Transverse isotropic shale formation brittleness index prediction method

Abstract

The invention discloses a transverse isotropic shale formation brittleness index prediction method. The method comprises the following steps of determining a shale anisotropic rigidity coefficient according to the full wave train acoustic logging information; calculating a stiffness matrix, a shale anisotropic elastic modulus and a Poisson ratio of the transverse isotropic shale; calculating a flexibility matrix of the transverse isotropic shale under the stratum coordinates; calculating a shale stiffness matrix and a flexibility matrix under any azimuth angle and hole drift angle conditions; calculating shale elastic modulus and Poisson's ratio under any well deviation and azimuth borehole observation coordinates; and calculating the transverse isotropic shale formation brittleness index. According to the method, the anisotropic characteristics of the shale are considered, the transverse isotropic shale formation brittleness index is evaluated from the angle of actual drilling holes, a defect that the traditional shale brittleness index neglects the anisotropic influence is overcome, and the anisotropic characteristics of the shale brittleness index and the characteristics of the shale brittleness index influenced by hole tracks can be reflected more accurately; scientific basis and decision support can be provided for drilling and fracturing of the shale gas horizontal well.

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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