Fluvial Channel in Shallow Marine Environment. Is it Possible? A Case Study of A-1 well in Central Luconia, Sarawak

A-1 well drilled in July 2012 one of PETRONAS well in offshore Sarawak has resulted to a hydrocarbon discovery in shallow reservoirs between the depth of 800m and 1300m. Multiple stratigraphic plays were mapped, and two of them were identified as channel plays of (Upper Miocene) Cycle V/VI Sand namely as CH-1 and CH-2. These CH-1 and CH-2 reservoirs are stratigraphically sitting right above The Central Luconia Carbonate platforms, within the post-carbonate levels which were previously interpreted to be deposited in a shallow marine inner neritic environment. Now the questions arise how is it possible to have fluvial channel in the area interpreted as shallow marine environment? To unveil the answer, an integrated approach was made by combining seismic attribute analysis, recent well data and sequence stratigraphic study. The presence of alternating marine and fluvial deposits in the 1000m of the Central Luconia basin indicates exposure and submergence of the shelf numerous times during the Miocene. Ultimately, this study has unveiled the complexity of depositional environment within the area. New depositional model could be applied in surrounding area. Basically it opens up new opportunities in chasing the fluvial channels for future prospects.