Towards quantifying subsurface methane emissions from energy wells with integrity failure

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

“…Overall, the presence of surface casing vent flows and gas migration are indicators of well integrity failures, which increase the potential for methane emissions and groundwater contamination. 13,14,16,20 Well integrity failures are not necessarily addressed through well plugging and can persist after the well is properly plugged. Plugged wells are wells that have been permanently sealed (plugged) within the wellbore along zones that are required to be protected by regulations (e.g., groundwater, coal seams, oil, and gas reservoirs).…”

“…12,13 Subsurface leakage pathways at oil and gas wells include the production tubing and annular spaces between and outside casings, which can lead to gas in the surface casing and gas migration through soil. 7,14 In Canada, surface casings are vented, leading to surface casing vent flows in the presence of subsurface leakage; in the U.S., surface casing vents tend to be closed, causing casing pressures to build up in the presence of leakage. 12 Gas migration represents outside-of-the-casing leakage into subsurface environments, including groundwater, and can lead to gas emissions at the ground surface from soils surrounding the wells.…”

“…Well integrity is the ability of wellbore barriers to contain production fluids within the wellbore and prevent uncontrolled subsurface leakage, groundwater contamination, and/or emissions. , Subsurface leakage pathways at oil and gas wells include the production tubing and annular spaces between and outside casings, which can lead to gas in the surface casing and gas migration through soil. , In Canada, surface casings are vented, leading to surface casing vent flows in the presence of subsurface leakage; in the U.S., surface casing vents tend to be closed, causing casing pressures to build up in the presence of leakage . Gas migration represents outside-of-the-casing leakage into subsurface environments, including groundwater, and can lead to gas emissions at the ground surface from soils surrounding the wells. , Gas migration and surface casing vent flows are indicators of wellbore integrity issues and require wellbore treatments such as cement squeezes and casing repair. ,− In contrast, methane emissions from the aboveground wellhead infrastructure often are relatively easy fixes, such as tightening of joints and replacement of parts, and are more likely to originate from the producing formation, indicating that plugging can reduce the emissions. Overall, the presence of surface casing vent flows and gas migration are indicators of well integrity failures, which increase the potential for methane emissions and groundwater contamination. ,,, …”

“…Gas migration represents outside-of-the-casing leakage into subsurface environments, including groundwater, and can lead to gas emissions at the ground surface from soils surrounding the wells. , Gas migration and surface casing vent flows are indicators of wellbore integrity issues and require wellbore treatments such as cement squeezes and casing repair. ,− In contrast, methane emissions from the aboveground wellhead infrastructure often are relatively easy fixes, such as tightening of joints and replacement of parts, and are more likely to originate from the producing formation, indicating that plugging can reduce the emissions. Overall, the presence of surface casing vent flows and gas migration are indicators of well integrity failures, which increase the potential for methane emissions and groundwater contamination. ,,, …”

Composition and Origin of Surface Casing Fluids in a Major US Oil- and Gas-Producing Region

“…Of these wells, over 900 000 are currently active . Interest in characterizing the environmental risks posed by oil and gas wells has grown substantially over the past decade. − Numerous studies have focused on monitoring groundwater ,− and air quality − near oil and gas operations to quantify the potential impacts of leakage from wells and their affiliated infrastructure. A subset of studies have also directly evaluated leakage at the wellhead. ,,,− Many of these efforts are field studies that focus on quantifying emissions from abandoned wells. ,,,, While leakage from abandoned wells is a major potential source of fugitive emissions, recent work suggests that emissions from active wells may be higher in some regions …”