Surfactant related chemical flooding has great potential for improving oil recovery in carbonate reservoirs, as surfactants are able to effectively lower the oil/water interfacial tension (IFT) and alter wettability toward water-wet. The loss of surfactant during the propagation process in the reservoir is one of the major concerns in determining the feasibility of a chemical flooding project. Many efforts have been made to reduce the surfactant adsorption in various scenarios to make the project economically successful. The addition of polymer in the chemical formulation is commonly used in the applications, which can not only be used to control the water/oil mobility ratio but also affect the surfactant adsorption in different ways.This paper presents the results of a laboratory study on the effect of polymer on reducing the surfactant adsorption onto carbonate reservoir cores. An amphoteric surfactant and a sulfonated polyacrylamide were used in three series of dynamic adsorption tests conducted at reservoir conditions, including surfactant only, polymer followed by surfactant, and mixture of surfactant and polymer (SP). The experimental results showed that when surfactant alone was injected, the surfactant adsorption on the carbonate reservoir cores ranged from 0.125 to 0.203 mg/g-rock, with an average value of 0.163 mg/g-rock. When the surfactant was injected following the injection of a pre polymer slug, the surfactant adsorption reduced to 0.0739 to 0.0848 mg/g-rock, with an average reduction of 51.3%. If SP mixture was injected, the surfactant adsorption ranged from 0.0794 to 0.0872 mg/g-rock, with an average reduction of 48.9%. It indicates that the adsorptions of surfactant and polymer take place competitively on the sites of the rock surfaces. This laboratory study helps understand the synergetic effect of surfactant and polymer in SP formulations and design the injection schemes of chemical flooding processes.

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The loss of surfactant from aqueous solutions during the propagation in the reservoirs, especially carbonate reservoirs, is one of the major concerns with chemical oil recovery processes. This is due to the loss of effectiveness of the chemical solution to reduce the oil-water interfacial tension and thus renders the process economically unfeasible. This paper presents, in detail, 10 runs of core flooding tests on dynamic adsorption and desorption of an amphoteric surfactant (OCT-1) onto permeable carbonate rocks, which were conducted in natural carbonate core plugs at reservoir temperature of 100°C and pore pressure of 3100 psi. The surfactant solution was continuously injected into the core plug until the effluent surfactant concentration approached that of the injected surfactant solution, followed by seawater injection until no surfactant was present in the effluent. The effluent surfactant concentrations were analyzed by means of titration technique. Amount of dynimc adsorption and desorption of surfactant solutions was calculated using a new definite integral method. The results showed that the adsorption of the surfactant decreases with increase in the value of the pore geometry parameter, (K/Ф) 0.5 . The adsorption ranges from 0.223 mg/g-rock to 0.597 mg/g-rock for the rocks with permeabilities from 688 md to 110 md. For surfactant concentration of 0.2 wt% OCT-1 in seawater that was used in the study, this level of adsorption implies the surfactant is applicable from adsorption point of view. It was also observed that the adsorption varied with the initial surfactant concentration, as well as relationship between dynamic adsorption and despersion. The value of dispersion, mechanical mixing coefficients and matching adsorption were obtained using dispersion/adsorption equations to match experimental data. This paper presents insights into the adsorption and desorption of the amphoteric type of surfactant on carbonate rocks which could help the application design for a chemical flooding process.

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As part of the screening process for chemical EOR, several polymers have been screened as co-injectants in a surfactant-aided water flood scheme. Due to their higher viscosity, polymers improve sweep efficiency and reduce the permeability of rock matrix, therefore help to improve oil recovery. Aimed at a representative carbonate reservoir in the Middle East, a polymer screening study has been conducted with respect to polymer solubility and viscosity retention in high salinity brines, equivalent to our reservoir parameters. The polymers have to pass through a stringent screening process to meet the harsh conditions encountered in the reservoir: high temperature, high salinities and carbonate nature. Salinity effect was studied in a range of brines that included shallow formation water, produced water, and connate water. Among the polymers studied, six were found compatible and have been short-listed. Based on rheological measurements and flow curves, the concentrations of polymers have been determined to achieve the target viscosity under reservoir conditions. Long-term stability and adsorption tests were conducted to ensure the efficiency of the polymer exposed to reservoir conditions. Oil displacement tests with a selected polymer showed an increased oil recovery factor of 11% by polymer flooding and 18% by surfactant-polymer flooding. This study demonstrates the potential application of polymers under extremely harsh reservoir conditions and their promise to be good additives for chemical flooding.