A Three-Phase Study on Pre-Flush Stage in SandstoneAcidizing:Experimental and Modeling Analysis of Evolved CO2 in an Oil andAqueous Environment

摘要

This paper presents a detailed study on the effects of evolved CO2 due to carbonate mineral dissolution,and its ensuing activity,during the preflush phase in matrix acidizing of sandstone reservoirs.Sandstoneacidizing in the presence of different rock saturations conditions is seldom investigated.The presence ofoil during preflush may change the perception of acid with carbonate minerals.The cores were acidized viacoreflood experiments and validated through simulation studies using three-phase numerical model.Theacid was injected into 100% brine saturated rock with 15 wt% hydrochloric acid(HCl)at a temperatureof 150 F and at a back-pressure of 1200 psi.This was done to calibrate and initially test the numericalmodel.The numerical model was able to match the performed coreflood experiments at different saturationconditions to a good level of accuracy.The HCl-calcite and HCl-dolomite chemical reaction parameterswere fixed in all cases to ensure consistency in analyses.Oil production was observed,with an average of25% recovery of the residual oil in place at pore pressures of 1,200 psi.The swelling of oil by the solubleCO2 was inferred as the main mechanism for additional oil production during the 15 wt% HCl injection.Adirect symmetry was observed between the oil recovery and average CO2 moles in the oil phase based on thenumerical model prediction of the conducted experiments.The recovery curve flattened once surroundingoil reached its full-saturation level with CO2.The successful capability of the numerical model to effectivelymimic the preflush stage sets a new bar in the area of sandstone acidizing.The potential of CO2,a by-productof acidizing,towards its contribution in swelling the surrounding oil,and thus mobilizing the trapped oilhas been depicted in this study.