Study on the Effect of Borehole Size on Gas Extraction Borehole Strength and Failure Mode

Abstract

In the coal mine industry, the instability failure of an extraction borehole is one of the main factors leading to the decrease in gas extraction rate. The study on borehole strength and failure mode with different sizes can provide a theoretical basis for the optimization and selection of a gas extraction borehole. In this paper, biaxial loading tests are carried out on similar coal specimens, and the prediction model of borehole strength is proposed and verified. At the same time, numerical simulation of similar specimens is carried out to analyze the failure process of boreholes of different sizes. The results show that hole size has a great influence on hole strength, and the hole strength decreases with an increase of hole size. Size change has a great influence on the strength of a small-size borehole, and the strength of the borehole gradually stabilizes with an increase of size. The process of borehole failure can be divided into three stages, borehole top failure, borehole deformation, and crack extension. Stress concentration and a large number of cracks occur on the two wings of the borehole, and these cracks reduce the strength of the borehole. The stress concentration area of the borehole is X-shaped distribution, and the through crack mainly extends along this area and leads to the failure of the specimen.

Coupling a void growth model with an elastoplastic material model for a simultaneous prediction of the borehole plastic zone and critical collapse pressure

“…40, 41, and 42). This agrees with the generally observed behavior in borehole failure tests and numerical simulations (Gao and Ren, 2022;Meier et al 2013). The plastic extent around the borehole also increases as the borehole size increases.…”

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Fracture initiation pressure prediction of hydraulic fracturing for layered reservoirs considering borehole deformation

“…Zhai et al (2015) observed that a circular borehole in an on-site coal seam became elliptical after redistributing in situ stresses. Gao and Ren. (2022) found that circular boreholes deform into elliptical boreholes due to stress exertion in hydraulic fracturing.…”

Study on the test of coal mass fracture grouting sealing with coal-based materials and its application

“…Ultimately, disasters such as coal and gas outburst are likely to occur (Huang et al, 2019;Hao et al, 2021;Bao et al, 2022). Gas extraction is an important technical method to develop and utilize gas resources and prevent gas disasters in coal mines (Yu et al, 2015;Zhang et al, 2022a;Bi et al, 2022;Zhang et al, 2022b;Gao and Ren, 2022). However, under the influence of the excavation and mining of the roadway and borehole, the coal layer could be damaged by different degrees of deformation, so there are a large number of fractures and leakage channels around the extraction borehole Wang et al, 2021;Li et al, 2022a).…”