From Carbon Sequestration Initiative

Contents 1 MS³ Overview 2 MS³ Projects 2.1 Micromodel Pore-Scale Studies of Caprock-Sealing Efficiency and Trapping Mechanisms 2.2 Multiscale Investigation of CO2 Behavior in Subsurface Under Extreme Conditions 2.3 Computational Framework for Diagnostics, Validation, and Intercomparison of Numerical Simulators for Geologic Sequestration 2.4 Predicting the Feasibility of Geologic Co-Sequestration of CO2, SOx and NOx Under a Broad Range of Conditions 2.5 Development of Coupled Flow, Thermal and Geomechanical Capability for Carbon Sequestration

MS³ Overview

MS³ will address the following scientific challenges in simulation:

• representation of chemistry in simulators when CO₂ is the solvating fluid
• full coupling of geochemistry, hydrology, and geomechanics within simulators
• transition from equations of fluid flow (Navier-Stokes flow) in an individual pore to the Darcy equation at larger scales.

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MS³ Projects

Micromodel Pore-Scale Studies of Caprock-Sealing Efficiency and Trapping Mechanisms

PIs: Mart Oostrom, Jay Grate, Changyong Zhang, SK Sundaram

Supercritical carbon dioxide (scCO₂) sequestration in deep saline aquifers or reservoirs is, to a large extent, affected by porous medium properties, fluid properties, and interfacial interactions. Interfacial interactions at fluid-fluid and fluid-mineral interfaces include capillarity, mass transfer, interfacial tension, and wettability. Data related to these interactions are scarce and fundamental knowledge of displacement processes is limited. To improve our understanding of subsurface scCO₂ storage, pore-scale experimental and numerical studies of processes related to caprock-sealing efficiency and trapping are needed. The caprock-sealing efficiency is a measure of the capillary pressure at the caprock – reservoir interface that needs to be exceeded before scCO₂ can move into the caprock. The major trapping mechanisms include storage of free-phase gas through hydrodynamic and capillary trapping, dissolution in formation brines, and mineral trapping through geochemical reactions. Of these trapping mechanisms, at the reservoir scale, hydrodynamic and capillary trapping processes may occur on much smaller timescales than mineral and dissolution trapping. In this work we will complete a series of micromodel experiments at supercritical conditions addressing the following scientific challenges:

• roles that porous medium properties, fluid properties, and wettability (including contact angle hysteresis) play during hydrodynamic (primary) trapping, when scCO₂ displaces brine, and during capillary (secondary) trapping, when brine displaces scCO₂
• effects of fluid-fluid interfacial tension, pore-size geometry, and wettability on caprock-sealing efficiency
• relationships between capillary pressure, fluid saturation, relative permeability during pore-scale displacement processes.

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Multiscale Investigation of CO₂ Behavior in Subsurface Under Extreme Conditions

PIs: Alexandre Tartakovsky, Andres Marquez, Sebastien Kerisit, Guang Lin

Sequestration of carbon dioxide in deep geologic reservoirs is proved to be a viable way for stabilizing global atmospheric concentrations of greenhouse gases, providing the time needed to transition from principally fossil fuel energy sources to renewable alternatives. This project is addressing the fundamental challenge of understanding the properties and processes associated with complex and heterogeneous subsurface mineral assemblages comprising porous rock formations, and the equally complex fluids that may reside in and flow through those formations. Specifically, we will focus on the understanding of the geochemical interactions of the caprock with ambient water and supercritical and dissolved CO₂.

Existing field scale models of CO₂ sequestration rely heavily on constitutive relationships that describe interactions of different solid and liquid phases in subsurface. Since these relationships are not grounded in first principles, accuracy of constitutive relationships and field scale models is hard to estimate a priori. Pore-scale transport models have proved to be a valuable tool for estimating the constitutive relationships for non-reactive two-phase flows and to study the effect of complex pore-morphology on entrapment and dissolution of non-aqueous phases. We are developing multiscale multiphase flow and transport models to simulate a CO₂ behavior (flow and precipitation) in the caprock at the pore and sub-pore scales. This hybrid model will be able to bridge molecular dynamics (MD) surface chemistry models and pore-scale models and will be able to describe a complex behavior of CO₂ in subsurface in general and in the caprock, specifically. The hybrid model will serve as a basis for the upscaling of the CO₂ behavior from the fundamental scales to the scale of practical importance. ____________________________________________________________________________________

Computational Framework for Diagnostics, Validation, and Intercomparison of Numerical Simulators for Geologic Sequestration

PIs: Mark White, Peter Hui, Vicky Freedman, Diana Bacon

Important advancements have been made in numerical simulation codes for geologic sequestration since the last intercomparison of simulators was conducted seven years ago. The current standard for numerical simulator includes capabilities for predicting hydraulic trapping, nonisothermal conditions, transitions to subcritical conditions, ground-surface interactions, injection wells, geochemistry, coupled hydrology-geochemistry-geomechanics, heterogeneous basin-scale domains, and wettability transitions. These capabilities, contained in a suite of science-based simulators, are continuously being updated to analyze sequestration processes in deep saline reservoirs. This increasing complexity in numerical simulators requires frequent validation and intercomparison of simulators and should be a critical component of the code development process.

A computational environment, operating within the Geologic Software Simulation Suite (GS³) is being designed, developed, populated with data, and demonstrated for the diagnostics, validation, and intercomparison of numerical simulators for geologic sequestration of greenhouse gases in deep saline reservoirs. The following five products will be completed under this project: 1) computational framework for diagnosis and intercomparison; 2) a suite of validation problems and solutions; 3) observational data sets for model validation; 4) standardized documentation of code features and characteristics; and 5) systematic accounting of disagreements for validation problems. The simulator development community at other national laboratories and universities will be involved in the design and validation problem set. ____________________________________________________________________________________

Predicting the Feasibility of Geologic Co-Sequestration of CO₂, SO_x and NO_x Under a Broad Range of Conditions

PIs: Diana Bacon, Mark White, Yilin Fang, Steve Yabusaki

Geologic co-sequestration of emissions gases may be feasible in some geologic formations, greatly reducing the costs associated with post-emissions capture. In addition, recent studies have shown that co-sequestered gases may enhance mineralization in calcium-rich igneous and weathered igneous mineral systems. New tools are needed to predict the impact of geologic co-sequestration of CO₂, NO_x and SO_x on target formation and caprock hydraulic properties under a broad range of mineralogical and phase conditions.

Numerical simulation of the co-sequestration of CO₂, SO_x and NO_x into deep geologic reservoirs requires modeling complex, coupled hydrologic, chemical, and thermal processes, including multi-component, multi-fluid flow and transport, partitioning of CO₂, SO_x and NO_x into the aqueous phase, and chemical interactions with aqueous fluids and rock minerals. What is lacking is an approach that combines the physics of multi-component/multi-phase mixtures with the chemical effects of mineral dissolution and precipitation. Also lacking are modeling studies on the impacts of co-sequestration of NO_x. Although NO_x may form a smaller percentage of the flue gas, it forms a stronger acid and could have a significant impact on mineral dissolution and precipitation rates. A new simulator that incorporates all of these complex processes will be developed. This simulator will be used for a survey of the effects of co-sequestration under a wide range of reservoir hydrogeochemical conditions. ____________________________________________________________________________________

Development of Coupled Flow, Thermal and Geomechanical Capability for Carbon Sequestration

PIs: Yilin Fang, Zhijie Xu, Steven Yabusaki

One methodology for reducing greenhouse gas emitted by coal-fired power plants is to capture the gaseous CO2 effluent and inject it into deep geologic reservoirs as supercritical CO2. The long duration (~50 years), large volume (~1 MMT/y), and high pressure result in large displacements of pore fluids and large stress changes on natural fractures and faults. These alterations can damage the integrity of the caprock seal, reduce sequestration capacity, and initiate seismic activity. Geomechanical analyses of potential CO2 sequestration sites are critical to evaluate the overall suitability of the geological reservoir for safe CO2 injection, long-term subsurface containment of CO2 and associated risks. Such analyses rely on predicting the evolution of effective stresses in rocks and faults during CO2 injection. A highly scalable simulation capability will be needed to address such a problem.

In this project, we will incorporate a geomechanical model into the existing parallel subsurface nonisothermal, multiphase flow and reactive transport code (eSTOMP-CO2) to provide coupled geomechanical and multiphase flow capabilities for the suite of simulation tools. Enhanced discrete element methods at the mesoscale will be used to examine the structure-property relationship in and close to individual fractures, capture the relevant dominating micro-mechanisms that cannot be accurately treated at larger scales, and provide reliable and robust submodels for model integration. Methods will be developed to couple models at the mesoscale and continuum scale.

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