This work is a part of a fundamental study investigating the efficiency of the alkaline- surfactant-polymer (ASP) flooding process. While heterogeneity in pore structure is a key concern of our research, it is necessary first to have a clear understanding of the baseline behavior when porosity, permeability and throat size are tightly controlled. This control was achieved by manufacturing a homogenous carbonate-cemented sandstone using the calcite in-situ precipitation system (CIPS). We present the multiphase flow properties of the artificial CIPS rocks, including previously unpublished results on oil/water capillary behavior and relative permeability.
In the core flooding experiments described here we used zero clay content and kept the same throat size and pore size distribution and kept the same chemical composition of the ASP slug. The polymer that was used in the flooding was polyacrylamide (1560 ppm) and the surfactant was alpha olefin sulfonate (1% w/w) and the alkaline was NaOH (0.5% w/w). Along with ASP floods, two surfactant floods were run with concentrations of 1% and 0.1% (w/w). Two identical specially fabricated CIPS carbonate cemented cores were used. The silica grains of both cores are primarily silica cemented by calcite. Both cores have a permeability of 1.8 Darcy and porosity of 19.4%. The only experimental variable was then the oils type and we choose oils such that their viscosities have close values. Australian heavy crude oil (18 API) and highly refined paraffinic oil (Ondina 68) were used in the core flooding study.
Two ASP floods were run, and although all the physical parameters were kept same except oil type, the outcome was significantly different. While recovery of both the refined oil and the crude oil was the same after initial waterflood, the crude oil was mobilized more by the ASP process, through both microemulsion and banking processes. The experiment with the refined paraffinic oil produced less ultimate recovery, and only the microemulsion process was significant.