--> Source Rock Evaluation and Maturity Modeling, Tatau Province, Offshore Sarawak, Malaysia, Gebregergis, Tedros M. Wan Yusoff, Wan , #90100 (2009)

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Source Rock Evaluation and Maturity Modeling, Tatau Province, Offshore Sarawak, Malaysia

Gebregergis, Tedros M.1
 Wan Yusoff, Wan I.1

1Petroleum Geoscience, universiti teknologi PETRONAS, Tronoh, Malaysia.

The Sarawak basin (Malaysia) represents rich petroleum provinces. This study is to model deep-seated mature source rock within a selected field in Tatau Province, called JL field. The Tatau Province comprises the Half graben sub province and South West Luconia sub province where there are also half graben structures overlain by clastics and carbonate formations. The Miocene Tatau group comprises one of its major reservoirs. Data from about 5 wells, drilled in a limited sector corresponding to the western edge of south west Luconia graben system, permit analysis of several geological events that led to the formation of this reservoir.

The temperature (T) and vitrinite reflectance (VR) data formed the basis for maturity study while incorporation of burial history analysis provided the understandings in maturation and hydrocarbon expulsion windows. In addition, seismic signatures interpretation of the source rock provided clues to the distributions of the source rock facies.

The JL field is within the South West Luconia sub province, cycle I/II rocks strata where, oil and gas have been produced. The cycle I/II rocks strata are found thicker and deeper in the South West Luconia province compared to the half graben sub province. The relatively thick Oligocene and Miocene sediments are with very high sedimentation rate during cycle I/II strata, and the accumulations of organic matter were suitable for the maturation and generation of hydrocarbon. In this study the oil generation has been observed to begin much earlier than gas generation. Substantial oil and gas generation occurred during the deposition of cycle II. The generation and accumulation of gas increased over oil possibly due to thermal cracking of oil into gas.

The thermal maturity models from IFP suggested that organic matter maturation started at more than 45 Ma, where as the maturation developed the Oligocene and Lower Miocene (15-20 Ma) is due to the accumulation of sediments enhanced by total tectonic subsidence from the continental margin. During this period, the relatively brief time spent by the source rock in a given temperature interval was remunerated by increase in temperature.

Generally, coal or shale are an effective source rock with oil generation window started at Vitrinite Reflectance (VR) of 0.6 % and gas generation window at VR of 1.1 %. This implies that substantial of oil may have been generated and migrated in to the traps in the vicinity of the JL field.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil