Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order t...Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order to mitigate or prevent gas channeling, ethylenediamine is chosen for permeability profile control. The reaction mechanism of ethylenediamine with CO2, injection performance, swept volume, and enhanced oil recovery were systematically evaluated. The reaction product of ethylenediamine and CO2 was a white solid or a light yellow viscous liquid, which would mitigate or prevent gas channeling. Also, ethylenediamine could be easily injected into ultra-low permeability cores at high temperature with protective ethanol slugs. The core was swept by injection of 0.3 PV ethylenediamine. Oil displacement tests performed on heterogeneous models with closed fractures, oil recovery was significantly enhanced with injection of ethylenediamine. Experimental results showed that using ethylenediamine to plug high permeability layers would provide a new research idea for the gas injection in fractured, heterogeneous and ultra-low permeability reservoirs. This technology has the potential to be widely applied in oilfields.展开更多
Coalbed gas extraction is an important means of exploiting and utilizing gas resources,as well as a means of preventing coal mine disasters.In view of the low gas extraction rate from coalbeds with high gas content an...Coalbed gas extraction is an important means of exploiting and utilizing gas resources,as well as a means of preventing coal mine disasters.In view of the low gas extraction rate from coalbeds with high gas content and low permeability,a method of improving permeability through deep-hole cumulative blasting is applied to develop initial directional fractures using a jet flow.Under the action of the blasting stress wave and detonation gas wedge,the fractures extend over a large range within the coal,thereby improving coalbed permeability.This study focuses on the criteria of cumulative blasting-induced coalbed fracturing based on a literature review of the penetration effect of cumulative blasting.On this basis,we summarize the coal fracturing zone,crack extension process,and the key technologies of charging and hole sealing for cumulative blasting.In addition,the latest research progress in the optimization of field test drilling and blasting parameters for cumulative blasting is introduced.Research findings indicate that the permeability improvement mechanism of cumulative blasting could be further enhanced,and the technology and technical equipment are in urgent need of improvement.Finally,development trends in the cumulative blasting permeability improvement technique are identified.展开更多
The permeability is a key factor to determine the efficiency of coalbed methane(CBM)production.The borehole enlargement technology using hydraulic and mechanical measures to cut coal is an effective method to increase...The permeability is a key factor to determine the efficiency of coalbed methane(CBM)production.The borehole enlargement technology using hydraulic and mechanical measures to cut coal is an effective method to increase the coal seam permeability and improve the efficiency of gas drainage.Reasonable design of the layout of boreholes is the prerequisite for efficient and economical gas drainage.In this paper,based on the strain-softening model,the stress and permeability model of the coal seam around the enlarged borehole was built,and based on the dual-medium model,the gas migration model in the coal seam was established.Then the borehole enlargement gas drainage engineering of E9/10 coal seam in Pingdingshan No.8 coal mine was simulated by using COMSOL Multiphysics software.The distribution of stress and permeability in the coal seam around a borehole was analyzed,and the reasonable borehole radius of 0.25 m and reasonable borehole spacing of 6 m were determined.Finally,in Pingdingshan No.8 coal mine,field application was carried out in E9/10 coal seam-21070 working face from the high-level gas drainage roadway.The results show that the actual average coal slag discharge rate is 77.82%,which achieved borehole enlargement.The natural gas flow rate from an enlarged borehole is 2.3–7.3 times that of a normal borehole,and the influence range of enlarged boreholes is more than 6 m.The average gas drainage concentration of a group of enlarged boreholes is about 42%,and the average gas drainage amount is about 0.53 m3/min.After two months of gas extraction,the outburst risk in this area was eliminated,which provides a guarantee for safe coal mining.展开更多
Coal permeability is a measure of the ability for fluids to flow through coal structures. It is one of the most important parameters affecting the gas drainage performance in underground coal mines. Despite the extens...Coal permeability is a measure of the ability for fluids to flow through coal structures. It is one of the most important parameters affecting the gas drainage performance in underground coal mines. Despite the extensive research conducted on coal permeability, few studies have considered the effect of coal damage on permeability. This has resulted in unreliable permeability evaluation and prediction. The aim of this study is to investigate the effect of coal damage on permeability and gas drainage performance. The Cui-Bustin permeability model was improved by taking into account the impact of coal damage on permeability. The key damage coefficient of the improved permeability model is determined based on the published permeability data. A finite-element numerical simulation was then developed based on the improved permeability model to investigate the damage areas and the permeability distribution around roadway. Results showed that the tensile failure occurs mainly on the upper and lower sides of the roadway while the shear failure symmetrically occurs on the left and right sides. With the increase in the friction angle value, the damage area becomes small. A good agreement was obtained between the results of the improved permeability model(c = 3) and the published permeability data. This indicated a more accurate permeability prediction by the improved permeability model. It is expected that the findings of this study could provide guidance for in-seam gas drainage borehole design and sealing, in order to enhance the gas drainage performance and reduce gas emissions into underground roadways.展开更多
In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves...In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method(BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater's width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.展开更多
Based on the difficult situation of gas drainage in a single coal bed of high gas content and low permeability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger moveme...Based on the difficult situation of gas drainage in a single coal bed of high gas content and low permeability, 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 L/min at the highest point.The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2times 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
基金Financial support for this work from National Sciencetechnology Support Plan Projects (No. 2012BAC26B00)the Science Foundation of China University of Petroleum, Beijing (No.2462012KYJJ23)
文摘Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order to mitigate or prevent gas channeling, ethylenediamine is chosen for permeability profile control. The reaction mechanism of ethylenediamine with CO2, injection performance, swept volume, and enhanced oil recovery were systematically evaluated. The reaction product of ethylenediamine and CO2 was a white solid or a light yellow viscous liquid, which would mitigate or prevent gas channeling. Also, ethylenediamine could be easily injected into ultra-low permeability cores at high temperature with protective ethanol slugs. The core was swept by injection of 0.3 PV ethylenediamine. Oil displacement tests performed on heterogeneous models with closed fractures, oil recovery was significantly enhanced with injection of ethylenediamine. Experimental results showed that using ethylenediamine to plug high permeability layers would provide a new research idea for the gas injection in fractured, heterogeneous and ultra-low permeability reservoirs. This technology has the potential to be widely applied in oilfields.
基金The project was supported by the National Science Foundation of China(41430640,U1704242).
文摘Coalbed gas extraction is an important means of exploiting and utilizing gas resources,as well as a means of preventing coal mine disasters.In view of the low gas extraction rate from coalbeds with high gas content and low permeability,a method of improving permeability through deep-hole cumulative blasting is applied to develop initial directional fractures using a jet flow.Under the action of the blasting stress wave and detonation gas wedge,the fractures extend over a large range within the coal,thereby improving coalbed permeability.This study focuses on the criteria of cumulative blasting-induced coalbed fracturing based on a literature review of the penetration effect of cumulative blasting.On this basis,we summarize the coal fracturing zone,crack extension process,and the key technologies of charging and hole sealing for cumulative blasting.In addition,the latest research progress in the optimization of field test drilling and blasting parameters for cumulative blasting is introduced.Research findings indicate that the permeability improvement mechanism of cumulative blasting could be further enhanced,and the technology and technical equipment are in urgent need of improvement.Finally,development trends in the cumulative blasting permeability improvement technique are identified.
基金supported by the Assistance Program for Future Outstanding Talents of China University of Mining and Technology(No.2020WLJCRCZL041)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX20_0816).
文摘The permeability is a key factor to determine the efficiency of coalbed methane(CBM)production.The borehole enlargement technology using hydraulic and mechanical measures to cut coal is an effective method to increase the coal seam permeability and improve the efficiency of gas drainage.Reasonable design of the layout of boreholes is the prerequisite for efficient and economical gas drainage.In this paper,based on the strain-softening model,the stress and permeability model of the coal seam around the enlarged borehole was built,and based on the dual-medium model,the gas migration model in the coal seam was established.Then the borehole enlargement gas drainage engineering of E9/10 coal seam in Pingdingshan No.8 coal mine was simulated by using COMSOL Multiphysics software.The distribution of stress and permeability in the coal seam around a borehole was analyzed,and the reasonable borehole radius of 0.25 m and reasonable borehole spacing of 6 m were determined.Finally,in Pingdingshan No.8 coal mine,field application was carried out in E9/10 coal seam-21070 working face from the high-level gas drainage roadway.The results show that the actual average coal slag discharge rate is 77.82%,which achieved borehole enlargement.The natural gas flow rate from an enlarged borehole is 2.3–7.3 times that of a normal borehole,and the influence range of enlarged boreholes is more than 6 m.The average gas drainage concentration of a group of enlarged boreholes is about 42%,and the average gas drainage amount is about 0.53 m3/min.After two months of gas extraction,the outburst risk in this area was eliminated,which provides a guarantee for safe coal mining.
基金financially supported by the CSC-UQ Scholarshipthe University of Queensland Top Up Assistance Scholarship
文摘Coal permeability is a measure of the ability for fluids to flow through coal structures. It is one of the most important parameters affecting the gas drainage performance in underground coal mines. Despite the extensive research conducted on coal permeability, few studies have considered the effect of coal damage on permeability. This has resulted in unreliable permeability evaluation and prediction. The aim of this study is to investigate the effect of coal damage on permeability and gas drainage performance. The Cui-Bustin permeability model was improved by taking into account the impact of coal damage on permeability. The key damage coefficient of the improved permeability model is determined based on the published permeability data. A finite-element numerical simulation was then developed based on the improved permeability model to investigate the damage areas and the permeability distribution around roadway. Results showed that the tensile failure occurs mainly on the upper and lower sides of the roadway while the shear failure symmetrically occurs on the left and right sides. With the increase in the friction angle value, the damage area becomes small. A good agreement was obtained between the results of the improved permeability model(c = 3) and the published permeability data. This indicated a more accurate permeability prediction by the improved permeability model. It is expected that the findings of this study could provide guidance for in-seam gas drainage borehole design and sealing, in order to enhance the gas drainage performance and reduce gas emissions into underground roadways.
基金financially supported by the Direction Général des Enseignements et de la Formation Supérieure of Algeria(Grant CNEPRU No.G0301920140029)
文摘In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method(BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater's width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.
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 permeability, 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 L/min at the highest point.The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2times 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.