Abstract:
A low friction stabilizer having a body and a plurality of small contact pads configured to function with the effectiveness of a single, larger contact pad is described. The assemblage and configuration of the small contact pads enable the performance of stabilization while reducing rotational drag and while allowing high annular flow around the stabilizer.

Description:
FIELD 
       [0001]    Embodiments usable within the scope of the present disclosure relate, generally, to drill string stabilizers configured within drill strings and used in earth boring operations, and in particular designs of stabilizers which reduce rotational drag and improve drilling fluid flow during operation. 
       BACKGROUND OF THE INVENTION 
       [0002]    Drill string stabilizers are well-known in the field of oil and gas well drilling as a means to avoid unintentional destabilizing forces known to occur in drilling operations. Stabilizers are commonly used to reduce vibrations, sidetracking and other unwanted effects of drilling through geologic formations. The use of stabilizers, in addition, can aid in maintaining the orientation of the drill bit as well as the drill string during operation, reducing the possibility of drift. 
         [0003]    Stabilizers operate by making physical contact with the interior wall of the borehole. Typically, stabilizers are constructed with one or more ribs, ridges, blades, or gage pads which protrude from the main body of the tool. These protuberances are placed in physical contact with the borehole wall, thereby providing stability. Contact, however, is made at the cost of rotational drag forces created between the protuberances and the borehole wall. Being placed in direct contact with the walls of the borehole, stabilizer protuberances must be constructed of durable materials. When used to stabilize the drill string within the borehole, protuberances are typically constructed from or with wear resistant materials. Rotational drag forces created by the contact of the protuberances with the borehole wall can lead to damage or fouling of the stabilizer. Further, vibration caused by these rotational drag forces can lead to breakage of some other parts of the drill string. 
         [0004]    Stabilizers can be designed to hold the drill string in a fixed orientation or can be designed to allow orientational changes, such as are necessary in directional drilling. Variation of the length of the protuberances along the main body of the tool allows the drill string either to be held in a fixed position relative to direction, such as when longer protuberances are used, or to allow flexing of the drill string to allow orientation or reorientation of the drill string during directional drilling, such as when shorter protuberances are used. 
         [0005]    Moreover, stabilizers must be constructed so as not to obstruct the flow of drilling fluid, which is pumped into the borehole in part to cause the removal of pieces of rock cut away from the geologic formation by the drill bit, thereby cleaning the borehole. An interstitial area is commonly placed between the protuberances, through which the drilling fluid is circulated, carrying rock cuttings and other debris with the drilling fluid. Such an interstitial area between two protuberances known in the art would be generally of the same shape as the protuberances. That is, if the protuberances are straight, the interstitial area will be straight lithe protuberances are curviform, the interstitial area between them will be curviform. 
         [0006]    While stabilizers must, therefore, be designed to withstand the harsh conditions of the borehole during drilling operations, they must also be designed not to impede the flow of drilling fluid, which is equally necessary for effective drilling operations. Current stabilizer designs are typically seen either to contain large, straight protuberances, which allow the stabilizer to stand up against frictional forces, or stylized or curviform designs which reduce frictional forces but impede the flow of drilling fluid. 
         [0007]    Specifically, current stabilizer designs are generally seen to contain large, straight protuberances designed for soft formations and maximum fluid flow or bypass area or they contain spiral-shaped or helical protuberances with larger contact surfaces to retain outer diameter and maximize centralization. 
         [0008]    In typical stabilizer design, longer and wider protuberances, whether straight or curviform, improve stability but impede the passage of drilling fluid. Longer protuberances likewise typically reduce flexing of the drill string, while shorter protuberances allow more flexing. Protuberance length is determined by the need for directional drilling capabilities of the drill string. Longer and/or wider protuberances also increase rotational drag forces. Longer and wider protuberances, in reducing or impeding drilling fluid flow, can lead to cleaning issues or cause cuttings to foul or aggregate and pack off the fluid passage below the projections. At the same time, the constricted space between protuberances causes increased fluid speed between the protuberances, which may fluffier lead to erosion or abrasion of the protuberances caused by the impact of rock cuttings or other debris against the sides of the protuberances. Exemplary designs of stabilizers are found in U.S. Pat. No. 3,642,079, U.S. Pat. No. 5,330,016, and Chinese patent publication 201,635,674. These examples reflects designs in which stabilizer protuberances are curviform (the &#39;079 patent), straight (&#39;016) or a combination of straight and curviform design elements (the &#39;674 patent). 
         [0009]    There is a need for a stabilizer design which effectively moderates these requirements of sturdy design for longevity, a reduced frictional contact surface between the projections and the wall of the borehole, flexibility as to directional containment or directional reorientation, and protuberance design which does not impede or reduce the flow of drilling fluid circulating in the borehole. 
         [0010]    The present invention incorporates design elements improving the performance characteristics of the stabilizer as to each of the above needs. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention optimizes stabilizer protuberances in the form of contact pad design to reduce friction, increase fluid flow between such stabilizer contact pads and allow variable flexure without compromising stabilizer strength. The stabilizer contact pads of this invention are based in part on curviform stabilizer pad design while allowing linear flow for drilling fluid axially along the body of the stabilizer. Instead of a single, elongate and curved stabilizer pad, the present invention uses a plurality of smaller contact pads assembled in the approximate shape of a single, curviform stabilizer pads but in which the assemblage of a plurality of contact pads results in a stabilizer pad with reduced surface area and improved flow characteristics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the detailed description of various embodiments of the present invention presented below, reference is made to the accompanying drawings, in which: 
           [0013]      FIG. 1  depicts a perspective view of an exemplary stabilizer known in the art. 
           [0014]      FIG. 2A  depicts a cross-sectional view of the exemplary stabilizer known in the art. 
           [0015]      FIG. 2B  depicts a side view of the exemplary stabilizer known in the art. 
           [0016]      FIG. 3  depicts a perspective view of an embodiment of the high annular area, low friction stabilizer design usable within the scope of the present disclosure. 
           [0017]      FIG. 4  depicts a perspective view of an alternative embodiment of a high annular area, low friction stabilizer design usable within the scope of the present disclosure. 
           [0018]      FIG. 5  depicts a perspective view of an additional alternative embodiment of a high annular area, low friction stabilizer design usable within the scope of the present disclosure. 
           [0019]      FIGS. 6A and 6B  depict a cross-sectional view and a side view of the embodiment of the high annular area, low friction stabilizer as shown on  FIG. 4 . 
           [0020]      FIGS. 7A and 7B  depict a cross-sectional view and a side view of the embodiment of the high annular area, low friction stabilizer as shown on in  FIG. 3 . 
           [0021]      FIG. 8A  depicts a flow pattern of the known stabilizer depicted in  FIG. 1 . 
           [0022]      FIG. 8B  depicts a flow pattern of the alternative embodiment of the high annular area, low friction stabilizer design depicted in  FIG. 4 . 
           [0023]      FIG. 8C  depicts a flow pattern of the preferred embodiment of the high annular area, low friction stabilizer design depicted in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    Before explaining selected embodiments of the present inventions in detail, it is to be understood that the present invention is not limited to the particular embodiments described herein and that the present invention can be practiced or carried out in various ways. 
         [0025]      FIG. 1  depicts a perspective view of a stabilizer known in the art. A hollow or semi-hollow body  14  contains a proximal end  12   a  and a distal end  12   b . Each of these ends  12   a  and  12   b  provide means for connecting the body  14  to another drill string element, not depicted. Connection means are not substantive to the present invention and are not described in detail here. The majority of the body  14  comprises an elongate tubular structure  13 , the diameter of which is fixed, in general, except where protuberances in the form of stabilizer contact pads are placed. The body  14  comprises three substantially identical contact pads  10 , each of which contact pads are curviform in shape and are positioned substantially axially between the proximal end  12   b  and the distal end  12   a . The length of each contact pad  10  is less than the length of the body  14 , with the length of a particular contact pad  10  depending upon the specific application of the stabilizer. Longer contact pads  10  are used in drilling operations in which less flexure is required. Shorter contact pad  10  length is used in drilling operations in which more flexure is required, such as in directional drilling operations. Between each contact pad  10  is a junk slot  11  through which drilling fluid containing rock cuttings and other materials flow during drilling operations. 
         [0026]      FIGS. 2A and 2B  depict cross-sections of the contact pads  10  and junk slots  11  as shown in  FIG. 1 . Of significance in these figures is the curviform nature of each of the contact pads  10  as well as junk slots  11 . The curviform nature of each of these results in there being no straight path in any junk slot  11  from the proximal end to the distal end of body  14 . 
         [0027]      FIG. 3  depicts a perspective view of a preferred embodiment of the present invention. This preferred embodiment comprises a body  34 , containing a proximal end  32   a  and a distal end  32   b , each of which having connecting means to other or additional drill string components not described here. A plurality of interrupted contact pads  30  are placed on the body  34 . Junk slots  31  are co-located with the contact pads  30 , being formed naturally by the placement of any contact pad  30  in close proximity of any other contact pad  30 . In this preferred embodiment, one contact pad  30  may be paired with a closely positioned second contact pad  30 , although this is not necessarily so in other embodiments of the invention. The placement of the contact pads  30  is such that a series of the contact pads  30  are laid out so as to approximate the curviform contact pad of  FIG. 1 . To each of the contact pads  30  have been affixed one or more diamond wear elements  33 . 
         [0028]      FIG. 4  depicts a perspective view of an alternative embodiment of the present invention. Body  43  provides proximal end  42   a  and distal end  42   b  thereof in  FIG. 4 , a plurality of contact pads  40  and junk slots  41  are laid out in a curviform pattern similar to that as shown in  FIG. 3 . In  FIG. 4 , however, each contact pad  40  is larger than each contact pad  30  on  FIG. 3 , resulting in fewer contact pads on the body  43 . To each of the contact pad  40  have been affixed one or more diamond wear elements  44 . In this embodiment, the contact pads  40  are not associated pairwise as in  FIG. 3 . 
         [0029]      FIG. 5  depicts a perspective view of an additional alternative embodiment of the present invention. Body  54  provides proximal end  52   a  and distal end  52   b . In  FIG. 5 , the size, shape and orientation of the contact pads  50  and junk slots  51  are identical to the corresponding features shown on  FIG. 4 .  FIG. 5  reflects the construction of the invention per  FIG. 4  without diamond wear elements  44 . Similarly, the preferred embodiment of  FIG. 3  may be constructed without diamond wear elements  33 . 
         [0030]      FIG. 6A  depicts a cross-section of the embodiment as shown on  FIG. 4 . Contact pads  40  and junk slots  41  are shown.  FIG. 7A  depicts a cross-section of the preferred embodiment as shown on  FIG. 3 , similarly depicting contact pads  30  and junk slots  31 . 
         [0031]      FIG. 6B  depicts a side-view of the embodiment as shown on  FIG. 4  showing the layout of the contact pads  40  and junk slots  41 . The substantially curviform layout of the plurality of the contact pads  40  is shown.  FIG. 7B  depicts a similar side-view of the preferred embodiment as shown on  FIG. 3 . 
         [0032]      FIG. 8A  depicts a side-view as shown on  FIG. 21B  highlighting the flow path F 1  of drilling fluid through a junk slot  11   FIG. 8B  depicts a side-view as shown on  FIG. 6B  highlighting the flow path F 2  of the drilling fluid through the junk slots  41 . A similar depiction of the flow path F 3  of drilling fluid through the junk slots  31  on  FIG. 7B  is depicted in  FIG. 8C . 
         [0033]    The shortcomings of the exemplary stabilizer design depicted in  FIG. 1  are evident in that figure. In order to provide stability and/or reduce flexibility, the contact pads  10  must be of a certain length. The curviform shape of the contact pads  10  aid in reducing rotational drag when the upper surfaces of the contact pads are placed against the wall of the borehole during drilling operations. The contact site  15  of the contact pad which is in contact with the wall of the borehole is shown in  FIG. 2A . Rotational drag relates directly to the total surface combined surface area of the three contact pads  10 . In the known stabilizer, the total area of the three contact pads in contact with the wall of the borehole is approximately 77 square inches. The total volume of the junk slots  11  in the known stabilizer is approximately 53 cubic inches. 
         [0034]    As shown on  FIGS. 3 ,  7 A,  7 B and  8 C, the design of the preferred embodiment significantly changes that. The present invention uses a plurality of small contact pads  30  manufactured or affixed on the body  34  and set, thereon in approximately curviform form using a series of substantially pair-wise contact pads  30  such that stability or flexure can be achieved depending on the overall length and number of the contact pads. However, the plurality of contact pads  30  allows a, total area in contact with the wall of the borehole to be substantially less than required in the exemplary embodiment of  FIGS. 1 ,  2 A,  2 B and  8 A. In the preferred embodiment of  FIG. 3 , for example, the total area of the contact pads  30  in contact with the wall of the borehole is approximately 46 square inches, while maintaining the same contact length. Similarly, the volume of the junk slots  31  is increased proportionally to the decreased surface area of the contact pads  30 . In the preferred embodiment shown on  FIG. 3 , the volume of the junk slots  31  is approximately 77 cubic inches. Specific sizes, shapes, and configurations of assembled features may be modified so as to increase or decrease the total area of the contact pads  30  or the volume of the junk slots  31  as indicated by a particular drilling operation. Likewise, the shape or flow pattern through the junk slots  31  may be modified by the specific placement of the assembled features. 
         [0035]    Robustness of the stabilizer depicted in  FIG. 3  is maintained by the use of superhard materials for the stabilizer in general and the contact pads  30  in particular. 
         [0036]    The layout of the plurality of contact pads  30  on  FIG. 3  is approximately uniform and substantially similar to the curviform design of the known stabilizer shown on  FIG. 1 . A critical advantage of the present invention is the ability to create and maintain substantially straight flow patterns of drilling fluid between and around the contact pads  30  during drilling operations. As depicted in  FIG. 8B  and  FIG. 8C , embodiments of the invention include contact pads design such that junk slots  41  and  31 , respectively, and flow paths F 3  and F 2 , respectively, run unimpeded from end to end of the body  44  and  34  of each embodiment. Unimpeded flow substantially improves operation in multiple ways. First, unimpeded flow improves the ability of the drilling, fluid to remove rock cuttings by avoiding contact between rock cutting and the sides of contact pads. In curviform contact pads, such as depicted in  FIG. 8A , rock cuttings must change direction as the flow path F 1  changes direction, increasing the chance for contact with the side of a contact pad. 
         [0037]    Further, in each of the embodiments illustrated on  FIGS. 3 ,  4  and  5 , increased junk slot volume over the prior art stabilizer of  FIG. 1  allows an increase of overall flow of drilling fluid In the known stabilizer of  FIG. 1 , the small volume of junk slots  11  reduces flow overall, which may result in rock cuttings and other debris falling out of suspension and not being removed from the borehole. By contrast, the increased volume of junk slots  31 ,  41  and  51  in the present invention depicted in  FIGS. 3 ,  4  and  5  reduces the chance that rock cuttings or other debris may foul or obstruct the fluid passages in the respective junk slot areas. These larger junk slots likewise reduce the tendency of the drilling fluid flow to create areas of turbulent flow, which can increase energy consumption needed to cause the drilling fluid to flow. 
         [0038]    The configuration of contact pads and junk slots illustrated on  FIGS. 3 ,  4  and  5  reflect similar improvements in operation during tripping. It is well known in the field that known stabilizer contact pads drag against the low side of the wall of the borehole when the drill string is removed from the borehole. This drag may result in fouling of the stabilizers caused by balling or packing off the contact pads by the accumulation of particles on such contact pads when pulled through the borehole. In the present invention, as illustrated on  FIGS. 3 ,  4  and  5 , when the stabilizer is tripped out of the well, the drill string is not in rotation. As such, the contact pads  30 ,  40  and  50 , respectively, are aligned vertically, with corresponding channels free of protuberances similarly aligned. This allows cuttings to move unobstructed past the protuberances without any change in trajectory required for spiral pads of traditional configuration. In the event debris starts to accumulate against the side of any of the contact pads  30 ,  40  and  50 , respectively, such debris is removed by the drilling fluid as the stabilizer is pulled through the drilling fluid, thereby reducing the chance for balling or packing off. 
         [0039]    The configuration as to contact pads  30 ,  40  and  50 , and junk slots  31 ,  41 , and  51  on  FIGS. 3 ,  4  and  5  is also advantageous in horizontal and extended reach wells where beds of cuttings exist in the annulus during drilling. The positioning of the contact pads  30 ,  40  or  50  is such that they form an interrupted screw shape. Thus when the stabilizer is lying on the low side of a wellbore and rotated, the contact pads effectively push the cuttings towards surface and above each stabilizer. The straight flow channels existing between the contact pads (see  FIGS. 8B and 8C ) contribute a hydraulic force that is longitudinally oriented, which assists the screw-type arrangement of the contact pads in forcing bedded cuttings upwards. This helps to reduce or spread out the beds of cuttings in these wells, where rotating torque is a large limitation to drilling depth, by pushing them towards the surface as each stabilizer is rotated. 
         [0040]    While various embodiments of the present inventions have been described with emphasis, it should be understood that within the scope of the appended claims, the present invention might be practiced other than as specifically described herein.