Classification method for tight sandstone gas reservoir

Abstract

The invention relates to the technical field of gas reservoir grading methods, in particular to a compact sandstone gas reservoir grading method which comprises the steps that multiple evaluation indexes of a plurality of compact sandstone gas reservoirs are obtained; based on the multiple evaluation indexes of the tight sandstone gas reservoir stratums, determining a comprehensive evaluation index value of each tight sandstone gas reservoir stratum; and based on the comprehensive evaluation index value of each tight sandstone gas reservoir, grading the tight sandstone gas reservoir by adopting a cumulative frequency method. According to the classification method for the tight sandstone gas reservoir, calculation is easy, the classification method is suitable for engineering practice, evaluation indexes in the reservoir classification method are determined, regional representativeness is achieved, consumed time is short, and the classification method is easy to achieve in engineering practice.

Description

Technical Field

[0001] The invention relates to the technical field of gas reservoir stratum classification methods, in particular to a classification method for tight sandstone gas reservoir stratum. Background Art

[0002] Tight gas is stored in low-porosity (porosity less than 10%) and low-permeability (permeability less than 0.1mD) reservoirs with low gas saturation (less than 60%). The Sulige tight sandstone gas reserves are considerable and show great potential under the existing economic and technical conditions. However, after a long and complex diagenesis and structural transformation, the reservoir has the characteristics of large distribution area, poor reservoir properties, complex microscopic pore structure, and strong heterogeneity. It is difficult to develop and it is necessary to identify high-quality development reservoirs. The existing methods for grading tight sandstone gas reservoirs usually have the following defects: the reservoir evaluation indicators are complicated and general, and are not representative of the region; most grading methods are complex to calculate, time-consuming, and difficult to implement in engineering practice. Summary of the invention

[0003] The present invention provides a classification method for tight sandstone gas reservoirs, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problems in the existing reservoir classification methods that the evaluation indicators are complicated and general, not representative of the region, the classification methods are complex to calculate, time-consuming, and difficult to implement in engineering practice.

[0004] The technical solution of the present invention is achieved by the following measures: A classification method for tight sandstone gas reservoirs, comprising:

[0005] Step 101: obtaining multiple evaluation indicators of several tight sandstone gas reservoirs;

[0006] Step 102: determining a comprehensive evaluation index value of each tight sandstone gas reservoir based on the multiple evaluation indexes of the plurality of tight sandstone gas reservoirs;

[0007] Step 103: Based on the comprehensive evaluation index value of each tight sandstone gas reservoir, the tight sandstone gas reservoir is graded using a cumulative frequency method.

[0008] The following are further optimizations and / or improvements to the above technical solutions:

[0009] Furthermore, in the above step 101, the multiple evaluation indicators include obtaining the reservoir thickness, porosity, gas saturation, permeability, natural gamma, natural potential, deep resistivity, brittleness index and strain energy release rate of each reservoir based on the logging curve; classifying the reservoir thickness, porosity, gas saturation, permeability and brittleness index as positive indicators; and classifying the natural gamma, natural potential, deep resistivity and strain energy release rate as negative indicators.

[0010] Furthermore, in the above step 102, the entropy weight method is used to calculate the weight of each evaluation index, and based on the weight of each evaluation index, the standardized evaluation index is substituted into the comprehensive evaluation index calculation model to obtain the comprehensive evaluation index value corresponding to each tight sandstone gas reservoir.

[0011] Furthermore, the calculation formula of the above comprehensive evaluation index calculation model is as follows:

[0012]

[0013] Among them, Feci is the comprehensive evaluation index value;

[0014] P i-normal is the normalized positive indicator, N i-normal It is the normalized reverse indicator;

[0015] The subscripts i and j are the serial numbers of the positive and negative indicators, respectively;

[0016] n and m are the number of positive and negative indicators, respectively;

[0017] W is the weight of each indicator.

[0018] Furthermore, the above-mentioned standardization process of the evaluation indicators is specifically as follows:

[0019] Assume that k evaluation indicators X1, X2, X3…X are given k , where the evaluation index X i ={x1,x2,x3…x n}, n represents the number of data for each evaluation index, then the evaluation index and its value constitute a k×n matrix. Assume that the standardized value of each evaluation index data is Y 1j ,Y 2j ,Y 3j …Y kj , where j∈(1,n);

[0020]

[0021] In the formula, X ij is the actual value of the evaluation index; Y ij is the standardized value of the evaluation index.

[0022] Furthermore, in the above step 103, the reservoirs are divided into levels I, II and III based on the comprehensive evaluation index values ​​corresponding to the cumulative frequencies of 60% and 30%.

[0023] Furthermore, in the classification results of the above tight sandstone gas reservoirs, the development performance of the Class I reservoir is the best, the development performance of the Class II reservoir is second, and the development performance of the Class III reservoir is the worst.

[0024] Furthermore, when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is less than 0.1618, it means that the development performance of the reservoir is poor; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is between 0.1618 and 0.2060, it means that the development performance of the reservoir is average; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is greater than 0.2060, it means that the development performance of the reservoir is better.

[0025] The classification method for tight sandstone gas reservoirs of the present invention has simple calculation, is applicable to engineering practice, clarifies evaluation indicators in the reservoir classification method, has regional representativeness, is short in time, and is easy to implement in engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Attached Figure 1 A flow chart of a classification method for tight sandstone gas reservoirs provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0028] The present invention will be further described below in conjunction with embodiments:

[0029] Example 1: Figure 1 As shown, the classification method for tight sandstone gas reservoirs comprises:

[0030] Step 101: obtaining multiple evaluation indicators of several tight sandstone gas reservoirs;

[0031] Step 102: determining a comprehensive evaluation index value of each tight sandstone gas reservoir based on the multiple evaluation indexes of the plurality of tight sandstone gas reservoirs;

[0032] Step 103: Based on the comprehensive evaluation index value of each tight sandstone gas reservoir, the tight sandstone gas reservoir is graded using a cumulative frequency method.

[0033] Example 2: As an optimization of the above example, in step 101, multiple evaluation indicators include obtaining the reservoir thickness, porosity, gas saturation, permeability, natural gamma, natural potential, deep resistivity, brittleness index and strain energy release rate of each reservoir based on the logging curve; the reservoir thickness, porosity, gas saturation, permeability and brittleness index are classified as positive indicators; the natural gamma, natural potential, deep resistivity and strain energy release rate are classified as reverse indicators.

[0034] Example 3: As an optimization of the above example, in step 102, the entropy weight method is used to calculate the weight of each evaluation index. Based on the weight of each evaluation index, the standardized evaluation index is substituted into the comprehensive evaluation index calculation model to obtain the comprehensive evaluation index value corresponding to each tight sandstone gas reservoir.

[0035] Embodiment 4: As an optimization of the above embodiment, the calculation formula of the comprehensive evaluation index calculation model is as follows:

[0036]

[0037] Among them, Feci is the comprehensive evaluation index value;

[0038] P i-normal is the normalized positive indicator, N i-normal It is the normalized reverse indicator;

[0039] The subscripts i and j are the serial numbers of the positive and negative indicators, respectively;

[0040] n and m are the number of positive and negative indicators, respectively;

[0041] W is the weight of each indicator.

[0042] Embodiment 4: As an optimization of the above embodiment, the evaluation index is standardized, specifically:

[0043] Assume that k evaluation indicators X1, X2, X3…X are given k , where the evaluation index X i ={x1,x2,x3…x n}, n represents the number of data for each evaluation index, then the evaluation index and its value constitute a k×n matrix. Assume that the standardized value of each evaluation index data is Y 1j ,Y 2j ,Y 3j …Y kj , where j∈(1,n);

[0044]

[0045] In the formula, X ijis the actual value of the evaluation index; Y ij is the standardized value of the evaluation index.

[0046] Embodiment 5: As an optimization of the above embodiment, in step 103, the reservoirs are divided into Class I, Class II, and Class III based on the comprehensive evaluation index values ​​corresponding to the cumulative frequencies of 60% and 30%.

[0047] Example 6: As an optimization of the above example, in the classification results of tight sandstone gas reservoirs, the development performance of Class I reservoirs is the best, the development performance of Class II reservoirs is second, and the development performance of Class III reservoirs is the worst.

[0048] Example 7: As an optimization of the above example, when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is less than 0.1618, it means that the reservoir development performance is poor; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is between 0.1618 and 0.2060, it means that the reservoir development performance is average; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is greater than 0.2060, it means that the reservoir development performance is better.

[0049] Implementation Cases:

[0050] Taking the He 8-Shan 1 reservoir in the Sudong area of ​​the Sulige gas field as an example, this reservoir is a typical tight sandstone gas reservoir in the Ordos Basin, which contains rich natural gas resources and has great economic potential. This reservoir is a fluvial phase deposit, with rapid reservoir space changes, strong heterogeneity, and poor reservoir properties. Compared with conventional oil reservoirs, it is more difficult to develop and it is necessary to identify high-quality development reservoirs.

[0051] 128 tight sandstone gas reservoirs in the region were selected, and seven parameters of each reservoir, including reservoir thickness, porosity, gas saturation, permeability, natural gamma, natural potential and deep resistivity, were obtained based on the well logging curves. The two parameters, brittleness index and strain energy release rate, were obtained through secondary interpretation of well logging by formula calculation, and a tight sandstone gas reservoir evaluation data set was constructed, as shown in Table 1. The entropy weight method was used to calculate the weights of each evaluation index, and the calculation results are shown in Table 2.

[0052] Based on the weights in Table 2, the nine standardized evaluation indicators are substituted into the comprehensive evaluation indicator calculation model to obtain the comprehensive evaluation indicator value corresponding to each tight sandstone gas reservoir.

[0053] The cumulative frequency method is used to rearrange the comprehensive evaluation indicators in order from small to large values, and the comprehensive evaluation index values ​​corresponding to the cumulative frequencies of 60% and 30% are used as the boundaries to divide the reservoirs into Class I, II, and III. Among them, Class I reservoirs are the best and Class III reservoirs are the worst. The classification results of tight sandstone gas reservoirs are shown in Table 3 below.

[0054] Based on the classification results of tight sandstone gas reservoirs and the evaluation index data of new tight sandstone gas reservoirs to be developed shown in Table 3, the new tight sandstone gas reservoirs to be developed can be classified. When the calculated comprehensive evaluation index value of the new tight sandstone gas reservoir to be developed is less than 0.1618, it means that the reservoir development performance is poor; when the calculated comprehensive evaluation index value of the new tight sandstone gas reservoir to be developed is between 0.1618 and 0.2060, it means that the reservoir development performance is average; when the calculated comprehensive evaluation index value of the new tight sandstone gas reservoir to be developed is greater than 0.2060, it means that the reservoir development performance is good.

[0055] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

[0056] Table 1 Tight sandstone gas reservoir evaluation indicators

[0057]

[0058] Table 2 Weights of various evaluation indicators

[0059]

[0060] Table 3 Classification results of tight sandstone gas reservoirs

[0061] Reservoir classification Level I reservoir (excellent) Level II reservoir (middle) Class III reservoir (poor) Comprehensive evaluation index value >0.2060 0.1618-0.2060 <0.1618

Claims

1. A classification method for tight sandstone gas reservoirs, characterized in that include: Step 101: obtaining multiple evaluation indicators of several tight sandstone gas reservoirs; Step 102: determining a comprehensive evaluation index value of each tight sandstone gas reservoir based on the multiple evaluation indexes of the plurality of tight sandstone gas reservoirs; Step 103: Based on the comprehensive evaluation index value of each tight sandstone gas reservoir, the tight sandstone gas reservoir is graded using a cumulative frequency method.

2. The classification method for tight sandstone gas reservoir according to claim 1, characterized in that In step 101, multiple evaluation indicators include obtaining the reservoir thickness, porosity, gas saturation, permeability, natural gamma, natural potential, deep resistivity, brittleness index and strain energy release rate of each reservoir based on the logging curve; classifying the reservoir thickness, porosity, gas saturation, permeability and brittleness index as positive indicators; and classifying the natural gamma, natural potential, deep resistivity and strain energy release rate as negative indicators.

3. The classification method for tight sandstone gas reservoir according to claim 1 or 2, characterized in that In step 102, the entropy weight method is used to calculate the weight of each evaluation index. Based on the weight of each evaluation index, the standardized evaluation index is substituted into the comprehensive evaluation index calculation model to obtain the comprehensive evaluation index value corresponding to each tight sandstone gas reservoir.

4. The classification method for tight sandstone gas reservoir according to claim 3, characterized in that The calculation formula of the comprehensive evaluation index calculation model is as follows: Among them, Feci is the comprehensive evaluation index value; P i-normal is the normalized positive indicator, N i-normal It is the normalized reverse indicator; The subscripts i and j are the serial numbers of the positive and negative indicators, respectively; n and m are the number of positive and negative indicators, respectively; W is the weight of each indicator.

5. The classification method for tight sandstone gas reservoir according to claim 3, characterized in that The standardized processing of evaluation indicators is as follows: Assume that k evaluation indicators X1, X2, X3…X are given k , where the evaluation index X i ={x1,x2,x3…x n }, n represents the number of data for each evaluation index, then the evaluation index and its value constitute a k×n matrix. Assume that the standardized value of each evaluation index data is Y 1j ,Y 2j ,Y 3j …Y kj , where j∈(1,n); Where, X ij is the actual value of the evaluation index; Y ij is the standardized value of the evaluation index.

6. The classification method for tight sandstone gas reservoir according to claim 4, characterized in that The standardized processing of evaluation indicators is as follows: Assume that k evaluation indicators X1, X2, X3…X are given k , where the evaluation index X i ={x1,x2,x3…x n }, n represents the number of data for each evaluation index, then the evaluation index and its value constitute a k×n matrix. Assume that the standardized value of each evaluation index data is Y 1j ,Y 2j ,Y 3j …Y kj , where j∈(1,n); Where, X ij is the actual value of the evaluation index; Y ij is the standardized value of the evaluation index.

7. The classification method for tight sandstone gas reservoir according to claim 1, 2, 4, 5 or 6, characterized in that In step 103, the reservoirs are divided into Class I, Class II, and Class III based on the comprehensive evaluation index values ​​corresponding to the cumulative frequencies of 60% and 30%.

8. The classification method for tight sandstone gas reservoir according to claim 3, characterized in that In step 103, the reservoirs are divided into Class I, Class II, and Class III based on the comprehensive evaluation index values ​​corresponding to the cumulative frequencies of 60% and 30%.

9. The classification method for tight sandstone gas reservoir according to claim 7, characterized in that In the classification results of tight sandstone gas reservoirs, the development performance of Class I reservoirs is the best, the development performance of Class II reservoirs is second, and the development performance of Class III reservoirs is the worst; When the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is less than 0.1618, it means that the development performance of the reservoir is poor; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is between 0.1618 and 0.2060, it means that the development performance of the reservoir is average; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is greater than 0.2060, it means that the development performance of the reservoir is better.

10. The classification method for tight sandstone gas reservoir according to claim 8, characterized in that In the classification results of tight sandstone gas reservoirs, the development performance of Class I reservoirs is the best, the development performance of Class II reservoirs is second, and the development performance of Class III reservoirs is the worst; When the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is less than 0.1618, it means that the development performance of the reservoir is poor; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is between 0.1618 and 0.2060, it means that the development performance of the reservoir is average; when the calculated comprehensive evaluation index value of the new reservoir of the tight sandstone gas reservoir to be developed is greater than 0.2060, it means that the development performance of the reservoir is better.

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