Mangala is the largest discovered oil field in the Barmer Basin, India. Initial oil production began in September 2009, and an alkaline-surfactant-polymer (ASP) pilot will start-up early in 2010. Details on the design of the ASP pilot including the laboratory evaluations and simulation studies have been presented earlier. Laboratory evaluations involved screening and optimisation of the ASP slug formulation based on IFT measurements, adsorption measurements, polymer rheological and thermal stability studies, and a series of linear and radial corefloods. Additional experiments were conducted for refinement and optimization of the chemical selection, specifically targeting even lower residual oil saturations than what was attained previously.

These experiments focused on new surfactant types that are more suitable for solubilising the viscous and waxy Mangala oil. The focus was on detailed phase behaviour evaluation rather than physical measurement of IFT, which allowed relatively quick analysis of a number of surfactants in a short time period. Both salinity scans and oil scans were performed because of significant acidic components in the Mangala crude which react very favourably with injected alkali to produce in situ soap. The resulting phase diagram confirmed the presence of a favourable salinity gradient for the ASP flooding. The best chemical formulation was used in long (1ft) Berea and composite Mangala corefloods and showed very high displacement efficiency for relatively low surfactant concentration, which confirmed the robustness of the phase behavior approach for chemical selection. Mechanistic simulations using the UTCHEM simulator assisted in further optimization of the ASP slug formulation. These experiments helped refine the chemical selection for the planned EOR pilot and reduced the technical risks by improving the robustness of the slug design.

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