Dare to Think Outside the Box: A Success Story in Shallow HC Reservoirs in Offshore Sarawak, Malaysia

Mustafa, Mohamad Sharir S.; Wafa, Sharifah S.; Kamarudzaman, Khairul Amry A.; M Sabirin, Azlan A.
PETRONAS Exploration, Petronas Carigali Sdn Bhd, Ampang, Malaysia.

What can we do in an overly matured basin like the Central Luconia province? With top oil and gas companies having explored the area exhaustively, there exists a crucial need to find better ways or implement new mindsets in seeking and finding hydrocarbons (HC). If all conventional plays are already tested and we still need to find more HC, the question will be "what else are we still missing?" Therefore, finding new plays is vital and necessary.

Presence of Low Resistivity HC was recently proven through a couple of wells successfully drilled by PETRONAS. This section was actually overseen by previous operators in the area; however, the wells yielded hundreds cubic feet of gas. Thus, a new approach has been adopted to look at the stratigraphic plays within the area. A detailed seismic interpretation and mapping were done in order to extract accurate amplitude for attribute analysis.Recently, one of PETRONAS' well in offshore Sarawak yielded a successful HC discovery in shallow reservoirs where the depth ranged from 600m to 1100m. Two Plays were identified - Cycle VI Structural Stratigraphic Play and Cycle V/VI Stratigraphic Play. The Cycle VI reservoir showed a strong amplitude response where amplitude anomalies conformed to the structure on the northern and western parts related to fluid change with the southern section displaying facies change. The reservoir was trapped by NE-SW normal faults separating the western and eastern blocks. Cycle V/VI reservoir was purely stratigraphic and exhibited non-conformance to structure. Amplitude shut off corresponded to free water level and this was confirmed by the presence of water in another well at the edge of the amplitude. The seismic facies was interpreted as Convergent Thinning High Amplitude (Cth) facies with the traits of a parallel high amplitude reflector and thinning on the side. Cycle VI and Cycle V/VI reservoirs have low resistivity readings of four and two ohm respectively that were normally regarded as unpromising reservoirs. Analysis indicated that the reservoirs were thinly bedded which camouflaged the reading of tools to be of shale dominant beds. Samples were taken and production tests have proven the existence of HC in the area.

The recent discovery proved there was high potential of shallow HC in Central Luconia, Offshore Sarawak. It basically opens up new opportunities for shallow HC reservoir prospectivity initiatives.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012