W10-20 - Department of Resources, Energy and Tourism

most of the Exmouth Plateau is now under permit, with indicative work program commitments since
2004 totalling approximately $1 billion, including nine guaranteed deepwater wells to be drilled in
WA-404-P held jointly by Hess corporation and Woodside, and two exploration wells in the recently
renewed WA-346-P permit adjacent to Release Areas W10-20 to W10-22. 3d seismic and AVO
technology are key exploration tools that contribute to high success rates on the Exmouth Plateau
(longley et al, 2002; Korn et al, 2003; Williamson and Kroh, 2007).
Well Control
no wells have been drilled within the Release Areas, but several are in close proximity (Jupiter 1,
scarborough 1, thebe 1 and 2, Kentish Knock 1) and others provide important stratigraphic control
or nearby gas discoveries (Figure 1).
InvestIgator 1 (1979)
investigator 1 was drilled by Esso Australia ltd to test delta front sandstones of the lower
cretaceous barrow Group in a large closure formed by a combination of northward depositional dip
on the delta front, regional south to southeast tilting of the Exmouth Plateau and gentle cenozoic
arching about a northeast-trending axis (EssO Australia ltd, 1980a). the well was drilled in a water
depth of 841 m and reached a td of 3745 mKb. it penetrated and sampled an Albian-barremian
succession of claystone, marl and siltstone to 1492 mKb, overlying a 1748 m thick section of basinal
to prodelta and delta front claystone, siltstone and sandstone of the target barrow Group. the
barrow Group was underlain by a 15 m section of upper Jurassic claystone, middle-lower Jurassic
marl (44 m), upper triassic (Rhaetian) marl (65 m) and upper triassic (norian) interbedded sandstone,
siltstone claystone and minor coal of the mungaroo formation (382 m thick to td). sandstones of
good reservoir quality occur within the barrow Group (13–30% porosity), but those within the upper
triassic mungaroo formation were generally poor (5–16% porosity).
no significant hydrocarbon shows were recorded in the target barrow Group reservoir, but elevated
mud gas levels and small amounts of wet gas and questionable oil films in wireline tests were
recorded in low permeability sandstones of the mungaroo formation. log analysis indicates 48–86%
water saturation in these sandstones. the lack of hydrocarbons in the barrow Group sands was
attributed to the absence of effective migration pathways for any hydrocarbons generated within the
deeper mungaroo section.
JupIter 1 (1979)
Jupiter 1 was drilled by Phillips Australian Oil company in water depths of 960 m to test a
tilted triassic horst (Figure 5). the well reached a total depth of 4946 mRt in a thick section of
interbedded triassic siltstone, claystones, sandstone and minor coal and dolomite (A. reducta to
S. quadrifidus spore/pollen zones) of the mungaroo formation (Phillips Australian Oil company,
1980a). the well penetrated 466 m of inferred calcareous ooze and marl of Holocene to late
cretaceous age without returns, and sampled cretaceous chalk, calcareous claystone and siltstone
to 1857 m, and a 15 m section of upper Jurassic claystone to 1872 m. this Jurassic claystone was
unconformably underlain by 23 m of upper triassic (Rheatian) carbonate and claystones 39 m of
transgressive marine siltstone and sandstone (ascribed to the brigadier formation by crostella
and barter, 1980) and a thick section of upper-middle triassic deltaic sediments of the mungaroo
formation (1895-4946 m td). this is the maximum drilled thickness of triassic section on the
Exmouth Plateau.
A 22.5 m gas column was discovered in upper triassic sandstones (1911-1933 mKb; brigadier
formation) with reserves of about 0.15 tcf (4 bcm; Walker, 2007). this accumulation has a strong
flat-spot dHi on seismic data, which indicates the spill-point of the gas into the bounding fault and
venting through to a gas-chimney evident on seismic (barber, 1988).
Geology of Release Areas W10-20, W10-21 and W10-22 | www.petroleum-acreage.gov.au 4