Graduation Year

2025

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Jeffrey Cunningham, Ph.D.

Committee Member

Mahmood Nachabe, Ph.D.

Committee Member

Eric Sonnenthal, Ph.D.

Keywords

Carbon Sequestration, CCS, TOUGHREACT, TOUGH, Climate Change

Abstract

Carbon capture and storage (CCS) is a strategy for mitigating climate change by reducing greenhouse gas emissions from large stationary sources like fossil-fuel-fired power stations. One method of CCS involves carbon dioxide (CO2) sequestration in deep saline aquifers, where supercritical CO2 is injected into an aquifer. The success of such projects depends on accurate predictions of CO2 behavior within the subsurface, which are obtained through numerical simulations.

TOUGHREACT, a renowned simulation tool, models subsurface fluid flow, geochemical interactions, and solute transport, providing insights into the feasibility of CO2 sequestration projects. A critical aspect of these simulations is the apportioning of CO2 injection across different vertical layers of the aquifer. There exist hydrogeological algorithms (referred to in this thesis as the “k-h method”) that are used to estimate CO2 distribution based on overall injection rate, layer thickness, and horizontal permeability. However, this “k-h” method neglects the effects of wellbore pressure dynamics and pressure gradients within the injection well and surrounding aquifer. Omitting these factors introduces uncertainty in the accuracy of simulation results. This uncertainty could potentially affect the accuracy of key feasibility metrics for CCS projects. The objective of this research then is to determine whether it is necessary to account for the effects of wellbore pressure and fluid flow within the injection well while simulating CO2 injection into deep saline aquifers, or whether these factors can be safely ignored. This determination will ensure that simulation results from TOUGHREACT are accurate and interpreted appropriately when assessing the feasibility of a proposed CCS project.

Through a set of TOUGHREACT simulations, I have determined that it is unacceptable to ignore wellbore effects during CO2 injection into narrow injection wells that are screened across the entire injection zone. However, if the wellbore is sufficiently wide, and/or if the well is screened only in the bottom portion of the injection zone, then it might be acceptable to ignore wellbore effects and use simpler simulation methods.

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