Value of core for reservoir and top-seal analysis for carbon capture and storage projects

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 .