A Prediction Method for Brittleness Index of Transversely Isotropic Shale Formation

Abstract

The invention discloses a method for predicting the brittleness index of a transversely isotropic shale formation, which includes determining the anisotropic stiffness coefficient of the shale according to the full wave train acoustic logging data; calculating the stiffness matrix of the transversely isotropic shale, the shale Anisotropic elastic modulus and Poisson's ratio; calculate the flexibility matrix of transversely isotropic shale in formation coordinates; calculate the shale stiffness matrix and flexibility matrix under the condition of arbitrary azimuth and well inclination angle; calculate arbitrary well inclination Shale elastic modulus and Poisson's ratio under the coordinates of wellbore observation and azimuth; calculate the brittleness index of transversely isotropic shale formations. The invention considers the anisotropy characteristics of shale, evaluates the brittleness index of transversely isotropic shale formation from the perspective of actual drilling, overcomes the defect that the traditional shale brittleness index ignores the influence of anisotropy, and can more accurately reflect the shale brittleness index The characteristics of anisotropy and its influence on well trajectory can provide scientific basis and decision-making support for drilling and fracturing of shale gas horizontal wells.

Description

technical field [0001] The invention relates to a method for predicting the brittleness index of a transversely isotropic shale formation, belonging to the technical field of drilling and completion engineering. Background technique [0002] The brittleness of shale is one of the important properties of rock, and the shale brittleness index is an important basis for wellbore stability analysis, hydraulic fracturing segmentation and optimization. During the drilling process, the higher the brittleness index, the higher the probability of "rockburst" instantaneous failure of the rock on the well wall, and the more likely the well wall will collapse and fall off, which will lead to complex instability such as drill sticking and buried drilling. Accidents, in severe cases, even lead to the failure of the wellbore. In the process of hydraulic fracturing, the brittleness index is a key parameter to evaluate the shale's compressibility. In addition to controlling the difficulty of...

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Problems solved by technology

Because shale has significant anisotropy characteristics, it usually exhibits transverse isotropy, that is, the brittleness index perpendicular to the bedding plane and the brittleness index parallel to the bedding plane are usually inconsistent, and most current studies focus on The anisotropy of wave velocity, Young's modulus and Poisson's ratio is ignored, and the brittleness anisotropy of shale formations is neglected, which may lead to distortion or even serious errors in the evaluation results of shale brittleness index

In the existing methods, the shale brittleness evaluation method based on mineral components cannot evaluate the brittle anisotropy of shale formations, while the method based on elastic parameters to evaluate the brittleness index can only evaluate the brittleness characteristics perpendicular to the bedding plane.

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