Efficient-safe gas extraction in the superimposed stress strong-outburst risk area: Application of a new hydraulic cavity technology

Abstract

Coal and gas outbursts pose significant risk in coal mining, especially in high-stress areas. The F15-22080 haulage roadway of the No. 8 Mine, known for its high outburst risk with superimposed stress, presents challenges such as low permeability and frequent borehole outbursts during gas extraction. To address these issues, this study introduced an innovative, efficient, and safe gas extraction technique paired with an air-hydraulic drilling integrated anti-outburst platform. The stress and outburst characteristics of the roadway reservoir were analyzed using FLAC3D simulation and experimental testing, leading to the classification of the reservoir into the general stress area (GSA) and superimposed stress area (SSA). Focusing on the SSA, the borehole outburst mechanism was investigated. Building on these insights, a comprehensive gas zoning control plan for extraction was developed. In the GSA with low risk of borehole outburst, hydraulic cavity boreholes were directly implemented to boost extraction efficiency and minimize construction costs. In the SSA, a multistep collaborative extraction strategy was adopted. This strategy involved an initial "air-flushing conventional borehole pre-extraction" step to prevent borehole outbursts, followed by a "hydraulic cavity borehole strengthening-extraction" step to ensure efficient gas extraction. The fluid-solid coupling model consistent with the gas flow around boreholes was established, and the extraction effects of the regional control plan were simulated and analyzed using COMSOL, thereby establishing the construction parameters. The successful field application of this technique, evidenced by data from gas extraction and roadway excavation, validates the effectiveness of it.