Investigation of chemical enhanced oil recovery core flooding processes with special focus on rock-fluid interactions

Abstract

Chemical Enhanced Oil Recovery (cEOR) methods have been established since several decades. Despite the continuous research and development challenging reservoir with temperature above 80°C and salinities of more than 100 g/l cannot be targeted commercially yet. During the course of this work these high salinity and high temperature cEOR processes were investigated. It was discovered that combinations of anionic, cationic and non-ionic surfactant systems can be used under these conditions. The focus during the initial phase was lain on a carbonate formation, which poses harsh reservoir conditions at 110°C and 234 g/l salinity. At a later stage a sandstone field was focussed on, with its reservoir properties of 80°C and 48.5 g/l salinity. These less harsh conditions allowed for a wider range of surfactant systems to be tested for EOR purposes. At first, prior to core flooding evaluations a micromodel screening was performed for each surfactant system supplied. During the screening 40 different surfactant solutions were tested for their oil recovering potential against the reservoir dead oil in order to find the most suitable candidate for the following core flooding evaluation. By this method, the number of solutions to be tested in time consuming core floods was reduced down to one solution per individual surfactant system. A significant number of surfactant solutions reach ultra low interfacial tension (IFT) values in phase behavior tests, but only few cases could solubilize and recover significant remaining oil from the micromodel. The potential of microfluidics was proven for surfactant EOR with the visual access gained to the displacment process. In combination with the low oil volume required for this part of the screening, the micromodel experiments could be performed quick and reliable. Hereby it could be seen that surfactant solution in micromodels performed worst when significant amounts of oil were solubilized inside the aqueous phase during the phase behavior tests and performed best when the aqueous phase was most translucent. This came into play in cases when the phase behavior tests were inconclusive or could not be interpreted properly even when a Windsor III type microemulsion was present. Second, the chosen candidates for core flooding investigation were brought to the test utilizing the designated core flooding experimental setup. This setup was constructed, tested and optimized for minimal dead volume and corrosion resistivity at high temperature and high salinity conditions. More than 30 single- and multiphase core flooding experiments were performed in order to determine the oil recovery potential for EOR applications and the investigation of the injectivity, retention/adsorption and chromatographic effects of surfactant solutions. Finally, spontaneous imbibition experiments and rheological characterization were performed, supplemented by the investigation of oil-surfactant emulsion properties. Ultimately, the high adsorption rates observed of the tested surfactants lead to suboptimal…