Geochemical evaluation of CO2 injection into storage reservoirs based on case-studies in the Netherlands

AbstractOver the past few years several geochemical evaluations of CO2 storage in Dutch potential reservoirs are carried out, including predictions of the short- and long-term impact of CO2 on the reservoir using geochemical modelling. The initial mineralogy of the reservoir is frequently obtained from core analysis and is then used to compute the formation water composition. In this paper geochemical modelling with TOUGHREACT is used to predict and compare the short- and long-term geochemical impact of CO2 injection into three reservoirs. The mineralogical composition of these reservoirs is an assemblage based on commonly observed minerals from the Buntsandstein and Rotliegend formations. These formations contain potential onshore and offshore CO2 storage locations in the Netherlands. The results predict drying out and salt precipitation in the near-well area, due to water evaporation by the injected dry CO2. Several mineral transformations are predicted, dominated by the transformation of albite into dawsonite, thereby fixing CO2. Due to the relatively low density of dawsonite, the porosity significantly decreases, which can lead to a pore pressure increase. Disabling of dawsonite precipitation in the simulations, thereby taking into account the ongoing debate on dawsonite stability, only shows a small increase of the porosity. Future (experimental) work should be focused on dawsonite occurrence for accurate predictions of the long-term reservoir integrity

Modelling of long-term along-fault flow of CO2 from a natural reservoir

Geological sequestration of CO2 requires the presence of at least one competent seal above the storage reservoir to ensure containment of the stored CO2. Most of the considered storage sites are overlain by low-permeability evaporites or mudrocks that form competent seals in the absence of defects. Potential defects are formed by man-made well penetrations (necessary for exploration and appraisal, and injection) as well as (for mudrocks) natural or injection-induced fracture systems through the caprock. These defects need to be de-risked during site selection and characterisation. A European ACT-sponsored research consortium, DETECT, developed an integrated characterisation and risk assessment toolkit for natural fault/fracture pathways. In this paper we describe the DETECT experimental-modelling workflow, which aims to be predictive for fault-related leakage quantification, and its application to a field case example for validation. The workflow combines laboratory experiments to obtain single-fracture stress-sensitive permeabilities; single-fracture modelling for stress-sensitive relative permeabilities and capillary pressures; fracture network characterisation and modelling for the caprock(s); upscaling of properties and constitutive functions in fracture networks; and full compositional flow modelling at field scale. We focus the paper on the application of the workflow to the Green River Site in Utah. This is a rare case of leakage from a natural CO2 reservoir, where CO2 (dissolved or gaseous) migrates along two fault zones to the surface. This site provides a unique opportunity to understand CO2 leakage mechanisms and volumes along faults, because of its extensive characterisation including a large dataset of present-day CO2 surface flux measurements as well as historical records of CO2 leakage in the form of travertine mounds. When applied to this site, our methodology predicts leakage locations accurately and, within an order of magnitude, leakage rates correctly without extensive history matching. Subsequent history matching achieves accurate leak rate matches within a-priori uncertainty ranges for model input parameters

Molecular Exchange of CH₄ and CO₂ in Coal: Enhanced Coalbed Methane on a Nanoscale

Molecular Exchange of CH₄ and CO₂ in Coal: Enhanced Coalbed Methane on a Nanoscal

Using Reaktoro for mineral and gas solubility calculations with the Extended UNIQUAC model

The extended UNIQUAC model is a thermodynamic model able to estimate thermodynamic properties of aqueous electrolyte solutions under a wide range of temperature, pressure, and composition conditions. Thermodynamic properties include species activity coefficients, excess molar Gibbs energy, excess molar enthalpy, excess molar heat capacity. These properties are important for aqueous speciation calculations, mineral and gas solubility computations, chemical kinetic modeling of mineral dissolution and precipitation, and in reactive transport simulations considering chemically complex aqueous electrolyte solutions. In this paper we present a brief literature review on the extended UNIQUAC model, we report on its im-plementation in C++ in the Reaktoro framework for modeling chemically reactive systems, and we show its use from Python for computing mineral and gas solubilities in aqueous solutions at a wide range of temperature, pressure, and salinity conditions. We validated the calculations against experimental data and against results obtained through the software ScaleCERE implementing the extended UNIQUAC model. Our conclusion is that the extended UNIQUAC model has been successfully implemented into the Reaktoro framework, thereby providing a suitable activity model for geochemical and reactive transport modeling

Modelling of long-term along-fault flow of CO2 from a natural reservoir

Geological sequestration of CO2 requires knowledge of the flow properties of fault-related fracture networks in the low-permeability shale caprocks that overly most of the considered storage sites. A safe, sustainable and economical storage operation requires a profound understanding of these risks, recognising that quantification is challenging due to the many length and timescales involved and the very limited availability of data. The Green River site in Utah is a rare case of leakage from a natural CO2 reservoir, where CO2 (dissolved or gaseous) migrates along two fault zones to the surface. This provides a unique opportunity to understand CO2 leakage mechanisms and volumes along faults. A successful modelling of measured leakage rates will provide confidence in modelling approaches and will help select safe storage sites, de-risk storage operations and guide containment monitoring. Here, we present an integrated workflow to model the measured leakage rates and locations at this site. We combine laboratory experiments to obtain single-fracture stress-sensitive permeabilities; single-fracture modelling for stress-sensitive relative permeabilities and capillary pressures; fracture network characterisation and modelling for the primary and secondary caprocks; upscaling of properties and constitutive functions in fracture networks; and full compositional flow modelling at field scale modelling. Our results predict locations accurately and, within an order of magnitude, leakage rates correctly without extensive history matching. Subsequent history matching achieves accurate leak rate matches within a-priori uncertainty ranges for model input parameters