Dual riser assembly, deep water drilling method and apparatus

• US 6,443,240 B1
• Filed: 10/06/1999
• Issued: 09/03/2002
• Est. Priority Date: 10/06/1999
• Status: Expired due to Term

• Current Assignee: Transocean Offshore Co.
• Original Assignee: Transocean Sedco Forex, Inc. (Transocean Limited)
• Inventors: Scott, Robert J.
• Primary Examiner(s): NEUDER, WILLIAM P
• Application Number:
  US09/413,030
• Time in Patent Office: 1,063 Days
• Field of Search: 175/5, 175/7, 166/352, 166/353, 166/354, 166/358, 166/367, 166/359
• US Class Current: 175/7
• CPC Class Codes: E21B 17/01 Risers
• CPC Class Codes: E21B 33/038 Connectors used on well heads, e.g. for connecting blow-out preventer and riser

Abstract

A dual riser assembly for use with an offshore multi-activity drilling assembly to conduct drilling operations from a deck above the surface of a body of water into the bed of the body of water utilizing two risers, a first and a second, which extend from a location above the surface of a body of water to a common location adjacent to the bed of the body of water. Each riser terminates, at a distal end, into a dual riser assembly, allowing for selective open internal communication between each of the two risers and a single wellhole.

Claims

1. A dual riser assembly for use with an offshore multi-activity drilling assembly designed to conduct drilling operations from a deck above the surface of a body of water and into the bed of the body of water using a first riser and a second riser extending from a location above the surface of the body of water to a location adjacent the bed of the body of water, said dual riser assembly comprising:

a first riser segment being operable to be connected at one end to a distal end of said first riser and having a central longitudinal axis extending substantially coincident to a central longitudinal axes of said first riser;

a second riser segment operable to be connected at one end to a distal end of said second riser and having a central longitudinal axis extending substantially coincident to a central longitudinal axis of said second riser;

said first riser segment and said second riser segment being connected and merged together at their other ends into open internal communication with an acute angle being formed by the central longitudinal axes of said first riser segment and said second riser segment;

a first valve connected at approximately said one end of said first riser segment to selectively isolate the first riser from the first riser segment;

a second valve connected at approximately said one end of said second riser segment to selectively isolate the second riser from the second riser segment; and

means for operably connecting the merged other ends of said first riser segment and said second riser segment to a well hole to be drilled.

2. A dual riser assembly as defined in claim 1 wherein said mean for operably connecting comprises:

a direct connection between the merged other ends of said first riser segment and said second riser segment to said well head of a well hole to be drilled.

3. A dual riser assembly as defined in claim 2 and further comprising:

a blowout preventer stack positioned between said means for operably connecting and the well head of said well hole to be drilled.

4. A dual riser assembly as defined in claim 3 and further comprising:

a flex segment connected between the merged other ends of said first and second riser segments and the top of the blowout preventer stack.

5. A dual riser assembly as defined in claim 1 and further comprising:

means connected to and being operable for maintaining a fixed spatial relationship of said first riser segment and said second riser segment.

6. A dual riser assembly as defined in claim 5 and further comprising:

a cylindrical column extending about and supporting a portion of said first riser segment and said second riser segment.

7. A dual riser assembly as defined in claim 6 and further comprising:

a taper joint extending between a bottom portion of said cylindrical column and the other ends of the merged first and second riser segments.

8. A dual riser assembly as defined in claim 7 and further comprising:

a flex joint connected at a base portion of said taper joint and interposed between the taper joint of said dual riser assembly and a well head of a well to be drilled.

9. A dual riser assembly as defined in claim 1 wherein said first valve connected to first riser segment comprises:

blind rams.

10. A dual riser assembly as defined in claim 1 wherein said second valve connected to second riser segment comprises:

blind rams.

11. A dual riser assembly as defined in claim 1 wherein:

said first riser segment and said second riser segment have substantially equal diameters.

12. A dual riser assembly as defined in claim 1 wherein:

said first riser segment has a larger diameter than said second riser segment.

13. A dual riser assembly as defined in claim 12 wherein:

said first riser segment has a diameter measuring approximately twenty-one inches (21″

) and said second riser segment has a diameter measuring approximately thirteen and five-eighths inches (13⅝

″

).

14. A dual riser assembly as defined in claim 12 wherein:

said means for operably connecting the merged ends of said first riser segment and said second riser segment comprises;

a tubular column which operably encompasses the merged junction of said first riser segment with said second riser segment and operably fixes a spatial angular relationship of the first and second riser segments.

15. A dual riser assembly as defined in claim 14 wherein:

said means of operably connecting and fixing spatial and angular relationship of the first and second riser segments further comprises a taper joint extending from a base segment of said tubular column to a reduced diameter flange operable for connecting to a blowout preventer assembly for said well hole.

16. A dual riser assembly as defined in claim 1 wherein:

said acute angle between the central longitudinal axes of said first riser segment and said second riser segment being approximately ten degrees.

17. A method for conducting offshore drilling operations on a single well hole from a multi-activity drilling assembly having a first riser extending from above the body of water to the seabed and a second riser extending from above the body of water to the seabed, said method comprising the steps of:

joining the first riser with the second riser in fluid communication at a distal end adjacent a well hole to be drilled into the seabed;

closing the second riser from fluid communication with the first riser;

conducting drilling operations from a first drilling assembly into the well hole from the multi-activity drilling assembly through the first riser; and

during at least a portion of said drilling operations extending a second drilling assembly from the multi-activity drilling assembly through the second riser to a position adjacent to a subsea well head of a well hole to be drilled.

18. A method for conducting offshore drilling operations on a single well hole from a multi-activity drilling assembly as defined in claim 17 and further comprising the steps of:

withdrawing the first drilling assembly from the well hole up into the first riser above a means for closing the first riser at approximately the seabed;

closing the first riser at approximately the seabed from fluid communication with the second riser;

opening the second riser at approximately the seabed; and

conducting drilling operations from the second drilling assembly from the multi-activity drilling assembly into the well hole from the second riser.

19. A method for conducting offshore drilling operations on a single well hole from a multi-activity drilling assembly as defined in claim 18 and further comprising the steps of:

prior to conducting drilling operations from the second drilling assembly through the second riser, laterally adjusting the angular position of the second drilling assembly to generally axially align the second riser with a central longitudinal axis of the well hole.