Gross seismic facies mapping of the Tertiary overburden and implications for shallow hazards, Browse Basin, North West Shelf, Australia
Honours Degree, 2010
University of Adelaide
Biostratigraphic data from Carbine-1 suggests that the depositional environment of this facies varies over time from an open marine bank to an inner to middle neritic system back to an open marine bank.
5.6.2 - Facies type 2 (VASC)
This facies interval defines the change from a moderate amplitude inboard reflector package to a more variable amplitude, semi-continuous reflector package. The overall reflection geometries are parallel to sub-parallel in a gross sense (Figure 5.4). The top and bottom reflectors tend to follow the orientation of the upper and lower bounding TO and T seismic stratigraphic horizons.
The variability in this reflector package comes from amplitude and not geometry (Figure 5.4). The amplitude variations are lateral and vertical in nature with patches of higher amplitudes dispersed amongst lower amplitude sections.
This facies type has a good well control, with the majority of the wells located around the Ichthys gas fields intersecting the facies. Five wells intersect this facies type, all the wells contain lithological and petrophysical descriptions. This facies type is composed primarily of medium grained sandstone with interbedded with calcarenite (Figure 5.7). The lower quarter of the facies interval is defined as a calcareous claystone with minor sandstone; this facies type is very consistent in its lithological descriptions.
The variability in amplitudes may be attributed to acoustic impedance differences between lithologies, an example being an increase in carbonate/claystone thickness amongst predominately sandstone.