We imaged a sandstone at connate water saturation, residual waterflood oil saturation, residual surfactant flood oil saturation and residual polymer flood oil saturation at high resolution in 3D with a micro-computed tomograph. We measured oil saturations, porosities, residual oil cluster size distributions and oil cluster surface areas on each image. We found that the waterflood and polymer flood reduced the oil saturations significantly (from 68.4% initial oil in place to 38.3% after waterflooding and 28.5% after polymer flooding). The surfactant flood was ineffective, which is probably due to the formulation we used and/or the fluid equilibration times we applied. The residual oil cluster size distributions and cluster surface area-volume relationships followed power-law relations, consistent with previous experimental measurements. We conclude that micro-computed tomography can enhance understanding of pore-scale fluid dynamics significantly.
With a growing global population and simultaneously shrinking crude oil reserves (note that crude oil still is the most important energy resource (IEA 2010)) it is vital that advanced technologies are developed which can recover additional oil (so called unconventional oil). Such techniques are usually classified as enhanced oil recovery (EOR) methods, and they include gas injection (e.g. N2 or CO2, Iglauer et al. 2013, Blunt et al. 1993), surfactant injection (e.g. Xie et al. 2005, Iglauer et al. 2010, Al-Sulaimani et al. 2012) and polymer injection (e.g. Zaitoun et al. 2012, Iglauer et al. 2010, Seright et al. 2011, Zhang et al. 2012). Recovery of heavier oils can also be increased by steam injection or combustion drive (Lake 1990), i.e. through oil viscosity reduction.
We focus here on surfactant EOR (SEOR), which has been tested in a range of field operations (e.g. Ferrell et al. 1988, Reppert et al. 1990, Maerker and Gale 1992). Typically small surfactant concentrations are used (Iglauer et al. 2010) to minimize costs. One of the main problems with SEOR is, however, surfactant adsorption (= loss) to the rock surface (e.g. Gale and Sandvik 1973, Pursley and Graham 1975, Wu et al. 2010, Green and Willhite 1998).
