ABSTRACT

This paper outlines the problems, and their solutions, associated with the production, storage and gas disposal facilities of Shell Espana's successful Single Anchor Leg Storage (SALS) development of the Castellon Field, situated in some 380 feet waterdepth, offshore Eastern Spain. An underwater completed well produces some 10,000 bbl/day, with Gas/Oil ratio of 125 scf/bbl, via a single anchor leg mooring system to a weather-vaning tanker, where separation, gas disposal and storage facilities are provided and whence the oil is exported via a shuttle tanker. The separation and storage systems are briefly described but the main interest centres on gas-associated problems since disposal of gas by conventional methods of flaring, venting or dilution was unacceptable if production was continue uninterruptedly during transfer of oil to the export shuttle tanker. The alternative of closed incinerators adjacent to the funnel was considered and consultation with Holec Gas Generators/ Smit Ovens Nijmegan B.V., manufacturers of inert-gas generators, led to modification and extension of Holec's basic concepts, resulting in their design of closed, water cooled units acceptable to the vessel's classification society for mounting on the aft superstructure. The facilities described represent the likely minimum requirements for the production of a small offshore field. The short period between project initiation and first production - some eleven months - imposed the necessity for using straight-forward and reliable equipment and the success achieved underlines the suitability of a tanker-based system, of which the incinerators are seen as an almost integral feature, for the economic development of small or marginal fields for which more conventional methods are not viable.

INTRODUCTION

In September 1976 Shell Espana N.V. took the decision to proceed with the development of the Castellon field, offshore Eastern Spain, some thirty miles to the north-east of the Ebro Delta, in 380 ft waterdepth. For reasons connected with the terms of the concession, development had to be such as allow production to commence in less than a year but, fortunately, testing of the single exploration well drilled into the structure indicated that this well was so prolific that, if permanently completed, it would suffice for the drainage of the entire field. The management of the project was entrusted to Shell Internationale Petroleum Maatshappij which, after evaluations of a wide range of alternative development schemes, identified as the most attractive, on grounds both of cost and of speed of execution, the use of a permanently moored tanker-based production and storage system. Oil would flow from the underwater completed wellhead, via a sea-bed flowline to the base of the "SALS? mooring system and thence, along the single anchor leg to surface where, via a number of swivels, it would reach a weather-vaning tanker carrying production and gas disposal facilities which would store the oil until it was offloaded by a shuttle tanker and so conveyed to shore. A factor of over-riding importance was that the system would be installed offshore of the most popular and thickly thronged holiday beaches in Europe so that pollution in any form would have the most far-reaching consequences. Further details of the conduct of the project can be obtained from PaperS3142 of the 1978 OTC (Ref. 1) which describes how the project was completed in eleven months from the original decision to proceed.

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