A geological study of the deepwater fold-thrust belt on the northwest borneo margin and its application to petroleum system analysis

Ogawa, Kazuhiro; Back, Stefan (Thesis advisor); Littke, Ralf (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

This thesis investigates the deformation mechanisms in the deepwater fold-thrust belt of the northwest Borneo margin offshore Sabah, Malaysia. The complex petroleum systems in this area, are discussed and the interactive tectonics and sedimentary evolution of the fold-thrust belt and its associated petroleum system is documented and described. The thesis research is fundamentally based on analyses of regional 3D seismic-reflection and borehole data, which allow to establish a comprehensive insight into subsurface structures, subsurface stratigraphy, fold-thrust development over time, syn-kinematic sedimentation and petroleum system development. The research presented contributes to a better understanding of the tectonics and petroleum geology of northwest Borneo and therefore provides insights into fundamental processes for future subsurface resource development and CCS purposes offshore northwest Borneo. The study is furthermore important beyond the study area in that it contributes to the general knowledge on tectonics, sedimentation and petroleum systems in deepwater fold-thrust belts. The key outcomes of the research are summarized as follows.1.A northwest-oriented deepwater sediment system was identified as source for the Upper Miocene hydrocarbon reservoir interval in the study area. This system was influenced by syn-depositional morphological variations induced by syn-sedimentary tectonics, in particular folding and uplift blocking and deflecting deepwater sediment-flow pathways.2.It was discovered that the deepwater reservoirs along the northwest Borneo were supplied by multiple, line-sourced sediment feeder systems originating from different hinterland provinces carrying and depositing different rock associations.3.The fold-thrust belt exhibits different deformation styles and different timing of tectonic activity in the southwestern and northeast study area. The major deformation driving-mechanism was interpreted as gravity-driven in the southwestern study area. In contrast, in the northeastern study area deformation was dominantly driven by deep-seated crustal tectonics.4.Structural features in each structural province developed independently and were preserved largely without mixing/interfingering in the fold-thrust belt; with the exception of an interference zone of ca. 15 km in width.5.Pockmarks and gas clouds related to thermogenic hydrocarbons are widely observed in the 3D seismic-reflection data, suggesting a widespread subsurface distribution of matured source rocks. The most reasonable source-rock unit is of Middle Miocene age and corresponds to the thrust detachments; this unit is characterized by anomalously low seismic interval velocity.6.Petroleum-systems modeling shows that hydrocarbon expulsion started in the Upper Miocene for oil and in the Pliocene for gas. In the crustal tectonic-driven northwest of the deepwater fold-thrust belt, activity preceded these expulsions. Hydrocarbons expelled from the source-rock sequence accumulated preferentially turbiditic sandstones in the respective crests of thrusted-hangingwall-anticlines by hydrocarbon migration through carrier beds and faults.7.In the more southeastern, gravity-driven thrust system offshore northwest Borneo, thrust development started contemporaneously with reaching the oil window in the source rock. Fault activity then reached its peak deformation within the gas window. This observation is fundamentally important in that it suggests subsurface geochemical processes as a potential controlling parameter for folding and thrusting in gravity-driven deepwter fold-thrust belts.In summary, this thesis presents detailed analyses of subsurface geophysical data of a major deepwater fold-thrust belt offshore northwest Borneo. The work presented documents a major structural, morphological and lithological diversity in this system that is a result of interacting sedimentological, tectonic and fluid-system processes. It can be concluded that an integrated and interdisciplinary research approach such as that presented in this thesis is appropriate for advancing the geological understanding of complex deepwater fold-thrust belts and associated petroleum systems.

Institutions

• Division of Earth Sciences and Geography [530000]
• Chair of Geology and Paleontology and Geological Institute [531110]