Geochemical Impacts
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  A three-dimensional, high-resolution digital stratigraphy has been constructed based on physical sedimentation data created from scanning a laboratory flume deposit; it exhibits detailed and multiscale sedimentary heterogeneity reflecting salient features of natural systems. By assuming different end-member mineral compositions for the stratigraphy, a comprehensive uncertainty analysis within a fully coupled simulation framework is being conducted to understand and quantify the sources of uncertainty that control the complex physicochemical phenomena accompanying carbon storage over multiple spatial and temporal scales. (University of Wyoming; DE-FE0009238) (click to enlarge)
   

The Geochemical Impacts key technology area seeks to understand geochemical processes associated with CO2 injection, and how chemical reactions impact physical processes in the storage formation, the caprock, the wellbore, and along potential release pathways like faults and fractures.

Description

Understanding and accounting for formation fluid-CO2-formation interactions is essential to the development of a subsurface analysis. Effects of chemical reactions induced by CO2 include changes in porosity and permeability of the injection zone; an overall drop in formation fluid pH, which might affect the stability of the target confining zone; and, reactions to form solid carbonate precipitates, which can chemically trap CO2 in place.

Research Agenda and Challenges

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Residual oil zone depiction via oil saturation profile for the Permian Basin as part of the UT Austin project in optimizing CO2 sweep efficiency based on the geochemical characteristics of candidate storage reservoirs. (DE-FE0024375) (click to enlarge)  

Study of chemical interactions between rock, CO2, and formation fluids is relevant to assess storage integrity, to evaluate behavior of injected CO2, and to guide monitoring during and after injection. Some of the storage integrity issues which can be addressed by reactive transport modeling of CO2 and other fluid flows in the subsurface include confinement in the injection zone, CO2 partitioning into the rock and fluid phases via mineralization and dissolution, and the impacts to groundwater from CO2 leakage.

Geochemical impacts research is needed to understand chemical processes related to CO2 storage, including aqueous speciation, dissolution/precipitation, microbial-mediated redox reactions, ion-exchange between solutions and minerals, and surface chemical reactions occurring at phase interfaces. All of these reactions will have impacts on the physical/chemical processes taking place in the storage formation and caprock and along potential release pathways. Computer simulations are used to model these impacts, and improvements are needed to improve the accuracy and computational efficiency of these models.

Research pathways for this key technology are:

  • By 2020: Assess geochemical changes related to CO2 injection and integrate results into basin-scale models. Studies are investigating mineralization rates, CO2-water interactions, and changes in microbial communities related to injection and integration into basin-scale models.

  • By 2030: Develop advanced, coupled, geochemical and bio-geochemical/fluid flow models for optimizing injection efficiency, reducing cost, and increasing certainty; and use these models to assess and mitigate geochemical impacts of injection in formations encountered in broad deployment projects.

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Storage GSRA Geochemical Impacts R&D Timeline (click to enlarge)

NETL-Supported Geochemical Impacts Research

NETL supports projects that are addressing research challenges within the Geochemical Impacts key technology area. Examples of projects supporting this key technology area include (1) development of efficient models of the coupling between CO2 injection and fault mechanical deformation; (2) development of high-resolution computational methods to better predict capillary and solubility trapping and application of models of fault poromechanics and CO2 migration and trapping to synthetic reservoirs; and (3) development of simulation and upscaling methodology that is generally applicable to sedimentary environments that are characterized by complex coupled physical and chemical processes.

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A preliminary high-resolution simulation of plume migration in a homogeneous, horizontal aquifer under the effect of convective dissolution trapping. The simulation employs the fluid properties of the analogue fluid system (water and propylene-glycol) and a very low value of the Rayleigh number (Ra = 1; 000). (Massachusetts Institute of Technology project DE-FE0009738)

The GSRA webpage offers links to detailed information on projects performing research in this area.