Civil Engineering ETDs


Steven Gomez

Publication Date



Subsurface geologic formations used for extracting resources such as oil and gas can subsequently be used as a storage reservoir for the common greenhouse gas CO2, a concept known as Carbon Capture and Storage (CCS). Pre-existing wellbores penetrate the reservoirs where supercritical CO2 is to be injected. These wellbores can potentially be a pathway for contamination if CO2 leaks through wellbore flaws to an overlying aquifer or the atmosphere. Characterizing wellbore integrity and providing zonal isolation by repairing these wellbore flaws is of critical importance to the long-term isolation of CO2 and success of CCS. This research aims to characterize the microannulus region of the cement sheath-steel casing interface in terms of its compressibility and permeability, as well as understand the mechanical behavior of a flaw upon repairing it with an epoxy nanocomposite material. Numerical models are used to analyze stress and displacement conditions along the casing-cement interface. These numerical results provide excellent agreement with closed-form elastic solutions. Models with flaws of varying dimensions along the casing-cement interface were then developed to describe the microannulus region. The mechanical response of the microannulus region is studied under flawed and repaired conditions; repair materials including an epoxy repair material and cement. A joint model is used to describe the hydraulic aperture of the microannulus region, whose mechanical stiffness is altered in response to the imposed stress state across the joint interface. The aperture-stress behavior is based upon laboratory measurements of hydraulic aperture (interpreted from flow measurements) as a function of imposed stress conditions. This investigation found that the epoxy wellbore seal-repair material exhibits a mechanical response desired in the behavior of a flawed wellbore repair material, that microannulus permeability can satisfactorily be described by a joint model, and that the constitutive model imposed in a numerical simulation can play a significant role in the solution behavior and agreement to experimental data. Recommendations for future work include an application of the joint model with a thermally active large-scale reservoir coupled with pore pressure caused by dynamic CO2 injection and subsequent microannulus region affects.


wellbore, microannulus, nanocomposite, CO2 sequestration, numerical modeling, fracture, zonal isolation, Carbon Capture and Storage (CCS), joint model, permeability


This work is supported by the Department of Energy under Award Number DE-FE0009562. Sandia National Laboratories is a multi-program laboratory managed and oper- ated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corpora- tion, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND Number: 2013-6867 C.

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Advisor

Stormont, John

First Committee Member (Chair)

Taha, Mahmoud

Second Committee Member

Matteo, Edward

Third Committee Member

Sobolik, Steve