查看更多>>摘要：Evaluation of the gas inflow profile of horizontal wells (GIPHW) is one of the key technologies to achieve a high efficiency and stable gas production in heterogeneous gas reservoirs. However, the gas inflow profiles of the YB gas reservoir cannot be determined by current methods such as theoretical modeling and production logging. In this paper, a new experimental evaluation method is proposed to determine GIPHW in the YB gas reservoir. First, gas inflow profile experiments were conducted considering different permeability combinations and injection pressure differences. Then, the drawdown-permeability-gas production chart was generated based on experiments. Finally, based on these charts, a new evaluation method for GIPHW was developed and applied in the YB gas reservoir. The numerical simulation and experimental results for GIPHW in the YB gas reservoir showed good consistency. The sensitivity analysis demonstrated three points: (1) Although the number of cores increases when the permeability difference is maintained, the GIPHW does not change. Meanwhile, gas production increases with an increasing proportion of three types of reservoir, but the reservoir-type proportion has little influence on the GIPHW. (2) Gas production increases with increasing pressure difference. The Type I reservoir has the highest production increment, followed by Type II reservoir and Type III reservoir. (3) The reservoir proportion changes in descending order affecting the GIPHW are Type I reservoirs, Type II reservoirs, and Type III reservoirs. This work provides technical support for the determination of the GIPHW and the complete optimization of horizontal wells in the gas reservoir.
查看更多>>摘要：Evaluation of the gas inflow profile of horizontal wells (GIPHW) is one of the key technologies to achieve a high efficiency and stable gas production in heterogeneous gas reservoirs. However, the gas inflow profiles of the YB gas reservoir cannot be determined by current methods such as theoretical modeling and production logging. In this paper, a new experimental evaluation method is proposed to determine GIPHW in the YB gas reservoir. First, gas inflow profile experiments were conducted considering different permeability combinations and injection pressure differences. Then, the drawdown-permeability-gas production chart was generated based on experiments. Finally, based on these charts, a new evaluation method for GIPHW was developed and applied in the YB gas reservoir. The numerical simulation and experimental results for GIPHW in the YB gas reservoir showed good consistency. The sensitivity analysis demonstrated three points: (1) Although the number of cores increases when the permeability difference is maintained, the GIPHW does not change. Meanwhile, gas production increases with an increasing proportion of three types of reservoir, but the reservoir-type proportion has little influence on the GIPHW. (2) Gas production increases with increasing pressure difference. The Type I reservoir has the highest production increment, followed by Type II reservoir and Type III reservoir. (3) The reservoir proportion changes in descending order affecting the GIPHW are Type I reservoirs, Type II reservoirs, and Type III reservoirs. This work provides technical support for the determination of the GIPHW and the complete optimization of horizontal wells in the gas reservoir.
查看更多>>摘要：Wave propagation and thermal conduction properties can indicate structural damage to hot dry rock (HDR) caused by thermal shocks. Granite from the central paleo-uplift belt in the Daqing area in the northern Songliao Basin is the focus of this research. Wave propagation tests and thermal conduction tests were conducted on high-temperature specimens after natural cooling and water cooling. The influence of the cooling process with water on the apparent temperature and thermal shock velocity of rock masses is discussed. Changes in the P- and S-wave velocities, specific heat capacity, thermal diffusion coefficient, and thermal conductivity coefficient of specimens under different heat treatment conditions are analyzed and compared. The relationships between the wave propagation characteristics and the thermal conductivity values are established. The results indicate the following: (1) The apparent temperature and thermal shock velocity values of high-temperature rock masses show nonconstant rates of change from fast to slow. Rock masses with higher initial temperatures exhibit a continuous and strong thermal shock effect, and water temperature differences have only a limited effect on the thermal shock velocity over 20 s of cooling with water. (2) As the initial temperature increases or water temperature decreases, the P-wave velocity, S-wave velocity, thermal diffusion coefficient, and thermal conductivity coefficient values of high-temperature rock masses decrease overall, while the specific heat capacity values increase. The amplitude of change after water cooling is higher than that after natural cooling. When the initial temperature is below 100 degrees C, the free water content is the main factor influencing the wave propagation characteristics and changes in the thermal conduction characteristics. When the initial temperature is greater than 300 degrees C, the changes in both properties depend on the amount of thermal damage done to the rock mass. (3) The fitting results suggest that the wave propagation and thermal characteristics are closely related, and the damage factors are strongly consistent. The deviation of fitting coefficients is mainly due to the limited development of fractures in the small-sized specimens. The research results provide a reference for studies on thermal damage in HDR in the geothermal development process, and a method to determine the in situ thermal conductivity of reservoirs is proposed.
查看更多>>摘要：Wave propagation and thermal conduction properties can indicate structural damage to hot dry rock (HDR) caused by thermal shocks. Granite from the central paleo-uplift belt in the Daqing area in the northern Songliao Basin is the focus of this research. Wave propagation tests and thermal conduction tests were conducted on high-temperature specimens after natural cooling and water cooling. The influence of the cooling process with water on the apparent temperature and thermal shock velocity of rock masses is discussed. Changes in the P- and S-wave velocities, specific heat capacity, thermal diffusion coefficient, and thermal conductivity coefficient of specimens under different heat treatment conditions are analyzed and compared. The relationships between the wave propagation characteristics and the thermal conductivity values are established. The results indicate the following: (1) The apparent temperature and thermal shock velocity values of high-temperature rock masses show nonconstant rates of change from fast to slow. Rock masses with higher initial temperatures exhibit a continuous and strong thermal shock effect, and water temperature differences have only a limited effect on the thermal shock velocity over 20 s of cooling with water. (2) As the initial temperature increases or water temperature decreases, the P-wave velocity, S-wave velocity, thermal diffusion coefficient, and thermal conductivity coefficient values of high-temperature rock masses decrease overall, while the specific heat capacity values increase. The amplitude of change after water cooling is higher than that after natural cooling. When the initial temperature is below 100 degrees C, the free water content is the main factor influencing the wave propagation characteristics and changes in the thermal conduction characteristics. When the initial temperature is greater than 300 degrees C, the changes in both properties depend on the amount of thermal damage done to the rock mass. (3) The fitting results suggest that the wave propagation and thermal characteristics are closely related, and the damage factors are strongly consistent. The deviation of fitting coefficients is mainly due to the limited development of fractures in the small-sized specimens. The research results provide a reference for studies on thermal damage in HDR in the geothermal development process, and a method to determine the in situ thermal conductivity of reservoirs is proposed.
查看更多>>摘要：Understanding of the fracture network propagation behavior is necessary for improvement of hydraulic fracture operation in shale gas reservoirs, in particular under the influences of geological and field operation parameters. In this paper, a three-dimansional numerical model was used to simulate the propagation of the hydraulic fracture network in field scale, considering a wellbore-fracture-pore triple flow system under the full hydromechanical coupling. The numerical model was verified by simulating the propagation and interaction between natural and hydraulic discontinuities. Finally, the numerical model was applied to evaluate the behavior of complex fracture propagation in hydraulic fracturing operation in a shale gas reservoir based on field operation parameters. Some conclusions can be drawn: (i) both tensile and shear cracking can occur during the hydraulic fracture network propagation, depending on the stress anisotropy and deviation of natural discontinuities; (ii) a certain deviation of natural and layered discontinuities from principal stress directions is one of the main preconditions for forming a complex fracture network under high-stress anisotropy; (iii) a relatively larger control volume can be obtained when the natural fractures are orthogonally crossed and the complexity factor of the fracture network is higher when the cross type is X; and (iv) adequate fluid viscosity should be applied to control the fluid leak-off, thus increasing the complexity and extent of the stimulated reservoir volume. These results can provide a theoretical basis for the optimization of the hydraulic fracturing in shale gas reservoirs.
查看更多>>摘要：Understanding of the fracture network propagation behavior is necessary for improvement of hydraulic fracture operation in shale gas reservoirs, in particular under the influences of geological and field operation parameters. In this paper, a three-dimansional numerical model was used to simulate the propagation of the hydraulic fracture network in field scale, considering a wellbore-fracture-pore triple flow system under the full hydromechanical coupling. The numerical model was verified by simulating the propagation and interaction between natural and hydraulic discontinuities. Finally, the numerical model was applied to evaluate the behavior of complex fracture propagation in hydraulic fracturing operation in a shale gas reservoir based on field operation parameters. Some conclusions can be drawn: (i) both tensile and shear cracking can occur during the hydraulic fracture network propagation, depending on the stress anisotropy and deviation of natural discontinuities; (ii) a certain deviation of natural and layered discontinuities from principal stress directions is one of the main preconditions for forming a complex fracture network under high-stress anisotropy; (iii) a relatively larger control volume can be obtained when the natural fractures are orthogonally crossed and the complexity factor of the fracture network is higher when the cross type is X; and (iv) adequate fluid viscosity should be applied to control the fluid leak-off, thus increasing the complexity and extent of the stimulated reservoir volume. These results can provide a theoretical basis for the optimization of the hydraulic fracturing in shale gas reservoirs.
查看更多>>摘要：Although great progress has been achieved in numerical simulation on porous flow in rock in decades, experiments performed on reservoir-on-a-chip (ROC) have been emphasized as the most sufficient and direct way to investigate the subsurface fluid flow at pore scale. This paper applies the cutting-edge three-dimensional printing (3DP) technique into the fabrication of ROC and the visualized two-phase fluids experiments. The structure of 3D-printed ROC is quantitatively characterized using the surface scanning analyzer and stereomicroscope, and then validated by comparison with the original digital structure. Then immiscible (oil-water) two-phase flow experiments are conducted on the 3D-printed ROC and imaged using the high-resolution camera in real time. The typical fingering phenomenon caused by the heterogeneity of pore-throat structure is observed, and the effects of surface wettability on the interfacial shape evolution are analyzed. Comparing to traditional fabrication methods (e.g., chemical etching and soft lithography), 3D-printed ROC is approved to be a novel approach to manufacture the morphology, topology, and connectivity of the pore network, while reducing the cost and the time required.
查看更多>>摘要：Although great progress has been achieved in numerical simulation on porous flow in rock in decades, experiments performed on reservoir-on-a-chip (ROC) have been emphasized as the most sufficient and direct way to investigate the subsurface fluid flow at pore scale. This paper applies the cutting-edge three-dimensional printing (3DP) technique into the fabrication of ROC and the visualized two-phase fluids experiments. The structure of 3D-printed ROC is quantitatively characterized using the surface scanning analyzer and stereomicroscope, and then validated by comparison with the original digital structure. Then immiscible (oil-water) two-phase flow experiments are conducted on the 3D-printed ROC and imaged using the high-resolution camera in real time. The typical fingering phenomenon caused by the heterogeneity of pore-throat structure is observed, and the effects of surface wettability on the interfacial shape evolution are analyzed. Comparing to traditional fabrication methods (e.g., chemical etching and soft lithography), 3D-printed ROC is approved to be a novel approach to manufacture the morphology, topology, and connectivity of the pore network, while reducing the cost and the time required.
查看更多>>摘要：It is of great significance to evaluate the fracture permeability after reservoir stimulation for geothermal extraction. This paper is focused on evaluating the permeability of two kinds of fractures-shear and tensile fracture generated by mechanical force in a laboratory. It is found that the permeability of tensile fractures is 1.5-3.5 times as much as the shear fracture under loading and unloading stress from 1 to 60 to 1 MPa. Both shear and tensile fractures experience a relative high permeability reduction (i.e., up to 99%) under loading stress, while the absolute permeability reduction of a shear fracture is much lower than that of a tensile fracture. The tensile fracture experiences a much higher absolute permeability enhancement under unloading stress. When it comes to the whole loading and unloading cycle, shear fracture has a lower absolute but a higher relative permeability reduction. Three models (i.e., the exponential, power, and Walsh models) were used to evaluate the stress dependence of permeability. In total, the stress sensibility of permeability in loading stress is higher than that in unloading stress. And this sensibility for shear fractures is higher than that of tensile fractures in loading stress while it is lower than that of tensile fractures in unloading stress, which causes the higher relative permeability reduction in shear fractures. The suitability check of the models shows that the exponential model is not suitable for data under unloading stress, the Walsh model has a better suitability for data under loading stress than that under unloading stress, and the power-law model is suitable for data under both loading and stresses.
查看更多>>摘要：It is of great significance to evaluate the fracture permeability after reservoir stimulation for geothermal extraction. This paper is focused on evaluating the permeability of two kinds of fractures-shear and tensile fracture generated by mechanical force in a laboratory. It is found that the permeability of tensile fractures is 1.5-3.5 times as much as the shear fracture under loading and unloading stress from 1 to 60 to 1 MPa. Both shear and tensile fractures experience a relative high permeability reduction (i.e., up to 99%) under loading stress, while the absolute permeability reduction of a shear fracture is much lower than that of a tensile fracture. The tensile fracture experiences a much higher absolute permeability enhancement under unloading stress. When it comes to the whole loading and unloading cycle, shear fracture has a lower absolute but a higher relative permeability reduction. Three models (i.e., the exponential, power, and Walsh models) were used to evaluate the stress dependence of permeability. In total, the stress sensibility of permeability in loading stress is higher than that in unloading stress. And this sensibility for shear fractures is higher than that of tensile fractures in loading stress while it is lower than that of tensile fractures in unloading stress, which causes the higher relative permeability reduction in shear fractures. The suitability check of the models shows that the exponential model is not suitable for data under unloading stress, the Walsh model has a better suitability for data under loading stress than that under unloading stress, and the power-law model is suitable for data under both loading and stresses.
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