Aiming at the uncontrollable problem of extension direction of coal seam hydraulic fracturing,this study analyzed the course of fractures variation around the boreholes in process of hydraulic fracturing,and carried o...Aiming at the uncontrollable problem of extension direction of coal seam hydraulic fracturing,this study analyzed the course of fractures variation around the boreholes in process of hydraulic fracturing,and carried out the numerical simulations to investigate the effect of artificial predetermined fractures on stress distribution around fractured holes.The simulation results show that partial coal mass occurs relatively strong shear failure and forms weak surfaces,and then fractures extended along the desired direction while predetermined fractures changed stress distribution.Directional fracturing makes the fractures link up and the pressure on coal mass is relieved within fractured regions.Combining deep hole controlling blasting with hydraulic fracturing was proposed to realize the extension guiding-controlling technology of coal seam fractures.Industrial experiments prove that this technology can avoid local stress concentration and dramatically widen the pressure relief scope of deep hole controlling blasting.The permeability of fractured coal seam increased significantly,and gas extraction was greatly improved.Besides,regional pressure relief and permeability increase was achieved in this study.展开更多
Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial load...Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial loading was developed.Based on the monitor methods of pressure sensor and acoustic emission,the trials of two patterns of pulse hydraulic fracturing of single frequency and variable frequency were carried out,and at last fracturing mechanism was analyzed.The results show that the effect of variable frequency on fracture extension is better than that of single frequency based on the analysis of macroscopic figures and AE.And the shortage of single frequency is somewhat remedied when the frequency is variable.Under variable frequency,the pressure process can be divided into three stages:low frequency band,pressure stability band and high frequency band,and rupture pressure of the sample is smaller than that of the condition of single frequency.Based on the Miner fatigue theory,the effect of different loading sequences on sample rupture is discussed and the results show that it is better to select the sequence of low frequency at first and then high frequency.Our achievements can give a basis for the improvement and optimization of the pulse hydraulic fracturing technology.展开更多
In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection(PI), the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydr...In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection(PI), the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydrostatic injection(HI). The results show that the kinetic curves of methane desorption based on PI and HI are consistent with each other, and the diffusion model can best describe the characteristics of methane desorption. Initial velocity, diffusion capacity and ultimate desorption amount of methane desorption after PI are greater than those after HI, and the ultimate desorption amount increases by 16.7–39.7%.Methane decay rate over the time is less than that of the HI. The PI influences the diffusion model parameters, and it makes the mass transfer Biot number B0 idecrease and the mass transfer Fourier series F00 increase. As a result, PI makes the methane diffusion resistance in the coal smaller, methane diffusion rate greater, mass transfer velocity faster and the disturbance range of methane concentration wider than HI.Therefore, the effect of methane desorption based on PI is better than that of HI.展开更多
基金supported by National Natural Science Foundation of China(Grant No.51274195)Natural Science Foundation of Jiangsu Province(Grant No.BK2012571)+2 种基金China Post-doctoral Science Foundation(Grant No.20090450930)National Basic Research Program of China(973 Project)(Grant No.2011CB201205)Youth Foundation of China University of Miningand Technology(Grant No.2007A003)
文摘Aiming at the uncontrollable problem of extension direction of coal seam hydraulic fracturing,this study analyzed the course of fractures variation around the boreholes in process of hydraulic fracturing,and carried out the numerical simulations to investigate the effect of artificial predetermined fractures on stress distribution around fractured holes.The simulation results show that partial coal mass occurs relatively strong shear failure and forms weak surfaces,and then fractures extended along the desired direction while predetermined fractures changed stress distribution.Directional fracturing makes the fractures link up and the pressure on coal mass is relieved within fractured regions.Combining deep hole controlling blasting with hydraulic fracturing was proposed to realize the extension guiding-controlling technology of coal seam fractures.Industrial experiments prove that this technology can avoid local stress concentration and dramatically widen the pressure relief scope of deep hole controlling blasting.The permeability of fractured coal seam increased significantly,and gas extraction was greatly improved.Besides,regional pressure relief and permeability increase was achieved in this study.
基金Financial support for this work,provided by the National Basic Research Program of China(No.2011CB201205)the Natural Science Foundation of Jiangsu Province(No.BK2012571)+1 种基金the Program for New Century Excellent Talents in University(No.NCET-120959)the"Qing-Lan Project"and Collegial Graduate Research and Innovation Program of Jiangsu Province(No.CXZZ13_0955)
文摘Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial loading was developed.Based on the monitor methods of pressure sensor and acoustic emission,the trials of two patterns of pulse hydraulic fracturing of single frequency and variable frequency were carried out,and at last fracturing mechanism was analyzed.The results show that the effect of variable frequency on fracture extension is better than that of single frequency based on the analysis of macroscopic figures and AE.And the shortage of single frequency is somewhat remedied when the frequency is variable.Under variable frequency,the pressure process can be divided into three stages:low frequency band,pressure stability band and high frequency band,and rupture pressure of the sample is smaller than that of the condition of single frequency.Based on the Miner fatigue theory,the effect of different loading sequences on sample rupture is discussed and the results show that it is better to select the sequence of low frequency at first and then high frequency.Our achievements can give a basis for the improvement and optimization of the pulse hydraulic fracturing technology.
基金financially supported by the National Basic Research Program of China (No. 2011CB201205)the National Natural Science Foundation of China (No. 51274195)+2 种基金the Natural Science Foundation of Jiangsu Province of China (No. BK2012571)the National Major Scientific Instrument and Equipment Development Project of China (No. 2013YQ17046309)the Education Department Science and Technology Key Project of Henan Province of China (14B440007)
文摘In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection(PI), the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydrostatic injection(HI). The results show that the kinetic curves of methane desorption based on PI and HI are consistent with each other, and the diffusion model can best describe the characteristics of methane desorption. Initial velocity, diffusion capacity and ultimate desorption amount of methane desorption after PI are greater than those after HI, and the ultimate desorption amount increases by 16.7–39.7%.Methane decay rate over the time is less than that of the HI. The PI influences the diffusion model parameters, and it makes the mass transfer Biot number B0 idecrease and the mass transfer Fourier series F00 increase. As a result, PI makes the methane diffusion resistance in the coal smaller, methane diffusion rate greater, mass transfer velocity faster and the disturbance range of methane concentration wider than HI.Therefore, the effect of methane desorption based on PI is better than that of HI.
