The ‘Buntsandstein’ gas play of the Horn Graben (German and Danish offshore): dry well analysis and remaining hydrocarbon potential

Abstract

AbstractAn analysis of the Lower Triassic ‘Buntsandstein’ gas play in the underexplored Mesozoic rift system of the German–Danish Horn Graben is presented. Dry hole information from four well penetrations is analysed alongside the development of a 3D basin model. It is demonstrated that the dry holes do not preclude the existence of a working hydrocarbon system. Reservoir and seal elements are present, although details of quality and distribution are uncertain. Carboniferous coal preservation is likely, in a limited area, within the graben and can be constrained through seismic mapping. Vertical gas migration through the Zechstein interval is considered likely due to a large thickness variability (driven by halokinesis and facies changes). The overlap of peak gas-expulsion timing and halokinetic movements make rollover/turtle-back traps risky in terms of breaching or underfill. Dry wells in Denmark are explained by a combination of this relative timing and uncertainty over longer distance migration. This play analysis demonstrates a general agreement with previously published 1D basin models with respect to gas-expulsion timing. However, in contrast to published examples, it is shown that the Zechstein interval can allow for vertical gas migration. Considerable uncertainty in parameters, such as depth conversion, amount of erosion and migration paths, are recognized. Exploration opportunities remain, albeit relatively high risk, in the German area of the graben both in the ‘Buntsandstein’ play and at other stratigraphic levels.