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.

X reservoir in one of Iraq's field, is a medium pore, low permeability and small pore throat limestone oil reservoir with poor petrophysical characteristics. This reservoir group in which X reservoir is in constitutes to about 20% of the total resource in place. Conventional development allows only about 0.3% of reserves to be developed and this needed to be improved further. The mixed results of various stimulation campaigns (for example matrix acidising and acid fracturing) carried out earlier for this reservoir has prompted the Operator to evaluate the hydraulic fracturing stimulation, first of its kind in Iraq to further gauge its effectiveness and feasibility for field implementation. This paper will discuss the steps undertaken before, during and after the hydraulic fracturing execution. In planning for this campaign, steps were taken to analyse the rock properties and mechanics of the formation to understand the challenges for the hydraulic fracturing and to enable optimisation of the fracturing parameters. Fracture fluid design, proppant optimisation and treatment design were proposed to systematically optimise the process of the hydraulic fracturing. As a deduction, the principles and recommendations of design optimisation for hydraulic fracturing in carbonate reservoirs will be presented in this paper. The preliminary production gain from this pilot hydraulic fracturing exceeded the pre-job stimulation more than 10 times, showing promise of a new way of developing this challenging reservoir in the future. Comprehensive analysis of the reservoir characteristics and suitable fracturing design are key to this achievement. This approach will be the benchmark for future hydraulic fracturing jobs planned in the field. The optimisation study in this paper could serve as a reference to improve hydraulic fracturing efficiency and success in other similar carbonate reservoirs. Being the first ever hydraulic fracturing campaign ever performed in Iraq, this paper will focus on the challenges, execution and preliminary results.

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