Earth Ocean and Atmospheric Science, University of British Columbia, 2020-2007 Main Mall, Vancouver, BC V6T 1Z4, Canada.
The Lyell Centre, Heriot-Watt University, Research Avenue South, Edinburgh EH14 4AP, United Kingdom.
Sci Total Environ. 2021 May 15;769:144678. doi: 10.1016/j.scitotenv.2020.144678. Epub 2021 Jan 17.
Oil and gas wells are engineered with barriers to prevent fluid movement along the wellbore. If the integrity of one or more of these barriers fails, it may result in subsurface leakage of natural gas outside the well casing, a process termed fugitive gas migration (GM). Knowledge of the occurrence and causes of GM is essential for effective management of associated potential risks. In the province of British Columbia, Canada (BC), oil and gas producers are required to report well drilling, completion, production, and abandonment records for all oil and gas wells to the provincial regulator. This well data provides a unique opportunity to identify well characteristics with higher likelihoods for GM to develop. Here we employ Bayesian multilevel logistic regression to understand the associations between various well attributes and reported occurrences of GM in 0.6% of the 25,000 oil and gas wells in BC. Our results indicate that there is no association between the occurrence of GM and hydraulic fracturing. Overall, there appears to be no well construction or operation attribute in the study database that is conclusively associated with GM. Wells with GM more frequently exhibit indicators of well integrity loss (i.e., surface casing vent flow, remedial treatments, and blowouts) and geographic location appears to be important. We ascribe the spatial clustering of GM cases to the local geologic environment, and we speculate that there are links between particular intermediate gas-bearing formations and GM occurrence in the Fort Nelson Plains Area. The results of this study suggest that oil and gas wells in high GM occurrence areas and those showing any attribute associated with integrity failure (e.g., surface casing vent flow) should be prioritized for monitoring to improve the detection of GM.
油井和气井都经过工程设计，以防止井筒内的流体流动。如果这些屏障中的一个或多个完整性失效，可能会导致天然气在井套管外的地下泄漏，这一过程称为逸散性气体迁移（GM）。了解 GM 的发生和原因对于有效管理相关潜在风险至关重要。在加拿大不列颠哥伦比亚省（BC），石油和天然气生产商必须向省级监管机构报告所有油井和天然气井的钻井、完井、生产和废弃记录。这些井数据提供了一个独特的机会，可以识别出更有可能发生 GM 的井特征。在这里，我们采用贝叶斯多层次逻辑回归来理解各种井属性与 BC 中 25000 口油井中 0.6%报告的 GM 发生之间的关联。我们的结果表明，GM 的发生与水力压裂之间没有关联。总体而言，在研究数据库中似乎没有任何井构造或操作属性与 GM 有明确的关联。发生 GM 的井更频繁地出现井完整性丧失的迹象（即，表层套管通风、补救处理和井喷），地理位置似乎很重要。我们将 GM 病例的空间聚类归因于当地地质环境，并推测在 Fort Nelson Plains 地区，特定的中间含气地层与 GM 发生之间存在联系。这项研究的结果表明，GM 发生频率较高的油井和那些显示出与完整性失效相关的任何属性（例如，表层套管通风）的油井应优先进行监测，以提高 GM 的检测。
