Migration Modeling and Phase Prediction Within the Taranaki Basin in New Zealand: A Multidisciplinary Approach Highlights New Plays in a Mature Basin

Abstract

The Taranaki Basin is located offshore west of the North Island of New Zealand and covers an area of approximately 40,000 km2. The Taranaki Basin started as an extensional basin associated with Cretaceous rifting and break‐up of the Gondwana supercontinent and underwent, after the initial rifting, several compressional and extensional phases. The on‐ and offshore parts of the Taranaki Basin comprise approximately 1.1 boe of recoverable resources. The most prominent offshore hydrocarbon accumulation is the Maui gas‐condensate and oil field, which contained more than 3.5 tcf of gas, 193 mmbbls of condensate and 32 mmbbls of oil recoverable. High exploration potential is recognized in Miocene channel systems within the northern part of the Taranaki Basin. Age equivalent channel systems host the Maari oil field in the southern part of the Taranaki Basin. Regional play based evaluation highlights the most prospective areas within the northern part of the Taranaki Basin and focusses detailed seismic mapping as well as basin modelling. Syn‐ and post‐rift coals and coaly mudstones constitute the main source rocks (SR) within the basin and are were correlated with discovered oil and gas fields. Detailed seismic attribute analysis was carried out to define reservoir presence and distribution. Occurrence of pockmarks on high resolution 3D seismic furthermore confirms hydrocarbon migration within the area of interest and coincides with the onset of HC expulsion of the underlying coals. Vertical migration is focused on areas in the proximity of faults and has been proven in the southern part of the basin. A detailed migration model was run based on detailed seismic interpretation and attribute analysis, fault seal analysis, source rock facies distribution and regional source rocks expulsion maps. Sensitivity analysis was carried out on the seal properties of individual layers and the model was calibrated to hydrocarbon shows in offset wells. Due to the high expulsion GORs of these liquid prone coals, seal capacity has a major impact on hydrocarbon phase. Fault seal analysis was carried out on the main prospect within the area, a Miocene aged deep marine channel complex within a lowside three way structural trap. The results of the fault seal analysis were incorporated into a prospect specific high resolution petroleum system model, which captures the interaction between migration vs. fluid phase behavior and trap closure vs. fault seal capacity. The interaction of fault seal capacity and trap configuration leads, in multiple scenarios, to retention of a significant oil column in the target trap. This study clearly shows the potential of this underexplored play within a mature basin and de‐risks a significant drill ready prospect, which has been identified on 3D seismic. These results could only be achieved by incorporating all available geological data (e.g. fault seal, reservoir, seismic and SR data) and shows the high value of a detailed petroleum system assessment in a mature basin.

AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019