Appraisal drilling in the Gidgealpa Field which has a 20 year production history has confirmed the existence of a significant oil rim underlying the Permian Age Tirrawarra Sandstone gas reservoir and a large extension of the Jurassic Age Hutton Formation oil reservoir.

An oil leg to the Tirrawarra Sandstone reservoir gas pool in the South Dome could be inferred from the geophysical, geological, and production performance data obtained from Gidgealpa-7 and Gidgealpa −16. A PVT analysis of a gas sample collected more recently from Gidgealpa-34 was strong evidence to support this interpretation. Gidgealpa −41 drilled on the northeast flank of a four way dip closed anticline flowed oil at 600 BOPD from clastic Permian aged Tirrawarra Sandstone, consequently confirming an oil leg to a known gas cap.

The relatively low decline in production performance of the southern region of the Hutton Sandstone oil pool indicated a reservoir extension. Alternate seismic mapping techniques using isopachs and recognition of high velocity layers were successful in eliminating high velocity calcareous zones in the Jurassic Age Namur Sandstone Member which previously hampered mapping of the field. Appraisal drilling successfully extended the Hutton reservoir limit by 1.5 kilometres to the south.

Renewed focus has thus centred on these two (Hutton and Tirrawarra) oil pools which require separate development strategies.

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