Society and Industry recognize the need to minimize and document unwanted Green House Gases (GHG) emissions from oil fields. Here we present δ13C contour maps of fugitive gas for the WCSB, which ranks #4 in world hydrocarbon production. Natural gases form under a wide range of conditions which are reflected in their isotopic fingerprint. WCSB production gases range from biogenic (δ13C methane = -70‰, VPDB) to over mature shale gases (δ13C methane = -23‰) thus δ13C is an effective tool to identify the source depth of gas. The unwanted emissions are surface casing vent flows (SCVF) and ground migration (GM), which we have previously demonstrated originate mostly from formations shallower than the intended targets. Leaks from newer, multifractured horizontal wells also fit this pattern. We contour mapped δ13C methane, ethane and propane of 2800 SCVF, and 1200 GM gases across the WCSB. The maps reveal both regional and local trends in the isotope fingerprint of fugitive gas. Leaks result from flaws in well completion and cementing. Inspection of the maps shows such failures are not random but are controlled by not only geology but also geomorphology and topography. The maps are powerful tools warning operators drilling new wells where to be extra careful cementing the formations known to be prone to leakage, thus minimizing the risk to the environment. Significant savings can be anticipated in the cost of remediating and abandoning clusters of wells. On average the WCSB contributes GHG from SCV’s with δ13C1 = 58.4 ± 8.6‰, δ13C2= - 41.5 ± 7.9‰, and δ13CO2 = -15.8 ± 7.9‰. The GM gas averages are δ13C1 = -57.3 ± 8.9‰, δ13C2= - 41.7 ± 7.5‰, and δ13CO2 = -34.3 ± 18.8 ‰, values in line with recent atmospheric measurements in WCSB. The small difference in methane values, but a large difference in CO2 values, between SCV and GM gases is due to bioalteration of gas in soils.

Regional variation of the isotopic fingerprint of fugitive gases across the Western Canada Sedimentary Basin (WCSB)

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.