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A proposed solution to the challenge of producing oil reserves from offshore marginal fields in the Natuna Sea of Indonesia

Proceedings Title : Proc. Indon. Petrol. Assoc., 15th Ann. Conv., 1986

This paper presents the work performed by CONOCO INDONESIA and COFLEXIP to develop a method that will permit the efficient and economical recovery of hydrocarbon reserves from offshore finds which fall in the category of marginal fields, such as Conocos Kepiting Field in 300 of water in the contract area known as BlockB in the Natuna Sea of Indonesia.The challenge was to find a system that would permit safe and reliable production operations from sea floor completions, and at the same timeallow for well reentry by conventional wireline methods and techniques in order to service downhole safety valves, install or replace artificial lift equipment, set plugs, open/close sliding sleeves, etc.The critical component of the system was identified as the submarine link connecting the seafloor completions to a specially designed Floating Production Storage and Offtake Barge (FPSO), which was to be located directly above the wells and moored in a spread fashion by eight anchor lines.Two flexible pipe riser system alternatives were thoroughly analyzed, one known asChinese Lantern configuration, and the other a combination ofFree Hanging production control lines and special risers for wireline operations. The risers in aChinese Lantern configuration are equipped with flotation such that the risers bow with uniform curvature throughout, thus permitting wireline tool entry. Two risers thus equipped and designed to bow in opposite directions form the shape of a paper lantern, hence the termChinese Lantern.Free Hanging risers also are equipped with flotation, however the tops of the risers have no flotation and bend over, orfree-hang from a surface buoy. These risers must be pulled to the surface and held in tension for wireline entry.This paper describes :1. The predicted behavior of theChinese Lantern flexible riser under various producing conditions and barge positions.2. The proposed design and configuration of the special Wireline Riser under theFree Hanging riser system.3. The proposed method of .tying the Wire Line Riser into the FPSO, and provisions required to accomplish wireline work.4. How a maximum of four seafloor completions can be connected and produced into the FPSO.The flexible riser solution which i s described in the paper is not the final solution used in the Kepiting development.

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