A Guide for Selection of Aging Time and Temperature for Wettability Alteration in Various Rock-Oil Systems

Wettability alteration has been identified to be oneof the importantmechanisms to improve the microscopic recovery in many of the enhancedoil recovery (EOR) methods including polymer flood, surfactant flood,low salinity flood, microbial flood, alkaline flood, etc. Ensuringthe oil-wet nature of the formation before flooding in the laboratoryis necessary to study the efficiency of the EOR process, which targetsmicroscopic recovery through wettability alteration. Nevertheless,altering the wettability depends on several parameters, such as agingtime, aging temperature, core nature, oil properties, etc. Althoughseveral researchers investigated the effect of individual parameterson wettability alteration, the literature is scarce, and the questionof what is the shortest and yet the most reliable aging time for ensuringwettability alteration for the specific rock-oil system at differenttemperatures remains unclear. This paper attempts to seek an answerto this question by compiling the relevant literature to find theeffect of individual parameters such as different aging times, temperatures,oil compositions, and rock lithologies on wettability alteration.Results observed from data analysis showed different windows for agingconditions depending on the core sample lithology, initial wettability,and type of oil used. It was noticed that the higher the asphaltenecontent in the crude oil used, the lower the time and temperaturethat it takes to alter the sample wettability. Aging a sandstone coreunder 80 & DEG;C using crude oil with 11 wt % % asphaltene took 7days to shift the core from strongly water-wet to neutral-wet. Thesame wettability alteration was achieved in 14 days when aging thesandstone sample at 90 & DEG;C using crude oil with 0.85 wt % asphaltenecontent. Generally, it was observed that the aging time decreasedas the temperature increased. Moreover, as the sample has a lowerinitial water wettability condition, the time that it needs to beaged becomes higher. Results indicated that carbonates in generalrequire less aging time to alter their wettability condition to oil-wet,around 1-7 days, compared with sandstones, around 14-21days.