Carbon dioxide storage in the Captain Sandstone aquifer: determination of in situ stresses and fault-stability analysis

Abstract

The Lower Cretaceous Captain Sandstone Member of the Inner Moray Firth has significant potential for the injection and storage of anthropogenic CO 2 in saline aquifer parts of the formation. Pre-existing faults constitute a potential risk to storage security owing to the elevated pore pressures likely to result from large-scale fluid injection. Determination of the regional in situ stresses permits mapping of the stress tensor affecting these faults. Either normal or strike-slip faulting conditions are suggested to be prevalent, with the maximum horizontal stress orientated 33°-213°. Slip-tendency analysis indicates that some fault segments are close to being critically stressed under strike-slip stress conditions, with small pore-pressure perturbations of approximately 1.5 MPa potentially causing reactivation of those faults. Greater pore-pressure increases of approximately 5 MPa would be required to reactivate optimally orientated faults under normal faulting or transitional normal/strike-slip faulting conditions at average reservoir depths. The results provide a useful indication of the fault geometries most susceptible to reactivation under current stress conditions. To account for uncertainty in principal stress magnitudes, high differential stresses have been assumed, providing conservative fault-stability estimates. Detailed geological models and data pertaining to pore pressure, rock mechanics and stress will be required to more accurately investigate fault stability.

Quantitative constraints to the complete state of stress from the combined borehole and focal mechanism inversions: Fox Creek, Alberta

“…In certain areas, the stress orientation  of the greatest horizontal compression S H may be inferred from existing compilations such as the World Stress Map (Heidbach et al, 2010). Finding the magnitudes of both S H and the least horizontal compression S h is difficult, and usually researchers make various assumptions based on extrapolations of quantitative results (Schwab et al, 2017;Weides et al, 2014), consistency with local earthquakes (Chang et al, 2010;Morris et al, 2017), frictional limits (Çiftçi, 2013;Schwab et al, 2017), constraints from various well tests (Chang et al, 2010;Konstantinovskaya et al, 2012), extrapolated empirical relationships (Adewole and Healy, 2017;Williams et al, 2016), or borehole stabilities (Peška and Zoback, 1995;Williams et al, 2016;Valley and Evans, 2019). As most of these authors indicate, the lack of proper measurements of the horizontal stress magnitudes, particularly with regards to S H for which direct measurement remains elusive, is the most significant source of uncertainties in their stability analyses.…”

Impact of in situ stress and fault reactivation on seal integrity in the East Irish Sea Basin, UK

“…Kingdon et al (2016) and structural features as denoted in Figure 1. Inset map places new data into regional context showing quality A-D SHmax orientations from WSM as grey markers (Heidbach et al 2016) and recently published data from the Inner Moray Firth within stippled box (Williams et al 2016). Location of earthquake focal mechanisms used by Baptie (2010) shown by graduated circles (Magnitudes 2.8-5.4).…”

“…The regional orientation is controlled principally by plate boundary forces, reflecting the configuration of plate boundaries and tectonic forces (Müller et al 1992;Gölke & Coblentz 1996). Variable orientations of SHmax are seen in some parts of the UK Continental Shelf because thick Permian evaporites decouple the stress field in the post-Permian sedimentary succession from stresses affecting the basement rocks (Hillis & Nelson 2005;Williams et al 2015), or because structural features such as mechanically weak or active faults locally deflect stress orientations (Holford et al 2016;Williams et al 2016).…”

“…Accurate determination of the effective in situ stress conditions is critical for effectively managing subsurface resources, particularly in mature hydrocarbon provinces such as the East Irish Sea Basin (EISB). Characterisation of the in situ stress state is essential for a range of subsurface engineering and energy applications (Bell 1996;Hillis & Nelson 2005;Tingay et al 2005), including seal integrity studies relating to exploration and storage of hydrocarbons (Wiprut & Zoback 2000;Finkbeiner et al 2001;Reynolds et al 2003;Meng et al 2017), and carbon capture and storage (Lucier et al 2006;Chiaramonte et al 2008;Williams et al 2016). Detailed stress field information is also commonly applied to the study of fluid flow through or along faults, as faults can constitute a risk to hydrocarbon exploration and subsurface fluid storage while also contributing positively to flow in tight, unconventional or geothermal reservoirs (Barton et al 1995;Bjørlykke et al 2005;Mildren et al 2005;Bretan et al 2011;Hennings et al 2012).…”

Stress magnitudes across UK regions: New analysis and legacy data across potentially prospective unconventional resource areas

“…Knowledge of the in-situ stress field is a key constraint in the exploitation of the subsurface and development of any subsurface resources including, storage of carbon dioxide, radioactive waste disposal, mining, unconventional hydrocarbon exploration, civil engineering and fault stability (Nirex, 1997;Zoback et al, 2003;Tingay et al, 2005;Williams et al, 2016). In particular, the stress field is critical to understanding fracture mechanics.…”