A semi-analytical interpretation model of pulse decay measurement on ultra-tight rocks

This contribution presents a new semi-analytical model for the evaluation of the initial (early time) stage of pulse decay permeability tests, i.e. before reaching quasi-steady state flow conditions and prior to a significant pressure increase in the downstream reservoir. The analytical model considers gas compressibility and slippage effects. In order to validate the proposed method, measurements were performed on a core sample of the Cretaceous Eagle Ford shale, Texas, USA, under different pore and confining pressures. Helium was used as the test fluid to minimize effects from adsorption. Permeability coefficients obtained from this new approach agree well with those from the classical pulse decay evaluation while the duration of tests was reduced from hours to minutes. The present model is a good supplement for the pulse decay method and suitable for measurements of ultra-low-permeability rocks.