About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
AAPG Bulletin, V.
Modification of fracture porosity by multiphase vein mineralization in an Oligocene nontropical carbonate reservoir, Taranaki Basin, New Zealand
1Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand; email: [email protected]
2Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand; email: [email protected]
3Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand; email: [email protected]
Steven Hood is a postdoctoral research fellow in the Department of Earth Sciences at the University of Waikato in Hamilton, New Zealand. While recipient of a University of Waikato doctoral scholarship, he completed a Ph.D. on the subsurface stratigraphy and petrology of the middle Tertiary Tikorangi Formation fracture reservoir in Taranaki Basin in 2000. His research interests are currently focused on the petrology, paragenesis, and petroleum geology of cool-water carbonates, especially in New Zealand.
Cam Nelson received B.Sc. and B.Sc. (honors) degrees in geology at Victoria University, Wellington. He lectured in the Department of Geology at the University of Auckland, where he received his Ph.D. before joining the Department of Earth Sciences at the University of Waikato in Hamilton in 1971 as its founding geological staff member. He was department chairperson from 1988 to 1996 and has been a professor since 1991. His research interests are in sedimentary and marine geology and stratigraphy and Cenozoic paleooceanography and paleoclimatology of the southwest Pacific region. He is past president and office holder of the Geological Society of New Zealand and was elected a fellow of the Royal Society of New Zealand in 1994.
Peter Kamp is professor of Earth Sciences at the University of Waikato in Hamilton. He received his M.Sc. degree and his Ph.D. from the University of Waikato. His research interests are in the analysis of sedimentary basins, particularly those of Late Cretaceous–Cenozoic age in New Zealand. Another major research interest involves the techniques of fission-track analysis and (U–Th)/He thermochronometry. His research applications involve the thermal history of sedimentary basins and the exhumation history of basement provinces–mountain belts.
We thank Petrocorp Exploration, now Shell Petroleum Mining, for access to drill-core and in-house petroleum reports and the New Zealand Ministry of Economic Development for assistance in the Petroleum Report Library and core storage facilities, Wellington. We are grateful to John Collen for providing perceptive insights about the topic and Brian Ricketts for reviewing an early draft of the manuscript. We are grateful to Jeffrey Dravis and Mark Longman for constructive referee comments and to John Lorenz (AAPG editor) for his helpful suggestions. We acknowledge funding from the University of Waikato Postgraduate Scholarship and the New Zealand Foundation for Research Science and Technology (UOW815).
The nontropical Oligocene carbonate-rich Tikorangi Formation is an important oil producer in the Taranaki Basin, New Zealand. Hydrocarbons are hosted and produced from mineralized, natural fracture systems. Petrographic, trace-element, stable-isotope (18O and 13C), and fluid-inclusion data have enabled a complex sequence of eight paragenetic events to be determined. The Tikorangi Formation host rock was cemented by low-Mg calcite (event 1) during burial diagenesis, from temperatures of 27C, corresponding to 0.5 km burial, and continued until 37C, 1-km burial depth, producing tight, pressure-dissolved fabrics with essentially no porosity and permeability. The host rock was partially dolomitized (5–50%) (event 2) by Ca- and Fe-rich dolomite rhombohedra at burial depths and temperatures of 1.0–1.5 km and 35–50C without secondary porosity development. Subsequent brittle fracturing formed by Neogene compression (event 3) is constrained to a period following lithification and dolomitization, but before precipitation of first-generation vein calcite (event 4). This initial ferroan low-Mg vein calcite formed after a period of burial from Fe-rich, meteorically modified fluids at temperatures of about 50–60C and 1.4–1.9 km burial depth. Baroque dolomite formed (event 5), following a period of Mg-enriched basinal fluid input precursory to hydrocarbon emplacement per se. The dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2–2.5 km and temperatures of 65–80C. Formation of celestite and quartzine phases (event 6) coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements. Second-generation ferroan vein calcite formed (event 7) at cooler temperatures (53–65C), perhaps resulting from the introduction of cooler meteoric fluids from upsection. The presence of petroleum-fluid inclusions in the second-generation calcite suggests precursory hydrocarbon-bearing fluids have migrated, along with aqueous fluids from about 10 Ma, with hydrocarbon emplacement (event 8) occurring in the last 6 m.y. following a period of rapid late Miocene burial. An improved understanding of the paragenesis of the Tikorangi Formation may assist in hydrocarbon production from its reservoirs.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
|Watermarked PDF Document: $14
|Open PDF Document: $24
Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].