Numerical Simulation of Integrated Mechanics of Drilling and Mechanical Cavitation in Coal Seam

Abstract

For coal and gas outburst and difficult extraction in soft, low-permeability, and high-gas seam, the integration technology of drilling and mechanical cavitation is put forward to relieve pressure and improve permeability of coal seam. Through the test of mechanical parameters of the coal body, the physical model of drilling and cave-making in coal seam is established, and the mechanical characteristics of drilling and mechanical cavitation are simulated numerically. The results show that the peak strength of coal increases linearly with confining pressure. When the drill bit just touches the coal, the maximum stress occurs at the center of the coal sample. With the increase in the drilling depth of the drill bit, the maximum stress point shifts to the depth. When the coal at the center of the sample is broken, the position of the maximum stress shifts to the surrounding. With the increase of drilling depth, the maximum contact number between the drill bit and coal body increases sharply. When the bit body basically enters the coal body, the maximum contact number between the drill bit and coal body remains unchanged. When the drill pipe rotates, the reaming tool collides with the hole wall at the reaming position on the axis. In general, the contact area increases with the opening of the reaming tool, but the contact between the reaming tool and the hole wall is random. As time increases, the contact force begins to increase and then basically stabilizes; at this time the reaming tool has been fully opened.

Research on the Development of Hydraulic Flushing Caverning Technology and Equipment for Gas Extraction in Soft and Low Permeability Tectonic Coal Seams in China

“…The equipment applies mechanical cutters, assisted with high-pressure water jet coal breaking technology, which makes up for the deficiency of submerged jet. 58 …”

“…As shown in Figure , the drilling and mechanical cutting packaged equipment was developed on the basis of the drilling and hydraulic flushing packaged equipment. The equipment applies mechanical cutters, assisted with high-pressure water jet coal breaking technology, which makes up for the deficiency of submerged jet …”

“…The equipment applies mechanical cutters, assisted with high-pressure water jet coal breaking technology, which makes up for the deficiency of submerged jet. 58 The hole enlarging cutters are closed in the groove of the equipment in the drilling process, and the water supply is pressured up when enlarging the hole. The cutter will open when the water pressure reaches 10 MPa.…”

Mechanical behaviour and fracture evolution of coal specimens containing an over‐excavated hole: Experimental study and numerical modelling

“…31 In recent years, the new technology of the mechanically over-excavated cavity along the borehole is used in soft coal seams to overcome the problems (Figure 1). [32][33][34] A mechanically over-excavated drill bit was used to cut coal to generate a series of cavities along the borehole similar to the structure of 'candied haws on a stick' (Figure 1c). The mechanism of permeability-increasing is the same as hydraulic flushing.…”

New Technology of Mechanical Cavitation in a Coal Seam to Promote Gas Extraction

“…Figure 1. Main components of drilling and cavitation integrated equipment: (a) BLY800/2 mining crawler mud pump truck; (b) ZDY10000LPS mining crawler full hydraulic tunnel drill; (c) high-pressure sealed drill pipe;(d, e) variable diameter mechanical cavitation device; and (f) drill bit 38. …”