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Towards a Road Map for Mitigating the Rates and Occurrences of Long-Term Wellbore Leakage

Towards a Road Map for Mitigating the Rates and Occurrences of Long-Term Wellbore Leakage

Key findings:

  • “… the severity of the problem is not known because neither industry or oil and gas regulators are collecting the data.”
  • Natural gas seeping from 500,000 wellbores represent “a threat to environment and public safety” due to groundwater contamination, greenhouse gas emissions and explosion risks wherever methane collects in unvented buildings and spaces.
  • Plugging a faulty wellbore can cost $150,000, but in some problematic fields remediation costs can go as high as $600,000… but no guarantee of success.
  • 10% of all active and suspended gas wells in British Columbia (BC) now leak methane.
  • Some hydraulically fractured shale gas wells in BC have become super methane emitters that spew as much as 2,000 kilograms of methane a year.

ABSTRACT
Wellbore leakage, the seepage of natural gas through cement channels, casing annuli and behind the outermost casing string, is a problem reported across Canada. Wellbore leakage is a threat to the environment and public safety because of potential groundwater quality deterioration, contributions to greenhouse gas emissions and explosion risks if methane gas accumulates in inadequately ventilated areas. Leakage rates remain poorly quantified and remedial workovers are often challenging. Subsequent costs attributed to remedial workovers are often significant and present an economic strain on the industry as well as lost profit, reduced exploration and
production and, therefore, foregone royalties.

The purpose of this report has been to (1) identify persistent problems that result in wellbore leakage, (2) discuss potential approaches that appear to reduce the rates and occurrences of wellbore leakage, (3) describe methods for detecting and monitoring for wellbore leakage, and (4) discuss methods that have improved the efficiency of remedial workovers. Our motivation has been to outline the need for a Canadian Road Map for Wellbore Integrity that identifies future research and development (R&D) needs and identifies where the resources for such R&D might be found. Several key processes were identified that lead to the potential development of a leakage problem, working to either prevent the initial creation of an adequate cement seal or compromising the integrity of the cement sheath over time. The pathways produced by these processes include microannuli, channels and fractures due to poor mud removal, invasion by fluids during setting, stresses imposed by operations, cement shrinkage and casing corrosion.

Intermediate-depth formations, i.e., non-commercial gas zones, are often found to be the source of the buoyant fugitive gases that migrate up these pathways.

‘Doing it right the first time’ – i.e., creating a robust seal during primary cementation – was uniformly agreed by industry and regulators to be the best approach for reducing leakage development over the operational and post-operational lifetime of a well. Even if an adequately sealed wellbore was achieved during primary cementation, there remains the possibility that a leakage problem may develop due to corrosion or cement shrinkage. Therefore, in addition to ‘doing it right the first time’, new cement formulations, wellbore designs and abandonment approaches are needed. Wellbore monitoring needs to be improved by adopting the use of newer technologies and undergoing more thorough subsurface monitoring. Remedial workovers require advances in source identification (such as enhanced acoustic logging technology and isotopic fingerprinting) and alternative-sealing materials.

Wellbore leakage will likely only become worse with time as new wells are completed and old wells are abandoned. We recommend that a Canadian working group be established to develop a Road Map for Wellbore Integrity R&D to improve long-term wellbore integrity.

Hydraulic fracturing is perceived as a threat by many in the public, however, we believe that this concern is misplaced. Because of the real issues associated with greenhouse gas emissions and possible groundwater quality deterioration, we believe the more significant issue affecting the social license of the oil and gas industry is long-term wellbore integrity.

Bibliography:
Maurice B. Dusseault¹, Richard E. Jackson² and Daniel MacDonald¹
Towards a Road Map for Mitigating the Rates and Occurrences of Long-Term Wellbore Leakage.
University of Waterloo and Geofirma Engineering Ltd, May 12, 2015
¹ Department of Earth and Environmental Sciences, University of Waterloo
² Geofirma Engineering Ltd, Adjunct Professor, University of Waterloo

See also:
Andrew Nikiforuk, Canada’s 500,000 Leaky Energy Wells: ‘Threat to Public’. Badly sealed oil and gas wellbores leak emissions barely monitored, experts find. TheTyee.ca, 5 Jun 2014

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