Study on the Shadow Effect of the Stress Field around a Deep-Hole Hydraulic-Fracturing Top-Cutting Borehole and Process Optimization

Abstract

The clean utilization and green development of coal resources have become a research focus in recent years. Underground hydraulic fracturing technology in coal mines has been widely used in roof pressure relief, top coal pre-splitting, gas drainage, roadway pressure relief and goaf disaster prevention. Different in situ stress types cause great differences in the stress field around the boreholes, the critical pressure of the fracture initiation, and the direction of the fracture expansion trend; in addition, the stress shadow effect generated by the superposition of stress fields between boreholes relatively close together has a mutual coupling effect on the evolution of the stress field, the development of the plastic zone, and the crack propagation of the rock mass. Therefore, an effective method to solve the problem is to establish a mechanical model of hydraulic fracturing in boreholes for theoretical calculation, determine the influence mechanism of the crack shadow effect, and design a numerical simulation experiment of the equivalent stress fluid–solid coupling of hydraulic fracturing under different pore diameters and spacings. In addition, combining rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of the equivalent stress and the plastic zone is one of the important advances in this paper. Considering the engineering background of the site, the geological conditions and the requirements of general regulations, it is considered that the parameter selection of roof fracturing hydraulic fracturing technology in the Yushen mining area is more suitable when 0.12 m hole diameter and 3.5 m hole spacing are selected.

A Case Study on Strong Strata Behaviors Mechanism of Mining Reserved Roadway and Its Prevention Techniques

“…According to the mechanics of materials, the maximum normal stress of a pure bending beam occurs at the furthest distance from the neutral axis. The relationship between the maximum tensile stress and the maximum bending moment can be obtained as shown in Equation (1).…”

“…where b is the width of the rectangle interface (m). Take b = 1 m, substitute Equations ( 2) and (3) into Equation (1), and the relationship between the periodic breaking step distance of the key stratum and its tensile strength can be obtained. If σ max = RT, then:…”

“…The degree of roof collapse after coal mining is related to the strength and structure of the overlying rock [1][2][3]. Overlying rocks with stronger rock strength and more complete structure are not easy to collapse.…”

Special Issue “Process Safety in Coal Mining”

“…The technical methods they provided allowed for the fine control of pumping hole design, construction, measurement, and repair. Shuanlin Wang and coworkers [12] combined rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of equivalent stress and the plastic zone. Zhie Wang and coworkers [13] analyzed the deformation characteristics of boreholes under three typical coal-rock conditions and analyzed the stress, strain, and plastic deformation of rocks around boreholes with different diameters.…”