Petrophysical Investigation on Gas Transport Properties of the Barnett Shale

Abstract

Abstract This paper provides a comprehensive study of shale gas porosity, permeability, and excess sorption measurements utilizing the pulse decay method technique to better understand the connectivity and flow mechanism of shale gas rocks. Several experiments were conducted to measure these petrophysical properties using different gasses for possible recovery enhancement techniques. Other experiments were also conducted to measure the effect of depletion of shale gas permeability. The main question that is being invistgiated is how sensitive are shale physical properties to the gas saturating the pore space. Because of the small size of helium molecules, initial speculation suggested that helium effective porosity is greater than the effective methane porosity leading to overestimated shale pore volumes. Experimental results reported here for a Barnett shale sample, however, indicate otherwise. Porosity and permeability measurements were carried out using several gases including He, N2, CH4 and CO2 over a wide range of pore pressures. The storage capacity of helium was in fact lower than that of CH4. This comparison with different gases also shows a decreased permeability as we move to more sorbing gases. Gibb's excess sorption utilizing the volumetric method is also measured and, in fact, confirms the impact of sorption on the permeability and storage capacity measurements. These two key reservoir rock properties representing the storage and flow capacity of rocks remain of primary importance to petroleum engineering. Better understanding of these petrophysical properties of shale gas will be essential for future field development, production forecasts, and reserve estimations.