Accounting method for actual carbon dioxide sequestration amount of ultra-low permeability reservoir

Abstract

The invention relates to an ultralow permeability reservoir carbon dioxide actual sequestration amount accounting method which comprises the steps that a three-dimensional geologic model of carbon dioxide oil displacement and sequestration is established, the three-dimensional geologic model comprises at least one gas injection well and at least two oil production wells, and a relational expression of a simulated production gas-oil ratio and a simulated sequestration rate is obtained through numerical simulation; the simulated production gas-oil ratio is corrected through the actual average gas-oil ratio after gas injection, and a corrected simulated production gas-oil ratio and simulated storage rate relational expression is obtained; the background value of each monitoring object before the first gas injection well starts to be injected and the monitoring value of each monitoring object at the moment to be detected are obtained, and the sum of the absolute values of the difference values of the background values and the corresponding monitoring values of all the monitoring objects is the carbon dioxide leakage rate; the sum of the product of the actual carbon dioxide injection rate and the simulated sealing rate and the carbon dioxide leakage rate from the beginning of injection of the first gas injection well to the to-be-detected moment serves as the actual carbon dioxide sealing amount.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield carbon dioxide flooding, storage and safety monitoring, and in particular to a method for calculating and verifying the actual storage amount of carbon dioxide in an oil reservoir. Background Art

[0002] The possible leakage risk paths of CO2 flooding and storage are wellbore, faults or cracks, caprock or other closed zones. Since the permeability of ultra-low permeability reservoirs is less than 1mD, the CO2 injection pressure is high. As the amount of CO2 injected increases, the reservoir pressure increases, which can easily cause the opening of existing cracks in the caprock or other closed zones and the generation of new cracks. Due to the high density of injection and production wells in the reservoir, and the influence of factors such as injection and production system and wellbore integrity, the risk of wellbore leakage is further increased, which may cause CO2 to leak into groundwater, atmosphere, etc. Different from CO2 storage in saline layers, the CO2 flooding and storage process includes two stages of "oil flooding-well shut-in", covering multiple succession processes of "simultaneous injection and production-production only without injection-stop injection and production". At the same time, CO2 will be produced from production wells due to factors such as low CO2 viscosity, formation cracks and strong heterogeneity. Under the coupling influence of the above uncertain factors, the actual storage amount of CO2 in ultra-low permeability reservoirs is difficult to determine.

[0003] The actual storage volume of carbon dioxide in oil reservoirs is the key to clarifying the emission reduction volume, and it is also the basis for the inclusion of CCUS projects (carbon capture, utilization and storage) in the carbon trading market. At present, domestic CCUS projects all believe that there is no geological leakage of carbon dioxide, but they are limited by the short operation time and small scale of the projects, the short monitoring cycle and the lack of monitoring data support. At the same time, the actual storage volume of carbon dioxide accounting methods are based on theoretical analysis, and it is impossible to accurately calculate the actual storage volume of carbon dioxide at different stages. Yanchang Oilfield has carried out large-scale and long-term field practice of carbon dioxide flooding and storage, and established a method for calculating the actual storage volume of carbon dioxide in ultra-low permeability oil reservoirs based on field practice. Summary of the invention

[0004] The present invention aims to solve the above problems and propose a method for calculating the actual carbon dioxide storage capacity in ultra-low permeability reservoirs.

[0005] The technical solution of the present invention is: A method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs is as follows: A three-dimensional geological model of carbon dioxide flooding and storage is established, wherein the three-dimensional geological model includes at least one gas injection well and no less than two oil production wells, and a relationship between a simulated production gas-oil ratio and a simulated storage rate is obtained through numerical simulation; the simulated production gas-oil ratio is corrected by the actual average gas-oil ratio after gas injection, and a relationship between the corrected simulated production gas-oil ratio and the simulated storage rate is obtained; Obtain the background value of each monitoring object before the first gas injection well starts injection and the monitoring value of each monitoring object at the time of testing. The sum of the absolute values ​​of the differences between the background values ​​of all monitoring objects and the corresponding monitoring values ​​is the carbon dioxide leakage; The actual storage capacity of carbon dioxide is taken as the sum of the product of the actual injection volume of carbon dioxide and the simulated storage rate from the start of injection of the first gas injection well to the time of testing and the carbon dioxide leakage.

[0006] The specific process of determining the relationship between the simulated production gas-oil ratio and the simulated storage rate is as follows: numerical simulation is carried out on the three-dimensional geological model, and the simulated storage rate is determined according to the simulated injection volume and the simulated storage volume of the gas injection well; the simulated production gas-oil ratio is determined according to the simulated gas production and the simulated oil production of the oil production well, and the relationship between the simulated production gas-oil ratio and the simulated storage rate is obtained by fitting.

[0007] The relationship between the simulated production gas-oil ratio and the simulated storage rate is specifically: ; Where: is the simulated storage rate, dimensionless; To simulate the production gas-oil ratio, dimensionless.

[0008] The relationship between the corrected simulated production gas-oil ratio and the simulated storage rate is specifically obtained as follows: the gas-oil ratio of all oil producing wells is monitored to obtain the sum of the gas-oil ratios of all oil producing wells, and the arithmetic mean thereof is taken as the actual average gas-oil ratio; the simulated production gas-oil ratio is compared with the actual average gas-oil ratio. Make a fitting correction: ; Where: is the actual average gas-oil ratio, dimensionless; is the corrected simulated production gas-oil ratio, dimensionless; Then the corrected simulated production gas and oil Ratio and simulated storage rate The relationship is: .

[0009] The specific process of obtaining the carbon dioxide leakage is as follows: ; ; Where: is the amount of carbon dioxide leakage, in t (tons); i is any monitoring object, with values ​​of 1, 2…i…m, dimensionless; j is the time to be measured, dimensionless; is the leakage volume of the ith monitoring object from the first gas injection well to the time of measurement, dimensionless; is the background value of the i-th monitoring object; is the monitoring value of the i-th monitoring object at the time to be tested.

[0010] The monitoring objects at least include caprock, wellbore and groundwater.

[0011] The specific process of obtaining the actual storage amount of carbon dioxide is as follows: ; Where: S is the actual storage amount of carbon dioxide, in tons; I It is the actual amount of carbon dioxide injected from the start of injection into the first gas injection well to the time of measurement, in t.

[0012] The three-dimensional geological model is established based on petrel software and adopts a multi-level phase-controlled modeling method.

[0013] The numerical simulation is realized by eclipse software.

[0014] The technical effects of the present invention are: The present invention can accurately calculate the actual storage volume of carbon dioxide, clarify the emission reduction volume of CCUS projects, and provide a scientific basis for the inclusion of CCUS projects in the carbon trading market, so that the certified emission reduction volume can enter the carbon market for trading or be used for corporate tax subsidies. At the same time, it can promote the development and market application of CCUS technology; at the same time, it can verify, quantify and validate the safety of geological storage of carbon dioxide to ensure the reliability and long-term stability of the storage process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the relationship between the simulated production gas-oil ratio and the simulated storage rate.

[0016] Figure 2 This is the fitting diagram of the actual average gas-oil ratio versus the simulated production gas-oil ratio.

[0017] Figure 3 This is a chart showing the actual amount of carbon dioxide injected and the actual amount of carbon dioxide stored. DETAILED DESCRIPTION

[0018] Specific application cases Yanchang Oilfield A test area, the first gas injection well started injection in August 2012; the actual carbon dioxide storage volume after 10 years of gas injection (2022) is calculated as follows: Step 1: Based on the petrel software, a multi-level phase-controlled modeling method was used to establish a three-dimensional geological model of CO2 flooding and storage in the A test area of ​​Yanchang Oilfield. The three-dimensional geological model includes 2 CO2 injection wells and 10 oil production wells. The three-dimensional geological model was numerically simulated based on the eclipse software, and the simulated storage rate was determined based on the simulated injection volume and simulated storage volume of the CO2 injection wells. ; Determine the simulated production gas-oil ratio based on the simulated gas production and simulated oil production of the oil well , fitting simulation production gas-oil ratio Simulated storage rate Relational formula: .

[0019] Step 2: Carry out gas-oil ratio monitoring on oil production wells to obtain the actual gas-oil ratio of 10 oil production wells R 1 、R 2… R 10 , and then obtain the actual average gas-oil ratio of the reservoir where the oil well is located The actual average gas-oil ratio in 2022 is 285. The simulated production gas-oil ratio To make corrections: ; Then the corrected simulated production gas-oil ratio is obtained and simulated storage rate Relational formula: .

[0020] Step 3: From May 2011 to May 2012, a one-year background value monitoring was carried out, and the monitoring objects included the caprock, wellbore, deep groundwater, shallow groundwater, surface water, surface soil gas and atmosphere: After the first gas injection well began injection in August 2012, leakage risk monitoring was carried out to obtain the monitoring values ​​of each monitoring object; the monitoring values ​​are detailed in Table 1; Table 1 Monitoring values ; Cover layer: No microseismic events were detected in the cover layer; Wellbore: The background value of the corrosion rate of the gas injection wells at depths of 400m, 1000m and 1600m is 0.008~0.016mm / a, and the monitoring value is 0.011~0.016mm / a. Both the monitoring value and the background value are lower than the corrosion rate of 0.076mm / a specified by the industry standard; Deep groundwater: pH background value is 6.87~7.17, Ca 2+ The background value of the concentration is 3.95~20.84mg / L, Mg2+ The background value of concentration is 167.73~360.71mg / L; the monitoring value of pH is 6.98~7.05, Ca 2+ The monitored concentration values ​​are 3.99~20.04mg / L, Mg 2+ The monitored concentration values ​​were 170.22~360.11mg / L; Shallow groundwater: pH background value is 7.72~7.95, Ca 2+ The background value of the concentration is 86.25~138.95mg / L, Mg 2+ The background value of the concentration is 55.07~99.89mg / L; the pH monitoring value of shallow groundwater after gas injection is 7.73~7.93, Ca 2+ The concentration monitoring value is 89.55~131.05mg / L, Mg 2+ The concentration monitoring value is 61.07~95.07mg / L; Surface water: pH background value is 7.68~8.07, Ca 2+ The background value of the concentration is 55.34~56.99mg / L, Mg 2+ The background value of the concentration is 37.99~41.06mg / L; the monitoring value of pH is 7.85~8.02, Ca 2+ The monitored concentration values ​​are 55.43~56.19mg / L, Mg 2+ The monitored concentration values ​​were 38.21~40.98mg / L; Surface soil gas: The background value of carbon dioxide concentration is 0.91%~1.38%, and the monitoring value of carbon dioxide concentration is 0.91%~1.36%; Atmosphere: The background value of carbon dioxide concentration is 0.04%~0.041%, and the monitoring value of carbon dioxide concentration is 0.04%~0.041%; Comparing the background value and monitoring value of each monitoring object, no significant changes were found in each monitoring object. It was comprehensively judged that no leakage occurred in the A test area of ​​Yanchang Oilfield; that is, .

[0021] Step 4: Based on the actual situation, the actual amount of carbon dioxide injected from the first gas injection well in August 2012 to 2022 I 9.8×10 4 t, calculate the actual storage capacity of carbon dioxide in the Yanchang Oilfield A test area in 2022: .

[0022] Results verification: Combined with the article "Lake et al Fifty years of field observations Lessons for CO2 storage from CO2 enhanced oil recovery", and based on the function between the actual CO2 storage and the actual CO2 injection summarized from more than 100 CO2 oil recovery projects that have been carried out in the United States, a chart of the actual CO2 injection and actual CO2 storage was obtained; The pore volume of the A test area of ​​Yanchang Oilfield is about 85.8×10 4 t, actual CO2 injection volume from the first gas injection well in August 2012 to 2022 I 9.8×10 4 t, converted to 0.114 PV; combined with the actual carbon dioxide injection volume and the actual carbon dioxide storage volume chart, the corresponding actual carbon dioxide storage volume is 0.08 PV, which is 6.86×10 4 t.

[0023] The error between this calculation method and the method reported in the article is only ; Where: K is the error, dimensionless.

[0024] Therefore, the error between this calculation method and the method reported in the article is less than 5%, which meets the error range, indicating that the method for calculating the actual storage capacity of carbon dioxide in ultra-low permeability reservoirs proposed in the present invention is reasonable.

Claims

1. A method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs, characterized in that: Here’s how: A three-dimensional geological model of carbon dioxide flooding and storage is established, wherein the three-dimensional geological model includes at least one gas injection well and no less than two oil production wells, and a relationship between a simulated production gas-oil ratio and a simulated storage rate is obtained through numerical simulation; the simulated production gas-oil ratio is corrected by the actual average gas-oil ratio after gas injection, and a relationship between the corrected simulated production gas-oil ratio and the simulated storage rate is obtained; Obtain the background value of each monitoring object before the first gas injection well starts injection and the monitoring value of each monitoring object at the time of testing. The sum of the absolute values ​​of the differences between the background values ​​of all monitoring objects and the corresponding monitoring values ​​is the carbon dioxide leakage; The actual storage capacity of carbon dioxide is taken as the sum of the product of the actual injection volume of carbon dioxide and the simulated storage rate from the start of injection of the first gas injection well to the time of testing and the carbon dioxide leakage.

2. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 1 is characterized in that: The specific process of determining the relationship between the simulated production gas-oil ratio and the simulated storage rate is as follows: numerical simulation is carried out on the three-dimensional geological model, and the simulated storage rate is determined according to the simulated injection volume and the simulated storage volume of the gas injection well; the simulated production gas-oil ratio is determined according to the simulated gas production and the simulated oil production of the oil production well, and the relationship between the simulated production gas-oil ratio and the simulated storage rate is obtained by fitting.

3. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 2 is characterized in that: The relationship between the simulated production gas-oil ratio and the simulated storage rate is specifically: ； Where: is the simulated storage rate, dimensionless; To simulate the production gas-oil ratio, dimensionless.

4. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 3 is characterized in that: The relationship between the corrected simulated production gas-oil ratio and the simulated storage rate is specifically obtained as follows: the gas-oil ratio of all oil producing wells is monitored to obtain the sum of the gas-oil ratios of all oil producing wells, and the arithmetic mean thereof is taken as the actual average gas-oil ratio; the simulated production gas-oil ratio is compared with the actual average gas-oil ratio. Make a fitting correction: ； Where: is the actual average gas-oil ratio, dimensionless; is the simulated production gas-oil ratio after correction, dimensionless; Then the corrected simulated production gas-oil ratio is obtained and simulated storage rate The relationship is: 。 5. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 4 is characterized in that: The specific process of obtaining the carbon dioxide leakage is as follows: ； ； Where: is the carbon dioxide leakage, unit is t; i is any monitoring object, with values ​​of 1, 2…i…m, dimensionless; j is the time to be measured, dimensionless; is the leakage volume of the ith monitoring object from the first gas injection well to the time of measurement, dimensionless; is the background value of the i-th monitoring object; is the monitoring value of the i-th monitoring object at the time to be tested.

6. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 5 is characterized in that: The monitoring objects at least include caprock, wellbore and groundwater.

7. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 6 is characterized in that: The specific process of obtaining the actual storage amount of carbon dioxide is as follows: ； Where: S is the actual storage amount of carbon dioxide, unit is t; I is the actual amount of carbon dioxide injected from the start of injection into the first gas injection well to the time of measurement, in t.

8. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 1 is characterized in that: The three-dimensional geological model is established based on petrel software and adopts a multi-level phase-controlled modeling method.

9. The method for calculating the actual storage amount of carbon dioxide in ultra-low permeability reservoirs according to claim 1, characterized in that: The numerical simulation is realized by eclipse software.

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