Compositional Modeling and Calibration of ASP Carbonate Corefloods

Abstract The shortage and high cost of CO2 and/or Hydrocarbon gases, in some areas, makes chemical EOR a practical option for tertiary oil recovery. Alkaline, Surfactant and Polymer, ASP, formulations continue to evolve to withstand challenges in relation to reservoir heterogeneity, complex mineralogy, high temperature and high formation water salinity of carbonate reservoirs. Such advanced ASP formulations have been considered to evaluate the performance of tertiary oil recovery process in a Kuwaiti carbonate reservoir. Successful performance has been seen in the lab through the evaluation of ASP coreflood experiments using composite carbonate cores. This paper presents the results of these coreflooding experiments and the steps followed to build representative ASP flooding simulation models as well as the workflow to calibrate these models to the observed experimental data. Moreover, the paper highlights the challenges associated with ASP coreflooding process and its modeling in the difficult environment of carbonate reservoirs. The paper also presents the techniques followed to overcome some of these challenges. The modeling of two corefloods are presented in this paper, the first is for high-pressure live oil ASP coreflood, and the second is for low-pressure, surrogate oil ASP coreflood. The carbonate composite cores were first flooded with seawater down to residual oil saturation, Sorw. The ASP coreflood started with pre-flushing phase using softened seawater, followed by an ASP slug, and ended by injecting a number of pore volumes of polymer solution for mobility control. The representative ASP flooding simulation models of this paper captured the vital mechanisms involved in the ASP chemical EOR process, such as: Micro-emulsion phase behavior, surfactant solubility ratios and resulting IFT changes Saponification process by the reaction of naphthenic acids of the crude oil with the injected alkali Adsorption of surfactant and polymer on the carbonate rocks as a function of pH and time The geochemistry of aqueous and oleic phase reactions Updating reservoir capillary number, resulting from the changes to IFT and wettability Effect of changes in capillary number is reflected by different sets of interpolation Kr curves The rheological behavior of polymer solutions Optimum salinity and salinity gradient effect. Assisted history matching software was employed in the calibration of the two corefloods following a stepwise procedure by first matching the water flood results, then matching the surfactant production values, and finally matching the remainder of the ASP flood results. This paper discusses the parameters that needed to be tuned in order to attain a match of both waterflood and ASP flood results. The matched results included the oil recovery, flow pressure differential, and the concentration of chemical effluents traced during the experiments. The profile of ASP oil recovery in these carbonate composite cores is more gradual, and is different from those observed in sandstone corefloods.