Overview of the structural framework and hydrocarbon plays in the Penyu Basin, offshore Peninsular Malaysia

Abstract

The Penyu Basin is moderately explored but may still have undiscovered hydrocarbon potential for small to moderate size accumulations. Despite the much publicised Rhu-1 oil discovery made in 1991, the Penyu Basin, with only a couple of sub-economic oil discoveries made, has not had much success ever since. This was generally attributed to the poorly developed generative or immature source rocks most likely present in isolated half-grabens within the basin. The Penyu Basin was formed on continental crust, although the exact formation is not properly understood and most authors generally consider it as a pull-apart or "rift-wrench" basin. This is supported by the presence of major strike-slip and associated normal faults being the main basin-bounding faults. The initial half-graben basins developed into isolated lacustrine systems which provide source-rock facies that may have potentially charged traps in the synrift and post-rift sequences. Trap styles identified include compressional anticlines, basement drape structures and synrift stratigraphic/structural traps. Further data acquisition through the last two decades of exploration activities, such as new 3D seismic, geochemical fingerprinting and fluid inclusion investigations, and full tensor gradiometry (FTG) gravity data adding to the past understanding, has enabled a more refined review of the geology and also of the petroleum potential. Undoubtedly, more detailed mapping of new previously undetected structures, coupled with seismic amplitude analyses and advanced quantitative interpretation (QI) techniques may lead to a better understanding of the structural evolution and, hence, to an increase of hydrocarbon prospectivity by identification of additional plays, new leads and to a potential reduction of exploration risk.

Pre-Tertiary Basement Subcrops Beneath The Malay And Penyu Basins, Offshore Peninsular Malaysia: Their Recognition And Hydrocarbon Potential

“…This rift system includes the onshore Thai basins, the Gulf of Thailand basins (including Pattani Trough), and the Malay-Penyu-West Natuna basin complex, which seem to have developed along the Three Pagodas-Malay-Natuna shear system (Morley, 2004). In similar tectonic models, the Malay and Penyu basins are interpreted to have developed from pull-apart along major NW-SE strike-slip fault zones (Madon & Watts, 1998;Madon et al, 2019).…”

“…This is now proven by the presence of Eocene synrift sediments in the Penyu Basin wells Janglau-1 and Ara-1 shown earlier in Figure 2 (Kessler et al, 2020). Post-rift sedimentation in both basins during early Miocene to Recent were accompanied by basin inversion from late Early Miocene to Pliocene times (Madon et al, 2006(Madon et al, , 2019. A summary of the stratigraphy and major tectonic phases is given in Figure 3B.…”

“…BTU is Base-Tertiary Unconformity, the unconformity that separates Mesozoic basement from Tertiary basin-fill above; also named "SE Asia Unconformity" by Clements et al (2011). Tectonic phases are partly based on Madon et al (2019), while inversion phase and approximate hydrocarbon charge timing are based on Madon et al (2006). The main phase of fracture generation in the pre-Tertiary basement, based on observations in the Anding-Sotong area (this study), is believed to be during late synrift to early post-rift phases.…”

“…During that same period, Texaco drilled more wells in the Penyu Basin, including several on the Rhu and Soi structures, and encountered volcanic basement. In 2011-2012 Lundin drilled a few more wells in the basin (Batu Hitam-1, Janglau-1, and Merawan Batu-1) and penetrated pre-Tertiary granite and metasediments (Madon et al, 2019).…”

“…Reservoir -Based on the onshore pre-Tertiary geology, potential oil reservoirs may exist in a variety of rock types, since various granitic, basaltic, felsic volcanics, metamorphic, limestone and sedimentary rocks have all been encountered (Fontaine et al, 1990;Madon, 1992;Madon et al, 2019). In the fractured basement play, regardless of rock type, pervasive occurrence of natural fractures is likely to be associated with major strike-slip faults or shear zones.…”