盖层微渗漏散失机理与定量模型

微渗漏是天然气通过盖层散失的重要方式之一。天然气进入盖层孔隙后会在后者表面会发生吸附现象,当该表面的吸附层达到一定厚度时便出现毛细孔凝聚现象,气相变成“似液相”充满于孔隙内,这种似液相物质是以胶束状态存在的。当这种凝聚发生作用时,气体凝聚量会不断增加,气体变成具有与液体相似的性质,分子之间的粘滞力增大,其粘度便接近孔喉中水的粘度。2种不同物质的液体在粘度相似的情况下则会发生互溶现象,轻烃则呈胶束状态的微气泡形式发生准垂直向上的渗漏运移,即微渗漏。通过微渗漏机理的分析,建立了微渗漏散失的定量模型,并通过实际气藏定量估算了地史时期天然气通过盖层的微渗漏散失量。

DIFFUSION MECHANISM AND QUANTITATIVE MODEL OF MICROLEAKAGE IN CAPROCKS

Microleakage is one of the most important pathways in which the natural gas diffuses through caprocks.When natural gas enters the pore surfaces of caprocks,the phenomenon of adsorption appears.When adsorbed layer of the solid surface has reached a certain thickness,the condensation of capillary void happens,and the gas phase becomes "liquidoidlike",filling the hole.The liquidoidlike matter exists in the form of micellar.When this kind of condensation happens,the quantity of gas condensation will increase unceasingly,and then the gas becomes something whose nature is similar to the liquid.Its viscous force between moleculars increases and approaches the viscosity of water.Two different kinds of liquids may be mutually soluble when their viscosity is similar.In the form of micell,light hydrocarbons in the state of air bubble migrate vertically upward through leakage,this phenomenon is called microleakage.Based on the analysis of the microleakage mechanism,this paper establishes a quantitative model of microleakage diffusion,and calculates how much nature gas leaks through the period of geological history by a case study.