Method for conducting offshore well operations

• US 5,486,070 A
• Filed: 09/30/1994
• Issued: 01/23/1996
• Est. Priority Date: 12/10/1990
• Status: Expired due to Term

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Huete, David A.
• Primary Examiner(s): BRITTS, RAMON S
• Application Number:
  US08/316,200
• Time in Patent Office: 480 Days
• Field of Search: 405/195.1, 405/202, 405/203, 405/223.1, 405/224, 405/224.2, 114/264, 114/265, 166/350, 166/353, 166/359, 166/366, 166/367, 175/7
• US Class Current: 405/202
• CPC Class Codes: B63B 21/50 Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
• CPC Class Codes: E21B 19/002 specially adapted for underwater drilling E21B19/09, E21B19/143 take precedence
• CPC Class Codes: E21B 41/0014 Underwater well locating or reentry systems
• CPC Class Codes: E21B 7/128 from floating support with independent underwater anchored guide base

Abstract

A method for conducting offshore well operations is disclosed in which a compliant platform is restrained out of its normal position substantially over a well pattern by adjusting a first lateral mooring system connecting the compliant platform to a first array of anchors secured to an ocean floor. An offshore drilling vessel is then positioned over a selected well site of the well pattern at a location at the surface of the water not accessible to the offshore drilling vessel with the compliant platform in its normal position by adjusting a second lateral mooring system connecting the compliant platform to a second array of anchors on the ocean floor. Well operations are then conducted through a substantially vertical riser while maintaining a clearance to prevent direct contact between the compliant platform and the offshore drilling vessel.

Claims

1. A method for conducting offshore well operations, comprising:

installing a compliant platform having a normal position in substantially vertical alignment with a well site;

positioning the offshore drilling vessel over a selected well site, comprising;

biasing the compliant platform out of substantially vertical alignment with the well site and securing this position with respect to the ocean floor; and

substantially vertically aligning a drilling derrick of the offshore drilling vessel over the well site and securing this position with respect to the ocean floor and the well site situated thereon for well operations while continuing to restrain the relative position of the offshore drilling vessel with respect to the compliant platform by their respective positions as defined in relation to the ocean floor; and

conducting well operations from the offshore drilling vessel through a riser.

2. A method for conducting offshore well operations, comprising:

installing a compliant platform at a first position with respect to an ocean floor which is in substantial vertical alignment with a well site;

positioning an offshore drilling vessel over a selected well site by driving the compliant platform out of its first position with respect to the ocean floor and substantially vertically aligning a drilling derrick of the offshore drilling vessel over the selected well site and independently securing the offshore drilling vessel in this position with respect to the ocean floor for well operations without direct, load transmitting structural connection therebetween;

conducting well operations from the offshore drilling vessel through a substantially vertical drilling riser; and

transferring a production riser from the offshore drilling vessel to the compliant platform.

3. A method for conducting offshore well operations in accordance with claim 2 wherein biasing the compliant platform out of substantially vertical alignment with the well site comprises adjusting a plurality of catenary mooring lines which define the position of the compliant platform.

4. A method for conducting offshore well operations in accordance with claim 3 wherein positioning the offshore drilling vessel comprises adjusting a plurality of catenary mooring lines which define the position of the offshore drilling vessel with respect to the ocean floor.

5. A method for conducting offshore well operations in accordance with claim 3 wherein positioning the offshore drilling vessel in substantially vertical alignment with the well site comprises utilizing a dynamic positioning system including a set of thrusters.

6. A method for conducting offshore well operations, comprising:

restraining a compliant platform at a position defined in relation to the ocean floor which is out of its normal position substantially over a well pattern;

positioning an offshore drilling vessel at a position defined in relation to the ocean floor which is over a selected well site of the well pattern at a location at the surface of the water not accessible to the offshore drilling vessel with the compliant platform in its normal position; and

conducting well operations through a substantially vertical riser while maintaining a space between the offshore drilling vessel and the compliant platform;

whereby the relative position of the offshore drilling vessel with respect to the compliant platform is defined indirectly as each is positioned in relation to its environment.

7. A method for conducting well operations in accordance with claim 6 wherein restraining a compliant platform at a position defined in relation to the ocean floor comprises adjusting a first set of catenary mooring lines and positioning the offshore drilling vessel in relation to the ocean floor comprises adjusting a second set of catenary mooring lines.

12. A method for conducting well operations in accordance with claim 6 wherein restraining a compliant platform at a position defined in relation to the ocean floor comprises adjusting a first set of catenary mooring lines and positioning the offshore drilling vessel in relation to the ocean floor comprises adjusting a second set of catenary mooring lines.

8. A method for conducting offshore well operations, comprising:

restraining a compliant platform out of its normal position substantially over a well pattern by adjusting a first lateral mooring system connecting the compliant platform to a first array of anchors secured to an ocean floor;

positioning an offshore drilling vessel over a selected well site of the well pattern at a location at the surface of the water not accessible to the offshore drilling vessel with the compliant platform in its normal position by adjusting a second lateral mooring system connecting the compliant platform to a second array of anchors on the ocean floor; and

conducting well operations through a substantially vertical riser while maintaining a clearance between the offshore drilling vessel and the compliant platform through the respective first and second lateral mooring lines.

9. A method for conducting offshore well operations, comprising:

installing a compliant platform having a normal position in substantially vertical alignment with a well site;

positioning the offshore drilling vessel over a selected well site, comprising;

biasing the compliant platform out of substantially vertical alignment with the well site and securing this position with respect to the environment; and

substantially vertically aligning a drilling derrick of the offshore drilling vessel over the well site and securing this position with respect to the environment and the well site on the ocean floor for well operations while continuing to restrain the relative position of the offshore drilling vessel with respect to the compliant platform by restraining their respective positions independently and without structural interconnection; and

conducting well operations from the offshore drilling vessel through a riser.

10. A method for conducting offshore well operations in accordance with claim 9 wherein biasing the compliant platform out of substantially vertical alignment with the well site comprises adjusting a plurality catenary mooring lines which define the position of the compliant platform;

and

wherein positioning the offshore drilling vessel comprises adjusting a plurality of catenary mooring lines which define the position of the offshore drilling vessel with respect to the ocean floor independent of the restraint of the compliant platform.

11. A method for conducting offshore well operations, comprising:

restraining a compliant platform at a position defined in relation to the ocean floor which is out of its normal position substantially over a well pattern;

positioning an offshore drilling vessel at a position defined in relation to the ocean floor which is over a selected well site of the well pattern at a location at the surface of the water not accessible to the offshore drilling vessel with the compliant platform in its normal position; and

conducting well operations through a substantially vertical riser while maintaining a space between the offshore drilling vessel and the compliant platform;

whereby the relative position of the offshore drilling vessel with respect to the compliant platform is defined indirectly as each is positioned in relation to its environment and without direct load transmitting interconnection therebetween.