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Quantifying CH4 concentration spikes above baseline and attributing CH4 sources to hydraulic fracturing activities by continuous monitoring at an off-site tower
Atmospheric Environment ( IF 5 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.atmosenv.2020.117452
Sarah J. Russell , Chante’ D. Vines , Gil Bohrer , Derek R. Johnson , Jorge A. Villa , Robert Heltzel , Camilo Rey-Sanchez , Jaclyn H. Matthes

Abstract Hydraulic fracturing (hydrofracking) for natural gas has increased rapidly in the area of the Marcellus Shale in the last thirty years and estimates of CH4 emissions from hydrofracking operations are still uncertain. Previous studies on CH4 emissions at hydrofracking operations have used bottom-up approaches collected at discrete timepoints or discrete aerial surveys covering a wide spatial area, constraining the temporal scale of inference regarding these emissions. This project monitored atmospheric CH4 concentrations and stable carbon isotopes at a half-hourly temporal resolution from a 20-m tower downwind of a hydrofracking well pad in West Virginia for eighteen months. We collected four months of baseline observations prior to onsite well development to construct an empirical artificial neural-network model of baseline CH4 concentrations. We compared measured CH4 concentrations against the ANN-modeled CH4 baseline to identify CH4 concentration spikes that coincided with different stages of onsite well development, from the baseline period through fracking. CH4 concentration spikes were significantly more frequent than baseline conditions during the vertical drilling and fracking phases of operations. We found that the median magnitude of CH4 concentration spikes during the vertical drilling phase was 316% larger than that of the baseline phase, and the median magnitude of CH4 concentration spikes was 509% larger in the hydraulic stimulation (fracking) stage compared to the baseline phase. We also partitioned the sources of measured CH4 concentrations to biogenic ruminant and geologic shale gas isotopic signatures by measuring 13CH4 gas at high temporal resolution and using a source-partitioning 13CH4 model. The measured median value of half-hourly CH4 concentration spikes attributed to a geologic shale gas isotopic origin was 27% larger than the median CH4 concentration spikes attributed to ruminants, and the maximum half-hourly CH4 concentration spike attributed to shale gas was up to 179% higher than maximum CH4 concentration spike for ruminant-dominated half-hours. This study developed a framework for off-site, single tower measurements to identify CH4 concentration spikes associated with the phases of unconventional natural gas well development in a complex CH4 emissions airshed.

中文翻译:

通过在异地塔进行连续监测,量化高于基线的 CH4 浓度峰值并将 CH4 源归因于水力压裂活动

摘要 在过去的三十年里,马塞勒斯页岩地区的天然气水力压裂(水力压裂)迅速增加,水力压裂作业产生的 CH4 排放量估计仍然不确定。以前对加氢压裂作业中 CH4 排放的研究使用了在离散时间点收集的自下而上的方法或覆盖广泛空间区域的离散航空调查,从而限制了关于这些排放的推断的时间尺度。该项目从西弗吉尼亚州一个水力压裂井台下风向的 20 米塔以半小时的时间分辨率监测大气 CH4 浓度和稳定碳同位素 18 个月。我们在现场井开发之前收集了四个月的基线观察结果,以构建基线 CH4 浓度的经验人工神经网络模型。我们将测量的 CH4 浓度与 ANN 建模的 CH4 基线进行比较,以确定与现场油井开发的不同阶段(从基线期到压裂)一致的 CH4 浓度峰值。在垂直钻井和压裂作业阶段,CH4 浓度峰值明显高于基线条件。我们发现垂直钻井阶段 CH4 浓度峰值的中值幅度比基线阶段大 316%,水力增产(压裂)阶段 CH4 浓度峰值的中值幅度比基线大 509%阶段。我们还通过以高时间分辨率测量 13CH4 气体并使用源划分 13CH4 模型,将测量的 CH4 浓度来源划分为生物反刍动物和地质页岩气同位素特征。地质页岩气同位素来源的半小时 CH4 浓度峰值测量值比反刍动物的 CH4 浓度峰值中值大 27%,页岩气半小时 CH4 浓度峰值峰值高达 179 % 高于反刍动物占主导地位的半小时的最大 CH4 浓度峰值。本研究开发了一个用于场外单塔测量的框架,以识别与复杂 CH4 排放气域中非常规天然气井开发阶段相关的 CH4 浓度峰值。
更新日期:2020-05-01
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