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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2012. The American Association of Petroleum Geologists. All rights reserved.
Normal faults and gas migration in an active plate boundary, southern Taranaki Basin, offshore New Zealand
Bradley R. Ilg,1 Samuel Hemmings-Sykes,2 Andrew Nicol,3 Jan Baur,4 Miko Fohrmann,5 Rob Funnell,6 Mike Milner7
1GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; present address: New Zealand Petroleum and Minerals, Ministry of Economic Development, P.O. Box 1473, Wellington, New Zealand; [email protected]
2GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; School of Earth Sciences, Victoria University of Wellington, Wellington, New Zealand; present address: ExxonMobil, 12 Riverside Quay, Southbank Victoria 3006, Melbourne, Australia; [email protected]
3GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; [email protected]
4GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; present address: Total Exploration and Production, Scientific and Technical Center Jean Feger, Avenue Larribau, Pau, France; [email protected]
5GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; [email protected]
6GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; [email protected]
7GNS Science, P.O. Box 30368, Lower Hutt, New Zealand; present address: OMV, 10 Brandon Street, Wellington, New Zealand; [email protected]
ABSTRACT
The function of normal faults in upsequence flow of gas has been examined using two-dimensional and three-dimensional seismic-reflection data from the southern Taranaki Basin, New Zealand. The spatial distributions of late-stage normal faults, gas chimneys, thickness of the Oligocene mudstone-rich seal
(Otaraoa Formation), and modeled hydrocarbon expulsion volumes are compared. Gas chimneys are most common above Cretaceous source rocks modeled to have expelled hydrocarbons. Most (
70%) of the observed gas chimneys follow, and/or are rooted in, late-stage normal faults. These faults are the primary
seal
bypass mechanism for hydrocarbons, where they displace the
seal
(or intersect faults that displace the
seal
) and the
seal
is thick (e.g., more than
340 m [
1115 ft]). Active vertical gas flow through the
seal
commenced after the onset of faulting (
3.6 Ma), whereas subseal lateral flow started significantly earlier at approximately 15 Ma and resulted in an early charge of structural highs. Gas flow up along faults in low-permeability mudstones (
1 md) is channelized with steep chimneys commonly occurring close to fault tips and relay ramps. In these cases, gas flow may be focused by the presence of high densities of open fractures locally elevating upsequence bulk permeabilities to approximately 1 to 400 md.
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