New method of predicting optimum surfactant structure for EOR
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Chemical enhanced oil recovery (CEOR) has gained a rapid momentum in the recent past due to depleting reserves of “easy-oil” and soaring oil prices. Hence, CEOR is now being considered for several candidates with varied oils and reservoir conditions, which demands the need for large hydrophobe surfactants. A new class of thermally and chemically stable large hydrophobe surfactant, Guerbet alkoxy carboxylates (GAC) has been tested. Unlike Guerbet alkoxy sulfates, GAC are stable at all pH and can be extremely useful in cases where alkali usage is prohibitive. They also exhibit synergistic behavior with internal olefin sulfonates (IOS) and alkyl benzene sulfonates (ABS), with the mixture showing enhanced calcium tolerance than the individual surfactants. Furthermore, in an attempt to diversify the raw material base, a new class of hydrophobe, viz. tristyrylphenol (TSP) based on petrochemical feed stock has also been developed and evaluated. Given the fact that there are hundreds of surfactants that can be tested for a particular candidate, the difficulty often lies in choosing the right surfactant to begin with. In an attempt to simplify that, a new correlation to predict the optimum surfactant structure has been developed. It relates the optimum surfactant structure to the formulation variables like oil properties, salinity, and temperature, including the parameters like PO and EO for new-generation surfactants. The correlation can serve as a guideline in choosing the optimum surfactant and will help in improving our understanding of the relationship among variables affecting the optimum surfactant structure. Surfactant retention is an important factor affecting the economics of chemical flooding and has to be studied carefully. Using an extensive data obtained from core flood studies a new correlation for predicting surfactant retention including the variables like pH, TAN, salinity, mobility ratio, temperature, co-solvent, and surfactant molecular weight has been developed. All these are new and highly significant advance in the optimization of chemical EOR processes that will greatly reduce the time and cost of the effort required to develop a good formulation as well as to improve its performance.