Abstract Carbon capture and storage (CCS) initiatives to mitigate greenhouse gas emissions are being planned in many countries, including offshore settings in the UK. To start with, almost all of these initiatives have utilized core that was originally collected to help with oil and gas exploration, appraisal and development projects. The objectives of core-based studies for CCS are subtly different to those for oil and gas studies. There are several significant reasons why core should be valued in CCS projects. Data from core provide a chance to calibrate lithology and porosity interpretations made from wireline logs that are used to characterize the subsurface and populate geocellular models. Permeability-related attributes, especially directional permeability ( k v and k h ) and relative permeability in CO 2 –water mixed fluid systems, are essential to predict CO 2 injection rates and CO 2 movement patterns in the reservoir and can only be acquired from core. Although many geomechanical data, necessary to undertake safe injection of CO 2 and avoid induced fracturing, can be acquired from wireline logs, borehole imaging and downhole tests, core samples from the reservoir and top-seal are required to reveal tensile strength and to calibrate elastic and other geomechanical properties acquired from logs. Top-seal performance is critical for carbon capture and storage; core samples from top-seals are the best way to determine capillary entry pressure and so define the maximum CO 2 column height and possible CO 2 leakage rates. The possibility of dissolution reactions between formation water, acidified by high pressure CO 2 , and minerals in both the reservoir and top-seal is best assessed by detailed petrographic and mineralogical study of core samples and a combination of modelling and core flow-through experiments. In summary, core is essential to CCS projects to determine CO 2 storage efficiency, CO 2 injection rates and the optimum way to safely store CO 2 .

Abstract The growing importance of subsurface carbon storage for tackling carbon emissions requires an accurate characterization of potential reservoirs to understand their capabilities. In this context, the use of legacy data originally acquired in the last fifty years for scientific projects and petroleum exploration and production activities would represent a suitable cost-effective solution and help to maximize the value of this extended national asset. Core material represents the only direct observation of subsurface deposits and must be preserved from the current disposal process related to the decommissioning of hydrocarbon fields. In this contribution, a suite of samples from core material stored at national (i.e. British Geological Survey) and local (i.e. Department of Earth Sciences, Royal Holloway, University of London) core repositories, previously characterized at the micro scale using X-ray micro-computed tomographic (μCT) imaging are discussed. Using this technique, it has been possible to investigate how pore and grain geometries control crucial features of a suitable reservoir such as porosity and permeability. The aim of this contribution is to describe the methodology behind digital image analysis (DIA) following μCT imaging applied to core material. We show how DIA can be used to provide significant measures of reservoir suitability when making initial assessments of storage reservoirs, without the need for expensive and time-consuming analyses.

Abstract Brittle structures are crucial for enabling several key natural processes in the Earth's upper crust. In addition, understanding the 3D characteristics and geological evolution of these features is equally important to support various developmental objectives, such as those, inter alia , linked to natural gas, groundwater, hydrothermal minerals and seismicity. In this study, we map various fractures of Gondwana based on the available geological information, satellite imagery and digital elevation data. The lengths and orientations of more than 10 000 fractures in their present-day position reveal four clearly defined patterns, with those striking NW being predominant. Archean–Paleoproterozoic domains are defined by fractures oriented north and NE, whereas the Mesoproterozoic has dominant NNW-striking fractures. In contrast, the Neoproterozoic has mostly NE-striking fractures and the Phanerozoic sequences are defined by a predominant NW and a subordinate west fracture pattern. The style and geometry of these structures can be linked to major geodynamic events that led to the formation of Gondwana building blocks during the Eburnean ( c. 2.2–1.8 Ga), Kibaran ( c. 1.4–1.0 Ga) and Pan African–Brasiliano ( c. 800–550 Ma) orogens, and amalgamation of Pangaea ( c. 350–250 Ma). Many structures were reactivated and new faults formed during opening of the Atlantic and Indian oceans ( c. 180–120 Ma), the India–Asia collision and rifting across East Africa since about 40 Ma. Although the changes in palaeogeography remain difficult to model with accuracy, major structural orientations are corroborated by the occurrence of major mineral deposits and seismicity. The spatial distribution of mapped patterns across the different continents also correlates well with large shale gas prospects and increased groundwater yields. Thus, Gondwana fractures need to be considered in more detail for informing future development related to water and energy use, especially across regions of Africa.