This paper describes a new subsea manifold developed for the Argyll Floating Production System. The new manifold replaces the original one and incorporates several changes. The changes made were based on the many experiences and lessons learned during the first four years of operation and Sedco-Hamilton's experience on other floating production systems.
Hamilton Brothers Oil Company, et a1, discovered the Argy11 Fie1d in the winter of 1971/1972. Because of substantial cost overruns and schedule delays associated with construction of the fixed steel platform originally selected for Argyll, a Floating Production Facility, or FPF, was chosen to produce the field. The main theme in developing a method for producing this small field was to utilize as much proven equipment and existing "know how" as possible. Over four years of operating experience has proved that all of the engineering design and equipment chosen was conservative. The Argyll facility was the first FPF installation and has produced over 30,000,000 barrels of oil since going on stream in June, 1975.
The Argyll Field FPF has been in operation for almost five years with a very good track record for efficient production and equipment operation. Time has proved the initial design of almost all equipment to have been completely satisfactory.
The initial concept placed heavy emphasis on designing a unit that was easy to install and maintain. Also, as in the case of most new ventures, much of the equipment was built to provide backups and dual features that, in operation, actually proved to be unnecessary. Such was the case with the subsea manifold.
The subsea manifold originally designed and used at Argyll provided for six production circuits, four water injection circuits, high and low pressure service circuits, many crossover circuits, two flowlines per well with a common return service header and dual export flowlines. (Ref. Fig. 1 and 5) The dual circuits and crossovers were provided to enable pigging of the lines in expectation of paraffin buildup which has never occurred. Reservoir performance has shown that water injection will not be required.
The manifold was designed to be installed on a permanent case structure which is secured to a mass anchor on the sea floor. The permanent base is the link between the manifold and the subsea flowlines to each well. Stab receptacles are used on the permanent base to allow the manifold to be retrieved in event a major repair is required.
To incorporate all of the desired features into the manifold and still retain the size and layout necessary to allow ease of installation by the FPF and accessibility for diver maintenance was difficult. However, the manifold functioned success'fu11y for four years. Installation was accomplished during calm weather conditions and diver maintenance on the manifold components had been good.
Divers were used to good advantage to perform a number of tasks related to the manifold. These tasks include helping coordinate the subsea installation, routine inspection and maintenance and non-routine maintenance. Maintenance operations that have been performed include tightening loose bolts, replacing faulty valves and/or valve actuators and replacement of various hydraulic control components. All of the maintenance operations had been accomplished without retrieving the manifold.