Determining Relative Permeability and Capillary Pressure from Steady-State-Transient Test Under Formation Damage

Abstract

Previous works develop the method to simultaneously determine relative permeability (Kr) and capillary pressure (Pc) from corefloods – so-called steady-state-transition test (SSTT), which was designed for constant water composition. The SSTT procedure comprises simultaneous injection of water and oil with piecewise-constant increasing injected water fraction until stabilization, measuring pressure drop and effluent water cut during transition periods between the steady-states. In this work, we developed SSTT for high-salinity (HS) and low-salinity (LS) water – HS SSTT is performed in secondary imbibition mode, then the core is fully re-saturated, which follows by LS SSTT in tertiary imbibition mode. To validate SSTT, we performed continuous waterflood by HS and LS after secondary and tertiaty imbibition SSTTs, respectively. The type curves for pressure drop and average saturation are determined by numerical simulation; the raw measured data are approximated by the type curves, yielding regularization of the originally ill-posed inverse problem. The well-posed inverse algorithm produced Kr and Pc curves for HS and LS floods in Berea sandstone. Significant decrease in Kr for water and some decrease in residual oil after LS water injection is explained by mobilization of kaolinite fines by LS water, followed by fines migration and their consequent straining in thin pores: straining of fines causes the permeability decline in the carrier water and sweep improvement at the micro-scale.