Low-permeability reservoir CO2 drive gas channeling channel identification method

Abstract

The invention relates to a low-permeability reservoir CO2 drive gas channeling channel identification method which comprises the following steps: S1, collecting geological data and production dynamic data of a target block well group, and calculating a gas channeling channel discrimination index; s2, calculating the weight of each gas channeling channel discrimination index; s3, calculating an onrush coefficient and correcting a boundary; s4, calculating a membership degree, and standardizing each gas channeling channel discrimination index according to the membership degree to meet the condition that the numerical value is between 0 and 1; s5, static and dynamic index comprehensive discrimination coefficients of the injection wells and the production wells are calculated; s6, calculating comprehensive weights of static and dynamic indexes of each injection well and each production well; s7, calculating a total discrimination coefficient; and S8, determining a three-level classification standard of the gas channeling channel, and judging the development direction of the gas channeling channel. The method solves the problem that an existing gas channeling channel identification method is low in accuracy of gas channeling channel identification due to the fact that the existing gas channeling channel identification method lacks research on a low-permeability conglomerate oil reservoir and does not fully utilize dynamic and static data.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, specifically relating to a method for identifying CO2 gas channeling pathways in low-permeability oil reservoirs. Background Technology

[0002] Gas injection development can effectively improve oil displacement efficiency and increase crude oil recovery. However, due to reservoir heterogeneity and the significant difference in flow capacity between gas and crude oil, gas channeling is highly likely to occur during gas injection, causing a sharp increase in the production gas-oil ratio of the well and a deterioration in reservoir development. Therefore, it is urgent to identify the gas channeling pathways that are prone to form during gas injection development to provide guidance for the design of subsequent control and mitigation strategies.

[0003] Patent application CN202010960492.4 discloses a method and device for predicting gas channeling time in CO2 miscible flooding wells in low-permeability reservoirs. This method only predicts gas channeling time and lacks identification of the gas channeling pathways. Patent application CN201710231158.3 discloses a method for dynamically inverting gas channeling pathways in CO2-flooded reservoirs based on the correspondence between characteristic parameters of the gas-oil ratio curve and an inversion index system. This method only considers the changing characteristics of the gas-oil ratio curve and neglects the application of other dynamic production data, resulting in significant errors. Patent application CN201710786398.X discloses a method for characterizing the degree of gas channeling using a comprehensive CO2 gas channeling index. This method uses the experimentally obtained relationship between CO2 injection rate and CO2 gas content as input data, which is idealized and lacks integration with actual field production. The invention patent application with application number CN201910360031.0 discloses a method and device for rapid inversion of gas channeling in carbon dioxide flooded oil reservoirs. However, this method uses a simple arithmetic average to divide the gas injection volume of the injection well into the direction of different production wells, without considering the influence of geological factors and development factors in the actual oil reservoir on the gas flow process. Therefore, the calculation results have a large deviation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying CO2-driven gas channeling in low-permeability reservoirs, in order to solve the problem that existing gas channeling identification methods have low accuracy due to a lack of research on low-permeability conglomerate reservoirs and insufficient utilization of dynamic and static data.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for identifying CO2 gas channeling pathways in low-permeability reservoirs includes:

[0007] S1. Data Collection and Indicator Optimization

[0008] Collect geological data and production dynamic data of well groups in the target block, and calculate the indicators for identifying gas channeling.

[0009] S2. Weight Calculation

[0010] Calculate the weight of each indicator in the gas channel discrimination index;

[0011] S3. Calculation of Advance Coefficient and Boundary Correction

[0012] Calculate the surge coefficient of each index in the gas channel discrimination index, and correct the semi-trapezoidal mathematical model based on the surge coefficient;

[0013] S4. Membership Degree Calculation

[0014] Based on the different relationships between the magnitude of each gas channel discrimination index and the degree of gas channel development, an ascending semi-trapezoidal mathematical model and a descending semi-trapezoidal mathematical model are established respectively, and the membership degree is calculated. Based on the membership degree, each gas channel discrimination index is standardized to satisfy the value between 0 and 1.

[0015] S5. Calculation of the comprehensive discrimination coefficient of dynamic and static indicators

[0016] Based on the weights and membership degrees of various gas channel discrimination indicators, the comprehensive discrimination coefficients of static indicators and the comprehensive discrimination coefficients of dynamic indicators for each injection well and production well in the block are calculated.

[0017] S6. Calculation of the combined weight of dynamic and static indicators

[0018] Calculate the combined weight of static and dynamic indicators for each injection well and production well in the block;

[0019] S7. Calculation of Total Discriminant Coefficient

[0020] Combine the static index comprehensive discrimination coefficient and dynamic index comprehensive discrimination coefficient obtained from S5 with the static index comprehensive weight and dynamic index comprehensive weight obtained from S6 to calculate the total discrimination coefficient of gas channeling channels for each injection well and production well in the block.

[0021] S8. Classification and Direction of Gas Channels

[0022] Based on the on-site feedback regarding the development of gas channeling in the block well group, and combined with the geological and production dynamic data collected by S1, a three-level classification standard for gas channeling was determined, and the development direction of the gas channeling was identified.

[0023] Furthermore, in S1, the geological data includes the porosity, permeability, and effective thickness of the oil layer; the production dynamic data includes the daily gas injection volume, cumulative gas injection volume, injection pressure of the injection well, the maximum CO2 content at the wellhead of the production well, the daily gas production volume, the daily oil production volume, the wellhead oil pressure, and the cumulative gas production volume.

[0024] The gas channel discrimination index includes static discrimination indexes and dynamic discrimination indexes. The static discrimination indexes include formation coefficient, average porosity, average permeability, permeability variation coefficient, and permeability surge coefficient. The dynamic discrimination indexes are divided into injection well category and production well category. The injection well category includes apparent gas intake index, average daily gas injection volume, cumulative injection volume per unit thickness, gas injection intensity, and average injection pressure. The production well category includes maximum CO2 content at the wellhead, average daily gas production, gas-oil ratio, wellhead oil pressure surge coefficient, cumulative gas production per unit thickness, and oil production intensity.

[0025] Furthermore, in S2, the formula for calculating the weight of each indicator in the gas channel discrimination index is as follows:

[0026]

[0027] In the formula: A i The coefficient of variation for each indicator;

[0028] a i Let be the standard deviation of the i-th indicator;

[0029] The average value of the i-th indicator;

[0030] ω i The weight of each indicator.

[0031] Furthermore, in S3, the formula for calculating the surge coefficient is as follows:

[0032]

[0033] In the formula: D i Let be the breakthrough coefficient of the i-th indicator.

[0034] x i,max The maximum value of the i-th indicator.

[0035] is the average value of the i-th indicator.

[0036] Furthermore, the mathematical formula for calculating the semi-trapezoid is as follows:

[0037]

[0038] The mathematical formula for calculating the semi-trapezoid is:

[0039]

[0040] In the formula: B(x) represents the membership degree of each indicator.

[0041] a1 is the minimum boundary value of each indicator.

[0042] a2 represents the maximum boundary value of each indicator.

[0043] x is the indicator for identifying gas leakage channels.

[0044] Furthermore, in S5, the formula for calculating the comprehensive discrimination coefficient of the static index is:

[0045]

[0046] The formula for calculating the comprehensive discrimination coefficient of dynamic indicators is:

[0047]

[0048] In the formula: C j This is a comprehensive discrimination coefficient for static indicators;

[0049] C d The dynamic indicator comprehensive discrimination coefficient;

[0050] B i represents the membership degree of the i-th dynamic or static indicator;

[0051] ω i The weight of the i-th dynamic or static indicator;

[0052] i and n are natural numbers.

[0053] Furthermore, in S6, the formula for calculating the comprehensive weight of the static index is:

[0054]

[0055] In the formula: ω j The static index of each injection well or production well is assigned a comprehensive weight.

[0056] ω m For each injection well or production well, the weight of the m-th static index is...

[0057] m and n are natural numbers, where m ≥ 2.

[0058] The formula for calculating the comprehensive weight of dynamic indicators is:

[0059]

[0060] In the formula: ω d The dynamic indicators of each injection well or production well are comprehensively weighted.

[0061] ω l For each injection well or production well, the weight of the l-th dynamic indicator is...

[0062] l and n are natural numbers, where l ≥ 2.

[0063] Furthermore, in S7, the formula for calculating the total discriminant coefficient is:

[0064] C t =C j *ω j +C d *ω d

[0065] In the formula: C t The total discrimination coefficient for gas channeling in each injection well or production well.

[0066] C j The comprehensive discrimination coefficient of static indicators for each injection well or production well.

[0067] C d The comprehensive discrimination coefficient for dynamic indicators of each injection well or production well.

[0068] ω j The static index of each injection well or production well is assigned a comprehensive weight.

[0069] ω d The dynamic indicators of each injection well or production well are comprehensively weighted.

[0070] Furthermore, the three-level classification standard for gas channeling is as follows:

[0071] When the total discrimination coefficient of the gas channel is C t A value ≥0.5 indicates a strong degree of gas channel development;

[0072] When the total discrimination coefficient of the gas channel is 0.4 ≤ C t <0.5 indicates a weak degree of development of the gas channel;

[0073] When the total discrimination coefficient of the gas channel is C t <0.4 indicates that the gas channel is underdeveloped;

[0074] Furthermore, the method for determining the development direction of the gas channel is as follows: if the sum of the total discrimination coefficients of the gas channel of a pair of injection wells and production wells in the same well group is the largest and both are ≥0.4, then the development direction of the gas channel is the direction of the line connecting the injection wells and production wells.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] 1. Compared to existing methods for identifying gas channeling, this invention selects a large number of geological and production dynamic discrimination indicators and, based on research findings on gas channeling mechanisms, influencing factors, and characteristics, employs data mining and grey relational analysis to identify gas channeling during gas injection development. Therefore, this invention can comprehensively consider the influence of various geological and development factors during gas injection, can perform calculations on large amounts of data, and features high accuracy and convenience. When gas channeling occurs in a well group, the source of gas channeling in the production well can be quickly determined, the target injection well can be identified, plugging and control strategies can be formulated, and data can be closely monitored and updated to achieve the goal of delaying the gas channeling time of the dominant channel and enhancing the overall gas injection displacement effect.

[0077] 2. The gas channel identification method for low-permeability conglomerate reservoirs described in this invention employs a relatively simple and practical calculation method to achieve quantitative identification of gas channeling.

[0078] 3. The gas channel identification method for low-permeability conglomerate reservoirs described in this invention facilitates early warning of gas channeling and determination of the direction of the gas channel after gas channeling.

[0079] The above description is merely an overview of the technical solution of the present invention. To make the above content of the present invention more obvious and understandable, preferred embodiments are described below in conjunction with the accompanying drawings for detailed explanation. Attached Figure Description

[0080] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other design solutions and drawings can be obtained based on these drawings without creative effort.

[0081] Figure 1 This is a flowchart of the CO2 gas channel identification method for low-permeability reservoirs described in this invention.

[0082] Figure 2 A schematic diagram of the mathematical model of a semi-trapezoid;

[0083] Figure 3 A schematic diagram of the mathematical model of a descending semi-trapezoid;

[0084] Figure 4 This is a statistical chart showing the development of gas channeling.

[0085] In the picture:

[0086] a1 is the boundary minimum value; a2 is the boundary maximum value. Detailed Implementation

[0087] The invention can be further understood in conjunction with the following detailed description of preferred embodiments and included examples. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. If any definition of a specific term disclosed in the prior art differs from any definition provided herein, the definition provided herein shall prevail.

[0088] This embodiment relates to a method for identifying CO2 gas channeling pathways in low-permeability oil reservoirs, including the following steps:

[0089] S1. Data Collection and Indicator Optimization

[0090] Collect geological data and production dynamic data of well groups in the target block, and calculate the indicators for identifying gas channeling.

[0091] The geological data includes the porosity, permeability, and effective thickness of the oil layer; the production dynamic data includes the daily gas injection volume, cumulative gas injection volume, injection pressure of the injection well, the maximum CO2 content at the wellhead of the production well, the daily gas production, the daily oil production, the wellhead oil pressure, and the cumulative gas production.

[0092] Furthermore, the gas channel discrimination indicators include static discrimination indicators and dynamic discrimination indicators. The static discrimination indicators include formation coefficient, average porosity, average permeability, permeability variation coefficient, and permeability surge coefficient. The dynamic discrimination indicators are divided into injection well category and production well category. The injection well category includes apparent gas intake index, average daily gas injection volume, cumulative injection volume per unit thickness, gas injection intensity, and average injection pressure. The production well category includes maximum CO2 content at the wellhead, average daily gas production, gas-oil ratio, wellhead oil pressure surge coefficient, cumulative gas production per unit thickness, and oil production intensity.

[0093] S2. Weight Calculation

[0094] The weights of each gas channel discrimination index are calculated using the following formula:

[0095]

[0096] In the formula: A i The coefficient of variation for each indicator;

[0097] a i Let be the standard deviation of the i-th indicator;

[0098] X i The average value of the i-th indicator;

[0099] ω i The weight of each indicator.

[0100] S3. Calculation of Advance Coefficient and Boundary Correction

[0101] Calculate the breakthrough coefficients of various gas channel discrimination indicators, and correct the semi-trapezoidal mathematical model based on the breakthrough coefficients;

[0102] Furthermore, the formula for calculating the surge coefficient is as follows:

[0103]

[0104] In the formula: D i Let be the breakthrough coefficient of the i-th indicator.

[0105] x i,max The maximum value of the i-th indicator.

[0106] is the average value of the i-th indicator.

[0107] S4. Membership Degree Calculation

[0108] Based on the different relationships between the magnitude of each gas channel discrimination index and the degree of gas channel development, an ascending semi-trapezoidal mathematical model and a descending semi-trapezoidal mathematical model are established respectively, and the membership degree is calculated. Based on the membership degree, each gas channel discrimination index is standardized to satisfy the value between 0 and 1.

[0109] S5. Calculation of the comprehensive discrimination coefficient of dynamic and static indicators

[0110] Based on the weights and membership degrees of various gas channel discrimination indicators, the comprehensive discrimination coefficients of static indicators and the comprehensive discrimination coefficients of dynamic indicators for each injection well and production well in the block are calculated.

[0111] S6. Calculation of the combined weight of dynamic and static indicators

[0112] Calculate the combined weight of static and dynamic indicators for each injection well and production well within the block;

[0113] S7. Calculation of Total Discriminant Coefficient

[0114] Combine the static index comprehensive discrimination coefficient and dynamic index comprehensive discrimination coefficient obtained from S5, and the static index comprehensive weight and dynamic index comprehensive weight obtained from S6, calculate the total discrimination coefficient of gas channeling channels for each injection well and production well in the block.

[0115] S8. Classification and Direction of Gas Channels

[0116] Based on the on-site feedback regarding the development of gas channeling in the block well group, and combined with the geological and production dynamic data collected by S1, a three-level classification standard for gas channeling was determined, and the development direction of the gas channeling was identified.

[0117] It is worth mentioning that in S3, when modifying the semi-trapezoidal mathematical model based on the advance coefficient, any boundary values ​​that do not meet the advance coefficient Di≤1.5 need to be redefined in combination with the actual situation on site.

[0118] Furthermore, based on the different relationships between the magnitudes of various gas channel discrimination indicators and the development degree of gas channel pathways, ascending half-trapezoidal mathematical models and descending half-trapezoidal mathematical models are established respectively. Specifically, among the gas channel discrimination indicators, the magnitudes of injection pressure and oil recovery intensity are inversely proportional to the development degree of gas channel pathways. Therefore, a descending half-trapezoidal mathematical model is adopted (e.g., Figure 3 As shown), the magnitudes of the other gas channel discrimination indices are directly proportional to the degree of gas channel development, and all adopt a semi-trapezoidal mathematical model (e.g., Figure 2 (As shown).

[0119] Furthermore, the mathematical formula for calculating the semi-trapezoid is as follows:

[0120]

[0121] The mathematical formula for calculating the semi-trapezoid is:

[0122]

[0123] In the formula: B(x) is the membership degree of each indicator, a1 is the minimum boundary value of each indicator, a2 is the maximum boundary value of each indicator, and x is the gas channel discrimination index.

[0124] Furthermore, in S5, the formula for calculating the comprehensive discrimination coefficient of the static index is:

[0125]

[0126] The formula for calculating the comprehensive discrimination coefficient of dynamic indicators is:

[0127]

[0128] In the formula: C j This is a comprehensive discrimination coefficient for static indicators;

[0129] C d The dynamic indicator comprehensive discrimination coefficient;

[0130] B i represents the membership degree of the i-th dynamic or static indicator;

[0131] ω i The weight of the i-th dynamic or static indicator.

[0132] i and n are natural numbers.

[0133] Furthermore, in S6, the formula for calculating the comprehensive weight of the static index is:

[0134]

[0135] In the formula: ω j The static index of each injection well or production well is assigned a comprehensive weight.

[0136] ω m For each injection well or production well, the weight of the m-th static index is...

[0137] m and n are natural numbers, where m ≥ 2;

[0138] The formula for calculating the comprehensive weight of dynamic indicators is:

[0139]

[0140] In the formula: ω d The dynamic index of each injection well or production well is weighted comprehensively, ω l The weight of the l-th dynamic indicator for each injection well or production well is given, where l and n are natural numbers, and l ≥ 2.

[0141] Furthermore, in S7, the formula for calculating the total discriminant coefficient is:

[0142] C t =C j *ω j +C d *ω d

[0143] In the formula: C t C is the total discrimination coefficient for gas channeling in each injection or production well. j C is the comprehensive discrimination coefficient of static indicators for each injection well or production well. d ω is the comprehensive discrimination coefficient for dynamic indicators of each injection well or production well. j ω represents the comprehensive weight of static indicators for each injection well or production well. d The dynamic indicators of each injection well or production well are comprehensively weighted.

[0144] Furthermore, the three-level classification standard for gas channeling is as follows:

[0145] When the total discrimination coefficient of the gas channel is ≥0.5, the development degree of the gas channel is determined to be strong;

[0146] When the total discrimination coefficient of the gas channel is 0.4 ≤ C t <0.5 indicates a weak degree of development of the gas channel;

[0147] When the total discrimination coefficient of the gas channel is C t<0.4 indicates that the gas channel is underdeveloped;

[0148] Furthermore, the method for determining the development direction of gas channel is as follows:

[0149] If the sum of the total discrimination coefficients of the gas channel between a pair of injection wells and production wells in the same well group is the largest and both are ≥0.4, then the development direction of the gas channel is the direction of the line connecting the injection wells and production wells.

[0150] The present invention will be further described below with reference to specific embodiments:

[0151] Example 1

[0152] This embodiment relates to a method for identifying CO2 gas channeling pathways in low-permeability oil reservoirs, referring to... Figure 1 This includes the following steps:

[0153] Step 1: Collect geological and production dynamic data for Block X. Geological data includes the porosity, permeability, and effective thickness of the oil-bearing reservoir. Production dynamic data includes the daily gas injection volume, cumulative gas injection volume, injection pressure of injection wells, maximum CO2 content at the wellhead of production wells, daily gas production, daily oil production, wellhead oil pressure, and cumulative gas production. Calculate static and dynamic discrimination indicators based on this data.

[0154] Step 2: Calculate the weights using the coefficient of variation method. Specifically, the formula for calculating the weight of each indicator in the gas channel discrimination index is as follows:

[0155] in

[0156] In the formula: A i a is the coefficient of variation for each indicator; i X is the standard deviation of the i-th indicator; i ω is the average value of the i-th indicator; i The weight of each indicator.

[0157] The weighting of gas injection wells is divided into static and dynamic parts, and the calculation results are shown in Tables 1 and 2:

[0158] Table 1 Static Discrimination Indicators for Gas Injection Wells

[0159]

[0160] Table 2 Weights of Dynamic Indicators for Gas Injection Wells

[0161]

[0162] The production well weight is divided into static and dynamic parts, and the calculation results are shown in Tables 3 and 4:

[0163] Table 3 Weights of Static Indicators for Production Wells

[0164]

[0165]

[0166] Table 4 Weights of Dynamic Indicators for Production Wells

[0167]

[0168] Step 3: Calculation of Advance Coefficient and Boundary Correction

[0169] The surge coefficients of each indicator in the gas channel discrimination index are calculated using the following formulas.

[0170] In the formula: D i Let be the breakthrough coefficient of the i-th indicator.

[0171] x i,max The maximum value of the i-th indicator.

[0172] is the average value of the i-th indicator.

[0173] The calculation results are shown in Tables 5-8.

[0174] The semi-trapezoidal mathematical model was modified based on the advance coefficient. It should be further noted that when modifying the semi-trapezoidal mathematical model based on the advance coefficient, the boundary values ​​were redefined for any index that did not meet the advance coefficient Di≤1.5.

[0175] Table 5 Static Indicators and Breakthrough Coefficient of Gas Injection Wells

[0176]

[0177] Table 6 Dynamic Indicators of Gas Injection Wells: Breakthrough Coefficient

[0178]

[0179] Table 7 Static Indicators of Production Wells: Breakthrough Coefficient

[0180]

[0181] Table 8. Dynamic Indicators of Production Wells: Breakthrough Coefficient

[0182]

[0183] Step 4: Membership Degree Calculation

[0184] Among the indicators for identifying gas channeling, the magnitudes of injection pressure and oil production intensity are approximately inversely proportional to the degree of gas channel development. This is illustrated by the aforementioned semi-trapezoidal mathematical model (e.g., Figure 3 As shown), the magnitudes of the remaining gas channel discrimination indices are approximately proportional to the degree of gas channel development, and all adopt the aforementioned semi-trapezoidal mathematical model (e.g. Figure 2 (As shown).

[0185] Furthermore, the mathematical formula for calculating the semi-trapezoid is:

[0186]

[0187] The mathematical formula for calculating the semi-trapezoid is:

[0188]

[0189] In the formula: B(x) is the membership degree of each indicator, a1 is the minimum boundary value of each indicator, and a2 is the maximum boundary value of each indicator.

[0190] Step 5: Calculate the comprehensive discriminant coefficient of dynamic and static indicators. Specifically, the formula for calculating the comprehensive discriminant coefficient of static indicators is as follows: The formula for calculating the comprehensive discrimination coefficient of dynamic indicators is:

[0191] In the formula: C j C is the comprehensive discriminant coefficient of static indicators; d B is the comprehensive discrimination coefficient of dynamic indicators. i ω represents the membership degree of the i-th dynamic or static index; i The weight of the i-th dynamic or static indicator.

[0192] The calculation results of the comprehensive discrimination coefficients of dynamic and static indicators for gas injection wells and production wells are shown in Tables 9 and 10, respectively.

[0193] Table 9 Comprehensive Discrimination Coefficients for Gas Injection Wells

[0194] hashtag Static comprehensive coefficient Dynamic comprehensive coefficient Overall composite coefficient A1 0.67 0.59 0.64 A2 0.59 0.21 0.45 A3 0.20 0.99 0.50 A4 0.12 0.82 0.39 A5 0.61 0.10 0.42 A6 0.17 0.86 0.44 A7 0.84 0.39 0.67 A8 0.88 0.07 0.57 A9 0.34 0.33 0.34 A10 1.00 0.36 0.76 A11 0.85 0.74 0.81 A12 0.19 0.87 0.45 A13 1.00 0.12 0.66

[0195] Table 10 Comprehensive Discrimination Coefficients for Production Wells

[0196]

[0197]

[0198]

[0199] Step Six: Calculate the combined weight of dynamic and static indicators. Specifically, the formula for calculating the combined weight of static indicators is as follows: The formula for calculating the comprehensive weight of dynamic indicators is:

[0200] In the formula: ω jThe static index of each injection well or production well is assigned a comprehensive weight.

[0201] ω m The weight of the m-th static index for each injection well or production well;

[0202] ω d The dynamic indicators of each injection well or production well are comprehensively weighted.

[0203] ω l The weight of the l-th dynamic indicator for each injection well or production well.

[0204] The calculation results are shown in Table 11.

[0205] Table 11 Calculation of Comprehensive Weights for Dynamic and Static Indicators

[0206] Static data weight of gas injection wells 0.62 Dynamic data weight of gas injection wells 0.38 Production well static data weights 0.34 Production well dynamic data weighting 0.66

[0207] Step 7: Calculate the total discriminant coefficient. The specific calculation formula is as follows:

[0208] C t =C j *ω j +C d *ω d

[0209] In the formula: C t The total discrimination coefficient for gas channeling in each injection well or production well.

[0210] C j The comprehensive discrimination coefficient of static indicators for each injection well or production well.

[0211] C d The comprehensive discrimination coefficient for dynamic indicators of each injection well or production well.

[0212] The calculation results of the total discrimination coefficients for gas injection wells and production wells are shown in Tables 12 and 13, respectively.

[0213] Table 12 Calculation of Total Discriminant Coefficient for Gas Injection Wells

[0214]

[0215] Table 13 Calculation of Total Discriminant Coefficient for Production Wells

[0216]

[0217]

[0218] Step 8: The classification and direction of gas channeling in this block were determined.

[0219] According to statistics, the development of gas channeling in the 13 gas injection wells in the block is as follows: Figure 4 As shown, 1 injection well had no gas channel development, 5 wells had weak gas channel development, and 7 wells had strong gas channel development; among the 39 production wells, 9 production wells had no gas channel development, 7 wells had weak gas channel development, and 23 wells had strong gas channel development. This has significant reference value for adjusting the working system and optimizing the injection volume.

[0220] In summary, the CO2-driven gas channel identification method for low-permeability reservoirs described in this invention has preliminarily determined the development direction of gas channel in well groups, which has significant reference value for the implementation of sealing and profile control measures, and can effectively reduce the occurrence of gas channeling.

[0221] The above description is merely a preferred embodiment of the present invention and is illustrative in nature, not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims.

Claims

1. A method for identifying CO2 gas channeling pathways in low-permeability oil reservoirs, characterized in that, include: S1. Data Collection and Indicator Optimization Collect geological data and production dynamic data of the target block well group, and calculate the gas channel discrimination index based on the geological data and production dynamic data; S2. Weight Calculation Calculate the weight of each gas channel discrimination index; S3. Calculation of Advance Coefficient and Boundary Correction Calculate the breakthrough coefficients of various gas channel discrimination indicators, and correct the semi-trapezoidal mathematical model based on the breakthrough coefficients; S4. Membership Degree Calculation Based on the different relationships between the magnitude of each gas channel discrimination index and the degree of gas channel development, an ascending semi-trapezoidal mathematical model and a descending semi-trapezoidal mathematical model are established respectively, and the membership degree is calculated. Based on the membership degree, each gas channel discrimination index is standardized to satisfy the value between 0 and 1. S5. Calculation of the comprehensive discrimination coefficient of dynamic and static indicators Based on the weights and membership degrees of various gas channel discrimination indicators, the comprehensive discrimination coefficients of static indicators and the comprehensive discrimination coefficients of dynamic indicators for each injection well and production well in the block are calculated. S6. Calculation of the combined weight of dynamic and static indicators Calculate the combined weight of static and dynamic indicators for each injection well and production well in the block; S7. Calculation of Total Discriminant Coefficient Combine the static index comprehensive discrimination coefficient and dynamic index comprehensive discrimination coefficient obtained from S5 with the static index comprehensive weight and dynamic index comprehensive weight obtained from S6 to calculate the total discrimination coefficient of gas channeling channels for each injection well and production well in the block. S8. Classification and Direction of Gas Channels Based on the on-site feedback regarding the development of gas channeling in the block well group, and combined with the geological and production dynamic data collected by S1, a three-level classification standard for gas channeling was determined, and the development direction of the gas channeling was identified.

2. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S1, the geological data includes the porosity, permeability, and effective thickness of the oil layer; the production dynamic data includes the daily gas injection volume, cumulative gas injection volume, injection pressure of the injection well, the maximum CO2 content at the wellhead of the production well, the daily gas production volume, the daily oil production volume, the wellhead oil pressure, and the cumulative gas production volume. The gas channel discrimination index includes static discrimination index and dynamic discrimination index. The static discrimination index includes formation coefficient, average porosity, average permeability, permeability variation coefficient, and permeability surge coefficient. The dynamic discrimination indicators are divided into injection wells and production wells. Injection wells include apparent gas intake index, average daily gas injection volume, cumulative injection volume per unit thickness, gas injection intensity, and average injection pressure. Production wells include maximum CO2 content at the wellhead, average daily gas production, gas-oil ratio, wellhead oil pressure surge coefficient, cumulative gas production per unit thickness, and oil production intensity.

3. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S2, the formula for calculating the weight of each indicator in the gas channel discrimination index is as follows: In the formula: A i The coefficient of variation for each indicator; a i Let be the standard deviation of the i-th indicator; The average value of the i-th indicator; ω i The weight of each indicator; i and n are natural numbers.

4. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S3, the formula for calculating the surge coefficient is as follows: In the formula: D i Let be the breakthrough coefficient of the i-th indicator. x i,max The maximum value of the i-th indicator. is the average value of the i-th indicator.

5. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, The mathematical formula for calculating the semi-trapezoid is as follows: The mathematical formula for calculating the semi-trapezoid is: In the formula: B(x) represents the membership degree of each indicator. a1 is the minimum boundary value of each indicator. a2 represents the maximum boundary value of each indicator. x is the indicator for identifying gas leakage channels.

6. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S5, the formula for calculating the comprehensive discrimination coefficient of the static index is: The formula for calculating the comprehensive discrimination coefficient of dynamic indicators is: In the formula: C j This is a comprehensive discrimination coefficient for static indicators; C d The dynamic indicator comprehensive discrimination coefficient; B i represents the membership degree of the i-th dynamic or static indicator; ω i The weight of the i-th dynamic or static indicator; i and n are natural numbers.

7. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S6, the formula for calculating the comprehensive weight of the static index is: In the formula: ω j The static index of each injection well or production well is assigned a comprehensive weight. ω m The weight of the m-th static index for each injection well or production well; m and n are natural numbers, where m ≥ 2; The formula for calculating the comprehensive weight of dynamic indicators is: In the formula: ω d The dynamic indicators of each injection well or production well are comprehensively weighted. ω l For each injection well or production well, the weight of the l-th dynamic indicator is... l and n are natural numbers, where l ≥ 2.

8. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S7, the formula for calculating the total discriminant coefficient is: C t =C j *oh j +C d *oh d In the formula: C t The total discrimination coefficient for gas channeling in each injection well or production well. C j The comprehensive discrimination coefficient of static indicators for each injection well or production well. C d The comprehensive discrimination coefficient for dynamic indicators of each injection well or production well. ω j The static index of each injection well or production well is assigned a comprehensive weight. ω d The dynamic indicators of each injection well or production well are comprehensively weighted.

9. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S8, the three-level classification standard for gas channel leakage is as follows: When the total discrimination coefficient of the gas channel is C t A value ≥0.5 indicates a strong degree of gas channel development; When the total discrimination coefficient of the gas channel is 0.4 ≤ C t <0.5 indicates a weak degree of development of the gas channel; When the total discrimination coefficient of the gas channel is C t <0.4 indicates that the gas channel is underdeveloped.

10. The method for identifying CO2 gas channeling pathways in low-permeability reservoirs according to claim 1, characterized in that, In S8, the method for determining the development direction of the gas channel is as follows: if the sum of the total discrimination coefficients of the gas channel of a pair of injection wells and production wells in the same well group is the largest and both are ≥0.4, then the development direction of the gas channel is the direction of the line connecting the injection wells and production wells.

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