Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2007 Main Mall, Vancouver, BC V6T 1Z4, Canada.
Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2007 Main Mall, Vancouver, BC V6T 1Z4, Canada.
Sci Total Environ. 2019 Feb 20;652:356-366. doi: 10.1016/j.scitotenv.2018.10.217. Epub 2018 Oct 16.
Global methane (CH) emissions are becoming increasingly important due to the contribution of CH to global warming. Leaking oil and gas wells can lead to subsurface CH gas migration (GM), which can cause both aquifer contamination and atmospheric emissions. Despite the need to identify and quantify GM at oil and gas well pads, effective and reliable monitoring techniques are lacking. In this field study, we used CH and carbon dioxide (CO) efflux measurements together with soil gas stable carbon isotopic signatures to identify the occurrence and to characterize the spatio-temporal migration of fugitive gas across 17 selected well pads in Northeastern British Columbia, Canada. At 13 of these sites, operators had previously reported the occurrence of GM; however, subsequent inspections based on visual, olfactory or auditory evidence only identified GM at two of these sites. Using the soil gas efflux method, evidence for GM was found at 15 of the 17 well pads with CH and CO effluxes ranging from 0.017 to 180μmolms(0.024 to 250gCHmd) and 0.50 to 32μmolms (1.9 to 122gCOmd), respectively. Stable carbon isotopic composition was assessed at 10 of the 17 well pads with 9 well pads showing evidence of GM. The isotopic values indicated that CH in soil gas was from the same origin as CH in the surface casing vent flow gas. There was no correlation between CH effluxes and the distance from the well head; an equal portion of elevated effluxes were detected >10m from the well head as were detected <5m from the well head. In addition, CH effluxes varied temporally with values changing by up to an order of magnitude over 2h. Although the study was carried out in Northeastern British Columbia, the results are applicable on a global scale, suggesting that inspections mostly based on visual evidence (e.g. bubbling at the well head) are not reliable for the identification of GM and, that infrequent survey measurements at predefined locations close to the well head may overestimate, underestimate or even miss CH effluxes. Repetitive and relatively densely spaced gas efflux measurements using a dynamic closed chamber method proved to be a useful tool for detecting GM.
由于甲烷（CH）对全球变暖的贡献，全球甲烷排放变得越来越重要。漏油油井和天然气井会导致地下 CH 气体迁移（GM），这可能导致含水层污染和大气排放。尽管需要识别和量化油井和天然气井场的 GM，但缺乏有效和可靠的监测技术。在这项实地研究中，我们使用 CH 和二氧化碳（CO）通量测量以及土壤气体稳定碳同位素特征来识别并描述在加拿大不列颠哥伦比亚省东北部的 17 个选定井场的逸散气体的时空迁移。在其中 13 个地点，运营商此前曾报告过 GM 的发生；然而，随后基于视觉、嗅觉或听觉证据的检查仅在其中两个地点发现了 GM。使用土壤气体通量方法，在 17 个井场中的 15 个井场发现了 GM 的证据，CH 和 CO 通量范围分别为 0.017 至 180μmolms（0.024 至 250gCHmd）和 0.50 至 32μmolms（1.9 至 122gCOmd）。在 17 个井场中的 10 个井场评估了稳定碳同位素组成，其中 9 个井场有 GM 的证据。同位素值表明，土壤气体中的 CH 与地表套管通风口气流中的 CH 来自同一来源。CH 通量与距井口的距离之间没有相关性；在距井口 10m 以外和 5m 以内检测到的升高通量比例相等。此外，CH 通量随时间变化，在 2 小时内变化幅度高达一个数量级。尽管该研究在不列颠哥伦比亚省东北部进行，但结果在全球范围内适用，表明主要基于视觉证据（例如井口冒泡）的检查对于 GM 的识别不可靠，并且在靠近井口的预定位置进行不频繁的测量可能会高估、低估甚至错过 CH 通量。使用动态封闭室方法进行重复和相对密集的气体通量测量被证明是检测 GM 的有用工具。
