A Unique Approach to the Offshore Gas Disposal Problem: Castellon SALS Production Facilities

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-ft waterdepth, offshore Eastern Spain. An underwater completed well produces some 10,000 bbl/day, with Gas/Oil ratio of 125 sdf/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 centers on gas-associated problems since disposal of gas by conventional methods of flaring, venting or dilution was unacceptable if production was to 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 Nijmegen 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 11 mo — imposed the necessity for using straightforward 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.