressure, MPa.

[0061] Specifically, the soaking stage simulates the imbibition process of crude oil in the matrix. Excessive soaking time can lead to injection pressure diffusion, increase the cost of the injection medium, and affect the throughput effect. Excessive soaking time can affect the mass transfer of oil and gas components and the efficiency of carbonized water throughput, reducing the crude oil recovery rate. During the soaking stage, the crude oil imbibition rate tends to slow down with increasing soaking time, and the oil-water imbibition replacement in the matrix reaches a relatively stable state. This is the ideal soaking time for optimal oil production, and opening the well for production can achieve the best oil yield. Therefore, determining the soaking limit time is particularly important during the experiment. Furthermore, because gas has greater fluidity than water, carbon dioxide is injected in the early stages of pressure-driven water injection to achieve miscible drive, allowing gas to reach the matrix pores along fractures. Furthermore, during the soaking stage, the CO2 injection solubilizes and expands the crude oil, while extracting it, effectively capturing the residual oil in the small pores of the matrix.

[0062] Among them, in step S5, open the port a and port c of the five-way valve 16, set the injection pressure of the first high-pressure displacement pump 2 to the core fracture pressure P f , push the formation water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30 MPa, close the port a and port c of the five-way valve 16, simulate the formation 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 soaking time in the pressure drive water injection stage is determined using the soaking limit calculation model.

[0063] The simulated production process is shown in Figure 4 (c) and Figure 4 In figure (d), water is injected under rock fracture pressure, forming intricate micro-cracks around the original main fractures around the well. The pressure difference caused by pressure-driven water injection causes the injected gas-crude oil composite system to further spread, significantly increasing the affected range. During the soaking stage, the oil-gas-water three-phase mass transfer occurs, effectively replenishing the formation energy. In addition, undissolved carbon dioxide forms carbonated water with formation water, increasing 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] wherein t is the pressure flooding soak 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 permeability of the matrix, mD; is the viscosity of the formation water, mPa·s; P 1-1 is the inlet pressure, MPa; P 3-1 is the outlet pressure, MPa.

[0067] Specifically, the pressure flooding injects a large amount of water in a short time at a high injection pressure, further increases the formation pore pressure to promote the prefrontal CO2 to continue to flow to the deep part of the matrix, and at the same time, a large number of micro cracks are formed in the near wellbore area to increase the permeability around the injection well. With the increase of soak time, the injection-production pressure difference between the inlet pressure and the outlet pressure gradually decreases, and carbonated water is gradually formed after the contact of CO2 and water, the density of carbonated water increases, and the mobility ratio of crude oil decreases, which is beneficial to improve the rapid finger phenomenon of single gas injection medium. Under the interaction of CO2-water-rock, the oil-water interfacial tension is reduced, the amount of crude oil adhering to the surface of the rock is reduced, and the calcium carbonate is dissolved to improve the permeability of the fracture and the matrix.

[0068] wherein in step S6, the positions of the fracture core clamping unit 8 and the matrix core clamping unit 9 are exchanged, the three-way valve 17 is opened until the outlet end pressure is reduced to 10 MPa, the three-way valve 17 is closed, the oil production V o1 , the water production V w1 and the gas production V g1 are recorded respectively, and the gas-oil ratio GOR1, the water cut f w1 and the recovery degree R w1 of the water-gas alternation first cycle pressure-soak injection-production oil displacement stage are calculated.

[0069] The simulated production process is shown in (e) of Figure 4 After the four steps of gas injection miscible phase-soak pressure flooding injection of water-soak, the reservoir formation energy is sufficient, the carbonated water preferentially swallows the cracks and large pore oil around the well after the well is opened, under the action of injection-production pressure difference, carbon dioxide flows from the deep reservoir along the high permeability flow channel to the wellbore, continues to promote the remaining carbonated water in the reservoir to speed up the efficiency of washing oil around the well, and at the same time, carbon dioxide will displace the remaining oil in the micro cracks and small pores, and fully develop the oil displacement potential of the water-gas composite medium.

[0070] The gas-oil ratio calculation model of the pressure-soak injection-production oil displacement stage is as follows:

[0071]

[0072] wherein GOR1 is the gas-oil ratio of the pressure-soak injection-production oil displacement stage, unit m 3 / m3 ;V o1 V is the oil production of the pressure-steaming injection-production stage, unit mL; V w1 V is the water production of the pressure-steaming injection-production stage, unit mL; V g1 V is the gas production of the pressure-steaming injection-production stage, unit mL.

[0073] Further, the water content calculation model of the pressure-steaming injection-production stage is as follows:

[0074]

[0075] In the formula, f w1 V is the water content of the pressure-steaming injection-production stage, unit %; V o1 V is the oil production of the pressure-steaming injection-production stage, unit mL; V w1 V is the water production of the pressure-steaming injection-production stage, unit mL.

[0076] Further, the recovery degree calculation model of the pressure-steaming injection-production stage is as follows:

[0077]

[0078] In the formula, R w1 V is the water content of the pressure-steaming injection-production stage, unit %; V o1 V is the oil production of the pressure-steaming injection-production stage, unit mL; V is the saturated oil volume of the core rapid saturation stage, unit mL.

[0079] Specifically, in step S6, with the increase of the cycle injection-production round, the water content gradually rises, and the water content rising rate presents the trend of slow increase of early water content, accelerated water content in the middle period, and slow water content increase in the later period. In the low water content or high water content stage (the water content is less than 30% or the water content is higher than 90%), the water content of the reservoir rises slowly, and the water content rising rate is less than 2%; in the medium-high water content stage (the water content is 30%-90%), the water content of the reservoir rises faster, and the water content rising rate is about 5%.

[0080] Please refer to Figures 5 to 8 The application further provides a simulation of the water-gas alternating pressure-steaming injection-production numerical simulation of the fracture-matrix coupled reservoir.

[0081] Considering that the three types of reservoirs have no injection-production system or imperfect injection-production relationship at isolated well points, the numerical simulation takes the single well model single round pressure-steaming injection-production as an example, sets the model size to 50*50*5, the plane grid to 10m*10m, and the longitudinal grid to 0.5m. The reservoir permeability is 0.1mD, the porosity is 9%, the main fracture permeability is 3000mD, when the formation pressure reaches the fracture pressure, a plurality of micro-fractures are randomly generated around the well and the micro-fracture permeability is 300mD, and the fracture and matrix in the model adopt two sets of relative permeability curves.

[0082] The model scheme sets the gas injection volume of the injection well at the mixed phase stage to 3000m 3 / d, bottom hole pressure is 60MPa (formation fracture pressure 58MPa), gas injection time is 60 days, after three days of shut-in, pressure drive water injection is switched, 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 it is opened for production for 90 days, and the oil production of the 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-simmering injection-production oil recovery can be divided into the following aspects:

[0084] S101 gas injection mixed phase stage: The bottom hole 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 micro cracks 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 As can be seen from (a), the reservoir pressure around the well increases from the original formation pressure of 30MPa to 40MPa.

[0085] S102 Well soaking 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 crude oil volume to expand. Figure 5 From (b), we can see that the pressure around the well expands outward in a small range, and the pressure field is more uniform. Figure 8 The pressure change in the wellbore area after gas injection shows that after the wellbore is completed, the bottom hole flowing pressure drops from 60 MPa to 58 MPa due to pressure diffusion.

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

[0087] S104 Well shut-in stage: After the pressure drive water injection is completed, the well is shut down. Figure 5 As can be seen from the pressure field in (d), 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 changes in the wellbore area after pressure-driven water injection show 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 mobility 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 stewing injection production stage: the initial production, water content reaches 90% Figure 7 ), daily oil production stable 0.9 days from 8m 3 / d rapidly decreased to 0.3m 3 / d (. Figure 6 ), the reservoir pressure from 58.9MPa to 12.5MPa (. Figure 8 ), this process is mainly carbonized water flooding; with the increase of bottom hole and reservoir pressure difference, carbon dioxide carrying crude oil rapidly to the bottom, the bottom hole injection well flow pressure increased by about 4MPa and maintained for a long period of time (. Figure 8 ), the water content of oil well rapidly reduced to 5% (. Figure 7 ), daily oil production stable at 8m 3 / d (. Figure 6 ). From the pressure field in (e) of Figure 5 , the bottom hole pressure remained at about 12MPa for 30 days of production, indicating that carbon dioxide huff and puff effectively maintain reservoir pressure; from the pressure field in (f) of Figure 5 , the bottom hole pressure decreased from 60MPa to 10MPa, the pressure around the well decreased from 48MPa to 22MPa, water and gas composite medium pressure stewing injection production technology effectively supplement the formation energy, expand the oil sweeping area, improve the oil washing efficiency.

[0089] The above disclosed only for the preferred embodiment of the present application, of course, can not be limited by the scope of the present invention, those skilled in the art can understand the implementation of all or part of the above processes, and the equivalent changes made by the present invention claims, still belong to the scope of the invention covered.

Claims

1. A method for simulating multiple rounds of gas-water alternating pressure-simmering injection and recovery, characterized in that: The method is based on simulating a multi-round pressure-simmer injection-production oil recovery system with alternating gas and water. The system includes 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 c port of the five-way valve. The fracture core clamping unit is arranged The inlet pressure gauge is located on a side away from the five-way valve, the intermediate pressure gauge is located on a side away from the inlet pressure gauge of the fracture core clamping unit, the matrix core clamping unit is located on a side away from the intermediate pressure gauge of the fracture core clamping unit, the metering unit is located on a side away from the intermediate pressure gauge of the fracture core clamping unit via a three-way valve, the outlet pressure gauge is located 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 within the constant temperature box, and the metering unit is located outside the constant temperature box; The sampling unit includes a formation water sampler, a formation crude oil sampler, and a carbon dioxide sampler, wherein the formation water sampler, the formation crude oil sampler, and the carbon dioxide sampler are respectively connected to port a, port b, and port d 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; The method comprises the following steps: S1: Check the sealing performance of the simulated gas-water alternating multi-round pressure-stem injection-production flooding system, select a fracture core A and a matrix core B, record the length L1 and permeability K1 of core A, and the length L2 and permeability K2 of core B, place the cleaned cores A and B in a constant temperature box, bake at 105°C for 4 hours, reduce the temperature to the formation temperature of 75°C and continue baking for 4 hours, then place the dried cores A and B in the fracture core clamping unit and the matrix core clamping unit, respectively. The constant temperature box simulates a formation temperature of 75°C and a confining pressure of 60 MPa. 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 holder outlet. 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 rate until only oil but no water comes out of the core holder outlet. S3: Close port c of the five-way valve and open the three-way valve to simulate the flow of matrix crude oil toward the fracture end until the outlet pressure drops to 10 MPa. Then close the three-way valve and record the oil production, water production, and gas production, and calculate the gas-oil ratio, water cut, 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 c port of the five-way valve to simulate 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 formation water in the sample preparation unit at a set speed until the outlet pressure reaches the original formation pressure of 30 MPa, close the a port and c port of the five-way valve, simulate the formation water soaking stage, and record the reading of the inlet pressure gauge P 1-1 and the outlet pressure gauge reading P 3-1 , the soaking time in the pressure drive water injection stage is determined using the soaking 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 outlet pressure drops to 10 MPa, closing the three-way valve, recording the oil production, water production, and gas production, and calculating the gas-oil ratio, water content, and recovery degree of the first cycle of gas-water alternating pressure-simmering flooding; S7: Repeat steps S4 to S6 for a preset number of times to respectively calculate the gas-oil ratio, water content, and recovery degree of multiple rounds of pressure-simmering injection and recovery.

2. The simulated gas-water alternating multiple rounds of pressure-simmering injection-production oil recovery method according to claim 1, 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.

3. The simulated gas-water alternating multiple rounds of pressure-simmering injection-production oil recovery method according to claim 2, 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.

4. The simulated gas-water alternating multiple rounds of pressure-simmering injection-production oil recovery method according to claim 3, characterized in that: The metering unit includes an oil-water separator and a gas meter. One side of the oil-water separator is connected to the second core clamp through the three-way valve, and the other side of the oil-water separator is connected to the gas meter. The outlet pressure gauge is installed on the three-way valve. The oil-water separator and the gas meter are both located outside the constant temperature box.

5. The simulated gas-water alternating multiple rounds of pressure-simmering injection-production oil recovery method according to claim 1, characterized in that: In step S1, the fractured core is subjected to a triaxial tester by gradually adjusting the axial pressure until fractures are generated in the core.

6. The simulated gas-water alternating multiple-round pressure-simmering injection-production oil recovery method according to claim 5, characterized in that: In steps S4 and S5, the soaking stage is used to simulate the imbibition process of crude oil in the matrix. During the soaking stage, pressure propagates from the fracture to the matrix boundary. The soaking time is the seepage time for the fluid at the injection end to reach the matrix boundary along the fracture. The soaking limit calculation model is derived based on Darcy's 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; is the fluid viscosity, mPa·s; △P is the pressure difference between the core inlet and outlet, MPa.

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