Boring or penetrating the earth – Processes
Reexamination Certificate
2001-03-23
2002-06-25
Suchfield, George (Department: 3672)
Boring or penetrating the earth
Processes
C166S077300, C166S384000, C175S162000, C175S173000
Reexamination Certificate
active
06408955
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to coiled tubing injectors, and apparatus and methods for combining conventional sectional tubing drilling with drilling using coiled tubing. More particularly, a collapsible mast and a rotary table can be arranged for operation with both a catwalk for sectional tubulars and with a coiled tubing unit. A linear coiled tubing injector is sufficiently narrow to coexist in the mast while tripping conventional tubulars.
BACKGROUND OF THE INVENTION
The general background relating to coiled tubing injector units is described in U.S. Pat. Nos. 5,839,514 and 4,673,035 to Gipson which are incorporated herein by reference for all purposes.
Apparatus for conventional drilling with sectional tubing is very well known.
Coiled tubing has been a useful apparatus in oil field operations due to the speed at which a tool can be run in (injected) and tripped out (withdrawn) from a well bore. Coiled tubing is supplied on a spool. An injector at the wellhead is used to grip and control the tubing for controlled injection and withdrawal at the well. As coil tubing cannot be rotated, drilling with coiled tubing is accomplished with downhole motors driven by fluid pumped downhole from the surface.
The use of coiled tubing has advantages over conventional drilling due to the potential to significantly speed drilling and reduce drilling costs through the use of continuous tubing. The most significant cost saving factors include the reduced pipe handling time, reduced pipe joint makeup time, and reduced leakage risks.
Exclusive use of coiled tubing is associated with several limitations. Certain stages of drilling operations still require making up of threaded joints, the means for which are not typically provided with coiled tubing rigs. Further, a coiled tubing injector has limited pulling strength as compared to the draw works provided with conventional sectional tubing masts. Further, a conventional wellhead injector tends to inject tubing which has a residual bend therein. Residual bend results in added contact and unnecessary forces on the walls of the drilled hole or casing, increasing frictional drag and causing an offset positioning of the tubing within the hole. Occasionally the coiled tubing can wad up in the hole (like pushing a resilient rope through a tube) and cannot be injected any further downhole or ever actually reach total depth.
As described in U.S. Pat. No. 5,842,530 to Smith et al. (Smith), apparatus is disclosed which is directed to providing a single rig having both conventional and coiled tubing capability. Smith describes how sectional tubing is used during the vertical, and substantially linear, drilling and switching to non-rotation tubing and downhole motors after deviating the well to the horizontal. However, by combining the two technologies in a single rig, Smith's mast is limited in its crown and draw works capacity. Further, Smith discloses the use of a conventional injector.
A conventional injector comprises two continuous, parallel and opposing conveyors having grooved shoes or blocks mounted thereon such as that disclosed in U.S. Pat. No. 5,533,668 to Council et al. for Halliburton Company, Oklahoma. The opposing conveyors have facing portions where the multiplicity of gripping blocks run parallel for gripping the tubing therebetween, typically positioned inline, directly adjacent and above the wellhead.
One characteristic of the dual conveyor injectors is that the facing grooved blocks must have absolutely synchronous timing and engagement with the coiled tubing, the failure to do so being associated with damage to the coiled tubing. Damage to the coiled tubing further reduces the lifespan of tubing already suffering a short lifespan due to reversing stresses inherent in the technique.
In U.S. Pat. No. 5,839,514 to Gipson, an improved injector comprises a grooved reel and hold-down rollers for imparting the gripping force necessary to drive the coiled tubing. This reel type injector, while causing less damage to the tubing than the block type is limited in pull capability, in part due to the short tubing gripping length. The gripping length of reel-type coiled tubing drives is limited by the circumference of the reel; the maximum circumference being limited to less than 360 degrees due to the inability to permit overlap tubing wrapped around a grooved driving reel.
Deeper wells can be accessed, for either workover or drilling purposes if the pull strength can be increased. Further, deeper wells usually require larger diameter tubing to handle greater string weight and to minimize fluid pumping power requirements. As the fluid for driving mud motors is delivered down the bore of tubing, fluid friction causes significant pressure drop and thus requires large power sources at the pumps. The larger the tubing, the lower the fluid friction losses and the lower the power requirements.
Rigs utilizing either the dual conveyor or the reel type injectors have had difficulty in dealing with larger diameter tubing. Further, while the use of coiled tubing has enabled faster operation to depth and out again, the equipment has a higher capital and operating cost. For example, coiled tubing rigs use more complicated and expensive equipment, have higher power requirements for overcoming fluid friction losses and the repeatedly deformed coiled tubing has a limited life which requires periodic replacement with new coiled tubing.
Further, coiled tubing apparatus is typically provided on a single transportable rig which provides a spool of coiled tubing, an injector and its own mast which is designed for light or small diameter coiled tubing, portability and generally low pull weight. In summary, the mast and rigs generally are not suitable for work with deeper wells.
SUMMARY OF THE INVENTION
Linear Injector
In one aspect the linear injector of the present invention extends coiled tubing capability beyond that known heretofore. In combination with a conventional jointed drilling rig, none of the functionality of the conventional rig is sacrificed while achieving enhanced capabilities by the addition of coiled tubing.
In the preferred embodiment, coiled tubing is driven along a linear section of an endless chain conveyor with an opposing linear array of rollers. Using prior art dual conveyors, gripper blocks pull on both sides of the coiled tubing and the present invention only pulls on one side. Applicant has found that by eliminating the prior art parallel chain drives, the difficulty to synchronize the two drives is avoided and the substitution of non-driving rollers for one side of the tubing injector results in less damage to the coiled tubing. Further, by eliminating the challenge of maintaining dual chain synchronicity, the novel injector is able to take unrestricted advantage of an extended length of a linear driving section, thus providing superior injection and pulling capability.
Accordingly, in one preferred aspect of the invention, deep wells can be drilled with coiled tubing even from the surface due to the combination of enabling the use of full diameter tubing, implementing a straightener and using an injector which is capable of applying both significant injector force on a drilling bit and full pulling capability for tripping out of the deep wells. An injector of 20 feet in length is capable of a nominal pulling capacity of about 100,000 lb. force. Further, suspension of the preferred injector in a conventional derrick having strong draw works and a rotary table permits operation with both conventional sectional tubing, including BHA, and simplifying the making up to coiled tubing.
In a broad aspect of the invention then, coiled tubing injection apparatus is provided comprising:
a chain conveyor extending about an endless path and having at least one linear section aligned with the wellbore;
a multiplicity of gripper blocks conveyed and driven by the chain conveyor, the gripper blocks forming a substantially continuous coiled tubing support while traversing the linear portion;
a linear array of a multiplicity of rollers
Precision Drilling Corporation
Sheridan & Ross P.C.
Suchfield George
LandOfFree
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