Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger move...Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.展开更多
It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely.In view of this,a technical idea of composite pulsating hydraulic fracturing of radial horizontal wells w...It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely.In view of this,a technical idea of composite pulsating hydraulic fracturing of radial horizontal wells which is conducive to blockage removing and stimulation was put forward in this paper.Speaking of the hydraulic jetting in a multi-branch radial well,it is to conduct pulsating hydraulic fracturing moderately through a high-diversion radial hole,so as to crush and break coal beds near the main hole to the uttermost.Thus,an extensive pressure relief and permeability increase area where high-diversion pathways are combined with fracture networks is formed.Then,to verify its technical principles,laboratory tests on pulsating hydraulic fracturing of radial wells were designed and carried out.Besides,the relationships of the features of acoustic emission(AE)response during the formation of fractures by composite fracturing of radial horizontal wells vs.coal breaking degree and macro fracture morphology were experimentally studied by using a pulse servo fatigue testing machine and an acoustic emission detector.And the following research results were obtained.First,under experimental conditions,fractures initially occur when the pressure of composite pulsating hydraulic fracturing of radial horizontal wells is 1/3–1/4 of the peak pressure of conventional fracturing,and the amount of its AE events is 1.38–7.07 times that of conventional fracturing.Second,when composite pulsating hydraulic fracturing of radial horizontal wells is conducted,AE emission signals respond strongly,the peak pressure for macro fracturing is lower and a larger fracture network can be generated more easily under the same condition.Third,radial laterals amount,borehole length,dynamic loading frequency and amplitude are the important factors affecting the effect of composite pulsating hydraulic fracturing of radial horizontal wells.In conclusion,composite pulsating hydraulic fracturing of radial horizontal wells provides a new idea of removing the blockages in CBM reservoirs and developing CBM efficiently,realizing effective blockage removing and stimulation of CBM wells.展开更多
基金the National Natural Science Foundation of China(No.51274195)the National Basic Research Program of China(No.2011CB201205)+1 种基金the Ph.D.Foundation of Henan Polytechnic University(No.60207005)the Education Department of Hennan Province(No.14B440007)
文摘Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.
基金supported by National Natural Science Foundation of China-General Program“Study on fracturing control mechanism for radial drilling through water jet in coal rocks”(No.:51674275)National Natural Science Foundation of China-Major Program“Theory of safe and quality drilling for shale oil and gas development under the mode of multi-coupling”(No.:51490652)。
文摘It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely.In view of this,a technical idea of composite pulsating hydraulic fracturing of radial horizontal wells which is conducive to blockage removing and stimulation was put forward in this paper.Speaking of the hydraulic jetting in a multi-branch radial well,it is to conduct pulsating hydraulic fracturing moderately through a high-diversion radial hole,so as to crush and break coal beds near the main hole to the uttermost.Thus,an extensive pressure relief and permeability increase area where high-diversion pathways are combined with fracture networks is formed.Then,to verify its technical principles,laboratory tests on pulsating hydraulic fracturing of radial wells were designed and carried out.Besides,the relationships of the features of acoustic emission(AE)response during the formation of fractures by composite fracturing of radial horizontal wells vs.coal breaking degree and macro fracture morphology were experimentally studied by using a pulse servo fatigue testing machine and an acoustic emission detector.And the following research results were obtained.First,under experimental conditions,fractures initially occur when the pressure of composite pulsating hydraulic fracturing of radial horizontal wells is 1/3–1/4 of the peak pressure of conventional fracturing,and the amount of its AE events is 1.38–7.07 times that of conventional fracturing.Second,when composite pulsating hydraulic fracturing of radial horizontal wells is conducted,AE emission signals respond strongly,the peak pressure for macro fracturing is lower and a larger fracture network can be generated more easily under the same condition.Third,radial laterals amount,borehole length,dynamic loading frequency and amplitude are the important factors affecting the effect of composite pulsating hydraulic fracturing of radial horizontal wells.In conclusion,composite pulsating hydraulic fracturing of radial horizontal wells provides a new idea of removing the blockages in CBM reservoirs and developing CBM efficiently,realizing effective blockage removing and stimulation of CBM wells.
