Description and structural implications of fractures in late Jurassic sandstones of the Troll Field, northern North Sea

Mapping of fractures in sandstones of the Troll Field, northern North Sea, has shown that deformation
outside the major faults is relatively mild. The fractures have been divided into three groups - single
fractures, fracture swarms and macrofaults. Single fractures represent the 'background deformation',
and are present in all the investigated cores. Fracture swarms are concentrations of single fractures, and
may grade in to breccias. The fracture swarms are more unevenly distributed, and are believed to represent smaller faults with normal throws of less than 15 m. Macrofaults are faults which are large enough to be detected in reflection seismic sections. Tests indicate that permeability is reduced by up to one order of magnitude across single fractures. However, neither single fractures nor fracture swarms are considered to be of significance for reservoir communication in the Troll reservoir.