BACKGROUND OF THE INVENTION
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.
- SUMMARY OF INVENTION
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.
BRIEF DESCRIPTION OF THE DRAWINGS
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.
FIG. 1A shows an elevation view of one embodiment of a tool of this invention in replacement pipe being placed below the sea floor and above the stub of an original conductor pipe. FIG. 1B shows a top view of the tool inside the replacement pipe.
FIG. 2 shows a tool of this invention after a fluid jet has deflected the tool to partially offset the stub of the original conductor pipe.
FIG. 3 shows a tool of this invention set at a lower position after the drill string has been lowered and the offset tool has contacted the stub of the original conductor pipe.
FIG. 4 shows the position of a tool of this invention after it has been offset and lowered such that the replacement conductor pipe is near the stub of the original conductor pipe.
FIG. 5 shows the position of a tool of this invention and replacement conductor pipe after the replacement conductor pipe has bypassed the stub of the original conductor pipe.
FIG. 6 shows the position of the replacement and original conductor pipes after removal of a tool of this invention from the replacement conductor pipe.
FIG. 7A shows results of displacement calculations for two configurations of supported load for a 26-inch o.d., 1-inch wall thickness casing. FIG. 7B shows the configuration of each support and load combination.
FIG. 8 shows calculated nozzle reaction force as a function of seawater flow rate for a ⅞-inch nozzle.
FIG. 9 shows a surface configuration that can be used for emplacing the tool and practicing the methods disclosed herein.
Referring to FIG. 1A, sea floor 10 has been penetrated by previously driving an original drive pipe through sea floor sediments 11. A top segment of the original drive pipe has been cut off and removed at a selected depth below sea floor 10, to form stub 13. The diameter of shaft 12 above stub 13 may be increased by running a “hole-opener” tool from the top of the stub to the mud line. When sediments 11 are soft, the hole-opener may not be necessary and the original diameter of shaft 12 may remain above the stub when the methods of this invention are applied. Replacement conductor pipe 14 is being lowered into shaft 12. Within replacement pipe 14, one embodiment of offset apparatus 16 used for deflecting pipe 14 as it approaches stub 13 is shown. In this embodiment, offset apparatus 16 includes cylinder 16 a. On the outside surface of cylinder 16 a are gussets 16 b. Gussets 16 b are sized to form a selected clearance inside replacement pipe 14. On the bottom of cylinder 16 a is plate 16 c and on the top of cylinder 16 is plate 16 d. The plates may be placed at a selected angle to the axis of offset tool 16 to assist in passing offset tool 16 past stub 13. A preferred value of this angle is in the range from about 20 to about 60 degrees from the axis of the tool. Support pipe 15 passes through cylinder 16 a and is attached thereto, preferably by welding. Support pipe 15 may be a segment of 5-inch drill pipe, heavy weight drill pipe or drill collar, for example, with a length of about 20 to 40 feet. Cylinder 16 a of offset tool 16 may be made from 20-inch casing and may have a length from about 15 feet to about 30 feet, for example. New conductor pipe 14 and drill string 20 may be placed in the well using apparatus and methods that will be described below. Lower plate 16 c may have area 30 of abrasive material applied thereto, which may be formed by silicon carbide particles in a matrix, for example, to afford a grinding action as plate 16 c passes over the edge of stub 13. Preferably, gussets 16 b are disposed such that a gusset, having a slope angle from about 20 to 60 degrees from the axis of cylinder 16, acts to bridge the gap between plate 16 c and the bottom of replacement conductor pipe 14. The outside surface of the bottom of replacement pipe 14 may also be shaped so as to ease movement past stub 13. A top view of offset apparatus 16 in pipe 14 is shown in FIG. 1B.
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.
Referring to FIG. 2, replacement drive pipe 14 and offset tool 16 have been lowered down to a short distance above pipe stub 13. Fluid circulation has begun down drill string 20 and a jet of fluid is emerging from jet sub 17. The jet is directed so as to move bullnose 19 in a preferred direction by the reaction force from the jet. The required flow rate through jet sub 17 to achieve a suitable reaction force will be discussed below.
Referring to FIG. 3, replacement drive pipe 14 and offset tool 16 have been lowered farther toward stub 13 and plate 16 c may be assisting in displacing offset tool 16 horizontally such that it can bypass stub 13. Flow rate through jet sub 17 may be increased to assist in displacing offset tool 16 around stub 13 as drill string 20 is lowered. Flow rate may be increased sufficiently to allow the bottom of replacement pipe 14 to clear the top of stub 13 without use of the deflecting force from plate 16 c.
Referring to FIG. 4, replacement drive pipe 14 and offset tool 16 have been lowered so as to allow replacement drive pipe 14 to begin to pass around stub 13. Because the sediments around stub 13 are generally soft, stub 13 may also be displaced horizontally as offset tool 15 is lowered, so as to decrease the amount of deflection required in replacement pipe 14. Likewise, if a hole-opener tool has not be run above stub 13 of the old conductor pipe, sufficiently soft sediments may allow replacement pipe 14 to be displaced horizontally in response to the reaction force on jet sub 17 by flow of sediments around replacement pipe 14. Lower plate 16 c may be used to assist in removing metal from the top of stub 13, by moving the plate along the axial direction of stub 13 and causing repeated movement of abrasive area 30 on contact stub 13.
FIG. 5 illustrates the position when replacement pipe 14 has bypassed stub 13 of the original pipe. FIG. 6 shows the pipes in position after offset tool 16 and attached apparatus have been removed from replacement pipe 14. Replacement pipe 14 is now in position to be driven or lowered to a selected depth below the mud line to complete a new slot for the platform.
FIG. 7A is a graph of the predicted forces required to displace the end of a 26-inch casing having a wall thickness of 1 inch. FIG. 7B shows the configurations of the casing load and support points used for the deformation calculations. The top curve of FIG. 7A shows results for a cantilevered pipe with the load applied 85 feet from the fixed end of the pipe. This curve would apply for a replacement pipe to be displaced horizontally at a distance 85 feet below the bottom guide on a platform, assuming the pipe is fixed at that guide and cantilevered below. The bottom curve of FIG. 7A would apply for a replacement pipe to be placed 85 feet below the bottom guide on a platform, assuming the pipe also deflects between the bottom guide and a second guide 80 feet above. This configuration is also illustrated in FIG. 7B. The calculations ignore the effect of sediments on deflection of the casing, but because of the soft nature of the sediments and the opportunity for removal of sediments around the replacement casing, it is believed that the calculations are a good approximation of the deflection obtained for various values of force or load at the end of the pipe.
FIG. 8 shows predicted nozzle reaction force as a function of flow rate of 8.5 lbs/gal fluid (sea water) through a ⅞-inch nozzle. A flow rate of about 800 gal/minute is predicted to produce a force of about 1500 pounds. Reference to FIG. 7 a shows that this force will produce a deflection of the 26-inch casing of about 6 inches. Similar observations indicate that a flow rate of 900 gal/minute should produce a defection of about 8 inches. These flow rates are reasonably attained with equipment on many drilling rigs. On large rigs, flow rates of more than 2000 gal/minute are possible, which will produce must larger reaction forces and deflections of the replacement conductor pipe. If desired, friction-reducing polymer may be added to the fluid to decrease pressure losses down the drill pipe during pumping.
Referring to FIG. 9, drill pipe 20 may be placed in the well using top drive 23. Drill pipe 20 may include side entry sub 30, through which wireline 26 may be placed inside the drill pipe through wire line packoff 28. Drill pipe 20 may be connected to pump 22 through a hose. Pump 22 is sized so as to pump fluid, commonly sea water, down the drill pipe at a selected rate and pressure to achieve the required deflection of the bottom of support pipe 15. Casing elevator 32, attached to the traveling block of a drilling rig (not shown) is used to control the lowering of replacement pipe 14 to the desired level, using slips 24 at rig floor 21. Replacement pipe 14 may then be further driven into the subsurface using well known methods.
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 FIG. 1 a, is also added to the bottom of the drill pipe. In yet another embodiment, a bullnose is further added to the muleshoe sub or jet sub. A short distance above the jet sub an offset tool may be inserted in the drill pipe, as also shown in FIG. 1A. The offset tool may include gussets such that it is more closely fitted inside a replacement drive pipe to be placed in a well. Using equipment such as illustrated in FIG. 9, drill pipe and replacement drive pipe may be simultaneously placed down the shaft or hole, adding one joint of drive pipe and one joint of drill pipe alternately, until the bull nose is only a short distance above the stub. This distance may be only 1 foot, for example. A gyroscopic survey instrument may then be placed in the drill pipe and lowered into the muleshoe sub, so that it can be used to determine the direction of the jet sub. The survey instrument may be lowered on wire line 26 until it is seated in muleshoe sub 18 (FIG. 1A). Gyroscopes in the instrument, well known in industry, can be used to obtain a surface read-out of the direction of the jet. After the preferred direction of the jet sub is obtained, pumps are started at the surface and pump rate is selected to apply the required force at the bottom of the drill pipe to displace the replacement drive pipe the required amount in the preferred direction from the center line of the stub. The well survey instrument, which may also include accelerometers with a surface readout, may then be used to measure the amount of deflection of the bottom of the drill string as a result of flow through the jet. If offset tool 16 is present in the drill string, lower plate 16 c (FIG. 1A) may also be used to deflect replacement drive pipe 14 around stub 13. If abrasive surface 30 has been formed on plate 16 c, drill pipe 20 may be repeatedly raised and lowered a few inches to cause an abrasive action on the edge of the top of stub 13. While continuing to pump fluid at a selected rate, the casing and drill pipe may be lowered farther, allowing replacement drive pipe 14 to pass the top edge of stub 13. Replacement drive pipe 14 may then be set on slips. Drill pipe 20 and any equipment at the bottom of the string may then be withdrawn from the well.
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.