Structural evolution of the Tenggol Arch and its implication for basement fracture patterns in the Malay Basin, Malaysia

Abstract

The aim of this thesis is to evaluate the hydrocarbon potential of the Tenggol Arch, a basement high that forms part of the western margin of the Malay Basin, offshore peninsular Malaysia. Fractured crystalline basement rocks in this area have previously been identified as possible targets for hydrocarbon exploration, but, due to the lack of well data, little is known about the origin, distribution, geometry or hydrodynamic properties of these fractures. The first part of this study develops a new kinematic model to explain the tectonic evolution of the western Malay Basin, thereby providing a geological framework in which to understand the nature and timing of basement fracturing. The second part uses geophysical attribute analysis to better characterize the geometric properties of the basement fractures on the Tenggol Arch, and to discuss the implications of these findings for hydrocarbon exploration in this region. The integration of previous published and unpublished research with offshore well data and new structural and stratigraphic interpretations of a 3D seismic dataset from the Tenggol Arch suggests that the pre-Tertiary to Late Oligocene history of the Malay Basin was characterized by basin opening during the Upper Cretaceous. This was followed by Paleocene to Late Oligocene NW- SE sinistral strike-slip and possible NE-SW extension. Previous workers have highlighted evidence for Late Miocene N-S shortening (E-W trending folds) in the north and centre of the Malay Basin contemporaneous with extension along NW- striking normal faults on the western margin of the Malay Basin and on the Tenggol Arch. This study has been able to reconcile these apparently conflicting observations by developing a model of Late Miocene/Pliocene dextral transtension. This new model has implications for geological risk evaluations of structural and fractured basement plays on the Tenggol Arch specifically and in the Malay Basin generally. Geophysical attribute analysis of 3D seismic data over the basement complex on the upthrown fault block of the Tenggol Arch was able to identify deep-seated, well connected basement fracture sets. These fractures appear to be tectonic in origin. A set of east-striking fractures (similar to fracture trends mapped in the AU-1 exploration well) appears to be restricted to the shallowest sections of the basement and may represent a set of cooling joints within igneous rocks on the southern Tenggol Arch. However, attribute analysis alone is not sufficient to fully evaluate the hydrocarbon potential of fractured basement on the Tenggol Arch. New geological and petrophysical data (from new wells and further study of onshore analogues identified in this study) are required to mature the fractured basement play into potential drilling candidates.