1 / 40

Petroleum Engineering 406

Station Keeping. Environmental Forces Mooring Anchors Mooring Lines Dynamic Positioning. . Station Keeping. The ability of a vessel to maintain position for drilling determines the useful time that a vessel can effectively operate. Stated negatively, if the vessel cannot stay close enough over the well to drill, what good is the drilling equipment? .

leda
Download Presentation

Petroleum Engineering 406

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. Petroleum Engineering 406

    2. Station Keeping Environmental Forces Mooring Anchors Mooring Lines Dynamic Positioning

    3. Station Keeping The ability of a vessel to maintain position for drilling determines the useful time that a vessel can effectively operate. Stated negatively, if the vessel cannot stay close enough over the well to drill, what good is the drilling equipment?

    4. Station Keeping - cont’d Station keeping equipment influences the vessel motions in the horizontal plane. These motions are: surge, sway, and yaw. Generally, surge and sway are the motions that are considered. Yaw motion is decreased by the mooring system but is neglected in most mooring calculations.

    5. Station Keeping When investigating or designing a mooring system, the following criteria should be considered:

    6. Operational Stage 1. The vessel is close enough over the well for drilling operations to be carried out. This varies between operators, but is usually 5% or 6% of water depth. Later, other criteria, based on riser considerations, will be discussed.

    7. Non-operational but Connected 2. The condition from the operational stage up to 10% of water depth. Drilling operations have been stopped, but the riser is still connected to the wellhead and BOPs.

    8. Disconnected 3. The riser is disconnected from the wellhead and the BOPs, and the vessel can be headed into the seas.

    9. Station Keeping - cont’d Example Water Depth = 1,000 ft Drilling: 50-60 ft Connected: 100 ft max

    10. Environmental Forces Acting on the Drilling Vessel (i) Wind Force (ii) Current Force (iii) Wave Force

    11. The Station Keeping System Must be designed to withstand the environmental forces Two types: Mooring System (anchors) Dynamic Positioning

    12. (i) Wind Force The following equation is specified by the American Bureau Shipping (ABS) and is internationally accepted:

    13. Wind Force Where:

    18. Where:

    19. Fc = 1 * 1 * 22 * 30 * 400 Fc = 48,000 lbf = 48 kips

    20. (iii) Bow Forces:

    21. Where:

    22. Bow Forces:

    23. Beam Forces:

    24. Beam Forces:

    27. Station Keeping

    28. Station Keeping 4. Beyond about 5,000 feet, use dynamic positioning 5. Calm water tension should be determined to hold the vessel within the operating offset under the maximum environmental conditions specified for operation.

    29. Station Keeping, Continued 6. Once the riser is disconnected, the vessel heading may be changed to decrease the environmental forces on the vessel.

    34. Chain Quality Inspection

    35. Dynamic Positioning Dynamic positioning uses thrusters instead of mooring lines to keep the vessel above the wellhead. Glomar Challenger used dynamic positioning as early as 1968. ODP uses dynamic positioning.

    36. Advantages of Dynamic Positioning (i) Mobility - no anchors to set or retrieve - Easy to point vessel into weather - Easy to move out of way of icebergs (ii) Can be used in water depths beyond where conventional mooring is practical (iii) Does not need anchor boats

    37. Disadvantages of Dynamic Positioning (i) High fuel cost (ii) High capital cost (?) (iii) Requires an accurate positioning system to keep the vessel above the wellhead. Usually an acoustic system - triangulation

    39. To understand the operating principles of acoustic position referencing, assume that: 1. The vessel is an equilateral triangle. 2. The kelly bushing (KB) is in the geometric center of the vessel.

    40. 3. The hydrophones are located at the points of the triangular vessel. 4. The subsea beacon is in the center of the well. 5. No pitch, no roll, no yaw and no heave are permitted.

More Related