DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows current deflecting a riser that is plugged at the bottom;
FIG. 2 is a close in view of the riser bottom showing the plug;
FIG. 3 shows the riser filled with a heavy fluid and generally aligned with the wellhead;
FIG. 4 shows the riser connected to the wellhead; and
FIG. 5 shows the riser connected and the plug removed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a floating rig 10 set over a subsea wellhead 12 and supporting a riser 14 that is being deflected by currents active between the sea bed 16 and the surface 18. Near the lower end 20 of the riser 14 is a plug 22 that can be installed when the riser string 14 is assembled or later after it is fully assembled by running it in using a variety of known techniques. In the event the plug 22 is initially installed in the lowermost joint or joints of the riser string 14, drilling mud or seawater, for example, can be added above the plug 22 as each stand of riser pipe is connected at the surface and lowered in. FIG. 2 shows the lower end 20 closer up showing the plug 22 and schematically illustrating the connecting hardware 24 to attach to the wellhead 12. The plug can be deployed or dropped into the riser 14 and displaced with heavy fluid to a seat within the riser 14. Alternatively, the plug can be in position at the lower end of the riser but not seated off so as to allow heavy fluid to be spotted above it displacing the seawater, after which the plug can be seated off or set, depending on the type used. The plug can be an inflatable, or mechanical or a non-elstomer type. It can also be wiper that lands on a seat in the riser 14.
FIG. 3 shows the riser 14 full of heavy fluid 26. There are many choices for this fluid with the criteria being to provide stiffness and fully take advantage of gravity to counteract the applied force from currents. In the ideal condition with the rig 10 above the wellhead 12 the riser 14 dangles straight down over the wellhead 12, as shown in FIG. 3. FIG. 4 shows the riser 14 stabbed in, or simply connected such as with divers or an ROV with the plug 22 still in place.
FIG. 5 illustrates the plug 22 released with known tools and brought to surface with flow from the well that also displaces the heavy fluid 26 out of the riser 14. Other alternatives to get to the FIG. 5 condition are contemplated. The plug can be milled or drilled with the cuttings going to the surface with the heavy fluid. Alternatively, the plug can be removed with a known technique and the heavy fluid simply pumped downhole instead of being allowed to be displaced to the surface. Alternative to heavy fluids, such as high weight drilling fluids other fluids or gels can be used as long as they are easily pumped into position and just as simply displaced out of the way or pumped out of the way. Solids can be included in the heavy fluid in various shapes such as spheres using preferably dense metals and sizing the objects so that flow from the well, for example, will bring them out to the surface.
In the end, the method allows placement of the rig 10 over the wellhead 12 with little or no concern over lateral deflection of the string 14 away from the wellhead 12 due to current force. The need to guess in advance the deflection effects of currents, which can be highly variable, is greatly reduced or eliminated. The rig 10 is unlikely to need repositioning during the procedure of running the riser 14 and connecting it to the wellhead.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
Patent Application
20070272414
