A method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding.

Abstract

The present application relates to the technical field of oil and gas exploration and development, and discloses a method for determining gas-gas relative permeability curve in CO2 injection and CH4 displacement process.The present application establishes an experimental test and mathematical processing method for gas-gas two-phase seepage mechanism by regarding supercritical CO2 and CH4 as two independent fluids, aiming at the blank of lacking effective gas-gas relative permeability determination means in the prior art.The method comprises the following steps: core and fluid preparation, CH4 saturation, and CO2 injection and displacement test.The key of the method is as follows: the gas chromatograph is used to monitor the output gas components in real time, so that the components can be finely metered;the high temperature and high pressure volume correction mathematical model is introduced to convert the ground measurement value into the fluid volume under the formation condition;and the double gas permeability calculation and saturation normalization processing model is constructed to realize quantitative and accurate determination of the gas-gas relative permeability curve.The present application solves the problems that the components are difficult to distinguish and the relative permeability parameters are difficult to obtain in the gas displacement process, and provides high-precision basic data for dynamic evaluation of the reservoir gas displacement.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development technology, and in particular to a method for determining the gas-gas phase permeation curve during the CO2 injection-CH4 flooding process. Background Technology

[0002] In the mid-to-late stages of gas reservoir development, formation pressure rapidly depletes, natural extraction energy becomes insufficient, and gas production declines rapidly. Currently, CO2 injection for enhanced gas recovery is a promising development method. This is because injecting CO2 into the formation of gas reservoirs in the mid-to-late stages of development not only replenishes formation pressure and improves gas recovery but also achieves geological storage of CO2. Furthermore, CO2 exhibits a supercritical state with gas viscosity and liquid density under high-temperature and high-pressure formation conditions, which is beneficial for improving the volumetric sweep efficiency and micro-displacement benefits of CO2 in the gas reservoir. However, driven by pressure and concentration gradients, CO2 displacement of natural gas in porous media involves diffusion, resulting in no clear displacement interface between CO2 and natural gas during the displacement process. This makes evaluating the effectiveness of gas reservoir development difficult. In the process of gas reservoir development, relative permeability curves are one of the important basic data. These curves can be used to determine residual gas saturation, identify reservoir type, and analyze pore structure.

[0003] Currently, there is no mature and effective method for determining gas-gas phase permeation curves in gas-driven gas development research. Therefore, it is very necessary to establish a method for determining gas-gas phase permeation curves during CO2 injection to drive CH4. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for determining the gas-gas phase permeation curve during CO2 injection to drive CH4, filling a gap in gas-gas phase permeation measurement methods in gas-driven gas development research and providing important basic data for gas reservoir development.

[0005] The method for determining the gas-gas phase permeation curve during the CO2-driven CH4 process provided by this invention includes the following steps: S1. Core preparation: After extracting, cleaning, and drying the core samples retrieved from the site, the length L, diameter d, porosity φ, and permeability K of the core samples were measured. S2, Fluid Preparation: Place the two intermediate containers for assembling the experimental fluid into an oven, and assemble CO2 gas and CH4 gas into the two intermediate containers respectively. Then raise the temperature of the oven to the experimental temperature T, and pressurize the intermediate containers to the experimental pressure P0. S3, saturated CH4: The dried core is placed into the core holder, and the core holder is placed into the drying oven; Turn on confining pressure pump 2 to apply appropriate confining pressure to the core. After setting a constant experimental temperature T in the oven, set a constant pressure P0, start the injection pump, open the switch of the intermediate container containing CH4, and inject CH4 gas into the core until the CH4 content in the gas component produced at the outlet of the core holder is 100%. Then close the outlet switch and maintain the inlet injection pressure P0 until the internal pressure of the core stabilizes and then close the inlet switch. S4, Phase permeation test of CO2 displacement of CH4 process, which includes the following sub-steps: S5. Gas production correction: Convert the gas production value recorded under surface conditions to the gas production value under formation conditions. ; ; in, This is the volume index of CO2. is the volume factor of CH4.

[0006] S6. Calculate the relative CO2 permeability K at each time point. r1 Relative permeability K of CH4 r2 and the CO2 saturation S at the rock sample outlet end face CO2e And perform normalization: , , , ,

[0007] , ,

[0008] , Normalization process: ;

[0009]

[0010] in: —Percentage containing CH4, decimal; —Dimensionless cumulative CH4 collection; —Dimensionless cumulative gas production; —Porosity of the rock sample; —Relative permeability of CH4, decimal; —Relative CO2 permeability, decimal; —Relative injection capacity or flow capacity ratio, dimensionless; —Gas production flow rate at the rock sample outlet face at time t, in cm 3 / s; —Initial CH4 flow rate at the rock sample outlet face, cm 3 / s; —Initial displacement pressure difference, MPa; —Displacement pressure difference at time t, MPa; — The viscosity of CO2 at time t under the corresponding temperature and pressure conditions, in MPa·s; — The viscosity of the gas produced at the outlet under the corresponding temperature and pressure conditions at time t, in MPa·s; — CO2 saturation at the rock sample outlet face, decimal; a, b – parameter adjustment indices, generally related to core physical properties; — Normalized CO2 saturation, decimal; —Bound CO2 saturation, decimal; — Residual CH4 saturation, decimal.

[0011] Preferably, step S4 includes the following sub-steps: S4.1 Set the constant pressure P0, start the injection pump, and at the same time open the outlet switch of the core holder to start recording experimental data; S4.2 Record the pressure difference ΔP(t) at the inlet and outlet of the core holder at each time point, collect the produced gas, and record the experimental data. S4.3 Analyze the component content of the produced gas collected at each time point using a gas chromatograph, and record the amount of CO2 produced, G. CO2 (t) and CH4 gas production G CH4 (t); S4.4 The gas drive continues until the outlet gas no longer contains CH4, i.e., the bound gas state. The experiment ends after measuring the effective CO2 permeability under the bound gas state.

[0012] Preferably, during fluid preparation, the assembly and heating of CO2 and CH4 gases are carried out under controlled conditions to ensure the accuracy of experimental temperature and pressure.

[0013] Preferably, in the CH4 saturation step, the inlet switch is closed only after the pressure inside the core has stabilized to avoid pressure fluctuations affecting the experimental results.

[0014] Preferably, in the phase permeability test of the CO2 injection process displacing CH4, the experimental conditions are adjusted in real time by continuously recording the pressure difference at both ends of the core and the composition of the produced gas, so as to obtain accurate phase permeability data.

[0015] Compared with related technologies, the method for determining the gas-gas phase permeation curve during the CO2-driven CH4 process provided by this invention has the following advantages: This invention provides a method for determining the gas-gas phase permeation curve during the CO2-to-CH4 flooding process: 1. This invention takes into account the influence of high temperature and high pressure conditions in the formation on gas volume, which is more in line with actual production. The experimental data has high utilization value. Through experiments, the gas driving and seepage process of reservoir gas can be more closely approximated, thus improving the accuracy of experimental data.

[0016] 2. This invention utilizes a gas chromatograph to analyze the component content of the extracted gas, thereby enabling the measurement of the extracted amount of each component gas. 3. The method for determining the gas-gas phase permeation curve during CO2 injection to drive CH4 provided by this invention fills the gap in gas-gas phase permeation determination methods in gas-driven gas development research, and provides important basic data for gas reservoir development. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a preferred embodiment of the method for determining the gas-gas phase permeation curve during the CO2-driven CH4 process provided by the present invention. Figure 2 This is a CO2-CH4 phase permeation curve. Figure 3 The shape of the relative permeability curve obtained by conventional methods.

[0018] The following are labeled in the diagram: 1. Core holder; 2. Confining pressure pump; 3. Injection pump; 4. Intermediate container one; 5. Intermediate container two; 6. Drying oven; 7. Pressure gauge; 8. Gas chromatograph. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Please refer to the following: Figure 1-3The present invention proposes a method for determining the gas-gas phase permeation curve during the CO2-driven CH4 process, comprising the following steps: S1. Core Preparation: After extracting, cleaning, and drying the core samples retrieved from the site, measure the core length L=30cm, diameter d=2.5cm, and core porosity. Given a permeability K = 30 mD, calculate the pore volume V of the core. P =32.29cm 3 .

[0021] S2. Fluid preparation: Place intermediate containers 4 and 5, which are used to assemble the experimental fluid, into oven 6. Then, assemble CO2 gas and CH4 gas into intermediate containers 4 and 5, respectively. Raise the temperature of oven 6 to the experimental temperature of 81℃, and pressurize intermediate containers 4 and 5 to the experimental pressure of 35MPa.

[0022] S3, Saturated CH4: Place the dried core into the core holder 1, and place the core holder 1 into the oven 6; turn on the confining pressure pump 2 to apply a confining pressure of 40 MPa to the core; set a constant experimental temperature T to the oven 6, then set a constant pressure of 35 MPa, start the injection pump 3, open the switch of the intermediate container 5 containing CH4, and inject CH4 gas into the core until the CH4 content in the gas component produced at the outlet of the core holder 1 is 100%, close the outlet switch, and then maintain the inlet injection pressure of 35 MPa until the internal pressure of the core stabilizes and then close the inlet switch.

[0023] S4, Phase permeation test of CO2 displacement of CH4 process, which includes the following sub-steps: S4.1 Set the constant pressure to 35MPa, start the injection pump 3, and at the same time open the outlet switch of the core holder 1 to start recording experimental data; S4.2 Record the pressure difference ΔP(t) at the inlet and outlet of the core holder at each time point, collect the produced gas, and record the experimental data. S4.3 Analyze the component content of the produced gas collected at each time point using a gas chromatograph, and record the amount of CO2 produced, G. CO2 (t) and CH4 gas production G CH4 (t); Table 1 shows the CO2 and CH4 gas production at the surface of the core sample: ; S4.4 The gas drive continues until the outlet gas no longer contains CH4, i.e., the bound gas state. The experiment ends after measuring the effective CO2 permeability under the bound gas state.

[0024] S5. Gas production correction: Convert the gas production value recorded under surface conditions to the gas production value under formation conditions. ; ; in, This is the volume index of CO2. is the volume factor of CH4.

[0025] Table 2 shows the corrected CO2 and CH4 gas production from the core: ; S6. Calculate the relative CO2 permeability K at each time point. r1 Relative permeability K of CH4 r2 and the CO2 saturation S at the rock sample outlet end face CO2e And perform normalization: , , , ,

[0026] , ,

[0027] , Normalization process: ;

[0028]

[0029] in: —Percentage containing CH4, decimal; —Dimensionless cumulative CH4 collection; —Dimensionless cumulative gas production; —Porosity of the rock sample; —Relative permeability of CH4, decimal; —Relative CO2 permeability, decimal; I – Relative injection capacity or flow capacity ratio, dimensionless; —Gas production flow rate at the rock sample outlet face at time t, in cm 3 / s; —Initial CH4 flow rate at the rock sample outlet face, cm 3 / s; —Initial displacement pressure difference, MPa; —Displacement pressure difference at time t, MPa; — The viscosity of CO2 at time t under the corresponding temperature and pressure conditions, in MPa·s; — The viscosity of the gas produced at the outlet under the corresponding temperature and pressure conditions at time t, in MPa·s; — CO2 saturation at the rock sample outlet face, decimal; a, b – parameter adjustment indices, generally related to core physical properties; — Normalized CO2 saturation, decimal; —Bound CO2 saturation, decimal; — Residual CH4 saturation, decimal.

[0030] Table 3 shows the data after normalization: ; Based on Table 3, plot the CO2-CH4 phase permeation curve, as shown below. Figure 2 As shown; The morphology of the relative permeability curve obtained by conventional methods, such as Figure 3 As shown.

[0031] Compared with the morphology of the relative permeability curve obtained by conventional methods, this method takes into account the influence of high temperature and high pressure conditions in the formation on the gas volume, which is more in line with actual production. The experimental data has high utilization value, and the experiment can more closely approximate the gas driving and seepage process of reservoir gas, thus improving the accuracy of the experimental data.

[0032] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding, characterized in that, The steps include the following: S1. Core preparation: After extracting, cleaning, and drying the core samples retrieved from the site, the length L, diameter d, porosity φ, and permeability K of the core samples were measured. S2, Fluid Preparation: Place the two intermediate containers for assembling the experimental fluid into an oven, and assemble CO2 gas and CH4 gas into the two intermediate containers respectively. Then raise the temperature of the oven to the experimental temperature T, and pressurize the two intermediate containers to the experimental pressure P0. S3, saturated CH4: The dried core is placed into the core holder, and the core holder is placed into the drying oven; Turn on the confining pressure pump to apply appropriate confining pressure to the core. After setting a constant experimental temperature T in the oven, set a constant pressure P0, start the injection pump, open the switch of the intermediate container containing CH4, and inject CH4 gas into the core until the CH4 content in the gas component produced at the outlet of the core holder is 100%. Then close the outlet switch and maintain the inlet injection pressure P0 until the internal pressure of the core stabilizes and then close the inlet switch. S4. Phase permeation test of CO2 displacing CH4 process, including the following sub-steps: S4.1 Set the constant pressure P0, start the injection pump, and at the same time open the outlet switch of the core holder 1 to start recording experimental data; S4.2 Record the pressure difference ΔP(t) at the inlet and outlet of the core holder at each time point, collect the produced gas, and record the experimental data. S4.3 Analyze the component content of the produced gas collected at each time point using a gas chromatograph, and record the amount of CO2 produced, G. CO2 (t) and CH4 gas production G CH4 (t); S4.

4. The gas drive continues until the outlet gas no longer contains CH4, i.e., the bound gas state. The experiment ends after measuring the effective CO2 permeability under the bound gas state. S5. Gas production correction: Convert the gas production values ​​recorded under surface conditions to gas production values ​​under formation conditions: ； ； in, This is the volume index of CO2. The volume index of CH4; S6. Calculate the relative CO2 permeability K at each time point. r1 Relative permeability K of CH4 r2 and the CO2 saturation S at the rock sample outlet end face CO2e And perform normalization: ， ， ， ， ， ， ， ， ， Normalization process: ； ； ； in: —Percentage containing CH4, decimal; —Dimensionless cumulative CH4 collection; —Dimensionless cumulative gas production; —Porosity of the rock sample; —Relative permeability of CH4, decimal; —Relative CO2 permeability, decimal; —Relative injection capacity or flow capacity ratio, dimensionless; —Gas production flow rate at the rock sample outlet face at time t, in cm 3 / s; —Initial CH4 flow rate at the rock sample outlet face, cm 3 / s; —Initial displacement pressure difference, MPa; —Displacement pressure difference at time t, MPa; — The viscosity of CO2 at time t under the corresponding temperature and pressure conditions, in MPa·s; — The viscosity of the gas produced at the outlet under the corresponding temperature and pressure conditions at time t, in MPa·s; —CO2 saturation at the rock sample outlet face, decimal; a, b – parameter adjustment indices, generally related to core physical properties; — Normalized CO2 saturation, decimal; —Bound CO2 saturation, decimal; — Residual CH4 saturation, decimal.

2. The method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding according to claim 1, characterized in that, During fluid preparation, the assembly and heating of CO2 and CH4 gases were carried out under controlled conditions to ensure the accuracy of experimental temperature and pressure.

3. The method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding according to claim 1, characterized in that, In the CH4 saturation step, the inlet switch is closed only after the pressure inside the core has stabilized to avoid pressure fluctuations affecting the experimental results.

4. The method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding according to claim 1, characterized in that, In the CO2 injection process for CH4 displacement phase permeability testing, the pressure difference between the two ends of the core and the composition of the produced gas are continuously recorded, and the experimental conditions are adjusted in real time to obtain accurate phase permeability data.

5. The method for determining the gas-gas phase permeation curve during CO2-driven CH4 flooding according to claim 1, characterized in that, When calculating the relative permeability and saturation of gas at various times, a specific formula is used to normalize the data in order to eliminate experimental errors and improve the comparability of the data.

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