Abstract

The giant Hibernia Oilfield in the Jeanne d’Arc Basin, the first hydrocarbon development on the Grand Banks of Newfoundland, began production from an ice-resistant, concrete gravity base platform in November 1997. An estimated 615 × 10⁶ BBL recoverable oil reserves are trapped in a highly faulted and south-plunging anticline.

The tectonic stresses experienced on the western North Atlantic margin have largely controlled the density and size distribution of faults which limit and partition the Hibernia structure. More than 30 fault blocks have been identified at one major oil and gas reservoir alone, the fluvial–deltaic Hibernia Formation. Interpretations of relationships between the times of tectonism and changing stress directions with fault ages, orientations, and styles are based on comparison of a 1991 vintage 3D seismic survey along with data from one discovery, nine delineation and two development wells. There appear to have been three main episodes of extension that affected the oilfield.

The first extensional episode spanned the Late Triassic into the Early Jurassic. Adjacent to the Hibernia Oilfield, initial rifting resulted in growth of NE-trending, en echelon faults that were subsequently amalgamated into the major basin-bounding Murre Fault. Deposition of the Hibernia Formation sandstones occurred during the second tectonic episode that spanned Late Jurassic into Early Cretaceous time. Faults of this vintage in the Hibernia Oilfield are normal and mostly formed synthetic to the re-activated Murre Fault in response to E–W oriented extension. The most marked fault growth occurred during the third tectonic episode. This late Early Cretaceous rift episode was co-eval with deposition of another major oil reservoir (the marginal to shallow marine ‘Avalon’ formation) which is targeted for development. Numerous normal faults formed orthogonal to the basin margin, thereby transecting and rotating the Hibernia structure. Fault development during the latest rift episode also responded to basin margin effects as a result of reactivation of the Murre Fault as a zone of oblique-slip. For example, the character of the large Rankin and Nautilus faults changes from relatively planar to distinctly listric moving from east to west. Additionally, sinistral deflections in the trace of the Murre Fault corresponding to linkages of the en echelon offsets formed during the first rift episode are interpreted to have controlled the location of the largest northeast dipping faults formed during the third rift episode.

The largest faults formed during the third rift episode clearly compartmentalize the Hibernia reservoir while the sealing capacity of faults formed during deposition of the Hibernia sandstones remains unquantified.