A method and system for measuring gas-water relative permeability curve

Abstract

The invention relates to a method and a system for determining a gas-water relative permeability curve, and belongs to the technical field of petroleum and natural gas. The method comprises the following steps: saturating a core to be tested with formation water; calculating a displacement pressure of a gas drive and a displacement flow rate of a water drive according to an external environment of a source of the core to be tested; performing a gas-drive-water experiment and a water-drive-gas experiment, and calculating a relative permeability of a gas phase and a relative permeability of a water phase in a gas drive process according to the mass / flow rate of formation water driven out by the gas drive and the gas flow rate; calculating a relative permeability of a gas phase and a relative permeability of a water phase in a water drive process according to the displacement flow rate of the water drive and the gas flow rate driven out by the water drive; and constructing a gas phase relative permeability curve and a water phase relative permeability curve to solve the problem that the existing gas-water relative permeability curve cannot truly describe the actual conditions of each stage of the gas storage, and that the injection and production engineering of a gas reservoir-type gas storage is low in efficiency and difficult in nature.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum and natural gas, and in particular to a method and system for determining a gas-water relative permeability curve. Background Art

[0002] The gas-water relative permeability curve is an important tool for describing the flow law of gas-water two-phase in porous media. It is an important basis for the safe construction, efficient operation and smooth implementation of subsequent related special research of gas reservoir-type gas storage.

[0003] Gas reservoir-type gas storage has three major functions: seasonal peak regulation, accident emergency response, and national energy strategic reserve. Its functions determine that the gas storage needs to carry out special working conditions for multi-cycle injection and production. Under multi-cycle injection and production working conditions, the gas-water two-phase seepage law will change with the injection and production cycle, and it is not static. Therefore, the conventional gas-water relative permeability curve can only represent the situation of the gas injection or gas production stage in an injection and production cycle. This curve cannot accurately describe the changes in the gas-water two-phase seepage after multi-cycle injection and production in the actual working process, resulting in deviation from reality when studying the construction and application of gas storage.

[0004] Moreover, in the currently commonly used gas-water relative permeability test method, the gas-water relative permeability is usually tested by gas-driven water. In the actual operation of the gas storage, the gas production stage is mainly water-driven gas, and the gas-water relative permeability curve is greatly affected by the fluid saturation sequence. The relative permeability curve tested by gas-driven water cannot reflect the actual situation in the underground gas storage, and has little guiding significance for the development of actual water-driven gas reservoirs. Therefore, since the existing gas-water relative permeability curve cannot truly describe the actual situation of each stage of the gas storage, the related research and application using the gas-water relative permeability curve do not conform to the actual engineering practice, thereby increasing the difficulty of implementing multi-cycle injection and production and reducing engineering efficiency. Summary of the invention

[0005] The present invention aims to provide a method and system for determining a gas-water relative permeability curve, so as to solve the problem that the existing gas-water relative permeability curve cannot truly describe the actual conditions of each stage of the gas storage, resulting in low efficiency and great difficulty in the injection and production engineering of gas reservoir-type gas storage.

[0006] To achieve the above object, the technical solution of the present invention is as follows: The present invention provides a method for determining a gas-water relative permeability curve, comprising the following steps:

[0007] 1) Saturate the core to be tested with formation water;

[0008] 2) Calculate the displacement pressure of gas drive and the displacement flow rate of water drive according to the external environment of the core source to be tested;

[0009] 3) Carry out gas-displacing water experiment:

[0010] Inject gas into the core to be tested according to the displacement pressure of the gas drive, and measure the mass / flow rate of the driven formation water and the gas flow rate in real time; and then calculate the relative permeability of the gas phase and the relative permeability of the water phase in the gas drive process;

[0011] 4) Carry out water drive gas experiment:

[0012] Injecting formation water into the core to be tested according to the displacement flow of the water drive, measuring the gas flow driven out by the water drive in real time, and calculating the relative permeability of the gas phase and the relative permeability of the water phase in the water drive process according to the displacement flow and the gas flow driven out by the water drive;

[0013] 5) Construct gas phase relative permeability curve and water phase relative permeability curve.

[0014] The present invention fully simulates the actual operating environment of the gas storage reservoir injection and production cycle. In each cycle, the gas-driven water experiment simulates the gas injection work of the gas storage reservoir, and the water-driven gas simulates the gas production work of the gas storage reservoir. The corresponding gas phase relative permeability curve and water phase relative permeability curve are respectively measured in the displacement experiments of the two stages. The curve measurement process is highly close to the actual working environment in the gas storage reservoir. The obtained gas-water relative permeability curve can truly describe the actual situation of the gas storage reservoir at each stage, effectively improve the efficiency of the injection and production engineering of the gas reservoir type gas storage reservoir, and create favorable conditions for the multi-cycle injection and production work of the gas storage reservoir.

[0015] Furthermore, in order to be more in line with engineering practice, in the gas-displacing-water experiment, gas is injected from one side of the core to be tested, and in the water-displacing-gas experiment, formation water is injected from the other side of the core to be tested.

[0016] Furthermore, in order to obtain the actual relative permeability of different injection and production cycles, steps 3) to 5) are repeated to obtain gas phase relative permeability curves and water phase relative permeability curves of multiple cycles.

[0017] Furthermore, the step 2) also includes calculating the confining pressure, and performing a gas-displacing-water experiment and a water-displacing-gas experiment under the confining pressure; the confining pressure is greater than the displacement pressure.

[0018] Furthermore, in order to improve the accuracy of the measurement process, step 3) and step 4) also include the step of evacuating the experimental pipeline before the experiment.

[0019] Furthermore, in step 2), the calculation formulas for the relative permeability of the gas phase, the relative permeability of the water phase and the irreducible water saturation are:

[0020] S wi =(G w -G wi ) / Gw

[0021] △P i =P 1i -P 2i

[0022] Q wi =G wi / ρ w

[0023] K rwi =(Q wi μ w L) / (kA△P i )

[0024] K rgi =(Q gi μ g L) / (kA△P i )

[0025] S wc1 =(G w -G wit ) / G w

[0026] Where: S wi G is the water saturation of the core at time t during gas flooding; wi G is the average mass of formation water driven out continuously for n seconds during gas drive; w is the wet weight of the core at normal pressure; P 1i is the average pressure at the core inlet at time t during gas drive; P 1i is the core outlet pressure at time t during gas drive; △P i Q is the pressure difference between the two ends of the core at time t during gas drive; wi is the formation water flow rate at time t during gas drive; Q gi is the gas flow rate at time t during gas drive; K is the absolute permeability of the core; K rwi is the water saturation S wi Relative permeability of water phase under K rgi is the water saturation S wi Gas phase relative permeability under wc1 is the bound water saturation; G wit It is the total mass of formation water driven out during the gas drive process.

[0027] Furthermore, in step 3), the calculation formulas for the relative permeability of the gas phase and the relative permeability of the water phase are:

[0028] S wj =S wc1 +(nρ w Q wj ) / Gw

[0029] △P j =P 2j -P 1j

[0030] K rwj =(Q wj μ w L) / (kA△P j )

[0031] K rgj =(Q gj μ g L) / (kA△P j )

[0032] Among them, S wj is the water saturation of the core during water flooding, Q gj is the average gas flow rate during water flooding, Q wj is the displacement flow rate of water-driven gas, S wc1 is the irreducible water saturation of gas-driven water, and n is the time.

[0033] Furthermore, the step 4) further includes calculating the residual gas saturation according to the irreducible water saturation and the displacement flow rate, and the calculation formula is:

[0034] S gr1 =1-S wc1 -TQ wj

[0035] Where: S gr1 is the residual gas saturation during water flooding; T is the experimental time.

[0036] The present invention also provides a system for measuring a gas-water relative permeability curve, comprising:

[0037] A core holder, used to hold the core to be tested;

[0038] A displacement pump, used to provide displacement power;

[0039] An air-drive water pipeline, to which the displacement pump and the core holder are connected, and is used for conducting an air-drive water experiment;

[0040] A water-drive gas pipeline, to which the displacement pump and the core holder are connected, for conducting a water-drive gas experiment;

[0041] A gas flow meter, arranged downstream of the gas-driven water pipeline and the water-driven gas pipeline, for detecting the gas flow;

[0042] The formation water quality / flow detector is arranged downstream of the gas drive water pipeline and the water drive gas pipeline, and is used to detect the formation water quality / flow.

[0043] The present invention sets a gas-driven water pipeline and a water-driven gas pipeline in the gas-water relative permeability curve determination system. In each cycle, the gas-driven water experiment is used to simulate the gas injection work of the gas storage reservoir, and the water-driven gas simulation is used to simulate the gas production work of the gas storage reservoir. The corresponding gas phase relative permeability curve and water phase relative permeability curve are respectively determined in the displacement experiments of the two stages. The curve determination process is highly close to the actual working environment in the gas storage reservoir. The obtained gas-water relative permeability curve can truly describe the actual situation of the gas storage reservoir at each stage, effectively improve the efficiency of the injection and production engineering of the gas reservoir type gas storage reservoir, and create favorable conditions for the multi-cycle injection and production work of the gas storage reservoir.

[0044] Furthermore, in the gas-drive water pipeline, gas enters from the first end of the core holder and is output from the second end of the core holder; in the water-drive gas pipeline, formation water enters from the second end of the core holder and is output from the first end of the core holder. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 1 is a schematic diagram of the structure of a measuring system used in an embodiment of a method for measuring a gas-water relative permeability curve of the present invention;

[0046] Figure 2 is a method flow chart of an embodiment of a method for determining a gas-water relative permeability curve of the present invention;

[0047] In the figure, 1-confining pressure pump, 2-back pressure pump b, 3-displacement pump, 4-PC control end, 5-back pressure valve a, 6-valve c, 7-valve d, 8-valve e, 9-hexagon valve a, 10-three-way valve a, 11-pressure sensor a, 12-valve g, 13-core holder, 14-valve h, 15-pressure sensor b, 16-three-way valve b, 17-hexagon valve b, 18-back pressure valve b, 19-valve i, 20-back pressure pump a, 21-drying pipe b, 22-balance b, 23-gas flow meter, 24-valve b, 25-high pressure gas source, 26-valve a, 27-formation water, 28-vacuum gauge a, 29-valve f, 30-vacuum gauge b, 31-valve j, 32-drying pipe a, 33-balance a, 34-vacuum pump, 35-constant temperature box. DETAILED DESCRIPTION

[0048] The following are three implementation methods of an embodiment of a method for measuring a gas-water relative permeability curve of the present invention.

[0049] Implementation 1:

[0050] The gas-liquid relative permeability curve is an important reference material for dynamic analysis and numerical simulation of gas reservoir development. This curve is usually obtained by steady-state or non-steady-state testing in the laboratory using real gas reservoir cores. Since the basic principle of the steady-state method is one-dimensional Darcy flow, there are three main limitations in the steady-state method for testing gas-water relative permeability: First, the experimental process of using the steady-state method to test gas-water relative permeability must be under the condition of ensuring that no turbulence is generated, which requires maintaining a small displacement pressure difference to ensure a small gas flow rate, and using a small displacement pressure difference is difficult to eliminate the influence of the end effect during the experiment; second, the existing gas-water relative permeability test standard stipulates that the gas permeability of the core being tested must be greater than 0.5mD, so its scope of application is limited; third, the cycle of the steady-state method for testing gas-water relative permeability is very long.

[0051] Due to the many limitations of the steady-state method, the currently commonly used gas-water relative permeability test method is the non-steady-state method. However, the existing non-steady-state method for testing gas-water relative permeability also has certain limitations. For example, when the existing non-steady-state method is used to determine the gas-water relative permeability curve, the test is usually carried out by gas-driven water. In the actual gas reservoir development process, due to processes such as edge water advancement, the state of water-driven gas is usually presented, and the gas-water relative permeability curve is greatly affected by the fluid saturation sequence. Therefore, the relative permeability curve tested by gas-driven water has little guiding significance for the actual water-driven gas reservoir development.

[0052] In order to better fit the actual operating environment in the gas storage, a more accurate gas-water relative permeability curve is obtained, thereby providing an effective basis for the effective analysis of the gas storage operation dynamics, operation efficiency adjustment, and injection and production capacity analysis. In this embodiment, the gas-water relative permeability curve is comprehensively determined by gas-displacing water experiment and water-displacing gas experiment.

[0053] In this embodiment, the main Figure 1 The measurement system shown includes a core holder, which is placed in a constant temperature box, and the confining pressure end of the core holder is connected to a confining pressure pump. The measurement system mainly includes an air-driven water pipeline and a water-driven air pipeline to realize an air-driven water experiment and a water-driven air experiment.

[0054] The a end (left side) of the core holder is connected in sequence to valve g, pressure sensor a, valve No. 3 and valve No. 1 of three-way valve a, valve No. 4 and valve No. 1 of hexagon valve a. Valve No. 1 of hexagon valve a has two branches in parallel, valve c, formation water source, and valve a are connected in sequence on the first branch, valve d, back pressure valve a, high pressure gas source, and valve b are connected in sequence on the second branch, and the two branches are connected to the displacement pump after merging, and the back pressure end of the back pressure valve a is connected in sequence to valve e and back pressure pump b; the b end (right side) of the core holder is connected in sequence to valve h, pressure sensor b, valve No. 1 and valve No. 3 of three-way valve b, valve No. 1 and valve No. 4 of hexagon valve b, back pressure valve b, drying pipe b, and gas flow meter b, the drying pipe b is placed on an electronic balance b for weighing, and the back pressure end of the back pressure valve b is connected in sequence to valve i and back pressure pump a;

[0055] Valve No. 5 of hexagon valve a is connected to valve No. 2 of three-way valve b through a pipeline, and valve No. 2 of three-way valve a is connected to valve No. 2 of hexagon valve b through a pipeline. Vacuum gauge a, valve f, valve j, and vacuum gauge b are connected in sequence between valve No. 3 of hexagon valve a and valve No. 3 of hexagon valve b. The inlet of drying tube a is connected between vacuum gauge a and vacuum gauge b. The outlet of drying tube a is connected to a vacuum pump. The drying tube a is placed on an electronic balance a for weighing. Valve No. 6 of hexagon valve a and valve No. 6 of hexagon valve b are used for venting.

[0056] The confining pressure pump, the back pressure pump a, the back pressure pump b, the displacement pump, the electronic balance a and the electronic balance b are connected to the computer respectively.

[0057] In this embodiment, the purpose of the hexagonal valve a, hexagonal valve b, three-way valve a and three-way valve b is mainly to form two independent pipelines to connect the core holder in the gas-drive-water experiment and the water-drive-gas experiment. As an improvement to this embodiment, two parallel pipelines can also be directly used, and a one-way valve is set in each pipeline.

[0058] In this embodiment, the relative permeability curve measured in an injection-production cycle is taken as an example to explain the determination method in detail. Figure 2 As shown, it mainly includes the following parts:

[0059] Step S1, experimental preparation:

[0060] 1) Measure the dry weight G of the core to be tested d , length L, diameter R, cross-sectional area A, porosity And basic physical parameters such as permeability K;

[0061] 2) Set the volume V w Formation water weight m w , and calculate the configured formation water density ρ w ,

[0062] ρ w =m w / V w

[0063] Where: m w is the mass of formation water, kg; V w is the volume of formation water, m 3 ρ w is the formation water density, kg / m 3 ,

[0064] 3) Test and calculate the viscosity μ of formation water and experimental gas under the designed core holder outlet back pressure and experimental temperature conditions respectively w and μ g ;

[0065] 4) Wash and dry the core to be tested and saturate it with formation water for experiment (formation water is prepared according to the mineralization of formation water in the core sampling area, hereinafter referred to as formation water);

[0066] 5) Place the core to be tested in the core holder and add confining pressure. Use gas to displace the core until no water comes out. Then use the displacement pump to drive the experimental formation water at a constant flow rate. Observe the pressure sensor reading at the core inlet. If the sensor reading keeps rising and does not tend to be stable, reduce the flow rate set by the displacement pump until the pressure sensor reading can tend to a stable value. This flow rate is used as the displacement flow rate Q of water-displacement gas. wj ,

[0067] 6) Dry the core again and saturate it with experimental formation water (formation water is prepared according to the mineralization of formation water in the core sampling area), and weigh the wet weight of the core G w1 .

[0068] Step S2: Simulating the gas storage operation environment:

[0069] 1) Keep all valves closed, load the core to be tested into the core holder, open valves g and h at both ends of the core holder, set the confining pressure according to the overburden pressure of the gas storage reservoir where the core is sourced, and start the confining pressure pump (determined according to the overburden pressure of the gas storage reservoir where the core is sourced, but at least greater than the designed displacement pressure by 3 MPa to ensure the airtightness of the experimental system);

[0070] 2) Open valves 3 and 4 of hexagon valve a, valves 1 and 3 of three-way valve a, valves 1 and 3 of three-way valve b, valves 1 and 3 of hexagon valve b, valves f and valve j, turn on the vacuum pump, pump for 3 to 5 seconds, then close valves g and valve h, and then continue to pump the formation water in the pipeline into the drying pipe a, then turn off the vacuum pump, close valves 3 and 4 of hexagon valve a, valves 1 and 3 of three-way valve a, valves 1 and 3 of three-way valve b, valves 1 and 3 of hexagon valve b, valves f and valve j, and record the mass G of the formation water extracted by the electronic balance aw2 , calculate the wet weight G of the core under pressurized conditions w ;

[0071] G w =G w1 -G w2

[0072] Where: G w1 is the wet weight of the core at normal pressure, kg; G w2 is the mass of formation water pressed out from the core under confining pressure conditions, kg;

[0073] 3) Open valve i and back pressure valve b, calculate the back pressure according to the original formation pressure of the core source gas storage and the designed injection-production pressure difference of the gas storage, and set the back pressure pump a according to this back pressure and start it;

[0074] 4) The thermostat is set up and started according to the reservoir temperature of the core-source gas storage reservoir, so that the experimental temperature is constant at the reservoir temperature of the core-source gas storage reservoir.

[0075] Step S3, gas-driven water experiment simulates the gas injection workflow of the gas storage reservoir:

[0076] 1) Open valves 1, 3, and 4 of hexagon valve a, valves 1 and 3 of three-way valve a, valves 1 and 3 of three-way valve b, valves 1 and 3 of hexagon valve b, valves f and valve j, turn on the vacuum pump, observe vacuum gauge a and vacuum gauge b, and after the displacement system pipelines and valves are evacuated to vacuum, turn off the vacuum pump, close valve 3 of hexagon valve a, valve 3 of hexagon valve b, valve f and valve j, and open valve b, valve d, valve e, back pressure valve a, and valve 4 of hexagon valve b;

[0077] 2) Set the back pressure pump according to the designed displacement pressure and start it, then turn on the displacement pump, and use a displacement pressure higher than the set back pressure pump pressure to allow gas to enter the core from one end of the core holder, and drive the formation water from the other end of the core holder into the drying tube b. Read the value of the high-precision electronic balance b in real time, continuously record the mass of the driven formation water for n seconds, and calculate the average value G wi and the formation water flow rate Q in n seconds wi , real-time record of high-precision gas flow meter data within n seconds, and obtain the average gas flow Q gi , and simultaneously record the average value P of the pressure sensor readings at the core inlet and outlet within n seconds 1i and P 2i (At this time, pressure sensor a is the inlet pressure sensor, and pressure sensor b is the outlet pressure sensor), calculate the pressure difference △P at both ends of the core i , calculate the core water saturation S according to the mass of the driven formation water wi, calculate the relative permeability of gas and formation water at the water saturation according to the gas flow rate, formation water flow rate and core absolute permeability (each mass of expelled formation water can calculate a water saturation value, corresponding to a gas flow rate and pressure difference), and obtain at least 7 groups of data to ensure that the relative permeability curve is relatively smooth;

[0078] S wi =(G w -G wi ) / G w

[0079] △P i =P 1i -P 2i

[0080] Q wi =G wi / ρ w

[0081] K rwi =(Q wi μ w L) / (kA△P i )

[0082] K rgi =(Q gi μ g L) / (kA△P i )

[0083] Where: S wi is the water saturation of the core at time t; P 1i is the core inlet pressure at time t, Pa; P 1i is the core outlet pressure at time t, Pa; △P i is the pressure difference between the two ends of the core at time t, Pa; Q wi is the formation water flow rate at time t, m 3 / s;Q gi is the gas flow rate at time t, m 3 / s; K is the absolute permeability of the core, m 2 ; K rwi is the water saturation S wi Relative permeability of water phase under K rgi is the water saturation S wi The relative permeability of the gas phase under

[0084] 3) When the reading of the electronic balance b no longer changes, the water saturation in the core has reached the irreducible water saturation S wc1, continuously measure the pressure difference and gas flow rate under three sets of irreducible water saturation, calculate the relative permeability of the gas phase at this time, until its relative error is less than 3%, and calculate the irreducible water saturation S of the first gas drive water in the core based on the recorded mass of the driven formation water wc1 ;

[0085] S wc1 =(G w -G wit ) / G w

[0086] Where: G wit is the total mass of the driven formation water, kg,

[0087] 4) Turn off the displacement pump, open valve No. 6 of hexagon valve a and valve No. 6 of hexagon valve b to vent the system, and then close all valves.

[0088] Step S4: Water drive gas experiment simulates the gas storage gas extraction workflow:

[0089] 1) Evacuate the pipeline that will be used for water-displacement gas experiment to avoid interference of gas and formation water in the pipeline on the experimental results:

[0090] 2) Displace formation water flow Q according to the design wj Set up the displacement pump and start it, so that the formation water enters the core from the core holder end b, and drives the gas in the core from the core holder end a to the drying tube b. Record the high-precision gas flow meter data in real time within n seconds to obtain the average gas flow Q gj , and simultaneously record the average value P of the pressure sensor readings at the core inlet and outlet within n seconds 1j and P 2j , calculate the pressure difference △P at both ends of the core j , the mass of formation water pumped into the core is calculated according to the displacement time (n seconds) of the displacement pump, thereby calculating the core water saturation S wj , calculate the relative permeability of gas and formation water at the water saturation according to the gas flow rate, formation water flow rate and core absolute permeability (each mass of expelled formation water can calculate a water saturation value, corresponding to a gas flow rate and pressure difference), and obtain at least 7 groups of data to ensure that the relative permeability curve is relatively smooth;

[0091] S wj =S wc1 +(nρ w Q wj ) / G w

[0092] △P j =P 1j -P 2j

[0093] K rwj =(Q wj μ w L) / (kA△P j )

[0094] K rgj =(Q gj μ g L) / (kA△P j )

[0095] 3) When the reading of the gas flow meter no longer changes, the gas saturation in the core has reached the residual gas saturation S gr1 , continuously measure the pressure difference and formation water flow rate under three sets of residual gas saturation, calculate the relative permeability of the water phase at this time, until its relative error is less than 3%, and calculate the residual gas saturation S of the first water drive of the core based on the recorded mass of pumped formation water gr1 ;

[0096] S gr1 =1-S wc1 -TQ wj

[0097] Where: S gr1 is the residual gas saturation of the first water drive; T is the experimental time, s, and n is the time, s,

[0098] 4) Turn off the displacement pump, open valve No. 6 of hexagon valve a and valve No. 6 of hexagon valve b to vent the system, and then close all valves.

[0099] Step S5: Plotting the gas-water relative permeability curve for one injection-production cycle

[0100] A rectangular coordinate system was established with the core water saturation value as the horizontal coordinate and the relative permeability value as the vertical coordinate, and smooth curves were used to draw the gas phase relative permeability curves and water phase relative permeability curves corresponding to different core water saturations.

[0101] During the above experiment, the pipeline between the core holder outlet and the drying tube needs to be flooded with soapy water several times before the experiment to minimize the influence of capillary force on the movement of formation water; the placement height of the drying tube and the electronic balance must be level with the placement height of the core holder to eliminate the influence of gravity on the movement of formation water.

[0102] The above only proposes a preferred measurement system structure. The present invention is not limited to the use of the above measurement system. The main purpose of the present invention is to provide a test method for relative permeability curves. Any system that can simultaneously perform gas-displacing water experiments and water-displacing gas experiments can be used as the experimental basis for the implementation of the measurement method in the present invention.

[0103] Implementation 2:

[0104] The difference between this embodiment 2 and the above embodiment 1 is that in this embodiment, in order to be more in line with engineering practice, in the gas-driven water experiment, gas is injected from one side of the core to be tested, and in the water-driven gas experiment, formation water is injected from the other side of the core to be tested.

[0105] Specifically, in the gas-driven water pipeline, gas enters from the first end of the core holder (end a of the core holder) and is discharged from the second end of the core holder (end b of the core holder); in the water-driven gas pipeline, formation water enters from the second end of the core holder (end b of the core holder) and is discharged from the first end of the core holder (end a of the core holder). Figure 1 When the system shown in FIG. 1 performs the water drive gas experiment in step S4, the steps performed are as follows:

[0106] 1) Open valves 1, 3, and 5 of hexagon valve a, valves 2 and 3 of three-way valve a, valves 1 and 2 of three-way valve b, valves 2 and 3 of hexagon valve b, valve f and valve j, turn on the vacuum pump, observe vacuum gauge a and vacuum gauge b, and after the displacement system pipelines and valves are evacuated to vacuum, turn off the vacuum pump, close valve 3 of hexagon valve a, valve 3 of hexagon valve b, valve f and valve j, and open valve a, valve c, valve e, back pressure valve a, and valve 4 of hexagon valve b;

[0107] 2) Displace formation water flow Q according to the design wj Set up the displacement pump and start it, so that the formation water enters the core from the core holder end b, and drives the gas in the core from the core holder end a to the drying tube b. Record the high-precision gas flow meter data in real time within n seconds to obtain the average gas flow Q gj , and simultaneously record the average value P of the pressure sensor readings at the core inlet and outlet within n seconds 1j and P 2j (At this time, pressure sensor b is the inlet pressure sensor, and pressure sensor a is the outlet pressure sensor), calculate the pressure difference △P at both ends of the core j , the mass of formation water pumped into the core is calculated according to the displacement time (n seconds) of the displacement pump, thereby calculating the core water saturation S wj , calculate the relative permeability of gas and formation water at the water saturation according to the gas flow rate, formation water flow rate and core absolute permeability (each mass of expelled formation water can calculate a water saturation value, corresponding to a gas flow rate and pressure difference), and obtain at least 7 groups of data to ensure that the relative permeability curve is relatively smooth.

[0108] Implementation 3:

[0109] Under multi-cycle injection and production working conditions, the gas-water two-phase seepage law will change with the injection and production cycle and is not static. In order to accurately analyze the situation in each injection and production cycle and improve the accuracy of the measurement process, the difference between this embodiment and the above-mentioned embodiments 1 and 2 is that steps S3 to S5 in the above-mentioned embodiments 1 and 2 are repeated to complete multiple cycles of gas-water mutual drive phase permeability tests and obtain multi-cycle mutual drive gas-water relative permeability curves.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for determining a gas-water relative permeability curve, characterized in that: The determination method is implemented by a determination system, which includes a core holder, a displacement pump, an air-drive water pipeline and a water-drive gas pipeline; the confining pressure end of the core holder is connected to the confining pressure pump, one end of the core holder is connected to the air-drive water pipeline and the water-drive gas pipeline through valves, the air-drive water pipeline is connected to valve d, back pressure valve a, high pressure gas source and valve b in sequence, the other end of valve b is connected to the displacement pump, the back pressure end of back pressure valve a is connected to valve e and back pressure pump b in sequence, and the method includes the following steps: 1) Saturate the core to be tested with formation water; 2) Calculate the displacement pressure of gas drive and displacement flow rate of water drive according to the external environment of the source of the core to be tested. The displacement pressure of gas drive is determined according to the formation pressure and the injection-production pressure difference of the gas storage reservoir. Set the confining pressure according to the overlying formation pressure of the gas storage reservoir where the core to be tested comes from and start the confining pressure pump. Calculate the wet weight Gw of the core to be tested under pressurized conditions, Gw = Gw1-Gw2, Gw1 is the wet weight of the core to be tested under normal pressure; Gw2 is the mass of formation water pressed out from the core to be tested under confining pressure conditions; 3) Conduct gas-displacement water experiment: Open the back pressure valve a and valve e, set the back pressure pump b according to the displacement pressure of the gas drive and start it, then turn on the displacement pump, inject gas into the core to be tested, and measure the mass / flow rate of the driven formation water and the gas flow rate in real time; then calculate the gas phase relative permeability, water phase relative permeability and irreducible water saturation under the water saturation of the gas drive process according to the mass / flow rate of the formation water, the gas flow rate and the wet weight of the core to be tested. The calculation formula of irreducible water saturation is: S wc1 =(G w -G wit ) / G w Where: S wc1 is the bound water saturation; G wit It is the total mass of formation water driven out during gas flooding; 4) Conduct water drive gas experiment: According to the displacement flow rate of the water drive, formation water is injected into the core to be tested, and the gas flow rate driven out by the water drive is measured in real time. The relative permeability of the gas phase and the relative permeability of the water phase under the water saturation of the water drive process are calculated according to the displacement flow rate and the gas flow rate driven out by the water drive; the water saturation S of the water drive process wj The calculation formula is: S wj =S wc1 +(nρ w Q wj ) / G w Where n is time, ρ w is the formation water density, Q wj The displacement flow rate for water-displacing gas; 5) Construct gas phase relative permeability curve and water phase relative permeability curve; 6) Repeat steps 3)-5) to complete multiple cycles of gas-water mutual drive relative permeability test to obtain multi-cycle mutual drive gas-water relative permeability curves.

2. The method for determining the gas-water relative permeability curve according to claim 1, characterized in that: In the gas-displacing-water experiment, gas is injected from one side of the core to be tested, and in the water-displacing-gas experiment, formation water is injected from the other side of the core to be tested.

3. The method for determining the gas-water relative permeability curve according to claim 1, characterized in that: The step 2) also includes calculating the confining pressure, and performing a gas-displacing-water experiment and a water-displacing-gas experiment under the confining pressure; the confining pressure is greater than the displacement pressure.

4. The method for determining the gas-water relative permeability curve according to claim 1, characterized in that: The steps 3) and 4) also include the step of evacuating the experimental pipeline before the experiment.

5. The method for determining the gas-water relative permeability curve according to claim 1, characterized in that: In step 3), the calculation formulas for the gas phase relative permeability and the water phase relative permeability are: S wi =(G w -G wi ) / G w △P i =P 1i -P 2i Q wi =G wi / r w K rwi =(Q wi μ w L) / (kA△P i ) K rgi =(Q gi μ g L) / (kA△P i ) Where: S wi G is the water saturation of the core at time t during gas flooding; wi P is the average mass of formation water driven out continuously for n seconds during gas drive; 1i is the average pressure at the core inlet at time t during gas drive; P 2i is the core outlet pressure at time t during gas drive; △P i Q is the pressure difference between the two ends of the core at time t during gas drive; wi is the formation water flow rate at time t during gas drive; Q gi is the gas flow rate at time t during gas drive; k is the absolute permeability of the core; K rwi is the water saturation S wi Relative permeability of water phase under K rgi is the water saturation S wi The relative permeability of the gas phase under w is the formation water density, μ w is the viscosity of the water phase, μ g is the gas phase viscosity, A is the cross-sectional area of ​​the core, and L is the length of the core.

6. The method for determining the gas-water relative permeability curve according to claim 5, characterized in that: In step 4), the relative permeability K of the gas phase rgj , relative permeability of water phase K rwj The calculation formula is: △P j =P 2j -P 1j K rwj =(Q wj μ w L) / (kA△P j ) K rgj =(Q gj μ g L) / (kA△P j ) Among them, Q gj is the average gas flow rate during water flooding, △P j is the pressure difference between the two ends of the core during water flooding, P 1j P is the average pressure at the core inlet within n seconds during water flooding; 2j is the average pressure at the core outlet during water flooding within n seconds, △P j It is the pressure difference between the two ends of the core during water flooding.

7. The method for determining the gas-water relative permeability curve according to claim 6, characterized in that: The step 4) also includes calculating the residual gas saturation according to the irreducible water saturation and the displacement flow rate, and the calculation formula is: S gr1 =1- S wc1 -TQ wj Where: S gr1 is the residual gas saturation during water flooding; T is the experimental time.

8. A system for measuring gas-water relative permeability curve, characterized in that: include: A core holder, used to hold the core to be tested; A displacement pump, used to provide displacement power; An air-drive water pipeline, the displacement pump and the core holder are connected to the air-drive water pipeline, and is used for conducting an air-drive water experiment. A back-pressure valve is connected to the air-drive water pipeline, and the back-pressure end of the back-pressure valve is connected to the valve and the back-pressure pump in sequence. In the air-drive water experiment, the back-pressure valve and the valve are opened before the displacement pump is opened; A water-drive gas pipeline, to which the displacement pump and the core holder are connected, for conducting a water-drive gas experiment; A gas flow meter, arranged downstream of the gas-driven water pipeline and the water-driven gas pipeline, for detecting the gas flow; A formation water quality / flow detector is arranged downstream of the gas drive water pipeline and the water drive gas pipeline, and is used to detect the formation water quality / flow; the system includes a unit for implementing the method for determining the gas-water relative permeability curve according to claim 1.

9. The system for measuring the gas-water relative permeability curve according to claim 8, characterized in that: In the gas-drive-water pipeline, gas enters from the first end of the core holder and is output from the second end of the core holder; in the water-drive-gas pipeline, formation water enters from the second end of the core holder and is output from the first end of the core holder.

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