LSASF in Unconventional Sandstone Reservoirs

Abstract

In order to unlock large quantities of heavy crude oil, thermal enhanced oil recovery (EOR) must keep pace with the other EOR development, such as low salinity (LS) water flooding. Injecting steam alone is accompanied by gravity override, which leads to early breakthroughs without contacting the whole heavy oil bank. Water alternating steam process (WASP) is a steam sweep efficiency improver, but using LS water provides the same feature with an extra benefit, which is wettability alteration and named low salinity alternating steam flooding (LSASF). Changing reservoir rocks wettability from oil-wet towards water-wet is highly desired during designing EOR projects. This study presents injecting steam into heavy oil accumulation in the purpose of decreasing its viscosity and ease its flow and intermitting steam with LS water flooding to improve steam sweep efficiency and to alter sandstone wettability towards being more water-wet, which unlock extra heavy oil by LS water too. In this study, core flooding experiments have been carried out on a reservoir core plugs were taken from Bartlesville Sandstone Reservoir (located in Eastern Kansas) saturated with a heavy crude oil of 600 cp from the same reservoir. The reservoir core plugs were saturated by formation water (FW) with 104,550 ppm salinity and heavy crude oil. FW was firstly injected in the secondary stage, followed by different LS waters to examine the optimum formula of LS water that needs to be injected with steam. Each injected LS water was alternating with steam. Four kinds of LS water with 3000 ppm salinity were evaluated and named LSNaCl, LSCaCl2, LSMgCl2, and LSMix, where each subscript refers to the only salt dissolved in the LS water. Spontaneous imbibition test was also conducted to study the wettability change. The results obtained showed that LS water and steam flooding improved oil recovery at all proposed scenarios. Still, the highest was LS water contains NaCl only (LSNaCl) followed by LS water contains CaCl2 (LSCaCl2), then LSMix, and the lowest was LSMgCl2. The spontaneous imbibition results agree with core flooding results. Based on the results of this work, it is possible to inject LSNaCl and steam that gives the lowest residual oil saturation.