Abstract

Apatite fission track analysis (AFTA) has been applied to samples from four hydrocarbon well sections to study the thermal and tectonic history and the hydrocarbon prospectivity of the southern part of the Taranaki basin (New Zealand). Data from three of the wells (1 Fresne, 1 North Tasman, 1 Surville) show that the successions were exposed to higher temperatures in the past through deeper burial. Cooling from elevated paleotemperatures was effected by late Miocene uplift and erosion of 3.0+ or -0.3 km of section in 1 Fresne, 2.0+ or -0.5 km in 1 Surville, and 1.0+ or -0.3 km in 1 North Tasman. In the fourth well, 1 Kupe, formations are currently at their maximum temperatures since deposition. AFTA provides unique constraints on the timing of hydrocarbon generation in relation to trap formation. The proposed source rocks in 1 Fresne passed through the oil formation window (100-150 degrees C) and into the zone of gas production (150-200 degrees C) during the middle Miocene, prior to the formation of potential trapping structures. Those in 1 North Tasman passed into the oil formation zone about the same time, and source rocks in 1 Surville have probably never been heated enough to produce oil. AFTA indicates considerable prospectivity remains in the region of 1 Kupe, where generation would have occurred after trap formation.

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