Research — Wellbore Integrity and Leakage
Wellbore Leakage Study – “Towards a Road Map for Mitigating the Rates and Occurrences of Long-Term Wellbore Leakage”
Click here for the final report of the uWaterloo/Geofirma Wellbore Integrity report. Pdf may not view properly in the Firefox browser. This paper in Groundwater, which was co-authored by Richard Jackson, also summarises the issues of wellbore integrity and unconventional gas extraction.
The report conclusions can be summarized as:
- Wells that slowly seep gas upwards outside the casing because of inadequate primary cementation, and because there is a source of gas (generally a thin, undepleted and non-commercial gassy formation at intermediate depth), are commonplace. Slow seepage can develop many years after a successful well abandonment procedure. The seepage gas is usually close to 100% – methane.
- Because methane is not a toxic gas and the geochemical deterioration products do not strongly effect human health, the issue of leaking wells appears to be a moderate public health issue only.
- However, leaky wellbores and the very long-term maintenance of wellbore integrity remain issues, for two major reasons
- Emission of greenhouse gases (methane, perhaps a small amount of ethane)
- Entry of methane into the shallow aquifers where it may undergo geochemical deterioration and degrade the quality of the groundwater making it unfit for human consumption
- There is a very low risk of damaging explosions if methane accumulates in an enclosed space (We know of only one such case in Canada and that was not due to gas-well drilling)
- Because the regulatory agencies do not require groundwater quality assessment and monitoring (using proper monitoring wells, although rural wells can give some useful information) nor surveillance of any abandoned wells after the abandonment guidelines have been met, the magnitude of the GHG emissions and the amount entering shallow aquifers are not known.
- The development of multi-well pads for shale gas development means that the overall impact from leaky wellbores will also be more localized, and hence easier to detect, but if well leakage continues to be an issue, multiple wells on one pad could mean greater local impact on groundwater around the pad.
- Because of GHG impacts, there is reason to pursue a nation-wide discussion of issues arising. This should involve all oil and gas regulatory agencies in Canada in order to minimize gas leakage and to determine what should be considered an acceptable gas leakage rate (given the widespread unregulated emission of methane by cattle).
For more information, please contact Richard Jackson, Principal.