Sources of Permeability of Tight and Unconventional Reservoirs

Permeability in tight shale-gas plays is a key factor in stimulation design and prediction. Permeability is one of the most challenging parameters to be accurately and reliably measured, mainly due to factors such as reservoir heterogeneity, measurement scale, different fluids used for measurement, and reproduction of in-situ fluid saturations, pore pressure and effective stress conditions. The interconnected maturation-induced pore volume of mudrocks provides flow paths for the hydrocarbons. The increased pore pressure created through hydrocarbon generation could also result in maturation-induced microcracks that may provide increased conductivity for flow. This porous system is surrounded by the host-rock matrix, which has negligible permeability (nanodarcy). Permeability measurements performed on crushed samples, fail to uphold this texture for flow paths. The production flow capacity in most unconventional shale wells is frequently two orders of magnitude or higher than the laboratory measurements.