Test device and test method for crack evolution and seepage characteristic of gas-containing shale

Abstract

A test device and a test method for crack evolution and seepage characteristic of gas-containing shale. The test device and the test method belong to the technical fields of rock engineering and unconventional natural gas engineering. The device includes a three-shaft pressure chamber, a bias pressure loading system, a hydrostatic pressure loading system, an upper-end fluid system, a lower-end fluid system, a vacuumizing system, a constant temperature system, and a data control and acquisition system. According to the test method, a strain gauge is replaced by a displacement sensor so that problem of leakage of oil and gas caused by wires of the strain gauge is solved. Circular displacement sensors are arranged respectively on an upper part, a middle part and a lower part of a sample so that crack growing situations at different positions of the sample can be detected. Deformation of the whole sample is detected through an axial displacement sensor. According to a reference standard of the crack evolution and the seepage characteristic in a cracking process of a gas-containing shale sample and a reference standard of the whole crack evolution of the cracking process of a gas-containing shale sample, a crack evolution state in the cracking process of a gas-containing shale sample is analyzed and variation trend of a whole crack in the cracking process of the gas-containing shale sample is determined.

Description

technical field [0001] The invention belongs to the field of rock engineering and unconventional natural gas engineering, and mainly relates to a test device and method for gas-bearing shale fracture evolution and seepage characteristics. Background technique [0002] Gas-bearing shale reservoirs are very tight, and relying on the natural decompression of the reservoirs to exploit them has low production and fast attenuation. To achieve the purpose of commercial development, fracturing technology must be used to increase production. Gas-bearing shale has a high clay content. Using high-pressure water for fracturing will cause the clay in the gas-bearing shale to absorb water and swell, and water molecules will wrap the clay particles, making it difficult to desorb and migrate the gas in the water-wrapped clay particles, resulting in a production increase effect bad. Gas fracturing does not have the above-mentioned problems, the gas viscosity is small, and the adsorption of ...

AI Technical Summary

Problems solved by technology

The existing test methods have the following problems: (1) The fluid used is distilled water, and the permeable medium in the actual reservoir is gas, so gas must be used as the permeable medium to study the permeability performance in the process of gas fracturing; (2) only The permeability performance can be used to reflect the final expansion of gas-bearing shale fractures under different bias pressures, but it cannot reflect the dynamic evolution of gas-bearing shale fractures under bias stress in real time; (3) because the permeability test method used is the transient method, It cannot reflect the flow change during gas shale fracture

In the existing test, the flow collection end is connected to the atmosphere, which leads to deviation from the actual engineering

[0007] Due to the comprehensive effects of sedimentary diagenetic process, geological transformation, in-situ stress, and fracturing transformation, the gas-bearing shale has the characteristics of heterogeneity and anisotropy. During the test, the fractures in different parts of the sample are different. To monitor the deformation characteristics, while the existing testing devices and methods only monitor the deformation in the middle of the sample, which is not enough to represent the overall deformation of the sample

Existing deformation tests are mostly carried out with strain gauges, and strain gauge wires often cause oil and air leakage problems, resulting in inaccurate tests

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