Coupling Low Salinity Water Flooding and Steam Flooding for Heavy Oil in Sandstone Reservoirs; Low Salinity-Alternating-Steam Flooding LSASF: A Novel EOR Technique

摘要

Recently Al-Saedi and Flori et al. (2018a) studied the potential of low salinity alternating steam flooding (LSASF) in laboratory Berea sandstone cores and the results were promising for increasing heavy oil recovery. In this study, we applied the new LSASF method on oil-impregnated reservoir sandstone cores from the Bartlesville sandstone reservoir in eastern Kansas. These samples contain high viscous oil up to 600 cp. Combining low salinity water (LS water) flooding and steam flooding is a novel idea which takes advantage of the relative strengths of both methods. LS water has been extensively studied by many researchers with promising results. Steamflooding is also much studied for applications particularly in heavy oil fields where recovery is increased by reducing the oil viscosity. The density difference between steam and heavy oil raises difficult problems in some reservoirs that can only be solved by injecting water with steam. In particular, those problems are gravity override, channeling, and early breakthrough. In this study, numerous reservoir sandstone cores were retrieved from the Bartlesville sandstone reservoir and cleaned, dried, vacuumed, and saturated with formation water (FW) that was identical to the reservoir FW. The water was displaced with a heavy crude oil to achieve S_(wi), and pre-aged for five weeks at 90°C. These cores were then flooded with 2 PV FW and then followed by different cycles of LS water + steam. A variety of LS water salinities were used (d_(4FW), d_(8FW), and d_(40FW)). The laboratory experiments showed that optimum recovery is achieved by diluting the FW 40 times and using the same water in a shorter steam cycle. The oil recovery was 70.6% of the OOIP, which represents a quite high percentage of oil recovery in heavy oil reservoirs. The results of contact angle showed that the cores flooded using the novel LSASF were shifted to more water-wet conditions. Chemical analyses showed that using this novel LS water plus steam method improves recovery by enhancing the permeability of the rock, reducing precipitation caused by LS water flooding, and increasing dissolution of minerals which increased oil recovery. We also developed the LS water alternating steam flood in order to gather the benefits of LS water itself and to reduce oil viscosity by steam and prevent the aforementioned steam problems by using LS water.