Advancing Surfactant-Based Chemical EOR in High-Salinity, High-Temperature Carbonate Reservoirs of Sultanate of Oman

Carbonate reservoirs, which account for over 60% of global oil reserves, are predominantly oil-wet which limits their oil recovery factors from using conventional primary and secondary methods. In Oman, these reservoirs are further challenged by high reservoir temperatures up to 85°C, brine salinities up to 180,000 ppm, and geological heterogeneity. This study aims to identify and validate wettability-altering surfactants to enhance oil recovery in two such carbonate reservoirs (Natih and Lower Shuaiba) under high-salinity, high-temperature (HSHT) conditions. A two-phase screening methodology was employed. First, a broad analytical pre-screening combined SPE-established criteria with machine learning techniques applied to public-domain performance data to shortlist ten potential surfactants suitable for HSHT environments. These candidates were subjected to detailed experimental evaluation, including compatibility and stability testing, phase behavior analysis under reservoir conditions, and contact angle testing to assess wettability alteration. Reservoir-specific criteria were used to further narrow the list for core flood testing. From the ten initial candidates, four surfactants were identified as promising—two for each reservoir. These surfactants exhibited strong thermal and salinity stability, favorable phase behavior, and showed wettability alteration in contact angle test. Core flood experiments under reservoir conditions were conducted to quantify incremental oil recovery and confirm the effectiveness of the selected surfactants. Good incremental recovery gains were observed compared to baseline waterflooding, validating the surfactants' performance, and supporting their potential for field deployment. The dual-track evaluation—common and reservoir-specific—ensured optimal alignment with the unique properties of each reservoir. This work demonstrates a replicable, cost-effective framework for CEOR surfactant selection in HSHT carbonate reservoirs. The integration of data-driven pre-screening with robust lab testing enables rapid identification of effective, wettability-alteration surfactants tailored to specific geological and operational conditions. The approach not only enhances oil recovery but also considers environmental and economic sustainability. The methodology provides a valuable reference for similar EOR applications across the Middle East and other carbonate-reservoir dominated oil regions globally.