Onshore Oil & Gas: Development of a Soil-Gas Monitoring Protocol for Assessing the Integrity of Decommissioned Wells

This project focuses on the use of soil-gas measurements to infer the integrity status of decommissioned onshore oil and gas wells in England. The integrity of buried decommissioned wells may be impaired by long-term degradation of well materials and seals, so that fugitive gas may be released through the overlying soil. Previous studies have measured soil-gas to try and infer integrity, but the measurements and inferences have been variable - so the integrity status of decommissioned wells remains uncertain. This project will develop and trial a protocol for making, interpreting and reporting soil-gas measurements, so that integrity status can be determined with more confidence. The project will start with a desk-based review of existing methods for measuring and interpreting soil-gas to infer decommissioned well integrity. An initial concept scheme for monitoring soil gas will then be developed and trialled at a minimum of 3 decommissioned production wells. The results of the review and trial will be used to develop a systematic monitoring protocol, which will include examples and advice on how it may be used to confirm the presence, or absence, of fugitive releases from decommissioned wells. The work will be summarised in a report that will make recommendations for improving the protocol, and will discuss how soil-gas monitoring compares with other techniques for assessing well integrity. It will also use expert judgement to comment on up to 3 related technical issues such as: (i) the role of low permeability surficial sediments in containing fugitive releases, (ii) the potential for using the protocol in other situations involving engineered sub-surface containment of gases. The protocol will focus on methane, but will include accompanying gases if they help to identify methane sources. The protocol will cover basic reconnaissance methods for "screening" decommissioned well sites, and more detailed "follow-up" methods for investigating "screened in" sites that may have fugitive releases from decommissioned wells. The protocol will consider the criteria to be used when deciding if monitoring at a site should escalate from reconnaissance to detailed investigation. It will distinguish between methane signals and variations due to (a) background levels, (b) natural soil processes including diurnal and seasonal cycles, (c) potential confounding sources e.g. agricultural emissions, and (d) any additional methane (i.e. additional to a-c) that may be a fugitive emission from a decommissioned well. The protocol will consider uncertainties so that a level of confidence can be associated with any assessment that fugitive methane is, or is not, present from a decommissioned well. It will also consider how the emission flux of methane from a decommissioned well may be determined from soil gas measurements.