• Energy Research
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• Norwegian Geotechnical Institute close

Characterization of caprock shale is critical in CO2 storage site evaluation because the caprock shale acts as a barrier for the injected buoyant CO2 plume. The properties of shales are complex and influenced by various processes; hence, it is challenging to evaluate the caprock quality. An integrated approach is therefore necessary for assessing seal integrity. In this study, we investigated the caprock properties of the Lower Jurassic Drake Formation shales from the proposed CO2 storage site Aurora (the Longship/Northern Lights CCS project), located in the Horda Platform area, offshore Norway. Wireline logs from 50 exploration wells, various 2D seismic lines, and two 3D seismic cubes were used to investigate the variations of the caprock properties. The Drake Formation was subdivided into upper and lower Drake units based on the lithological variations observed. Exhumation and thermal gradient influencing the caprock properties were also analyzed. Moreover, rock physics diagnostics were carried out, and caprock property maps were generated using the average log values to characterize the Drake Formation shales. In addiiton, pre-stack seismic-inverted properties and post-stack seismic attributes were assessed and compared to the wireline log-based analysis. The sediment source controlled at 61° N significantly influenced the depositional environment of the studied area, which later influenced the diagenetic processes and had various caprock properties. The upper and lower Drake units represent similar geomechanical properties in the Aurora area, irrespective of significant lithological variations. The Drake Formation caprock shale near the injection site shows less-ductile to less-brittle brittleness values. Based on the caprock thickness and shaliness in the Aurora injection site, Drake Formation shale might act as an effective top seal. However, the effect of injection-induced pressure changes on caprock integrity needs to be evaluated.

Climate change is already being felt in Europe, unequivocally affecting the regions’ geo-structures. Concern over this is rising, as reflected in the increasing number of studies on the subject. However, the majority of these studies focused only on slopes and on a limited geographical scope. In this paper, we attempted to provide a broader picture of potential climate change impacts on the geo-structures in Europe by gathering the collective view of geo-engineers and geo-scientists in several countries, and by considering different geo-structure types. We also investigated how geo-structural concerns are being addressed in national adaptation plans. We found that specific provisions for geo-structural adaptation are generally lacking and mainly come in the form of strategies for specific problems. In this regard, two common strategies are hazard/risk assessment and monitoring, which are mainly implemented in relation to slope stability. We recommend that in future steps, other geo-structures are likewise given attention, particularly those assessed as also potentially significantly affected by climate change. Countries considered in this study are mainly the member countries of the European Large Geotechnical Institutes Platform (ELGIP).

Characterizing the top seal integrity of organic-rich caprock shale is critical in hydrocarbon exploration and fluid storage sites assessment because the caprock acts as a barrier to the low-density upward migrating fluids. This study investigated the geomechanical properties of the Upper Jurassic caprock shales of various basins from the Norwegian Continental Shelf. Usually, paleo-deposition and diagenesis vary from basin to basin, which influences the geomechanical properties of caprock shale; hence, the seal integrity. Fourteen (14) wells from four (4) different basins within the Norwegian Continental Shelf were analyzed to evaluate the effects of various processes acting on caprock properties. Comparative mineralogy-based caprock properties were also investigated. We include a thorough review of the distribution of organic and inorganic components utilizing SEM and 3D microtomography as they relate to the development and propagation of microfractures. Five (5) wells from three (3) basins contain measured shear sonic logs. These wells were used for petrophysics and rock physics analysis. Three elastic properties-based brittleness indices were estimated and compared. The percentage of different mineral fractions of the studied wells varied significantly between the studied basins, which is also reflected in the mineralogical brittleness indices evaluation. Irrespective of the studied basins, relative changes in caprock properties between wells have been observed. The Young’s Modulus–Poisson’s ratio-based empirical equation underestimated the brittleness indices compared with mineralogy- and acoustic properties-based brittleness estimation. A better match has been observed between the mineralogy- and acoustic properties-based brittleness indices. However, as both methods have limitations, an integrated approach is recommended to evaluate the brittleness indices. Brittleness indices are a qualitative assessment of the top seal; hence, further investigation is required to quantify sealing integrity.