The Structural-Stratigraphic Framework And Petroleum Systems Of The Sandakan Basin, Offshore East Sabah, Malaysia

Abstract

Decades of exploration activities in the Sandakan Basin offshore eastern Sabah, Malaysia, since the 1970s have yet to yield commercial hydrocarbon discoveries. Of the nineteen wells that have been drilled in the basin up to 2015, only five are classified as discoveries, all made between 1970 and 1995. There are essentially two main proven play types: (1) Early to Middle Miocene “Segama play”, in which the reservoir targets are the Tanjong Formation equivalents within the Segama Group, which were deposited as part of the synrift sequence. (2) Middle to Late Miocene “Sebahat play” in which the reservoirs belong to the Sebahat Formation, characterised by prograding deltaic shoreface and shelf sequences, advancing eastwards and southwards from an uplifting hinterland in central and northern Sabah. The best reservoir facies are shoreface sands, which have porosities greater than 20%, particularly at depths shallower than ~2000 m. Although the generative source rocks have not been penetrated, geochemical data indicate that they are present at depths greater than 3200 m. The source rocks are characterised by predominantly Type III and Types II/III organic matter, which are typical of deltaic settings. The data indicate that hydrocarbons were generated by source rocks with a maturity range of 0.7 – 0.8% vitrinite reflectance (Ro). The Sandakan Basin was affected by several compressional deformation events which are expressed as major erosional unconformities; most significantly, the Middle Miocene (“D2 event”, 13.0 Ma) and Late Miocene (“D3 event”, 8.6 Ma). The unconformities were the result of compression and faulting which, while being responsible for trap formation, may also pose significant risk to trap integrity and preservation. Modelling results indicate that hydrocarbon generation and migration took place during Late Miocene–Early Pliocene and continues today. The basin’s prospectivity, therefore, critically depends on the delicate interplay between the timing of trap formation and hydrocarbon migration. Understanding these processes requires detailed understanding of the structural evolution and petroleum systems of the basin.

Geochemistry of Cenozoic coals from Sarawak Basin, Malaysia: implications for paleoclimate, depositional conditions, and controls on petroleum potential

“…The Sarawak Basin is one of Malaysia's prolific hydrocarbon-producing basins, accounting for 80% of coal resources, 23% of known oil reserves, and 51% of its proven natural gas reserves (Madon 1999b). The Basin, which forms the southern margin of the Oligocene-Recent South China Sea, was initiated as a foreland basin and thereafter developed into a passive continental margin (Madon 1999a, b).…”

“…Furthermore, seven structural-stratigraphic provinces have been identified in the Sarawak Basin, namely SW Sarawak, Tatau, Balingian, Tinjar, Central Luconia, West Luconia, and North Luconia (Madon 1999a). The onshore Sarawak Basin can also be classified into three zones based on tectonostratigraphic history: Miri, Sibu, and Kuching Zones (Madon 1999b). Detailed information on the tectonic evolution of the Sarawak Basin is provided by Mat-Zin and Swarbrick (1997), Madon (1999a), Mat-Zin and Madon 1999a;Murtaza et al 2018;this research, and B: Hennig-Breitfeld et al 2019) Tucker (1999), and Lunt and Madon (2017).…”

マレーシア•サラワク沖における炭化水素鉱床中の二酸化炭素の起源：マイグレーションモデリングをもちいた簡便な手法による検討からの示唆

“…There are a couple of views regarding the tectonic evolution of the basin: One interpretation is that the basin was formed by NW-SE oriented strike-slip tectonics during the Late Oligocene -Early Miocene (Mat-Zin, 1996;Mat-Zin and Swarbrick, 1997) . Another view is that it is a foreland basin formed after the Late Cretaceous -Late Eocene orogeny of the Rajang fold and thrust belt, which was later modified by regional extension during the Early Miocene (Madon, 2000a, b;Madon et al, 2013) .…”

“…3B) . It is considered that terrestrial and marine-influenced organic-rich sediments deposited in deltaic to offshore environments during pre-and post-MMU periods are source rocks for the petroleum systems in the area (Madon, 2000a;Madon and Abu Hussan, 2000a;Tan et al, 2000) . Oil and gas accumulations were discovered in both siliciclastic and carbonate reservoirs in the pre-and post-MMU intervals.…”

“…Closely spaced faults develop offshore Sarawak (Fig. 4; Madon, 2000a;Madon and Jong, 2022) , which can be vertical conduits for fluid migration. The presence of such dense faults tends to make a sedimentary basin suitable for vertical fluid migration rather than long lateral migration (Damaison and Huizinga, 1991) .…”