Effectiveness of surfactants composition injection in low-permeable layers under high-temperature conditions

Nowadays, there is a gradual decline in oil production from conventional reservoirs, and it leads to introduction of unconventional hydrocarbon sources into the development. Shale oil production is one of the focus areas of potential unconventional hydrocarbon reserves development. Besides ultralow permeability, low porosity, and high reservoir temperature, its production is complicated due to the lack of geological information, complex reservoir structure and physical processes occurring during multiphase fluid flow. Injection of surfactants is proposed as one of the methods for enhanced shale oil recovery. The aim of the present work was to estimate the oil displacement capacity of high-temperature surfactants injected in shale formation. A number of anionic and nonionic surfactants and their blends in different proportions were evaluated to select an effective composition. Solutions were prepared based on reservoir water and studied for aqueous stability, thermostability, interfacial tension at the boundary with oil and wettability alteration ability. Then one most effective composition was selected, and a core flooding test was conducted to evaluate the oil displacement capacity. The core flooding test with a formation brine under thermobaric conditions revealed the 7.96% of oil displaced. During the core flooding experiment with the chosen surfactant solution the amount of additional oil displaced was 32.56%, and general oil displacement efficiency was 40.52%. In a repeated experiment the oil displaced by brine was 45.94%, and additional amount of oil displaced by surfactant composition was 1.71%. General oil displacement efficiency reached 47.65%. Difference in experimental results shows difficulty of performing experiments on efficiency of surfactant injection in the low-permeable shale formations.