Reducing oil and gas well leakage: a review of leakage drivers, methane detection and repair options

Abstract

Oil and gas wells (OGWs) with integrity failures can be a conduit for methane and contaminant leakage to groundwater aquifers, surface water bodies and the atmosphere. Recent reviews have addressed OGW leakage but focused on specific types of wells (conventional/unconventional) or specific geographic regions. Here, we conduct a literature review and focus on factors and policies affecting leakage of active and abandoned OGWs, studies quantifying OGW methane emissions, and leakage repair and emission reduction options. Of the 38 factors reviewed here in published literature, studies find that 15 (39%) factors, including geographic location, well deviation, casing quality and plugging status consistently affect OGW leakage. For 15 (39%) factors, including surface casing depth, well elevation and land cover, one or two studies show that they do not affect OGW leakage. For the remaining eight (21%) factors, including well age, studies show conflicting results. Although increased frequency of well monitoring and repair can lead to reduced OGW leakage, several studies indicate that monitoring and repair requirements are not always enforced. Moreover, we find that while 27 studies quantify OGW methane emissions to the atmosphere at the oil and gas wellhead scale, there still are major gaps in the geographical distribution of the collected data, especially for abandoned and orphaned wells. Although studies measuring abandoned wells may include measurements from orphaned wells, these measurements are not separated by well status (orphaned/abandoned), which is important for policy makers aiming to plug thousands of orphaned wells. To repair OGW leakage, we find that most studies focus on well cement and casing repair, and other studies focus on improving the cement mixture to avoid the need for repairs. Alternatives to cement and casing repair for methane emission reductions, such as soil methane oxidation to reduce leakage from OGWs may be effective, but their widespread applicability requires further study. Overall, our review of factors affecting OGW leakage can be used to guide OGW leakage monitoring and repair policies to target wells with high leakage potential, thereby reducing climate and environmental impacts.

Environmental risks and opportunities of orphaned oil and gas wells in the United States

“…Even for risks that we consider here, there are data gaps, such as in groundwater and surface water quality, air pollution, and health studies. There is also a need to better understand factors contributing to orphaned well leakage [60][61][62]. It is hoped that the BIL, in addition to plugging wells, will also result in data on environmental impacts, which can facilitate analysis of the environmental risks of both documented and undocumented orphaned wells.…”

Methane Emissions from Abandoned Oil and Gas Wells in Alberta and Saskatchewan, Canada: The Role of Surface Casing Vent Flows

“…Geographic regions have consistently been identified in a published literature as a factor that can impact leakage and emissions from oil and gas wells. 9 Therefore, we measured eight subprovincial regions from Estevan in southeastern Saskatchewan to Grand Prairie in northwestern Alberta (Figure 1). We found strong subprovincial and interprovincial variations.…”

“…We found strong subprovincial and interprovincial variations. Despite this, there still are provinces/states/ territories with ongoing or historical oil and gas production that have no published measurements such as Manitoba, Quebec, Northwest Territories, Alaska, and North Dakota, 9,27 and even where measurements are available (e.g., Ontario), they can be highly localized. 21 Because additional measurements of superhigh emitters can substantially change emission estimates, it may be worthwhile to explore opportunities for aerial or vehicle-based surveys to detect superhigh emitters, 11,28−30 which can then be followed up with component-specific measurements requiring site access.…”

“…8 There are many engineering/construction, geological, and policy factors linked to high emitters, and the geographical region, which encompasses all factors, has consistently been shown to be an important predictor of high emitters. 9 However, prior to this study, there have been no published direct measurements of abandoned oil and gas wells in Alberta and Saskatchewan, the provinces with 87% of all abandoned oil and gas wells in Canada. 10 Therefore to reduce uncertainties, improve inventory estimates, and inform mitigation strategies, additional measurements of methane emission rates from abandoned oil and gas wells in Canada, especially Alberta and Saskatchewan, are needed.…”

Methane Emissions from Non-producing Oil and Gas Wells and the Potential Role of Seismic Activity: A Case Study in Northeast British Columbia, Canada

“…This large range means that identifying the few high emitters is critical to mitigating overall methane emissions. Risk factors that have been considered include well age, well type, plugging status, and geographical region. ,,,− Although seismic activity has been identified as a possible driver for enhanced leakage and emissions from non-producing wells, , to our knowledge, a systematic study with field measurements evaluating the role of seismic activity has not been conducted.…”