Energi Simulation IAP on Carbon Utilization and Storage, Ryosuke Okuno
Overview
Wettability alteration has been studied as a potential way to enhance oil recovery from tight formations. One of the commonly used wettability modifiers is surfactant, which is expected to make rock surfaces less oil-wet and lower the oil/water interfacial tension (IFT). Shortcomings of using surfactants include i) it unlikely affects fluid flow in tight matrices where the molecular size is greater than pore sizes even as a surfactant monomer, ii) the lowered oil/water IFT tends to reduce the water imbibition, iii) many surfactants are unstable at high-temperature high-salinity conditions (e.g., carbonate reservoirs in the Middle East), and iv) the total cost for an effective surfactant formulation can be high. This project aims to develop ketone EOR technologies for enhanced oil recovery from conventional and unconventional reservoirs. The central hypothesis in this project is that aqueous ketone solution can alter the wettability of rock surfaces to more water-wet by rapidly penetrating matrices through oil and water phases in small pores without affecting the oil/water IFT. We found that 3-pentanone or diethyl ketone is the most effective ketone for EOR in shales and carbonates, as also confirmed by other academic and industrial research groups. The molecular size of 3-pentanone was reported to be 0.4-0.79 nm and stable under high-salinity and high-temperature conditions. The cost is approximately $2/lb. The solubility of 3-pentanone in brine is usually below 3 wt% and decreases with increasing salinity. Primary collaborators on this topic include OXY for shale reservoirs, and INPEX and Cosmo Energy for carbonates.
Figure 1. Coreflood of dead oil with injection brine (IB) followed by 3-pentanone solution (3pIB) using a preserved shale core at 183°F. IB’s salinity was 5155 ppm with a sulfate concentration of 1966 ppm. The 3-pentanone solubility in IB was 2.6 wt%. Repeated corefloods with different levels of oil wetness showed that the incremental oil recovery by 3pIB was more significant for a more oil-wet core.
Figure 2. Huff-n-puff experiments of dead oil with shale cores by using two concentrations (2.6 wt% and 1.3 wt%) of 3-pentanone in injection brine at 2500 psia and 183°F. The 2.6 wt% case resulted in a more rapid response of oil recovery and a greater oil recovery factor. However, the 1.3 wt% case achieved a similar rate of oil recovery as observed by the systematically delayed response of oil recovery in comparison to the 2.6 wt% case.