STRAIN LOCALISATION AND TRAP GEOMETRY AS KEY CONTROLS ON HYDROCARBON PRESERVATION IN THE LAMINARIA HIGH AREA

Abstract

A strong relationship between the distribution of Late Miocene to recent (post-rift) strain, trap geometry and remaining oil columns is recognised in the heavily re-activated Laminaria High area. Preferential localisation of post-rift strain onto larger faults in the population resulted in the smaller faults accommodating progressively less strain with time. The strain localisation process appears to have protected some fault-bound traps with favourable geometries from breaching during fault re-activation, but promoted breaching of others. Where faults with high postrift strain are located at the crest of a trap, oil columns are not preserved. In contrast, where high strain post-rift faults are located down-dip of the trap crest, oil columns are preserved down to the depth of the critical high strain fault-top reservoir intersection. These observations suggest that a relatively simple assessment of the basic structural geometry of a trap may provide a first order approximation of trap integrity risks and could also be predictive of preserved hydrocarbon column heights.