Most of the coal reservoirs in China are of low-permeability, so hydraulic fracturing is widely used to improve the per- meability in the extraction of gas by ground drilling. The ground stress around the well was ana...Most of the coal reservoirs in China are of low-permeability, so hydraulic fracturing is widely used to improve the per- meability in the extraction of gas by ground drilling. The ground stress around the well was analyzed by using theory of elasticity. The pressure when the well fractured is formulated and the effect of ground stress on pressure is discussed. The effect of ground-stress-differences on hydraulic fracturing was analyzed by using the numerical software RFPA2D-Flow in reference to the tectonic stress in Jincheng coal area. The results show that: 1) the position where initial fracture appears is random and fracture branches emerge when the fractures expand if ground stresses in any two directions within a horizontal plane are equal; 2) other- wise, the fractures expand in general along the direction of maximum ground stress and the critical pressure decreases with in- creasing ground-stress-differences and 3) the preferred well-disposition pattern is diamond shaped. The preferred well spacing is 250 m×300 m. This study can provide a reference for the design of wells.展开更多
For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dime...For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.展开更多
基金Projects 2007CB209400 supported by the National Basic Research Program of China50490273 by the National Natural Science Foundation of China
文摘Most of the coal reservoirs in China are of low-permeability, so hydraulic fracturing is widely used to improve the per- meability in the extraction of gas by ground drilling. The ground stress around the well was analyzed by using theory of elasticity. The pressure when the well fractured is formulated and the effect of ground stress on pressure is discussed. The effect of ground-stress-differences on hydraulic fracturing was analyzed by using the numerical software RFPA2D-Flow in reference to the tectonic stress in Jincheng coal area. The results show that: 1) the position where initial fracture appears is random and fracture branches emerge when the fractures expand if ground stresses in any two directions within a horizontal plane are equal; 2) other- wise, the fractures expand in general along the direction of maximum ground stress and the critical pressure decreases with in- creasing ground-stress-differences and 3) the preferred well-disposition pattern is diamond shaped. The preferred well spacing is 250 m×300 m. This study can provide a reference for the design of wells.
基金Financial supports for this work,provided by the National Natural Science Foundation of China (No.51104191)the China Postdoctoral Science Foundation (2016M602655)the Program for Changjiang Scholars and Innovative Research Team in University of China (No.IRT13043)
文摘For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.
