The Research On Multi-point Control Hydraulic Fracturing Mechanism And Application

Most of the coal mines in China have the characteristic of the high gas and low permeability,that coal and gas outburst is one of the major disaster threating operation safe in the coal mine.Gas pre-drainage large area is an effective measure preventing the gas disaster,which the gas permeability is the key factor influencing the extracting result.Improving the permeability of the coal seam,enhancing the gas drainage rate and eliminating outburst risk rapidly have the significance for operating safe and effective.Hydraulic fracturing underground can increase the permeability of the coal seam obviously,reduce the ground stress in the coal seam and improve the drainage effect.Traditional hydraulic fracturing has the problem that fracture direction is uncertain,and the area of fracturing is small.A great demand is made on pumping pressure range.Aiming at the problem,the multi-point control hydraulic fracturing is researched.Firstly the fracturing process and the control hole influencing on the fracturing hole are analyzed theoretically.Secondly,according to the gas geological conditions in the21431 working face of Hebi 6th mine,RFPA2D-Integrated is applied to simulate multi-point control hydraulic fracturing process.Simple-hole hydraulic fracturing and multi-point control hydraulic fracturing model are established.The crack initiation and propagation objectivity of hydraulic fracturing crack is simulated under the different ground stress and the different the space between the control holes.Finally according to the simulate result,the paper optimizes the fracturing parameter and selects the fracturing equipment.Research results showed that control hole has the impact of pressure relief and guiding on the fracturing crack extending of the fracturing hole,and when the fracturing hole is located in the effect radius of the control hole,it can decrease the crack initiation of the fracturing hole.It can play a role in pressure relief and guiding under the condition of appropriate spacing with the continually approach of fracturing range even though the fracturing hole is outside of the control hole’s influencing range.Simulate results showed that when range between two control holes is 5-8m,fracturingcrack extends along the control hole’s direction,and the control hole is the key factor affect the crack extends.When the space between two control holes is 10 m,the maximum principal stress is the major factor.Drainage effect is improved obviously,reaching the goals that eliminating the outburst risk after carrying out the multi-point control hydraulic fracturing in the HeBi sixth mine 21431 working facing.