Quantitative Reservoir Characterization of Ommelanden Formation for CO2 Storage Assessment

Abstract

This research provides an evaluation of the Ommelanden Formation (Upper Cretaceous chalk) and general CCS applications. Based on the core description and analyses (sedimentology of cores, petrophysical properties, thin sections petrography, and micro-CT) of the Ommelanden Formation interval in two wells (Harlingen Field, the Netherlands), the study aims to define the reservoir characteristics in a quantitative approach and evaluate its potential for storing CO2. We determined the reservoir facies by studying the core lithology, sediment structures, and inferred depositional conditions provided by the description of the sedimentary core and thin sections. We interpret the Ommelanden Formation facies as bioturbated chalk with varying degrees of bioturbation and stylolites. It is characterized by medium- to high bioturbation enhancing heterogeneity in the formation. The study found that the intensity of burrowing is associated with stylolites formation. Petrophysical analysis defines porosity, permeability, and the ability of fluids to flow through reservoirs, which are important in determining the reservoir’s suitability. Plug porosity measurements range from 11% to 33% of HRL_02 and HRL_04, while cement-reduced porosity estimates from thin sections of both wells are between 1% and 6%. TinyPerm measures 100–120 mD in HRL_02's less fractured zone and 180–200 mD in the fractured zone. By using micro-CT imaging, we can see the pore networks and rock fabrics in great detail. This shows how the main stylolites, which are laterally extended and opened, will be moving fluids through the chalk matrix. All these techniques are integrated to provide a systemic analysis of the reservoir heterogeneity and to help assess the attendant dynamic behavior. Based on the petrophysical properties and fractures observed in this study, we determined four optimal injection zones for CO2 injection. The most suitable intervals for HRL_02 are 1060.4 m to 1062.4 m and 1073.9 m to 1082.4 m. The most optimal zones in HRL_04 are 1038 m to 1052 m and 1052 m to 1056 m. These outcomes are useful for the decision process, including CCS site selection. This research improves our understanding of the future use of chalk reservoirs for sustainable CCS applications.