Understanding and Mitigating Leakage Pathways in Oil and Gas Well Cements

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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 percent of the total GHG emissions. Upstream oil and gas industry 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 the 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 with regard to 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. De-bonding can be caused by thermal stresses due to thermal cycling induced by injection of a relatively cold or hot fluid down the well. It may also be caused by mechanical loads due to changing in-situ stresses (caused by multi-stage hydraulic fracturing and re-fracturing, reservoir depletion or CO2 injection); by chemically active fluids; or by a combination of the above factors. Understanding the mechanism of leakage pathway formation is crucial for assessment and improvement of cement performance in oil and gas wells, whether it is producing or plugged and abandoned. Comprehensive experimental and numerical studies of the mechanisms of cement failure and de-bonding and how this impacts fluid movement through the cement microstructure are, therefore, proposed. Direct imaging and subsequent modeling of the cement pore structure, cement/casing, and cement/formation interfaces pre and post-failure, as proposed in this project, will allow for the design and development of robust cementing systems that can be used for more cost effective mitigation of fugitive methane emissions.