Method for predicting brittleness index of shale

Abstract

The invention provides a method for predicting a brittleness index of shale, and belongs to the field of oil and natural gas prospecting. The method comprises the following steps of (1) preparing geology, logging and seismic data; (2) analyzing contents of quartz, clay and carbonate rocks in data by using rock mineral constituents of the shale and calculating the ratio of the content of brittle minerals to the content of total minerals, namely calculating a rock mineral brittleness index; (3) calculating rock mechanics characteristic parameters by using longitudinal wave velocity, shear wave velocity and a density curve in dipole acoustic logging data; (4) establishing a multiple regression model between a rock mineral brittleness index curve and a rock mechanics characteristic parameter curve at the position of a well point; (5) performing prestack inversion to obtain longitudinal wave velocity, shear wave velocity and density data bodies and calculating rock mechanics characteristic parameter data bodies; and (6) calculating by using the multiple regression model obtained in the step (4) and the rock mechanics characteristic parameter data bodies obtained in the step (5) to obtain brittleness index data bodies.

Description

technical field [0001] The invention belongs to the field of petroleum and natural gas exploration, and in particular relates to a method for predicting shale brittleness index. Background technique [0002] Shale itself has the characteristics of low porosity and low permeability. Generally speaking, large-scale fracturing of shale reservoirs is required. During the fracturing process, various forms of fractures are continuously generated and a fracture network is formed to obtain higher commercial production capacity. The formation of the fracture network in shale is not only related to the magnitude and distribution of in-situ stress, but also the brittleness of rock is also an important factor affecting the fracturing effect. Therefore, some studies on shale brittleness have been carried out at home and abroad in recent years. For example, in the article "APractical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clone of the Barne...

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Problems solved by technology

[0003] (1) There are various definitions of rock ore brittleness index, and there is no unified standard. In most cases in actual exploration and production, it is only described qualitatively;

[0004] (2) The static elastic parameters of the rock are obtained based on the laboratory mechanical test data, while the dynamic elastic parameters are calculated from the logging data, and there will be certain errors in the conversion process of the dynamic and static elastic parameters;

[0005] (3) Most of the laboratory mechanical test data can only give the brittleness index of the rock at the sampling point at the well point, and it is difficult to reflect the change of the rock brittleness index on the plane

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