Abstract

Low salinity (LS) water flooding is a promising EOR method which has been examined by many experimental studies and field pilots for a variety of reservoirs and oils. This paper investigates applying LS flooding to a heavy oil. Increasing the LS water temperature improves heavy oil recovery by achieving higher sweep efficiency and improving oil mobility by lowering its viscosity. Steam flooding projects have reported many problems such as steam gravity override, but override can be lessened if the steam is is alternated with hot LS water. In this study, a series of reservoir sandstone cores were obtained from Bartlesville Sandstone (in Eastern Kansas) and aged with heavy crude oil (from the same reservoir) at 95°C for 45 days. Five reservoir cores were used in this study, and five treatments were performed. They were flooded with (a) steam; (b) formation hot water (FHW); (c) low salinity hot water (LSHW; (d) steam + FHW; and (e) steam + LSHW (so-called LSASF). The laboratory experiments showed that basic water flooding using FW recovered approximately 50% of OOIP. After that initial flood, upon switching to the various steam, FHW, LSHW, steam + FHW, and steam + LSHW treatments, the incremental oil recoveries were 5, 3.1, 6.3, 7.5, and 12% OOIP, respectively. The contact angle measurements showed that injecting steam + LSHW alters the wettability considerably more than using steam + FHW. The results of this work show that water flooding using LSHW in reservoir cores could improve oil recovery significantly because it both reduces oil viscosity and alters the rock wettability towards more water-wet. The results also showed using LSHW alternated with steam is more beneficial than using steam only or alternated with regular water due to the combined benefits of reducing gravity override and altering the wettability. Using LSHW water is more economical than using steam and gives significantly improved oil recovery, and using LSHW is more beneficial than ambient temperature LS water.

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