Abstract:
A drilling motor for directional drilling in a wellbore has a drill bit at a downhole end, a bent housing having a first bend spaced above the drill bit and defining a first angle, the first bend having an inside bend surface and an outside bend surface, and a guide element that biases the first bend toward the first angle when the bent housing is positioned within a straight section of the wellbore. The guide element may be a pad, a centralizer or a second bend in the bent housing.

Description:
TECHNICAL FIELD 
       [0001]    This relates to a directional drilling motor, such as a drilling motor that is attached to bottom end of a drill string with a drill bit attached to the bottom end. 
       BACKGROUND 
       [0002]    A drilling motor with a bent housing is usually used in directional drilling. When the drilling motor has fluid pumped through it to provide rotation to the bit and the drill string and drilling motor is stationary, the drilled well bore follows a generally curved path in the direction of the bent housing. When the drilling motor has fluid pumped through it to provide rotation to the bit and the drill string and drilling motor is rotated, the drilled well bore follows a generally straight path due to the rotation of the bent housing. 
         [0003]    The combination of the curved and straight path segments allows the directional control of a well bore to follow a predetermined course. 
       SUMMARY 
       [0004]    According to an aspect, there is provided a drilling motor for directional drilling in a wellbore, the drilling motor having a drill bit at a downhole end, the drilling motor comprising a bent housing having a first bend spaced above the drill bit and defining a first angle, the first bend having an inside bend surface and an outside bend surface. A guide element biases the first bend toward the first angle when the bent housing is positioned within a straight section of the wellbore. 
         [0005]    According to a further aspect, the guide element may comprise a pad positioned adjacent to the inside bend surface of the first bend, the pad biasing the outside bend surface toward an inner surface of the straight section of the wellbore. The pad may comprise a portion of a centralizer carried by the bent housing adjacent to the first bend. 
         [0006]    According to a further aspect, the bent housing may comprise a second bend that is spaced above the first bend relative to the drill bit, and the guide element may further comprises the second bend. The drilling motor may further comprise a pad positioned adjacent to the inside bend surface of the first bend, the pad biasing the outside bend surface toward an inner surface of the straight section of the wellbore and the guide element may further comprise the pad. 
         [0007]    According to an aspect, there is provided a drilling motor for directional drilling in a wellbore. The drilling motor has a drill bit at a downhole end. The drilling motor comprises a first housing section between the drill bit and a first bend, and a second housing section between the first bend and a second bend. The first housing section and the second housing section lie in a plane, wherein the first housing section lies in the plane on a first side of the second housing section. The drilling motor further comprises a third housing section extending away from the second bend relative to the second housing section, the third housing section extending away from the first side of the second housing section. 
         [0008]    According to another aspect, the first housing section, the second housing section, and the third housing section each lie in the plane. 
         [0009]    According to another aspect, the drilling motor further comprises a wear pad on an outside surface of at least one of the first bend and the second bend. 
         [0010]    According to another aspect, the drilling motor further comprises a pad on an inside surface of the first bend, the positioning pad being sized to maintain the first bend above a minimum angle within the wellbore. 
         [0011]    According to another aspect, the first bend has an angle of about 1.5 degrees and the second bend has an angle of about 1 degree. 
         [0012]    According to another aspect, a respective length of the first, second and third housing sections and a respective angle of the first and second bends result in a side load at the bit of less than about 300 lbs, a side load at the bit of less than about 150 lbs, or substantially no side load at the bit when the housing is in a straight section of the wellbore. 
         [0013]    According to another aspect, there is provided a method of directional drilling. The method comprises the steps of attaching a drill bit to a motor housing of a downhole drilling motor as described above; drilling a curved section of the borehole by operating the drill bit While maintaining the motor housing in a fixed rotational position within the borehole, the curved section being in the direction of the first bend; and drilling a straight section of the borehole by operating the drill bit while rotating the motor housing relative to the borehole. 
         [0014]    According to an aspect, there is provided a drilling motor for directional drilling in a wellbore, the drilling motor having a drill bit at a downhole end. The drilling motor comprises a bent housing having a first bend spaced above the drill bit and defining a first angle, the first bend having an inside bend surface and an outside bend surface; and a pad adjacent to the inner surface of the first bend, the pad biasing the first bend toward the first angle when the bent housing is positioned within a straight section of the wellbore. 
         [0015]    According to an aspect, the pad may comprise a portion of a centralizer carried by the bent housing adjacent to the first bend. 
         [0016]    According to an aspect, the drilling motor may further comprise a second bend positioned above the first bend relative to the drill bit, the second being having a second angle that is opposite the first angle. 
         [0017]    In other aspects, the features described above may be combined together in any reasonable combination as will be recognized by those skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    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 hot intended to be in any way limiting, wherein: 
           [0019]      FIG. 1A-1D  are side elevation views of prior art drilling motors in a well bore. 
           [0020]      FIG. 2A-2D  are detailed side elevation views of drilling motors in well bores showing the well bore interference for the different bends shown in  FIG. 1A-1D . 
           [0021]      FIG. 3A-3C  are progressive side elevation views with approximated applied loads to fit the drilling motor into the well bore with a bend of 2.38°. 
           [0022]      FIG. 4A-4C  are side elevation views of the lower section of the drilling motor and bit with approximated applied loads shown in  FIG. 3C . 
           [0023]      FIG. 5  is an enlarged side elevation view of the approximate mid-point of the lower section of the drilling motor in  FIG. 4A-4C  indicating the resulting axial flex of the lower tubular section when fitted into the well bore. 
           [0024]      FIGS. 6A and 6B  are an enlarged side elevation view of the bit in  FIG. 3A-3C  and an approximate change in the hit face angle relative to a plane that is normal to the well bore. 
           [0025]      FIG. 7A-7D  are representations of a drilling motor with a stabilizer or pad located between the bend and the bit, and the resulting side loads. 
           [0026]      FIG. 8A-8D  are representations of a drilling motor in a horizontal well and the resulting side loads as the motor rests on the bottom of the well as a result of its weight. 
           [0027]      FIG. 9A-9D  are representations of a “double bend” drilling motor where the bends are opposing, with the lower bend being 1.50° and the upper bend being 1.00° in a direction 180° to the 1.50° bend. 
           [0028]      FIG. 10A-10D  are representations of a single bend drilling motor where the bend is reduced to achieve the same interference at the top of the drilling motor and maintain the same bit face angle as the double bend motor in  FIG. 9A-9D . 
           [0029]      FIG. 11A-11D  are representations of a well bore, drilled 39″ with the single bend drilling motor in  FIG. 10A-10D . 
           [0030]      FIG. 12A-12D  are representations of a well bore, drilled 39″ with the double bend drilling motor in  FIG. 9A-9D . 
           [0031]      FIG. 13A-13D  are representations of a well bore, drilled 39″ with the single bend drilling motor in  FIG. 10A-10D , with the addition of a pad opposite the bend on the high side. 
           [0032]      FIG. 14A-14F  are three combinations of bends and pads to be placed in the drilling motor. 
           [0033]      FIG. 15A-15D  are a representation of the side loads resulting from a double bend drilling motor with a 1.50° bend combined with a 1.00° in the opposite direction. 
           [0034]      FIG. 16A-16B  are a representation of the side loads resulting from the two methods with the addition of a centraliser on top of the drilling motor in a horizontal well. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Referring to  FIG. 1A-1D , there is shown a drilling motor, generally identified by reference  10 . Drilling motor  10  is designed with a bend  26  that enable motor  10  to drill a well bore  24  with a curved section  30  when the drill pipe  32  and drilling motor  10  are held rotationally stationary. The curved section  30  of well bore  24  that is produced by drilling motor  10  when weight is applied to the top of drilling motor  10  is generally determined by the magnitude of bend  26 .  FIG. 1A-1D  show four bends, 1.50°, 1.83°, 2.12°, and 2.38°.With each bend  26 , there is an interference that drilling motor  10  experiences when inserted into a straight section  34  of well bore  24 . Due to their length, a drilling motor  10 , with a typical bend  26 , will not “fit” in straight section  34  of well bore  24 .  FIG. 2A-2D  represent the resulting interference at the top of the drilling motor  10  for each bend. As can be seen, drill bit  14  is centralized in the well bore  32  and the “low” side of the bend  26  is in contact with the wall of straight section  34  of well bore  24 , usually with a wear resistant pad  36  providing the contact point  22 . Drilling a curved section  30  in a well bore  24  to change its direction is dependent on the magnitude of the interference resulting from the selected bend. Larger bends, resulting in greater interferences, generally drill sharper curves to produce larger changes in the well bore direction. This method of directional drilling requires three points of contact to induce the appropriate side loading and produce the desired curve in the well bore. The three points are (1) the centralized bit  14  in the well bore  24 , (2) the “low” side of the bend  22 , in contact with the wall of well bore  24 , and (3) the top  38  of the drilling motor  10  in contact with the wall of well bore  24 . 
         [0036]      FIG. 3A-3C  represent the applied physical forces required to “fit” a drilling motor with a 2.38° bend into the straight section  34  of well bore  24 .  FIG. 3  shows an example of the resulting side loads at each of the 3 contact points. In particular, there is shown a drilling motor that is 325 inches with a bit  14  that is 55 inches from bend  22 . The top tubular portion  11  of drilling motor  10  flexes when inserted into the straight section  34  of well bore  24 . For this discussion, it is assumed that the force required to fit the drilling motor into the straight section  34  of well bore  24  remains at the top  38  of the drilling motor  10 , and is estimated to be  300  lbs. The estimated 300 lbs load at the top  38  of the drilling motor  10  produces a load on the side of the bit  14 , of 1473 lbs and a contact load on the “low” side of bend  22  of 1773 lbs.  FIGS. 4A and 4B  are enlarged details of the loading and resulting flex the lower tubular portion  12  experiences when fit into the straight section  34  of well bore  24 .  FIG. 5  is an enlarged view of the centre axis  13  of the lower tubular section  12 , and the flex of the centre axis  13  to the measured axis position  17  when the drilling motor  10  is fit into the well bore  24 . The bit  14  accommodates side loading, but is not restricted from rotating due to the flexing of the tubular section  12 . Approximated from actual measurements,  FIGS. 6A and 6B  represent the change in the angle of bit  14  when the drilling motor  10  is fit into well bore  24 . That is to say that, the centralized bit  14  and the contact point  22  in  FIG. 1A-1D  position the bit  14  at an angle of 0.39°, relative to straight section  34  of well bore  24 . When drilling motor  10 , with a 2.38° bend  26 , is fit into straight section  34 , the face of bit  14  rotates from 0.39° to 0.06° due to the loads imposed by straight section  34 . Because the face of bit  14  flattens as drilling motor  10  is fit into straight section  34 , the ability to produce a curve in well bore  24  when drilling ahead is greatly diminished. This trend is particularly noticeable in hard-rock formations with PDC (polycrystalline diamond cutter) bits, because they drill sideways effectively. Currently, the trend is to use larger bends, 2.50° or higher. This solution increases the side loading on bit  14 , which in turn increases the loads on lower tubular portion  12  of drilling motor  10 . These increased loads often result in failures of the drilling motor  10 . 
         [0037]      FIG. 7A-7D  represent another method used to increase the side loading of bit  14 , with a “near bit” pad or stabilizer  28 . To be effective, the pad or stabilizer  28  must contact the well bore  24  before the bend contact point  22 . This being the case, the loading on bit  14  and pad or stabilizer  28  is greatly increased as shown in  FIGS. 7C and 7D . Horizontal drilling of a well bore also provides insight into the limitations of the 3-point contact method.  FIG. 8A-8D  represent the pertinent considerations of a drilling motor  10  in a well bore  24 .  FIG. 8C  represents the effect of the weight of tubular section  11  of drilling motor  10 , and the added weight of tubular section (not shown) attached above drilling motor  10  in horizontal well  24 . The top of drilling motor  10  rests on the bottom of the well bore, increasing the side load on bit  14 , and the contact point  22  of the drilling motor  10 .  FIG. 8D  indicates the loading when the contact point  22  is in contact with the top of the well bore. The top of the drilling motor  10  remains on the bottom of the well bore  24  and the loading on bit  14  and contact point  22  are reduced. When drilling motor  10  is rotated to drill a straight section, the 3-point method shown in  FIG. 8A-8D  causes the well bore  24  to turn in a direction that is “up” and “left”. The “up” directional portion is due to the uneven loading as drilling motor  10  rotates in the horizontal section and reaches higher side loads at bit  14  when contact point at bend  22  is on the bottom of well bore  24 . The left directional portion is due to the right hand rotation of drill bit  14 , and the increased side load on bit  14 , as it nears and reaches the top of well bore  24  in rotation of the drill string and drilling motor  10 .  FIGS. 8C and 8D  represent the change in the side loading of bit  14  as the bend contact point  22  reaches the bottom and top of well bore  24 . 
         [0038]      FIG. 9A-9B  represents an alternate approach to the 3-point contact method. Drilling motor  10  is fit with two bends  26  and  29  to provide an improved method for directional drilling well bore  24 .  FIG. 9A  shows drilling motor  10  with a bit  14  attached to the bottom. Drilling motor  10  has a first bend  26 , for example 1.50° as shown, with a second bend  29  and a second contact point  23  placed a short distance above first bend  26 , for example 1.00° in the opposite the direction of first bend  26 .  FIG. 9B  is an enlarged view of the lower tubular section  12 , with bends  26  and  29  and contact points  22  and  23 . At second bend  29 , there is a second contact point  23 . With the angles and lengths selected, second contact point  23  as shown is not in contact with well bore wall in straight section  34  of well bore  24 , but will contact the wall of well bore  24  when the well is curved to change direction.  FIG. 9C  represents the interference at the top of drilling motor  10  of 0.25″, with the depicted double bend configuration. Other angles and other lengths may result in more or less than this, but should be designs such that the interference is less than would otherwise be the case in a single bend design. In the depicted example, the corresponding load to “fit” the top of the drilling motor  10  into well bore  24  is 9 lbs. This interference is small compared to the 3-point method discussed earlier and, if desired, may be completely eliminated by increasing the magnitude of upper bend  29 .  FIG. 9D  represents the angle of bit  10 , with the double bend configuration and will remain at 0.39° with a side load on bit  14  of 43 lbs. 
         [0039]      FIG. 10A-10D  represents a further alternate method to reduce side loading in the 3 point contact method. In the depicted example, bend  26  is reduced to 0.61°, which results in the same interference at the top of drilling motor  10  as the double bend drilling motor in  FIG. 9A .  FIG. 11A-11D  demonstrates the ability of drilling motor  10  in  FIG. 10A  to effectively curve the well bore  24  after drilling ahead for approximately 39″ without rotating.  FIGS. 11B and 11C  show how drilling motor  10  follows curved well bore  24 , until the top of the drilling motor  10  contacts the wall  31  of well bore  24 . Continued drilling would create interference at the top of the drilling motor until contact point  22  at bend  26  is no longer in contact with well bore  24 . When this occurs, bit  14  begins to lose angle and the curves section  30  of well bore  24  begins to straighten. This is undesirable When trying to change the direction of well bore  24 .  FIG. 12A-12D  represents the drilling motor  10  in  FIG. 11A , drilling the same distance. Continued drilling with this embodiment does not produce the same result as seen in  FIG. 11A  because contact point  23  prevents drilling motor  10  from straightening. Curved section  30  in well bore  24  will continue as the same bit angle is maintained.  FIG. 13A-13D  represents an alternate method to allow drilling motor  10  in  FIG. 11A  to maintain the proper angle on the Face of bit  10  when drilling a curved section  30 . Drilling motor  10  in  FIG. 13A-13D  is fitted with a pad  28  on the opposite side of contact point  22 . Pad  28  has a slight clearance to well bore  24 , when point  22  is in contact with well bore  24 . When a curved section  30  is drilled beyond  39 , the top of drilling motor  10  will be in contact with well bore  24 , and wall  31  cannot cause the face of bit  10  to flatten due to the presence of the pad  28 . 
         [0040]      FIG. 14A -14F  represent additional ways to secure the position of bend  26 , in relation to centralized bit  14 , and minimize the side loading on the lower tubular section  12  of drilling motor  10 .  FIGS. 14A and 14B  depict a double bend configuration with 1.50° on bottom bend  26  and 1.00° on top bend  29 , in the opposite direction of the 1.50°. The net effect is a 0.50° degree bend with an upper pad  27  at contact point  23 , to prevent the drilling motor  10  from lifting the low side pad  25  at contact point  22  from the well bore wall  24 , when generating a curved section  30  in the well bore  24 .  FIGS. 14C and 14D  depict a single bend with a pad  28  on the inside bend surface, directly opposite the “low” side pad  22 , on the outside bend surface, to prevent the drilling motor,  10 , from lifting the “low” side pad from the well bore wall,  24 .  FIGS. 14E and 14F  depict an “offset” stabilizer at the bend  26 , which keeps that point in a fixed relation relative to centralized bit  14  in any orientation. All three methods ensure that bend point  26  is off the central axis of well bore  24  to “tip” the bit  14  at an angle and enable the lower tubular section  12  to generate a curved portion  30  in well bore  24  when drilling motor  10  is not rotated. The smaller bend  26  results in reduced interference at the top of the drilling motor  10  and ensures that the side loading at contact point  22  and bit  14  remain minimal. The reduced loading in turn ensures lower tubular section  12  is not significantly “flexed” to change the angle of the face of bit  14 . It should be noted that the angles used in this explanation are a result of the geometry and size of the drilling motor,  10 , and the well bore  24 . Other angles may be used by design and physical parameters, or within a range of side loads that are sufficiently low to avoid undesirable straightening of bit  14 . 
         [0041]      FIG. 15A-15D  represent the results of the loading analysis of one embodiment when positioned in a horizontal well bore  24 . The double bend motor  10  shown in  FIG. 14A  is used as a representation, and the resulting loads do not consider the stiffness or weight of the tubular members. It can be seen that the side loading at the contact points is greatly reduce in all cases as compared to the 3 point loading method discussed with respect to  FIG. 8A-8D . These reduced loads result in a straighter well bore  24  when drilling motor  10  is rotated to drill ahead.  FIGS. 16A and 16B  represent a comparison between the two methods discussed in a horizontal well, with the addition of a centralizing tool added to the top of the drilling motor  10 .  FIG. 16A  is the 3-point method used in the prior art and results in much higher side loads.  FIG. 16B  is uses a double bend design to reduce the side loading, it will be understood that design changes could reduce these loads to 0 lbs if desired. Additionally, larger bends could be chosen that increase the side loading to within an acceptable range that still maintains a suitable bit face angle. It will be also understood that one or both of bends  26  and  29  may be either adjustable or fixed angle bends. 
         [0042]    While particular angles have been discussed above, it will be understood that these angles may be set according to the requirements of the situation. In some embodiments, the bends in drilling motor  10  may be adjustable, whereas in others, the bends may be set. Furthermore, using the principles described above, the specific geometry of the bends, including the angles of the bends and the length of the housing between the bit and the first bend and between the first and second bends, may be designed to achieve a desired angle of curvature of the curved section of the wellbore when drilling motor  10  is not rotating. As the angle of bit  14  will be more predictable and consistent, it may be necessary to adjust the operating procedures, which may be designed to take into account some side-loading initially. 
         [0043]    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 elements is present, unless the context clearly requires that there be one and only one of the elements. 
         [0044]    The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.