Wells – Submerged well – Connection or disconnection of submerged members remotely...
Reexamination Certificate
2001-10-24
2004-06-08
Lagman, Frederick L. (Department: 3673)
Wells
Submerged well
Connection or disconnection of submerged members remotely...
C166S077200, C166S351000, C166S342000
Reexamination Certificate
active
06745840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a compliant guide for accessing seabed installations such as sea-based oil or gas wells, systems using the guides, methods for dispensing coiled tubing with the compliant guide to such installation and methods for making and using same.
More particularly, this invention relates to a system for accessing seabed installations including a compliant guide for coiled tubing, flexible shafts or other similar apparatus. The compliant guide attaches at its first end to an injector apparatus and at its second end to a seabed installation providing a guide conduit for coiled tubing or other apparatus to feed same to the seabed installation. This invention also relates to methods for making the guide and systems and methods for using the guide and system.
2. Description of the Related Art
When inserted into an oil well, coiled tubing has a wide variety of uses such as drilling, logging and production enhancement according to known art. Coiled tubing can be withdrawn from a well immediately following a well treatment, or it can be permanently left in the well as part of the well completion. When coiled tubing is used, it is necessary to provide an annular well seal where the coil tubing enters the well. This seal is sometimes referred to as the “stuffing box” or “stripper”, and its function is to provide a dynamic, pressure tight seal around the coiled tubing to prevent leakage of the well fluids from the oil well at the point where the coiled tubing enters the oil well. Prior art methods and apparatus have positioned the annular well seal close to the injector, typically only a few inches away, for the primary purpose of avoiding buckling failure of the coiled tubing between the injector and the annular well seal.
According to the prior art, oil wells on land require a lubricator. This is a device that can be many tens of feet tall and is temporarily attached to the wellhead or tree of the well. The injector must be held in place above this lubricator, close to the annular well seal. Substantial cranage or support structure is required to lift and hold the injector in place. Providing such cranage or structures adds to the cost, complexity, and duration of coiled tubing operations.
According to the prior art, underwater oil wells with surface wellheads are similar to land oil wells in that they require that the injector be lifted and held in place above the lubricator and close to the annular well seal. An additional disadvantage is that the injector must be lifted from a floating vessel onto the facility that has the surface wellheads. Many off-shore platforms do not have installed cranes adequate for this task, and the cost of temporarily providing such cranes may preclude the economical use of coiled tubing altogether.
According to the prior art, coiled tubing may be used in the case of underwater oil wells with temporary surface wellheads. In some instances a drilling vessel is connected to the underwater oil well with a temporary riser. This would occur during the drilling phase of an underwater oil well. A lubricator is sometimes attached to the temporary surface wellhead, and in such instances the injector must be transferred from a floating vessel, lifted and held above the lubricator close to the annular well seal. Since the drilling vessel floats freely without mooring, the injector must be heave compensated.
Underwater oil wells, with subsea wellheads which do not have any type of platform structure on the surface above the well, are generally accessed from a drill ship or semi-submersible drilling type vessel. According to the prior art, coiled tubing access from such vessels requires that the pressurized well bore to be temporarily extended by use of a tensioned rigid riser from the wellhead to the vessel and associated large heave compensation and riser handling equipment. This then allows the annular well seal to be close to the injector. Examplary of such prior art are U.S. Pat. No. 4,423,983 which discloses a fixed or rigid marine riser extending from a subsea facility to a floating structure located substantially directly above; and U.S. Pat. No. 4,470,722 which discloses a marine production riser for use between a subsea facility (production manifold, wellhead, etc.) and a semi-submersible production vessel. Other related prior art includes U.S. Pat. No. 4,176,986 which discloses a rigid marine drilling riser with variable buoyancy cans. Drill ships or semi-submersible drilling type vessels and associated equipment required for tensioned rigid risers have a high daily cost. For example, routine coiled tubing access performed on a subsea well may have a substantial daily cost in excess of one hundred thousand dollars per day.
In an effort to preclude the need for tensioned rigid risers and riser heave compensation systems, prior art that uses flexible risers in place of rigid risers has been disclosed. Examplary of such prior art are U.S. Pat. No. 4,556,340 and U.S. Pat. No. 4,570,716 that disclose the use of flexible risers or conduits between a subsea facility and a floating production facility; and U.S. Pat. No. 4,281,716 that discloses a flexible riser to facilitate vertical access to a subsea well to perform wireline maintenance. Other related prior art includes U.S. Pat. No. 4,730,677 that discloses a method and system for servicing subsea wells with a flexible riser and U.S. Pat. No. 5,671,811 that discloses a tube assembly for servicing a subsea wellhead by injecting an inner continuous coiled tubing into an outer continuous coiled tubing. What this prior art has in common is the extension of the pressurised well bore from the wellhead to the floating facility to allow the annular well seal, for either wireline or coiled tubing, to be above the water surface or close to the injector.
Damage, failure or emergency disconnection of a riser connected between a subsea wellhead and a floating vessel, or of tubing between a facility with surface wellheads and a floating vessel, can create safety hazards and a pollution risk if there are pressurised well fluids inside the riser or tubing. These risk factors are of significant concern and are often cited as the reason for not carrying out a particular oilfield operation. These concerns are heightened if the floating vessel is maintained in position by means of dynamic positioning instead of anchors. Such a vessel can accidentally move off station and reach the geometric or structural limit of the riser very quickly, within a few tens of seconds, depending on the water depth. Concerns about fatigue failure also arise if this riser or tubing is a homogeneous steel structure that is subjected to both pressure and varying stresses due to the relative motion between the wellhead and floating vessel and due to environmental forces.
Prior art methods and systems for accessing subsea wells with wireline exist which do not use risers to temporarily extend a pressurised well bore up to a floating vessel. Instead, a subsea lubricator may be used which connects directly onto a subsea tree or wellhead. A subsea lubricator is a free standing structure on a subsea tree. It is generally 50 ft. to 100 ft. tall with an annular well seal at the top that allows a wireline to enter from ambient pressure into a lubricator that is at well pressure. The top of a subsea lubricator remains underwater at a sufficient depth to allow for at least the draft of a floating support vessel which holds a wireline winch and ancillary support equipment. Subsea lubricators can be dispatched from vessels that are not drill ships or semi-submersible drilling type vessels and thus provide the flexibility to use vessels with a lower daily cost and other advantageous attributes such as rapid mobilization time offered by dynamically positioned vessels. Exemplary of this prior art are U.S. Pat. No. 4,993,492 that discloses a method of inserting wireline equipment into a subsea well using a subsea wireline lubricator; and U.S. Pat. No. 4,825,953 that discloses a wireline well servicing
Gordon Alan H.
Lagman Frederick L.
Strozier Robert W.
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