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Abstract: Depositional Systems of Cycle VI M in Helang and Layang Structures, Offshore Sarawak, East Malaysia

Mohamed Taha, Hideki Kitagawa

A study was conducted on the P-1 and P-1a sands of Cycle VI M, which penetrated the Helang and Layang wells. The aim of the study is to define the sedimentologic characteristics and depositional environments of such sands. To achieve this target, all accessible data, including borehole electrical imagery, were incorporated.

The study indicates that the sands of interest in the Helang and Layang wells were deposited as elongated bodies parallel to the paleostrand line within a coastal plain area. In addition, the study reveals that the sandstone reservoirs were accumulated during reverted phases of small-scale progradation and retrogradation within a major marine transgression cycle. The P-1a sand member in the Helang wells has been considered to be deposited as a middle shoreface in a wave/storm-dominated coastal environment. The facies in the Layang-1 well seems to be deposited in a low-energy deposition environment of the sand flats of either a barrier island or a chenier ridge.

The study manifests that the P-1 sand member in the Helang wells is possibly deposited as a lower shoreface. High bioturbation activity resulted in obliterating the various types of bedforms within the facies. In the Layang 1 well, it is thought to be deposited either as a discontinuous chenier-like beach ridge or as an inner bar within a low-wave energy strand plain. The top part of P-1 sand in the Helang and Layang wells that consists of interlaminated calcareous siltstone and shell layers is considered to be deposited by marine transgression.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994