Seismic Characterization of the Zechstein Carbonates in the Dutch Northern Offshore (2014)
Deze MSc scriptie is geschreven door oud-stagiair Sjoerd Tolsma.
The presence of Zechstein carbonate platform facies is often controlled by the pre-existing paleo-geography and commonly occur on uplifted fault blocks and along the margins of the Southern Permian Basin. Present day Zechstein distribution maps suggest that these platform facies are absent along the margins of the Elbow Spit High in the Dutch northern offshore, while based on the general geological setting their presence might be expected. Only several Dutch and UK wells have drilled the Zechstein or older formations in the study area. Well E02-02 and A16-01 have strong positive indicators for the presence of Zechstein platform facies, with good reservoir characteristics. Well E02-02 drilled a Zechstein platform structure, which was confirmed by a side-wall core sample. A16-01 found stromatolites along the SW margin of the Elbow Spit High, indicating a shallow water environment. Therefore it cannot be ruled out that platform facies exists in a large area along the margins of the Elbow Spit High. This has been investigated with the use of seismic data. First, seismic and petrophysical data will be used to characterize the Zechstein on seismic. That will be used, together with Zechstein analogues from the North-East Netherlands, to identify potential Zechstein platform structures. Second, top and base Zechstein is mapped in great detail and in specific areas the top Zechstein-3 Anhydrite Member is mapped as well. The identified potential Zechstein platform structures are then compared and compared to the proven E02-02 platform. The results show that the Zechstein Group contains several characteristic seismic properties that can be used to identify potential Zechstein platform structure, since a low amplitude seems to correlate with Zechstein platform structures. This study illustrates that Zechstein platform facies exists along the western and eastern margins of the Elbow Spit High, away from the wells that encountered this facies. A modified Zechstein distribution map has been proposed showing the areas with Zechstein platform facies along the Elbow Spit High. This map is based on the identified Zechstein platform structures and well data in the study area. Also a new area with possible Zechstein platform facies is proposed, that roughly correlates with the Step High.