摘要
Gas flow in shales follows a number of physical mechanisms that include Knudsen diffusion,Darcy flow,and adsorption in the matrix and micro pores.The aim of the study is to resolve the interplay of gas transport in these media at increased effective stress as well as net pore pressure.In this research,we investigated the nature of gas transport in the matrix of shale by sending He,CH_(4)and CO_(2)gases through a transient upstream pressure pulse decay instrument.A series of experiments were conducted at constant pore pressures and a gradually increasing confining pressure.The same study was done in three different scenarios,injecting He,CO_(2)and CH_(4).At a constant pore pressure,gas permeability appears to decrease with an increasing confining pressure and effective stress.With increasing effective stress,the slip factor also decreases along with the permeability.The decrease in slip could be attributed to prestressing,that is likely to create new fractures.Among the three purged gases,permeability of shale to CH_(4)is the highest,and that to CO_(2)is the lowest owing to its high adsorption.Higher permeability of CH_(4)against He,could be attributed to the dual transport mechanism.
