Primary cold production for the extra-heavy oils (4-10°API) of La Faja Petrolifera del Orinoco (FPO), Venezuela, is currently a low percentage (<5%) of the Original Oil in Place (OOIP). Chemical EOR studies are being accomplished in order to increase oil recovery in those thin-bedded reservoirs which host up to 35% of the OOIP, where thermal EOR methods are not convenient in terms of heat losses and environmental issues. Specifically, Surfactant-Polymer (SP) flooding is now considered as a feasible approach to achieve both mobility control and mobilization of residual oil in the FPO's target zones for chemical EOR.

The objectives of this experimental study were to identify the mechanisms in play when surfactant and polymer solutions are injected in cores to displace extra-heavy oil and to assess for the potential of SP flooding for one of the FPO's reservoir. The tests reported were performed with a dead crude oil of 9°API and 4500 cP, an injection water salinity of 6.4 g/L with low hardness and at a temperature of 50°C. The SP formulation consisted of a standard HPAM at rather high concentration to achieve high viscosity and an alkaline-free surfactant formulation providing both low interfacial tension (IFT) and good compatibility with polymer even at high polymer concentration.

A set of surfactant and polymer injection tests has been performed on Bentheimer outcrop cores. These tests allowed demonstrate that injection of the SP formulation after a secondary polymer flood was able to achieve a significant reduction of the residual oil (ΔSo = 80% ROIP). Results of secondary injections of either water, surfactant solution or SP formulation have also shown that mobility control is of tremendous importance to achieve high recovery, even at the core-scale. Oil production data have been confirmed by determination of the CT-scan saturation profiles carried out at each step of the experiments. The results of this study stand as first insights demonstrating at core scale the potential of SP formulation to increase recovery of Venezuelan extra-heavy oils.

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