ELEMENTS OF PALEOZOIC HYDROCARBON PLAYS AROUND PENINSULAR MALAYSIA: A NEW VIEWPOINT

Exploration efforts in Malaysia have, so far, focused mainly on Tertiary deposits. Over the years, some efforts have been undertaken to evaluate the hydrocarbon potential of pre-Tertiary deposits, especially on Paleozoic formations. However, no hydrocarbons have yet to be discovered in pre-Tertiary in Malaysia. Paleozoic sedimentary deposits are exposed in several locations in Peninsular Malaysia and may contain all the elements of a hydrocarbon system. A research project aimed at documenting these Paleozoic deposits is currently carried out at Universiti Teknologi PETRONAS (UTP). Initial observations, mainly in the Kinta Valley, suggest the presence of source rocks, reservoirs and seals within the Paleozoic interval. The limestone hills of the Kinta Valley were the initial focus of this research project after considering an accessibility and uniqueness of karstification. The hills cover an area of about 200km2 are remnants of extensive limestone beds over a 1,200 km2 area, which are part of a very large Paleozoic carbonate complex that covered large parts of South-East Asia. The limestone beds are interbedded with sandstone, siltstone and carbonaceous shale over a thickness of up to 3000m. Several layers of black carbonaceous shale, rich in organic matter are part of the clastic sequences and could constitute potential source rocks. Clay and shale layers within the clastic sequences will act as intraformational seals whereas the base Tertiary unconformity may have regional stratigraphic sealing capacity. The carbonate and the clastic sequences contain potential reservoir intervals, either as sandstone layers or shallow marine limestones. An initial analysis of the Kinta Valley limestone has led to a schematic palaeogeographic reconstruction of the Permian carbonate complex that suggests the potential reservoirs could be found in the eastern part and off the eastern coast of Peninsular Malaysia. However, the Kinta Valley limestones have extensively metamorphosed to marble by younger Triassic granite intrusion. In spite of the metamorphism, sedimentary structures, such as thin laminations, slumps and meter-thick beds of brecciated shallow-marine fragments are still clearly visible in some places. These indicate that the Paleozoic limestone of the Kinta Valley was deposited on a slope. The dip and strike directions of the syn-depositional slump structures indicate the presence of a north-south oriented shallow marine platform margin to the east of the Kinta Valley, towards Central Peninsular Malaysia. The limestone outcrops in eastern Peninsular Malaysia, around Biwah and Taat confirm the presence of a shallow marine platform, with potential reservoir horizons, that probably extended eastwards, far into the South China Sea.