Chemical Mechanism of Low Salinity Water Flooding in Sandstone Reservoirs

Austad, Tor; Rezaeidoust, Alireza; Puntervold, Tina

doi:10.2523/129767-ms

Cited by 67 publications

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“…Moreover, the presence of clay minerals is seen to be a key requirement for low-salinity EOR to operate. 4,[6][7][8] This is due to the role that clays play in determining the wettability state of a rock. Clay minerals and quartz grains are widely present in the pores of sandstone reservoirs, where they form surface coatings.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamic Simulations of Montmorillonite–Organic Interactions under Varying Salinity: An Insight into Enhanced Oil Recovery

et al. 2015

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Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Journal of physical chemistry C, copyright c 2015 American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see http://dx.doi.org/10.1021/acs.jpcc.5b00555Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractEnhanced oil recovery is becoming commonplace in order to maximise recovery from oilfields. One of these methods, low-salinity enhanced oil recovery (EOR) has shown promise, however the fundamental underlying chemistry requires elucidating. Here, three mechanisms proposed to account for low-salinity enhanced oil recovery in sandstone reservoirs are investigated using molecular dynamic simulations. The mechanisms probed are electric double layer expansion, multicomponent ionic exchange and pH effects arising at clay mineral surfaces. Simulations of smectite basal planes interacting with uncharged non-polar decane, uncharged polar decanoic acid and charged Nadecanoate model compounds are used to this end. Various salt concentrations of NaCl are modelled: 0% , 1% , 5% and 35% to determine the role of salinity upon the three separate mechanisms. Furthermore, the initial oil/water-wetness of the clay surface is modeled. Results show that electric double layer expansion is not able to fully explain the effects of low-salinity enhanced oil recovery. The pH surrounding a clays basal plane, and hence the protonation and charge of acid molecules is determined to be one of the dominant effects driving low-salinity EOR. Further, results present that the presence of calcium cations can drastically alter the oil wettability of a clay ⇤To whom correspondence should be addressed mineral surface. Replacing all divalent cations with monovalent cations through multicomponent cation exchange dramatically increases the water wettability of a clay surface, and will increase EOR.

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Section: Introductionmentioning

confidence: 99%

“…The free hydroxyl ion interacts with a polar organic, for example a carboxylic acid, and depending on the pH level, deprotonates the organic, removing the hydrogen bonding mechanism tethering the organic to the clay. 8 Clay RCOOH + OH * ) Clay + RCOO + H 2 O…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamic Simulations of Montmorillonite–Organic Interactions under Varying Salinity: An Insight into Enhanced Oil Recovery

et al. 2015

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“…(Loahardjo et al 2007) Many hypotheses have been proposed to explain the oil recovery mechanism of low salinity water injections. Those included migration of detached mixed-wet clay particles with absorbed residual oil drops (Tang and Morrow 1999), wettability alteration toward increased water-wetness (Tang and Morrow 1999;Ligthelm et al 2009;Austad and Puntervold 2010;Sorbie and Collins 2010), saponification (McGuire et al 2005), and cation exchange (Lager et al 2006;Lebedeva et al 2009;Austad and Puntervold 2010). However, none of these hypotheses has been verified by experiments.…”

Section: Introductionmentioning

confidence: 94%

Oil Recovery by Low Salinity Water Injection into a Reservoir: A New Study of Tertiary Oil Recovery Mechanism

2011

Transp Porous Med

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Low salinity water injections for oil recovery have shown seemingly promising results in the case of clay-bearing sandstones saturated with asphaltic crude oil. Reported data showed that low salinity water injection could provide up to 20% pore volume (PV) of additional oil recovery for core samples and up to 25% PV for reservoirs in near wellbore regions, compared with brine injection at the same Darcy velocity. The question remains as to whether this additional recovery is also attainable in reservoirs. The answer requires a thorough understanding of oil recovery mechanism of low salinity water injections. Numerous hypotheses have been proposed to explain the increased oil recovery using low salinity water, including migration of detached mixed-wet clay particles with absorbed residual oil drops, wettability alteration toward increased water-wetness, and emulsion formation. However, many later reports showed that a higher oil recovery associated with low salinity water injection at the common laboratory flow velocity was neither necessarily accompanied by migration of clay particles, nor necessarily accompanied by emulsion. Moreover, increased water-wetness has been shown to cause the reduction of oil recovery. The present study is based on both experimental and theoretical analyses. Our study reveals that the increased oil recovery is only related to the reduction of water permeability due to physical plugging of the porous network by swelling clay aggregates or migrating clay particles and crystals. At a fixed apparent flow velocity, the value of negative pressure gradient along the flow path increases as the water permeability decreases. Some oil drops and blobs can be mobilized under the increased negative pressure gradient and contribute to the additional oil recovery. Based on the revealed mechanism, we conclude that low salinity water injection cannot be superior to brine injection in any clay-bearing sandstone reservoir at the maximum permitted injection pressure. Through our study of low salinity water injection, the theory of tertiary oil recovery has been notably improved. Keywords

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“…This was done to try to disentangle a pure MIE mechanism from one combined with a variation in pH, as it has been reported that pH can play a large role in determining the oil adsorption capacity (or adhesion) [5,7,33]. Figure 3 shows the results from experiments kao-Si-1 and kao-Si-2.…”

Section: Effect Of Cacl 2 Concentrationmentioning

confidence: 99%

“…Therefore, for the experiments performed at a pH ≈ 5.5, it can be expected that the AFM probe will contain a similar number of -COOH and -COO-groups, and therefore has an overall negative charge. Strand et al [5] and Austad et al [7] explained the observed high affinity of organic matter to clay surfaces at near-to-neutral pH through the formation of hydrogen bonds between the carbonyl oxygen and protons adsorbed to the clay surface, in addition to bonds between the hydrogen in the -COOH molecule and the negative charge on the clay mineral. The presence of Ca 2+ , however, complicates this picture as there will be competition with protons for surface sites, which may lead to the At the experimental conditions (constant pH), the protonation state of the -COOH will remain unchanged and, therefore, should be critical in determining the adhesion to the kaolinite surface.…”

Section: Effect Of Cacl 2 Concentrationmentioning

confidence: 99%

Chemical Force Microscopy Study on the Interactions of COOH Functional Groups with Kaolinite Surfaces: Implications for Enhanced Oil Recovery

et al. 2017

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Clay-oil interactions play a critical role in determining the wettability of sandstone oil reservoirs, which, in turn, governs the effectiveness of enhanced oil recovery methods. In this study, we have measured the adhesion between -COOH functional groups and the siloxane and aluminol faces of kaolinite clay minerals by means of chemical force microscopy as a function of pH, salinity (from 0.001 M to 1 M) and cation identity (Na + vs. Ca 2+ ). Results from measurements on the siloxane face show that Ca 2+ displays a reverse low-salinity effect (adhesion decreasing at higher concentrations) at pH 5.5, and a low salinity effect at pH 8. At a constant Ca 2+ concentration of 0.001 M, however, an increase in pH leads to larger adhesion. In contrast, a variation in the Na + concentration showed less effect in varying the adhesion of -COOH groups to the siloxane face. Measurements on the aluminol face showed a reverse low-salinity effect at pH 5.5 in the presence of Ca 2+ , whereas an increase in pH with constant ion concentration resulted in a decrease in adhesion for both Ca 2+ and Na + . Results are explained by looking at the kaolinite's surface complexation and the protonation state of the functional group, and highlight a more important role of the multicomponent ion exchange mechanism in controlling adhesion than the double layer expansion mechanism.

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Chemical Mechanism of Low Salinity Water Flooding in Sandstone Reservoirs

Cited by 67 publications

References 0 publications

Molecular Dynamic Simulations of Montmorillonite–Organic Interactions under Varying Salinity: An Insight into Enhanced Oil Recovery

Molecular Dynamic Simulations of Montmorillonite–Organic Interactions under Varying Salinity: An Insight into Enhanced Oil Recovery

Oil Recovery by Low Salinity Water Injection into a Reservoir: A New Study of Tertiary Oil Recovery Mechanism

Chemical Force Microscopy Study on the Interactions of COOH Functional Groups with Kaolinite Surfaces: Implications for Enhanced Oil Recovery

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