The Dulang field, discovered in 1981, is a major oil field located offshore Malaysia in the Malay Basin. The Dulang Unit Area constitutes the central part of this exceedingly heterogeneous field. The Unit Area consists of 19 stacked shaly sandstone reservoirs which are divided into about 90 compartments with multiple fluid contacts owing to severe faulting. Current estimates put the Original-Oil-In-Place (OOIP) in the neighbourhood of 700 million stock tank barrels (MMSTB). Production commenced in March 1991 and the current production is more than 50,000 barrels of oil per day (BOPD). In addition to other more conventional means, reservoir simulation has been employed from the very start as a vital component of the overall strategy to develop and manage this challenging field. More than 10 modelling studies have been completed by Petronas Carigali Sdn. Bhd. (Carigali) at various times during the short life of this field thus far. To add to that, Esso Production Malaysia Inc. (EPMI) has simultaneously conducted a number of independent studies. These studies have dealt with undersaturated compartments as well as those with small and large gas caps. They have paved the way for improved reservoir characterization, optimum development planting and prudent production practices. This paper discusses the modelling approaches and highlights the crucial role these studies have played on an ongoing basis in the development and management of the complexly - faulted, multi-reservoir Dulang Unit Area.
Introduction
The Dulang field is one of the most significant offshore oil fields in the Malay Basin which is also home to several other major fields such as Seligi, Tapis, Guntong etc. Dulang field is located about 130 km off the east coast of Peninsular Malaysia in water depths of about 76 m. in the South China Sea (Figure 1).
Following field discovery in 1981, an additional 13 exploration / appraisal wells were drilled confirming an oil and gas column of up to 130 m in 19 stacked sandstones (classified into Groups D and E) of Middle - Late Miocene age (Figure 2). The Dulang field is an anticline which is approximately 24 km long and 3.3 km wide. The western and eastern portions are operated separately by Carigali and EPMI, respectively. Carigali, in addition, operates the central area which was unitized in 1988 and is referred to as the Dulang Unit Area (Figure 3). Both Carigali and EPMI are contractors to Petronas, the National Oil Company of Malaysia and operate under production sharing contracts (PSC's). The OOIP is in the order of 700 MMSTB. The field came on stream in March 1991 and is at present producing in excess of 30,000 BOPD. Cumulative oil produced amounted to about 60 MMSTB at the end of 1994. The crude gravity averages about 390 API. A summary of the range of reservoir and fluid properties is shown on Table 1. The associated gas production is about 43 million standard cubic feet per day and it contains more than 30% CO2.
P. 161
