Gas Transport Processes In Shale

This chapter presents three common unsteady-state methods for the permeability measurement of ultra-low-permeability shale rocks: the pulse-decay method, the crushed sample test, and the canister desorption test. The pulse-decay method presents more details on the general form of the underlying equations, the fundamental definitions of the physical parameters. The crushed sample test is performed on a pack of small rock particles to determine the porosity, adsorption isotherms, and permeability. The canister desorption test is performed on the drill cores to estimate the rock permeability and diffusion. The cumulative desorbed gas volumes are recorded and used to determine the permeability and diffusivity. The chapter describes two general workflows for the determination of pressure-dependent permeability models: an analytical and a numerical method. It concludes with a discussion on the measurement of gas molecular diffusion into kerogen.