A method for calculating the actual carbon dioxide storage volume in an ultra-low permeability reservoir

Abstract

The present invention relates to a method for calculating the actual carbon dioxide storage volume in an ultra-low permeability reservoir. A three-dimensional geological model for carbon dioxide flooding and storage is established, which includes at least one gas injection well and no less than two oil production wells. The relationship between the simulated production gas-oil ratio and the 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 to obtain the relationship between the corrected simulated production gas-oil ratio and the simulated storage rate; the background values of each monitoring object before the first gas injection well starts injecting and the monitoring values of each monitoring object at the measurement moment are obtained, and the sum of the absolute values of the differences between the background values and the corresponding monitoring values of all monitoring objects is the carbon dioxide leakage amount; the sum of the product of the actual carbon dioxide injection amount and the simulated storage rate and the carbon dioxide leakage amount during the period from the start of injection of the first gas injection well to the measurement moment is used as the actual carbon dioxide storage volume.

Description

Technical Field

[0001] The present invention relates to the technical fields of carbon dioxide flooding and storage in oilfields and safety monitoring, and specifically relates to a method for calculating and verifying the actual carbon dioxide storage volume in an oil reservoir. Background Technique

[0002] Possible leakage risk paths for carbon dioxide flooding and storage are wellbores, faults or fractures, cap rocks or other sealing zones. Since the reservoir permeability of ultra-low permeability oil reservoirs is less than 1 mD and the carbon dioxide injection pressure is high, as the carbon dioxide injection volume increases, the reservoir pressure rises, which easily causes the opening of existing fissures and the generation of new fractures in the cap rock or other sealing zones; due to the large density of injection-production well patterns in the oil reservoir and the influence of factors such as injection-production production systems and wellbore integrity, the wellbore leakage risk is further increased, which may lead to the leakage of carbon dioxide into groundwater, the atmosphere, etc.; different from carbon dioxide storage in saline aquifers, the carbon dioxide flooding and storage process includes two stages of "oil flooding - well shut-in", covering multiple replacement processes of "simultaneous injection and production - only production without injection - stop injection and stop production", and at the same time, affected by factors such as low carbon dioxide viscosity, formation fractures and strong heterogeneity, carbon dioxide will be produced from production wells. Under the combined influence of the above uncertain factors, it is difficult to determine the actual carbon dioxide storage volume in ultra-low permeability oil reservoirs.

[0003] The actual carbon dioxide storage volume in an oil reservoir is the key to clarifying the emission reduction volume and is also the basis for CCUS projects (carbon capture, utilization and storage) to be included in the carbon trading market. At present, domestic CCUS projects all believe that there is no geological leakage of carbon dioxide, but limited by the short operation time, small scale, short monitoring period and lack of monitoring data support of the projects, and at the same time, the carbon dioxide actual storage volume calculation methods are all based on theoretical analysis and cannot accurately calculate the actual carbon dioxide storage volume in different stages. Yanchang Oilfield has carried out large-scale and long-term carbon dioxide flooding and storage field practices and established a method for calculating the actual carbon dioxide storage volume in ultra-low permeability oil reservoirs based on field practices. Summary of the Invention

[0004] The present invention aims to address the above problems and proposes a method for calculating the actual carbon dioxide storage volume in extra-low permeability oil reservoirs.

[0005] The technical solution of the present invention lies in:

[0006] A method for calculating the actual carbon dioxide storage volume in ultra-low permeability oil reservoirs is as follows:

[0007] Establish a three-dimensional geological model of carbon dioxide flooding and storage, which includes at least one gas injection well and no less than two production wells. Obtain the relationship between the simulated production gas-oil ratio and the simulated storage rate through numerical simulation; correct the simulated production gas-oil ratio with the actual average gas-oil ratio after gas injection to obtain the relationship between the corrected simulated production gas-oil ratio and the simulated storage rate;

[0008] Obtain the background values of each monitoring object before the first gas injection well starts gas injection and the monitoring values of each monitoring object at the moment to be measured. The sum of the absolute values of the differences between the background values and the corresponding monitoring values of all monitoring objects is the carbon dioxide leakage amount;

[0009] The sum of the product of the actual carbon dioxide injection amount and the simulated storage rate and the carbon dioxide leakage amount from the start of gas injection of the first gas injection well to the moment to be measured is used as the actual carbon dioxide storage amount.

[0010] The specific determination process of the relationship between the simulated production gas-oil ratio and the simulated storage rate is as follows: Carry out numerical simulation on the three-dimensional geological model. Determine the simulated storage rate according to the simulated injection amount and the simulated storage amount of the gas injection well; Determine the simulated production gas-oil ratio according to the simulated gas production amount and the simulated oil production amount of the oil production well, and fit to obtain the relationship between the simulated production gas-oil ratio and the simulated storage rate.

[0011] The relationship between the simulated production gas-oil ratio and the simulated storage rate is specifically:

[0012] ;

[0013] In the formula: is the simulated storage rate, dimensionless; is the simulated production gas-oil ratio, dimensionless.

[0014] The relationship between the corrected simulated production gas-oil ratio and the simulated storage rate is specifically obtained as follows: Carry out gas-oil ratio monitoring on all oil production wells, obtain the sum of the gas-oil ratios of all oil production wells, and use its arithmetic mean as the actual average gas-oil ratio; Fit and correct the simulated production gas-oil ratio through the actual average gas-oil ratio:

[0015] ;

[0016] In the formula: is the actual average gas-oil ratio, dimensionless; is the corrected simulated production gas-oil ratio, dimensionless;

[0017] Furthermore, the corrected simulated production gas-oil ratio and the simulated storage rate relationship is:

[0018] .

[0019] The specific process for obtaining the carbon dioxide leakage amount is as follows:

[0020] ; ;

[0021] In the formula: Lis the carbon dioxide leakage amount, with the unit of t (ton);

[0022] i is any monitoring object, taking values 1, 2…i…m, dimensionless; j is the moment to be measured, dimensionless;

[0023] L i is the leakage amount of the i-th monitoring object from the first gas injection well to the moment to be measured, dimensionless;

[0024] M b , i is the background value of the i-th monitoring object; M i , j is the monitoring value of the i-th monitoring object at the moment to be measured.

[0025] The monitoring objects at least include the caprock, wellbore and groundwater.

[0026] The specific obtaining process of the actual carbon dioxide storage amount is as follows:

[0027] ;

[0028] In the formula: S is the actual carbon dioxide storage amount, with the unit of t;

[0029] I is the actual carbon dioxide injection amount from the first gas injection well to the moment to be measured, with the unit of t.

[0030] The three-dimensional geological model is established based on petrel software by using the multi-level facies-controlled modeling method.

[0031] The numerical simulation is realized through eclipse software.

[0032] The technical effect of the present invention is as follows:

[0033] The present invention can accurately calculate the actual carbon dioxide storage amount, can clarify the emission reduction amount of the CCUS project, provides a scientific basis for the CCUS project to be included in the carbon trading market, enables the verified emission reduction amount to enter the carbon market for trading, or be used for the tax subsidy of enterprises, and at the same time can promote the development and market application of CCUS technology; at the same time, it can verify, quantify and verify the safety of carbon dioxide geological storage, and ensure the reliability and long-term stability of the storage process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the relational formula between the simulated production gas-oil ratio and the simulated storage rate.

[0035] Figure 2 It is a fitting graph of the simulated production gas-oil ratio against the actual average gas-oil ratio.

[0036] Figure 3 It is a chart of the actual carbon dioxide injection volume and the actual carbon dioxide storage volume. Specific implementation manners

[0037] Specific application cases

[0038] In the A test area of the Yanchang Oilfield, the first gas injection well started injecting gas in August 2012; calculate the actual carbon dioxide storage volume 10 years after gas injection (in 2022). The specific process is as follows:

[0039] Step 1: Based on the Petrel software, adopt the multi-level facies-controlled modeling method to establish a three-dimensional geological model for carbon dioxide flooding and storage in the A test area of the Yanchang Oilfield. The three-dimensional geological model includes 2 carbon dioxide injection wells and 10 oil production wells; carry out numerical simulation on the three-dimensional geological model based on the Eclipse software. According to the simulated injection volume and simulated storage volume of the carbon dioxide injection wells, determine the simulated storage rate ; according to the simulated gas production volume and simulated oil production volume of the oil production wells, determine the simulated production gas-oil ratio , and fit the simulated production gas-oil ratio with the simulated storage rate Relationship:

[0040] .

[0041] Step 2: Conduct gas-oil ratio monitoring on the oil production wells to obtain the actual gas-oil ratios 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 production wells are located . The actual average gas-oil ratio in 2022 is 285. Use the actual average gas-oil ratio to correct the simulated production gas-oil ratio :

[0042] ;

[0043] Then obtain the corrected simulated production gas-oil ratio and the simulated storage rate Relationship:

[0044] .

[0045] Step 3: From May 2011 to May 2012, conduct a one-year background value monitoring. The monitoring objects include caprock, wellbore, deep groundwater, shallow groundwater, surface water, surface soil gas and atmosphere. After the first gas injection well started injecting gas in August 2012, conduct leakage risk monitoring to obtain the monitoring values of each monitoring object. The monitoring values are shown in Table 1;

[0046] Table 1 Monitoring Values

[0047] ;

[0048] Caprock: No microseismic events were detected in the caprock;

[0049] Wellbore: The background values of the corrosion rates of the gas injection wells at well depths of 400m, 1000m and 1600m are 0.008 - 0.016 mm / a, and the monitoring values are 0.011 - 0.016 mm / a. Both the monitoring values and the background values are lower than the corrosion rate of 0.076 mm / a specified by the industry standard;

[0050] Deep groundwater: The background value of pH is 6.87 - 7.17, the background value of Ca 2+ concentration is 3.95 - 20.84 mg / L, and the background value of Mg 2+ concentration is 167.73 - 360.71 mg / L; The monitoring value of pH is 6.98 - 7.05, the monitoring value of Ca 2+ concentration is 3.99 - 20.04 mg / L, and the monitoring value of Mg 2+ concentration is 170.22 - 360.11 mg / L;

[0051] Shallow groundwater: The background value of pH is 7.72 - 7.95, the background value of Ca 2+ concentration is 86.25 - 138.95 mg / L, and the background value of Mg 2+ concentration is 55.07 - 99.89 mg / L; After gas injection, the monitoring value of pH of shallow groundwater is 7.73 - 7.93, the monitoring value of Ca 2+ concentration is 89.55 - 131.05 mg / L, and the monitoring value of Mg 2+ concentration is 61.07 - 95.07 mg / L;

[0052] Surface water: The background value of pH is 7.68 - 8.07, the background value of Ca 2+ concentration is 55.34 - 56.99 mg / L, and the background value of Mg 2+ concentration is 37.99 - 41.06 mg / L; The monitoring value of pH is 7.85 - 8.02, the monitoring value of Ca 2+ concentration is 55.43 - 56.19 mg / L, and the monitoring value of Mg 2+The monitored concentration is 38.21 - 40.98 mg / L;

[0053] Surface soil gas: The background value of carbon dioxide concentration is 0.91% - 1.38%, and the monitored value of carbon dioxide concentration is 0.91% - 1.36%;

[0054] Atmosphere: The background value of carbon dioxide concentration is 0.04% - 0.041%, and the monitored value of carbon dioxide concentration is 0.04% - 0.041%;

[0055] By comparing the background values and monitored values of each monitoring object, no significant changes were found in each monitoring object. Through comprehensive judgment, it is determined that there is no leakage in the A test area of the Yanchang Oilfield; that is

[0056] .

[0057] Step 4: Considering the actual situation, from the first gas injection well starting to inject gas in August 2012 to the actual carbon dioxide injection volume in 2022 I is 9.8×10 4 t, calculate the actual carbon dioxide storage volume in the A test area of the Yanchang Oilfield in 2022:

[0058] .

[0059] Result verification: Referring to the article "Lake et al Fifty years of field observations Lessons for CO 2 storage from CO 2 enhanced oil recovery" (Fifty years of field practice experience: Insights into carbon storage from carbon dioxide enhanced oil recovery technology), according to the function between the actual carbon dioxide storage volume and the actual carbon dioxide injection volume summarized from more than 100 carbon dioxide enhanced oil recovery projects carried out in the United States, obtain the graph of the actual carbon dioxide injection volume and the actual carbon dioxide storage volume;

[0060] The pore volume of the A test area of the Yanchang Oilfield is approximately 85.8×10 4 t. From the first gas injection well starting to inject gas in August 2012 to the actual carbon dioxide injection volume in 2022 I is 9.8×10 4 t, which is converted to 0.114 PV. Combining with the graph of the actual carbon dioxide injection volume and the actual carbon dioxide storage volume, the corresponding actual carbon dioxide storage volume is 0.08 PV, that is, 6.86×10 4 t.

[0061] The error between this calculation method and the method reported in the article is only

[0062] ;

[0063] where: K is the error, dimensionless.

[0064] Therefore, the error between this calculation method and the method reported in the article is less than 5%, meeting the error range, indicating that the method for calculating the actual carbon dioxide sequestration volume in ultra-low permeability reservoirs proposed by 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 volume of carbon dioxide is 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 to be tested and the carbon dioxide leakage volume; in, 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; 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: ； The specific process of obtaining the carbon dioxide leakage is as follows: ； ； Where: L 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; L i is the leakage volume of the ith monitoring object from the first gas injection well to the time of measurement, dimensionless; M b , i is the background value of the i-th monitoring object; M i , j is the monitoring value of the i-th monitoring object at the time to be tested.

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 1 is characterized in that: The monitoring objects at least include caprock, wellbore and groundwater.

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 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 of the first gas injection well to the time of measurement, in t.

5. 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.

6. 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 numerical simulation is realized by eclipse software.

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