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Fugitive emissions of methane from abandoned, decommissioned oil and gas wells ... al., 2014); the fugitive emission of CH4 to the atmosphere (Caulton et al., ...
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Fugitive emissions of methane from abandoned, decommissioned oil and gas wells

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Boothroyd, I.M.1, Almond S.1, Qassim, S.M.,1 Worrall, F1*. and Davies, R. J.,2

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1. Centre for Research into Earth Energy Systems (CeREES), Department of Earth

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Sciences, Durham University, Science Labs, Durham DH1 3LE, UK.

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2. School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon

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Tyne, Tyne and Wear, NE1 7RU, UK.

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Abstract

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This study considered the fugitive emissions of methane (CH4) from former oil and gas

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exploration and production wells drilled to exploit conventional hydrocarbon reservoirs

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onshore in the UK. This study selected from the 66% of all onshore wells in the UK which

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appeared to properly decommissioned (abandoned) wells came from 4 different basins and

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were between 8 and 79 years old. The soil gas above each well was analysed and assessed

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relative to a nearby control site of similar land use and soil type. The results showed that of

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the 102 wells considered 30% had soil gas CH4 at the soil surface that was significantly

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greater than their respective control. Conversely, 39% of well sites had significant lower

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surface soil gas CH4 concentrations than their respective control. We interpret elevated soil

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gas CH4 concentrations to be the result of well integrity failure, but do not know the source of

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the gas nor the route to the surface. Where elevated CH4 was detected it appears to have

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occurred within a decade of it being drilled. The flux of CH4 from wells was 364 ± 677 kg

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CO2eq/well/yr with a 27% chance that the well would have a negative flux to the atmosphere *

Corresponding author: [email protected]; tel. no: +44 (0)191 334 2295; fax no: +44 (0)191 334 2301

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independent of well age. This flux is low relative to the activity commonly used on

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decommissioned well sites (eg. sheep grazing), however, fluxes from wells that have not been

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appropriately decommissioned would be expected to be higher.

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Keywords: well integrity; greenhouse gases; shale gas

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1. Introduction

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There are numerous environmental concerns surrounding the oil and gas industry, including

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the production and discharge of wastewater leading to environmental violations (Manda et

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al., 2014); the fugitive emission of CH4 to the atmosphere (Caulton et al., 2014; Miller et al.,

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2013); and contamination of groundwater supplies (Rivard et al., 2014). It has been suggested

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that hydraulic fracturing, as a means of exploiting unconventional hydrocarbon resources,

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could be a cause of elevated CH4 concentrations in groundwater (Osborn et al., 2011), yet it

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has been argued that rather than being caused by hydraulic fracturing, groundwater

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contamination could have been caused by other processes, one of which is well integrity

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failure (Davies, 2011). Well integrity refers to the zonal isolation of liquids and gases (King

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and King, 2013) and failure occurs when cement and/or casing barriers fail, causing a loss of

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zonal isolation that creates pathways for the migration of fluids, including CH4, to

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