Patent Publication Number: US-7717197-B2

Title: Apparatus for keeping a down hole drilling tool vertically aligned

Description:
FIELD 
   The present patent document relates to an apparatus for use in keeping a down hole drilling tool vertically aligned when drilling a vertical well. 
   BACKGROUND 
   It is difficult to keep well bores vertically aligned when drilling an oil or gas well. An example of an apparatus that is commercially available to keep a down hole drilling tool vertically aligned when drilling a vertical well is a system known by the Trade Mark “VertiTrak” which is marketed by Baker Hughes Incorporated. Another example of an apparatus that is commercial available to keep a down hole drilling tool vertically aligned when drilling a vertical well is a system know by the Trade Mark “Power V” which is marketed by Schumberger Incorporated. 
   SUMMARY 
   Accordingly, there is provided an apparatus for keeping a down hole drilling tool vertically aligned. The apparatus includes a tubular outer housing having a first end, a second end, a longitudinal axis and a circumferential wall that defines an interior bore. Centralizers are provided in spaced relation around the circumferential wall at the second end of the tubular housing. The centralizers are pivotally mounted to the outer housing for pivotal movement between an extended position and a retracted position. Pistons are positioned in piston chambers which are arranged radially in relation to the longitudinal axis. The pistons have an extended position and a retracted position. The pistons underlie each of the centralizers such that, in the extended position the pistons provide a force to urge the centralizers to the extended position. A plurality of discrete drilling fluid chambers are provided. Each of the drilling fluid chambers communicates with one of the piston chambers of one of the pistons. The position of the piston is controlled by a hydraulic pressure in the drilling fluid chamber. Each of the drilling fluid chambers has an inlet through which drilling fluids enter and an outlet. The outlets for the drilling fluid chambers are arranged in an annular configuration. A tubular pendulum is provided that has a circumferential wall, a first end, and a second end. The first end is pivotally secured within the interior bore of the outer housing for omni-directional pivotal movement. The pendulum moves from a concentric pivotal position to an angularly offset pivotal position by force of gravity as the outer housing deviates from a vertical orientation such that, as the pendulum moves between the concentric pivotal position and the angularly offset pivotal position, the pendulum adjusts the hydraulic pressure in at least one drilling fluid chamber by controlling the flow of fluid through the corresponding outlet of the at least one drilling fluid chamber such that, as the hydraulic pressure changes, the piston in communication with the at least one drilling fluid chamber adjusts the position of the centralizers until the outer housing returns to the vertical position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope to the particular embodiment or embodiments shown, wherein: 
       FIG. 1  is a side plan view in section of a lower portion of the apparatus. 
       FIG. 2  is a side plan view in section of an upper portion of the apparatus. 
       FIG. 3  is a detailed side plan view in section of the piston chamber. 
       FIG. 4  is a detailed side plan view in section of the fluid chamber outlet. 
       FIG. 5  is a perspective view of the outlet plate. 
       FIG. 6  is a detailed side plan view in section of an alternative of the fluid chamber outlet. 
       FIG. 7  is a detailed side plan view in section of a further alternative of the fluid chamber outlet. 
       FIG. 8  is a detailed side plan view in section of a further alternative of the fluid chamber outlet. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The preferred embodiment, an apparatus for keeping a down hole drilling tool vertically aligned generally identified by reference numeral  10 , will now be described with reference to  FIG. 1 through 5 . Alternative embodiments will be described with reference to  FIG. 6 through 8 . 
   Structure and Relationship of Parts: 
   Referring to  FIGS. 1 and 2 , apparatus for keeping a down hole drilling tool vertically aligned  10  includes a tubular outer housing  12  and an inner mandrel  11 . Outer housing has a first end  14 , a second end  16 , a longitudinal axis  18  and a circumferential wall  20  that defines an interior bore  22 . There are centralizers  24  in spaced relation around circumferential wall  20  at second end  16  of tubular housing  12 . Centralizers  24  are pivotally mounted at a pivot point  23  to outer housing  12  for pivotal movement between an extended position and a retracted position. Referring to  FIG. 3 , an annular collar  25  is provided to limit outward movement of centralizers  24  in the extended position. Pistons  26  are positioned in piston chambers  28  and are arranged radially in relation to longitudinal axis  18 , where one piston  26  underlies each centralizer  24  and provides a force to urge centralizer  24  to the extended position. There are also a plurality of discrete drilling fluid chambers  30 , such that each drilling fluid chamber  30  communicates with a corresponding piston chamber  28 , thereby providing hydraulic pressure to maintain piston  26 , and therefore centralizer  24 , in the extended position. Referring to  FIG. 3 , each drilling fluid chamber  30  has an inlet  32 , through which drilling fluids enter, and, referring to  FIG. 4 , an outlet  34  extending through outlet plate  35 . Referring to  FIG. 5 , outlet plate  35  is secured using connectors (not shown) through holes  37 . Outlets  34  for drilling fluid chamber  30  are also arranged in an annular configuration. Referring to  FIG. 3 , a flow restrictor  39  is positioned in inlet  32  to drilling fluid chamber  30  to control flow. A pair of concentric metal sleeves  52  and  54  are positioned upstream of inlet  32  to the drilling fluid chamber to grind up large particles in the drilling fluid before they reach the inlet  32 . Thus, each centralizer  24  has a corresponding piston chamber  28  with piston  26  and fluid chamber  30  with inlet  32  and outlet  34  positioned radially in a equally spaced manner about housing  12 , as are outlets  34  shown in  FIG. 5 . 
   Referring to  FIGS. 1 and 2 , a tubular pendulum  36  is provided within tubular housing  12  that has a circumferential wall  38 , a first end  40 , and a second end  42 . First end  40  is pivotally secured within interior bore  22  of outer housing  12  for omni-directional pivotal movement. These are radial bearings provided both above and below tubular pendulum  36 , those bearings, in the form of concentric tungsten carbide sleeves, are upper radial bearings  62 , first intermediate radial bearing  56  above tubular pendulum  36 , second intermediate radial bearing  58  below tubular pendulum  36  and low radial bearing  60 . There are also axial bearings  48  provided at first end  40  to withstand axial forces between inner mandrel  11  and outer housing  12 . Optionally, there may be provided biasing springs  50  at first end  40  of pendulum  36  to facilitate axial adjustment during assembly. It has been determined, however, that if care is taken as to the tolerances, springs  50  may be eliminated. 
   Operation: 
   Referring to  FIG. 1 through 5 , apparatus  10  is provided as depicted and described above. Apparatus is preferably attached as a section in a drilling string used for making vertical holes. Mud flows in inlet  32 , filling piston chamber  28  and fluid chamber  30 , and flows toward outlet  34 . When tool positioning places pendulum  36  in the vertical position, or a concentric pivotal position, second end  42  of pendulum  36  is suspended over the annular configuration of outlets  34  such that pendulum  36  substantially blocks each outlet  34  when in the concentric pivotal position to create a flow restriction. This places each drilling fluid chambers  30  in a balanced pressure equilibrium with the others, such that each piston  26  applies an equal force against each corresponding centralizer  24 . It is thus important that pistons and centralizers are equally spaced about housing  12 , such that in this position, the net force in any one direction is zero. In the preferred embodiment, this is done by using an annular contact member  44  mounted at second end  42  of pendulum  36 . Valve seat/bearing surfaces  47  allow annular contact member  44  to slide easily along outlet plate  35 . Annular contact member  44  is then biased by biasing springs  46  into engagement with the annular configuration of outlets  34 , such that annular contact member  44  closes outlets  34  when pendulum  36  is in the concentric pivotal position. Once the biasing force of biasing springs  46  are overcome, drilling fluids are allowed to bleed past. This is useful to regulate pressure during operation, and also to lubricate valve seat/bearing surfaces  47  so that pendulum  36  tends to hydroplane. Flow restrictor  39  limits the flow rate. 
   If outer housing  12  deviates from a vertical orientation, pendulum  36  will swing by force of gravity to assume the angularly offset pivotal position (relative to outer housing  12 ), thereby relieving the flow restriction on one or two of outlets  34  for corresponding drilling fluid chambers  30  and resulting in an increased flow of fluid. This reduces hydraulic force acting upon one or two of pistons  26  and causes the corresponding centralizer  24  to at least partially retract toward the retracted position. The differential pressure from the other centralizers  24  acts to urge outer housing  12  back toward the vertical position until pendulum  26  again assumes the concentric pivotal position and the balanced pressure equilibrium in the drilling fluid chambers is restored. As shown in  FIG. 5 , there are four outlets  34  illustrated. If pendulum  36  swings directly outwardly from one of outlets  34 , that one outlet will be open to fluid flow. However, pendulum  36  will sometimes swing outwardly between two outlets  34 , opening those two outlets to fluid flow. 
   By way of example, operation will be described with apparatus  10  operating in a 12¼ inch hole with 10 pounds per gallon of drilling fluid and the tool oriented in a starting orientation which is a vertical position. Referring to  FIG. 4 , we will assume a pressure drop across the bit of 750 pounds per square inch (psi) and that springs  46  biasing contact member  44  at second end  42  of pendulum  36  against valve seal/bearing surface  47  and outlet  34 , causes pressure in fluid chambers  30  to be maintained at 400 psi. Referring to  FIG. 3 , this 400 psi. pressure will cause each of the four pistons  26  to expand blades  24  with a force of 3068 pounds, since the cross-sectional area of each piston is 7.67 inches. Retaining ring  25  will restrict blades  24  from expanding more than the diameter of the hole being drilled. Referring to  FIG. 4 , any pressure above 400 psi. in fluid chambers  30  will cause the contact member  44  at second end  42  to be forced away from valve seat/bearing surface  47  allowing fluid to bleed through outlet  34 . The amount of fluid that will pass through the passage provided by drilling fluid chambers  30 , will be the amount of drilling fluid that can pass through the four one eighth inch nozzles  34  at a pressure of 350 psi (the difference between the pressure drop across the bit of 750 psi and the back pressure of 400 psi caused by biasing springs  46 ). At 350 psi and 10 pounds per gallon of drilling fluid, the amount of fluid would be 30 gallons per minute. Referring to  FIGS. 1 and 2 , this fluid will either exit the tool through a port or through one of the radial bearings positioned above pendulum  36 , namely  56  or  62 . There will also be additional fluid leakage through the radial bearings positioned below pendulum  36 , namely  58  or  60 . If apparatus  10  is not vertical, pendulum  36  will swing by force of gravity. Referring to  FIG. 4 , there will be virtually no resistance to this swinging motion, as contact member  44  at second end  42  of pendulum  36  will hydroplane on the drilling fluid that is leaking through outlet  34 . The movement of pendulum  36  will cause one or two of outlets  34  to open. Assuming that one outlet  34  opened, the pressure across flow restrictor  39  at inlet  32  would be 750 psi. Referring to  FIG. 3 , the flow through drilling fluid chambers  30  is always limited by flow restrictor  39  positioned at inlet  32 . As previously described, any large particles in the drilling fluid which might otherwise plug inlet  32  are ground by concentric sleeves  52  and  54 . 
   Advantages: 
   The VertiTrak and Power V tools are relatively complex and expensive. By comparison, apparatus  10 , is simple and is activated by gravity. Apparatus  10  may be used both in circumstances in which the drill string is rotated from the top and in circumstances in which a down hole drilling motor is used. It is, however, important that apparatus  10  be positioned in the drill string with a stabilizer or other stabilizing means above it, so that apparatus  10  is stabilized at its upper end. It is often preferable to rotate the drilling string in order to avoid becoming stuck in the hole. Apparatus  10  is capable of operating even when the drill string is rotated by a down hole drilling motor. 
   Variations: 
   The embodiment described above relies upon spring  46  to maintain annular contact member  44  at a sufficient pressure against bearing surface  47 , and to block the flow of fluid from annular configuration of outlets  34 . It will be understood, however, that other configurations also allow pendulum  36  to adjust the hydraulic pressure in drilling fluid chambers  30  by controlling the flow of fluid through outlets  34  in order to cause centralizers  24  to urge housing  12  back to the vertical position. For example, referring to  FIG. 8 , instead of having annular contact member  44  block fluid flow from outlets  34  when the tool is vertical as described previously, it may allow fluid to flow when housing  12  is in the vertical position, and block flow from certain outlets  34  when it deviates from the vertical position. In this arrangement, the corresponding pistons  26  would become pressurized and cause the necessary centralizers  24  to move outward in order to urge housing  12  back to the vertical orientation while the other centralizers  24  remain in the retracted position. A possible drawback with this variation is that there will be more friction to the sliding action of the pendulum  24 . The reason for this is that fluid bypasses the pendulum  24  and does not hydraulically lift the pendulum  24  as is the case with the embodiment described previously. There will be greater fluid flow through the tool, as the fluid passageways are only blocked when the pendulum goes off centre, however the amount of fluid loss is not considered to be of particular importance. 
   Other alternatives also exist to maintain contact between annular contact member  44  and bearing surface  47 . Referring to  FIG. 6 , the weight of contact member  44  is used to maintain contact. A possible drawback with this variation is that vibration may bounce the pendulum off the seat resulting in the loss of sealing contract. In  FIG. 7 , a threaded engagement  64  provides fine adjustment of the length of pendulum  36 , and the appropriate gap between contact member  44  and bearing surface  47 . A possible drawback with this variation is that wear could adversely affect the adjustment, resulting in the gap being reduced or eliminated. 
   In this patent document the word “comprising” is used in its non-limiting sense to mean that items following the word are included but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.