Search

Abstract Recent studies have reported methane (CH 4) emissions from abandoned and active oil and gas infrastructure across the United States, where measured emissions show regional variability. To investigate similar phenomena in West Virginia, we measure and characterize emissions from abandoned and active conventional oil and gas wells. In addition, we reconcile divergent regional CH 4 emissions estimates by comparing our West Virginia emissions estimates with those from other states in the United States. We find the CH 4 emission factors from 112 plugged and 147 unplugged wells in West Virginia are 0.1 g CH 4 h−1 and 3.2 g CH 4 h−1, respectively. The highest emitting unplugged abandoned wells in WV are those most recently abandoned, with the mean emission of wells abandoned between 1993 and 2015 of 16 g CH 4 h−1 compared to the mean of those abandoned before 1993 of 3 × 10−3 g CH 4 h−1. Using field observations at a historic mining area as a proxy for state-wide drilling activity in the late 19th/early 20th century, we estimate the number of abandoned wells in WV at between 60,000 and 760,000 wells. Methane emission factors from active conventional wells were estimated at 138 g CH 4 h−1. We did not find an emission pattern relating to age of wells or operator for active wells, however, the CH 4 emission factor for active conventional wells was 7.5 times larger than the emission factor used by the EPA for conventional oil and gas wells. Our results suggest that well emission factors for active and abandoned wells can vary within the same geologic formation and may be affected by differences in state regulations. Therefore, accounting for state-level variations is critical for accuracy in greenhouse gas emissions inventories, which are used to guide emissions reduction strategies. Graphical abstract Unlabelled Image Highlights • WV CH 4 emissions of plugged, unplugged and active wells were 0.1, 3.2 and 138 g CH 4 h−1. • Methane emissions were higher at active wells compared to plugged and unplugged abandoned wells. • We estimate the number of abandoned wells in WV at between 60,000 and 760,000. • Average emission from active wells was 7.5 times larger than the EPA emission factor. • Well emission can vary along geologic formation and be affected by state regulations. [ABSTRACT FROM AUTHOR]

Since 1850 the atmospheric mixing ratio of methane (CH 4), a potent greenhouse gas, has doubled. This increase is directly linked to an escalation in emissions from anthropogenic sources. An inexpensive means to identify and monitor CH 4 emission sources and evaluate the efficacy of mitigation strategies is essential. However, sourcing reliable, low-cost, easy-to-calibrate sensors that are fit for purpose is challenging. A recent study showed that CH 4 mixing ratio data from a low-power, low-cost CH 4 sensor (Figaro TGS2600) agreed well with CH 4 mixing ratios measured by a high precision sensor at mixing ratios between 1.85 ppm and 2 ppm. To investigate, as a proof of concept, if this low-cost sensor could be used to measure typical ambient CH 4 mixing ratios, we operated a TGS2600 in conjunction with a Los Gatos Ultra-portable Greenhouse Gas Analyzer (UGGA) in controlled laboratory conditions. We then explored the sensor's long-term reliability by deploying the TGS2600 near an onshore gas terminal to calculate emissions from May to July 2018. Our initial studies showed that previously published linear algorithms could not convert TGS2600 output to CH 4 mixing ratios measured by the UGGA. However, we derived a non-linear empirical relationship that could be used to reliably convert the output of a TGS2600 unit to CH 4 mixing ratios over a range of 1.85–5.85 ppm that agree to a high-precision instrument output to ±0.01 ppm. Our study showed that the TGS2600 could be used to continuously measure variability in CH 4 mixing ratios from 1.82 to 5.40 ppm for three months downwind of the gas terminal. Using a simplified Gaussian Plume approach, these mixing ratios correspond to an emission flux range of 0–238 g CH 4 s−1, with average emission of 9.6 g CH 4 s−1 from the currently active North Terminal and 1.6 g CH 4 s−1 from the decommissioned South Terminal. Our work here demonstrates the feasibility of utilizing a low-cost sensor to detect methane leakage at concentrations close to ambient background levels, as long as the device is routinely calibrated with an accurate reference instrument. Having a widely deployed network of such low-cost CH 4 sensors would allow improved identification, monitoring and mitigation of a variety of CH 4 emissions. • Low-cost, low-power methane sensor is investigated for use in a measurement network. • Calibration shows a non-linear response to methane change between 2 and 6 ppm. • Long-term deployment shows sensor is reliable and can be used to measure autonomously. • Sensor can detect methane close to background but requires routine calibration. • A network of low-cost sensors could help identification and mitigation of methane. [ABSTRACT FROM AUTHOR]

Recent measurements of methane emissions from abandoned oil/gas wells show that these wells can be a substantial source of methane to the atmosphere, particularly from a small proportion of highemitting wells. However, identifying high emitters remains a challenge. We couple 163 well measurements of methane flow rates; ethane, propane, and n-butane concentrations; isotopes of methane; and noble gas concentrations from 88 wells in Pennsylvania with synthesized data from historical documents, field investigations, and state databases. Using our databases, we (i) improve estimates of the number of abandoned wells in Pennsylvania; (ii) characterize key attributes that accompany high emitters, including depth, type, plugging status, and coal area designation; and (iii) estimate attribute- specific and overall methane emissions from abandoned wells. High emitters are best predicted as unplugged gas wells and plugged/vented gas wells in coal areas and appear to be unrelated to the presence of underground natural gas storage areas or unconventional oil/gas production. Repeat measurements over 2 years show that flow rates of high emitters are sustained through time. Our attribute-based methane emission data and our comprehensive estimate of 470,000-750,000 abandoned wells in Pennsylvania result in estimated state-wide emissions of 0.04-0.07 Mt (1012 g) CH4 per year. This estimate represents 5-8% of annual anthropogenic methane emissions in Pennsylvania. Our methodology combining new field measurements with data mining of previously unavailable well attributes and numbers of wells can be used to improve methane emission estimates and prioritize cost-effective mitigation strategies for Pennsylvania and beyond. [ABSTRACT FROM AUTHOR]