Publication Name: PESA's Eastern Australasian Basin Symposium II
Authors: L. Johnson, M. Lisk, A. Gartrell and P. Boult
Date Published: December 2004
Number of Pages: 28
Reference Type: Book Section
Abstract:
The hydrocarbon charge history of the Gidgealpa Oilfield has been investigated to test an existing trap integrity model proposed for the Hutton-Birkhead reservoir-seal couplet. Conventional oil show data have been supplemented with grains with oil inclusions (GOI?) data to assess the palaeo-oil saturation and to define the location of the palaeo-oil water contact (P-OWC).These data confirm the existence of a much larger oil column in the past, with a common P-OWC approximately 28 m below the current FWL in six of the seven wells analysed. The palaeo-column height closely matches the interpreted seal capacity and is also approximately coincident with the mapped closure. A deeper contact was observed in Gidgealpa-27 and appears to indicate the presence of either a lateral barrier separating the southwest flank of the field or stacked palaeooil columns, sealed by intraformational shales.
3D structural restoration has provided insights into the trap evolution and constrained the charge history of the
Gidgealpa Oilfield. Incorporation of GOI-derived P-OWCs in the restoration suggests that only limited differential
modification of the contacts has occurred.
High GOI results from sands above the interpreted sealing interval of the Birkhead Formation suggest some areas
above the seal have received oil charge. Interestingly, the current oil saturation of these intervals is unknown so it remains unclear whether these are palaeo-oil columns or zones of bypassed pay.