Sequence Stratigraphy of the Wheatstone and Iago Fields, North West Shelf, Australia: Implications for Reservoir Characterisation

The Wheatstone and Iago fields supply the majority of the
gas to the Wheatstone liquified natural gas (LNG) project on the
North West Shelf of Australia. These giant gas and condensate
fields are hosted in Late Triassic, delta plain and shallow
marine reservoirs. Effective characterisation of these resources
is critical for maximising hydrocarbon recoveries from the
fields. Sequence stratigraphic subdivision of the reservoirs
using an integrated seismic, well log, core and biostratigraphic
approach has proven to be an effective technique enabling
maximum flexibility for characterising the reservoirs, building,
and updating 3D static reservoir models. In the delta-plain
dominated Mungaroo Formation, the lowstand systems tracts
exhibit the highest proportions of coarse-grained facies whilst
the transgressive systems tracts exhibit the highest proportions
of finer-grained facies. This differentiation is critical since
grain-size can be directly correlated to reservoir permeability.
Integration of palaeocurrents from borehole image logs with
seismic attribute data permits intra channel-belt-complex
trends in reservoir properties to be integrated into static
reservoir models. In the shallow marine Brigadier Formation,
subdivision of the stratigraphy into flooding-surface bounded
parasequences (potential reservoir flow units) and 4th and 3rd
order sequences has enabled maximal flexibility for distributing
reservoir properties (net to gross, porosity and permeability)
and for matching drill-stem tests (DST) and early production
data results. The parasequence architecture also permits
modelling and testing of key intra flow-unit heterogeneities
such as shale-draped deltaic clinoforms as well as permitting
analysis of production sensitivities to distributary channel
properties (e.g. high permeability fills versus shale fills).
Additionally, the sequence stratigraphic framework permits
correlation into adjacent fields and the potential to utilise
stratigraphically equivalent data from these fields to assist
in reservoir characterisation, and to understand the largescale
architecture of the stratigraphic units beyond the field
boundaries.