Chemical propagation in an Enhanced Oil Recovery (EOR) process involves various fluid-rock interactions, such as adsorption, dispersion, inaccessible pore volume (IPV), viscous fingering and chromatographic separation. In this paper, comprehensive effects on the propagation of surfactant and polymer in carbonate porous media were investigated experimentally and analytically in order to study the mechanism and quantify the contribution of each effect.
Single phase flow tests of surfactant, polymer and surfactant-polymer mixture were conducted on reservoir carbonate core plugs at reservoir conditions (high temperature and high salinity). A convection-dispersion model was used to interpret the effluent chemical concentration profiles. The effect of different factors on chemical propagation was taken into account in the model. The dynamic adsorptions of two amphoteric surfactants at 2,000 mg/L concentration were 0.21 and 0.17 mg/g-rock, respectively. The dynamic adsorptions of a sulfonated polymer at 2,000 and 5,000 mg/L were 0.11 and 0.17 mg/g-rock, respectively. Surfactant and polymer were co-injected to evaluate their competitive adsorption, and the surfactant adsorption was reduced by about 50%. The dispersion coefficient of the chemicals in carbonate cores was in the magnitude of 10–3 cm2/s. Both dispersion and adsorption caused chemical concentration reduction during the propagation in porous media. IPV and viscous fingering occurred during polymer injection or the subsequente water injection. IPV affected the calculation of adsorption/desorption process of polymer injection and IPV value cannot be solely determined by the model simulation. Chromatographic separation took place in the surfactant/polymer co-injection scheme, which was predicted by the model as well. The model results were compared with the chemical flood simulator of UTCHEM.