Mechanism Of Directional Hydraulic Fracturing Controlled By Linear Multiple Drillings

Directional hydraulic fracturing controlled by linear multiple drillings is recentlydeveloped by professor Huang Bingxiang. This technology is conducive todirectionally disposing hard roof, making hard top coal rupture in vertical direction,directional transfer of stress, preventing rock burst and coal-gas outburst andimproving the effect of gas extraction. Because of the advantages on simple method,convenient operation, security and reliability, this technology has extensivepracticability. As for the filed practice at YuLin Liuhang colliery, it works well andeffectively makes top coal weaken. Finally it achieves top coal caving in time.In order to deeply study on the mechanism of directional hydraulic fracturingcontrolled by linear multiple drillings, this paper takes hydraulic fracturing after waterpressure blasting for coal-rock mass as basis, elastic mechanics, structural mechanicsand permeation fluid mechanics as theoretical basis, and make comprehensive use ofhydraulic fracturing tests, RFPA2D-Flow numerical analysis and theoretical formuladerivation methods. According to research results, permeability influences directionalhydraulic fracturing controlled by linear multiple drillings and specimen porosity isproportional to fracturing effects in the case of other conditions unchanged. Principalstress difference, hole pitch (L/D) and the angle between hole arrangement directionand principal stress direction have larger influence on directional hydraulic fracturingcontrolled by linear multiple drillings. The smaller the former three, the betterfracturing effects are. However, test specimen joint fissure has certain influence onreorientation of hydraulic fractures, and makes directional effects poor. Numericalsimulation shows that water flooding method change has no too large effect ondirectional hydraulic fracturing controlled by linear multiple drillings. The stressdirection plays a decisive role on directional hydraulic fracturing controlled by linearmultiple drillings. Under the condition of radial crack stress field, specimens are stillfractured in radial direction, thereby cannot achieve the goal of porous linearfracturing (that is to produce axial cracks or crack band along hole arrangementdirection). Only under the condition of axial crack stress field, it is possible to realizedirectional hydraulic fracturing controlled by linear multiple drillings.There are42figures,8tables and72references in this paper.