Validation study of water weakening research from outcrop chalks performed on Eldfisk reservoir cores

Kallesten, Emanuela Iedidia; Cherif, Yosra; Madland, Merete Vadla; Korsnes, Reidar Inge; Omdal, Edvard; Andersen, Pål Østebø; Zimmermann, Udo

doi:10.1016/j.petrol.2020.108164

Cited by 9 publications

(3 citation statements)

References 27 publications

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“…To check the agreement of this enthalpy with other experimental data sets, we considered flooding tests with 0.219 M MgCl 2 solution performed on Kansas chalk at 130 °C and carried out by Sachdeva et al 88 Given the high electrolyte concentration, supersaturation with respect to magnesium-bearing minerals is expected; the precipitation of newly formed Mg minerals was disclosed through the core analysis after the flooding and also reported in other flowthrough experiments on chalk. 89 Contrary to the concentration profiles from Strand et al, 87 calcium was released from the core before magnesium, most probably due to calcite dissolution. To accommodate these experimental observations (i.e., precipitation of magnesium-containing minerals and calcite dissolution), we considered that, in each reaction cell, the solution is in equilibrium with dolomite, calcite, and magnesite; albeit suitable for calcite, this assumption carries more uncertainty when it comes to dolomite and magnesite dissolution/precipitation that are known for their slower kinetics compared to calcite.…”

Section: ■ Results and Discussionmentioning

confidence: 68%

“…A reaction enthalpy of around 50 kJ/mol is required to fit the magnesium concentration in the effluent at the four different temperatures (Figure ). To check the agreement of this enthalpy with other experimental data sets, we considered flooding tests with 0.219 M MgCl 2 solution performed on Kansas chalk at 130 °C and carried out by Sachdeva et al Given the high electrolyte concentration, supersaturation with respect to magnesium-bearing minerals is expected; the precipitation of newly formed Mg minerals was disclosed through the core analysis after the flooding and also reported in other flowthrough experiments on chalk . Contrary to the concentration profiles from Strand et al, calcium was released from the core before magnesium, most probably due to calcite dissolution.…”

Section: Resultsmentioning

confidence: 88%

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Thermodynamic Analysis of the Temperature Effect on Calcite Surface Reactions in Aqueous Environments

2021

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Reactive transport models for subsurface applications, particularly those for modified salinity waterflooding (MSW) in carbonates, have to be equipped with thermodynamic models that can reliably predict/describe adsorption phenomena at variable temperature conditions. To advance the understanding of the calcite reactivity at high temperatures, combining experimental and modeling studies is required. Therefore, we used a surface complexation model (SCM) to describe the reactivity at the calcite−water interface and obtained the enthalpies of the surface reactions by fitting the SCM either to hightemperature electrokinetic data obtained through streaming potential measurements on limestone samples or to the effluent concentration from single-phase flooding experiments. We assumed that the equilibrium constants of the surface reactions follow a temperature dependence according to van't Hoff equation. Our calculations suggest that calcite protonation is more exothermic compared to other minerals (e.g., silica, hematite) and that the adsorption of Ca 2+ , Mg 2+ , and SO 4 2− are all endothermic, with SO 4 2− having the highest reaction enthalpy. We further show that the inferred enthalpies were in agreement with enthalpy changes from published microcalorimetry experiments. Despite the consistency with microcalorimetry data, the obtained enthalpies are not undisputable, and additional data are necessary to unequivocally constrain the temperature effect on the calcite surface reactivity.

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Section: ■ Results and Discussionmentioning

confidence: 68%

Section: Resultsmentioning

confidence: 88%

Thermodynamic Analysis of the Temperature Effect on Calcite Surface Reactions in Aqueous Environments

2021

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“…Other proposed weakening mechanisms include pressure solution (Hellmann et al 2002). Chemical weakening has been demonstrated for Eldfisk (Kallesten et al 2021a) and Dan field reservoir chalk (Amour et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Reaction Kinetics Determined from Coreflooding and Steady-State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature

et al. 2022

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Summary A methodology is presented for determining reaction kinetics from coreflooding: A core is flooded with reactive brine at different compositions with injection rates varied systematically. Each combination is performed until steady state, when effluent concentrations no longer change significantly with time. Lower injection rate gives the brine more time to react. We also propose shut-in tests where brine reacts statically with the core for a defined period and then is flushed out. The residence time and produced brine composition are compared with the flooding experiments. This design allows characterization of the reaction kinetics from a single core. Efficient modeling and matching of the experiments can be performed as the steady-state data are directly comparable to equilibrating the injected brine gradually with time and do not require spatial and temporal modeling of the entire dynamic experiments. Each steady-state data point represents different information that helps constrain parameter selection. The reaction kinetics can predict equilibrium states and time needed to reach equilibrium. Accounting for dispersion increases the complexity by needing to find a spatial distribution of coupled solutions and is recommended as a second step when a first estimate of the kinetics has been obtained. It is still much more efficient than simulating the full dynamic experiment. Experiments were performed injecting 0.0445 and 0.219 mol/L MgCl2 into Stevns Klint (Denmark) and Kansas (USA) chalks at 100 and 130°C (North Sea reservoir temperature). Injection rates varied from 0.25 to 16 pore volume per day (PV/D), while shut-in tests provided equivalent rates down to 1/28 PV/D. The results showed that Ca2+ ions were produced and Mg2+ ions retained (associated with calcite dissolution and magnesite precipitation, respectively). This occurred in a substitution-like manner, where the gain of Ca was similar to the loss of Mg2+. A simple reaction kinetic model based on this substitution with three independent tuning parameters (rate coefficient, reaction order, and equilibrium constant) was implemented together with advection to analytically calculate steady-state effluent concentrations when injected composition, injection rate, and reaction kinetic parameters were stated. By tuning reaction kinetic parameters, the experimental steady-state data were fitted efficiently. The parameters were determined to be relatively accurate for each core. The roles of reaction parameters, pore velocity, and dispersion were illustrated with sensitivity analyses. The determined reaction kinetics could successfully predict the chemical interaction in reservoir chalk and outcrop chalk containing oil with strongly water-wet or mixed-wet state. The steady-state method allows computationally efficient matching even with complex reaction kinetics. Using a comprehensive geochemical description in the software PHREEQC, the kinetics of calcite and magnesite mineral reactions were determined by matching the steady-state concentration changes as function of (residence) time. The simulator predicted close to the identical production of Ca as loss of Mg. The geochemical software predicted much higher calcite solubility in MgCl2 than observed at 100 and 130°C for Stevns Klint and Kansas. The methodology supports reactive flow modeling in general, but especially oil-bearing chalk reservoirs, which are chemically sensitive to injected seawater in terms of wettability and rock strength.

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Water-Weakening and Time-Dependent Deformation of Organic-Rich Chalks

et al. 2023

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The Ghareb Formation is a shallowly buried porous chalk in southern Israel that is being considered as a host rock for a geologic nuclear waste repository. Setup and operation of a repository will induce significant mechanical, hydrological and chemical perturbations in the Ghareb. Developing a secure repository requires careful characterization of the rock behavior to different loads. To characterize hydromechanical behavior of the Ghareb, several short- and long-term deformation experiments were conducted. Hydrostatic loading tests were conducted both dry and water-saturated, using different setups to measure elastic properties, time-dependent behavior, and permeability. A set of triaxial tests were conducted to measure the elastic properties and rock strength under differential loading at dry and water-saturated conditions. The hydrostatic tests showed the Ghareb began to deform inelastically around 12–15 MPa, a relatively low effective pressure. Long-term permeability measurements demonstrated that permeability declined with increasing effective pressure and was permanently reduced by ~ 1 order of magnitude after unloading pressure. Triaxial tests showed that water saturation significantly degrades the rock properties of the Ghareb, indicating water-weakening is a significant risk during repository operation. Time-dependent deformation is observed during hold periods of both the hydrostatic and triaxial tests, with deformation being primarily visco-plastic. The rate of deformation and permeability loss is strongly controlled by the effective pressure as well. Additionally, during holds of both hydrostatic and triaxial tests, it is observed that when water-saturated, radial strain surpassed axial strain when above effective pressures of 13–20 MPa. Thus, deformation anisotropy may occur in situ during operations even if the stress conditions are hydrostatic when above this pressure range.

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Validation study of water weakening research from outcrop chalks performed on Eldfisk reservoir cores

Cited by 9 publications

References 27 publications

Thermodynamic Analysis of the Temperature Effect on Calcite Surface Reactions in Aqueous Environments

Thermodynamic Analysis of the Temperature Effect on Calcite Surface Reactions in Aqueous Environments

Reaction Kinetics Determined from Coreflooding and Steady-State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature

Water-Weakening and Time-Dependent Deformation of Organic-Rich Chalks

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