This paper discusses challenges in developing high CO2 gas fields based on project execution of Tangga Barat Cluster, the very first high CO2 gas cluster being developed offshore Peninsular Malaysia by PETRONAS Carigali. Discussion focuses on the intricacy and challenges specifically on designing offshore facilities to accommodate one of the largest Acid Gas Removal System (AGRS) offshore. It addresses steps and considerations in decision making, reaching the most advantageous solutions, in designing the AGRS as well as the overall facilities which involves the required supporting utilities. Data from well tests, FORGAS simulations, and process model from HYSYS among others shall be woven in the discussion. The discussions on the executed design strategy shall benefit future high CO2 gas fields projects by providing at the very least, a design guidance. The paper highlights the modus operandi in ensuring the final gas specifications of 8 mole% CO2 is met while accommodating different AGRS technology provider utilities requirements. The membrane technology was identified for the bulk CO2 removal of 35% down to 8% CO2 in sales gas. Due to distinctive differences in the technology provider's removal processes, several factors were considered in designing the process utilities, electrical, mechanical and structural aspect of the system. The overall project economics for hydrocarbon losses in both single and two stage systems were assessed to reach a decision with acceptable losses. The operating conditions of the AGRS were optimized through the analysis of the reservoirs pressure and the booster compressor optimization. In view of the high development costs associated with these acidic fields, it is the author's intent to contribute, to some degree, lessons learnt in the planning, design and execution for future acidic field developments. It is aspired that through costs, time and resources optimization, the overall project economics can be improved. 1.0 Introduction The future offshore gas fields development in Malaysian waters shall see a rapid rise in the development of high CO2 gas fields, attributed by the fact that past focus has been on the conventional or "easy fields", which has now been producing for the last 20 - 30 years and is at various stages of depletion. As one of Malaysia's leading operators, PETRONAS Carigali Sdn Bhd was entrusted with the challenge of executing one of the first cluster of high CO2 gas fields, known as Tangga Barat Cluster (TB Cluster) to meet the Peninsular Malaysia Gas Utilization demand in Q4 2010. TB Cluster is located 185 km offshore East Coast of Peninsular Malaysia in the PM 313 Block at a water depth range of 60m to 70m. Consisting of Melor, Laho, Tangga and Tangga Barat fields, TB Cluster shall have a total of 27 producing wells.

Field development planning is one of the core business processes in the upstream oil and gas industry. Before a discovered field can be developed and its hydrocarbon produced, proper evaluation and planning of the subsurface reservoirs and surface facilities are necessary to ensure that the field development plan is not only economical to undertake, but also flexible enough to cater for any deviation from the original plan during implementation as a result of inherent uncertainties in the reservoirs over the production life span of the field. This paper describes the approach taken to prepare a Field Development Plan (FDP) for a cluster of gas fields located offshore Peninsular Malaysia. The four gas fields namely Melor, Laho, Tangga and Tangga Barat ("Tangga Barat Cluster" in short) are located within a 25 km radius of each other at a common centre. One common denominator among these fields is the presence of carbon dioxide (CO2) in its reservoirs. The Tangga Barat Cluster fields will be developed with Tangga Barat as the central processing complex, designed for a peak capacity of 440 MMscf/d of raw gas with an initial blended CO2 level of 37 mol % prior to CO2 removal. The raw gas will be processed, pre-treated and CO2 content reduced to below 8 mol % for evacuation to Peninsular Malaysia via an existing infrastructure. The key areas emphasized in the preparation of the field development plan include the business driver, resource assessment, depletion strategy, development concept and selection, managing uncertainties, appraisal requirements, reservoir management, anticipating production problems and disposal of the excess CO2. Introduction The Tangga Barat Cluster fields are located about 150 to 170 km northeast of Kertih, Terengganu offshore Peninsular Malaysia (Figure 1). The Tangga Barat Cluster consists of four gas fields; Melor, Laho, Tangga and Tangga Barat. In the vicinity are two producing fields, Resak which is a gas development located about 51 km southwest of the Tangga Barat field and Dulang, an oil development situated about 20 km south of Tangga Barat. The Tangga Barat Cluster fields were discovered from 1980 to 1993; they remain undeveloped due to the presence of CO2 in its reservoirs, the content level of which is beyond the gas specification required for gas sales. Since then, a total of 10 exploration and appraisal wells have been drilled before the final FDP was submitted and approved by PETRONAS, the host authority for upstream oil and gas business in Malaysia.

This paper is a review of the gas fields development in Malaysia. The major subsurface engineering considerations for gas development include drive mechanism determination, well requirement, completion strategies, well deliverabilities, recovery factor and reservoir surveillance requirements. For surface engineering, the major considerations include offshore facilities function, platform configuration and sequence and process and compression requirements. The result of the review is the summary of some of the differences in gas fields development to date. Introduction The first gas field development in Malaysia started in 1982 when E-11 field, located offshore Sarawak, was developed. In the following years, four more gas fields namely Duyong, Jerneh, F-23 and F-6 were developed. The Duyong and Jerneh gas fields are located offshore Peninsular Malaysia while E-11, F-23 and F-6 fields are located offshore Sarawak (Figure 1). The fields are operated by PETRONAS Carigali Sendirian Berhad (PCSB), ESSO Production Malaysia Inc. (EPMl) and Sarawak SHELL Berhad (SSB), all are the PS Contractors to PETRONAS, the national oil company. In Peninsular Malaysia, the first development started in 1984 when Duyong field was developed by PCSB to provide the necessary offshore infrastructure for development of gas fields offshore Peninsular Malaysia. With the increasing demand for gas prompted by the onshore pipeline network installation by PETRONAS to fuel the power and industrial sector, sales from Jerneh, EPMI's first gas platform, was initiated in 1991. Gas demand is projected to continue to grow in the near future. To meet this growth, EPMI will develop another field, namely Lawit, for production in 1997. In addition, two gas reservoirs in existing producing oil fields were also developed in 1984. However, their development will not be discussed here. In Sarawak, E-11, being the closest to shore, was the first gas field developed by SSB. Delivery of gas to shore commenced in 1982. Shortly thereafter, in 1983 the second gas field F-23, came onstream. The third and the largest gas field, F-6, started production in 1987 Produced gas offshore Sarawak is delivered to Liquefied Natural Gas (LNG) plant and fertilizer plant. A small portion was used for power generation. Another LNG project is currently under construction and will commence operation in 1995. Development of gas fields dedicated for the second LNG project is currently in progress. This paper discusses the major subsurface and surface engineering considerations for gas fields development in Malaysia. It will also outline some of the differences in gas fields development to-date. GEOLOGY OF PRODUCING FIELDS In Peninsular Malaysia, hydrocarbon accumulations are found in the Upper Oligocene - Upper Miocene alluvial-coastal plain clastics. P. 549

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