3D reactive transport modeling of porosity evolution in a carbonate reservoir through dolomitization

Abarca, Elena; Idiart, Andrés; Grandía, Fidel; Rodríguez-Morillas, N.; Pellan, C.; Zen, M. T.; Ait-Ettajer, T.; Fontanelli, L.

doi:10.1016/j.chemgeo.2019.03.017

Cited by 18 publications

(9 citation statements)

References 59 publications

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“…4). The unlimited supply of Mg 2+ from seawater, coupled with a high geothermal heat flux in tectonically active/rifting settings, enables much more rapid reactions than suggested by previous RTM simulations of fault-controlled diagenesis that suggest timescales ranging from 60 kyr to a few million years, even assuming more favourable kinetics (Abarca et al, 2019;Consonni et al, 2018;Corbella et al, 2014). Our model simulates a single event lasting a few tens of kyr within a fault that retains its transmissivity, but many outcrop studies suggest multiple episodes of fluids flow, each with the potential to recrystallize the previous dolomite.…”

Section: Dolomitisation Timescalesmentioning

confidence: 92%

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

Benjakul¹,

Hollis²,

Robertson³

et al. 2020

Preprint

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Abstract. The dominant paradigm for petrogenesis of high-temperature fault-controlled dolomite, widely known as “hydrothermal dolomite” (HTD), invokes upwelling of hot fluid along faulted and fractured conduits from a deep over-pressured aquifer. However, this model has several inherent ambiguities with respect to fluid sources and their dolomitisation potential, as well as mechanisms for delivering enough of these reactive fluids to form substantial volumes of dolomite. Here, we use generic 2D and 3D reactive transport simulations of a single transmissive fault system to evaluate an alternative conceptual model whereby dolomitisation is driven by seawater being drawn down into the subsurface and heated. We examine the evolution of fluid chemistry and distribution of diagenetic alteration, including predictions of the rate, distribution, and temperature of HTD formation, and consider the possible contribution of this process to the Mg-budget of the World’s oceans. The simulations suggest that it is possible for convection of seawater along the fault damage zone to form massive dolomite bodies that extend hundreds of meters vertically and along the fault within a timescale of a few tens of kyr, with no significant alteration of the country rock. Dolomitisation occurs as a gradient reaction by replacement of host limestones and minor dolomite cementation, and results in discharge of Mg2+-poor, Ca2+-rich fluids to the sea floor. Fluids sourced from the basement contribute to the transport of heat that is key for overcoming kinetic limitations to dolomitisation, but the entrained seawater provides the Mg2+ to drive the reaction. Dolomite fronts are sharper on the “up-flow” margin where Mg2+-rich fluids first reach the threshold temperature for dolomitisation, and the “down-flow” dolomite front tends to be broader as the fluid is depleted in Mg2+ by prior dolomitisation. The model demonstrates spatial contrasts in the temperature of dolomitisation and the relative contribution of seawater and basement-derived fluids which are also commonly observed in natural fault-controlled dolomites. In the past, such variations have been interpreted in terms of major shifts in the system driving dolomitisation. Our simulations demonstrate that such changes may also be a product of emergent behaviour within a relatively stable system, with areas that are dolomitised more slowly recording the effect of changes in fluid flow, heat and solute transport that occur in response to diagenetic permeability modification. Overall, our models robustly demonstrate that high-temperature fault-controlled dolomite bodies can form from mixed convection and act as a sink for Mg in the circulating seawaters. In addition, comparison of our 3D simulations with simplifications to 2D, indicate that 2D models misrepresent critical aspects of the system. This has important implications for modelling of systems ranging from geothermal resources and mineralisation to carbonate diagenesis, including hydrothermal karstification and ore genesis as well as dolomitisation.

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Section: Dolomitisation Timescalesmentioning

confidence: 92%

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

Benjakul¹,

Hollis²,

Robertson³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…4). The unlimited supply of Mg 2+ from seawater, coupled with a high geothermal heat flux in tectonically active or rifting settings, enables much more rapid reactions than suggested by previous RTM simulations of faultcontrolled diagenesis that propose timescales ranging from 60 kyr to a few million years, even assuming more favourable kinetics (Abarca et al, 2019;Consonni et al, 2018;Corbella et al, 2014). Our model simulates a single event lasting a few tens of thousands of years within a fault that retains its transmissivity, but many outcrop studies suggest multiple episodes of fluid flow, each with the potential to recrystallise the previous dolomite.…”

Section: Dolomitisation Timescalesmentioning

confidence: 94%

“…We further investigate the effect of basal temperature by specifying a lower temperature (200 • C) at the base of the model, giving an initial geothermal gradient of 35 • C km −1 (Fig. 1) which is comparable to the average thermal gradient of 31.3 and 32.0 • C km −1 in the onshore Netherlands region (Bonté et al, 2012) and geothermal areas in Germany (Agemar et al, 2012) respectively. Finally, we evaluate the sensitivity of the system to the permeability of the caprock, reducing this to 0.5 and 0.1 mD from 1 mD in the baseline model.…”

Section: Lithological Unitsmentioning

confidence: 99%

Understanding controls on hydrothermal dolomitisation: insights from 3D reactive transport modelling of geothermal convection

et al. 2020

View full text Add to dashboard Cite

Abstract. The dominant paradigm for petrogenesis of high-temperature fault-controlled dolomite, widely known as “hydrothermal dolomite” (HTD), invokes upwelling of hot fluid along faulted and fractured conduits from a deep over-pressured aquifer. However, this model has several inherent ambiguities with respect to fluid sources and their dolomitisation potential, as well as mechanisms for delivering enough of these reactive fluids to form substantial volumes of dolomite. Here, we use generic 2D and 3D reactive transport simulations of a single transmissive fault system to evaluate an alternative conceptual model whereby dolomitisation is driven by seawater being drawn down into the subsurface and heated. We examine the evolution of fluid chemistry and the distribution of diagenetic alteration, including predictions of the rate, distribution, and temperature of HTD formation, and consider the possible contribution of this process to the Mg budget of the world's oceans. The simulations suggest that it is possible for convection of seawater along the fault damage zone to form massive dolomite bodies that extend hundreds of metres vertically and along the fault within a timescale of a few tens of thousands of years, with no significant alteration of the country rock. Dolomitisation occurs as a gradient reaction by replacement of host limestones and minor dolomite cementation, and it results in the discharge of Mg2+-poor, Ca2+-rich fluids to the sea floor. Fluids sourced from the basement contribute to the transport of heat that is key for overcoming kinetic limitations to dolomitisation, but the entrained seawater provides the Mg2+ to drive the reaction. Dolomite fronts are sharper on the “up-flow” margin where Mg2+-rich fluids first reach the threshold temperature for dolomitisation, and the “down-flow” dolomite front tends to be broader as the fluid is depleted in Mg2+ by prior dolomitisation. The model demonstrates spatial contrasts in the temperature of dolomitisation and the relative contribution of seawater and basement-derived fluids which are also commonly observed in natural fault-controlled dolomites. In the past, such variations have been interpreted in terms of major shifts in the system driving dolomitisation. Our simulations demonstrate that such changes may also be a product of emergent behaviour within a relatively stable system, with areas that are dolomitised more slowly recording the effect of changes in fluid flow, heat, and solute transport that occur in response to diagenetic permeability modification. Overall, our models robustly demonstrate that high-temperature fault-controlled dolomite bodies can form from mixed convection and act as a sink for Mg in the circulating seawaters. In addition, comparison of our 3D simulations with simplifications to 2D indicate that 2D models misrepresent critical aspects of the system. This has important implications for modelling of systems ranging from geothermal resources and mineralisation to carbonate diagenesis, including hydrothermal karstification and ore genesis as well as dolomitisation.

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“…If the molar ratio of this hydrochemical index is higher than 0.5 the Ca 2+ source is other than gypsum and in terms of the authors' study present are carbonate minerals [76]. There is also known that geothermal activity can favour the mechanism of dolomitization [83][84][85]. The presented research shows the undersaturation of Podhale thermal water relative to gypsum and supersaturation in relation to dolomite.…”

Section: Formation Of Water Chemical Compositionmentioning

confidence: 58%

Hydrogeochemistry and Related Processes Controlling the Formation of the Chemical Composition of Thermal Water in Podhale Trough, Poland

et al. 2020

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The most promising Polish region in terms of its geothermal resource potential is the Podhale Trough in the Inner West Carpathians, where the thermal water occurs in the Eocene-Mesozoic strata. The origin and conditions of formation of the chemical composition of the thermal water are different in a regional scale due to the impact of infiltrating water on the chemical compounds present in nearby thermal intakes, chemical processes responsible for the concentration of major elements and residence time. The article presents the regional conceptual model in regard to the factors controlling the chemistry of thermal water from Podhale Trough and the conditions of its exchange. It was allowed by performing the hydrogeochemical characteristics of studied water and analyzing its changes according to flow direction from HCO3-Ca-Mg type to SO4-Cl-Na-Ca and SO4-Ca-Mg types. The hydrogeochemical modelling was also made allowing identification of the impact of reservoir rocks on the formation of the chemical composition. For confirmation of the theories formulated and for more accurate interpretation of the results obtained from hydrogeochemical modelling, hydrochemical indices were calculated, i.e., rHCO3−/rCl−, rNa+/rCl−, rCa2+/rMg2+, rCa2+/(rCa2+ + rSO42−) and rNa+/(rNa+ + rCl−). The results revealed the most important processes evolving the chemistry of thermal water are progressive freshening of the thermal water reservoir, which in the past was filled with salty water, dissolution of gypsum, and ongoing dolomitization. Conducted research presents the important factors that in the case of increased exploitation of thermal water in the Podhale Trough, may influence the quality of thermal water in terms of its physical and chemical parameters.

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3D reactive transport modeling of porosity evolution in a carbonate reservoir through dolomitization

Cited by 18 publications

References 59 publications

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

Understanding controls on hydrothermal dolomitisation: insights from 3D reactive transport modelling of geothermal convection

Hydrogeochemistry and Related Processes Controlling the Formation of the Chemical Composition of Thermal Water in Podhale Trough, Poland

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