Abstract
A normal detaching fault in the Norwegian-Danish Basin around the D-1 well (the D-1 fault) has been mapped using seismic sections. The fault has been analysed in detail by constructing backstripped-decompacted sections across the fault, contoured displacement diagrams along the fault, and vertical displacement maps. The result shows that the listric D-1 fault follows the displacement patterns for blind normal faults. Deviations from the ideal displacement pattern is suggested to be caused by salt-movements, which is the main driving mechanism for the faulting. Zechstein salt moves primarily from the hangingwall to the footwall and is superposed by later minor lateral flow beneath the footwall. Backstripping of depth-converted and decompacted sections results in an estimation of the saltsurface and the shape of the fault through time. This procedure then enables a simple modelling of the hangingwall deformation using a Chevron model with hangingwall collapse along dipping surfaces. The modelling indicates that the fault follows the salt surface until the Middle Miocene after which the offset on the fault also may be accommodated along the Top Chalk surface.
Highlights
Structural hydrocarbon traps in a broad sense represent the habitat of the bulk of the already discovered petroleum reserves in the world
The shape of the faults may vary from planar to listric the latter generating a roll-over anticline in the hangingwall sediments reflecting the shape of the fault plane (Crans and Mandl, 1980, Hamblin, 1965, Waltham, 1989, White et al, 1986)
During the backstripping the fault beneath the Zechstein salt has been regarded as inactive, and the regional topography of the basement is used as reference level (details in the backstripping and decompaction procedure are given in Petersen et al (1993))
Summary
Structural hydrocarbon traps in a broad sense represent the habitat of the bulk of the already discovered petroleum reserves in the world. The cause for generation of the structural trap may vary from halokinesis, major faulting of the crust due to change in the regional horizontal stresses, differential compaction across former active faults and gravitationally introduced local changes in horizontal stresses. The latter involves not the faulting of the entire crust but only down to a dipping detachment surface of low viscosity material (most often undercompacted clays, or salt). The D-1 well (Fig. 2) has penetrated of Rotligendes volcanics, Zechstein evaporites (hereafter called Zechstein salt), Triassic, Jurassic, Cretaceous and Tertiary sediments. The lithostratigraphic subdivision and dating for the pre-Tertiary sediments has been adopted from Nielsen and Japsen (1991) whereas the dating of the Tertiary horizons is taken from wells in the adjacent Central Trough area dated by Stouge (1988) and correlated to seismic section by Clausen (1991)
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