Assessment of CO2 sequestration in saline formations in the Netherlands northern offshore: Upper Cretaceous Chalk

Abstract

The international energy agency has outlined that at least 15% of global emissions will be reduced through carbon capture and storage (Global CCS Institute 2022). Current studies and projects in the Netherlands are investigating the storage of CO2 in depleted gas fields, and as such all studies focus on storage in Permian and Triassic clastic reservoirs. Although the carbonates, specifically Chalk play, has been prolific source of hydrocarbon in the Norwegian, Danish, and British sectors of the North Sea, it has only been discovered in four fields in the Netherlands. This study is the first to address the potential for deep offshore storage in the Chalk group in the K and L blocks of the Dutch offshore sector. The aim to produce a general assessment for the Chalk group’s distribution, development, and quality of the main parameters that impact CO2 injectivity and retention. The study focuses on L-K blocks in the northern offshore and utilizes a 3D survey with several well penetration that encountered, logged, and marked biostratigraphic intervals within the Chalk. The study demonstrated a workflow to evaluate and assess the Chalk utilizing seismic interpretation and attributes extraction. As a product, a general guideline was produced for the exploration of subsurface potential in the Chalk. Furthermore, the two most promising prospects within the survey were evaluated representing the two types of depositional Chalk (autochthonous and allochthonous). Autochthonous prospect F is analogous to the proven Chalk fields discovered in the Netherlands while allochthonous Prospect G is analogous to reservoirs in the UK sector. Both prospects at this stage are risky due to the lack of well data and adequate research on the Chalk to constrain the observation made, with an added risk to allochthonous prospect attributed to it not being encountered in the Dutch offshore before. To de-risk these prospects, future work was highlighted including building a detailed intra-Chalk interpretation to isolate and map seismically the proven reservoir intervals within the Chalk (Danian and Maastrichtian). Also, a detailed tectono-stratigraphic study that evaluates the inversion events impacting reservoir development. As Chalk is primarily discovered via geophysical methods, reprocessing the seismic for Chalk exploration and conducting seismic inversion to translate and quantify the geophysical parameters obtained of the seismic anomalies to reservoir character models would be key.