Phase behavior and microemulsion studies on a Saudi Arabian crude.

Abstract

The knowledge of phase behavior of the slug as it proceeds through different stages is an important factor to maintain an efficient displacement of oil in micellar flooding systems. Coreflood experiments have shown that a considerable amount of oil is left behind when a slug breaks down into several phases. The amount of oil left by the slug may be drastically reduced if the interfacial tensions (IFT's) between the phases are kept as low as possible. In this regard, the phase behavior of the multiphase slug has been studied under relevant reservoir conditions of 20% salinity and 90 degree C of temperature for properties including interfacial tension and partition coefficients. Based on the above data optimal salinities were determined and pseudoternary diagrams constructed. A new finding of crucial importance to high-salinity and high temperature Saudi Arabian Limestone reservoirs is presented. The existence of a secondary optimal salinity which occurs at salinities higher than the primary optimal salinity (previously known as optimal salinity) has been revealed by this study. The presence of a secondary optimal salinity has been tested for ethoxylated sulfonates of varying ethoxylation number with an alkane and a crude oil. For example, for E0=8 while the primary optimal salinity at 90 degree C takes place at 8% salinity, the secondary optimal salinity occurs at 14% salinity. Increasing the E0 number shifts the primary and secondary optimal salinities to higher salinity levels further confirming the reality of this finding. Moreover, the data show that the secondary optimal salinity yields even lower interfacial tensions. Ternary representations with the ethoxylated sulfonate B1083, E0=15 revealed that 20% salinity which corresponds to the secondary optimal salinity, produced a symmetric three phase "triangle". This implies that the salinity level of 20% gives good IFT lowering and efficient displacemnt. More importantly, for the target conditions of salinity and temperature, the solutions remain in the three phase region the lowest IFT region with widely varying water to oil ratios. This feature can facilitate the prediction of the phase behavior under actual field conditions.