FMC has developed and operated riserless light well intervention (RLWI) equipment in the North Sea since 2003. The development work started in 1999 and has resulted in a separate operating unit within FMC, FMC Production Systems FPS, that now operates RLWI systems onboard three vessels from the 2009 season. Long-term contracts are established with both StatoilHydro and BP, and additional work has been carried out in the spot market both on Norwegian and UK sector of the North Sea.
The RLWI systems make it possible to perform wireline well interventions from mono-hull vessels, instead of using riser based systems that need to be operated from drilling rigs. The overall cost of the operations can therefore be reduced, and as a result, more subsea completed wells are intervened, and production rates and ultimate recovery can be improved.
From the recent past, a gap(12–14 percent) in recovery from the fixed platforms relative to the subsea fields has emerged, even though the properties of the reservoirs are basically the same. To a large extent this gap is related to the high cost in subsea operations in general and well operations in particular. Experience, however, shows that efficient (i.e. low cost) well intervention solutions are of the utmost importance for increased field recovery as well.
RLWI is one tool helping to close the recovery gap. RLWIs are steadily gaining industry acceptance since their introduction in 2003. This activity has significantly increased since 2005 in the North Sea, requiring at least two concurrent vessels for planned operations in 2010.
RLWI operations are now common in shallow water up to 600m (2000ft), and a few operations in the Gulf of Mexico have been performed down to 900m. For open-hole logging, a demonstration down to 3000m has been performed with a similar solution. However, the current concept is not the ultimate technical solution worldwide, just the first step. Considerable efforts have to be made to improve the concept with respect to efficiency, weather sensitivity and - last but not least - deep-water compatibility. It is envisaged 3000m (10,000ft) water depth is well within reach.
All traditional wireline tasks are performed from these vessels. There has been a gradual development into more complex downhole tasks as experience has been gained. From a humble start with mainly simple mechanical tasks, the operations suite today consists of the following:
Data gathering (production logging tool, or PLT)
Zone isolation (plug/straddle)
Inspection/repair/installation of insert downhole safety valve (DHSV)
Milling of short-scale bridges
Camera runs: visual or X-ray
Well killing operation
Pumping operations/scale treatments
Selective tracer injection or sampling
Change-out of gas lift valves
Sleeve operations - downhole instrumentation and control systems (DIACS) valves
Change-out of subsea trees
Plugging and abandoning (P&A) operations of subsea wells.
As a typical example of the results obtained from these operations, the following summary of a scale milling job is illustrative:
Scale milling on WL tractor (breakthrough for advanced RLWI operations)