Shale hydraulic fracture propagation prediction method

A fracture propagation and prediction method technology, which is applied in the field of shale hydraulic fracture propagation prediction, can solve the problems of prediction error and low accuracy rate, and achieve the effect of high accuracy, accuracy assurance, accuracy rate and accuracy

Active Publication Date: 2018-08-31
SOUTHWEST PETROLEUM UNIV
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Problems solved by technology

[0006] The purpose of the present invention is to: in the prior art, when using fracture mechanics theory and numerical simulation to study the propagation direction of shale hydraulic fractures, the accuracy rate is low and even easy to conduct research on the basis of simplified geological conditions. In order to solve the problem of prediction errors, a prediction method for shale hydraulic fracture propagation is provided. This prediction method is based on fracture mechanics, and hydraulic condition factors are introduced. The influence of shale bedding direction on the propagation direction of shale hydraulic fracturing fractures, so as to realize the accurate prediction of hydraulic fracture propagation and obtain a higher prediction accuracy

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  • Shale hydraulic fracture propagation prediction method

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Embodiment 1

[0066] In the shale hydraulic fracture propagation prediction method, in the operation process, the normal stress and tangential stress of oblique fractures under the compressive stress field are firstly calculated.

[0067] The stress of inclined cracks under the action of compressive stress field is as follows: figure 1 As shown, according to the pseudo-force method and superposition principle, the normal stress and tangential stress on the fracture surface are obtained as Equation 1:

[0068] In the formula, P is the normal pseudo force acting on the fracture surface, Q is the tangential pseudo force acting on the fracture surface, β is the angle between the fracture and the vertical compressive stress direction, σ x is the horizontal pressure, σ y is the vertical pressure.

[0069] After obtaining the normal pseudo-force of the fracture surface, the effect of water pressure Pw on the fracture surface is considered, as shown in figure 1 As shown, the normal stress of t...

Embodiment 2

[0103] This example provides the verification of the influence of natural fractures on the propagation direction of shale hydraulic fractures.

[0104] Using the prediction method process in Example 1, and based on the analysis model of bedding on the propagation direction of shale hydraulic fractures, set natural fractures at a distance of 0.5m from the front of the perforation. Natural fractures are replaced by weak unit areas, with a length of 1m and a thickness of 0.05m. The elastic modulus of natural fractures is 1 / 10 of the shale matrix, the tensile strength and critical energy release rate are 1 / 100 of the shale matrix, and the rest Poisson's ratio, permeability coefficient, fracturing fluid viscosity, fluid loss coefficient and shale matrix are the same. There is a certain included angle β between the maximum principal stress directions, which are 45°, 60°, and 75° respectively. The rock mass and numerical related parameters are shown in Table 2. Under the same groun...

Embodiment 3

[0110] This example provides verification of the influence of in-situ stress difference on the propagation direction of shale hydraulic fractures.

[0111] According to the model in Example 2, when the maximum principal stresses are 20MPa, 25MPa, and 30MPa, the horizontal ground stress differences are 0, 5, and 10MPa, respectively. The intersection angle of hydraulic fractures and natural fractures / angle change of hydraulic fractures crossing natural fractures can be obtained, and the results are shown in Table 3.

[0112] According to Table 3, the smaller the horizontal stress difference, the easier it is for the hydraulic fracture to deviate from the maximum principal stress direction and tend to be perpendicular to the natural fracture before penetrating into the natural fracture, and the easier it is for the hydraulic fracture to be parallel to the natural fracture inside the natural fracture. Crack direction expansion. And the larger the horizontal stress difference is, ...

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Abstract

The invention relates to the field of rock fracture prediction, in particular to a shale hydraulic fracture propagation prediction method. The method comprises the steps that 1, the normal direction,tangential stress and effect stress of an inclined fracture under the action of the external stress and water pressure are calculated; 2, a strain energy density function is obtained according to thetype of the fracture; 3, a strain energy density factor is obtained according to the strain energy density function; 4, the propagation direction and propagation angle of the fracture are judged according to a strain energy density criterion; 5, influences of stratification, natural fractures and the like on the propagation direction of hydraulic fractures are obtained through numerical simulation, so that fracture propagation under the effect of shale hydraulic pressure is predicted. The prediction method is based on fracture mechanics, a hydraulic condition factor is introduced, and the influences of different stratification directions on the propagation direction of the shale hydraulic fractures are obtained by researching the relation between the fracture propagation direction and themagnitude of the hydraulic pressure and utilizing an extended finite element method, so that accurate prediction of hydraulic fracture propagation is achieved, and higher prediction accuracy is obtained.

Description

technical field [0001] The invention relates to the field of rock fracture prediction, in particular to a shale hydraulic fracture propagation prediction method. Background technique [0002] Hydraulic fracturing technology was first used in gas well production in 1947. Subsequently, this technology has gone through three important stages in its development process, and it has been widely used in the petroleum industry today. Hydraulic fracturing is the use of surface high-pressure pumps to squeeze fracturing fluid with high viscosity into the oil layer through the wellbore. When the rate of injection of fracturing fluid exceeds the absorption capacity of the oil layer, a very high pressure will be formed on the oil layer at the bottom of the well. When this pressure exceeds the fracture pressure of the oil layer near the bottom of the well, the oil layer will be pushed open and fractures will be generated. At this time, if the fracturing fluid is continuously squeezed into...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): E21B43/26G06F17/50
CPCE21B43/26G06F30/23
Inventor 张伯虎骆庆龙姬彬翔刘玮丰田小朋周昌满马浩斌
Owner SOUTHWEST PETROLEUM UNIV
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