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The Angsi field in the offshore Terengganu, Malaysia was identified as the candidate for the pilot project to evaluate the effectiveness of the Alkaline Surfactant (AS) process in improving oil ultimate recovery through the reduction of residual oil saturation. The pilot project entails the injection of AS chemical into Angsi I-68 reservoir and will use a Single Well Tracer Test (SWCT) to determine the residual oil saturation in water-flooded area. This is the first chemical Enhanced Oil Recovery (EOR) pilot project in Malaysia and the results are crucial to support the decision making for a future full field and AS technology implementation in Malaysia. High reservoir temperature and high water salinity pushes the technical limit of AS application that adds complexity to the pilot design. The implementation of the pilot project in the offshore environment, on an unmanned satellite platform with limited space and facilities provide additional operational challenges to the project team. In addition, the utilization of new and volatile chemicals during the pilot requires an introduction of various field procedures to ensure the operation is carried out in a safe manner. The paper showcases, the key challenges in the planning and execution of the first offshore AS pilot project in the region. This challenging task demands the multi-disciplinary team to work together to develop the project execution plan with attention to detail during pilot design, planning and operation. As a result, critical parameters such as: treatment sequence, field procedures, equipment requirements and layout, and logistics were considered. The pilot design and procedures that are crucial for a successful pilot operation were developed within the constraints imposed by the offshore environment. Introduction In their quest to increase oil ultimate recovery and extend field life, PETRONAS spearheaded various Enhanced Oil Recovery (EOR) initiatives in Malaysia. The Chemical Enhanced Oil Recovery (CEOR) was identified as one of the EOR process that has good potential for the field implementation to increase ultimate recovery in Malaysian oil fields. Consequently, a research project was carried out to evaluate various CEOR processes and to identify candidate reservoir for a possible pilot implementation. The encouraging result (14.6% OOIP incremental recovery) for alkaline-surfactant (AS) process has proved that there is potential for CEOR application at Malaysian oil fields despite the harsh environment (high temperature and high salinity) for CEOR process1. The research has successfully identified suitable chemicals that can withstand the harsh environment and a suitable candidate reservoir for pilot implementation. The research works also included the design of AS formulation tailored to the test reservoir. Subsequently, the CEOR pilot project was proposed and implemented at Angsi I-68 reservoir to evaluate the effectiveness of the AS process at reservoir condition in improving oil ultimate recovery through the reduction of residual oil saturation, Sor. The AS technology combines synergistically, the interfacial tension reducing effect of added surfactants and those produced in the acidic crude oil by alkaline reaction of organic acids. AS flooding shows promise of being cost-effective because alkali, in addition to reinforcing the activity of surfactants, reduces the depletion of surfactant that occurs due to adsorption/retention in the reservoir 2–3 . The Angsi CEOR pilot project marked a significant milestone for the Malaysian oil and gas industry as it was the first CEOR project implementation in the country. The results of this pilot project are crucial in the future decision making for a large-scale full field and AS technology implementation with reduced technical risk. The result may be one of the keys in deciding the fate of the CEOR implementation in the Malaysian oilfields. In implementing this pilot project, together the team tackled and overcame significant technical and operational challenges.

Angsi K-sand is the first tight gas reservoir development in Malaysia, developed in 2002 to meet an increasing domestic gas demand. K-sand is high temperature (320 oF), multi-layered over pressured retrograde gas condensate reservoirs ranging from 10–90ft net thickness and permeability of 0.1 - 3.0 mD. It was developed through multi-staged propped hydraulic fracturing to improve well deliverability and to mitigate productivity impairment due to condensate dropout near the wellbore. In general, initial gas production from these wells exceeded expectation with condensate level significantly higher than initially anticipated in the development plan. However, several wells exhibited relatively faster and steeper production decline with indications of productivity loss related to the liquid drop out in the vicinity of the wellbore. Scale problem and proppant flow back were also observed at surface during clean-up of production facilities. There are many challenges in managing this complex reservoir and 'unconventional' well performance in an area with a history of conventional gas well operation only. The main challenge is to develop operating strategies in producing these wells at sufficient rate and recovery to meet the short term gas commitment and provides sufficient return on the projects economics. The strategies adopted are flexible enough to face the decision making required by this type of reservoir under anticipated production operations. Additionally, these strategies are the key in identifying opportunities, defining uncertainties and developing specific plans to gather information to allow fast response. Based on actual performance and surveillance data, various changes to the original plan are being implemented. Active reservoir surveillance planning and execution were carried out to provide a better understanding of well behavior and the effect of strategies to the well performance. This paper summarizes the reservoir management challenges, techniques and technologies applied to monitor and evaluate the reservoir performance and operating strategies. Introduction The Angsi Field is the largest integrated oil and gas development in Malaysia and in the region. It is located 170 km off the East Coast of Terengganu in Peninsular Malaysia. The location is shown in Figure 1. Angsi is a joint venture between PETRONAS Carigali Sdn. Bhd (PCSB) and ExxonMobil Exploration and Production Malaysia Inc. (EMEPMI). Angsi is operated by PCSB as a Production Sharing Contractor (PSC) to Petroliam Nasional Bhd. (PETRONAS), the Malaysian National Oil Company. The current development is only concentrated in four areas; Main, West, North and South, each with a separate wellhead platform in water depths of 70 m. The development is shown in Figure 2 and Figure 3. The field is a major contributor to the gas and oil production for PCSB Peninsular Malaysia Operations (PMO). The current gas production is about 350 MMscf/d which contributes 50% PCSB-PMO's production. The Angsi field is an asymmetrical anticline elongated in a north-west to south-east direction. It is part of the Angsi- Besar-Duyong regional structure trend. The Angsi development targets stacked sandstone reservoirs at depths ranging from 6,000 to 9,000 feet. Stratigraphically, hydrocarbons are found in the Group I, J and K sandstones of Lower Oligocene to Middle Miocene age. Volumetrically, the major gas bearing reservoirs are the I-1, I-85, I-100 and K-Sands while the I-35 and I-68 sandstones form the major oil bearing reservoirs. Figure 4 shows the cross section of the K-Sand.