A new integrated software solution was applied to assist in the development planning of gas assets located offshore Southeast Sumatra. This has enabled more detailed evaluation of investment and development options and a more robust plan than was previously practicable with existing tools.

The solution was required primarily to optimize the entire production system as outlined in the Plan of Development in order to deliver the target rates over the projected life of the gas contract, as well as to provide a means of evaluating various development options in terms of process infrastructure, well drilling and compression scheduling.

The solution adopted integrates reservoir data, material balance, well performance, surface pipeline configuration and facilities in a single model, which optimizes the system to meet contractual gas sales targets, fuel gas requirements and other constraints over a proposed eleven year production time frame.

The gas accumulations are located in a large number of small to medium sized fields, as well as in the form of associated gas from currently producing oil fields in the same area. A large inventory of gas reserves exists because until recently there has been no market for the gas. The initial gas contract is for a much smaller volume than currently carried in the operator's reserves book.

A key objective of this study was to optimize the field development by minimizing capital and operating costs over the economic life of the project. The operator is planning to develop the gas reserves, partly using existing infrastructure as well as installing new compression and separation facilities at strategic points in the network. The current development plan must meet the gas contract volumes from an inventory of 23 fields, 38 reservoirs produced across 16 platforms. Separation and compression facilities are located on three different platforms and one offshore island base.

This paper describes the total system model built from the reservoirs to the various delivery points. The integration of reservoir material balance models with a network optimizer via systems analysis is described. Particular attention is given to the surface network infrastructure which is complex in several key areas. The resulting model was "timestepped" forward on an annual frequency to generate the forecast profile.

The results from the study have confirmed the ability of the proposed production network to meet the operator's sales and fuel gas obligations. Other benefits include identification of compression requirements and scheduling which can be used directly in the full-field development planning. These results are not only of use in the early FEED, but are also important for investment planning throughout the life of the project.

The integrated model, besides capable of being used in a forward planning mode as at present, can also be migrated for eventual use in the optimization of production operations, both on and off line. Well, reservoir and facilities data incorporated into the model at this early stage thus provide an important element of knowledge capture for future planning and optimization of the asset.

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