Alkaline Surfactant Polymer ASP Process for Shaley Formation with Pyrite

Abstract

AbstractThe ASP process may still be promising for surfactant flooding of shaley formations that have high surfactant adsorption with conventional surfactant-polymer flooding. Positive sites on clays are sites where anionic surfactant adsorption occurs in conventional surfactant flooding. High pH of alkali converts positive clay sites to negative sites. In addition, sodium carbonate sequesters calcium ions due to the small solubility product of calcium carbonate. If the formation has pyrite or siderite present, the core material in the laboratory environment will likely have a coating of ferric oxide that contributes to the anionic surfactant adsorption sites. Thus the test core should be restored to reducing conditions to better represent in situ conditions.The ASP process has two sources of surface active materials. One is injected synthetic surfactant and the other is soap generated in-situ by reaction of alkali with naphthenic acids in crude oil. However, this adds to the complexity of the process because the optimal salinity becomes a function of both the concentration of injected surfactant and in-situ generated soap. Water soluble active soap number (WSASN) is used instead of total acid number (TAN) to estimate the optimal salinity. When WSASN rather than TAN is used to estimate the soap content, the logarithm of the optimal salinity is a linear function of the soap fraction. In this presentation, we demonstrate the technology to estimate the optimal salinity of soap/surfactant mixtures and use it to develop formulations with great potential to recover oil for a weakly consolidated sandstone reservoir.The potential of incremental oil recovery by the ASP formulation is evaluated by ASP flooding tests on both quartz sand packs and formation material. The ASP formulation recovered more than 95% of the water flooded residual oil using a 0.5 PV slug of either 0.3% or 0.5% NI blend surfactant. The sodium carbonate concentration was 1.0% and the polymer concentration was 0.3%. Moreover, it is found from simulation results that the development of soap/surfactant gradient in ASP flooding ensures the process passing through the optimal condition, where minimum IFT and low residual oil saturation will be attained.