DeepReservoir – Predicting reservoir properties in deep structures on the Norwegian Continental Shelf: The critical role of chlorite-coats

Most hydrocarbon resources on the Norwegian continental shelf are found in porous sandstone reservoirs. When sandstones are buried deeper than about 3 km, the pore space begins to fill with quartz cement. This reduces the reservoir’s capacity to store fluids such as oil, gas, or CO2. For this reason, deep reservoirs are considered high-risk exploration targets. In some cases, however, reservoirs buried as deep as 5 km may retain excellent properties because the grains are coated with the mineral chlorite. This coating inhibits the development of pore-filling quartz cement and can preserve good reservoir quality at great depths. At present, no geological concepts or technologies exist that allow us to predict whether a reservoir contains chlorite coatings. This presents two problems. First, discoveries in deep prospects near existing infrastructure could be economically viable and extend the operation of current installations. Without a reliable predictive tool to forecast the distribution of chlorite coatings, however, such targets may be deemed too risky. Second, chlorite has the potential to mineralize CO2, which represents a major advantage for CO2 storage. Without models to predict the distribution of chlorite in subsurface reservoirs, assessing the feasibility of permanent CO2 storage is difficult. The DeepReservoir project will develop new methods to predict the presence of chlorite coatings. In East Greenland, world-class geological outcrops exist where chlorite-coated sandstones are present. We have carried out an expedition to these areas to investigate the chlorite-coated zones and why they occur there. We will also study examples of chlorite coatings from the Norwegian shelf and examine modern environments where chlorite is abundant. In 2024, the key step in the data collection phase of the project was completed: the field expedition to Jameson Land in East Greenland. As expected, there were large variations in the degree of cementation in the sediments, and we were able to sample and collect data to map the dimensions of the uncemented zones, which is of primary importance for the project. Now in 2025, the project is now well underway with the conceptualization and integration of the results. The first articles have been submitted for peer review, and more will follow during the remainder of 2025 and 2026. The initial publications focus on the geometry and processes of reservoir quality preservation in the Smørbukk field, on new hypotheses concerning source areas for precursors to chlorite coatings, and on regional variations in paleogeography, sediment supply, and reservoir quality on the mid-Norwegian shelf.

With the largest and most easily accessible hydrocarbon resources on the Norwegian Continental Shelf already discovered, the future of Norwegian exploration lies in developing deeper and technically complex prospects close to existing infrastructure. Reservoir quality generally decreases with depth, leading to greater uncertainty in deeper prospects. However, some reservoirs contain sand grains coated with the mineral chlorite, which inhibit cementation and preserve excellent reservoir quality at great depth (3-6 km). It is difficult to predict where good reservoir properties are preserved with current models, and measures that can improve the predictability of chlorite coats in deep reservoirs will increase the commercial discovery rates, delay decommissioning, and maintain the competitiveness of the NCS. Chlorite-coated reservoirs, and reservoirs with precursor clays to chlorite coats, are well-suited storage sites for CO2 because chlorite promotes rapid, permanent mineralization of CO2. The DeepReservoir project promotes future value creation on the NCS by developing knowledge important for screening the potential of subsurface aquifers. In this project, we will map the distribution of chlorite coats on the NCS and investigate the processes controlling porosity preservation in deeply buried reservoirs. We will do this by investigating data from subsurface fields and utilize the globally unique outcrops on E Greenland, where chlorite-coated sandstones can be studied in unprecedented detail, and the well-studied modern occurrences of chlorite coat precursor clays in the Ravenglass Estuary, UK. To combine findings into a predictive model, we will integrate sedimentology, petrography, geophysics and hydrodynamic modelling in both subsurface, outcrop and modern analogue systems. This integrated approach was selected as the answers to our research questions lie in the intersection between these disciplines.