Measurement of methane emissions from abandoned oil and gas wells in Hillman State Park, Pennsylvania

Abandoned oil and gas wells, improperly plugged or unplugged, present a risk to current and future oil and gas development because they provide a potential pathway for unwanted gas and fluid migration to the surface. The appropriate emission factor for gaseous emissions from these wells is uncertain, as a limited number of studies have reported abandoned wells as a methane emissions source. A helicopter-based survey that mapped methane concentration and located wells by detecting magnetic anomalies was conducted in Hillman State Park in southwestern Pennsylvania. Although well finding via aerial survey was successful, elevated methane concentrations due to emissions from wells in the survey area were not detected by helicopter as abandoned wells were likely too small a source of methane to detect from elevations that helicopters fly at (tens of meters). Measurement of methane emission rates from 31 wells were collected using several techniques that are compared and evaluated for their effectiveness: Hi Flow sampler, field-portable flame ionization detector, infrared camera, dynamic flux chamber and bag sampling. Nine of the 31 wells were buried; average methane flux for these wells was not statistically different from the background. Mass flow rate from the remaining 22 wells ranged from non-detection (less than 0.09 kg CH₄/day) to 4.18 kg CH₄/day with a mean of 0.70 kg/well/day (median of 0.24 kg CH₄/day/well) and a sample standard of error of 0.21 kg CH₄/well/day. This emission factor, while not intended for exclusive use in developing a methane emissions inventory for abandoned oil and gas wells, contributes to the growing amount of methane emissions data for this source category. The results from the aerial survey, ground-based well location verification and emissions measurements, and the evaluation of measurement approaches described here, provide a comprehensive characterization of abandoned wells in one field that can inform future measurement studies.

未妥善封堵或完全未封堵的废弃油气井，会为有害气体与流体向地表运移提供潜在通道，进而对当前及未来的油气开发活动构成威胁。由于目前仅有少量研究将废弃油气井列为甲烷排放源，因此此类井的气体排放适用排放因子仍未明确。研究团队在宾夕法尼亚州西南部的希尔曼州立公园（Hillman State Park）开展了一项航空调查：通过探测磁异常来绘制甲烷浓度分布图并定位油气井。尽管航空勘测成功定位了部分油气井，但此次勘测并未检测到研究区域内井体排放导致的甲烷浓度升高——这是因为废弃油气井的甲烷排放量过低，而直升机飞行高度（数十米）使得机载设备无法捕捉到此类排放信号。研究团队采用多种技术对31口井的甲烷排放速率进行了测量，并对各技术的有效性开展对比评估，所使用的方法包括：高流量采样器（Hi Flow sampler）、现场便携式火焰离子化检测仪（field-portable flame ionization detector）、红外热像仪（infrared camera）、动态通量箱（dynamic flux chamber）以及袋式采样法（bag sampling）。31口井中有9口为掩埋状态，这类井的平均甲烷通量与背景值无统计学显著差异。其余22口井的质量流率范围为未检出（低于0.09 kg CH₄/日）至4.18 kg CH₄/日，平均排放速率为0.70 kg·井⁻¹·日⁻¹（中位数为0.24 kg CH₄·井⁻¹·日⁻¹），样本标准误为0.21 kg CH₄·井⁻¹·日⁻¹。尽管本研究得到的排放因子并非专为废弃油气井甲烷排放清单编制所设计，但它为该源类别的甲烷排放数据集补充了更多实测数据。本次航空勘测、井址地面验证以及排放速率测量的结果，结合对测量方法的评估，实现了对某一研究区域内废弃油气井的全面特征刻画，可为后续相关测量研究提供参考依据。