A Numerical Study of Microscale Flow Behavior in Tight Gas and Shale Gas Reservoir Systems

Abstract Tight gas and shale gas represent a significant energy resource. These types of reservoirs are geologically complex and the reservoir flow processes involved are unusual. While some investigators have modeled various aspects of these systems, there is currently no consensus on the significance of microscale diffusion on flow behavior over time. Pore throat diameters on the order of nanometers are known to result in non-Darcy flow conditions, which can be accounted for using the dusty-gas model coupled with various models for diffusivity estimation. This phenomenon is related to the Klinkenberg effect. In this work we implement the dusty-gas model into a reservoir modeling tool based on the TOUGH+ code. We examine the effects of Knudsen diffusion on flowing gas composition at low permeability. We show that for rock with small pore throat diameters, the composition of flowing gas is significantly different than the in situ stagnant conditions. We describe how gas composition measurement could be used to identify flow boundaries in these reservoir systems. We present a fit-for-purpose numerical model based on the TOUGH+ code for modeling microscale transport effects. This work contributes: A new multicomponent microscale transport model A new, fit-for-purpose numerical model based on the TOUGH+ code capable of characterizing reservoir flow effects including permeability adjustment and diffusion in micro- and nano-scale porous media.