Optimal selection method and system for CO2 oil displacement and sealing collaborative injection-production scheme

Abstract

The invention discloses an optimal selection method and system for a CO2 oil displacement and storage collaborative injection-production scheme, and relates to the technical field of oil and gas reservoir CO2 geological storage, and the optimal selection method comprises the steps that a geological model of carbon dioxide oil displacement and storage is established; different injection-production schemes are set according to actual conditions; the recovery ratio, the maximum value of global average effective stress reduction and the CO2 leading edge migration distance serve as injection-production scheme evaluation indexes; performing data standardization processing; establishing a judgment matrix of evaluation indexes by using an analytic hierarchy process, performing consistency check, and performing the next step after the consistency check is passed; determining the weight of each evaluation index according to the judgment matrix; and carrying out weighted summation on the evaluation indexes of the injection-production schemes, and preferably selecting an optimal scheme. According to the method, economy, safety and effectiveness of the CO2 oil displacement and storage synergistic effect are considered, on the basis of multi-objective optimization, the weight of each index is scientifically and reasonably determined, the optimal injection-production scheme is optimized, the crude oil recovery rate can be increased, and effective storage of CO2 in an oil reservoir can be guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 geological storage in oil and gas reservoirs, and in particular to an optimization method and system for a CO2 oil recovery and storage coordinated injection and production scheme based on an analytic hierarchy process. Background Art

[0002] CO2 flooding and storage technology is a hot topic in the field of oil production and CO2 emission reduction. By injecting CO2 into oil reservoirs, the recovery rate of crude oil can be increased, and at the same time, the geological storage of CO2 can be achieved, reducing greenhouse gas emissions. This technology can not only effectively utilize CO2, but also alleviate the problem of global climate change. Therefore, it is of great practical significance to study an efficient injection and production scheme with synergistic effects of CO2 flooding and storage.

[0003] The geological conditions of oil reservoirs are complex and uncertain. The geological characteristics of different regions will significantly affect the oil recovery effect and storage efficiency of CO2. In the process of CO2 oil recovery and storage, it is necessary to comprehensively consider multiple factors to determine the optimal injection and production plan to ensure the safe and effective storage of CO2 while maximizing the recovery rate. The recovery rate is an important indicator to measure the effect of injecting CO2 to improve crude oil recovery. It reflects the proportion of crude oil recovered in the reservoir. A high recovery rate means that more crude oil is produced, which improves the economic benefits of the oil field. Effective stress is a key parameter affecting reservoir stability. Excessive stress changes may cause deformation or damage to the reservoir. Controlling the change of global average effective stress helps maintain the stability of the reservoir and ensure the safety of CO2 oil recovery and storage. The CO2 front migration distance is an important indicator to measure the distribution and migration range of CO2 in the reservoir. It reflects the injection effect of CO2. A large CO2 front migration distance easily leads to CO2 advancing along the dominant channel, resulting in low recovery rate, CO2 leakage and other problems.

[0004] Therefore, in response to the above technical problems, it is urgent to establish a method for optimizing CO2 injection and production schemes that comprehensively considers multiple factors, so that the weights of various evaluation indicators can be set scientifically and reasonably, which can not only improve the oil and gas recovery rate but also achieve effective storage and geological safety of CO2. Summary of the invention

[0005] In order to solve the above technical problems, the present invention discloses a method and system for optimizing a CO2 oil recovery and storage coordinated injection and production scheme. The method establishes a geological model for CO2 oil recovery and storage coordination. Different well types, perforation layers, injection rates, etc. can be considered for injection wells and oil production wells. The recovery factor, the maximum value of the global average effective stress reduction and the CO2 front migration distance are used as evaluation indicators. The hierarchical analysis method is used to reasonably set the weights of each evaluation indicator, and finally the best CO2 oil recovery and storage coordinated injection and production scheme is optimized.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method and system for optimizing a CO2 flooding and storage coordinated injection-production scheme, specifically comprising the following steps:

[0008] S1. Use reservoir numerical simulation software to establish a geological model for CO2 flooding and storage;

[0009] S2. Set up different injection and production plans according to actual conditions;

[0010] S3. Use reservoir numerical simulation software to perform numerical simulation to obtain the recovery factor, the maximum value of global average effective stress reduction and the CO2 front migration distance of each injection-production scheme within a certain period as evaluation indicators of the injection-production scheme;

[0011] S4, performing data standardization processing on the obtained injection-production scheme evaluation index;

[0012] S5. Use the analytic hierarchy process to establish a judgment matrix for the evaluation indicators and perform a consistency test. If the test passes, proceed to the next step, otherwise repeat this step;

[0013] S6. Determine the weight of each evaluation index according to the judgment matrix;

[0014] S7. Perform weighted summation on the evaluation indicators of each injection-production scheme and select the best scheme.

[0015] Furthermore, in step S1, the component model is used to set the fluid components, and the initial conditions of the geomechanical grid and the initial geostress are set, including: matrix porosity, permeability, fluid saturation, pressure, initial effective stress, Young's modulus, Poisson's ratio, cohesion, internal friction angle, etc.

[0016] Furthermore, in step S2, at least one CO2 injection well and one oil production well are set in the geological model. The CO2 injection well considers different well types, injection layers and injection rates according to actual conditions, and the oil production well considers different production pressures, perforation layers, and distances from the CO2 injection well.

[0017] Further, in step S3, the recovery rate is the ratio of the amount of oil produced in a certain period to the initial underground crude oil content, the CO2 front migration distance is the distance between the CO2 front and the oil well on the CO2 gas saturation distribution map, and the average effective stress is the average value of the effective stresses in the three directions of I, J, and K obtained by three-dimensional stress calculation;

[0018] Mean effective stressσ eff The calculation is:

[0019]

[0020] In the formula, σ x , σ y , σ z are the total stresses in the I, J and K directions respectively, α is the Biot coefficient, and p is the fluid pressure.

[0021] Further, in step S4, the recovery factor is used as a positive indicator for data standardization, that is, the larger the recovery factor, the better the injection scheme; the maximum value of the global effective stress reduction and the CO2 front migration distance are used as negative indicators for data standardization, that is, the smaller their values, the better the injection scheme; wherein,

[0022] The positive indicator normalization method is:

[0023]

[0024] The negative indicator normalization method is:

[0025]

[0026] Where, X ij is the value before data standardization, Y ij is the value after data standardization, max(X i ) is the maximum value under a certain indicator, min(X i ) is the minimum value under a certain indicator.

[0027] Furthermore, in step S5, the criterion for passing the consistency check is that the consistency ratio is less than 0.1.

[0028] Furthermore, in step S6, the method for determining the weight of each evaluation index is: first normalizing the column vector of the judgment matrix A, then summing up each row of the matrix, and normalizing again to obtain the weight of each index.

[0029] On the other hand, the present invention also discloses a system using the above-mentioned preferred method, comprising: a model building and scheme design unit, a data acquisition and processing unit and a comprehensive evaluation unit, wherein:

[0030] Model building and scheme design unit, used to establish geological models for the coordination of CO2 flooding and storage, and to design different injection and production schemes;

[0031] Data acquisition and processing unit, used to obtain evaluation indicators and perform data standardization processing;

[0032] The comprehensive evaluation unit uses the hierarchical analysis method to calculate the weights of the evaluation indicators, evaluate each plan and select the best injection and production plan.

[0033] In addition, the present invention also discloses a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it executes the preferred method and system of the above-mentioned CO2 oil recovery and storage coordinated injection and production scheme.

[0034] The beneficial effect of the present invention is that, by establishing a geological model for the coordination of CO2 oil recovery and storage, different well types, perforation layers, injection rates, etc. can be considered for injection wells and oil production wells, and the recovery factor, the maximum value of the global average effective stress reduction and the CO2 front migration distance are used as evaluation indicators. The weight of each evaluation indicator is reasonably set using the hierarchical analysis method, and finally the best CO2 oil recovery and storage coordination injection and production scheme is selected.

[0035] This method can take into account the economy, safety and effectiveness of the synergistic effect of CO2 flooding and storage. On the basis of multi-objective optimization, it can scientifically and rationally determine the weight of each indicator and select the optimal injection-production plan. It can not only improve the crude oil recovery rate, but also ensure the effective storage of CO2 in the reservoir, which has important economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the process of the present invention;

[0037] Figure 2 A schematic diagram of a two-dimensional CO2 flooding and storage geological model in an embodiment of the present invention;

[0038] Figure 3 This is the CO2 gas saturation distribution diagram at the end of the simulation of Scheme 6 of the present invention;

[0039] Figure 4 is a curve showing the cumulative recovery rate of Scheme 6 of the present invention changing with time;

[0040] Figure 5 This is the average effective stress distribution diagram at the end of the simulation of Scheme 6 of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] A method and system for optimizing a CO2 flooding and storage coordinated injection-production scheme, specifically comprising the following steps:

[0043] 1. Use reservoir numerical simulation software to establish a geological model for CO2 flooding and storage; use the component model to set the fluid components and set the initial conditions of the geomechanical grid and initial geostress.

[0044] 2. Set up different injection and production plans according to actual conditions; at least one CO2 injection well and one oil production well are set up in the geological model. The CO2 injection well considers different well types, injection layers and injection rates according to actual conditions, and the oil production well considers different production pressures, perforation layers, and distances from the injection well.

[0045] 3. Use reservoir numerical simulation software to perform numerical simulation to obtain the recovery factor, the maximum value of the global average effective stress reduction and the CO2 front migration distance of each injection and production scheme within a certain period as evaluation indicators of the injection and production scheme.

[0046] The recovery rate is the ratio of the amount of oil produced in a certain period to the initial underground crude oil content. The CO2 front migration distance is the distance between the CO2 front and the oil well on the CO2 gas saturation distribution map. The average effective stress is the average value of the effective stresses in the three directions of I, J, and K obtained by three-dimensional stress calculation;

[0047] Mean effective stressσ eff The calculation is:

[0048]

[0049] In the formula, σ x , σ y , σ z are the total stresses in the I, J and K directions respectively, α is the Biot coefficient, and p is the fluid pressure.

[0050] S4. The obtained injection-production scheme evaluation indicators are subjected to data standardization. The recovery factor is used as a positive indicator for data standardization, that is, the larger the recovery factor, the better the injection scheme; the maximum value of the global effective stress reduction and the CO2 front migration distance are used as negative indicators for data standardization, that is, the smaller their values, the better the injection scheme; among them,

[0051] The positive indicator normalization method is:

[0052]

[0053] The negative indicator normalization method is:

[0054]

[0055] Where, X ij is the value before data standardization, Y ij is the value after data standardization, max(X i) is the maximum value under a certain indicator, min(X i ) is the minimum value under a certain indicator.

[0056] 5. Use the hierarchical analysis method to establish the judgment matrix of the evaluation indicators and perform a consistency test. If the test passes, proceed to the next step, otherwise repeat this step; the standard for passing the consistency test is that the consistency ratio is less than 0.1.

[0057] The steps to construct the judgment matrix A and the consistency test are as follows:

[0058] (1) Determine the scale a in the judgment matrix A ij The specific determination method is shown in Table 1.

[0059] Table 1 Scale a in the judgment matrix ij Method for determining

[0060] <![CDATA[Scale a ij > meaning 1 Indicates that two factors are equally important. 3 Indicates that one factor is slightly more important than the other factor. 5 Indicates that one factor is significantly more important than the other factor when compared with the other factor. 7 Indicates that one factor is more important than the other. 9 Indicates that one factor is extremely more important than the other. 2，4，6，8 The middle value of the above two adjacent judgments reciprocal <![CDATA[Judgment a for comparing factor i and j ij , then the judgment a for comparing factor j and i ij＝1 / a ij >

[0061] (2) Determine the judgment matrix A:

[0062]

[0063] (3) Calculate the consistency index CR. The calculation method of CR is as follows:

[0064]

[0065] In the formula, CI is the consistency index, λ max is the maximum characteristic root, N is the order of the judgment matrix A, and RI is the random consistency index, which is determined by Table 2.

[0066] Table 2 RI values

[0067] n 1 2 3 4 5 6 7 8 9 RI 0 0 0.58 0.90 1.12 1.24 1.32 1.41 1.45

[0068] The consistency test passes the standard of consistency ratio CR < 0.1. That is, when this condition is met, the constructed judgment matrix can be considered valid, otherwise the judgment matrix needs to be reconstructed.

[0069] 6. Determine the weight of each evaluation index based on the judgment matrix; the method for determining the weight of each index based on the judgment matrix is: first normalize the column vector of the judgment matrix A, then sum the rows of the matrix, and normalize again to obtain the weight of each index.

[0070] 7. Take the weighted sum of the evaluation indicators of each injection and production scheme and select the best scheme.

[0071] Application Examples

[0072] A method and system for optimizing the CO2 flooding and storage coordinated injection and production scheme, combined with Figure 1-Figure 5, the specific steps are as follows:

[0073] 1. Use the reservoir numerical simulation software CMG-GEM to establish a geological model for the synergy of CO2 flooding and storage, such as Figure 2 As shown in the figure, the model has two partitions: cap rock and reservoir. The cap rock top interface depth is 900m, the cap rock and reservoir thickness are 10m and 50m respectively, the model length is 1000m, and the grid is evenly discretized into 100×30 grids along the I and K directions. The cap rock porosity is 0.01 and the permeability is 1.0×10 -5 mD, the reservoir porosity is 0.3, the permeability is 2000mD, and the ratio of vertical to horizontal permeability is 0.1. The geomechanical grid uses the same grid as the reservoir, the Young's modulus of the rock is 30GPa, the Poisson's ratio is 0.3, the internal friction angle is 30°, the cohesion is 10MPa, and the initial effective stress of models I, J, and K is 2MPa.

[0074] 2. According to the injection well type, injection well perforation position, CO2 injection rate, and production well pressure, 9 groups of injection and production schemes were set up, as shown in Table 3. By adjusting the injection time, the cumulative CO2 injection volume of each scheme was kept consistent, all of which were 1.824×10 7 m 3 , the simulation time is 5 years.

[0075] Table 3 Injection and production plan settings

[0076] serial number Injection well type Injection well perforation location <![CDATA[CO2 injection rate, ×10 4 m 3 / d]]> Oil well pressure, MPa Solution 1 Naoi all 1 16 Solution 2 Naoi upper part 1 16 Solution 3 Naoi Central 1 16 Solution 4 Naoi lower part 1 14 Solution 5 Horizontal well upper part 1 16 Solution 6 Horizontal well Central 1 16 Solution 7 Horizontal well lower part 1 18 Solution 8 Naoi all 2 16 Solution 9 Horizontal well Central 2 16

[0077] 3. Use the reservoir numerical simulation software CMG-GEM to run each injection scheme to obtain the recovery factor during the storage process, the maximum value of the global average effective stress reduction, and the CO2 front migration distance. In this application example, the Biot coefficient is set to 1.0. Taking Scheme 6 as an example, Figure 3 This is the CO2 gas saturation distribution diagram at the end of the simulation of Scheme 6. Figure 4 is the curve of cumulative recovery rate of Scheme 6 changing with time, Figure 5 This is the average effective stress distribution diagram at the end of the simulation of Scheme 6. The evaluation indicators of each scheme are summarized in Table 4.

[0078] Table 4 Evaluation indicators of each scheme

[0079] serial number Recovery rate, % Maximum value of global average effective stress reduction, kPa <![CDATA[Migration distance of CO2 front, m]]> Solution 1 42.04 832 920 Solution 2 42.38 858 930 Solution 3 40.94 808 610 Solution 4 46.76 136 700 Solution 5 38.35 704 1000 Solution 6 39.27 668 720 Solution 7 36.88 1892 700 Solution 8 40.06 1151 770 Solution 9 42.41 1428 860

[0080] 4. The evaluation indicators obtained from each scheme are standardized. The recovery factor is used as a positive indicator for data standardization, and the maximum value of global effective stress reduction and CO2 front migration distance are used as negative indicators for data standardization. The standardized evaluation indicators are shown in Table 5.

[0081] Table 5 Evaluation indicators after standardization

[0082] serial number Normalized recovery factor Maximum value of normalized mean effective stress reduction <![CDATA[Standardized CO2 front migration distance]]> Solution 1 0.522 0.604 0.205 Solution 2 0.557 0.589 0.179 Solution 3 0.411 0.617 1.000 Solution 4 1.000 1.000 0.769 Solution 5 0.149 0.677 0.000 Solution 6 0.242 0.697 0.718 Solution 7 0.000 0.000 0.769 Solution 8 0.322 0.422 0.590 Solution 9 0.560 0.264 0.359

[0083] 5. Use the hierarchical analysis method to establish the judgment matrix of evaluation indicators, as shown in Table 6.

[0084] Table 6 Judgment matrix of three evaluation indicators

[0085]

[0086] Therefore, the judgment matrix A is

[0087]

[0088] The consistency ratio CR value of the above judgment matrix is ​​0.017, which is less than 0.10, and passes the consistency test.

[0089] 6. According to the judgment matrix, the weight of each evaluation index is determined to be [0.641, 0.264, 0.095].

[0090] 7. The evaluation indicators of each scheme are weighted and summed, and the results are shown in Table 7. It can be seen that the comprehensive result of Scheme 4 is the highest, which is 0.978. Therefore, Scheme 4 is the best scheme in this application example, that is, the injection well adopts a vertical well, perforates in the lower part of the reservoir, and the injection rate is 1×10 4 m 3 / d, the bottom hole pressure of the oil well is 14MPa.

[0091] Table 7 Comprehensive results of each scheme

[0092] serial number Comprehensive results Solution 1 0.514 Solution 2 0.529 Solution 3 0.521 Solution 4 0.978 Solution 5 0.274 Solution 6 0.407 Solution 7 0.073 Solution 8 0.374 Solution 9 0.463

[0093] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for optimizing a CO2 flooding and storage coordinated injection-production scheme, characterized in that: The specific steps include: S1. Use reservoir numerical simulation software to establish a geological model for CO2 flooding and storage; S2. Set up different injection and production plans according to actual conditions; S3. Use reservoir numerical simulation software to perform numerical simulation to obtain the recovery factor, the maximum value of global average effective stress reduction and the CO2 front migration distance of each injection-production scheme within a certain period as evaluation indicators of the injection-production scheme; S4, performing data standardization processing on the obtained injection-production scheme evaluation index; S5. Use the analytic hierarchy process to establish a judgment matrix for the evaluation indicators and perform a consistency test. If the test passes, proceed to the next step, otherwise repeat this step; S6. Determine the weight of each evaluation index according to the judgment matrix; S7. Perform weighted summation on the evaluation indicators of each injection-production scheme and select the best scheme.

2. The method for optimizing the CO2 flooding and storage coordinated injection-production scheme according to claim 1, characterized in that: In step S1, the component model is used to set the fluid components, and the initial conditions of the geomechanical grid and the initial geostress are set, including: matrix porosity, permeability, fluid saturation, pressure, initial effective stress, Young's modulus, Poisson's ratio, cohesion, and internal friction angle.

3. The method for optimizing the CO2 flooding and storage coordinated injection-production scheme according to claim 2, characterized in that: In step S2, at least one CO2 injection well and one oil production well are set in the geological model. The CO2 injection well considers different well types, injection layers and injection rates according to actual conditions, and the oil production well considers different production pressures, perforation layers, and distances from the CO2 injection well.

4. A method for optimizing a CO2 flooding and storage coordinated injection-production scheme as claimed in claim 3, characterized in that: In step S3, the recovery rate is the ratio of the oil volume produced in a certain period to the initial underground crude oil content, the CO2 front migration distance is the distance between the CO2 front and the oil well on the CO2 gas saturation distribution map, and the average effective stress is the average value of the effective stresses in the three directions of I, J, and K obtained by three-dimensional stress calculation; Mean effective stressσ eff The calculation is: In the formula, σ x , σ y , σ z are the total stresses in the I, J and K directions respectively, α is the Biot coefficient, and p is the fluid pressure.

5. The method for optimizing the CO2 flooding and storage coordinated injection-production scheme according to claim 4, characterized in that: In step S4, the recovery factor is used as a positive indicator for data standardization, that is, the larger the recovery factor, the better the injection scheme; the maximum value of the global effective stress reduction and the CO2 front migration distance are used as negative indicators for data standardization, that is, the smaller their values, the better the injection scheme; wherein, The positive indicator standardization method is: The negative indicator normalization method is: In the formula, X ij is the value before data standardization, Y ij is the value after data standardization, max(X i ) is the maximum value under a certain indicator, min(X i ) is the minimum value under a certain indicator.

6. A method for optimizing a CO2 flooding and storage coordinated injection-production scheme as claimed in claim 5, characterized in that: In step S5, the criterion for passing the consistency check is that the consistency ratio is less than 0.

1.

7. A method for optimizing a CO2 flooding and storage coordinated injection-production scheme as claimed in claim 6, characterized in that: In step S6, the method for determining the weight of each evaluation index is: first normalize the column vector of the judgment matrix A, then sum the rows of the matrix, and normalize again to obtain the weight of each index.

8. A system using the preferred method as claimed in claim 7, characterized in that: include: Model building and scheme design unit, data acquisition and processing unit and comprehensive evaluation unit, including: Model building and scheme design unit, used to establish geological models for the coordination of CO2 flooding and storage, and to design different injection and production schemes; Data acquisition and processing unit, used to obtain evaluation indicators and perform data standardization processing; The comprehensive evaluation unit uses the hierarchical analysis method to calculate the weights of the evaluation indicators, evaluate each plan and select the best injection and production plan.

9. A computer device, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the preferred method described in claim 7 when executing the computer program.

Images