考虑分子动力学的页岩气微观孔隙渗流模型  

A Model for Microscopic Pore Flow of Shale Gas with Molecular Dynamics

作　　者：王一帆[1] 董平川[1] Wang Yifan Dong Pingchuan(MOE Key Laboratory of Petroleum Engineering,China University of Petroleum,Beijing 102249)

机构地区：[1]中国石油大学(北京)石油工程教育部重点实验室,北京102249

出　　处：《中外能源》2017年第9期34-38,共5页Sino-Global Energy

基　　金：国家自然科学基金项目"页岩气扩散渗流机理及产气规律研究"(编号:51504269)资助

摘　　要：页岩储层纳米孔隙发育,页岩气在孔隙中渗流状态复杂,采用常用的达西渗流难以表征这一特点。综合考虑甲烷分子在纳米孔隙中的吸附、滑脱以及Knusden扩散等状态,依据分子动力学方法,建立了一种新的表征微观条件下页岩气渗流的数学模型。通过新模型下视渗透率的计算,对比分析了不同压力不同孔隙直径时达西渗透率与视渗透率的比值,以及Knudsen扩散流动、考虑滑脱效应流动和气体扩散流动状态下占视渗透率的比例变化情况。经过对比分析,验证了新模型的实用性和合理性:在新模型下,达西渗透率与视渗透率的比值随着孔隙直径的增大而增大,且不同压力下的增长趋势较为一致;在小孔隙情况下研究该类问题时不可忽略吸附效应、滑脱效应以及Knusden扩散;平均孔隙直径10nm是其他流动状态显著下降的节点,大于50nm时其他流动状态可忽略不计。Nanopores are developed in the shale gas reservoirs.The shale gas flow in the pores is complex, which is hard to be characterized by the common Darcy flow.Based on the molecular dynamics method,a new mathematical model was developed to characterize the shale gas flow under the microscopic condition by considering the adsorption,slippage and Knusden diffusion of methane molecules in the nanopores.According to the calculation of apparent permeability by the new model,the ratio of Darcy permeability and apparent per- meability at different pressures with different pore diameters was compared and analyzed,and the proportion of the apparent permeability under the flow of Knusden diffusion, slippage effect and gas diffusion was ana- lyzed.By contrast,the practicability and rationality of the new model was verified.h is concluded that the ratio of Darcy permeability and apparent permeability increases with the increase of pore diameters,and the growth trend at various pressures is almost the same.The adsorption effect,slippage effect and Knusden diffusion can not be neglected in the case of small pores.Ten nanometer of the average pore diameter is an important drop node at other flow states,and other flow state can be neglected when the average pore diameter is greater than 50nm.

关 键 词：页岩气 纳米 微观孔隙 分子动力学 渗流模型 

分 类 号：TE312[石油与天然气工程—油气田开发工程]