Experimental device and method for simulating coal mine hard roof rock stratum hydraulic fracturing

Abstract

The invention discloses an experimental device and method for simulating coal mine hard roof rock stratum hydraulic fracturing, and relates to the technical field of coal mine underground hydraulic fracturing. The experimental device comprises a sample, a pressurization system and a fracturing system, the pressurization system comprises a rubber pipe and a connector, and the fracturing system comprises a water tank, a high-precision flowmeter, a high-precision water pressure gauge, a water injection pipe and a fracturing rod. According to the experimental device and method for simulating coal mine hard roof rock stratum hydraulic fracturing, a transparent gelatin experimental material and a transparent pressurizing component are used, the whole process of crack initiation and expansion of a hydraulic fracture can be directly observed and recorded in a laboratory environment, a specially-made grooving tool is used, the device can effectively simulate the radial grooving in the experiment, systematic research is carried out on the grooving effect, the inclination angle of the fracturing hole in the hydraulic fracturing experiment can be adjusted at will, and the influence of the radial grooving at different angles on the hydraulic fracture initiation and extension track is simulated.

Description

technical field [0001] The invention relates to the field of underground hydraulic fracturing in coal mines, in particular to an experimental device and method for simulating hydraulic fracturing of hard roof strata in coal mines. Background technique [0002] Hydraulic fracturing technology originated in the field of oil exploitation. It creates artificial fractures by injecting high-pressure water into the reservoir to improve the permeability of the reservoir. Subsequently, this technology was introduced into the field of coal mining to improve the permeability of high-gas coal seams and enhance the caving ability of the top coal in caving face or the hard roof rock layer in primary mining full-height working face. Laboratory research on the hydraulic fracturing process is helpful to grasp the mechanism of hydraulic fracturing, improve the efficiency of on-site fracturing, and realize safe and efficient production of coal mines. When the permeability of high gassy coal s...

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Problems solved by technology

[0003] In the prior art, most of the experimental materials used in hydraulic fracturing experimental devices and the experimental components that apply confining pressure to the experimental materials are opaque, so it is impossible to directly observe and record the initiation and expansion trajectory of hydraulic fractures. Secondly, , the expansion form of hydraulic fractures is mainly divided into two types: axial and radial. When fracturing the hard coal rock mass to promote its caving, the hydraulic fractures are mainly in the radial form, and the radial expansion of the borehole is usually carried out before fracturing. Grooving treatment, the existing hydraulic fracturing experimental device lacks effective simulation of radial grooving before fracturing, so it is difficult to conduct laboratory research on the effect of grooving. The patent publication number is CN102031954A, and the name is "Coal Rock Drilling The patent of "Hydraulic Fracturing Device" discloses an experimental device for simulating hydraulic fracturing of coal and rock drilling. The experimental device uses acoustic emission technology to indirectly observe the expansion form of hydraulic cracks in opaque materials. However, acoustic emission technology There must be errors in the inversion of the internal damage of the material, and the accuracy of the inversion is difficult to calibrate and verify effectively. The paper titled "Investigation of Directional Hydraulic Fracturing Based on True Tri-axial Experiment and Finite Element Modeling" published by Deng et al. developed an experimental component that simulates radial grooves in a borehole prior to fracturing in the laboratory. The component is essentially an iron trough-shaped mold that is placed inside the experimental concrete material before it is formed, rather than in the Real grooving is performed inside the borehole, so the effect of stress concentration on the material when water pressure acts on the grooving surface cannot be effectively simulated

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