Measuring gas shale permeability tensor in the lab scale

Abstract

Permeability tensor measurements for three different gas shale samples were done using quasi-steady flow technique in specially designed apparatus in which confining pressure, upstream pore pressure, downstream pore pressure and temperature are independently controlled. The initial pressure difference between upstream and downstream changes only after the pressure pulse passes across the whole sample. Using the quasi-steady flow technique gives the ability to measure axial permeability of three different oriented plugs simultaneous at the same pressure temperature conditions. Measured intrinsic permeability anisotropy ratio in gas shale was 25 % in average. The anisotropy ratio remains almost constant with increasing effective pressure, however permeability magnitudes decrease by almost two orders. This reduction in permeability was described by a cubic k- law and explained by preferential flow through pore like-cracks. The anisotropy ratios response suggested a presence of this type of pores both parallel to and perpendicular to bedding which close upon increasing confining pressure. The pore like-crack throats could be small as the test fluid kinetic molecular diameter (e.g. 0.381 nm for natural gas “Methane”).