Date of Award

January 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Nejma Djabelkhir

Abstract

Ensuring wellbore integrity during CO2 injection is a critical challenge in Carbon Capture and Storage (CCS), as failures at the casing-cement and cement-formation interfaces can create potential leakage pathways. This dissertation presents a multi-scale, physics-based investigation into well integrity risks, integrating finite element analysis (FEA), thermal-mechanical-poroelastic modeling, and transient stress analysis to evaluate cement sheath stability, fracture-driven stress localization, and microannulus formation under various CCS conditions.

A key novelty of this research is the development of a fully coupled thermal-mechanical-poroelastic FEA framework using COMSOL Multiphysics, a renowned industry-standard software for multiphysics simulations. This model enables a dynamic, time-dependent assessment of stress evolution during different CO2 injection phases, improving upon traditional studies that focus solely on simplified steady-state models distributions. The results indicate that thermal contraction from low-temperature CO2 injection amplifies localized stress concentrations, increasing the risk of cement debonding, radial cracking, and microannulus formation at cement interfaces. Compared to traditional elasticity-based methods, the Drucker-Prager plasticity model provides a more realistic representation of material behavior. By capturing nonlinear deformation effects, this approach allows for a more accurate assessment of cement and formation stability. Additionally, high-resolution stress mapping identifies interface-specific failure risks, enhancing risk evaluation for caprock integrity and long-term CO2 storage.

This dissertation also introduces a novel approach to wellbore integrity assessment in fractured reservoirs, incorporating thermal, mechanical, and chemical interactions to evaluate CO2 injection effects under more realistic conditions. Unlike traditional models that assume homogeneous formations, this study quantifies how fracture networks influence stress redistribution, revealing that fractures increase localized failure risks and alter stress paths near the cement sheath. Furthermore, CO2 interactions with residual fluids (oil/water) cause acid-induced cement degradation, particularly at the cement-casing and cement-formation interfaces. The study confirms that fracture-concentrated acidic fluid pathways accelerate cement weakening, emphasizing the need for fracture-aware well integrity strategies for CCS. In comparison with conventional models, COMSOL Multiphysics provided a more accurate representation of fracture-driven stress changes.

A key contribution of this work is the development of a microannulus evolution model, which improves upon traditional resistor-based temperature models by employing a finite-difference method (FDM) for transient thermal behavior. The approach captures more accurately thermal stress cycles and their effects on wellbore integrity than standard analytical models, which cannot account for temperature fluctuations before and after shut-in. The improved model provides a robust framework for evaluating the integrity of CCS wells in varying thermal conditions.

Beyond active CO2 injection wells, this dissertation also examines well integrity risks in abandoned wells, where aging cement sheaths and mechanical degradation increase the likelihood of CO2 migration. By analyzing casing expansion, cement shrinkage, and zonal isolation failures, this study provides quantitative insights into long-term well integrity management and proposes enhanced cement design strategies to reduce long-term leakage risks.

By bridging reservoir-scale stress distribution with localized failure mechanisms, this dissertation advances CO2 well integrity assessment, offering:

  • Quantitative guidelines for cement optimization and failure mitigation
  • More realistic predictions of CO2-induced stress changes in fractured reservoirs
  • A refined understanding of transient thermal effects on microannulus formation
  • Improved risk assessment frameworks for active and abandoned CCS wells
  • Practical recommendations for well integrity regulations and long-term CO2 storage safety

The findings contribute to safer long-term CO2 storage, enhance predictive failure models, and support the development of advanced well integrity management strategies for carbon storage and enhanced oil recovery (EOR) applications.

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Available for download on Friday, June 05, 2026

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