Edwards A*, Ikon Science Ltd; Grobys J, Schoneich, S, Edwards, A, Netzeband, G, Stadt, N. and Szabados, A,The DEA Group
Regional effective stress maps were produced for key Jurassic horizons (see Figure 3) as well as BCU and Base Chalk. Naturally, the effective stress maps reflect the depth structure in each overpressure cell to some extent, while the general level of effective stress varies from one overpressure cell to
another. At the shown level the shallower structures are at risk regarding seal breach, while the deeper structures are more likely to be sealing. The effective stress mapping results match the 1D seal breach calculations except for two wells. At least one of these wells indicates an intraformational seal within the Upper Jurassic as the effective stress decreases significantly for the Top Reservoir level up to the BCU level.
As has been mentioned above, wells in the Danish Central Graben behave well according to a seal capacity threshold at Top Reservoir level. They do not (or do only partly) behave well according to seal capacity thresholds derived at shallower levels, such as BCU and Base Chalk. This shows that Base Chalk is not an ultimate seal in this part of the North Sea in contrast to the Central North Sea, although few wells may indicate vertical communication into the Lower Cretaceous. The differences between the Central North Sea and the Danish Central Graben indicate a lateral transition that needs to be further evaluated as well as the mechanisms that support local pressure communication in vertical direction.
The stress mapping workflow has the potential to assist de-risking and ranking prospects in the Danish Central Graben. However, where discrepancies between expected aquifer seal capacities and results from the mapping workflow occur, further reasons of dry wells have to be investigated.
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*Figure 3 - Effective stress map for an Upper Jurassic reservoir level. Red colours indicate effective stresses values below the regional threshold, green colours above the regional threshold, indicating a lower seal breach risk.