Experimental Investigation and Subsequent Modeling of the Cement Microstructure and Integrity of Cement/Casing and Cement/Formation Interfaces Under Downhole Stress Conditions

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Methane is a potent greenhouse gas (GHG) that is 25 times more powerful than carbon dioxide. In Canada, methane emissions make up about 15% of all GHG emissions. Upstream oil and gas facilities are Canada's largest industrial emitters of methane, releasing 44% of the country's total methane emissions. Within the upstream oil and gas industry, a significant fraction of methane emission results from fugitive leaks arising from surface casing vent flow (SCVF) and gas migration (GM). Bulk cement, as well as cement/casing and casing /rock interfaces, are likely to be the weak spots in oil and gas wells in terms of leakage and long term well integrity. Debonding of cement from casing and/or formation, and subsequent loss of zonal isolation, is a significant contributor to fugitive methane emissions from SCVF and GM in oil and gas wells. Understanding the mechanisms of leakage pathway formation is crucial for assessment and improvement of cement performance in oil and gas wells - whether the wells are producing or plugged and abandoned. Comprehensive experimental and numerical studies of the mechanisms of cement failure and debonding, and how these impact fluid movement through the cement microstructure, are therefore proposed. An Advanced Wellbore Simulator capable of investigating flow through cemented wellbore sections under realistic downhole conditions (i.e. 43 MPa and 120 °C) will be used to investigate the integrity of the cement body, as well as the cement/casing interfaces, under representative downhole stress conditions (i.e., cyclic pressure and thermal stress conditions). Nano-CT based digital image processing of downscaled samples simulating cement body and various interface conditions (e.g., cement-casing, cement-rock) will be used to analyze the effect of downhole stress conditions. This technique will be combined with a computational fluid dynamic modelling of formation fluid flow through the 3D microstructures of the samples. Together, this new methodology will assess the permeability of cemented wellbore sections, which represent potential microscale leakage pathways in a well. The experimental investigation and numerical model study proposed in this project will result in an improved understanding of the drivers behind fluid leakage (i.e. stresses creating microchannels along the cement/casing, cement/borehole interfaces and microfractures within the cement body). The results will allow for the design and development of new, more reliable barrier technologies that can be used for more cost-effective mitigation of fugitive methane emissions. As part of the Pan-Canadian Framework on Clean Growth and Climate Change, the Government of Canada reaffirmed its commitment to reduce GHG emissions 40-45% below 2012 levels by 2025. The proposed research is, therefore, well aligned with strategic direction of the Government of Canada's efforts to reduce GHG.