This chapter describes an oil and gas floating production facility in which the gas is converted to methanol to allow its export without the use of a pipeline. The particular concept is known as "MOPS" (Methanol and Oil Production System) and was developed jointly by Stone & Webster for the gas conversion and Norwegian Petroleum Consultants AS for the particular floating production concept.
The difficulties in exploiting or even disposing of gas when the field is marginal or remote and not adjacent or supportive of a pipeline have become more evident as the platform of North Sea exploration has developed. Pressure on authorities to exceptionally allow gas flaring for marginal fields is being resisted on ecological and energy conservation grounds.
In this context, the prospect of both being able to exploit the oil, and to export the gas transformed to a stable liquid such as methanol, using standard tankers, offers considerable attraction.
Gas to liquid conversion processes are traditionally large, bulky and heavy This has inhibited consideration of their use offshore for year-round use in hostile, severe environments such as the northern North Sea. The application of pressurized convective reforming as in the Stone & Webster power reforming process described in this chapter allows a very considerable saving in bulk and weight by eliminating the large brick-lined furnaces.
Even so, the combined oil and gas process facilities are too large to consider using a deepwater fixed platform or current designs of semisubmersible as the support. A large purpose-designed, turret-moored, ship-shaped vessel is proposed for exposed severe environments, as described in this chapter.
The processing facility described has of necessity been designed for typical conditions. For a particular field a more specific design is desirable, taking into account optimum oil and methanol production rates and the operator's tax and financing position, together with site data.
The MOPS concept of a methanol and oil production system represents a novel solution to the problem of utilizing the associated gas from those fields where no gas pipeline is available, reinjection into the reservoir is not desirable, and where long-term flaring of the gas is not permissible.
The MOPS concept, shown in Fig. 1, solves this problem of gas utilization by converting the associated gas, produced in oil production facilities mounted on the same floating production storage vessel, directly into 99% fuel grade methanol Wild crude production is fed to the FPSV from subsea wells via flexible risers and a turret mooring integral with its vessel.
The following basis has been utilized for the purposes of initial design and evaluation of the concept. For any particular field the optimum rates of oil and methanol production, and the optimum storage capacity (re offloading frequency) need to be assessed. However, the selected capacities are close to many marginal field requirements.
