Reservoir Potential Of The Eumerella Formation Sandstones
Geoscience Masters Degree, 2011
University of Adelaide
The Eumeralla Formation is an Aptian – Albian aged rift fill sequence within the Otway Basin, located in south-eastern Australia. The predominantly fine-grained sediments of the Eumeralla Formation have high source rock potential (Duddy, 1997), but the formation also contains three distinct groups of sandstones with unknown reservoir potential.
The three sandstone groups of the Eumeralla Formation are:
· Windermere Sandstone Member (WSM): laterally extensive fine-grained stacked channel sands.
· Intercalated coarse siltstone and fine sandstone beds within the Eumeralla Formation
· The Heathfield Sandstone: a locally deposited basement provenance channel sandstone.
The physical sedimentology and environments of deposition of each group are investigated from core based observations, and the detailed review of previous works. The petrological and petrophysical properties of each sandstone group are investigated using a suite of analytical techniques, including: transmitted light thin-section petrology; Automatic Mineral Analysis (AMA), utilising QEMSCAN R technology; Helium porosity; ambient air permeability; and Mercury Injection Capillary Pressure (MICP).
Mineralogical trends derived from petrological observations provide valuable evidence for the provenance of the Eumeralla Formation sandstone groups. The WSM shows evidence of dual provenance, with the major provenance source an intermediate volcanic terrane, and minor input from a local basement margin granitic terrane. The Eumeralla Formation intercalated siltstone and sandstones are compositionally immature, with provenance relationships suggesting a basic volcanic sediment source. The tectonic provenance of the Heathfield Sandstone indicate that it is derived shedding of basement terrane.
A combined synthesis of all results indicates that the WSM has the highest reservoir potential of the Eumeralla Formation sandstone groups. The Heathfield Sandstone forms sandstone bodies with low to moderate reservoir potential, but due to localised variations in deposition and sediment composition the reservoir quality of the group is difficult to predict. The intercalated Eumeralla Formation siltstones and fine-grained sandstones are classified as having poor reservoir potential.