Boring or penetrating the earth – Processes – Boring curved or redirected bores
Reexamination Certificate
1999-12-15
2001-11-20
Tsay, Frank (Department: 3672)
Boring or penetrating the earth
Processes
Boring curved or redirected bores
C175S073000
Reexamination Certificate
active
06318480
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to downhole assembly for drilling laterals or the like from a primary wellbore and in one aspect relates to a method and apparatus for drilling laterals such as drain holes and/or entries for short-radius horizontal wells which are to extend outward from a primary wellbore.
2. Background
In producing hydrocarbons from subterranean formations, it is not uncommon to drill a primary wellbore downward from the surface through the formations and then drill one or more horizontal wellbore(s) (sometimes called “laterals”) outward from the primary wellbore into the producing formation(s). This is an effective and economical way to increase the drainage of formation fluids into the primary wellbore thereby increasing the overall recovery of fluids through a single, primary well. These laterals may extend outwardly from the primary wellbore for substantial distances (e.g. 1300 feet or more) or they may be relatively short “drainholes” which extend only a few feet (e.g. 100 feet or less) into the formation.
Several techniques are known for drilling laterals from primary wellbores. For example, some of the first laterals were drilled using standard rotary drilling techniques wherein the lower end of the drill string included an articulated or flexible section (i.e. “wigglies”) positioned just above the bit which, when diverted by a whipstock in the wellbore, drilled a lateral having a pre-determined radius of curvature; see U.S. Pat. Nos. 2,397,070; 3,349,845; and 3,398,804.
While this technique works well for drilling relatively large-radius laterals, it requires a rotary drilling rig and crew to drill each lateral. This is both expensive and time consuming. Also, due to the actual construction of the flexible drill pipe section, the “build-up” angle of the lateral must be accurately predicted in order to insure that the lateral will end up within the zone of interest (e.g. production formation). Still further, due to the inherent flexibility of the articulated section of the drill pipe, directional control is difficult to maintain during drilling of the lateral.
With the advent of “coiled-tubing” and downhole mud motors, rotary drilling rigs are no longer required for the drilling of laterals from a wellbore. As will be understood in the art, “coiled tubing” is a long, continuous length of a relatively small-diameter, thin-walled steel tubing which is wound onto and off a large-diameter reel. Being of a continuous length, no joints of pipe have to be made-up or broken-out as the tubing is run into and out of the wellbore thereby saving substantial time, expense, and manpower. Also, since a downhole motor is used to drive the bit, the coiled tubing does not have to be rotated.
In drilling laterals with coiled tubing, a downhole mud motor having a drill bit at its lower end is connected onto the lower end of the coiled tubing string. As the coiled tubing is lowered into the primary wellbore, the bit is deflected by a whipstock in the wellbore towards the direction in which the lateral is to be drilled. A drilling fluid, e.g. mud, is pumped down the coiled tubing and through the downhole motor to rotate the bit to thereby drill the lateral away from the wellbore.
The inherent flexibility of the coiled tubing permits drilling with relatively large build-up angles (i.e. short radius of curvature) which is an important consideration since not only is drilling time for each lateral reduced but also the accuracy in positioning a particular lateral within its desired zone is increased. That is, a lateral can be “kicked-off” within the wellbore at a point much closer to its destination point within a desired zone since the transition from the relatively vertical wellbore to the relatively horizontal lateral will be much shorter.
However, the maximum build-up angle which may achieved with known coiled tubing techniques is limited, at least in part, by the length of the housing of the downhole motor, itself. The motor, which is at the leading edge of the coiled tubing, must enter and advance through the lateral as the lateral is being drilled away from the primary wellbore. That is, since the motor housing is inflexible, the radius of curvature of the lateral, as it is drilled and reamed from the relative vertical wellbore to its relative horizontal portion within the zone of interest, must be large enough to allow the motor to readily pass therethrough without binding.
Accordingly, it can be seen that there is always a need for new ways to further increase the build-up angle (i.e. shorten the radius of curvature) when drilling laterals from a primary wellbore. The shorter the radius, the quicker and less expensive the laterals can be drilled and the more accurately they can be placed within the zones of interests, i.e. production formation(s).
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for drilling a lateral, e.g. a drainhole, from a primary wellbore wherein large build-up angles (i.e. short radius-of-curvatures) are possible. Basically, a lateral is drilled by a downhole drilling unit which differs from prior art units of this type in that instead of connecting the drill bit directly to the downhole motor, a length of flexible drill pipe is used to connect the bit to the rotary power output of the motor. This length of flexible drill pipe below the downhole motor allows much larger build-up angles (e.g.
1
-
3
° per foot) which, in turn, reduces the time and expense for short-radius laterals and increase the accuracy of placement of the lateral within the zone of interest (e.g. production formation).
More specifically, the present invention provides a method and apparatus for drilling laterals from a primary wellbore wherein a downhole drilling unit is lowered into the primary wellbore on a workstring, e.g. coiled tubing. The downhole workstring is comprised of a conventional rotary mud motor which has a rotary power output and which is powered by a power fluid, e.g. drilling mud, flowing down the workstring. A length of flexible drill pipe, e.g. carbon-fiber composite pipe, is connected at its one end to the power output of said motor whereby operation of said motor will rotate the flexible drill pipe and the build-up assembly which is connected to the other end of the flexible drill pipe. The build-up assembly is comprised a knuckle-joint, a reamer, and a bit. connected to said reamer.
As the downhole drilling assembly is lowered into the primary wellbore by the coiled tubing, the bit of the build-up assembly contacts and is deflected off a whipstock which has been positioned within the primary wellbore at a point substantially adjacent the formation into which the lateral is to be drilled. Mud is pumped down the coiled tubing to operate the motor which, in turn, rotates the bit at the end of the flexible drill string. The flexibility of the drill string allows the bit to readily drill the transitional portion of the lateral in a relatively short, tight arc with a relatively small radius of curvature when compared to laterals drilled in prior art.
REFERENCES:
patent: 2397070 (1946-03-01), Zublin
patent: 3349845 (1967-10-01), Holbert et al.
patent: 3398804 (1968-08-01), Holbert
patent: 4523652 (1985-06-01), Schuh
patent: 4629012 (1986-12-01), Schuh
patent: 4653598 (1987-03-01), Schuh et al.
patent: 5195591 (1993-03-01), Blount et al.
patent: 5222554 (1993-06-01), Blount et al.
patent: 5346017 (1994-09-01), Blount et al.
patent: 5363929 (1994-11-01), Williams et al.
patent: 5383522 (1995-01-01), Hailey
patent: 5423389 (1995-06-01), Warren et al.
patent: 5826651 (1998-10-01), Lee et al.
patent: 5857531 (1999-01-01), Estep et al.
“Short-Radius Horizontal Drilling System Optimization in Yates Field Unit”; W. J. Tank; SPE Drilling & Completion, Mar., 1997 pp. 43-47.
Atlantic Richfield Company
Faulconer Drude
Tsay Frank
LandOfFree
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