(1) Elf Petroleum Norge as, Stavanger, Norway
(2) Elf Exploration Production, Pau, France
ABSTRACT: Reservoir Assessment and Holding Tank Model for the Ringhorne Dome (Mid. Norway): Structural Signature of Migration Pathways
The Ringhorne Anticline, one of the largest Cenozoic inversion domes on the Norwegian Margin, is located 80 km NW of the Ormen Lange discovery.
In this 383 km2 large four-way dip closure at Base Tertiary, three reservoir intervals are assumed from the interpretation of 3D seismic data: distal equivalents of the Ormen Lange Danian turbidites and two uncalibrated levels of Late Maastrichtian turbidites.
The Late Jurassic source rock is buried beneath 7-8 km of dominantly shaly sediments and was likely overmature at the time of trap formation.
Three structural intervals exhibiting different patterns of small scale faulting are defined. In the intervals below and above the suspected reservoirs, polygonal fault patterns formed during the dewatering and flattening of more shaly levels in the early stages of burial. Between these two intervals, the Late Maastrichtian - Early Eocene interval is characterized by segmentation into sags and saddles with associated E-W normal faults reflecting a higher competence during deformation.
Direct Hydrocarbon Indicators and dismigration structures suggest the presence of gas. The fault patterns recorded the passage of fluids. The depletion of a reservoir beneath the Base Maastrichtian is recorded by a concentric organization in the polygonal fault pattern. Above, the spatial relationship between the gas chimneys and the large collapse/dewatering structures in the Miocene suggest that the dewatering has been triggered by gas dismigration. The model proposed may suggest a holding tank mechanism. Gas may still be trapped in intermediate reservoirs as a valve mechanism is possible.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado