Abstract
FPSOs (Floating, Production, Storage and Offloading vessels) are ships with capacity to process, store and transfer oil. On the deck of the ship, there is a processing plant which separates and treats fluids from the wells. After separation, the oil is stored inside the vessel cargo tanks and, periodically, it is offloaded into a shuttle tanker through loading hoses.
The biggest FPSOs have capacity to process about 200 thousand barrels of oil per day. They are a good solution to develop exploration projects in offshore oil fields, especially in deep water, due to the comparatively low initial investment, short time for installation and great operational flexibility. However, FPSOs can experience problems arising from scale deposition in flexible sub-sea hoses.
Recently, in order to explore giant offshore oil fields in Brazil and to avoid the high installation cost of a great number of sub-sea pipelines, VLCCs (Very Large Crude Carriers) have been converted into FPSO's.
Over time, some of these converted floating plants have suffered production drops due to the obstruction of both production and gas lift lines by hydrate or scale depositions.
In many of these FPSOs, the reduced space and the lack of cranes in the areas close to the flow line access points were a barrier to restoring lost oil production. In some cases, it was necessary to shut-in production from some lines for several months to allow for the installation of a work-over rig. The financial consequences of such shut-in's were extreme.
In order to restore production faster and with lower cost, a pioneering method of intervention in FPSO production and gas lift lines was developed based on the use of coiled tubing.
This paper presents case histories of successful jobs that cleared two production lines and a gas lift line, including the description of logistics, rig-up process and operation of coiled tubing units in FPSOs. With minor modifications this method can be used in a wide variety of floating production vessels.
The FPSO is a floating, production, storage and offloading ship-shaped vessel. Production facilities are mounted on raised supports above the vessel deck. Reservoir fluids pass from subsea production wells, via flowlines and risers, up into the turret and then to the production facilities. Produced oil is stored in the vessel cargo tanks and periodically offloaded onto a shuttle tanker via a loading hose.
