Dinantian Carbonate Development and Related Prospectivity of the Onshore Northern Netherlands (2013)

This MSc thesis has been written by former intern Nynke Hoornveld.

A petroleum system may be present in the Carboniferous Dinantian carbonates in the Northern onshore Netherlands. This play has been evaluated by using seismic, well data and analogues. Only 2 wells penetrate this succession in the study area: UHM-02 and LTG-01. The Dinantian carbonate buildups were encountered at depths of approximately 4000m and comprise a muddy fine-grained matrix with a low initial porosity. Carbonate production in the Dinantian consists mostly of microbial mats, which grow typically underneath upwelling zones at low latitudes near continental shelves where sea water temperatures are warm to moderate. The post-Caledonian extension phase created a horst and graben system, where carbonate build-ups developed on the highs. Basinal, deep water shales onlap these build-ups, potentially providing hydrocarbon charge. Seismic mapping resulted in the identification of 4 carbonate build-up structures. The build-ups in the Southwestern part of the study area had been uplifted, resulting in the tilting of a flat topped platform while faulting isolated a part of the build-up. The Northeastern build-ups developed on paleotopography which might have been formed by a Devonian reef. The Hantum fault zone and the Lauwerszee Trough separated the western carbonate build-ups from the ones in the East. The Hantum fault zone has a high geothermal gradient probably resulting in (over)maturation of shale deposits in the Lauwerszee Trough. Analogues show that reservoir quality improves at progradating slope deposits and Belgian outcrops suggest a highstand in Late Visean, which can be related to progradation. On seismic, progradational sequences can be recognized in the study area. Also fractures are believed to be more abundant at the slope, simultaneously improving reservoir quality and possibly posing a risk to seal capacity. Because of the deep (maximum) burial depth and diagenetic changes in the carbonates, the reservoir quality will be dependent on the secondary porosity resulting from karstification, dolomitization and fracturing. Based on this evaluation, 5 prospective areas have been identified. The key risks are high temperatures leading to over-mature source rock and drilling hazards, gas quality (high Nitrogen content) and leaching by faults, for the seal must have been present at the end of the Carboniferous and must have been preserved. Would these leads not be gas bearing, then Enhanced Geothermal Systems (EGS) for a binary electricity generating system could be a fairly good option for these hot, ultra-deep leads.