Method and apparatus for preventing debris build-up in underwater oil wells

A method, of preventing settling of debris into a borehole in an underwater drilling operation wherein a riser pipe string, adapted to receive a tubular pipe string therewithin, extends between the water surface and an underwater wellhead assembly on an underwater floor, which comprises the steps of:

• a. inserting a device into the riser pipe string;
• b. positioning said device adjacent the lower portion of said riser pipe string thereby creating an annulus between said device and said riser pipe string throughout at least a substantial portion of the length of said lower portion of said riser pipe string;
• c. passing the tubular pipe string downwardly through the riser pipe string and wellhead assembly into the borehole, so as to create an annulus between said riser pipe string, wellhead assembly and borehole;
• d. circulating a liquid downwardly through the tubular pipe string and out the lower end thereof into said annulus;
• e. circulating said liquid upwardly through the portion of said annulus between the tubular pipe string and the borehole and through the portion of said annulus between the tubular pipe string and the wellhead assembly at a flow rate sufficient to cause said liquid to have an upward flow velocity faster than the settling rate of said debris in said liquid;
• and
• f. circulating said liquid upwardly from the interior of said wellhead assembly and through said annulus between the riser pipe string and the tubular pipe string while simultaneously using said device to restrict said annulus throughout at least a substantial portion of the length of said lower portion of said riser pipe string to a cross-section area sufficiently small to cause said liquid to flow therethrough with an upward velocity in excess of said settling rate of said debris.

A method of trapping debris from a borehole in an underwater drilling operation wherein a tubular pipe string extends downwardly from the water surface within a riser pipe string extending between the water surface and an underwater wellhead assembly on the underwater floor, comprising the steps of:

• a. passing the tubular pipe string downwardly through the wellhead assembly into the borehole;
• b. circulating a liquid downwardly through the pipe string and out the lower end thereof;
• c. circulating said liquid upwardly through the annulus between the pipe string and the borehole into the annulus between the pipe string and the wellhead assembly at an upward flow velocity sufficient to carry debris from the borehole therewith;
• d. circulating said liquid upwardly from the interior of said wellhead assembly into the lower portion of said riser pipe at an upward flow velocity sufficient to continue carrying the debris therewith;
• e. settling the debris entrained in the liquid in the riser pipe above the lower portion thereof into the lower portion thereof;
• f. trapping the settled debris in the lower portion of the riser pipe;
• and
• g. removing the trapped debris upwardly from the riser pipe.

A method of trapping cutting debris in an underwater drilling operation wherein a tubular drill string having a drill bit on the lower end thereof extends downwardly from the water surface within a riser pipe which extends between the water surface and an underwater wellhead assembly on the underwater floor, comprising the steps of:

• a. passing the drill string downwardly through the wellhead assembly to contact the underwater floor;
• b. actuating the drill string to form a borehole extending downwardly from the underwater floor;
• c. circulating liquid downwardly through the drill string and out the lower end thereof;
• d. circulating said liquid upwardly through the annulus between the drill string and the borehole into the interior of the wellhead assembly at a flow rate sufficient to carry cuttings and debris therewith;
• e. circulating said liquid upwardly from the interior of said wellhead assembly into the lower portion of the annulus between the drill string and the riser pipe at a flow rate sufficient to continue carrying cuttings and debris therewith;
• f. reducing the flow rate of the liquid at a point above the lower portion of the annulus between the drill string and the riser pipe sufficiently to prevent the continued upward movement of at least a portion of the cutting debris with the liquid;
• g. terminating the circulating of said liquid in the drill string, in the annulus between the drill string and the borehole in the interior of the wellhead assembly, and in the annulus between the drill string and the riser pipe;
• h. allowing the cuttings and debris entrained in the liquid in the annulus between the drill string and the riser pipe to settle to the lower portion of said annulus;
• i. trapping the cuttings and debris in the lower portion of the annulus between the drill string and the riser pipe;
• and
• j. removing the trapped cuttings and debris from the riser pipe to the water surface.

A drilling tool, for use with a drill string insertable within a riser pipe string having an internal shoulder in the lower portion thereof in underwater drilling operations, comprising:

• a first tubular member having an upper end portion, a lower end portion and an inner diameter greater than the outer diameter of at least a part of the drill string by less than a predetermined amount;
• support means for supporting said first tubular member at a first position within at least the lower end portion of said riser pipe string independently of said drill string;
• carrier means for carrying said tubular member on said drill string independently of said riser pipe string at positions above said first position;
• and
• flange means for seating said first tubular member on said internal shoulder in the lower portion of said riser pipe string when said first tubular member is supported in said first position within at least the lower end portion of said riser pipe string.

A drilling tool, for use in underwater drilling operations with a drill string insertable within a riser pipe string which mates with a wellhead assembly having an upwardly facing internal shoulder, said tool comprising:

• a first tubular member having an upper end portion, a lower end portion and an inner diameter greater than the outer diameter of at least a part of the drill string by less than a predetermined amount;
• support means for supporting said first tubular member at a first position within at least the lower end portion of said riser pipe string independently of said drill string;
• carrier means for carrying said tubular member on said drill string independently of said riser pipe string at positions above said first position;
• and
• flange means for seating said first tubular member on said upwardly facing internal shoulder of said wellhead assembly when said first tubular member is supported in said first position within at least the lower end portion of said riser pipe string.

A method, of preventing settling of debris into a borehole in an underwater drilling operation wherein a riser pipe string, adapted to receive a tubular pipe string therein, extends between the water surface and an underwater wellhead assembly on an underwater floor, which comprises the steps of:

• a. inserting a device into the riser pipe string;
• b. positioning said device adjacent the lower portion of said riser pipe string;
• c. extending said device upwardly through said riser pipe string to adjacent the top of said riser pipe string;
• d. passing the tubular pipe string downwardly through the riser pipe string and wellhead assembly into the borehole, so as to create an annulus between said tubular pipe string and said riser pipe, wellhead assembly and borehole;
• e. circulating a liquid downwardly through the tubular pipe string and out the lower end thereof into said annulus;
• f. circulating said liquid upwardly through the portion of said annulus between the tubular pipe string and the borehole and through the portion of said annulus between the tubular pipe string and the wellhead assembly at a flow rate sufficient to cause said liquid to have an upward flow velocity faster than the settling rate of said debris in said liquid;
• and
• g. circulating said liquid upwardly from the interior of said wellhead assembly and through said annulus between the riser pipe string and the tubular pipe string while simultaneously using said device to restrict said annulus throughout the length of said riser pipe string to a cross-sectional area sufficiently small to cause said liquid to flow therethrough with an upward velocity in excess of said settling rate of said debris.