Enhanced oil recovery methods are appealing to increase oil recovery from reservoirs due to market pressures in times of lower oil price. Chemical enhanced oil recovery (cEOR) methods such as ASP involve the use of alkali, surfactant, and polymer, to create an ultralow interfacial tension (IFT) between microemulsion and oil phases. These chemicals have the potential to interact with asphaltenes in crude oil and may cause either a decrease or an increase in asphaltene deposition. This paper presents an investigation into the effects of ASP chemicals on asphaltene precipitation.
Crude oil, from a cEOR-nominated Kuwaiti reservoir, was analyzed with an ASP formulation that was determined through microemulsion phase behavior experiments. Crude oil, chemical components, and incompatible solvent were added together, and light transmission was measured over a 15-minute period to determine asphaltene precipitation over time.
A blank graph of the crude in incompatible solvent showed a light transmission increase of 36.2% over the test duration indicating asphaltene precipitation. If asphaltenes remain suspended in oil, light transmission remains low and stable from the beginning to the end of the test. Addition of asphaltene inhibitor (AI) to the crude oil prevented asphaltene flocculation which was evidenced by a maximum light transmission of 3.0%, an efficiency of 91.7% dispersability relative to the blank sample. With addition of the ASP formulation, light transmission increased which indicates interaction between (1) chemical species of the ASP formulation with asphaltenes or (2) the alkali in the chemical package altering the pH and causing more asphaltene precipitation from suspension in the crude. Maximum light transmission of oil dosed with the chemical additives is 41.3% which is a decrease in asphaltene inhibition efficiency of 14.1% relative to the blank. With the addition of AI to the crude containing the chemical additives, the maximum light transmission is 6.5% indicating an efficiency of 82% asphaltene dispersability. Results indicate a clear relationship between addition of ASP chemicals and asphaltene precipitation. Conditions will differ for other crude oils and cEOR formulations, but asphaltene scaling issues should be considered for cEOR projects.