Identifying geological structures through microseismic cluster and burst analyses complementing active seismic interpretation

Journal Article · Mon Oct 18 04:00:00 EDT 2021 · Tectonophysics

DOI:https://doi.org/10.1016/j.tecto.2021.229107· OSTI ID:1977685

Dichiarante, Anna Marie ^[1]; Langet, Nadège ^[2]; Bauer, R. A. ^[3]; Goertz-Allmann, B. P. ^[2]; Williams-Stroud, Sherilyn C. ^[3]; Kühn, D. ^[4]; Oye, V. ^[2]; Greenberg, S. E. ^[3]; Dando, B. D. E. ^[2]

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1. NORSAR, Kjeller (Norway); OSTI
2. NORSAR, Kjeller (Norway)
3. Illinois State Geological Survey, Champaign, IL (United States)
4. NORSAR, Kjeller (Norway); Helmholtz-Zentrum Potsdam (HZP), (Germany). German Research Centre for GeoSciences

At the Decatur carbon capture and storage site (IL, USA) CO₂ has been injected from 2011–2014 and from 2017 to present near the base of the Lower Mt. Simon Sandstone saline reservoir, resulting in microseismicity. Microseismicity is mainly located in the basement and distributed in distinct spatial clusters. The lack of significant impedance contrasts within the basement makes the interpretation of active-source seismic reflection data challenging, however, recent reprocessing allowed to resolve faults above and at the top of the basement. These faults generally do not coincide with the location of microseismic events and their continuation to the general depth of the seismic events cannot be assumed. This paper shows how the interpretation of the microseismicity can complement structural interpretations of active-source seismic reflection data. In particular, we analyze clusters and bursts (abrupt increases) of microseismicity, identify unresolved, smaller-scale weaknesses and extract statistical parameters. These parameters allow comparisons with the interpreted faults, and with fracture sets intercepted by boreholes. During injection at the Decatur site, the injection pressure was kept far below fracture pressure, nevertheless, seismic events were induced and spread far beyond the expected extent of the CO₂ plume. We argue that local stress transfers related to the CO₂ injection reactivated pre-existing fractures within the critically stressed basement. Finally, we conducted a slip tendency analysis for faults interpreted from active seismic, selected cluster, bursts and nodal planes from focal mechanisms to determine if the interpreted structures are optimally oriented with respect to the stress regime. Our results suggest that the orientation of fractures close to the injection well, generally shows slight deviations from the optimal orientation for slip. This might indicate either slight local deviations of the maximum horizontal stress azimuth from the average direction used in the analysis, or the lack of optimally oriented fractures at this location.

• Research Organization: Univ. of Illinois at Urbana-Champaign, IL (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: FC26-05NT42588
• OSTI ID: 1977685
• Journal Information: Tectonophysics, Journal Name: Tectonophysics Journal Issue: C Vol. 820; ISSN 0040-1951
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
Geochemistry & Geophysics
basement
fractures
induced seismicity
seismicity bursts
stress state