Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

Handle URI:
http://hdl.handle.net/10754/625997
Title:
Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs
Authors:
Yutkin, Maxim P.; Mishra, Himanshu ( 0000-0001-8759-7812 ) ; Patzek, Tadeusz W. ( 0000-0002-9389-7579 ) ; Lee, John; Radke, Clayton J.
Abstract:
Low-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of calcite bulk and surface equilibria draws several important inferences about the proposed LSW oil-recovery mechanisms. Diffuse double-layer expansion (DLE) is impossible for brine ionic strength greater than 0.1 molar. Because of rapid rock/brine equilibration, the dissolution mechanism for releasing adhered oil is eliminated. Also, fines mobilization and concomitant oil release cannot occur because there are few loose fines and clays in a majority of carbonates. LSW cannot be a low-interfacial-tension alkaline flood because carbonate dissolution exhausts all injected base near the wellbore and lowers pH to that set by the rock and by formation CO2. In spite of diffuse double-layer collapse in carbonate reservoirs, surface ion-exchange oil release remains feasible, but unproved.
KAUST Department:
Biological and Environmental Sciences and Engineering (BESE) Division; Environmental Science and Engineering Program
Citation:
Yutkin MP, Mishra H, Patzek TW, Lee J, Radke CJ (2017) Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs. SPE Journal. Available: http://dx.doi.org/10.2118/182829-PA.
Publisher:
Society of Petroleum Engineers (SPE)
Journal:
SPE Journal
Issue Date:
25-Aug-2017
DOI:
10.2118/182829-PA
Type:
Article
ISSN:
1086-055X
Sponsors:
Author Clayton J. Radke acknowledges the Ali I. Al-Naimi Petroleum Engineering Research Center (ANPERC) of King Abdullah University of Science and Technology (KAUST) for hosting a sabbatical visit and Jagan Mahadevan for introducing this problem. Funding for this project has been provided by KAUST through ANPERC.
Additional Links:
https://www.onepetro.org/journal-paper/SPE-182829-PA
Appears in Collections:
Articles; Environmental Science and Engineering Program; Biological and Environmental Sciences and Engineering (BESE) Division

Full metadata record

DC FieldValue Language
dc.contributor.authorYutkin, Maxim P.en
dc.contributor.authorMishra, Himanshuen
dc.contributor.authorPatzek, Tadeusz W.en
dc.contributor.authorLee, Johnen
dc.contributor.authorRadke, Clayton J.en
dc.date.accessioned2017-10-30T08:39:49Z-
dc.date.available2017-10-30T08:39:49Z-
dc.date.issued2017-08-25en
dc.identifier.citationYutkin MP, Mishra H, Patzek TW, Lee J, Radke CJ (2017) Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs. SPE Journal. Available: http://dx.doi.org/10.2118/182829-PA.en
dc.identifier.issn1086-055Xen
dc.identifier.doi10.2118/182829-PAen
dc.identifier.urihttp://hdl.handle.net/10754/625997-
dc.description.abstractLow-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of calcite bulk and surface equilibria draws several important inferences about the proposed LSW oil-recovery mechanisms. Diffuse double-layer expansion (DLE) is impossible for brine ionic strength greater than 0.1 molar. Because of rapid rock/brine equilibration, the dissolution mechanism for releasing adhered oil is eliminated. Also, fines mobilization and concomitant oil release cannot occur because there are few loose fines and clays in a majority of carbonates. LSW cannot be a low-interfacial-tension alkaline flood because carbonate dissolution exhausts all injected base near the wellbore and lowers pH to that set by the rock and by formation CO2. In spite of diffuse double-layer collapse in carbonate reservoirs, surface ion-exchange oil release remains feasible, but unproved.en
dc.description.sponsorshipAuthor Clayton J. Radke acknowledges the Ali I. Al-Naimi Petroleum Engineering Research Center (ANPERC) of King Abdullah University of Science and Technology (KAUST) for hosting a sabbatical visit and Jagan Mahadevan for introducing this problem. Funding for this project has been provided by KAUST through ANPERC.en
dc.publisherSociety of Petroleum Engineers (SPE)en
dc.relation.urlhttps://www.onepetro.org/journal-paper/SPE-182829-PAen
dc.rightsArchived with thanks to the SPE Journal.en
dc.titleBulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirsen
dc.typeArticleen
dc.contributor.departmentBiological and Environmental Sciences and Engineering (BESE) Divisionen
dc.contributor.departmentEnvironmental Science and Engineering Programen
dc.identifier.journalSPE Journalen
dc.contributor.institutionUniversity of Californiaen
kaust.authorYutkin, Maxim P.en
kaust.authorMishra, Himanshuen
kaust.authorPatzek, Tadeusz W.en
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