Patent ID: 7264058
Filing Date: 2007-09-04
Classification: E21B

Abstract:
1. A drilling system for compensating for changes in equivalent mud circulation density (ECD) or dynamic pressure in an annulus bore in a well resulting from drilling activities during subsea drilling at great water-depths, comprising: a high pressure drilling riser extending from a seafloor wellhead to near the surface; a near surface BOP at the upper end of the drilling riser, the near surface BOP having an upper high pressure line; a subsea outlet in communication with the interior of the riser at a point above the seafloor wellhead; a flow return conduit running back to the surface; a pumping system suspended above the seafloor and connecting said subsea outlet to said flow return conduit; a valve adapted to isolate the riser from the pumping system; means for converting changes in pressure in said riser to an equivalent change in height of drilling fluid in the riser; means for adjusting the pump rate of said pumping system according to the difference of the height of drilling fluid in said riser and said equivalent change in height of drilling fluid; thereby adjusting the height of drilling fluid in the drilling riser so as to neutralize the changes in pressure in said annulus bore created by said drilling activities by varying the actual amount of drilling fluid in the riser; a subsea shut-off device at the sea floor, the shut off device having at least one by-pass line providing communication between the well below the shut-off device and the interior of the riser, the by-pass line containing at least one shut-off valve.