Method for measuring gas-gas phase permeability curve in process of injecting CO2 to drive CH4

Abstract

The invention relates to the technical field of petroleum and natural gas exploration and development, and discloses a method for measuring a gas-gas relative permeability curve in a CO2 injection CH4 displacement process, which comprises the following steps: S1, rock core preparation: extracting, cleaning and drying a rock core taken back on site, and measuring the length L, the diameter d, the rock core porosity phi and the permeability K of the rock core; s2, fluid preparation: putting the two intermediate containers filled with experimental fluid into a drying oven, and respectively filling CO2 gas and CH4 gas into the two intermediate containers; according to the method for measuring the gas-gas relative permeability curve in the process of injecting CO2 to drive CH4, the influence of high-temperature and high-pressure conditions of a stratum on the gas volume is considered, the method is more in line with actual production, the available value of experimental data is high, the method can be more close to the reservoir gas-driven gas seepage process through experiments, the experimental data precision is improved, and the method is suitable for popularization and application. The blank of a gas-gas relative permeability determination method in gas-driven gas development research is filled, and important basic data is provided for gas reservoir development.

Description

Technical Field

[0001] The invention relates to the technical field of oil and natural gas exploration and development, and in particular to a method for determining a gas-gas phase permeability curve in a process of injecting CO2 to drive CH4. Background Art

[0002] In the middle and late stages of gas reservoir development, the formation pressure is rapidly depleted, the natural mining energy is insufficient, and the gas reservoir production decreases rapidly. At present, CO2 injection to improve gas reservoir recovery is a mining method with great development potential. This is because injecting CO2 into the gas reservoir formation in the middle and late stages of development can not only supplement the formation pressure and improve the gas reservoir recovery rate, but also realize the geological storage of CO2. In addition, CO2 exhibits a supercritical state with gas viscosity and liquid density under high temperature and high pressure formation conditions, which is conducive to improving the volume sweep efficiency and microscopic displacement efficiency of CO2 in the gas reservoir. However, driven by the pressure gradient and concentration gradient, CO2 displaces natural gas in porous media and diffusion occurs. Therefore, during the displacement process, there is no obvious displacement interface between CO2 and natural gas, which makes it difficult to evaluate the development effect of gas reservoirs. In the process of gas reservoir development, the phase permeability curve is one of the important basic data. The phase permeability curve can be used to determine the residual gas saturation, judge the reservoir type, analyze the pore structure, etc.

[0003] At present, there is no mature and effective method for measuring gas-gas phase permeability curve in gas-driven gas development research, so it is very necessary to establish a method for measuring gas-gas phase permeability curve in the process of CO2 injection to drive CH4. Summary of the invention

[0004] To solve the above technical problems, the present invention provides a method for determining the gas-gas phase permeability curve during CO2 injection to drive CH4, which fills the gap in the gas-gas phase permeability determination method in gas drive gas development research and provides important basic data for gas reservoir development.

[0005] The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process provided by the present invention comprises the following steps:

[0006] S1. Core preparation:

[0007] After extracting, cleaning and drying the cores retrieved on site, the length L, diameter d, core porosity φ and permeability K of the cores were measured;

[0008] S2. Fluid preparation:

[0009] Put two intermediate containers equipped with experimental fluids into the oven, respectively assemble CO2 gas and CH4 gas into the two intermediate containers, then raise the oven temperature to the experimental temperature T, and pressurize the intermediate containers to the experimental pressure P0;

[0010] S3, saturated CH4:

[0011] The dried core is placed in a core holder, and the core holder is placed in an oven;

[0012] Open the confining pressure pump 2 to apply appropriate confining pressure to the core;

[0013] After setting the oven to a constant experimental temperature T, set a constant pressure P0, start the injection pump, turn on the switch of the intermediate container containing CH4, and inject CH4 gas into the core until the CH4 content in the output gas component at the outlet of the core holder is 100%, close the outlet switch, and then maintain the inlet injection pressure P0 until the internal pressure of the core is stable and then close the inlet switch;

[0014] S4, phase permeability test of the process of injecting CO2 to displace CH4, which includes the following sub-steps:

[0015] S5. Correction of gas production: Convert the gas production value recorded under ground conditions into the gas production value under formation conditions:

[0016] G' CO2 (t) = G CO2 (t)B CO2 ;

[0017] G' CH4 (t) = G CH4 (t)B CH4 ;

[0018] Among them, B CO2 is the volume coefficient of CO2, B CH4 is the volume coefficient of CH4.

[0019] S6. Calculate the CO2 relative permeability K at each moment r1 and CH4 relative permeability K r2 And the CO2 saturation S at the outlet of the rock sample CO2e , and normalize it:

[0020]

[0021] ΔP(t)=P1(t)-P2(t),

[0022] Normalization:

[0023]

[0024] in:

[0025] ——CH4 percentage, decimal;

[0026] ——There is no cumulative CH4 extraction;

[0027] V(t)——The cumulative gas production volume;

[0028] V P ——pore volume of rock sample;

[0029] K r2 ——CH4 relative permeability, decimal;

[0030] K r1 ——CO2 relative permeability, decimal;

[0031] I——Relative injectivity or flowability ratio, no reason;

[0032] Q(t)——gas flow rate at the outlet end of the rock sample at time t, cm 3 / s;

[0033] Q0——CH4 flow rate produced at the outlet end of the rock sample at the initial moment, cm 3 / s;

[0034] Δp0——initial displacement pressure difference, MPa;

[0035] Δp(t)——displacement pressure difference at time t, MPa;

[0036] ——The viscosity of CO2 under the corresponding temperature and pressure conditions at time t, mPa*s;

[0037] ——The viscosity of CH4 under the corresponding temperature and pressure conditions at time t, mPa*s;

[0038] S CO2e ——CO2 saturation at the outlet end of the rock sample, decimal;

[0039] a, b——adjustment index, generally related to core physical properties;

[0040] ——normalized CO2 saturation, decimal;

[0041] ——bound CO2 saturation, decimal;

[0042] ——Residual CH4 saturation, decimal.

[0043] Preferably, the step S4 includes the following sub-steps:

[0044] S4.1. Set the constant pressure P0, start the injection pump, turn on the outlet switch of the core holder, and start recording the experimental data;

[0045] S4.2. Record the pressure difference ΔP(t) between the inlet and outlet of the core holder at each moment, collect the produced gas, and record the experimental data;

[0046] S4.3. Use a gas chromatograph to analyze the component content of the output gas collected at each time and record the output CO2 gas volume G CO2 (t) and the amount of CH4 gas produced G CH4 (t);

[0047] S4.4. Gas drive is performed until the outlet output gas no longer contains CH4, i.e., bound gas state. The experiment is terminated after the effective permeability of CO2 in the bound gas state is measured.

[0048] Preferably, during the fluid preparation process, the assembly and heating of CO2 and CH4 gases are performed under controlled conditions to ensure the accuracy of the experimental temperature and pressure.

[0049] Preferably, in the CH4 saturation step, the inlet switch is closed only after the internal pressure of the core is stabilized to avoid pressure fluctuations affecting the experimental results.

[0050] Preferably, in the phase permeability test of the process of injecting CO2 to displace CH4, the pressure difference at both ends of the core and the produced gas composition are continuously recorded, and the experimental conditions are adjusted in real time to obtain accurate phase permeability data.

[0051] Compared with the related art, the method for determining the gas-gas phase permeability curve in the process of CO2 injection to drive CH4 provided by the present invention has the following beneficial effects:

[0052] The present invention provides a method for determining a gas-gas phase permeability curve during a CO2 injection to drive CH4:

[0053] 1. The present invention takes into account the influence of high temperature and high pressure conditions of the formation on the gas volume, which is more in line with production practice. The experimental data has high utilization value. Through the experiment, it can be closer to the gas drive gas seepage process of the reservoir, thus improving the accuracy of the experimental data.

[0054] 2. The present invention can analyze the component content of the produced gas by using a gas chromatograph to measure the produced amount of each component gas;

[0055] 3. The method for determining the gas-gas phase permeability curve during the CO2 injection to drive CH4 provided by the present invention fills the gap in the gas-gas phase permeability determination method in gas drive gas development research and provides important basic data for gas reservoir development. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A schematic structural diagram of a preferred embodiment of a method for determining a gas-gas phase permeability curve during a CO2 injection CH4 flooding process provided by the present invention;

[0057] Figure 2 It is the CO2-CH4 phase permeability curve;

[0058] Figure 3 This is the shape of the phase permeability curve obtained by conventional method.

[0059] Numbers in the figure: 1. core holder; 2. confining pressure pump; 3. injection pump; 4. intermediate container 1; 5. intermediate container 2; 6. oven; 7. pressure gauge; 8. meteorological chromatograph. DETAILED DESCRIPTION

[0060] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0061] Please refer to Figure 1-3 The present invention proposes a method for determining a gas-gas phase permeability curve during a CO2 injection CH4 flooding process, comprising the following steps:

[0062] S1. Core preparation: After extracting, cleaning and drying the cores retrieved from the site, measure the core length L = 30 cm, diameter d = 2.5 cm, core porosity φ = 10%, permeability K = 30 mD, and calculate the core pore volume V P =32.29cm 3 .

[0063] S2. Fluid preparation: Place the intermediate container 1 4 and the intermediate container 2 5 assembled with the experimental fluid into the oven 6, and respectively assemble the CO2 gas and the CH4 gas into the intermediate container 1 4 and the intermediate container 2 5, and then increase the temperature of the oven 6 to the experimental temperature of 81°C, and at the same time pressurize the intermediate container 1 4 and the intermediate container 2 5 to the experimental pressure of 35MPa.

[0064] S3, saturated CH4: put the dried core into the core holder 1, and put the core holder 1 into the oven 6; turn on the confining pressure pump 2, and apply a confining pressure of 40MPa to the core; after setting a constant experimental temperature T for the oven 6, set a constant pressure of 35MPa, start the injection pump 3, turn on the switch of the intermediate container 5 filled with CH4, and inject CH4 gas into the core until the CH4 content in the output gas component at the outlet of the core holder 1 is 100%, close the outlet switch, and then maintain the inlet injection pressure at 35MPa until the internal pressure of the core is stable and then close the inlet switch.

[0065] S4, phase permeability test of the process of injecting CO2 to displace CH4, which includes the following sub-steps:

[0066] S4.1. Set the constant pressure to 35 MPa, start the injection pump 3, turn on the outlet switch of the core holder 1, and start recording the experimental data;

[0067] S4.2. Record the pressure difference ΔP(t) between the inlet and outlet of the core holder at each moment, collect the produced gas, and record the experimental data;

[0068] S4.3. Use a gas chromatograph to analyze the component content of the output gas collected at each time and record the output CO2 gas volume G CO2 (t) and the amount of CH4 gas produced G CH4 (t);

[0069] Table 1 shows the CO2 gas volume and CH4 gas volume produced on the surface of the core:

[0070] Time / s <![CDATA[CO2 surface production, cm 3 > <![CDATA[CH4 surface production, cm 3 > 3314 0 5740 4205 182.98 232.02 5328 267.98 127.02 6439 298.48 106.52 7679 293.65 96.35 8419 315.69 89.31 9177 332.25 77.74 10044 321.21 78.79 10920 332.73 72.27 11760 342.75 62.25 12565 375.17 39.83 13311 363.15 36.85 14088 381.6 38.40 14841 367.78 32.22 15613 397.68 27.32 16418 383.8 26.20 17215 376.51 23.49

[0071] S4.4. Gas drive is performed until the outlet output gas no longer contains CH4, i.e., bound gas state. The experiment is terminated after the effective permeability of CO2 in the bound gas state is measured.

[0072] S5. Correction of gas production: Convert the gas production value recorded under ground conditions into the gas production value under formation conditions.

[0073] G' CO2 (t) = G CO2 (t)B CO2 ;

[0074] G' CH4 (t) = G CH4 (t)B CH4 ;

[0075] Among them, B CO2 is the volume coefficient of CO2, B CH4 is the volume coefficient of CH4.

[0076] Table 2 shows the corrected CO2 and CH4 gas output from the core:

[0077] Time / s <![CDATA[CO2 formation production, cm 3 > <![CDATA[CH4 formation production, cm 3 > 3314 0 20.77 4205 0.58 0.74 5328 0.77 0.36 6439 0.83 0.30 7679 0.81 0.27 8419 0.86 0.24 9177 0.89 0.21 10044 0.86 0.21 10920 0.89 0.19 11760 0.90 0.16 12565 0.98 0.10 13311 0.95 0.10 14088 1.00 0.10 14841 0.96 0.08 15613 1.02 0.07 16418 0..99 0.07 17215 0.97 0.06

[0078] S6. Calculate the CO2 relative permeability K at each moment r1 and CH4 relative permeability K r2 And the CO2 saturation S at the outlet of the rock sample CO2e , and normalize it:

[0079]

[0080]

[0081] ΔP(t)=P1(t)-P2(t),

[0082] Normalization:

[0083]

[0084] in:

[0085] ——CH4 percentage, decimal;

[0086] ——There is no cumulative CH4 extraction;

[0087] V(t)——The cumulative gas production volume;

[0088] V P ——pore volume of rock sample;

[0089] K r2 ——CH4 relative permeability, decimal;

[0090] K r1 ——CO2 relative permeability, decimal;

[0091] I——Relative injectivity or flowability ratio, no reason;

[0092] Q(t)——gas flow rate at the outlet end of the rock sample at time t, cm 3 / s;

[0093] Q0——CH4 flow rate produced at the outlet end of the rock sample at the initial moment, cm 3 / s;

[0094] Δp0——initial displacement pressure difference, MPa;

[0095] Δp(t)——displacement pressure difference at time t, MPa;

[0096] ——The viscosity of CO2 under the corresponding temperature and pressure conditions at time t, mPa*s; ——The viscosity of CH4 under the corresponding temperature and pressure conditions at time t, mPa*s;

[0097] S CO2e ——CO2 saturation at the outlet end of the rock sample, decimal;

[0098] a, b——adjustment index, generally related to core physical properties;

[0099] ——normalized CO2 saturation, decimal;

[0100] ——bound CO2 saturation, decimal;

[0101] ——Residual CH4 saturation, decimal.

[0102] Table 3 shows the normalized data:

[0103] Sco2 Krco2 Krch4 0.0000 0.0000 1.0000 0.0980 0.3184 0.8240 0.1960 0.4493 0.6636 0.2940 0.5496 0.5192 0.3920 0.6341 0.3911 0.4900 0.7085 0.2798 0.5880 0.7757 0.1857 0.6860 0.8375 0.1094 0.7840 0.8950 0.0519 0.8820 0.9489 0.0145 0.9800 1 0

[0104] According to Table 3, a CO2-CH4 phase permeability curve is drawn, such as Figure 2 As shown;

[0105] The phase permeability curve obtained by conventional method is as follows: Figure 3 shown.

[0106] Compared with the phase permeability curve obtained by conventional methods, this method takes into account the influence of high temperature and high pressure conditions of the formation on the gas volume, which is more in line with production practice. The experimental data has high utilization value. Through experiments, it can be closer to the gas drive gas seepage process of the reservoir, thus improving the accuracy of the experimental data.

[0107] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for determining the gas-gas phase permeability curve during CO2 injection to drive CH4, characterized in that: The steps include: S1. Core preparation: After extracting, cleaning and drying the cores retrieved on site, the length L, diameter d, core porosity φ and permeability K of the cores were measured; S2. Fluid preparation: Put two intermediate containers equipped with experimental fluids into an oven, respectively assemble CO2 gas and CH4 gas into the two intermediate containers, then raise the oven temperature to the experimental temperature T, and pressurize the two intermediate containers to the experimental pressure P0; S3, saturated CH4: The dried core is placed in a core holder, and the core holder is placed in an oven; Turn on the confining pressure pump and apply appropriate confining pressure to the core; After setting the oven to a constant experimental temperature T, set a constant pressure P0, start the injection pump, turn on the switch of the intermediate container containing CH4, and inject CH4 gas into the core until the CH4 content in the output gas component at the outlet of the core holder is 100%, close the outlet switch, and then maintain the inlet injection pressure P0 until the internal pressure of the core is stable and then close the inlet switch; S4, phase permeability test of the process of injecting CO2 to displace CH4; S5. Calibration of gas production: Convert the gas production value recorded under surface conditions into the gas production value under formation conditions: G’ CO2 (t)=G CO2 (t)B CO2 ; G’ CH4 (t)=G CH4 (t)B CH4 ; Among them, B CO2 is the volume coefficient of CO2, B CH4 is the volume coefficient of CH4. S6. Calculate the CO2 relative permeability K at each moment r1 and CH4 relative permeability K r2 And the CO2 saturation S at the outlet of the rock sample CO2e , and normalized.

2. The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process according to claim 1, characterized in that: The step S4 includes the following sub-steps: S4.

1. Set the constant pressure P0, start the injection pump, open the outlet switch of the core holder 1, and start recording the experimental data; S4.

2. Record the pressure difference ΔP(t) between the inlet and outlet of the core holder at each moment, collect the produced gas, and record the experimental data; S4.

3. Use a gas chromatograph to analyze the component content of the output gas collected at each time and record the output CO2 gas volume G CO2 (t) and the amount of CH4 gas produced G CH4 (t); S4.

4. Gas drive is performed until the outlet output gas no longer contains CH4, i.e., bound gas state. The experiment is terminated after the effective permeability of CO2 in the bound gas state is measured.

3. The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process 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.

4. The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process according to claim 1, characterized in that: In the CH4 saturation step, the inlet switch is closed only after the internal pressure of the core is stabilized to avoid pressure fluctuations affecting the experimental results.

5. The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process according to claim 1, characterized in that: In the phase permeability test of the CO2 injection to displace CH4 process, the pressure difference at both ends of the core and the produced gas composition are continuously recorded, and the experimental conditions are adjusted in real time to obtain accurate phase permeability data.

6. The method for determining the gas-gas phase permeability curve during the CO2 injection CH4 flooding process according to claim 1, characterized in that: When calculating the gas relative permeability and saturation at each moment, a specific formula is used to normalize the data to eliminate experimental errors and improve the comparability of the data.

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