Impact of Chemical Osmosis on Brine Imbibition and Hydrocarbon Recoveryin Liquid-Rich Shale Reservoirs

摘要

We present an assessment of the impact of low-salinity brine osmosis on oil recovery in liquid-rich shalereservoirs.The paper includes:(1)membrane behavior of shales when contacted by low-salinity brine,(2)numerical model of osmosis mass transport for low-salinity brine,and(3)enhanced oil recovery(EOR)potential of low-salinity osmosis in liquid-rich shale reservoirs.Capillary osmosis causes low-salinity brine to be imbibed into the shale matrix;thus,forcing expulsionof oil from the rock matrix.This oil recovery process is described by a multi-component mass transportmathematical model consisting of advective and molecular transport of water molecules and dissolved ions.In the transport model,the activity-corrected diffusion of the brine solution is used to calculate the volumeof brine imbibed into a shale core sample and the resulting expelled oil.We used the mathematical modelto match oil recovery from two carefully designed brine-imbibition experiments conducted at ColoradoSchool of Mines.We have concluded that,in oil-wet shale reservoirs,low-salinity brine invasion of the rock matrix is byosmosis rather than capillary force.Thus,osmosis is the only imbibing force that drives the low salinitybrine into the reservoir rock matrix.Furthermore,we believe brine osmosis can potentially enhance oilrecovery by expelling oil out of the rock matrix and into the micro-and macro-fractures existing in thestimulated reservoir volume.