When there is sufficient time for crude oil to interact with the rock (i.e., when the core is aged with crude oil), a fraction of the charged sites are neutralized by the charged components stemming from crude oil. At later stages, the components of the aqueous and oleic phases compete for the charged sites on the external surface or edges of the clays. Initially, the charged sites of the internal surface of the clays establish a new equilibrium by exchanging cations with the aqueous phase. The cation-exchange process occurs in two stages during two phase flow in porous media. We observe that in the presence of crude oil, ion exchange is a kinetically controlled process and its rate depends on residence time of the oil in the pore, the temperature, and kinetic rate of adsorption of the polar groups on the rock surface. The cation-exchange capacity (CEC) of the rocks was calculated using PHREEQC software (coupled to a multipurpose transport simulator) with the ionic composition of the effluent histories as input parameters. We perform experiments in which brine with a different composition than that of the in situ brine is injected into cores with and without remaining oil saturation. This study investigates the effect of oil type and composition on cation exchange on rock surfaces, relevant for a variety of oil-recovery processes. Cation exchange is an interfacial process during which cations on a clay surface are replaced by other cations.
0 Comments
Leave a Reply. |