Abstract

A very large number of newbuilt deepwater rigs has recently entered the fleet. While a lot of innovation has been achieved in the area of pipe & riser handling, the actual drilling process has not changed much compared to earlier rig generations. Among the leading deepwater drilling operators, the need for managed pressure drilling in deepwater becomes more and more apparent, given the type of wells that need to be drilled now and in the future. Dual Gradient drilling takes advantage of the long riser in the water column as a tool for managed pressure drilling, and so has emerged as a very desirable way of implementing MPD in deepwater. This paper demonstrates that such dual gradient capabilities also can be retrofitted to the existing rigs with no need to go to a shipyard, and thus not necessarily only can be incorporated when the rig is originally built. A field-proven retrofit dual gradient system using electrically powered mid-level riser pumping technology is presented. The benefits of such a system specifically for retrofitting existing deepwater rigs are described, The difference in pressure gradients in between such a pumped riser system and a backpressure (RCD) managed pressure system are shown. Specifically the areas of enhanced well control and kick recovery, water depth capability increase and significant operational flat time reduction are elaborated on. Capability envelopes with one and two pump skids on the riser are shown. The benefits of combining the controlled fluid level in the riser with a continuous circulation system are demonstrated. Finally, an overview of the steps required for retrofitting such a system to a typical deepwater rig are described, with a 6th generation rig used as an actual example. One such retrofit has already been performed and successfully used in the field on 3 commercial ultradeepwater exploration wells in a remote area of the Gulf of Mexico.

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