The Effects of Kaolinite Fine Particles in Sandstone Reservoir on Omani Medium Oil Recovery by Low-Salinity Water Flooding

Abstract

The effect of kaolinite fine particles migration and wettability alteration during low salinity water-flooding (LSW-flooding) has been investigated for Omani sandstone reservoirs. Water flooding by re-injecting the reservoir brine is currently operated in the subjected Omani oil fields, and LSW is one of the operations to improve the oil production. However, relatively large amount of precipitated oil sludge was observed in the production and surface facilities along with the produced crude oil. In present experimental study, Omani intermediate oil (API gravity of 30°) and oil sludge were sampled from a skimming tank in the production facility. The physical and chemical characteristics of the clay particles were analyzed by a laser particle size distribution analyzer, SEM, XRD, and SQX after separated from oil. Furthermore, water-flooding tests by brine and LSW were carried out using Berea sandstone cores saturated by three different conditions of the Omani oil and kaolinite fine particles to simulate clay particles in the reservoir conditions. The kaolinite-particles slurry of 0.4μm in average size were used for the tests. The first core was saturated with oil only, the second one was filled up with kaolinite fine particles slurry then saturated with the oil, and the third one was saturated with the mixture of kaolinite-particles slurry and the oil. The results of LSW flooding after brine flooding showed that 30 % increase of oil recovery was obtained in the cases including kaolinite fine particles compared to that of oil only. In addition, the wettability of the cores contained kaolinite fine particles showed stronger water-wettability than the core without kaolinite. Zeta potential was measured to investigate the surface charge of kaolinite-particles in brine and water. The kaolinite fine particles were negatively charged as -15 mV in the brine, while it was -50 mV in the LSW used for the LSW flooding test. This difference has explained that the increase of oil recovery ratio in the water-flooding test was induced by kaolinite fine particles in the cores. The ions were traced in the effluents in LSW flooding, and it was found that the concentration of Ca2+ and Mg2+ reduced sharply from their initial concentration of 722 and 788 ppm to 34 and 26 ppm respectively with pH increasing from 6.8 to below 9.0.Those results indicate clearly that the kaolinite fine particles have a function to reduce the Sor and shift the wettability to water-wet that attributed to the interactions between oil, water and kaolinite-particles in the process of LSW flooding.