Permeability from time dependent methane saturation monitoring in shales

Abstract

In this paper, we demonstrate the possibility to monitor the methane gas saturation of a shale sample down to fraction of percent porosity using a standard low field NMR core analyser instrument with a proton Larmor frequency of 2.2 MHz. The spontaneous shale gas production at ambient condition, following a saturation at 2000 psi (138 Bar), is monitored in near real time with T2 distributions acquired every few minutes for several days. The obtained dataset shows that gas produces with multiple characteristic rates even for single T2 populations. A model to convert remaining gas signal decays into permeability values is proposed, allowing to determine multiple permeabilities for each T2 and whole samples. The permeabilities calculated on full signal are in reasonably good agreement with pressure decay measurements on the same cores.