Preprints
https://doi.org/10.5194/se-2021-23
https://doi.org/10.5194/se-2021-23

  19 Mar 2021

19 Mar 2021

Review status: this preprint is currently under review for the journal SE.

Fault Interpretation Uncertainties using Seismic Data, and the Effects on Fault Seal Analysis: A Case Study from the Horda Platform, with Implications for CO2 storage

Emma A. H. Michie, Mark J. Mulrooney, and Alvar Braathen Emma A. H. Michie et al.
  • Department of Geosciences, University of Oslo, Sem Sælands Vei 1, Oslo 0371, Norway

Abstract. Significant uncertainties occur through varying methodologies when interpreting faults using seismic data. These uncertainties are carried through to the interpretation of how faults may act as baffles/barriers or increase fluid flow. How fault segments are picked when interpreting structures, i.e. what seismic line spacing is specified, as well as what surface generation algorithm is used, will dictate how detailed the surface is, and hence will impact any further interpretation such as fault seal or fault growth models. We can observe that an optimum spacing for fault interpretation for this case study is set at approximately 100 m. It appears that any additional detail through interpretation with a line spacing of ≤ 50 m adds complexity associated with sensitivities by the individual interpreter. Further, the location of all fault segmentation identified on Throw-Distance plots using the finest line spacing are also observed when 100 m line spacing is used. Hence, interpreting at a finer scale may not necessarily improve the subsurface model and any related analysis, but in fact lead to the production of very rough surfaces, which impacts any further fault analysis. Interpreting on spacing greater than 100 m often leads to overly smoothed fault surfaces that miss details that could be crucial, both for fault seal as well as for fault growth models.

Uncertainty in seismic interpretation methodology will follow through to fault seal analysis, specifically for analysis of whether in situ stresses combined with increased pressure through CO2 injection will act to reactivate the faults, leading to up-fault fluid flow/seep. We have shown that changing picking strategies alter the interpreted stability of the fault, where picking with an increased line spacing has shown to increase the overall fault stability. Picking strategy has shown to have minor, although potentially crucial, impact on the predicted Shale Gouge Ratio.

Emma A. H. Michie et al.

Status: open (until 30 Apr 2021)

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Emma A. H. Michie et al.

Emma A. H. Michie et al.

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Short summary
Generating an accurate model of the subsurface is crucial when assessing a site for CO2 storage, particularly for a fault bound storage site that may act as a seal or could reactivate upon CO2 injection. However, we have shown how picking strategy, i.e. line spacing, chosen to create the model significantly influences any subsequent fault analyses, but is surprisingly rarely discussed. This analysis has been performed on the Vette Fault bounding the Smeaheia potential CO2 storage site.