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Title: Impact of induced seismic events on seal integrity, Texas Gulf Coast

Recent publications have suggested that large-scale CO2 injection could trigger earthquakes and that even small- to moderate-sized earthquakes may threaten the seal integrity of the injection zone, and potentially damage buildings and other surface structures. In this study, we compared seal thickness to estimated fault displacement due to a single hypothetical seismic event in a selected area of the Texas Gulf Coast comprising an offshore strip of state waters along two Texas counties. To evaluate the slip generated by a single seismic event, we compiled well log information on shale/sand sequences and seismic information on fault geometric characteristics of a section of Lower Miocene age. The section is thousands of feet thick and is overlain and underlain by marine shales (Amph. B and Anahuac, respectively) that are relatively easy to correlate between wells. The Amph. B. shale is the secondary and ultimate seal for all injection intervals in the Lower Miocene. Given its thickness, no realistic seismic event or small series of seismic events will offset it significantly. However, this may not be true of smaller local primary seals. An analysis of geophysical logs of a total of 71 wells yielded a total of 2,871 sand / shale binary intervals.more » An analysis of the dedicated 3D seismic survey counted 723 fault traces at five roughly horizontal horizons within the Lower Miocene Fault displacement estimated using the product of the fault length times an uncertain multiplier coefficient assumed to follow a triangular distribution with a 10-3 to 10-5 range and a mode of 8 × 10-5. We then compared estimated single-event fault displacements to seal thicknesses by means of a Monte-Carlo analysis. Only 1.8% of thickness/displacement pairs display a displacement greater than 20% of the seal thickness. Only 0.26% of the pairs result in a displacement of half the seal thickness and only 0.05% of thickness/displacement pairs result in a clear seal rupture. The next step was to compare the magnitude of the event generated by such a displacement to documented magnitudes of “large” earthquakes generated by waterflooding and fluid disposal. Based on this analysis, we conclude that seismicity that may arise from CO2 injection appears not to be a serious complication for CO2 storage integrity, at least in the Gulf Coast area.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2]
  1. Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
1207905
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Energy Procedia
Additional Journal Information:
Journal Volume: 63; Journal Issue: C; Journal ID: ISSN 1876-6102
Publisher:
Elsevier
Research Org:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES induced seismicity; earthquakes; fluid injection; fault displacement; seal offset; CO2 leakage