Experimental investigation of low salinity water-flooding in tight chalk oil reservoirs

Chalk reservoirs, due to their high storage capacity and very low permeability, are one of the most interesting cases for reservoir engineering research on carbonates. They exhibit complex fluid-rock interactions because of their chemically active porous media. This study investigates the effect of...

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Veröffentlicht in:Journal of petroleum science & engineering 2022-01, Vol.208, p.109282, Article 109282
Hauptverfasser: Mokhtari, Rasoul, Anabaraonye, Benaiah U., Afrough, Armin, Mohammadkhani, Samira, Feilberg, Karen L.
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Sprache:eng
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Zusammenfassung:Chalk reservoirs, due to their high storage capacity and very low permeability, are one of the most interesting cases for reservoir engineering research on carbonates. They exhibit complex fluid-rock interactions because of their chemically active porous media. This study investigates the effect of brine composition, injection scenario, and temperature on oil recovery by low salinity water-flooding in chalk core samples from a Danish North Sea reservoir. The mechanisms governing oil-brine-rock interactions were also explored. Actual reservoir chalk core samples, without any open fractures, were selected using computed tomography analyses. These cores were saturated with representative fluids (crude oil and synthetic formation brine) and aged at reservoir conditions for approximately three weeks. The role of brine chemistry has been investigated through effluent analysis by ion chromatography, and results indicate that low salinity diluted seawater promotes rock-surface reactions if left to incubate for at least 48 h. Rock dissolution, observed through the monitoring of effluent ions, increased both with increase in temperature and decrease in brine salinity. The recovery curves show that formation water and diluted seawater produce significantly more oil (of the order of 10 % more) at the secondary stage compared to seawater. Additionally, there is also some indication of an effect of low salinity brine at the tertiary stage. These experiments were performed on reservoir materials and corresponding crude oil samples and provide new data on the low salinity flooding potential for chalk, and provide further evidence for the applicability of the low salinity effect in carbonates. •DSW and FW yield 11 % additional secondary recovery compared to SW in chalk.•Evidence for the low salinity effect was observed at the tertiary stage.•Evidence of magnesium mineral precipitation in low salinity flooding experiments.•Brine analyses of major ions show a piston-like flow and confirms rock dissolution.•Effect of increased temperature on the recovery was not observed in carbonate rock.
ISSN:0920-4105
1873-4715
DOI:10.1016/j.petrol.2021.109282