Boring or penetrating the earth – Processes – Boring curved or redirected bores
Reexamination Certificate
2000-12-19
2002-01-22
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
Processes
Boring curved or redirected bores
C175S073000
Reexamination Certificate
active
06340063
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a steerable rotary drilling device and a method for directional drilling using a rotary drilling string. Further, the present invention relates to a drilling direction control device and a method for controlling the direction of rotary drilling.
BACKGROUND OF INVENTION
Directional drilling involves varying or controlling the direction of a wellbore as it is being drilled. Usually the goal of directional drilling is to reach or maintain a position within a target subterranean destination or formation with the drilling string. For instance, the drilling direction may be controlled to direct the wellbore towards a desired target destination, to control the wellbore horizontally to maintain it within a desired payzone or to correct for unwanted or undesired deviations from a desired or predetermined path.
Thus, directional drilling may be defined as deflection of a wellbore along a predetermined or desired path in order to reach or intersect with, or to maintain a position within, a specific subterranean formation or target. The predetermined path typically includes a depth where initial deflection occurs and a schedule of desired deviation angles and directions over the remainder of the wellbore. Thus, deflection is a change in the direction of the wellbore from the current wellbore path.
It is often necessary to adjust the direction of the wellbore frequently while directional drilling, either to accommodate a planned change in direction or to compensate for unintended or unwanted deflection of the wellbore. Unwanted deflection may result from a variety of actors, including the characteristics of the formation being drilled, the makeup of the bottomhole drilling assembly and the manner in which the wellbore is being drilled.
Deflection is measured as an amount of deviation of the wellbore from the current wellbore path and is expressed as a deviation angle or hole angle. Commonly, the initial wellbore path is in a vertical direction. Thus, initial deflection often signifies a point at which the wellbore has deflected off vertical. As a result, deviation is commonly expressed as an angle in degrees from the vertical.
Various techniques may be used for directional drilling. First, the drilling bit may be rotated by a downhole motor which is powered by the circulation of fluid supplied from the surface. This technique, sometimes called “sliding drilling”, is typically used in directional drilling to effect a change in direction of the a wellbore, such as the building of an angle of deflection. However, various problems are often encountered with sliding drilling.
For instance, sliding drilling typically involves the use of specialized equipment in addition to the downhole drilling motor, including bent subs or motor housings, steering tools and nonmagnetic drill string components. As well, the downhole motor tends to be subject to wear given the traditional, elastomer motor power section. Furthermore, since the drilling string is not rotated during sliding drilling, it is prone to sticking in the wellbore, particularly as the angle of deflection of the wellbore from the vertical increases, resulting in reduced rates of penetration of the drilling bit. Other traditional problems related to sliding drilling include stick-slip, whirling, differential sticking and drag problems. For these reasons, and due to the relatively high cost of sliding drilling, this technique is not typically used in directional drilling except where a change in direction is to be effected.
Second, directional drilling may be accomplished by rotating the entire drilling string from the surface, which in turn rotates a drilling bit connected to the end of the drilling string. More specifically, in rotary drilling, the bottomhole assembly, including the drilling bit, is connected to the drilling string which is rotatably driven from the surface. This technique is relatively inexpensive because the use of specialized equipment such as downhole drilling motors can usually be kept to a minimum. In addition, traditional problems related to sliding drilling, as discussed above, are often reduced. The rate of penetration of the drilling bit tends to be greater, while the wear of the drilling bit and casing are often reduced.
However, rotary drilling tends to provide relatively limited control over the direction or orientation of the resulting wellbore as compared to sliding drilling, particularly in extended-reach wells. Thus rotary drilling has tended to be largely used for non-directional drilling or directional drilling where no change in direction is required or intended.
Third, a combination of rotary and sliding drilling may be performed. Rotary drilling will typically be performed until such time that a variation or change in the direction of the wellbore is desired. The rotation of the drilling string is typically stopped and sliding drilling, through use of the downhole motor, is commenced. Although the use of a combination of sliding and rotary drilling may permit satisfactory control over the direction of the wellbore, the problems and disadvantages associated with sliding drilling are still encountered.
Some attempts have been made in the prior art to address these problems. Specifically, attempts have been made to provide a steerable rotary drilling apparatus or system for use in directional drilling. However, none of these attempts have provided a fully satisfactory solution.
United Kingdom Patent No. GB 2,172,324 issued Jul. 20, 1988 to Cambridge Radiation Technology Limited (“Cambridge”) utilizes a control module comprising a casing having a bearing at each end thereof for supporting the drive shaft as it passes through the casing. Further, the control module is comprised of four flexible enclosures in the form of bags located in the annular space between the drilling string and the casing to serve as an actuator. The bags actuate or control the direction of drilling by applying a radial force to the drive shaft within the casing such that the drive shaft is displaced laterally between the bearings to provide a desired curvature of the drive shaft. Specifically, hydraulic fluid is selectively conducted to the bags by a pump to apply the desired radial force to the drilling string.
Thus, the direction of the radial force applied by the bags to deflect the drive shaft is controlled by controlling the application of the hydraulic pressure from the pump to the bags. Specifically, one or two adjacent bags are individually fully pressurized and the two remaining bags are depressurized. As a result, the drive shaft is deflected and produces a curvature between the bearings at the opposing ends of the casing of the control module. This controlled curvature controls the drilling direction.
United Kingdom Patent No. GB 2,172,325 issued Jul. 20, 1988 to Cambridge and United Kingdom Patent No. GB 2,177,738 issued Aug. 3, 1988 to Cambridge describe the use of flexible enclosures in the form of bags in a similar manner to accomplish the same purpose. Specifically, the drilling string is supported between a near bit stabilizer and a far bit stabilizer. A control stabilizer is located between the near and far bit stabilizers for applying a radial force to the drilling string within the control stabilizer such that a bend or curvature of the drilling string is produced between the near bit stabilizer and the far bit stabilizer. The control stabilizer is comprised of four bags located in the annular space between a housing of the control stabilizer and the drilling string for applying the radial force to the drilling string within the control stabilizer.
United Kingdom Patent Application No. GB 2,307,537 published May 28, 1997 by Astec Developments Limited describes a shaft alignment system for controlling the direction of rotary drilling. Specifically, a shaft, such as a drilling string, passes through a first shaft support means having a first longitudinal axis and a second shaft support means having a second longitudinal axis. The first and second shaft support mea
Cargill Edward James
Comeau Laurier E.
Hardin, Jr. John Ransford
Hay Rick
Maxwell Terrance Dean
Halliburton Energy Service,s Inc.
Kuharchuk Terrence N.
McCully Michael D.
Pezzuto Robert E.
Shull William
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