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Characterizing Modern Sediments to Better Understand Reservoir Sand Provenance, Taranaki Basin, New Zealand

Linda M. Doran1, Kathleen M. Marsaglia2, and Gregory H. Browne3
1California State University Northridge
2California State University
3GNS Science

The offshore Taranaki Basin is New Zealand’s most important area of petroleum exploration and production, but many known petroleum reservoirs are nearing depletion. Information facilitating discovery of additional reservoirs is of great interest. The objective of this study is to determine sediment provenance (source) of existing petroleum reservoirs to enable more targeted exploration. Paleoriver systems draining uplifted basement terranes were the likely source. Modern equivalents of these terranes crop out in the Nelson region of South Island. They include the variously metamorphosed Paleozoic Buller and Takaka terranes on the west side of the north-south trending Alpine Fault and the Late Paleozoic to Mesozoic Murihiku, Dun Mountain-­‐Maitai, Brook Street, Caples, and Torlesse composite terranes to the east. Intruding these terranes are Paleozoic to Mesozoic granitic batholiths. The testable hypothesis is that basement terranes continue to shed sandy sediment of distinct composition into modern river systems and these modern sands can be used to interpret the provenance of offshore petroleum reservoir sandstones. Characterization is based on detailed petrographic analysis. Samples are sieved into five sand fractions – from very coarse to very fine – to identify grain size-dependent changes in composition. Detailed point counts (400 per sample) of stained thin sections in 40+ categories enable estimates of the relative abundances of different grains. Results are compared with published reports describing offshore reservoirs.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013