Shale compressibility comprehensive evaluation method based on uniaxial strength experiment

Abstract

The invention provides a shale compressibility comprehensive evaluation method based on uniaxial strength experiment. The method comprises the steps of (1) taking a shale core sample for executing uniaxial compressive strength test, testing an elasticity parameter, and drawing a stress-strain curve diagram; (2) calculating normalized elasticity modulus and normalized poisson ratio to obtain a brittleness index; (3) obtaining key points on the stress-strain curve, and calculating the shape index of the stress-strain curve; (4) obtaining fracture distribution diagram of the side face of the fixed sample, and calculating a fracture distribution index through box-counting dimension method; (5) measuring spallation fragment mass distribution at different scales through a screen and a balance so as to obtain a block distribution index; and (6) calculating arithmetic mean value of the obtained brittleness index, shape index of the stress-strain curve, fracture distribution index and block distribution index of fragments to get the comprehensive compressibility index. The method provided by the invention is used for evaluating fracture net forming capability of the shale after being compressed, the experiment is simple and easy to carry out, and post treatment is visual and simple, so that the method is suitable for indoor evaluation and oilfield in-site application.

Description

technical field [0001] The invention relates to a shale compressibility comprehensive evaluation method based on a uniaxial strength test, which belongs to the technical field of petroleum development. Background technique [0002] The development of shale gas is a major demand of my country's energy strategy, but unlike the development of shale gas in the United States, my country's shale gas has the characteristics of complex occurrence and difficult development, ultra-low porosity, ultra-low permeability, and high clay content Large-scale hydraulic fracturing of long horizontal wells has become a necessary means for shale gas development. The study found that the initial damage degree and brittleness of shale have a significant impact on the effect of fracturing, and are also key indicators for evaluating the mechanical properties of shale reservoirs, and also have a significant impact on the stability of wellbore walls. Compressibility evaluation is particularly importan...

AI Technical Summary

Problems solved by technology

However, most of the existing shale compressibility indoor evaluation techniques use a single brittleness index based on brittle mineral components and elastic parameters, which is difficult to reflect the complex initial damage of shale, extremely developed bedding, heterogeneous composition, mechanical Non-linear and other characteristics, resulting in frequent downhole accidents during drilling and poor volume fracturing effects, which seriously restrict the exploration and development of shale gas in my country

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