4-D Tectono-stratigraphy, Inverted Fault Architecture and implications on Hydrocarbon Migration within the Taranaki Basin, Offshore New Zealand.pdf

Abstract

The Maari Field is a large oil and gas field located in the Southern Inversion Zone of the S. Taranaki Basin, New Zealand. The field is bounded by two major structures, the Eastern Mobile Belt and Western Stable Platform and produces 40,000 BOPD (Barrels of Oil per Day) from reservoirs in the Moki Formation. The field is distributed along the southern and central Taranaki shelf. 3-D seismic data and well logs were recorded by the Geco-Prakla Company and provided for analysis of the tectono-stratigraphic evolution of the Taranaki Basin, a sub-basin within the New Zealand region. The Maari Field, contains an excess of twenty faults that all play an important role in petroleum systems of the Taranaki Basin. Faults in this structurally complex region act as both barriers and conduits to the flow of hydrocarbons. An understanding of the relationship between fluid and gas migration and accumulation with faulting is often required during hydrocarbon exploration and production, and CO2 storage.Faults in the Maari Area tend to strike from the south toward the northeast. Seismic attributes, such as coherence, were mapped to interpret the major and minor faults. This thesis undertakes studies of the Maari Area’s structural development, examining growing fault architectures of inverted rift faults and associated fold structures as well as recent extensional faults of the Plio-Pleistocene. Data for this study are provided by high quality 2D and 3D seismic reflection lines. Structural development in the Maari Area was complex and provides a record of deformation since the Late Cretaceous to Recent. Basin strata up to 8 km thick record four main periods of deformation that reflect changing plate boundary configurations: 1st extensional phase, a post-extension relaxation period, and a compressional syn-inversion stage and 2nd extensional chapter until recent. Thus fault reactivation was common in the Maari Area, with the locations and orientations of pre-existing faults influencing the locations and geometries of younger faults and folds.Pliocene to Recent normal faults are highly segmented with low strain rates and small displacements, consistent with an immature fault system in which fault strike lengths were formed rapidly with subsequent fault growth achieved largely by accumulation of displacement.Plio-Pleistocene to Recent reactivation of Cretaceous rift faults provide evidence of negative inversion and allow gas migration through these open conduits from below the regional top seal in the Maari Area into shallower strata post Miocene, resulting in up-dip gas migration within the Plio-Pleistocene to Recent fault zones.These late-stage extensional faults have a strong spatial relationship with gas chimneys suggesting that these faults are capable of producing channelised pathways for up-dip hydrocarbon migration. All of these gas chimneys occur at geometrical complexities in Plio-Pleistocene fault structures (i.e. relay zones, lateral fault tips or fault intersections).