Stephanie M.S. Leong,* Liew Shiew Ling, Kenneth U. S. Wong and H.B. Heijna
The F23 carbonate gas field has some 10 years of production history. Annual TDT surveys are conducted to monitor compaction and gas-water contact movements in the central part of the field. These observed gas-water contact movements were not compatible to those predicted by material balance studies. There was also a fear of preferential flank water influx which might lead to early flooding at the wells. Since these have important consequences to gas deliverability, multidiscipline studies were initiated. This paper describes the material balance, simulation and seismic work undertaken to arrive at a rigorous interpretation.
The F23 gas field is located in the Central Luconia Province, some 200 km offshore Sarawak in a water depth of about 280 ft (Fig. 1). The accumulation consists of a Late Miocene layered platform type carbonate build-up with an areal extent of 22 km2 and a maximum gas thickness of over 1000 ft.
F23 is divided into five zones (Fig. 2), the peripheral flank Zone 5 surrounds the four horizontal zones (Zone 1 to Zone 4). An extensive aquifer lies at the bottom faces of Zones 4 and 5. The geology and reservoir properties in Zone 5 is one of the largest uncertainties in this study as no wells have yet penetrated this flank zone.
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