Method suitable for shale gas reservoir refracturing transformation position optimization

Abstract

The invention discloses a method suitable for shale gas reservoir refracturing transformation position optimization. The method comprises the steps that logging data of candidate wells are collected, compressibility parameters are calculated, and geologic characteristic parameters are constructed; carrying out normalization processing on the compressibility parameters and the geological characteristic parameters to respectively obtain normalized compressibility parameters and normalized geological characteristic parameters; based on the normalized compressibility parameter and the normalized geological characteristic parameter, obtaining a compressibility index and a geological characteristic index through an analytic hierarchy process, and obtaining a comprehensive index based on the compressibility index and the geological characteristic index; calculating an engineering index of primary fracturing; obtaining the remaining recoverable reserves per meter according to the production and profile test of the primary fracturing; and assigning the comprehensive index, the engineering index of the primary fracturing and the remaining recoverable reserves by utilizing a comprehensive evaluation method to realize optimization of the re-fracturing position of the shale gas well. The fracturing success rate and the shale gas recovery rate are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and natural gas development, and in particular relates to a method for optimizing the position of repeated fracturing transformation of shale gas reservoirs. Background Art

[0002] In the development of shale gas reservoirs, repeated fracturing and section selection are the key links to improve the recovery rate, but it is currently facing many thorny problems. The geological conditions of shale gas reservoirs are extremely complex, and the reservoirs are highly heterogeneous. The rock mechanical properties, pore structure and permeability in different regions vary significantly, which makes it extremely difficult to accurately determine which areas are suitable for repeated fracturing. For example, the rock brittleness index in some areas is difficult to accurately determine, resulting in the inability to effectively estimate the fracturing effect when selecting sections.

[0003] The fracture network formed by the previous fracturing greatly interferes with the selection of repeated fracturing sections. Due to the lack of effective monitoring methods, it is difficult to accurately identify the direction, length and connectivity of existing fractures. This may cause new fractures to interfere with old fractures during repeated fracturing, making it impossible to form effective diversion channels, reducing the fracturing effect.

[0004] Existing segment selection technologies have limitations in data collection and analysis. Most methods rely on a single data source, such as logging data alone, and cannot comprehensively consider multiple factors such as geology and engineering. In addition, data analysis methods are relatively simple and difficult to process massive and complex data, and cannot provide a comprehensive and accurate basis for segment selection. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method suitable for optimizing the location of repeated fracturing transformation in shale gas reservoirs. By integrating geological factors, engineering factors and multi-source data of remaining recoverable reserves, a basis is provided for selecting repeated fracturing sections to avoid invalid or interfered areas, thereby more accurately screening out the most potential repeated fracturing sections and improving the fracturing success rate and shale gas recovery rate.

[0006] To achieve the above object, the present invention provides a method for optimizing the location of repeated fracturing in shale gas reservoirs, comprising:

[0007] Collect well logging data of candidate wells, calculate compressibility parameters, and construct geological characteristic parameters;

[0008] Normalizing the compressibility parameter and the geological characteristic parameter to obtain normalized compressibility parameter and normalized geological characteristic parameter respectively;

[0009] Based on the normalized compressibility parameter and the normalized geological characteristic parameter, a compressibility index and a geological characteristic index are obtained by using a hierarchy analysis method, and a comprehensive index is obtained based on the compressibility index and the geological characteristic index;

[0010] Calculate the engineering index for the initial fracturing;

[0011] Based on the production profile test of the initial fracturing, the remaining recoverable reserves per meter are obtained;

[0012] The comprehensive index, the engineering index of the initial fracturing and the remaining recoverable reserves are assigned values ​​by using a comprehensive evaluation method to achieve the optimization of the repeated fracturing position of the shale gas well.

[0013] Optionally, calculating compressibility parameters, the compressibility parameters including horizontal differential stress coefficient, rock brittleness index, reservoir compressibility index and poroelastic diversion stress coefficient;

[0014] The horizontal difference stress coefficient is calculated as follows:

[0015]

[0016] In the formula, σ hmax , σ hmin are the maximum horizontal principal stress and the minimum horizontal principal stress respectively; K t is the horizontal stress difference number;

[0017] The rock brittleness index is calculated as follows:

[0018] E R =[(E s -1×10 4 ) / (8×10 4 -1×10 4 )]×100;

[0019] ν BRIT =[(ν s -0.4) / (0.15-0.4)]×100;

[0020]

[0021] In the formula, E R is the dynamic Young's modulus; E s is the static Young's modulus; ν BRIT is the dynamic Poisson's ratio; ν s is the normalized Poisson's ratio; B2 is the rock brittleness index;

[0022] The reservoir compressibility index is calculated as follows:

[0023]

[0024] Where, Fr is the reservoir compressibility index; B2 is the rock brittleness index; is the internal friction angle; K IC is the value of mode I fracture toughness; KIIC is the mode II fracture toughness value;

[0025] The poroelastic steering stress coefficient is calculated as follows:

[0026]

[0027] In the formula, Π pore is the poroelastic steering stress coefficient; σ hmax is the maximum in-situ horizontal stress; σ hmin is the minimum in-situ horizontal stress; σ * is the stress difference caused by the pore pressure gradient; Δσ h is the maximum minimum in-situ horizontal stress difference; γ is Poisson's ratio; α is the biot coefficient; p i is the initial reservoir pressure; p wf is the bottom hole flowing pressure.

[0028] Optionally, the geological characteristic parameters are constructed based on porosity, gas content and organic carbon content.

[0029] Optionally, normalizing the compressibility parameter and the geological characteristic parameter includes:

[0030]

[0031] Among them, λ, β are parameter standardization values; x max is the maximum value of the parameter; x min is the minimum value of the parameter; x is the parameter value.

[0032] Optionally, obtaining a comprehensive index based on the compressibility index and the geological characteristic index includes:

[0033]

[0034] Among them, FI is the comprehensive index; n is the number of indices; S i is the weight of each index; W i For each index.

[0035] Optionally, calculating an engineering index of the initial fracturing, wherein the engineering index of the initial fracturing includes an initial single-well fluid usage index and an initial single-well proppant usage index;

[0036] Among them, the initial single well fluid usage index is calculated as follows:

[0037]

[0038] In the formula, S f is the initial single-stage liquid intensity; W is the initial single-stage liquid volume; L is the single-stage length;

[0039] The initial single well proppant usage index is calculated as follows:

[0040]

[0041] In the formula, S p is the initial sand adding strength; W P is the initial proppant mass.

[0042] Optionally, based on the production profile test of the initial fracturing, the remaining recoverable reserves per meter include:

[0043]

[0044] Among them, N rm is the remaining recoverable reserves per meter; N rs is the remaining recoverable reserves of a single section; L is the length of a single section; N m is recoverable reserves per meter; N s is recoverable reserves; L a is the total length to be selected, 1 meter; η is the remaining recoverable reserves per meter.

[0045] Optionally, using a comprehensive evaluation method to assign values ​​to the comprehensive index, the engineering index of the primary fracturing, and the remaining recoverable reserves includes:

[0046] S g =S g1 +S g2 +S g3 ;

[0047] Among them, S g1 Assignment of the comprehensive index; S g2 S is the value assigned to the engineering index of the initial fracturing; g3 is the value of the remaining recoverable reserves; S g is the sum of the assigned values.

[0048] Technical effect of the invention: The present invention discloses a method suitable for optimizing the location of repeated fracturing transformation in shale gas reservoirs. By integrating geological factors, engineering factors and multi-source data of remaining recoverable reserves, a basis is provided for selecting repeated fracturing sections to avoid invalid or interfered areas, thereby more accurately screening out the most potential repeated fracturing sections and improving the success rate of fracturing and shale gas recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0050] Figure 1 A schematic flow chart of a method for optimizing locations for repeated fracturing in shale gas reservoirs according to an embodiment of the present invention;

[0051] Figure 2 This is a graph showing a change in the horizontal difference stress coefficient according to an embodiment of the present invention;

[0052] Figure 3 This is a graph showing the change in rock brittleness index according to an embodiment of the present invention;

[0053] Figure 4 A diagram showing changes in the reservoir compressibility index according to an embodiment of the present invention;

[0054] Figure 5 This is a graph showing changes in the poroelastic steering stress coefficient according to an embodiment of the present invention;

[0055] Figure 6 This is a porosity data diagram of an embodiment of the present invention;

[0056] Figure 7 This is a gas content data diagram of an embodiment of the present invention;

[0057] Figure 8 This is an organic carbon data diagram of an embodiment of the present invention;

[0058] Fig. 9 This is a comprehensive index diagram of an embodiment of the present invention;

[0059] Fig.10 This is a single well fluid usage index diagram of an embodiment of the present invention;

[0060] Fig.11 This is a proppant dosage index diagram for a single well in an embodiment of the present invention;

[0061] Fig.12 A diagram of the remaining recoverable reserves per meter according to an embodiment of the present invention;

[0062] Fig.13 A graph of the total and comprehensive evaluation of the embodiments of the present invention is given. DETAILED DESCRIPTION

[0063] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0064] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0065] like Figure 1 As shown, this embodiment provides a method for optimizing the location of repeated fracturing in shale gas reservoirs, including:

[0066] Collect well logging data of candidate wells, calculate compressibility parameters, and construct geological characteristic parameters;

[0067] Normalizing the compressibility parameter and the geological characteristic parameter to obtain normalized compressibility parameter and normalized geological characteristic parameter respectively;

[0068] Based on the normalized compressibility parameter and the normalized geological characteristic parameter, a compressibility index and a geological characteristic index are obtained by using a hierarchy analysis method, and a comprehensive index is obtained based on the compressibility index and the geological characteristic index;

[0069] Calculate the engineering index for the initial fracturing;

[0070] Based on the production profile test of the initial fracturing, the remaining recoverable reserves per meter are obtained;

[0071] The comprehensive index, the engineering index of the initial fracturing and the remaining recoverable reserves are assigned values ​​by using a comprehensive evaluation method to achieve the optimization of the repeated fracturing position of the shale gas well.

[0072] Specifically, in this embodiment, the comprehensive evaluation method is used to assign values ​​to the comprehensive sweet spot index, engineering index and remaining recoverable reserves. If the total value is 3 or 4, it is evaluated as poor; the total value is 5, 6 or 7, it is evaluated as medium; the total value is 8 or 9, it is evaluated as good. In this way, a method for optimizing the evaluation of the location of refracturing in shale gas wells is obtained, and the places with comprehensive evaluation as good are screened out to optimize the location of the well section.

[0073] Further, such as Figure 2-Figure 5 As shown, the compressibility parameters are calculated, and the compressibility parameters include horizontal difference stress coefficient, rock brittleness index, reservoir compressibility index and poroelastic steering stress coefficient;

[0074] The horizontal difference stress coefficient is calculated as follows:

[0075]

[0076] In the formula, σ hmax , σ hmin are the maximum horizontal principal stress and the minimum horizontal principal stress respectively; K t is the horizontal stress difference number;

[0077] The rock brittleness index is calculated as follows:

[0078] E R =[(E s -1×10 4 ) / (8×10 4 -1×10 4 )]×100;

[0079] νBRIT =[(ν s -0.4) / (0.15-0.4)]×100;

[0080]

[0081] In the formula, E R is the dynamic Young's modulus; E s is the static Young's modulus; ν BRIT is the dynamic Poisson's ratio; ν s is the normalized Poisson's ratio; B2 is the rock brittleness index;

[0082] The reservoir compressibility index is calculated as follows:

[0083]

[0084] Where, Fr is the reservoir compressibility index; B2 is the rock brittleness index; is the internal friction angle; K IC is the value of mode I fracture toughness; K IIC is the mode II fracture toughness value;

[0085] The poroelastic steering stress coefficient is calculated as follows:

[0086]

[0087] In the formula, Π pore is the poroelastic steering stress coefficient; σ hmax is the maximum in-situ horizontal stress; σ hmin is the minimum in-situ horizontal stress; σ * is the stress difference caused by the pore pressure gradient; Δσ h is the maximum minimum in-situ horizontal stress difference; γ is Poisson's ratio; α is the biot coefficient; p i is the initial reservoir pressure; p wf is the bottom hole flowing pressure.

[0088] Further, such as Figure 6-Figure 8 The geological characteristic parameters are constructed based on porosity, gas content and organic carbon content.

[0089] Furthermore, normalizing the compressibility parameter and the geological characteristic parameter includes:

[0090]

[0091] Among them, λ, β are parameter standardization values; x max is the maximum value of the parameter; x min is the minimum value of the parameter; x is the parameter value.

[0092] Furthermore, the judgment matrix is ​​constructed: the respective weights are determined by means of the hierarchical analysis method after normalization. The corresponding importance levels of the two schemes are expressed in the form of the ratio of the importance levels of the two schemes. The relative advantages and disadvantages of each evaluation index are ranked using the Santy 1-9 scale method, and the judgment matrix of the evaluation index is constructed in turn. The judgment matrix table of the compressibility index is shown in Table 1, and the judgment matrix table of the geological characteristic index is shown in Table 2.

[0093] Table 1

[0094]

[0095] Table 2

[0096] index Porosity Total gas content Organic carbon content Porosity 1 0.333 0.333 Gas content 3 1 1 Organic carbon content 3 1 1

[0097] The square root method is used to approximate the eigenvectors of a matrix.

[0098] The consistency of the judgment matrix was tested. The consistency test results of the compressibility index are shown in Table 3, and the consistency test results of the geological characteristic index are shown in Table 4. CI is an indicator for measuring the deviation of the judgment matrix from the consistency. The larger the CI, the worse the consistency of the judgment matrix. When CI is 0, the judgment matrix has complete consistency. When CR < 0.1, the consistency of the judgment matrix can be considered acceptable.

[0099]

[0100] CR = CI / RI;

[0101] In the formula, λ is the maximum eigenvalue of the judgment matrix; n is the order of the judgment matrix; CI is the index for measuring the deviation of the judgment matrix from the consistency; CR is the consistency ratio; RI is the average random consistency index.

[0102] Table 3

[0103]

[0104] Table 4

[0105]

[0106] Substitute the calculated parameter normalization values ​​and weight coefficients into the formula:

[0107] like Fig. 9 As shown, the comprehensive index obtained based on the compressibility index and the geological characteristic index includes:

[0108]

[0109] Among them, FI is the comprehensive index; n is the number of indices; S i is the weight of each index; Wi The comprehensive index weight table is shown in Table 5.

[0110] Table 5

[0111]

[0112] Furthermore, the engineering index of the initial fracturing is calculated, including two parameters: the initial fracturing fluid volume and the initial fracturing proppant dosage, to obtain the initial single well fluid usage index. The initial single well proppant dosage index includes:

[0113] Among them, Fig.10 As shown, the initial single well fluid usage index is calculated as follows:

[0114]

[0115] In the formula, S f is the initial single-stage liquid intensity; W is the initial single-stage liquid volume; L is the single-stage length;

[0116] like Fig.11 As shown, the initial single well proppant usage index is calculated as follows:

[0117]

[0118] In the formula, S p is the initial sand adding strength; W P is the initial proppant mass.

[0119] Furthermore, according to the production profile test of the initial fracturing, the remaining recoverable reserves per meter include:

[0120]

[0121]

[0122] Among them, N rm is the remaining recoverable reserves per meter; N rs is the remaining recoverable reserves of a single section; L is the length of a single section; N m is recoverable reserves per meter; N s is recoverable reserves; L a is the total length to be selected, 1 meter; η is the remaining recoverable reserves per meter. Fig.12 shown.

[0123] Further, such as Fig.13 As shown in Table 6, the comprehensive evaluation method is used to assign values ​​to the comprehensive index, the engineering index of the initial fracturing and the remaining recoverable reserves, including:

[0124] S g =S g1 +S g2 +Sg3 ;

[0125] Among them, S g1 Assignment of the comprehensive index; S g2 S is the value assigned to the engineering index of the initial fracturing; g3 is the value of the remaining recoverable reserves; S g is the sum of the assigned values.

[0126] Table 6

[0127]

[0128] In this embodiment, according to the assignment sum comprehensive evaluation diagram, the refracturing positions are finally obtained as follows: 3229-3300m, 3350-4540m and 4615-4750m. These sections can be used as refracturing positions.

[0129] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for optimizing the location of repeated fracturing in shale gas reservoirs, characterized in that: include: Collect well logging data of candidate wells, calculate compressibility parameters, and construct geological characteristic parameters; Normalizing the compressibility parameter and the geological characteristic parameter to obtain normalized compressibility parameter and normalized geological characteristic parameter respectively; Based on the normalized compressibility parameter and the normalized geological characteristic parameter, a compressibility index and a geological characteristic index are obtained by using a hierarchy analysis method, and a comprehensive index is obtained based on the compressibility index and the geological characteristic index; Calculate the engineering index for the initial fracturing; Based on the production profile test of the initial fracturing, the remaining recoverable reserves per meter are obtained; The comprehensive index, the engineering index of the initial fracturing and the remaining recoverable reserves are assigned values ​​by using a comprehensive evaluation method to achieve the optimization of the repeated fracturing position of the shale gas well.

2. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: Calculating compressibility parameters, wherein the compressibility parameters include a horizontal differential stress coefficient, a rock brittleness index, a reservoir compressibility index, and a poroelastic diversion stress coefficient; The horizontal difference stress coefficient is calculated as follows: In the formula, σ hmax , σ hmin are the maximum horizontal principal stress and the minimum horizontal principal stress respectively; K t is the horizontal stress difference number; The rock brittleness index is calculated as follows: AND R =[(And s -1×10 4 ) / (8×10 4 -1×10 4 )]×100; n BRIT =[(n s -0.4) / (0.15-0.4)]×100; In the formula, E R is the dynamic Young's modulus; E s is the static Young's modulus; ν BRIT is the dynamic Poisson's ratio; ν s is the normalized Poisson's ratio; B2 is the rock brittleness index; The reservoir compressibility index is calculated as follows: Where, Fr is the reservoir compressibility index; B2 is the rock brittleness index; is the internal friction angle; K IC is the value of mode I fracture toughness; K IIC is the mode II fracture toughness value; The poroelastic steering stress coefficient is calculated as follows: In the formula, Π pore is the poroelastic steering stress coefficient; σ hmax is the maximum in-situ horizontal stress; σ hmin is the minimum in-situ horizontal stress; σ * is the stress difference caused by the pore pressure gradient; Δσ h is the maximum minimum in-situ horizontal stress difference; γ is Poisson's ratio; α is the biot coefficient; p i is the initial reservoir pressure; p wf is the bottom hole flowing pressure.

3. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: The geological characteristic parameters are constructed based on porosity, gas content and organic carbon content.

4. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: The normalization process of the compressibility parameter and the geological characteristic parameter includes: Among them, λ, β are parameter standardization values; x max is the maximum value of the parameter; x min is the minimum value of the parameter; x is the parameter value.

5. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: Obtaining a comprehensive index based on the compressibility index and the geological characteristic index includes: Among them, FI is the comprehensive index; n is the number of indices; S i is the weight of each index; W i For each index.

6. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: Calculating an engineering index of the initial fracturing, wherein the engineering index of the initial fracturing includes an initial single-well fluid usage index and an initial single-well proppant usage index; Among them, the initial single well fluid usage index is calculated as follows: In the formula, S f is the initial single-stage liquid intensity; W is the initial single-stage liquid volume; L is the single-stage length; The initial single well proppant usage index is calculated as follows: In the formula, S p is the initial sand adding strength; W P is the initial proppant mass.

7. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: According to the production profile test of the initial fracturing, the remaining recoverable reserves per meter include: Among them, N rm is the remaining recoverable reserves per meter; N rs is the remaining recoverable reserves of a single section; L is the length of a single section; N m is recoverable reserves per meter; N s is recoverable reserves; L a is the total length to be selected, 1 meter; η is the remaining recoverable reserves per meter.

8. The method for optimizing the location of repeated fracturing in shale gas reservoirs according to claim 1, characterized in that: Assigning values ​​to the comprehensive index, the engineering index of the initial fracturing and the remaining recoverable reserves by using a comprehensive evaluation method includes: S g =S g1 +S g2 +S g3 ; Among them, S g1 Assignment of the comprehensive index; S g2 S is the value assigned to the engineering index of the initial fracturing; g3 is the value of the remaining recoverable reserves; S g is the sum of the assigned values.

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