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Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding

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ABSTRACT

Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates for the first time that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-water and oil-water interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between the oil-brine and mineral-brine interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. A new experimental method is presented that allows this. Results also show for the first time that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs. A key challenge for any model of CSW is to explain why IOR is not always observed. Here we suggest that failures using the conventional (dilution) approach to CSW may have been caused by a positively charged oil-water interface that had not been identified.

No MeSH data available.


Examples of (a,b,c) successful and (d) unsuccessful controlled salinity experiments in carbonates. Plots (a), (b) and (d) show core-flooding experiments (data from ref. 15 (a) and ref. 20 (b,d)). Plot (c) shows a spontaneous imbibition (SI) experiment (data from ref. 21). FMB denotes formation brine, SW denotes seawater, 100dFMB denotes formation brine diluted 100 times; 5dSW denotes seawater diluted 5 times; SW0S denotes seawater with SO42− removed; SW3S denotes seawater with SO42− increased by a factor of 3. Time in plots (a,b,d) is denoted in dimensionless pore-volumes (PV) injected.
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f1: Examples of (a,b,c) successful and (d) unsuccessful controlled salinity experiments in carbonates. Plots (a), (b) and (d) show core-flooding experiments (data from ref. 15 (a) and ref. 20 (b,d)). Plot (c) shows a spontaneous imbibition (SI) experiment (data from ref. 21). FMB denotes formation brine, SW denotes seawater, 100dFMB denotes formation brine diluted 100 times; 5dSW denotes seawater diluted 5 times; SW0S denotes seawater with SO42− removed; SW3S denotes seawater with SO42− increased by a factor of 3. Time in plots (a,b,d) is denoted in dimensionless pore-volumes (PV) injected.

Mentions: Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the composition of the brine injected during water-flooding in a process termed ‘controlled salinity water-flooding’ (CSW)89111213141516. In laboratory core-flooding experiments, oil is displaced from cylindrical rock samples (‘cores’) by injecting water of the desired composition into one end face of the core and producing oil (and water) from the opposing face in order to model the reservoir water-flooding process (e.g., Fig. 1a,b,d). In spontaneous imbibition (SI) experiments, core samples are immersed in water and the volume of oil that is spontaneously displaced by water is measured (e.g., Fig. 1c). These laboratory experiments are slow and expensive to undertake, as are field trials17. A reliable method for identifying the optimum composition for CSW is therefore essential.


Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding
Examples of (a,b,c) successful and (d) unsuccessful controlled salinity experiments in carbonates. Plots (a), (b) and (d) show core-flooding experiments (data from ref. 15 (a) and ref. 20 (b,d)). Plot (c) shows a spontaneous imbibition (SI) experiment (data from ref. 21). FMB denotes formation brine, SW denotes seawater, 100dFMB denotes formation brine diluted 100 times; 5dSW denotes seawater diluted 5 times; SW0S denotes seawater with SO42− removed; SW3S denotes seawater with SO42− increased by a factor of 3. Time in plots (a,b,d) is denoted in dimensionless pore-volumes (PV) injected.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120358&req=5

f1: Examples of (a,b,c) successful and (d) unsuccessful controlled salinity experiments in carbonates. Plots (a), (b) and (d) show core-flooding experiments (data from ref. 15 (a) and ref. 20 (b,d)). Plot (c) shows a spontaneous imbibition (SI) experiment (data from ref. 21). FMB denotes formation brine, SW denotes seawater, 100dFMB denotes formation brine diluted 100 times; 5dSW denotes seawater diluted 5 times; SW0S denotes seawater with SO42− removed; SW3S denotes seawater with SO42− increased by a factor of 3. Time in plots (a,b,d) is denoted in dimensionless pore-volumes (PV) injected.
Mentions: Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the composition of the brine injected during water-flooding in a process termed ‘controlled salinity water-flooding’ (CSW)89111213141516. In laboratory core-flooding experiments, oil is displaced from cylindrical rock samples (‘cores’) by injecting water of the desired composition into one end face of the core and producing oil (and water) from the opposing face in order to model the reservoir water-flooding process (e.g., Fig. 1a,b,d). In spontaneous imbibition (SI) experiments, core samples are immersed in water and the volume of oil that is spontaneously displaced by water is measured (e.g., Fig. 1c). These laboratory experiments are slow and expensive to undertake, as are field trials17. A reliable method for identifying the optimum composition for CSW is therefore essential.

View Article: PubMed Central - PubMed

ABSTRACT

Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates for the first time that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-water and oil-water interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between the oil-brine and mineral-brine interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. A new experimental method is presented that allows this. Results also show for the first time that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs. A key challenge for any model of CSW is to explain why IOR is not always observed. Here we suggest that failures using the conventional (dilution) approach to CSW may have been caused by a positively charged oil-water interface that had not been identified.

No MeSH data available.