Boring or penetrating the earth – Processes – Boring curved or redirected bores
Reexamination Certificate
1997-12-04
2001-04-10
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Processes
Boring curved or redirected bores
C175S073000, C175S076000
Reexamination Certificate
active
06213226
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to drilling systems for stabilizing and directing drilling bits and particularly to eccentric adjustable diameter stabilizers for stabilizing and controlling the trajectory of drilling bits and more particularly to bi-center bits.
In the drilling of oil and gas wells, concentric casing strings are installed and cemented in the borehole as drilling progresses to increasing depths. In supporting additional casing strings within the previously run strings, the annular space around the newly installed casing string is limited. Further, as successive smaller diameter casings are suspended within the well, the flow area for the production of oil and gas is reduced. To increase the annular area for the cementing operation and to increase the production flow area, it has become common to drill a larger diameter new borehole below the terminal end of the previously installed casing string and existing cased borehole so as to permit the installation of a larger diameter casing string which could not otherwise have been installed in a smaller borehole. By drilling the new borehole with a larger diameter than the inside diameter of the existing cased borehole, a greater annular area is provided for the cementing operation and the subsequently suspended new casing string may have a larger inner diameter so as to provide a larger flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly through the existing cased borehole and permitting the drilling assembly to drill a larger diameter new borehole than the inside diameter of the upper existing cased borehole. One such method is the use of underreamers which are collapsed to pass through the smaller diameter existing cased borehole and then expanded to ream the new borehole and provide a larger diameter for the installation of larger diameter casing. Another method is the use of a winged reamer disposed above a conventional bit.
Another method for drilling a larger diameter borehole includes a drilling assembly using a bi-center bit. Various types of bi-center bits are manufactured by Diamond Products International, Inc. of Houston, Tex. See the Diamond Products International brochure incorporated herein by reference.
The bi-center bit is a combination reamer and pilot bit. The pilot bit is disposed on the downstream end of the drilling assembly with the reamer section disposed upstream of the pilot bit. The pilot bit drills a pilot borehole on center in the desired trajectory of the well path and then the eccentric reamer section follows the pilot bit reaming the pilot borehole to the desired diameter for the new borehole. The diameter of the pilot bit is made as large as possible for stability and still be able to pass through the cased borehole and allow the bi-center bit to drill a borehole that is approximately 15% larger than the diameter of the existing cased borehole. Since the reamer section is eccentric, the reamer section tends to cause the pilot bit to wobble and undesirably deviate off center and therefore from the preferred trajectory of drilling the well path. The bi-center bit tends to be pushed away from the center of the borehole because the resultant force of the radial force acting on the reamer blade caused by weight on bit and of the circumferential force caused by the cutters on the pilot bit, do not act across the center line of the bi-center bit. Because this resultant force is not acting on the center of the bi-center bit, the bi-center bit tends to deviate from the desired trajectory of the well path.
The drilling assembly must have a pass through diameter which will allow it to pass through the existing cased borehole. The reamer section of the bi-center bit is eccentric. It is recommended that the stabilizer be located approximately 30 feet above the reamer section of the bi-center bit to allow it to deflect radially without excessive wedging as it is passes through the upper existing cased borehole. If the eccentric reamer section is located closer to the stabilizer, the drilling assembly would no longer sufficiently deflect and pass through the upper existing cased borehole. The stabilizer and collars must allow the bi-center bit to deflect radially without excessive wedging as it passes through the existing cased borehole.
Typically a fixed blade stabilizer is mounted on the drilling assembly. The fixed blade stabilizer includes a plurality of blades azimuthally spaced around the circumference of the housing of the stabilizer with the outer edges of the blades being concentric and adapted to contact the wall of the existing cased borehole. The stabilizer housing has approximately the same outside diameter as the bi-center bit. Obviously, the fixed blade stabilizer must have a diameter which is smaller than the inside diameter of the upper existing cased borehole, i.e. pass through diameter. In fact the fixed blade stabilizer must have a diameter which is equal to or less than outside diameter of the pilot bit of the bi-center bit. Therefore, it can be appreciated that the blades of the fixed blade stabilizer will not all simultaneously contact the wall of the new borehole since the new borehole will have a larger diameter than that of the upper existing cased borehole. By not all of the fixed blades engaging the wall of the new larger diameter borehole, the fixed blade stabilizer is not centralized within the new borehole and often cannot prevent the resultant force on the bi-center bit from causing the center line of the pilot bit from deviating from the center line of the preferred trajectory of the borehole.
An adjustable concentric blade stabilizer may be used on the drilling assembly. The adjustable stabilizer allows the blades to be collapsed into the stabilizer housing as the drilling assembly passes through the upper existing cased borehole and then expanded within the new larger diameter borehole whereby the stabilizer blades engage the wall of the new borehole to enhance the stabilizer's ability to keep the pilot bit center line in line with the center line of the borehole. As the eccentric reamer on the bi-center bit tends to force the pilot bit off center, the expanded adjustable stabilizer blades contacts the opposite side of the new borehole to counter that force and keep the pilot bit on center.
One type of adjustable concentric stabilizer is manufactured by Halliburton, Houston, Texas and is described in U.S. Pat. Nos. 5,318,137; 5,318,138; and 5,332,048, all incorporated herein by reference. Another type of adjustable concentric stabilizer is manufactured by Anderguage U.S.A., Inc., Spring, Tex. See Andergauge World Oil article and brochure incorporated herein by reference.
Even with adjustable concentric blade stabilizers, it is still recommended that the stabilizer be located at least 30 feet above the bi-center bit. The outside diameter of the housing of an adjustable concentric diameter blade stabilizer is slightly greater than the outside diameter of the steerable motor. The adjustable blade stabilizer housing includes a large number of blades azimuthally spaced around its circumference and extending radially from a central flow passage passing through the center of the stabilizer housing. To fit a large number of blades interiorally of the housing, it is necessary to increase the outer diameter of the housing. This produces an offset on the housing. However, the outside diameter of the adjustable stabilizer housing must not exceed the outside diameter of the pilot bit if the adjustable stabilizer is to be located within 30 feet of the bi-center bit. Even if the outside diameter is only increased ½ of an inch, for example, there would not be adequate deflection of the drilling assembly to allow the passage of the drilling assembly down through the existing cased borehole.
The stabilizer is so far away from the bi-center bit that it cannot prevent the eccentric reamer section from tending to push off the wall of the new borehole and cause the pilot bit to deviate from
Eppink Jay M.
Odell Albert C.
Rios-Aleman David E.
Conley & Rose & Tayon P.C.
Dang Hoang
Halliburton Energy Service,s Inc.
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