Surfactant-Polymer Formulations for EOR in High Temperature High Salinity Carbonate Reservoirs

Abstract

Harsh conditions, such as high temperature (>100 oC) and high salinity (>50,000 ppm TDS), can make the application of chemical enhanced oil recovery (EOR) challenging by causing many surfactants and polymers to degrade. Carbonate reservoirs also tend to have higher concentrations of divalent cations as well as positive surface charges that contribute to chemical degradation and surfactant adsorption. The objective of this work is to develop a surfactant-polymer (SP) formulation that can be injected with available hard brine, achieve ultra-low IFT in these harsh conditions, and yield low surfactant retention. Phase behavior experiments were performed to identify effective SP formulations. A combination of anionic and zwitterionic surfactants, cosolvents, brine, and oil was implemented in these tests. High molecular weight polymer was used in conjunction with the surfactant to provide a high viscosity and stable displacement during the chemical flood. Effective surfactant formulations were determined and five chemical floods were performed to test the oil recovery potential. The first two floods were performed using sandpacks from ground Indiana limestone while the other three floods used Indiana limestone cores. The sandpack experiments showed high oil recovery proving the effectiveness of the formulations, but the oil recovery was lower in the cores due to complex pore structure. The surfactant retention was high in the sandpacks, but it was lower in Indiana Limestone cores (0.29-0.39 mg/gm of rock). About 0.4 PV of surfactant slug was enough to achieve the oil recovery. A preflush of sodium polyacrylate improved the oil recovery.

Wettability-Based Retention of Encapsulated Petroleum Sulfonate in Carbonate Rocks at High-Temperature and High-Salinity Conditions

“…Sulfate surfactants have been widely used in reservoirs but experience severe hydrolysis problems at elevated temperatures (>60 °C) . Great efforts had been made in the past to identify and develop high-performance surfactants for EOR purposes in harsh conditions. − At high temperatures, sulfonates and carboxylate surfactants are recommended, and their properties can be readily adapted to specific oil reservoirs to achieve ultralow IFT through tuning the number of ethylene oxide (EO) and propylene oxide (PO) groups and modifying the type, carbon-chain lengths, and branching degree of the hydrophobes in the surfactant. ,− The final formulation typically consists of supplemental cosurfactants (e.g., alpha-olefin sulfonate and internal olefin sulfonates , ) and cosolvents (simple alcohols and their lower-numbered ethoxymers) to enhance its performance. However, the design of specific chemicals with customized functional groups can be expensive, and large quantities (tonnes) are usually needed to achieve the target properties, which further reduces the revenue of incrementally produced oil.…”