Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer...Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer solutions exhibit non-Newtonian and nonlinear flow behavior including shear thinning and shear thickening,polymer convection,diffusion,adsorption,retention,inaccessible pore volume,and reduced effective permeability.However,available well test model of polymer flooding wells generally simplifies these characteristics on pressure transient response,which may lead to inaccurate results.This work proposes a novel two-phase numerical well test model to better describe the polymer viscoelasticity and nonlinear flow behavior.Different influence factors that related to near-well blockage during polymer flooding process,including the degree of blockage(inner zone permeability),the extent of blockage(composite radius),and polymer flooding front radius are explored to investigate these impacts on bottom hole pressure responses.Results show that polymer viscoelasticity has a significant impact on the transitional flow segment of type curves,and the effects of near-well formation blockage and polymer concentration distribution on well test curves are very similar.Thus,to accurately interpret the degree of near-well blockage in injection wells,it is essential to first eliminate the influence of polymer viscoelasticity.Finally,a field case is comprehensively analyzed and discussed to illustrate the applicability of the proposed model.展开更多
The big underground powerhouse cavern of the China Baihetan hydropower plant is 438m long,34m wide,and 88.7m high.It is cut by a weak interlayer shear zone and its high sidewall poses a huge stability problem.This pap...The big underground powerhouse cavern of the China Baihetan hydropower plant is 438m long,34m wide,and 88.7m high.It is cut by a weak interlayer shear zone and its high sidewall poses a huge stability problem.This paper reports our successful solution of this problem through numerical simulations and a replacement-tunnel scheme in the detailed design stage and close site monitoring in the excavation stage.Particularly,in the detail design stage,mechanical parameters of the shear zone were carefully determined through laboratory experiments and site tests.Then,deformation of the surrounding rocks and the shear zone under high in situ stress conditions was predicted using 3 Dimensional Distinct Element Code(3DEC).Subsequently,a replacement-tunnel scheme was proposed for the treatment on the shear zone to prevent severe unloading relaxation of surrounding rocks.In the construction period,excavation responses were closely monitored on deformations of surrounding rocks and the shear zone.The effect of local cracking in the replacement tunnels on sidewall stability was evaluated using the strength reduction method.These monitoring results were compared with the predicted numerical simulation in the detailed design stage.It is found that the shear zone greatly modified the deformation mode of the cavern surrounding rocks.Without any treatment,rock mass deformation on the downstream sidewall was larger than 125mm and the shearing deformation of the shear zone was 60–70 mm.These preset replacement tunnels can reduce not only the unloading and relaxation of rock masses but also the maximum shearing deformation of the shear zone by 10–20 mm.The predictions by numerical simulation were in good agreement with the monitoring results.The proposed tunnel-replacement scheme can not only restrain the shear zone deformation but also enhance the safety of surrounding rocks and concrete tunnels.This design procedure offers a good reference for interaction between a big underground cavern and a weak layer zone in the future.展开更多
Brittle rock has the mechanical characteristics of a high ratio of uniaxial compressive strength to tensilestrength, brittle-ductile transition, and so on. The mineral meso-structure of brittle rock shows theinterlock...Brittle rock has the mechanical characteristics of a high ratio of uniaxial compressive strength to tensilestrength, brittle-ductile transition, and so on. The mineral meso-structure of brittle rock shows theinterlocking behavior and there are some microcracks between the mineral grains, so it is difficult toanalyze the mechanical characteristics accurately with a regular constitutive model. The previous numericalmodels have some limitations when applied to brittle rock, that they cannot provide sufficientinternal interlocking and are incapable of considering the microcracks. These limitations are addressedby using the updated flat-joint contact model to join notional polygonal particles with an initial gap andincreasing the particle coordination number by adding flat-joint contacts to more particles that arewithin some non-zero distance of one another via the range coefficient contact identification method. Acomparison of experimental and numerical results confirms that the updated flat-jointed model providesa good match with the mechanical properties of brittle rock. In this paper, we investigate the influence ofmineral meso-structure (micro-cracks, range coefficient, and radius multiplier) on the meso-mechanicalproperties of Jinping dolomitic marble via the updated flat-joint contact model under direct-tension testsand compression tests. It is found that the updated model can reproduce the microstructure effect ofbrittle rock and can better simulate the mechanical characteristics of the brittle rock than conventionalmodels, such as high strength ratio, brittle-ductile transition, initial nonlinearity, and different modulusin compression and tension.展开更多
基金supported by the National Natural Science Foundation of China(52104049)the Young Elite Scientist Sponsorship Program by Beijing Association for Science and Technology(BYESS2023262)。
文摘Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer solutions exhibit non-Newtonian and nonlinear flow behavior including shear thinning and shear thickening,polymer convection,diffusion,adsorption,retention,inaccessible pore volume,and reduced effective permeability.However,available well test model of polymer flooding wells generally simplifies these characteristics on pressure transient response,which may lead to inaccurate results.This work proposes a novel two-phase numerical well test model to better describe the polymer viscoelasticity and nonlinear flow behavior.Different influence factors that related to near-well blockage during polymer flooding process,including the degree of blockage(inner zone permeability),the extent of blockage(composite radius),and polymer flooding front radius are explored to investigate these impacts on bottom hole pressure responses.Results show that polymer viscoelasticity has a significant impact on the transitional flow segment of type curves,and the effects of near-well formation blockage and polymer concentration distribution on well test curves are very similar.Thus,to accurately interpret the degree of near-well blockage in injection wells,it is essential to first eliminate the influence of polymer viscoelasticity.Finally,a field case is comprehensively analyzed and discussed to illustrate the applicability of the proposed model.
基金Program of China Three Gorges Corporation,Grant/Award Number:BHT 0679-1。
文摘The big underground powerhouse cavern of the China Baihetan hydropower plant is 438m long,34m wide,and 88.7m high.It is cut by a weak interlayer shear zone and its high sidewall poses a huge stability problem.This paper reports our successful solution of this problem through numerical simulations and a replacement-tunnel scheme in the detailed design stage and close site monitoring in the excavation stage.Particularly,in the detail design stage,mechanical parameters of the shear zone were carefully determined through laboratory experiments and site tests.Then,deformation of the surrounding rocks and the shear zone under high in situ stress conditions was predicted using 3 Dimensional Distinct Element Code(3DEC).Subsequently,a replacement-tunnel scheme was proposed for the treatment on the shear zone to prevent severe unloading relaxation of surrounding rocks.In the construction period,excavation responses were closely monitored on deformations of surrounding rocks and the shear zone.The effect of local cracking in the replacement tunnels on sidewall stability was evaluated using the strength reduction method.These monitoring results were compared with the predicted numerical simulation in the detailed design stage.It is found that the shear zone greatly modified the deformation mode of the cavern surrounding rocks.Without any treatment,rock mass deformation on the downstream sidewall was larger than 125mm and the shearing deformation of the shear zone was 60–70 mm.These preset replacement tunnels can reduce not only the unloading and relaxation of rock masses but also the maximum shearing deformation of the shear zone by 10–20 mm.The predictions by numerical simulation were in good agreement with the monitoring results.The proposed tunnel-replacement scheme can not only restrain the shear zone deformation but also enhance the safety of surrounding rocks and concrete tunnels.This design procedure offers a good reference for interaction between a big underground cavern and a weak layer zone in the future.
基金funding support from the National Natural Science Foundation of China(NSFC,Grant No.51428902)the China Scholarship Council(CSC,Grant No.202306270120).
文摘Brittle rock has the mechanical characteristics of a high ratio of uniaxial compressive strength to tensilestrength, brittle-ductile transition, and so on. The mineral meso-structure of brittle rock shows theinterlocking behavior and there are some microcracks between the mineral grains, so it is difficult toanalyze the mechanical characteristics accurately with a regular constitutive model. The previous numericalmodels have some limitations when applied to brittle rock, that they cannot provide sufficientinternal interlocking and are incapable of considering the microcracks. These limitations are addressedby using the updated flat-joint contact model to join notional polygonal particles with an initial gap andincreasing the particle coordination number by adding flat-joint contacts to more particles that arewithin some non-zero distance of one another via the range coefficient contact identification method. Acomparison of experimental and numerical results confirms that the updated flat-jointed model providesa good match with the mechanical properties of brittle rock. In this paper, we investigate the influence ofmineral meso-structure (micro-cracks, range coefficient, and radius multiplier) on the meso-mechanicalproperties of Jinping dolomitic marble via the updated flat-joint contact model under direct-tension testsand compression tests. It is found that the updated model can reproduce the microstructure effect ofbrittle rock and can better simulate the mechanical characteristics of the brittle rock than conventionalmodels, such as high strength ratio, brittle-ductile transition, initial nonlinearity, and different modulusin compression and tension.
