The Guntong field is one of the largest oil fields in the Malay Basin. With almost twenty years of production history and currently at 80% depletion, Guntong production has been on the decline since the late 90s. Despite the complexities resulting from its multiple stacked reservoirs that are developed by 150 wells, and the challenges of maximizing oil recovery from a mature offshore field, the various oil recovery improvement measures implemented at Guntong have successfully resulted in the addition of almost 80 million barrels of oil to the overall field recovery within the last five years. This paper is an overview of these initiatives which include workovers to decommingle selected reservoirs and perform acid stimulations, in addition to three infill drilling programs that were conducted within a span of three years. A fourth infill program, requiring a new satellite platform, is scheduled for completion in 2005. Positive results were also achieved by revising the field's reservoir pressure maintenance program along with optimizing reservoir management strategies such as water injection patterns. The underlying key to the success of these efforts has been the holistic approach in analyzing the field data. A more comprehensive understanding of the reservoir behavior was achieved by integrating production data, geology, reservoir engineering as well as findings from the recent infill programs. A more accurate representation of the reservoir behavior was attained through iterative comparisons between the geologic description updates and the results derived from the reservoir simulation models. Predictions from these models, which were further supported by seismic timelapse and AVO analyses, have led to the successful identification of bypassed oil regions within the field. Moreover, the availability of reliable simulation models was also instrumental in testing out and fine-tuning reservoir management strategies before their implementation. Introduction The Guntong field is an east/west compressional anticline in the Tabu-Guntong-Palas trend, approximately 11km long and 6.5km wide. Fig. 1 shows the field's location in the Malay Basin as well as a map of the I-25 horizon with the locations of the platforms. Two major north/south trending normal faults, with maximum throws of 280m, separate the field into west, central and east fault blocks. As shown in Fig. 2, the field is made up of twenty-nine stacked reservoirs belonging to the Group I (I-10 Upper / Lower, I-15, I-20, I-23, I-25, I-27, I-30, I-35, I-40, I-45, I-50, I-60, I-62, I-68, I-70, I-75, I-80, I-85, I-90, I-98, I-100/102, I-104) and J reservoirs (J-18, J-19, J-19.5, J-20, J-20.5, J-21 and J-30) which are generally from the Lower to Middle Miocene periods. The Group I sandstones are a combination of tidal, deltaic and braided fluvial sediments while the Group J consists of shallow marine and tidally influenced deposits. As such, a broad range of reservoir quality and characteristics exist throughout the field. Table 1 summarizes the key reservoir parameters of the three major reservoir groups: Upper I reservoirs (I-10 through I-45 sands), the Lower I reservoirs (I-60 through I-104 sands) and the Group J reservoirs (J-15 through J-30). Between 1985 and 1994, four platforms were installed to develop the field (Fig. 1), three of which, Guntong A, B and C, develop the east and central fault blocks (ECFB). In addition to production from the B and C platforms, production from the Tabu and Larut fields also flow into Guntong A. The field's west fault block (WFB) is developed by Guntong D, which is a central production and processing facility dedicated to the production from the WFB and Palas field.

The Tapis field, located offshore peninsula Malaysia, has been producing since 1978 and about 90% of the original development estimated recoverable oil has been produced. Large gas caps remain for future development. Recovery to date has been primarily from line drive pattern waterflood. Continuous implementation of improved oil recovery (IOR) strategies has increased the recoverable reserves and production capacity for economic operation of the field. This paper describes technical studies completed at Tapis and the results of recent IOR work programs that added more than 20 million barrels of reserves. In addition, enhanced oil recovery techniques currently under evaluation for Tapis are described. The Tapis structure is an east-west trending anticline, approximately 16 km long and 7 km wide. Initially, only the northern and eastern areas were developed from four platforms. The other areas were only developed in recent years following studies to re-assess recovery from poorer quality reservoirs and application of more cost-effective technologies to commercialize them. This led to a fifth platform that developed the western area of the field. Recently, the southern flank with marginal reserves was developed from a sixth platform, which adopted the minimal facilities satellite platform concept. Reservoir risk for this development was mitigated by additional exploration/ delineation and development well data. The data confirmed that the reservoirs are oil-bearing and productive. This marginal development was a challenge due to reservoir quality uncertainties (extensive bioturbation), structural complexities (steep bed dips, close to a major reverse fault), and fluid contact uncertainties caused by production. Reservoir simulation study was carried out to address these uncertainties to aid development planning. Reservoir simulation study has also identified the potential for infill drilling and workovers to further improve recovery in the eastern area. This latest simulation study was conducted using finer layers, unstructured grids, and incorporated over 25 years of history matching. Given the advanced state of field depletion, early assessment utilizing compositional simulation model and laboratory tests are being carried out to investigate the potential for enhanced oil recovery processes. Processes under evaluation include double displacement and water alternating gas (WAG) displacement using various types of gas. Introduction The Tapis field was discovered in May 1969 in an average water depth of about 64 meters. It is located in the southern part of the Malay basin as shown in Figure 1. A total of fifteen exploration and delineation wells have been drilled to-date. Hydrocarbon bearing reservoirs are in the Group I, J, and K sandstones as shown in Figure 2. This paper focuses on the oil development in the Upper and Lower J reservoir groups only, which contain about one billion barrels of oil or 90% of the field's original oil in-place. The assessment and application of IOR started early and have been a continuous process; several IOR assessments have been conducted and associated work programs have been implemented. The application of Enhanced Oil Recovery (EOR) has also been evaluated in the past. These were mostly simple screening level assessments. A more detailed evaluation involving laboratory tests and compositional models has recently been initiated.

The Guntong field is currently the largest waterflood field and a major oil producer in Peninsula Malaysia. The field and its development are highly complex, resulting in various challenges in the areas of reservoir description, reservoir management, and facilities optimization. This paper showcases key challenges and the evolution of the field depletion plan as the complexities were identified and better defined. Based on actual performance, and updated geoscience and reservoir engineering studies, various changes to the original depletion plan are being implemented even after 17 years of production. The changes range from a revision in waterflood operating pressure strategy, to innovative facilities optimization, and the more expensive workovers and infill drilling,. Effective teamwork by multi disciplinary team members also played a major role in transforming the challenges into opportunities. The implemented changes to-date have successfully increased production and reserves. Introduction The Guntong field is a large anticline of about 12 km long and 7km wide, located 210km offshore Terengganu, Malaysia (Fig. 1). It was discovered in 1978 and a total of 9 exploration wells were drilled. Two major north-south trending faults divide it into three fault blocks; East, Central, and West. Field development started in 1985 and a total of 138 development wells have been drilled through 1997. ExxonMobil Exploration and Production Malaysia Inc. operates the field in partnership with PETRONAS Carigali Sdn Bhd, as Production Sharing Contract (PSC) contractors to PETRONAS, the national oil company of Malaysia. The first 3D seismic survey was acquired in 1985 and was extensively used to formulate and enhance the original field development plan. A newer 3D seismic survey was acquired in 1998 and fieldwide geologic studies were recently completed which integrate the seismic data, sequence stratigraphy, improved formation evaluation, and performance data. Reservoir Description Hydrocarbon-bearing reservoirs are primarily mid-Miocene sandstones deposited in fluvial/tidal/deltaic environments. There are fifteen vertically stacked, highly heterogeneous reservoirs, cut by numerous channels and faults. As depicted by the cross-section (Fig. 3), these reservoirs have variable reservoir thickness, quality, areal extent, gas cap size, fluid contacts, and oil column thickness. The main reservoirs are in the group I sandstones, sub-divided into the Upper I group consisting of the I-10 through I-45 reservoirs, and the Lower I group which is made up of the I-60 through I-104 reservoirs.The major reservoirs are the I-10, I-25, and I-70, containing close to 75% of the total field recoverable reserves. Reservoir quality varies significantly. An example is the contrast between the clean I-25, which consists largely of fluvial deposits and the more stratified I-10, which is mainly subtidal and intertidal deposits (Fig. 3) Also present are the group J reservoirs, which are generally of poorer quality with thinner oil columns. However, this paper focuses on the group I reservoirs, and primarily the I-10 and I-25 reservoirs.

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