Characterization and Classification of CO2 Storage Sites on the Norwegian Continental Shelf

Abstract

Depending on their specific geological properties, several types of geological formations can be used to store CO2. In the North Sea Basin, the greatest potential capacity for CO2 storage will be in deep saline-water saturated formations or in depleted oil and gas fields. The results presented in the CO2 Storage Atlas are based on studies of all relevant geological formations and hydrocarbon fields on the Norwegian Continental Shelf (NCS). Norwegian Petroleum Directorate (NPD) has access to all data collected from the petroleum industry and has a national management responsibility for these data. This is vested in the Norwegian Petroleum Law. More than 50 years of petroleum activity has generated a large quantity of data. These data and analyses together with many years of dedicated work to establish geological play models, have given us a good basis for the characterization and classification of potential CO2 storage sites. The first step in site selection is the screening of potentially suitable formations and structures using specific criteria. In the site selection process, it should be demonstrated that the potential sites have sufficient capacity to store the expected CO2 volume and sufficient injectivity for the expected rate of CO2 capture and supply. The integrity of the site must be assessed for the period required by the regulatory authority to avoid any unacceptable risks to the environment, human health or other uses of the subsurface. The aquifers were evaluated regarding reservoir quality and presence of relevant sealing formations. Those aquifers that may have a relevant storage potential in terms of depth, capacity and injectivity have been considered. The most attractive aquifers and structures were investigated by geomodelling and reservoir simulation. In all models, it is assumed that there will be no water production. The volumes of injected CO2 are constrained by the fracturing pressure. Our estimates of fracturing pressures are based on a large data base of leak-off tests and pore pressures in exploration wells. The regional fracture pressure trends are quite similar in North Sea and Norwegian Sea shelf, and somewhat lower in deeply eroded areas in the Barents Sea. The scores for capacity, injectivity and seal quality are based on evaluation of each aquifer/structure. The checklist for reservoir properties gives a more detailed overview of the important parameters regarding the quality of the reservoir. These parameters are set into different checklists for detailed grading.