Alkaline Surfactant Polymer enhanced oil recovery process
Doctor of Philosophy
This thesis improves the understanding of the Alkaline Surfactant Polymer (ASP) enhanced oil recovery process in order to optimize the ASP operational strategy. The conventional oil recovery methods leave large amounts of oil in the reservoir. ASP process is considered as a promising method for enhanced oil recovery. This dissertation reveals the ASP characteristics by using phase behavior, interfacial tension, surfactant consumption and numerical simulation techniques. The flooding experiments that I performed show that my ASP strategies successfully recover the oil trapped after waterflooding. The optimal salinity varies when either synthetic surfactant concentration or Water Oil Ratio (WOR) changes in ASP system. In this thesis, these results could be collapsed to a single curve for each synthetic surfactant/crude oil combination in which the optimal salinity depends only on the molar ratio of natural soap to synthetic surfactant, or soap fraction of total soap plus surfactant. The ASP system studied here has a much wider low IFT region (< 0.01 mN/m) than the system without alkali. In much of the Winsor I region where an oil-in-water microemulsion coexists with excess oil, a second surfactant-containing phase was seen to exist in colloidal form. This colloidal dispersion plays an important role in reaching the ultra-low tension. A new protocol, which significantly reduces the time that is required to reach equilibrium, is developed to assure that enough of the dispersed material is initially present to achieve low tensions but not so much as to obscure the oil drop during IFT measurements. Surfactant retention is one of the most significant barriers to the commercial application of ASP. It was found that Na2CO3 but not NaOH or Na2SO4, can substantially reduce adsorption of anionic surfactants on carbonate formations, especially at low salinities. A one-dimensional numerical simulator was developed to model the ASP process. By calculating transport of water, oil, surfactant, soap, salt, alkali and polymer, the simulations show that a gradient in soap-to-surfactant ratio develops with conditions shifting from over-optimum ahead of the displacement front to under-optimum behind the displacement front. This gradient makes the process robust and permits injection at conditions well below optimal salinity of the synthetic surfactant, thereby reducing adsorption and improving compatibility with polymer. More than 95% of waterflood residual oil was recovered in ASP sand pack experiments at ambient temperature with a slug containing a partially hydrolyzed polyacrylamide polymer and only 0.2 wt% of a particular anionic surfactant blend. The simulator predicts recovery curves in agreement with those found in the flooding experiments.