基于双重逾渗模型的裂隙多孔介质连通性研究

STUDY OF CONNECTIVITY OF FRACTURED POROUS MEDIA BASED ON DUAL-PERCOLATION MODEL

孔隙和裂隙是裂隙多孔介质的2种渗流通道。在低渗和特低渗情况下,孔隙和裂隙能否构成贯穿的通道,决定介质能否发生渗流。针对低渗和特低渗裂隙多孔介质的连通性,结合孔隙逾渗理论和裂隙逾渗理论,提出一种双重逾渗模型。基于该模型,提出能够反映和比较裂隙多孔介质连通性的2个量化参数A0和D,并重点讨论这2个量化参数物理意义。根据A0和D这2个参数分析裂隙多孔介质的连通性特征。分析结果表明,以D=2为临界值,可以将裂隙多孔介质分为3种类型:"弥散型"、"临界型"、"指向型"。当D>2时,介质具有自封闭趋势,属于"指向型";随着孔隙连通和裂隙方向随机性的增强,这种自封闭趋势会被破坏,使介质趋向于"弥散型",即利于连通。少量长裂隙的存在对介质的连通性起决定作用。

Pores and fractures are two main flow channels in fractured porous media.Under low and ultra-low permeability conditions,whether seepage occurs in media or not is decided by whether pores and fractures can form a penetrated channel or not.A dual-percolation model coupled the pore percolation theory and the fracture percolation theory is presented to study the conductivity of the low and ultra-low fractured porous media.Based on the presented dual-percolation model,two parameters and D are presented to reflect and compare the conductivities of fractured porous media;and the physical meaning of these two parameters is quantitatively discussed.The connectivity of low and ultra-low permeability fractured porous media is investigated based on these two parameters.It is shown that the low and ultra-low permeability fractured porous media can be generally divided into three types by taking as the critical value,i.e.dispersion type,critical type,and directional type.Media are self-sealing when and they can be named as directional type.However,with the enhancements of randomnesses of porous connectivity and fracture directions,the self-sealing tendency will be destroyed and the conductivity will increase,which causes the media tending to become dissipation type.A few long fractures can play a great role on the connectivity of media.