Publication Name: Australasian Exploration Geoscience Conference 2019
Authors: Nick Schofield*, Simon Holford, Alex Edwards
Date Published: September 2019
Number of Pages: 5
Abstract:
In situ overpressures in sedimentary basins are commonly attributed to disequilibrium compaction or fluid expansion mechanisms, though overpressures in shallow sedimentary sequences may also develop by vertical transfer of pressure from deeper basin levels, for example via faults. Mafic sill complexes are common features of sedimentary basins at rifted continental margins, often comprising networks of interconnected sills and dikes that facilitate the transfer of magma over considerable vertical distances to shallow basinal depths. Here we document evidence for deep sills (depths >5 km (16,000 ft)) hosting permeable, open fracture systems that may have allowed transmission of overpressure from ultra-deep basinal (>7 km (23,000 ft)) levels. Most notably, well 214/28-1 encountered overpressured, thin (<8 m (26 ft)) and fractured gas-charged intrusions, which resulted in temporary loss of well control.