テキサス州西部で発生した直近の地震と石油・ガス活動の関連性(Oil and Gas Activity Linked to Most Recent Earthquakes in West Texas)

ad
ad

2022-06-27 テキサス大学オースチン校(UT Austin)


The Yates Oil Field in the Delaware Basin. Credit: Jan Buchholtz.

研究者らは、2017年から2020年にかけて同地域の地震活動と石油・ガス生産を追跡したデータを振り返り、M1.5以上の地震の68%が、次の石油・ガス生産活動のうちの1つ以上と強く関連していることを発見しました:水圧破砕または浅いまたは深い地層への生産地層水の廃棄。地層水はすべての地下貯留層に存在し、石油やガスとともに生産される。企業は、生産された水を石油・ガス貯留層とは別の地層に注入することで処分します。
このような生産活動はすべて、地震を誘発するメカニズムである地下の間隙水圧を上昇させることが知られている。
統計解析と物理学に基づくモデリングを組み合わせることで、どの活動が過去の地震と関係があるのかを切り離すことができたという。
この論文は、石油・ガス活動と地震活動がどのように関連しているか、現在では多くのことが分かっていることを示しています。

<関連情報>

デラウェア州盆地における誘発地震の原因究明:水圧破砕法か廃水処理か Distinguishing the Causal Factors of Induced Seismicity in the Delaware Basin: Hydraulic Fracturing or Wastewater Disposal

Iason Grigoratos;Alexandros Savvaidis;Ellen Rathje
Seismological Research Letters  Published:June 22, 2022
DOI:https://doi.org/10.1785/0220210320

Abstract

Identifying the causal factors behind elevated seismicity rates in areas with multiple ongoing oil and gas activities has always been a challenging issue that is lacking a homogeneous response, hindering regulatory actions. A good example is the Delaware basin, in West Texas and New Mexico, where the seismicity rates have been gradually increasing since 2009. To study the area, we expand the framework presented in Grigoratos et al. (2020a) to daily hydraulic fracturing (HF) operations and pressure‐driven modeling of wastewater disposal (SWD). Our analysis hindcasts seismicity rates of magnitude (M) ≥1.5 events after 2017 on a 5 km grid using either HF or SWD data as input and compares them against the null hypothesis of solely tectonic loading. In the end, each block is assigned a p‐value, indicating the statistical confidence of its causal link with either HF, shallow SWD or deep SWD injection operations. Our results indicate that 68% of the earthquakes occurred in blocks with p ≤ 0.05 (95% confidence interval) for at least one examined causal factor and are thus triggered by oil and gas activities. This percentage increases to 81% for p ≤ 0.10 (90% confidence interval). Overall, more events than previously identified are associated with HF, especially within Reeves County. That said, shallow SWD is linked to many more earthquakes, likely reactivating parallel faults of significant length. We should note the seismicity around Pecos city seems to be affected by more than one injection activity, with higher frequency operational data and better depth resolution needed to fully decouple causality between HF and shallow SWD. Within Culberson County, and around the epicenter of the 2020 Mentone Mw<?XML:NAMESPACE PREFIX = “[default] http://www.w3.org/1998/Math/MathML” NS = “http://www.w3.org/1998/Math/MathML” />Mw 5.0 earthquake, the earthquakes occur predominantly within the basement, with the identified triggering mechanism being SWD from deep wells.

タイトルとURLをコピーしました