Method of riser deployment on a subsea wellhead

Abstract

The riser assembly is plugged adjacent its bottom end either as it is made up or after full makeup or anywhere in between. A heavy fluid is either added to the riser string as it is made up or delivered into the string after makeup to displace seawater or other fluids that may have been in the riser as it is assembled. The floating rig can be secured over the subsea well head and the riser now full of heavy fluid is less prone to be displaced by wave action and preferably simply dangles straight down so that the connection to the subsea wellhead can be simply accomplished. The effect of wave action is minimized or eliminated when deciding placement of the floating rig with respect to the wellhead. Repositioning of the rig takes less effort and is needed less frequently.

Description

FIELD OF THE INVENTION[0001]The field of this invention is riser placement on a subsea wellhead and more specifically when using a floating rig.BACKGROUND OF THE INVENTION[0002]Floating rigs are connected to subsea wellheads through a string called a riser that spans the distance between the rig floor and the wellhead located just above the sea floor. Floating rigs are normally positioned and secured to hold a selected position while still able to compensate for the rise and fall of the surface from wave action. Before or after a rig is positioned the riser assembly is made up in sections on the rig floor and run in. If the riser is made up before, the currents can be used to guide the rig closer to the subsea BOP. The water depths for some floating rigs can be in the thousands of meters and the wave action at the surface has a component below the surface that can deflect the riser string as it is made up and lowered toward the wellhead. The skewing effect is well known and in the p...

AI Technical Summary

Benefits of technology

[0004]The riser assembly is plugged adjacent its bottom end either as it is made up or after full makeup or anywhere in between. A heavy fluid is either added to the riser string as it is made up or delivered into the string after makeup to displace seawater or other fluids that may have been in the riser as it is assembled. The floating rig can be secured over the subsea well head and the riser now full of heavy fluid is less prone to be displaced by wave action and preferably simply dangles straight down so that the connection to the subsea wellhead can be simply accomplished. The effect of wave action is minimized or eliminated when deciding placement of the floating rig with respect to the wellhead. Repositioning of the rig takes less effort and is needed less frequently.

Problems solved by technology

The problem lies in the inherent unpredictability of the tidal forces both in strength and in direction.

Repositioning of the floating rig is time consuming and may require the riser string to be pulled back onto the rig before it can be repositioned.

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