US 20060260809 A1
Method and apparatus are provided for replacing a conductor pipe beneath a platform and providing a slot for drilling an additional well. The original conductor pipe is cut off to form a stub at a selected distance above or below the sea floor. Apparatus including a jet sub is assembled and lowered on drill pipe within a replacement conductor pipe. Fluid is pumped down the drill pipe to force the replacement conductor pipe in a selected direction around the top of the stub of the original conductor pipe so as to allow the replacement conductor pipe to pass alongside the top of the stub. An instrument may be lowered down the drill string to determine the direction of the fluid jet and the deflection of the replacement pipe from vertical. An offset tool is provided to assist in bypassing the stub with the replacement pipe. The replacement pipe may then be driven to a selected depth.
1. A method for placing a replacement conductor pipe beneath a platform, the replacement conductor pipe passing through the same guides on the platform as an original conductor pipe, comprising:
providing a jet sub having a selected nozzle size;
placing the jet sub on a drill string and placing the drill string inside the replacement conductor pipe such that the jet sub is below and in proximity to a lower end of the replacement conductor pipe;
lowering the drill string and replacement conductor pipe to a selected position beneath the platform and pumping fluid through the drill string at a selected rate to cause the lower end of the replacement conductor pipe to be displaced horizontally a distance such that the replacement conductor pipe can be lowered past a stub of the original conductor pipe; and
removing the drill string and jet sub from inside the replacement conductor pipe.
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7. Apparatus for placing a replacement conductor pipe beneath a platform, the replacement conductor pipe passing through the same guides on the platform as an original conductor pipe, comprising:
a jet sub having a selected nozzle size and being adapted to pass through the replacement conductor pipe;
a drill string to support and supply fluid to the jet sub; and
a pump for supplying fluid through the drill string.
8. The apparatus of
9. The apparatus of
10. The apparatus of
11. The apparatus of
12. An offset tool for placing a conductor pipe beneath a platform, comprising:
a cylindrical body having an axis, an upper end and a lower end, the lower end being cut in a plane lying at a selected angle to the axis;
a support pipe passing through the cylindrical body and being attached thereto, the support pipe being adapted for coupling to a drill string;
a plurality of gussets on an outside surface of the cylindrical body; and
a plate covering the lower end of the cylindrical body.
13. The offset tool of
14. The offset tool of
1. Field of the Invention
This invention pertains to drilling of wells from offshore platforms. More particularly, method and apparatus are provided for placing a new conductor pipe in a slot of a platform by lowering the new conductor pipe past the top of the stub of a previous conductor pipe.
2. Description of Related Art
Platforms used for drilling and producing offshore wells are used with large pipes that are driven into the subsea sediments beneath the platform to form what are called “conductor pipes” or “drive pipes.” Guide sleeves attached to the platform direct the conductor pipes in a preferred pattern underneath the platform, forming a selected number of “slots” through which wells can be drilled from the platform. The guide sleeves may be located at several spaced-apart locations through the vertical extent of the platform, a separate set of guide sleeves for each conductor pipe. Such guide sleeves, conductor pipes and slots are well known in the industry. A platform is designed to contain a selected number of slots, selected depending on the number of wells to be drilled on the platform and the size of the platform. If a well on a platform is abandoned for any reason, a slot may be made available to drill another well from the platform if a new conductor pipe is installed. The reuse of the slot with a replacement conductor pipe, using the same set of guide sleeves on the platform, can be very valuable in allowing drilling of another well for development of additional hydrocarbon reserves without construction of additional platform structures.
When a slot is to be salvaged for reuse, existing conductor pipe is cut off. The pipe may be cut off below the sea floor (or “mud line”) or above the sea floor. More often it is cut off about 75 feet below the mud line. The casing strings inside the conductor pipe may be cut off at the same level or lower. The original conductor pipe is then removed from the shaft that was formed when it was driven through the sediments, guided by the platform guides, leaving a stub of the original conductor pipe.
U.S. Pat. No. 4,733,732 describes one method for placing a replacement drive pipe past the top of the stub of an original conductor pipe by using a drive pipe whipstock. U.S. Pat. No. 6,247,541 also describes a method and apparatus for drive pipe or conductor pipe replacement beneath offshore platforms in deeper water using a whipstock. Method is disclosed in this patent for first cutting the top portion of the old drive pipe and placing a guide cable in the stub portion of the old drive pipe and lowering a new drive pipe which contains a whipstock at its lower end over the guide cable until the whipstock engages the stub.
What is needed is a method for placing a new conductor pipe through the platform guides, bypassing the stub of old conductor pipe, and placing the pipe into a position that is useful for drilling a new well without the use of a whipstock. This must be done in a manner to avoid other wells drilled from the platform. When the new conductor has bypassed the stub of the old conductor, it can then be lowered or driven to a suitable depth for a conductor or drive pipe of another well.
Apparatus and method are provided for placing a conductor pipe beneath a platform to replace an original conductor pipe that is no longer functional. After the original conductor pipe is cut off at a selected location and the pipe above the cut removed from its position below the platform, a replacement conductor pipe is lowered through guides on the platform to a position above the stub of the original pipe. Fluid is then pumped down a drill string inside the replacement conductor pipe and out a jet near the bottom of the drill string. Reaction force of the jet acts on the replacement conductor pipe to displace the pipe to a position such that the replacement pipe can be lowered past the top of the stub. A muleshoe sub may be placed near the jet sub, such that the direction of the jet may be measured with a wellbore surveying tool. A survey tool may also be used to measure the angle from vertical of the drill string, which indicates the displacement of the drill string as a result of the reaction force of the jet. An offset tool at the bottom of the drill string may be placed near the bottom of the replacement conductor pipe and used to assist in deflecting the replacement pipe past the stub.
Attached to the bottom of support pipe 15 is jet sub 17. Preferably, muleshoe sub 18 and steel bull nose 19, which may be combined into one tool, are also joined to jet sub 17. Muleshoe sub 18 may be used for orienting jet sub 17, as described below. Bull nose 19 may provide a rounded surface for lowering past stub 13.
The procedure for placing a replacement drive pipe in a well may be as follows: the drive pipe to be replaced is cut at a selected depth (often in the range of 80 ft below the mud line) and removed to form a stub at the selected depth. A hole-opening tool may then be run above the stub to increase the diameter of the shaft above the stub. The diameter may be increased to 72 inches, for example, using a standard tool. Then a jet sub, the jet sub having a selected nozzle diameter, is added to the bottom of drill pipe, such as the 5-inch drill pipe. In another embodiment, a muleshoe sub, as illustrated in
After replacement drive pipe is lowered past the upper end of the stub, it may be allowed to fall to the depth where resistance stops further descent. Additional force, as by hammering, for example, may then be applied to the replacement drive pipe to place it at a lower desired depth in the well.
Although the present invention has been described with reference to specific details, it is not intended that such details be regarded as limitations of the scope of the invention, except as and to the extent they are included in the accompanying claims.