Abstract
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 or barriers, or increase fluid flow. How fault segments are picked when interpreting structures, i.e. which seismic line orientation, bin spacing and line spacing are specified, as well as what surface generation algorithm is used, will dictate how rugose 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, both for accuracy of analysis but also for considering time invested. 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 locations of all seismic-scale 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. 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 a minor, although potentially crucial, impact on the predicted shale gouge ratio.
Highlights
In order to achieve targets to reduce emissions of greenhouse gases as outlined by the European Commission (IPCC, 2014, 2018; EC, 2018), methods of carbon capture and storage can be utilized to reach the maximum 2 ◦C warming goal of the Paris Agreement (e.g. Birol, 2008; Rogelj et al, 2016)
In order to address any uncertainty created by human error, we show how fault picking varies from one person to the by using the same fault picked at a 50 m line spacing by two separate interpreters with similar background experience (Fig. 16)
The line spacing chosen to pick both the fault segments and fault cutoffs will influence the analysis performed on the faults, with the results varying with picking strategy
Summary
In order to achieve targets to reduce emissions of greenhouse gases as outlined by the European Commission (IPCC, 2014, 2018; EC, 2018), methods of carbon capture and storage can be utilized to reach the maximum 2 ◦C warming goal of the Paris Agreement (e.g. Birol, 2008; Rogelj et al, 2016). One candidate for a CO2 storage site has been identified in the Norwegian North Sea, which is the focus of this study: the saline aquifer in the Sognefjord Formation at the Smeaheia site (Halland et al, 2011; Statoil, 2016; Lothe et al, 2019). Several studies have been performed on the feasibility of the Smeaheia CO2 storage site (e.g. Sundal et al, 2014; Lauritsen et al, 2018; Lothe et al, 2019; Mulrooney et al, 2020; Wu et al, 2021). It is necessary for the fault to have no reactivation potential Both of these parameters hinge on generating an accurate geological model, performed using suitable picking strategies, both for fault surface picking and for fault cutoff (horizon–fault intersection) picking
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