The Northwest Offshore Otway Basin Well Folio

Full description

The Otway Basin is a northwest-southeast trending rift basin which spans from onshore Victoria and South Australia into the deep-water offshore. The prospective supersequences within the basin are largely of Cretaceous age which host three possible petroleum systems (Austral 1, 2 and 3). While there is production from onshore depocentres, and the inboard Shipwreck Trough, the majority of the offshore basin remains underexplored. Recent regional studies have highlighted the need for further work across the underexplored parts of the basin and here we focus on the offshore northwest Otway Basin, integrating reinterpreted historical well data, newly acquired and recently reprocessed seismic data. This new Well Folio consists of composite logs and supporting data which includes interpreted lithologies, petrophysical analyses, the analysis of historic organic geochemistry and organic petrology. In addition, updated well markers are provided based on seismic interpretation and new biostratigraphy in key wells. This integrated study provides the basis for renewed prospectivity assessment in the northwest offshore portion of the Otway Basin.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Well composites were produced using Schlumberger’s Techlog software package. All data were either loaded into Techlog or results of interpretation using Techlog. The wells included in the well folio package are as listed below: Argonaut A1 Breaksea Reef 1 ST3 Chama 1A Copa 1 Crayfish 1A Morum 1 Sophia Jane 1 Triton 1 ST1 Troas 1 ST1 Trumpet 1 Voluta 1 The information used for the well folio were primarily extracted from well completion reports (WCRs) and destructive analysis reports (DARs), and the digital data are maintained in Geoscience Australia’s databases. These data include well header information, formation evaluation logging, cuttings, sidewall core and drill core lithology, organic geochemical data, oil and gas shows, and stratigraphy. To ensure uniformity across wells, geological names from Geoscience Australia’s Australian Stratigraphic Unit Database (https://www.ga.gov.au/data-pubs/datastandards/stratigraphic-units) were used and geological names from the original data sources were replaced where necessary. Well lithologies were interpreted and petrophysical analyses undertaken to characterise potential reservoir and source rock units. Organic geochemical, including total organic carbon (TOC) content from LECO and pyrolysis data, as well as organic petrological data were compiled to evaluate source rock quality and thermal maturity. The work flow was as follows: • Well header, casing shoe depth, drilled core interval, sidewall core data were derived from WCRs; • Hydrocarbon shows information originated from WCRs with interpretation as derived from Geoscience Australia’s Petroleum Wells (RESFACS) database (http://dbforms.ga.gov.au/www/npm.well.search); • Digital well logs were quality controlled, edited and depth aligned in Techlog; • Organic geochemistry programmed pyrolysis data (i.e. TOC, S1, S2, HI, PI and Tmax) and vitrinite reflectance (VR) maturity data originated from WCRs and DARs, which were derived from Geoscience Australia’s Organic Geochemical database (ORGCHEM) available through Geoscience Australia’s portal (https://portal.ga.gov.au/).

Notes

Purpose
Providing data to stakeholders for offshore Otway prospectivity