Improving the Estimations of Shale Permeability with Process-based Pore Network Modeling Approach

Abstract

In shale, kerogen and clay make the pore network intricate. For example, in kerogen subspherical pores are connected by cylindrical throats while in clay both pores and throats are triangular or sheetlike. To our knowledge, few studies considered the influence of kerogen and clay in reconstructing pore networks. This study uses a process-based modeling approach to reconstruct pore networks of shale. Our process-based approach considers the influence of kerogen and clay on pore morphology and distribution. The estimations of shale permeability based on generated pore networks are improved.

First of all, analysis of FE-SEM images gives grain size distributions of shale. With the grain size distributions and the process-based method (Øren and Bakke, 1997), this study develops a network A that connects interparticle pores, organic matter (OM) particles and clay agglomerates. With random sphere packing algorithm, this study extracts a network B which connects nanopores in OM particles and a network C which connects pores in clay agglomerates. The pore morphology is set to be different in networks B and C. Then networks B and C are inserted into the selected OM particles and clay agglomerates in network A for the final network D. The pore network D connects interparticle pores, subspherical nanopores and triangular/sheetlike pores in clay. Finally this study applies no-slip permeability equations in the network D and predicts no-slip permeability of shale. The permeability equations are modified according to pore morphology.

This study analyzed FE-SEM images of shales from Sichuan Basin in China and Appalachian basin and then built pore networks. The pore size distributions (PSD) of our pore networks matched well with the PSD defined by the mercury intrusion data. And the resulted permeability estimations are in good agreement with the reported lab measurements. Based on our pore networks, this study further investigated the effect of shale diagenesis on shale permeability.

It comes to our knowledge that no process-based approach and networks are exclusively developed for shale. Our process-based modeling considers the influence of kerogen and clay distribution on ultimate pore structure in shale.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016