C-WELL: CO2 injection well integrity under operational thermo-hydro-mechanical loading
Why is this research needed?
Deep geological storage of captured CO2 in UK Continental Shelf saline aquifers and depleted oil and gas reservoirs is seen as a large-capacity long-term solution for emissions mitigation towards Net Zero 2050. To ensure the long-term effectiveness of geological storage, we must fully understand the risks posed by possible leakage pathways. Any leakage, and subsequent unplanned CO2 migration, may affect environmental and human health or offset the intended climate change mitigation if leaked CO2 reaches the atmosphere. In response to this, our proposal focuses on the leakage risk associated with the injection wells themselves, which penetrate the confining layers of rock and will be newly constructed wells or repurposed oil and gas wells. These wells will unavoidably carry engineering defects of varying extents that can further develop to pose a leakage risk both during and long after CO2 injection. A review of UK North Sea oil and gas wells indicated that single barrier failures of cement and/or tubulars (e.g. steel casing, production tubing) affect around one third of wells, suggesting that such failures will remain a key consideration as we move towards CO2 storage at scale.
Ultimately, our research programme has been developed to provide an improved understanding of damage to CO2 injection wells under periodic loading, how this damage may be mitigated using novel well cements, and the translation of well damage into storage integrity risk for operators and regulators.
What is this research investigating?
Our investigation specifically concerns damage evolution of a well’s annular cement sheath in terms of its cracking and debonding from the steel casing and rock formation. Crucially, such damage may occur without leading to significant upward migration of CO2, such as when the cracking or debonding remains locally isolated. Hence, our project will address not just the likelihood of damage occurring but also its evolution, potential mitigation using novel cements, and translation of findings into CO2 storage risk.
Central to achieving our aims will be:
(1) the development and application of a numerical model capable of predicting damage evolution of the composite well construction under operational loads,
(2) design and laboratory characterisation of novel well cements using secondary and bio-based materials as additives for enhanced thermal and mechanical properties, and
(3) interpretation of research findings to improve the decision-making capabilities of project partner Quintessa’s risk-based decision support software being used for CO2 storage risk assessment for potential operators and regulators.
The numerical model will be developed within COMSOL Multiphysics and will account for injection well behaviour under the combined effects of hydraulic, thermal, and mechanical loading. Thermal loading is particularly interesting for CO2 injection wells due to the potential for large thermal disturbances from the combined effect of cold CO2 injection, Joule-Thomson cooling as the CO2 expands, and periodic injection due to well shutdowns or batch CO2 transport by ship. Damage will be included in the numerical model using the phase-field method for cracking and the cohesive zone method (CZM) for debonding. The phase-field method is preferred for cracking primarily since it does not require a priori knowledge of the crack path, as for many alternative discrete methods, and has ease of extension to coupled problems, whereas the CZM is preferred for debonding since it is available via COMSOL’s contact physics and is ideally suited for interface modelling. The modelling work will use material properties of novel well cements from laboratory characterisation performed in our Concrete Materials and Technology Lab, with the new quantitative evidence then feeding into Quintessa’s decision support software.
This research aims to determine the susceptibility of CO2 injection wells to loss of integrity considering the influence of preexisting defects, damage evolution under periodic pressure and thermal loading, and novel cement sheath mix design.
What does the research hope to achieve?
For CCS Operators and Regulators :
A core strength of the proposed project will be the translation of research outcomes into project partner Quintessa’s CCS operations with respect to geological store siting, subsurface risk assessment, and selection of seals during well decommissioning. This will include implementing new quantitative evidence on well damage evolution to improve decision trees of the TESLA decision support software. Hence, there are clear links between the planned research and effective decision-making as the UK CCS sector continues to grow. We envisage that the research findings may be especially important to develop better understanding of likely practical limits on CO2 injection, such as injection rates and any requirement for heating before injection, especially following liquefied CO2 shipping as is being considered by some of the UK’s industrial clusters, including our project partner The Solent Cluster. Although simulation scenario development will be conducted with UK conditions in mind, the results from our project will be of direct relevance and translatable to other countries pursuing geological CO2 storage. Net Zero Technology Centre, as project partner, is also partner of the ACT3 project RETURN and will facilitate dissemination to operators and regulators in the UK and overseas alongside our engagement in international conferences, workshops, and policy events as detailed in the work plan within the Case for Support.
Researchers in the CCS Area and Beyond:
The proposed research brings together fundamental state-of-the-art knowledge from the fields of fracture and damage prediction, coupled thermo-hydro-mechanical (THM) modelling, and materials science. Besides being of broad interest to researchers across these vast multi-disciplinary areas, the outcomes of our work will be of greatest interest to those involved in CCS well engineering and storage security. There will also be interest from researchers working on applications with related physics and engineering, such as geothermal energy recovery, unconventional gas, and geological nuclear waste disposal.
This research is ongoing. Outputs will be shared below as they become available.