SEDIMENTOLOGY, DEPOSITIONAL ENVIRONMENT AND RESERVOIR QUALITY OF SANDAKAN FORMATION, SABAH, EAST MALAYSIA (HARBOUR VIEW C AND ULU SIBUGA OUTCROPS)

Hydrocarbon exploration in shallow marine reservoir has been held for decades and the results has always been positive. By studying the analogue, additional insight can be gain especially in term of reservoir properties of different sedimentary facies. For this purpose, Sandakan Formation had been chosen and studied had been conducted to understand more regarding its sedimentology, depositional environment and reservoir quality. According to Lee (1970) Sandakan Formation is a Tertiary clastic sedimentary formation deposited in shallow marine environment approximately 10Ma years ago during the upper Miocene comprise of mudstone, sandstone and siltstone with coal seams conglomerate of at least 2300 meter in type area.
Two selected outcrops: Harbour View C and Ulu Sibuga were studied by using five sets of data; 1) Sedimentary log, 2) Permeability measurement 3) Gamma ray measurement, 4) Grain size distribution and 5) Petrography to examine and quantify eight sedimentary facies: F1) Clean and massive sandstone, thickness 1-8 m ; F2) Sandstone with bioturbation, thickness 1-2.5 m; F3) Amalgamated sandstone, thickness 1-2.5 m; F4) HCS sandstone, thickness 1- 1.5 m; F5) Interbedded sandstone-mudstone (lenticular bedding), thickness 3.5- 5 m; F6) Sandstone with carbonaceous materials (coal fragment and coal laminations), thickness 0.5- 1 m; F7)Sandstone with mud intraclast or lamination, thickness 0.5 -1 m; and F8)Interbedded HCS sandstone mudstone, thickness 10- 12 m.
The result shows that the clean and massive sandstone has good sorting with excellent permeability value (up to more than ≥250 mD) and low gamma ray value (low gamma ray value means low mud contain) with high bed thickness.. On the other hand, the interbedded sandstone mudstone has poor reservoir quality as it has poor sorting, poor permeability and high gamma ray value. Based on these reservoir quality related to facies association, the environment of deposition was interpreted and suggest that the wavestorm-dominated shallow marine environment shoreface (Harbour View and Ulu Sibuga B) provides a better reservoir quality compared to the upper offshore (Ulu SIbuga A).