Chemical-Enhanced-Oil-Recovery (CEOR) processes have been used for increasing oil recoveries from oil reservoirs following the primary recovery phase. At harsh reservoir conditions (high salinity and high temperature), many CEOR methods fail to achieve their objectives. This raises the challenge to design optimum recipes that tolerate these harsh conditions and hence attain maximum hydrocarbon recovery at the minimum possible cost.

This paper evaluates the effectiveness of a Thermo-Viscosifying Polymer (TVP) and an Acrylamido Tertiary Butyl Sulfonate (ATBS)/acrylamide (AM) copolymer in mobilizing residual oil from carbonate. The surfactants are carboxybetaine based amphoteric surfactants SS-880 and SS-885. These candidates were selected based on an intensive evaluation process carried out in previous works at KFUPM, which includes fluid rheology, long-term thermal stability, interfacial tension (IFT), adsorption and microfluidic studies. Furthermore, contact angles were measured at high pressure and high temperature using a captive drop analyzer. Slug size and injection sequence optimization were also investigated through core-flooding experiments. Different injection scenarios including SW-SP-SW, SW-P-S-SW, SW-S-SW-P-SW and SW-P-SW-S-SW were also investigated to identify the best injection scenario. The coreflooding experiments were conducted at 90°C. The seawater (SW) used in this study is Arabian Gulf seawater having salinity of 57,000 ppm.

The results showed that surfactant-polymer combination and SW-SP-SW injection scenario were the best in terms of oil recovery. The optimum chemical combination was found to be carboxybetaine (0.05% wt.) and ATBS/AM (0.25% wt.). It was also observed that the recoveries were increasing proportionally to the slug-size. This indicates that the chemical injection sequence and slug-size have a significant impact on ultimate oil recovery. This is believed to be due to the advantageous synergies between the chemicals. The core-flooding experiments confirmed the importance of optimizing the design of CEOR processes taking into consideration the type of chemicals, concentrations, slug sizes, and flooding sequence of the different combination of seawater (SW), surfactant (5) and polymer (P).

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