Prospectivity Analysis of the Northern Dutch Central Graben (2013)

Dit internship rapport is geschreven door oud-stagiair Jasper van Bruchem.

For this project, a prospectivity analysis of the B quadrant in the northern Dutch offshore has been carried out. The recently released Entenschnabel (ES02) dataset was used for this analysis; this is a 3D dataset of the northern Dutch offshore and through the German Entenschnabel into the southern Danish Central Graben and was obtained by Fugro in 2002. Seismic mapping of nine key horizons such as the base Chalk, base Schieland Group and top Zechstein resulted in the division of the geological model into eight layers. These layers were used as input for the time-depth conversion which was conducted using the Velmod 2 velocity model. After the first nine horizons were completed, more detailed mapping was carried out on play level. Four source rocks are probably present in the study area: the Jurassic Clay Deep Member and Posidonia Shale Formation, the Westphalian Maurits and Klaverbank Formations and the Namurian Geverik Member. The Posidonia and Clay Deep Member are probably only mature in the Central Graben; the Carboniferous source rocks may well be mature in the Step Graben in the west of the study area. Six plays were identified: the Chalk, Vlieland Sandstone, Scruff Greensand, Lower Graben, Lower Buntsandstein and Rotliegend play. Only the Scruff Greensand and Lower Graben plays have been proven successful in the study area by the F3-FA field. The most prospective plays are probably the Scruff Greensand and Vlieland Sandstone plays; in addition, a number of leads have been identified in the Chalk. The three most prospective leads are the Amethyst, Beryl and Bloodstone leads. The Amethyst lead is a fault-dip closure on top of the B16 salt wall in a Chalk reservoir which is probably fractured. Carboniferous source rocks probably provide charge which may migrate into the chalk via the large normal fault which runs along the salt wall. Bright spots in the Tertiary indicate that hydrocarbons may be present. The Beryl lead is a combined Scruff/Vlieland Sandstone lead located in the center of the B17 block. The closure consists of steeply dipping flanks against the northern flank of the B17 diapir which are truncated by the Chalk Group. Charge for this lead probably comes from Posidonia Shale and/or Clay Deep Member, which are probably mature in the Central Graben. Bright spots over the B17 diapir hint at charge. The Bloodstone lead is speculative: the Vlieland Sandstone has not been encountered by any wells in the study area, but may be present near structural highs. The trap of this lead consists of a four-way dip closure in the west of the B14 block.