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
On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new cal...On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new calculating method of gas content in coal seam influenced by in situ stress grads and ground temperature. At the same time, the contrast of the measuring results of coal bed gas pressure with the computing results of coal bed gas pressure and gas content in coal seam in theory indicate that the computing method can well reflect the authenticity of gas content in coal seam,and will further perfect the computing method of gas content in coal seam in theory,and have important value in theory on analyzing gas content in coal seam and forecasting distribution law of gas content in coal seam in deep mine.展开更多
In order to explain the mechanism for gas outburst, the process of evolving fractures in coal seams is described using system dynamics with variable boundaries. We discuss the failure modes of coal containing gas and ...In order to explain the mechanism for gas outburst, the process of evolving fractures in coal seams is described using system dynamics with variable boundaries. We discuss the failure modes of coal containing gas and then established the flow rules after failure. The condition under which states of deformation convert is presented and the manner in which these convert is proposed. In the end, the process of gas outbursts is explained in detail. It shows that a gas outburst is a process in which the boundaries of coal seams are variable because of coal failure. If the fractures are not connected or even closed owing to coal/rock stress, fractured zones will retain a certain level of carrying capacity because of the self-sealing gas pressure. When the accumulation of gas energy reaches its limit, coal seams will become unstable and gas outbursts take place.展开更多
Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical sol...Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume(SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.展开更多
Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorp...Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorption and abnormal development of natural fracture systems） as compared with the conventional reservoirs, the fractures propagate is difficult and the risk of damage to coal seam itself and the hydraulic fractures would be extremely high in the course of fracturing. As a result, losses would be suffered on the post-frac production of CBM wells.With the mean of numerical simulation, in this paper, the main factors have impact on the post-frac results as well as the extent to which the impact is brought were researched, and the technical solutions for the improvement of the fracturing performance was put forwards.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.
文摘On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new calculating method of gas content in coal seam influenced by in situ stress grads and ground temperature. At the same time, the contrast of the measuring results of coal bed gas pressure with the computing results of coal bed gas pressure and gas content in coal seam in theory indicate that the computing method can well reflect the authenticity of gas content in coal seam,and will further perfect the computing method of gas content in coal seam in theory,and have important value in theory on analyzing gas content in coal seam and forecasting distribution law of gas content in coal seam in deep mine.
基金financial support from the National Basic Research Program of China (No.2005CB221500)the National Natural Science Foundation of China (Nos.50534049,50674087 and 50974107)the Natural Science Foundation of Jiangsu Province (No.BK2007029)
文摘In order to explain the mechanism for gas outburst, the process of evolving fractures in coal seams is described using system dynamics with variable boundaries. We discuss the failure modes of coal containing gas and then established the flow rules after failure. The condition under which states of deformation convert is presented and the manner in which these convert is proposed. In the end, the process of gas outbursts is explained in detail. It shows that a gas outburst is a process in which the boundaries of coal seams are variable because of coal failure. If the fractures are not connected or even closed owing to coal/rock stress, fractured zones will retain a certain level of carrying capacity because of the self-sealing gas pressure. When the accumulation of gas energy reaches its limit, coal seams will become unstable and gas outbursts take place.
基金Project(2011ZX05015)supported by Important National Science and Technology Specific Projects of the "Twelfth Five-years" Plan Period,China
文摘Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume(SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.
文摘Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorption and abnormal development of natural fracture systems） as compared with the conventional reservoirs, the fractures propagate is difficult and the risk of damage to coal seam itself and the hydraulic fractures would be extremely high in the course of fracturing. As a result, losses would be suffered on the post-frac production of CBM wells.With the mean of numerical simulation, in this paper, the main factors have impact on the post-frac results as well as the extent to which the impact is brought were researched, and the technical solutions for the improvement of the fracturing performance was put forwards.
