A method for predicting gas cross-flow in different injection-production modes of CO2 flooding

Abstract

The present invention relates to the technical field of oilfield development, and in particular to a method for predicting gas crosstalk in different CO2 drive injection and production modes. The method comprises the following steps: component simulation of the original formation oil; establishing a corresponding CO2 drive gas additive component production chart according to the oil reservoir injection and production mode; sampling the oil reservoir on-site, and performing gas phase component analysis on the obtained output gas; comparing the obtained output gas gas phase components on the corresponding CO2 drive gas additive component output chart, and when the content of a specific additive component increases or decreases, it indicates that gas crosstalk will occur after a period of time. The method of the present invention takes into account the differences caused by different injection and production modes, improves the accuracy of gas crosstalk prediction, and provides a basis for injection and production regulation in the middle and late stages of CO2 drive.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to a method for predicting gas cross-over in different CO2 injection and production modes. Background Art

[0002] CO2 flooding can both improve oil recovery and reduce CO2 emissions, and is one of the most promising CO2 applications. However, due to the fact that CO2 mobility is much greater than crude oil mobility and the inherent heterogeneity of the reservoir, CO2 often flows preferentially along the permeability-dominant channel during gas flooding, forming gas channeling. The gas channeling phenomenon has directly limited the further improvement of CO2 flooding recovery, so the identification and prediction of gas channeling has become the difficulty and focus of current research. Since the interaction mechanism between CO2 and crude oil in CO2 flooding is complex and is greatly affected by the reservoir, fluid properties, and the temperature and pressure environment, there are also large differences in the gas channeling rules for different injection and production modes: immiscible continuous gas drive, miscible continuous gas drive, gas-water alternation, injection-production coupling, etc., and targeted predictions are needed.

[0003] At present, the main methods for predicting gas channeling include theoretical calculation method, CO2 characteristic component method, gas-oil ratio method, etc. The theoretical calculation method usually does not take into account the heterogeneity of the formation, and the prediction result is quite different from the actual situation; the CO2 characteristic component method generally uses gas and liquid chromatography to test the production rate of CO2 components, and the gas-oil ratio method predicts gas channeling based on the gas-oil ratio in the oil well. These two methods are more suitable for judging gas channeling of N2, air and other gases that are difficult to dissolve in oil, and have a slow response, so they are suitable for gas channeling identification rather than prediction. At the same time, these commonly used methods do not consider the different effects of different CO2 injection and production modes on the gas channeling law.

[0004] Chinese invention patent CN105003234B discloses a new method for judging gas channeling in CO2-driven oil reservoirs. The new method includes: step 1, collecting and collating the gas-oil ratio and the CO2 content of the oil wells in the CO2-driven oil reservoir, and drawing a relationship chart of the production gas-oil ratio and the CO2 content of the produced gas; step 2, dividing the relationship chart of the production gas-oil ratio and the CO2 content of the produced gas into multiple regions according to the current formation pressure level and the properties of the crude oil; step 3, analyzing the characteristics of each region, judging the relationship chart of the production gas-oil ratio and the CO2 content of the produced gas, and the upper right corner area is the area of ​​CO2 gas channeling. However, this patent can only be used to identify gas channeling after it occurs, and cannot be predicted in advance before gas channeling occurs. At the same time, it also does not consider the differential effects caused by different injection and production modes of CO2 drive.

[0005] Chinese patent application CN111209687A discloses a method for identifying gas channeling in CO2 flooding. The method comprises: step 1, calculating the crude oil dissolved gas-oil ratio curve of the target oil layer; step 2, calculating the formation water dissolved gas-oil ratio curve; step 3, calculating the critical gas-oil ratio curve under different water content conditions; step 4, judging gas channeling based on the relative position of the critical CO2 gas channeling gas-oil ratio on the curve obtained in step 3 under different water content conditions. This invention can also only be used to identify gas channeling after it occurs, and cannot be predicted in advance before it occurs. At the same time, it also does not take into account the differential effects caused by different injection and production modes of CO2 flooding. Summary of the invention

[0006] The main purpose of the present invention is to provide a new method for predicting gas crossover in different injection and production modes of CO2 flooding, which can respond before the production gas-oil ratio rises rapidly, and provide a basis for injection and production regulation in the middle and late stages of CO2 flooding.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for predicting gas crosstalk in different CO2 drive injection and production modes, which comprises the following steps: component simulation of original formation oil; establishing a corresponding CO2 drive gas additive component production chart according to the reservoir injection and production mode; sampling the reservoir on-site and performing gas phase component analysis on the obtained output gas; comparing the obtained gas phase components of the output gas on the corresponding CO2 drive gas additive component output chart, and when the content of a specific additive component increases or decreases, it indicates that gas crosstalk will occur after a period of time.

[0009] Preferably, the method for component simulation of the original formation oil comprises the following steps: performing high-pressure PVT phase analysis test and chromatographic analysis on the original formation oil of the target reservoir to obtain the full hydrocarbon component data and basic physical property parameters of the original formation oil;

[0010] During simulation, N2 / C1 was considered as one component; CO2 was considered as a single component; components with similar physical and chemical properties were fitted as one added component.

[0011] Further preferably, the basic physical property parameters include viscosity, density, volume coefficient, compressibility, and saturation pressure.

[0012] More preferably, the number of the added components is 8-12.

[0013] Further preferably, the error between the simulated fluid requirement and the full-component fluid phase diagram is less than 5%.

[0014] Preferably, the method for establishing the CO2 flooding gas additive component output chart comprises the following steps:

[0015] S1, using the E300 module in Eclipse, input the simulated component fluid and calculate the typical five-point unit well pattern gas drive process under different CO2 injection and production modes. The calculation cutoff point is the production gas-oil ratio of 2000m 3 / m 3 ;

[0016] S2, draw a graph showing the relationship between the added component gas phase production rate and the production gas-oil ratio over time under different injection and production modes.

[0017] Further preferably, different injection-production modes of CO2 drive include immiscible continuous gas drive, miscible continuous gas drive, gas-water alternation, and injection-production coupling.

[0018] Preferably, the method for comparing the gas phase components of the output gas obtained in different injection and production modes on the corresponding CO2 flooding gas phase component output chart is as follows:

[0019] Immiscible continuous gas drive: The C1 gas phase content begins to increase, indicating that gas channeling will occur after a period of time; the C2+ and C5+ gas phase contents begin to increase, indicating that gas channeling has already occurred;

[0020] Mixed-phase continuous gas drive: The rise of C1, C2+, and C5+ gas phase contents indicates that gas channeling will occur after a period of time. The rise of C1 and C2+ gas phase contents is earlier than that of C5+, which can be used for more advanced prediction; the rise of C7+ and C9+ gas phase contents indicates that gas channeling has already occurred;

[0021] Injection-production coupling: The rise of C2+, C5+, and C7+ gas phase contents indicates that gas channeling will occur after a period of time. The rise time of C2+, C5+, and C7+ gas phase contents is in sequence, which can be used for prediction at different lead times; the decline of C2+, C5+, and C7+ gas phase contents indicates that gas channeling has occurred;

[0022] Gas-water alternation: The increase in C2+ and C5+ gas phase content indicates that gas channeling will occur after a period of time. The increase in C2+ gas phase content is earlier than that in C5+, which can be used for more advanced prediction; the decrease in C2+ gas phase content indicates that gas channeling has occurred.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The method of the present invention establishes a CO2 flooding gas additive component output chart to analyze the component content change trend of the on-site output gas, and can respond before the production gas-oil ratio rises rapidly, thereby achieving advanced warning of gas channeling.

[0025] The method of the present invention takes into account the differences caused by different injection-production modes, improves the accuracy of gas channeling prediction, and provides a basis for injection-production regulation in the middle and late stages of CO2 flooding. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 It is a flow chart of a method for predicting gas cross-flow in different injection and production modes of CO2 flooding according to a specific embodiment of the present invention;

[0028] Figure 2 This is a typical gas phase component output chart;

[0029] Figure 3 This is the gas phase addition component output plate described in the specific application example 1 of the present invention.

[0030] Figure 4 This is the gas phase addition component output plate described in the specific application example 2 of the present invention.

[0031] Figure 5 This is the gas phase addition component output plate described in specific application example 3 of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0034] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0035] Example A method for predicting gas cross-flow in different injection and production modes of CO2 flooding

[0036] The method comprises the following steps:

[0037] Step 1. Simulate the components of the original formation oil:

[0038] The original formation oil of the target reservoir is subjected to high-pressure PVT phase analysis test and chromatographic analysis to obtain the full hydrocarbon component data and basic physical property parameters of the original formation oil; the basic physical property parameters include viscosity, density, volume coefficient, compressibility coefficient, and saturation pressure.

[0039] During simulation, N2 / C1 is taken as one component; CO2 is taken as one component alone; components with similar physical and chemical properties are fitted as one additional component. The number of the additional components is 8 to 12.

[0040] The error between the simulated fluid and the phase diagram of the full-component fluid is required to be less than 5%.

[0041] Step 2. According to the reservoir injection and production mode, establish the corresponding CO2 flooding gas addition component production chart:

[0042] S1, using the E300 module in Eclipse, input the simulated component fluid and calculate the typical five-point unit well pattern gas drive process under different CO2 injection and production modes. The calculation cutoff point is the production gas-oil ratio of 2000m 3 / m 3 ;

[0043] S2, draw a graph showing the relationship between the added component gas phase production rate and the production gas-oil ratio over time under different injection and production modes.

[0044] Different injection-production modes of CO2 flooding include immiscible continuous gas flooding, miscible continuous gas flooding, gas-water alternation, and injection-production coupling.

[0045] Step 3. Take samples at the reservoir site and analyze the gas phase components of the produced gas;

[0046] S1, on-site sampling of the reservoir, generally gas sampling is done once a week. When the content of gas phase components changes, the sampling frequency is increased to once a day.

[0047] S2, performing gas chromatography analysis on the obtained gas sample, and combining the analyzed components according to the simulated components in step 1. The gas chromatography analysis conditions are conventional chromatography conditions for reservoir gas phase detection.

[0048] Step 4. Compare the obtained gas phase components of the output gas on the corresponding CO2 flooding gas phase additive component output chart. When the content of a specific additive component increases or decreases, it means that gas channeling will occur after a period of time.

[0049] Immiscible continuous gas drive: The C1 gas phase content begins to increase, indicating that gas channeling will occur after a period of time; the C2+ and C5+ gas phase contents begin to increase, indicating that gas channeling has already occurred;

[0050] Mixed-phase continuous gas drive: The rise of C1, C2+, and C5+ gas phase contents indicates that gas channeling will occur after a period of time. The rise of C1 and C2+ gas phase contents is earlier than that of C5+, which can be used for more advanced prediction; the rise of C7+ and C9+ gas phase contents indicates that gas channeling has already occurred;

[0051] Injection-production coupling: The rise of C2+, C5+, and C7+ gas phase contents indicates that gas channeling will occur after a period of time. The rise time of C2+, C5+, and C7+ gas phase contents is in sequence, which can be used for prediction at different lead times; the decline of C2+, C5+, and C7+ gas phase contents indicates that gas channeling has occurred;

[0052] Gas-water alternation: The increase in C2+ and C5+ gas phase content indicates that gas channeling will occur after a period of time. The increase in C2+ gas phase content is earlier than that in C5+, which can be used for more advanced prediction; the decrease in C2+ gas phase content indicates that gas channeling has occurred.

[0053] Application Example 1

[0054] The G reservoir is a low permeability reservoir developed by CO2 injection, the injection pressure and the average reservoir pressure are below the miscible pressure, and the development mode is immiscible continuous gas drive. The method described in the above embodiment is used to predict gas channeling.

[0055] The original formation oil was simulated into 11 components: CO2, C1, C2+, C5+, C7+, C9+, C11+, C13+, C17+, C21+ and C26+;

[0056] Using the E300 module in Eclipse, input the simulated additive fluid, calculate the typical five-point unit well pattern gas drive process, and draw the CO2 miscible continuous gas drive gas additive component output chart, such as Figure 3 As shown;

[0057] Analysis of on-site produced gas sampling showed that the C1 content of the produced gas increased after 2260 days of development;

[0058] By comparing the on-site gas production sampling and analysis results with the gas phase added component output chart, it is expected that the gas-oil ratio of the oil reservoir will begin to increase after 150 days, and gas channeling will occur after 600 days. In order to delay gas channeling, the oil reservoir will be switched to injection-production coupling development in advance, which is expected to increase the recovery rate by 3%.

[0059] Application Example 2

[0060] The M oil reservoir is a fault block oil reservoir developed by CO2 injection, and the development mode is gas-water alternation. The method described in the above embodiment is used to predict gas crossover.

[0061] The original formation oil was simulated into 11 components: CO2, C1, C2+, C5+, C7+, C9+, C11+, C13+, C17+, C21+ and C26+;

[0062] Using the E300 module in Eclipse, input the simulated additive fluid, calculate the typical five-point unit well pattern gas drive process, and draw the CO2 gas-water alternating gas phase additive component output chart, as shown in the figure. Figure 4 As shown;

[0063] The on-site gas sampling and analysis showed that the C2+ content of the gas produced increased after 2710 days of development, and the C5+ content of the gas produced increased after 2730 days of development;

[0064] Comparing the on-site gas sampling and analysis results with the gas phase plus component output chart, it is expected that the gas-oil ratio of the reservoir will begin to rise after 50 days, and gas channeling will occur after 2000 days. In fact, the gas-oil ratio of the reservoir began to rise after 67 days, and after 800 days, it was transferred to the injection-production coupling development mode, which is expected to increase the recovery rate by 1.8%.

[0065] Application Example 3

[0066] The O reservoir is an ultra-low permeability reservoir developed by CO2 injection, and the development mode is CO2 injection-production coupling. The method described in the above embodiment is used to predict gas channeling.

[0067] The original formation oil was simulated into 11 components: CO2, C1, C2+, C5+, C7+, C9+, C11+, C13+, C17+, C21+ and C26+;

[0068] Using the E300 module in Eclipse, input the simulated additive fluid, calculate the typical five-point unit well pattern gas drive process, and draw the CO2 gas-water alternating gas phase additive component output chart, as shown in the figure. Figure 5 As shown;

[0069] The on-site gas sampling and analysis showed that the C2+ content of the gas produced increased after 3410 days of development, and the C5+ content of the gas produced increased after 3450 days of development;

[0070] By comparing the on-site gas sampling and analysis results with the gas phase component output chart, it is expected that the gas-oil ratio of the reservoir will begin to increase after 100 days. In fact, the gas-oil ratio of the reservoir began to increase after 122 days.

[0071] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A gas channeling prediction method applicable to different injection and production modes of CO2 flooding, characterized in that: The method comprises the following steps: simulating the components of the original formation oil, during which N2 / C1 is taken as one component; CO2 is taken as one component alone; components with similar physical and chemical properties are fitted as one additive component; according to the injection and production mode of the reservoir, a corresponding CO2 flooding gas additive component output chart is established; sampling is performed on site of the reservoir, and gas phase component analysis is performed on the obtained output gas; the gas phase components of the obtained output gas are compared on the corresponding CO2 flooding gas additive component output chart, and when the content of a specific additive component increases or decreases, it indicates that gas channeling will occur after a period of time; The method for establishing a CO2 flooding gas additive component output chart includes the following steps: S1, using the E300 module in Eclipse, input the simulated component fluid and calculate the typical five-point unit well pattern gas drive process under different CO2 injection and production modes. The calculation cutoff point is the production gas-oil ratio of 2000m 3 / m 3 ; S2, draw a graph showing the relationship between the added component gas phase production rate and the production gas-oil ratio over time under different injection and production modes.

2. The method according to claim 1, characterized in that: The method for component simulation of original formation oil comprises the following steps: performing high pressure PVT phase analysis test and chromatographic analysis on the original formation oil of the target oil reservoir to obtain the full hydrocarbon component data and basic physical property parameters of the original formation oil.

3. The method according to claim 2, characterized in that: The basic physical property parameters include viscosity, density, volume coefficient, compressibility, and saturation pressure.

4. The method according to claim 2, characterized in that: The number of the added components is 8 to 12.

5. The method according to claim 2, characterized in that: The error between the simulated fluid and the phase diagram of the full-component fluid is required to be less than 5%.

6. The method according to claim 1, characterized in that: Different injection-production modes of CO2 flooding include immiscible continuous gas flooding, miscible continuous gas flooding, gas-water alternation, and injection-production coupling.

7. The method according to claim 1, characterized in that: In the non-miscible continuous gas drive injection-production mode, the gas phase components of the produced gas are compared on the corresponding CO2 drive gas additive component output chart as follows: the increase in C1 gas phase content indicates that gas channeling will occur after a period of time; the increase in C2+ and C5+ gas phase contents indicates that gas channeling has already occurred.

8. The method according to claim 1, characterized in that: In the mixed-phase continuous gas flooding injection-production mode, the gas phase components of the produced gas are compared on the corresponding CO2 flooding gas phase component output chart as follows: The increase in C1, C2+, and C5+ gas phase contents indicates that gas channeling will occur after a period of time. The increase in C1 and C2+ gas phase contents is earlier than that of C5+, which can be used for more advanced predictions. The increase in C7+ and C9+ gas phase contents indicates that gas channeling has already occurred.

9. The method according to claim 1, characterized in that: In the injection-production coupling mode, the obtained gas phase components of the produced gas are compared on the corresponding CO2 flooding gas phase component output chart as follows: The rise of C2+, C5+, and C7+ gas phase contents indicates that gas channeling will occur after a period of time. The rise time of C2+, C5+, and C7+ gas phase contents is in sequence, which can be used for prediction at different lead times. The gas phase contents of C2+, C5+, and C7+ changed from rising to falling, indicating that gas channeling had occurred; Or in the gas-water alternating injection-production mode, the gas phase components of the produced gas obtained are compared on the corresponding CO2 drive gas additive component output chart as follows: the increase in C2+ and C5+ gas phase contents indicates that gas channeling will occur after a period of time, and the increase time of C2+ gas phase content is earlier than that of C5+, which can be used for more early prediction; the change from an increase to a decrease in C2+ gas phase content indicates that gas channeling has occurred.

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