Seismic geomorphology and reservoir conditions of a Middle Miocene submarine channel system in the Taranaki basin, New Zealand

Deepwater channels function as vital deep-sea hydrocarbon reservoirs and as major routes for moving terrestrial clastic sediment to deepwater environments. A high-resolution sequence stratigraphic framework was built for the deepwater area of the Taranaki Basin using high-resolution three-dimensional (3D) seismic data, and various seismic interpretation techniques, including seismic attribute analysis, were applied. The principal controlling factors and petroleum development potential of the Middle-Miocene channel system were investigated with sequence stratigraphy and seismic geomorphology. Four understandings were primarily attained in this study: (1) depending on the different levels of the channel surfaces, the channel system can be divided into five sedimentary units (SU1-SU5), which correspond to the five stages of channel system evolution. These surfaces include one primary draping surface (PDS), five secondary channel erosion surfaces (SCES), and several tertiary channel erosion surfaces (TCES). (2) with the use of seismic facies analysis, six sedimentary elements were identified in the channel system: pelagic deposits (PDs), mass transport deposits (MTDs), outer levee complex (OLC), inner levee and terrace complex (ILTC), and turbidite channel complexes (TCCs). (3) The sedimentary evolution of the channel system was jointly influenced by multiple factors. The sediment supply and submarine geomorphology can directly affect the internal stacking and migration patterns of the channel. In contrast, tectonic activity and relative sea level fluctuations can indirectly affect the sedimentary characteristics of the channel by regulating the components and scale of clastic sediment. (4) SU1, SU2, and SU3 are primarily filled with coarse-grained sediments, which can serve as high-quality hydrocarbon reservoirs. In contrast, SU4 and SU5 can serve as regional cap rocks because they are filled with fine-grained sediments, and the overall channel system can represent a potential hydrocarbon reservoir-cap combination, which can be viewed as a significant research target for upcoming deepwater exploration. Clarifying the sedimentary properties and primary controlling factors at the various evolutionary stages of deepwater channels is vital for predicting the hydrocarbon development potential of the basin and reducing the drilling risk. This also helps with the development of deepwater basins with similar sedimentary environments in New Zealand and elsewhere in the world.