Print this page
Syn-Kinematic Sediment and Facies
Distribution Across a Growth-Fault in the
Wave-Dominated Deltaic Succession of the Neogene
Champion System, Northwest Offshore
Lap, Lai Quoc, John K. Warren, University
Champion delta hosts multi-million barrel oil and gas fields in
shallow shelf sediments. At the scale of Mahrajah
Lela (ML) field, the depopod that makes up the
regional “delta” prism is actually a complex of smaller inter-related
depositional systems (shelf, shoreface and minor
tidal). Time variant sediment extent was controlled by eustacy
and was driven largely by fault activity at both the basin and local scales.
Rapid deposition and progradation of shelf sediment
initiated a seaward-steeping growth-fault FML in ML field, which then
interplayed with counter-regional Perdana
growth-fault, to create a variably-subsiding depocentre
in the area between these two faults.
If subsidence induced by the FML fault was greater than that of
the Perdana, then subsidence at early stage of each
active phase created substantial accommodation space across both sides of the
fault in the main ML field. Depending on rate of sediment influx into this
depression, infilling sediments prograded or aggraded
to fill the available space. However, when FML growth was slow, the regional Perdana growth-faults exerted greater influence, resulting
in retrogradational sedimentation in the ML field.
Interpretations
of core, borehole image, conventional wireline and
seismic data in footwall area indicate wave-dominated sandy facies are more locally distributed and tidal deposits
occur more frequent there. In contrast, layers in the hanging-wall are much
thicker with a greater degree of lateral continuity across the field. Shoreface sandstones in the hanging wall are also cleaner
and more petrophysically homogenous, while tidal
occurrences are diminished or absent. When supply was sub-parallel to axis of
FML fault, a much a greater volume of sediment accumulated in the down-thrown
block compared with the upthrown block.