Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study establis...Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.展开更多
随着新能源占总装机的比重不断提高,电池储能电站的容量和规模不断扩大,提升电池储能系统(battery energy storage system,BESS)单机容量具有重要的工程实践意义。为探究面向百兆瓦级应用更具优势的BESS拓扑,首先,分析了传统集中式BESS...随着新能源占总装机的比重不断提高,电池储能电站的容量和规模不断扩大,提升电池储能系统(battery energy storage system,BESS)单机容量具有重要的工程实践意义。为探究面向百兆瓦级应用更具优势的BESS拓扑,首先,分析了传统集中式BESS存在的问题及其单机电压等级和容量提升受限的原因;然后,通过计算分析了星型结构、三角形结构和模块化多电平结构3种高压直挂式BESS的单机容量;最后,以星型结构为例,展开详细研究。介绍了星型结构的拓扑结构和数学模型,分析了高压直挂式BESS的控制方法,包括网侧功率控制和荷电状态均衡控制。通过搭建35 kV/10 MW的仿真模型,验证了控制方法的有效性。研究结果表明,高压直挂式BESS在单机容量和扩容方面具有明显优势,更适用于高压、大容量的应用场合。展开更多
文摘Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.
