Johnson Derek, Heltzel Robert, Oliver Dakota
Center for Alternative Fuels, Engines, and Emissions, Mechanical and Aerospace Engineering Department, West Virginia University, P.O. Box 6106, Morgantown, West Virginia 26506, United States.
ACS Omega. 2019 Feb 19;4(2):3708-3715. doi: 10.1021/acsomega.8b03246. eCollection 2019 Feb 28.
Studies have aimed to quantify methane emissions associated with the growing natural gas infrastructure. Quantification is completed using direct or indirect methods-both of which typically represent only a snapshot in time. Most studies focused on collecting emissions data from multiple sites to increase sample size, thus combining the effects of geospatial and temporal variability (spatio-temporal variability). However, we examined the temporal variability in methane emissions from a single unconventional well site over the course of nearly 2 years (21 months) by conducting six direct quantification audits. We used a full flow sampling system that quantified methane mass emissions with an uncertainty of ±10%. Results showed significant temporal variation in methane mass emissions ranging from 86.2 to 4102 g/h with a mean of 1371 g/h. Our average emissions rate from this unconventional well pad tended to align with those presented in the literature. The largest contributor to variability in site emissions was the produced water tank which had emissions rates ranging from 17.3 to 3731 g/h. We compared our methane mass emissions with the total production for each audit and showed that relative methane loss rates ranged from 0.002 to 0.088% with a mean of 0.030%, typically lower than reported by the literature, noting that our data excluded well unloadings. We examined natural gas production, water production, and weather conditions for trends. The strongest correlation was between methane emissions and historical water production. Our data shows that even for a single site, a snapshot in time could significantly over-predict (3×) or under-predict (16×) methane emissions as compared to a long-term temporal average.
多项研究旨在量化与不断发展的天然气基础设施相关的甲烷排放量。排放量的量化是通过直接或间接方法完成的，这两种方法通常都只是反映某个时间点的情况。大多数研究集中于从多个地点收集排放数据以增加样本量，从而综合地理空间和时间变化（时空变化）的影响。然而，我们通过进行六次直接量化审计，研究了一个非常规井场在近2年（21个月）内甲烷排放的时间变化情况。我们使用了一个全流量采样系统，该系统对甲烷质量排放量进行量化，不确定度为±10%。结果显示，甲烷质量排放量存在显著的时间变化，范围为86.2至4102克/小时，平均为1371克/小时。我们这个非常规井场的平均排放率往往与文献中给出的排放率一致。该井场排放变化的最大贡献者是采出水罐，其排放率范围为17.3至3731克/小时。我们将每次审计的甲烷质量排放量与总产量进行了比较，结果表明，甲烷相对损失率范围为0.002%至0.088%，平均为0.030%，通常低于文献报道，需要注意的是我们的数据不包括井的卸载量。我们研究了天然气产量、水产量和天气状况的趋势。甲烷排放与历史水产量之间的相关性最强。我们的数据表明，即使对于单个井场，与长期时间平均值相比，某个时间点的情况可能会显著高估（3倍）或低估（16倍）甲烷排放量。
