Calculation method of length and width of shale oil and gas pressure fractures based on fracture conductivity

Abstract

The present invention provides a method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity. The method comprises: step 1, collecting reservoir geology, fluid properties, and fracturing operation parameters; step 2, calculating the optimal conductivity of the fracturing fracture based on the fracture operation parameters; step 3, calculating the optimal fracturing fracture length based on the optimal conductivity of the fracturing fracture obtained in step 2; and step 4, calculating the optimal fracturing fracture width based on the optimal fracturing fracture length obtained in step 3. This method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity is highly practical, convenient and fast, requires few parameters, is simple to apply, has good operability, and effectively realizes the calculation of fracture parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield development, and in particular to a method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity. Background Art

[0002] In shale oil and gas development, both hydraulic fracturing theory and current production practices demonstrate that maximizing productivity through hydraulic fracturing requires determining a unique optimal fracture conductivity (CfD). This unique fracture conductivity also determines the unique corresponding fracture length and width. Therefore, calculating fracture conductivity is crucial for both shale oil and gas fracturing design and productivity prediction. Previous studies have primarily determined the optimal fracture conductivity by reading it from a fitted relationship chart. In conditions of extremely low permeability or low sand loading, the optimal fracture conductivity is generally 1.6. This approach suffers from high uncertainty in the results and a lack of mathematical derivation, making it difficult to implement in programming. There is an urgent need for more convenient and scientific calculation methods.

[0003] Chinese patent application number CN201710374643.6 describes a method for modeling shale gas horizontal well network fractures based on microseismic events. The method includes the following steps: 1. Data preparation and import; 2. Establishing a main fracture model for the shale gas network fractures; 3. Combining fracturing microseismic monitoring data to generate a gridded microseismic event density model and a network fracture density model; 4. Establishing a branch fracture model for the shale gas network fractures; 5. Establishing a connecting fracture model for the shale gas network fractures; and 6. Combining the main fracture model, branch fracture model, and connecting fracture model to form a discrete fracture model for the shale gas horizontal well fracturing network fractures.

[0004] The Chinese patent application with application number CN201810154463.1 discloses a method for optimizing the conductivity of multi-stage fractures in shale reservoirs, including the following steps: S1. Optimizing complex fracture transformation bodies, obtaining reservoir characteristics of shale reservoirs, and obtaining the volume and permeability of the optimized transformation bodies based on oil and gas seepage mechanics theory; S2. Determining the optimal equivalent fracture permeability; S3. Determining the equivalent fracture conductivity; and S4. Calculating the optimal multi-stage fracture conductivity.

[0005] In the Chinese patent application with application number: CN201610982227.X, a new method for optimizing the conductivity of network fractures is involved. This method can be used to determine the conductivity required for the main fractures supported by proppants and the self-supporting fractures without proppants in the network fractures, thereby providing guidance for fracturing optimization design, forming a highly efficient supported fracture network, and improving the fracturing effect of shale gas and tight oil and gas reservoirs. This method is mainly based on the principle of hydropower similarity to optimize the complex network fractures by equivalently converting them into simple fracture bodies. First, the reservoir connected by the fracture network is equivalent to a high permeability zone, and the permeability of the high permeability zone is optimized using the optimal production; then, according to the principle of hydropower similarity, the equivalent fracture permeability is optimized; finally, the conductivity of the ceramsite-supported main fractures and the self-supporting branch fractures in the network fractures are optimized separately, thereby providing guidance for fracturing optimization design.

[0006] The above existing technologies are quite different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new analytical calculation method for the optimal fracture conductivity and fracture length and width of shale oil and gas fracturing production. Summary of the Invention

[0007] The purpose of the present invention is to provide a shale oil and gas pressure fracture length and width calculation method based on fracture conductivity that is highly practical, convenient and fast, has few parameter requirements, can quickly calculate the optimal fracture length and width, and is beneficial for guiding the improvement of fracture well productivity.

[0008] The object of the present invention can be achieved by the following technical measures: a method for calculating the length and width of shale oil and gas pressure fractures based on the fracture conductivity coefficient, the method for calculating the length and width of shale oil and gas pressure fractures based on the fracture conductivity coefficient comprises:

[0009] Step 1: Collect reservoir geology, fluid properties, and fracturing operation parameters;

[0010] Step 2, calculating the optimal conductivity of the hydraulic fracture according to the fracture construction parameters;

[0011] Step 3, calculating the optimal hydraulic fracture length according to the optimal hydraulic fracture conductivity obtained in step 2;

[0012] Step 4: Calculate the optimal hydraulic fracture width based on the optimal hydraulic fracture length obtained in step 3.

[0013] The purpose of the present invention can also be achieved by the following technical measures:

[0014] In step 1, the collected reservoir geological parameters include oil layer permeability, oil layer thickness, reservoir pressure, and reservoir drainage radius.

[0015] In step 1, the collected fluid properties include crude oil viscosity and crude oil volume coefficient.

[0016] In step 1, the collected fracturing operation parameters include crack half-length, crack height, and skin coefficient.

[0017] In step 2, the optimal fracture conductivity is calculated using the following formula:

[0018]

[0019] Where,

[0020] Y-comprehensive coefficient;

[0021] C fD is the optimal conductivity of the fracture;

[0022] x f The crack is half length.

[0023] In step 2, differentiating Equation 1 yields:

[0024]

[0025] When Y' is 0, the optimal conductivity coefficient C of the crack can be obtained fD The value of is 1.571.

[0026] In step 3, the optimal fracture length is calculated, the fracture half length X f and sand volume V f and the fracture conductivity C fD The relationship between them is:

[0027]

[0028] Where,

[0029] K f - fracture permeability;

[0030] V f -Total sand volume;

[0031] k-reservoir permeability;

[0032] h f - crack height;

[0033] C fD -Optimal conductivity of the fracture.

[0034] In step 4, the optimal fracture width is calculated using the following formula:

[0035]

[0036] Where,

[0037] Wopt - optimal fracture width;

[0038] V f -Total sand volume;

[0039] k-reservoir permeability;

[0040] K f - fracture permeability;

[0041] h-oil layer thickness.

[0042] The present invention's method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity relates to an analytical calculation method for determining the optimal fracture conductivity for shale oil and gas fracturing production. This method can derive the optimal fracture conductivity, which can be used to guide productivity improvements in fracturing wells. The present invention's method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity is highly practical, convenient, fast, requires few parameters, is simple to use, and offers excellent operability, effectively calculating fracture parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a specific embodiment of the method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity of the present invention;

[0044] Figure 2 This is a comparison chart of the average production of wells and blocks in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0045] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0046] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0047] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0048] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0049] The method for calculating the length and width of shale oil and gas pressure fractures based on the fracture conductivity of the present invention specifically includes the following steps:

[0050] Step 1: Collect reservoir geology, fluid properties, and fracturing parameters. Reservoir geology parameters include reservoir permeability, reservoir thickness, reservoir pressure, and reservoir drainage radius. Fluid properties include crude oil viscosity and crude oil volume fraction. Fracturing parameters include fracture half-length, fracture height, and skin factor.

[0051] Step 2: Calculate the optimal conductivity of the hydraulic fracture using the following formula:

[0052]

[0053] Where,

[0054] Y-comprehensive coefficient;

[0055] C fD is the optimal conductivity of the fracture;

[0056] x f The crack is half length.

[0057] Step 3: Calculate the optimal fracture length, half fracture length X f and sand volume V f The relationship between and the fracture conductivity is:

[0058]

[0059] Where,

[0060] K f - fracture permeability;

[0061] V f -Total sand volume;

[0062] k-reservoir permeability;

[0063] h f - Crack height.

[0064] Step 4: Calculate the optimal fracture width using the following formula:

[0065]

[0066] Where,

[0067] Wopt - optimal fracture width;

[0068] h-oil layer thickness.

[0069] The following are several specific embodiments of the present invention.

[0070] Example 1

[0071] In a specific embodiment 1 of the present invention, Figure 1 As shown, Figure 1 This is a flow chart of the method for calculating the length and width of shale oil and gas pressure fractures based on the fracture conductivity coefficient of this embodiment.

[0072] Step 101: Collect reservoir geology, fluid properties, and fracturing parameters. Reservoir geology parameters: Reservoir area A = 5,000,000 ft 2 , seepage radius re = 1300 ft, average reservoir permeability k = 1.5 md, volume coefficient Bo = 1.2, crude oil viscosity μ = 2 cp, reservoir thickness h = 50 ft, fracture height hf = 110 ft, reservoir skin coefficient s = 7, wellbore radius rw = 0.328 ft, fracture proppant permeability Kf = 60000 mD, sand volume under reservoir conditions Vf = 1000 ft 3 t.

[0073] Step 102, based on step 101, calculate the optimal conductivity of the hydraulic fracture: the optimal conductivity of the fracture is calculated using the following formula:

[0074]

[0075] Where,

[0076] Y-comprehensive coefficient;

[0077] C fD is the optimal conductivity of the fracture;

[0078] x f The crack is half length.

[0079] Taking the differential we can get:

[0080]

[0081] When Y' is 0, the optimal conductivity coefficient CfD of the crack is 1.571.

[0082] Step 103 : Based on step 102 , the optimal fracturing crack length is calculated.

[0083]

[0084] Where,

[0085] Kf - fracture permeability;

[0086] Vf-total sand volume;

[0087] k-reservoir permeability;

[0088] hf - crack height.

[0089]

[0090] Step 104, based on step 103, calculate the optimal fracturing crack width:

[0091]

[0092] Where,

[0093] Wopt - optimal fracture width;

[0094] h-oil layer thickness.

[0095]

[0096] Depend on Figure 2 It can be seen that the daily oil production increased significantly after fracturing transformation, achieving a good production increase effect.

[0097] Example 2

[0098] In a second specific embodiment of the present invention, the method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity of the present invention includes the following steps:

[0099] Step 101: Collect reservoir geology, fluid properties, and fracturing parameters. Reservoir geology parameters: Reservoir area A = 5,000,000 ft 2 , seepage radius re = 1300 ft, average reservoir permeability k = 1.0 md, volume coefficient Bo = 1.2, crude oil viscosity μ = 2 cp, reservoir thickness h = 60 ft, fracture height hf = 110 ft, reservoir skin coefficient s = 7, wellbore radius rw = 0.328 ft, fracture proppant permeability Kf = 50000 mD, sand volume under reservoir conditions Vf = 1100 ft 3 . .

[0100] Step 102, based on step 101, calculate the optimal conductivity of the hydraulic fracture: the optimal conductivity of the fracture is calculated using the following formula:

[0101]

[0102] Where,

[0103] Y-comprehensive coefficient;

[0104] C fD is the optimal conductivity of the fracture;

[0105] x fThe crack is half length.

[0106] Taking the differential we can get:

[0107]

[0108] When Y' is 0, the optimal conductivity coefficient CfD of the crack is 1.571.

[0109] Step 103 : Based on step 102 , the optimal fracturing crack length is calculated.

[0110]

[0111] Where,

[0112] Kf - fracture permeability;

[0113] Vf-total sand volume;

[0114] k-reservoir permeability;

[0115] hf - crack height.

[0116]

[0117] Step 104, based on step 103, calculate the optimal fracturing crack width:

[0118]

[0119] Where,

[0120] Wopt - optimal fracture width;

[0121] h-oil layer thickness.

[0122]

[0123] Example 3

[0124] In a specific embodiment 3 of the present invention, the method for calculating the length and width of shale oil and gas pressure fractures based on the fracture conductivity of the present invention includes the following steps:

[0125] Step 101: Collect reservoir geology, fluid properties, and fracturing parameters. Reservoir geology parameters: Reservoir area A = 5,000,000 ft 2 , seepage radius re = 1300 ft, average reservoir permeability k = 1.2 md, volume coefficient Bo = 1.2, crude oil viscosity μ = 2 cp, reservoir thickness h = 55 ft, fracture height hf = 110 ft, reservoir skin coefficient s = 7, wellbore radius rw = 0.328 ft, fracture proppant permeability Kf = 55000 mD, sand volume under reservoir conditions Vf = 1200 ft3 . .

[0126] Step 102, based on step 101, calculate the optimal conductivity of the hydraulic fracture: the optimal conductivity of the fracture is calculated using the following formula:

[0127]

[0128] Where,

[0129] Y-comprehensive coefficient;

[0130] C fD is the optimal conductivity of the fracture;

[0131] x f The crack is half length.

[0132] Taking the differential we can get:

[0133]

[0134] When Y' is 0, the optimal conductivity coefficient CfD of the crack is 1.571.

[0135] Step 103 : Based on step 102 , the optimal fracturing crack length is calculated.

[0136]

[0137] Where,

[0138] Kf - fracture permeability;

[0139] Vf-total sand volume;

[0140] k-reservoir permeability;

[0141] hf - crack height.

[0142]

[0143] Step 104, based on step 103, calculate the optimal fracturing crack width:

[0144]

[0145] Where,

[0146] Wopt - optimal fracture width;

[0147] h-oil layer thickness.

[0148]

[0149] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0150] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity, characterized in that: The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity includes: Step 1: Collect reservoir geology, fluid properties, and fracturing operation parameters; Step 2, calculating the optimal conductivity of the hydraulic fracture according to the fracture construction parameters; Step 3, calculating the optimal hydraulic fracture length according to the optimal hydraulic fracture conductivity obtained in step 2; Step 4, calculating the optimal hydraulic fracture width according to the optimal hydraulic fracture length obtained in step 3; In step 3, the optimal fracture length is calculated, the fracture half length X f and sand volume V f and the fracture conductivity C fD The relationship between them is: Where, K f - fracture permeability; V f -Total sand volume; k-reservoir permeability; h f - crack height; C fD -Optimal conductivity of the fracture; In step 4, the optimal fracture width is calculated using the following formula: Where, Wopt - optimal fracture width; V f -Total sand volume; k-reservoir permeability; K f - fracture permeability; h-oil layer thickness.

2. The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity according to claim 1, characterized in that: In step 1, the collected reservoir geological parameters include oil layer permeability, oil layer thickness, reservoir pressure, and reservoir drainage radius.

3. The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity according to claim 1, characterized in that: In step 1, the collected fluid properties include crude oil viscosity and crude oil volume coefficient.

4. The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity according to claim 1, characterized in that: In step 1, the collected fracturing operation parameters include crack half-length, crack height, and skin coefficient.

5. The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity according to claim 1, characterized in that: In step 2, the optimal fracture conductivity is calculated using the following formula: Where, Y-comprehensive coefficient; C fD is the optimal conductivity of the fracture; x f The crack is half length.

6. The method for calculating the length and width of shale oil and gas pressure fractures based on fracture conductivity according to claim 5, characterized in that: In step 2, differentiate Equation 1 to obtain: When Y' is 0, the optimal conductivity coefficient C of the crack is obtained fD The value of is 1.571.

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