Failure to predict igneous rocks encountered during exploration of sedimentary basins: a case study of the Bass Basin, Southeastern Australia

Douglas Watson, Simon Holford (Corresponding Author), Nick Schofield, Niall Mark

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The Bass Basin, a Mesozoic-Cenozoic intra-continental rift basin along the southern Australian continental shelf, offers an excellent natural laboratory for examining igneous rocks in the subsurface. Igneous material within the basin is manifested as a mixture of predominately mafic extrusive and intrusive rocks, mainly Cretaceous-Palaeocene and Oligo-Miocene in age. Igneous rocks have been encountered in 20 out of 36 (55.6%) exploration wells drilled within the Bass Basin, but the presence of these has historically been poorly predicted; of the first 11 exploration wells to penetrate igneous rocks, their presence was not predicted in pre-drill interpretations. We present a series of case studies from wells that unexpectedly encountered igneous rocks. The first of these wells (Bass-1) targeted a carbonate reef structure which instead penetrated the flank of a submarine volcano. In another notable example (Flinders-1 well), a relatively discontinuous high-amplitude seismic reflection thought to be a clastic reservoir was found to be an igneous intrusion with a relatively unusual composition. A number of these incidents, where igneous rocks were unexpectedly encountered, can be accounted for by human factors, such as a sparsity of good quality data and a lack of knowledge transfer as companies entered and left basin during different phases of exploration. However, a number of examples, particularly the unexpected occurrence of igneous intrusions, appear to have been caused by anomalously low acoustic impedance contrasts between igneous rocks and surrounding sedimentary sequences. Our findings have generic implications for other sedimentary basins impacted by magmatic activity, such as the importance of integrating available outcrop data in the absence of nearby well control, and the value of fully appraising previous exploration results.
Original languageEnglish
Pages (from-to)526-547
Number of pages22
JournalMarine and Petroleum Geology
Volume99
Early online date21 Oct 2018
DOIs
Publication statusPublished - Jan 2019

Fingerprint

igneous rocks
sedimentary basin
igneous rock
basin
well
intrusion
submarine volcano
reefs
acoustic impedance
outcrops
continental shelves
sedimentary sequence
data quality
volcanoes
Paleocene
seismic reflection
continental shelf
carbonates
outcrop
reef

Keywords

  • volcanics
  • exploration
  • pre-drill prediction
  • Southern Australia
  • Bass Basin
  • Pre-drill prediction
  • Bass basin
  • Volcanics
  • Exploration

ASJC Scopus subject areas

  • Economic Geology
  • Geology
  • Geophysics
  • Oceanography
  • Stratigraphy

Cite this

Failure to predict igneous rocks encountered during exploration of sedimentary basins : a case study of the Bass Basin, Southeastern Australia. / Watson, Douglas; Holford, Simon (Corresponding Author); Schofield, Nick; Mark, Niall.

In: Marine and Petroleum Geology, Vol. 99, 01.2019, p. 526-547.

Research output: Contribution to journalArticle

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