Continued access to invert drilling fluids is a pre-requisite for efficient drilling operations across much of the North Sea. However, legislation now specifies that the oily cuttings, generated in the drilling process, have to be cleaned to a target level of 1% residual oil, on a weight by dry weight basis, prior to discharge overboard or they have to be disposed of other than to the seabed.
A number of options for disposal are being developed (ref. 1) but one that appears particularly attractive is the grinding and slurrying of oily cuttings. The resultant fluid is used to induce fractures in the sub-surface formation within which its permanent disposal is achieved. This process has been utilised successfully onshore in Alaska and from fixed platforms offshore in the Gulf of Mexico, the Norwegian North Sea and on the UKCS (ref. 2 and 3).
In each case the wellheads have been easily accessible, providing simple access to the well or annulus for injection. For subsea wells drilled from a floating exploration drilling vessel, access to the annulus is much more complex, requiring modification to both the permanent guide base (PGB) and the subsea wellhead.
This paper is a report of a successful field trial of one such subsea system where the permanent guide base (PGB) and subsea wellhead have been modified to allow access to an appropriate annulus for slurry injection.