Use of Sulfate for Water Based Enhanced Oil Recovery during Spontaneous Imbibition in Chalk

Fernø, Martin A.; Grønsdal, R.; Åsheim, J.; Nyheim, A.; Berge, Morten; Graue, A.

doi:10.1021/ef200136w

Cited by 59 publications

(40 citation statements)

References 36 publications

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“…In the former case, connate water should be continuous, whereas, in the latter, it can be a discontinuous phase. Oil-wetness was, as described previously, established by silane modification according to the methodology of Grate et al (2013). Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Micromodels were rendered oil-wet with a slight modification of the procedure described by Grate et al (2013). The models were dried under nitrogen flow and filled with concentrated nitric acid with a syringe.…”

Section: Methodsmentioning

confidence: 99%

“…Unreacted HMDS was decanted into water, and the plugs were rinsed in hexane at 60 C for at least 24 hours, followed by drying at 80 C overnight. Some plugs were acid-rinsed before this HMDS treatment because this should promote wettability alteration (Grate et al 2013) of silica-type surfaces. These plugs were vacuum-imbibed with concentrated nitric acid, and kept at 100 C for approximately 24 hours in a closed glass bottle.…”

Section: Methodsmentioning

confidence: 99%

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Osmosis as Mechanism for Low-Salinity Enhanced Oil Recovery

et al. 2016

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We believe that osmosis has been overlooked as a possible mechanism for observed low-salinity enhanced-oil-recovery (EOR) effects. Osmosis can occur in an oil/water/rock system when injecting low-salinity water, because the system is full of an excellent semipermeable membrane-the oil itself.In the present work, water transport through oil films was visualized both in 2D micromodels and in sandstone cores imaged in a microcomputed tomography (CT). After treating these model systems with hexamethyldisilazane (HMDS) to render them more oil-wet, water became discontinuous, and it was possible to establish osmotic gradients. Either expansion or contraction of the connate water was observed, depending on the direction of the imposed salinity gradient.Because osmosis could be the underlying mechanism for lowsalinity EOR, two changes in research strategy are proposed: Most importantly, the use of spontaneous-imbibition tests as evidence for wettability alteration in low-salinity water should be critically reinvestigated. This is because observed production could have stemmed from "osmotic expansion" of the connate water rather than wettability change. Second, much research focus should be shifted from sandstone reservoirs to fractured oil-wet carbonates. Osmosis potentially yields larger responses for the latter reservoir type, whereas from a mechanistic perspective the reason behind low-salinity EOR functioning in both sandstones and carbonates deserves further attention.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Osmosis as Mechanism for Low-Salinity Enhanced Oil Recovery

et al. 2016

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“…In addition, it was found that PDIs become more effective as temperature increases through contact angle measurements on a calcite surface modified with oil and long-chain fatty acids, as reported by Tweheyo et al (2006) and Gomari et al (2006). Fernø et al (2011) concluded that different carbonate rocks may have different responses to the same brine composition. The authors studied the effect of sulfate concentration on oil recovery during spontaneous imbibition in different outcrop chalks (Stevns Klint, Rørdal and Niobrara).…”

Section: Effect Of Brine Salinity and Composition On Oil Recoverymentioning

confidence: 99%

Driving Mechanism of Low Salinity Flooding in Carbonate Rocks

et al. 2015

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Several studies conducted mainly on the laboratory scale indicate that in carbonate rocks oil displacement can be influenced by the ionic composition of the brine, providing an opportunity to improve recovery by optimizing the brine mixture used in secondary or tertiary recovery. In industry this topic has been termed "low salinity flooding (LSF) in carbonates" while the underlying mechanisms are not very well understood. The increased oil recovery has been attributed to wettability alteration to a more water-wet state. However, in some studies a positive low salinity effect (LSE) has been ascribed to dissolution of rock, which occurs on the laboratory scale but due to equilibration of brine with carbonate minerals on larger length scales this is not relevant for the reservoir scale. Therefore, the objective of this paper is to gain a better understanding of the underlying mechanism(s) and investigate whether calcite dissolution is the primary mechanism of the LSE. We used a model system where the contact angle of crude oil deposited on planar surfaces coated with crushed carbonate rock particles was monitored as a function of brine composition. The approach is similar to the one published in Mahani et al. (2014) for sandstone rock, but instead of clay minerals we used carbonate materials from natural limestone and Silurian dolomite rocks. Furthermore, the effective surface charge at the oil-water and water-rock interfaces was quantified via zeta-potential measurements at several salinity and pH levels in order to establish a link between changes in the intermolecular interactions at the solid-liquid interface and the contact angle at the brine-oil-rock contact line, which is an indicator for wettability change. The impact of mineral dissolution was addressed by comparing the response to brines that were fully equilibrated (and hence dissolution suppressed) and the response to those completely under-saturated with calcium carbonate (leading to dissolution). The investigation was accompanied by geochemical modeling using PHREEQC.It was observed that by switching from formation water (FW) to seawater (SW), diluted seawater (dSW) and diluted seawater equilibrated with calcite (dSWEQ), the limestone surface became less oil-wet reflected in contact angle decrease. The recession of the 3-phase contact line observed for both SW and dSWEQ, which are not impacted by dissolution, suggests that the LSE occurs even in the absence of mineral dissolution. The trends observed for the zeta-potential data on brine composition clearly support the surface-charge-change mechanism for limestone, where at lower salinities the charges at the limestone-brine interface become more negative, causing lower adhesion or even repulsion between oil and rock.Dolomite rock shows a different behavior. First, there is a much smaller response in terms of contact angle change. Also, the zeta-potential of dolomite shows generally more positive charges at higher salinities and less decrease at lower salinities, where in comparison to limestone the ele...

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“…Increasing the sulfate concentration in seawater resulted in more change of wettability towards water-wetness. Ferno et al (2011) performed spontaneous imbibition tests on different chalk outcrops (Stevns, Rordal, and Niobrara) using brines with and without sulfate. The effect of adding sulfate to the brines on wettability alteration was observed only in plugs from Stevns Klint chalk, but not from the other 2 chalk types.…”

Section: Introductionmentioning

confidence: 99%

Demonstrating the Potential of Low-Salinity Waterflood to Improve Oil Recovery in Carbonate Reservoirs by Qualitative Coreflood

Nasralla

Sergienko

Linde

et al. 2014

Day 4 Thu, November 13, 2014

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Low salinity waterflood (LSF) is a promising improved oil recovery (IOR) technology. Although, it has been demonstrated that LSF is an efficient IOR method for many sandstone reservoirs, the potential of LSF in carbonate reservoirs is still not well-established as only a limited number of successful coreflood experiments are available in the literature. Therefore, the aim of this study was to examine the oil recovery improvement by LSF in carbonate reservoirs by performing coreflood experiments.This paper proposes an experimental approach to qualitatively evaluate the potential of LSF to improve oil recovery and alter the rock wettability during coreflood experiments. The corefloods were conducted on core plugs from two Middle Eastern carbonate reservoirs with a wide variation of rock properties and reservoir conditions. Seawater and several dilutions of formation brine and seawater were flooded in the tertiary mode to evaluate their impacts on oil recovery compared to formation brine injection. In addition, a geochemical study was performed using PHREEQC software to assess the potential of calcite dissolution by LSF.The experimental results confirmed that lowering the water salinity can alter the rock wettability towards more water-wet, causing improvement of oil recovery in tertiary waterflood in plugs from the two reservoirs. Furthermore, seawater is more favorable for improved oil recovery than formation brine as injection of seawater after formation brine resulted in extra oil production. This demonstrates that the brine composition plays an important role during waterflooding in carbonate reservoirs, and not only the brine salinity. It was also observed that oil recovery can be improved by injection of brines that cannot dissolve calcite based on the geochemical modeling study. This implies that calcite dissolution is not the dominant mechanism of IOR by LSF.To conclude, this paper demonstrates that low-salinity waterflood has a good potential as an IOR technology in carbonate reservoirs. In addition, the proposed experimental approach ensures the verification of LSF effect, either it is positive or negative. However, more work is required to further explore the most influential parameters affecting LSF response and explain the dominant mechanisms.

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Use of Sulfate for Water Based Enhanced Oil Recovery during Spontaneous Imbibition in Chalk

Cited by 59 publications

References 36 publications

Osmosis as Mechanism for Low-Salinity Enhanced Oil Recovery

Osmosis as Mechanism for Low-Salinity Enhanced Oil Recovery

Driving Mechanism of Low Salinity Flooding in Carbonate Rocks

Demonstrating the Potential of Low-Salinity Waterflood to Improve Oil Recovery in Carbonate Reservoirs by Qualitative Coreflood

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