Oil Recovery From Bentheim Sandstone by Sequential Waterflooding and Spontaneous Imbibition
- Nina Loahardjo (University of Wyoming) | _ Winoto (University of Wyoming) | Norman R. Morrow (University of Wyoming)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- December 2013
- Document Type
- Journal Paper
- 547 - 553
- 2013. Society of Petrophysicists & Well Log Analysts
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- 218 since 2007
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Sequential waterflooding refers to cycles of flooding for which initial water saturation is re-established after a waterflood by flow of crude oil followed by further waterflooding (Loahardjo et al. 2012). Numerous tests have shown that sequential waterfloods can result in significant reduction in residual oil from one flood to the next. As part of an investigation of the mechanism of sequential flooding, an extensive study of sequential waterflooding and spontaneous imbibition has been performed on Bentheim Sandstone, an outcrop sandstone, which typically has high permeability and low clay content. The waterfloods showed systematic decrease in residual oil saturation from one flood to the next. After firing and acidizing, reduction in residual oil was no longer observed.
Extended aging of cores at residual oil saturation during the course of sequential waterflooding usually resulted in increased recovery for the next waterflood whereas aging at initial water saturation resulted in decreased recovery. The inference that variation in recovery by sequential flooding is related to wetting phenomena was tested through imbibition tests on companion Bentheim core samples with, and without a previous history of waterflooding. No additional oil recovery was obtained by forced displacement after spontaneous imbibition. The Amott (1959) index to water of unity indicated that for the tested crude oil, all of the cores were very strongly water wet. However, the rate of imbibition, a more direct test of wettability because it is closely related to the capillary driving force, increased for cores that had been previously waterfooded. These observations imply that the strong response in recovery behavior observed for sequential flooding of Bentheim sandstone is linked to transition in wetting behavior between conditions that would, traditionally, all be classed as very strongly water wet.
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