Abstract:
A method of hydraulically activating a mechanically operated wellbore tool in a bottom hole assembly includes: holding moveable elements of the wellbore tool in an unactivated position using a shear pin; inserting one or more drop balls into a drilling fluid; and flowing the drilling fluid with the drop balls to a flow orifice located in or below the wellbore tool. The flow orifice is at least partially plugged with the drop balls to restrict fluid flow and correspondingly increases the hydraulic pressure of the drilling fluid. The hydraulic pressure is increased to a point beyond the rating of the shear pin, thereby causing the shear pin to shear and allowing the moveable elements of the tool to move to an activated position.

Description:
CLAIM OF PRIORITY 
     This application is a US National Stage of International Application No. PCT/US2014/012928, filed on Jan. 24, 2014, which claims priority to U.S. Provisional Application No. 61/756,617, filed on Jan. 25, 2013, incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This specification generally relates to systems for and methods of hydraulic activation of a mechanically operated tool positionable in a bottom hole assembly used in drilling a wellbore. 
     BACKGROUND 
     During well drilling operations, a drill string is lowered into a wellbore. In some drilling operations, (e.g. conventional vertical drilling operations) the drill string is rotated. The rotation of the drill string provides rotation to a drill bit coupled to the distal end of a bottom hole assembly (“BHA”) that is coupled to the distal end of the drill string. The bottom hole assembly may include stabilizers, reamers, measurement-while-drilling (“MWD”) tools, logging-while-drilling (“LWD”) tools and other downhole equipment as known in the art. In some drilling operations, (e.g. if the wellbore is deviated from vertical), a downhole mud motor may be disposed in the bottom hole assembly above the drill bit to rotate the bit instead of rotating the drill string to provide rotation to the drill bit. 
     In some drilling operations, in order to pass through the inside diameter of upper strings of casing already in place in the wellbore, often times the drill bit will be of such a size as to drill a smaller gage hole than may be desired for later operations in the wellbore. It may be desirable to have a larger diameter wellbore to enable running further strings of casing and allowing adequate annulus space between the outside diameter of such subsequent casing strings and the wellbore wall for a good cement sheath. A borehole opener (“reamer”) may be included in the drill string to increase the diameter of the (“open”) borehole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example bottom hole assembly featuring a near-bit reamer. 
         FIG. 2A  is a side view of the lower end of the bottom hole assembly illustrating the near-bit reamer coupled to a drill bit. 
         FIG. 2B  is a cross-sectional side view of a portion of the near-bit reamer of  FIG. 2A . 
         FIGS. 3A-3C  are cross-sectional perspective, top, and side views of a drill bit fitted with a grate actuation assembly. 
         FIGS. 4A-4C  are sequential diagrams of a technique for using deformable drop balls to activate a near-bit reamer. 
         FIG. 5  is a flowchart illustrating a method of activating a near-bit reamer that involves creating a temporary flow restriction upstream of the near-bit reamer. 
         FIG. 6  is a flowchart illustrating a method of activating a near-bit reamer that involves introducing a highly viscous pill fluid to the bottom hole assembly. 
         FIG. 7  is a cross-sectional perspective view of a first example filter actuation assembly. 
         FIGS. 7A-7B  are sequential diagrams illustrating operation of the first example filter actuation assembly. 
         FIG. 8A  is an exploded diagram illustrating a second example of a filter actuation assembly. 
         FIGS. 8B and 8C  are perspective and cross-sectional side views of the second example filter actuation assembly in an assembled form. 
         FIGS. 8D-8F  are sequential diagrams illustrating operation of the second example filter actuation assembly. 
         FIG. 9  is a cross-sectional perspective view of a third example of a filter actuation assembly. 
         FIG. 10A  is a cross-sectional side view of a lower section of a bottom hole assembly featuring an activation bushing. 
         FIG. 10B  is a cross-sectional perspective view of the activation bushing of  FIG. 10A . 
         FIGS. 10C and 10D  are sequential diagrams illustrating operation of the activation bushing of  FIGS. 10A and 10B . 
     
    
    
     Some of the features in the drawings are enlarged to better show the features, process steps, and results. 
     DETAILED DESCRIPTION 
     The present disclosure includes methods and devices for hydraulic activation of a mechanically operated bottom hole assembly tool. In some implementations a near-bit borehole opener/enlargement tool, also known as a near-bit reamer (“NBR”), is disposed on the distal end (or “lower end”) of a tool string proximal to the drill bit. For example, the present disclosure relates to devices that may be used to activate cutting blocks of a borehole opener tool by adjusting the hydraulic pressure of the drilling fluid within a bottom hole assembly. 
       FIG. 1  is a diagram of an example bottom hole assembly  10 . The bottom hole assembly  10  is the lower component of a drill string  12  suspended from a drilling rig (not shown). In some implementations, the upper end of the bottom hole assembly  10  includes a conventional under reaming tool  14  (e.g., a Halliburton model XR Reamer or UR-type conventional under reaming tool). Below the conventional under reaming tool  14  is positioned a measurement-while-drilling (“MWD”) and/or a logging-while-drilling (“LWD”) tool string section  16 . The MWD/LWD tool string section  16  is positioned below the conventional under reaming tool  14  so that the enlarged borehole will not degrade performance of the MWD/LWD tools or the associated stabilizer elements  18 . Below the MWD/LWD tool string section  16  is a rotary steerable system (“RSS”) tool string  20  (e.g., Halliburton&#39;s Geo Pilot System) designed to facilitate directional drilling. Similar to the MWD/LWD tool string section  16 , the RSS tool string  20  is located below the conventional under reaming tool  14  in order to ensure its proper functioning. The lower end of the bottom hole assembly  10  features an NBR  100  mounted just above the drill bit  22  and below the RSS tool string  20 . 
     In the foregoing description of the bottom hole assembly  10 , various items of equipment, such as pipes, valves, fasteners, fittings, articulated or flexible joints, etc., may have been omitted to simplify the description. It will be appreciated that some components described are recited as illustrative for contextual purposes and do not limit the scope of this disclosure. 
       FIG. 2A  is a side view of the lower end of the bottom hole assembly  10  illustrating the NBR  100  and the drill bit  22 . In this example, the NBR  100  and the drill bit  22  are directly adjacent on the bottom hole assembly  10 . However, other arrangements where the NBR and drill bit are separated by one or more components are also within the scope of the present disclosure. As shown, the NBR  100  includes a plurality of cutting blocks  202  to engage to wall of the surrounding wellbore. The cutting blocks  202  are positioned circumferentially about an elongated body  204  of the NBR  100 . In this example, the NBR  100  includes three cutting blocks  202  located at circumferential intervals of 120°. Of course, any suitable arrangement of cutting blocks may be used in various other embodiments and implementations without departing from the scope of the present disclosure. 
     Each of the cutting blocks  202  includes a cutter element  206  disposed on a radial piston  208  disposed inside the elongated body  204 . The cutter elements are initially in a radially-retracted position. When the NBR  100  is actuated, the cutter elements  206  are moved radially outward relative to a central longitudinal axis  212  to contact the wellbore wall. As the NBR  100  is rotated, the cutter elements  206  abrade and cut away the formation, thereby expanding the diameter of the borehole. 
       FIG. 2B  is a cross-sectional side view of the NBR  100 . As shown, each of the radial pistons  208  includes an anchor plate  216 . The radial pistons  208  are held in place by shear pins  218  such that the cutter elements  206  are in the radially-retracted position. The cutter elements  206  are deployed by hydraulic pressure. That is, when the hydraulic pressure in the body  204  reaches a predetermined threshold, the pressure force acts on the anchor plates  216  to urge the radial pistons  208  radially outward with sufficient force to break the shear pins  218 . Without the shear pins  218  to hold the radial pistons  208  in place, the radial pistons are moved by the hydraulic pressure of the drilling fluid outward toward the wall of the wellbore, deploying the cutter elements  206 . The shear strength rating of the shear pins  218  determines the hydraulic pressure required to activate the NBR  100 . In some examples, the shear pins  218  have shear strength rating of 120 bars, which corresponds to a hydraulic activation pressure for the NBR  100 . 
     The NBR  100  further includes biasing members  220  (e.g., disk or coil springs) mounted between the anchor plates  216  of the radial pistons  208  and an outer flange  222  secured to the body  204 . When the hydraulic pressure is reduced to a point where the pressure force against the anchor plates  216  is overcome by the biasing members  220  (e.g., when the flow of drilling fluid sufficiently decreases or ceases entirely), the radial pistons  208  are pulled back such that the cutter elements  206  are returned to the retracted position. 
     As described above, the NBR  100  is activated by increasing hydraulic pressure of the drilling fluid beyond a predetermined threshold determined by the shear strength rating of the shear pins  218 . For example, in some implementations, the NBR may be activated by inserting one or more drop balls into a drilling fluid flow stream; pumping the drop balls in the drilling fluid down the drill string and into the bottom hole assembly; flowing the drilling fluid and drop balls through the NBR at a first hydraulic pressure; plugging one or more flow orifices (e.g., drill bit nozzles inlets or filter holes) thereby restricting flow of the drilling fluid upstream of the restriction and increasing the hydraulic pressure in the drilling fluid in the NBR upstream of the restriction to a predefined second hydraulic pressure. The increased hydraulic pressure acting on a surface of the NBR creates a shearing force on a shear pin which shears when it reaches a predetermined sheer force and allows the NBR to be activated with the predefined second hydraulic pressure of the drilling fluid flowing through the NBR. 
       FIGS. 3A-3C  are cross-sectional perspective, top, and side views of a drill bit  22  fitted with a grate actuation assembly  300  designed to facilitate a drop-ball technique for increasing hydraulic pressure to activate the NBR  100 . In this example, the drill bit  22  is a fixed cutter directional drill bit with multiple (in this case, seven) nozzle inlets  302  for ejecting drilling fluid. However, the NBR-activation techniques discussed in the present disclosure are applicable to other suitable drill bits as well. As shown, the grate actuation assembly  300  is located in a central fluid passage  304  defined by the shank  306  of the drill bit  22 . The grate actuation assembly  300  abuts the base of the central fluid passage  304  to cover the nozzle inlets  302 . 
     The grate actuation assembly  300  includes a generally cylindrical body  308  having a sloped top surface  310  including a series of guide slots  312 . The sloped surface  310  and the guide slots  312  are designed to direct one or more drop balls (not shown) towards an opening  314  proximal to the wall of the central fluid passage  304 . As shown, the opening  314  provides access to the nozzle inlets  302  of the drill bit  22 . The guide slots  312  are formed having a width less than the diameter of the drop balls. This configuration allows the drilling fluid to pass through the guide slots  312  to reach the nozzle inlets  302 , while preventing the drop balls from passing through. A directional surface  316  leads the drop balls through the opening  314  and towards the nozzle inlets  302 . Thus, in this example, the directional surface  316  slopes in a direction opposing the sloped top surface  310 . Other suitable configurations and arrangements for leading the drop balls towards the drill bit nozzle inlets are also contemplated. 
     When the one or more drop balls encounter the nozzle inlets  302 , the nozzle inlets become plugged—preventing the ejection of drilling fluid. Thus, plugging the nozzle inlets  302  restricts the flow of the drilling fluid through the bottom hole assembly  10 . The flow restriction causes a hydraulic pressure increase in the drilling fluid up stream of the restriction. In this example, the grate actuation assembly  300  further includes a gate structure  318  partitioning the area of the central fluid passage  304  near the nozzle inlets  302 , creating a protected area  320 . The gate structure  318  prevents the drop balls from entering the protected area  320  and encountering the nozzle inlets  302  within. In summary, the grate actuation assembly  300  is designed to facilitate plugging at least some of the nozzles  302  in a first unprotected area of the bit but not the nozzle inlets  302  in the second protected area  320 . The increased hydraulic pressure acting on the assembly creates a shearing force on a shear pin which shears when it reaches a predetermined shear force and allows the NBR to be activated with the predefined second hydraulic pressure of the drilling fluid flowing through the NBR. 
     This configuration allows the hydraulic pressure within the bottom hole assembly  10  to be increased by a sufficient amount to activate the NBR  100  without entirely preventing the ejection of drilling fluid from the bit. The magnitude of hydraulic pressure increase scales with the number of nozzle inlets  302  that are plugged by drop balls. Thus, the grate actuation assembly  300  can be designed to allow access by the one or more drop balls to a specific number of nozzle inlets  302 , via positioning of the gate structure  318 , in order to achieve a specific hydraulic pressure increase. 
       FIGS. 4A-4C  are sequential diagrams of a technique for using deformable drop balls  400  to activate the NBR  100 . The deformable drop balls are formed from a flexible material (e.g., a material including rubber, foam, and/or plastic). In this example, one or more deformable drop balls  400  are pumped through the bottom hole assembly  10  toward the nozzle inlets of the drill bit  22 . The deformable drop balls  400  encounter and plug the nozzle inlets to increase the hydraulic pressure within the bottom hole assembly  10  to a level sufficient to activate the NBR  100 . As the hydraulic pressure continues to increase within the bottom hole assembly  10 , the deformable drop balls  400  are eventually forced through the nozzle openings. For example, the deformable drop balls  400  can be designed to shred under hydraulic pressure and pass through the nozzle openings in smaller pieces. As another example, the deformable drop balls  400  can be designed to deform and compress (“squeeze”) through the nozzle openings under hydraulic pressure. In summary, the deformable drop balls  400  are designed to pass through the nozzle openings of the drill bit at a drilling fluid hydraulic pressure greater than what is required to activate the NBR  100 . 
     Controlling the hydraulic pressure increase within the bottom hole assembly  10  can be achieved by altering various process parameters (e.g., the number of deformable drop balls, the size of the deformable drop balls, the material properties of the deformable drop balls, etc.). In one example, the deformable drop balls  400  are Halliburton&#39;s Foam Wiper Balls, which are made of natural rubber of open cell design. In this example, the deformable drop balls are used to plug the nozzle inlets of the drill bit, but other configurations and arrangements are also contemplated. For example, the deformable drop balls can be used to plug any orifice(s) downstream of the NBR  100 . 
     The above-described technique involving deformable drop balls is an exemplary technique for temporarily increasing hydraulic pressure in the bottom hole assembly for activation of the NBR. However, other suitable techniques for temporarily increasing the bottom-hole-assembly hydraulic pressure are also contemplated. For example,  FIG. 5  is a flowchart illustrating a method  500  that involves temporarily creating an upstream flow restriction to generate a positive hydraulic pressure pulse sufficient to activate the NBR  100 . At step  502 , a flow restriction is created upstream of the NBR  100 . The flow restriction can be created, for example, using an activation technique for operating a different downhole assembly tool. In one implementation, the conventional under reaming tool  14  is activated using a drop-ball technique that creates the temporary upstream flow restriction. In some other examples, an electronically activated valve is at least partially closed to create the temporary upstream flow restriction. At step  504 , the hydraulic pressure pulse activates the NBR  100 . At step  506 , the upstream flow restriction is relieved to reestablish the flow of drilling fluid. 
       FIG. 6  is a flowchart illustrating yet another method  600  for creating a temporary pressuring increase sufficient to activate the NBR  100 . The method  600  involves a highly viscous pill fluid. At step  602 , a general-purpose drilling fluid is pumped through the bottom hole assembly  10 . At step  604 , a high-viscosity pill fluid is pumped through the bottom hole assembly  10  in place of the general-purpose drilling fluid. Pumping the high-viscosity pill fluid creates a hydraulic pressure increase within the bottom hole assembly  10  that is sufficient to activate the NBR  100 . At step  606 , the pumping of the high-viscous pill fluid is ceased and the general-purpose drilling fluid is reestablished in the bottom hole assembly  10 , restoring the original hydraulic pressure. In some examples, the pill fluid is a high-viscosity liquid (e.g., mud gunk, such as Halliburton&#39;s Geltone), such as used for well cleaning operations. In some examples, the pill fluid is a slurry-type fluid including liquid and small solid additives (e.g., Halliburton&#39;s fine Lubra-Beads or lost circulation material). 
     In some implementations, a filter actuation assembly positioned upstream of the drill-bit nozzles and downstream of the NBR is used in conjunction with drop balls to generate a sufficient hydraulic pressure increase for activating the NBR  100 . The filter actuation assembly can include a filter head supported by one or more shear pins. The filter head includes an array of flow orifices designed with a small diameter for plugging by the drop balls. Plugging the flow orifices on the filter head creates a flow restriction that causes a hydraulic pressure increase. When then hydraulic pressure reaches a certain level (which is greater than the NBR-activation hydraulic pressure), the pressure force bearing on the filter head causes the shear pins to break. Without the supporting shear pins, the filter head moves to a new position in the bottom hole assembly and opens a new flow path for the drilling fluid to pass, which relieves the hydraulic pressure buildup. 
       FIG. 7  is a cross-sectional perspective view of a first example filter actuation assembly  700 . The filter actuation assembly  700  includes a filter head  702 , a set of axially oriented pillars  704  and a base plate  706 . The filter head  702  is mounted on one or more secondary radial shear pins (see  FIGS. 7A-7B ). As shown, the filter head  702  defines an array of axial flow passages  708  aligned with the patterned flow openings  710  of the base plate  706 . The diameter of the axial flow passages  708  is smaller than the diameter of the drop balls, so that drop balls encountering the filter head  702  effectively plug the flow passages. 
     When the filter actuation assembly is free of any drop balls, the axial flow passages  708  and flow openings  710  allow drilling fluid to pass through the filter actuation assembly  700 . With the flow passages  708  being plugged by drop balls  712 , as shown in  FIG. 7A , the flow of drilling fluid is restricted to the ancillary flow passages  714  at the radial edge of the filter head  702  and base plate  706  (see  FIG. 7 ). The hydraulic pressure buildup eventually causes the shear pin  716  to break, allowing the filter head  702  to slide downward to rest against the base plate  706 . As the filter head  702  translates toward the base plate  706 , the pillars  704  project through the axial flow passages  708  to displace the drop balls  712  (See  FIG. 7B ). 
       FIG. 8A  is an exploded diagram illustrating a second example filter actuation assembly  800 .  FIGS. 8B and 8C  are perspective and cross-sectional side views of the filter actuation assembly  800  in an assembled form. As shown, the filter actuation assembly  800  includes a disc-shaped filter head  802  defining an array of axial flow passages  804 . The filter head  802  is supported in a hollow cylindrical rack  806 . The rack  806  includes an annular seat  808  for receiving the filter head  802 , three axially extending legs  810  that support the seat, and an annular base  812 . 
     A cylindrical sleeve  814  fits concentrically around the rack  806 . The sleeve  814  includes an inner sheath  816  and an outer sheath  818 . The inner sheath  816  defines an annular lip  820  that seals against the filter head  802  to prevent drilling fluid from leaking between the two filter-assembly components. The cylindrical side wall of the inner sheath  816  defines a plurality of axial slots  822 . As shown in  FIGS. 8B and 8C , the sleeve  814  is held in place against the rack  806  by secondary shear pins  824  traversing radial openings  826  in the legs  810  of the rack and radial openings  828  in the outer sheath  818 . 
       FIGS. 8D-8F  are sequential diagrams illustrating operation of the filter actuation assembly  800 . As shown in  FIG. 8D , when the flow passages  804  (see  FIGS. 8A to 8C ) of the filter head  802  are clear of any drop balls, drilling fluid flows downstream unimpeded through the filter head and the rack  806 . In  FIG. 8E , when the drop balls  830  encounter the filter head  802 , the flow passages  804  (see  FIGS. 8A to 8C ) become plugged, restricting the flow of drilling fluid through the bottom hole assembly  10  to build sufficient hydraulic pressure for activation of the NBR  100 . As the hydraulic pressure continues to build, the pressure acting on the filter head  802  and rack  806  create as force until the shear pins  824  are severed upon reaching a predetermined shear force. In  FIG. 8F , when the shear pins  824  break, the filter head  802  and rack  806  slide downward relative to the stationary sleeve  814 . When the filter head  802  and rack  806  are in the lowered position, the axial slots  822  in the side wall of the inner sheath  816  are exposed, which provides a new flow path for the drilling fluid to pass through the bottom hole assembly  10 . 
       FIG. 9  is a cross-sectional perspective view of a third example filter actuation assembly  900 . In this example, the filter actuation assembly  900  includes a support member  902  mounted to the an interior wall of the bottom hole assembly  10 , a filter head  904  coupled to the support member, and an axial flow orifice  906 . The filter head  904  includes an array of radial flow openings  908  distributed along a frustoconical sidewall  910 . Before introduction of the drop balls, drilling fluid flows freely through the filter head  904 , passing through the radial flow openings  908  and the axial flow orifice  906 . When the drop balls encounter and plug the radial flow openings  908 , flow through the filter head  904  is severely inhibited, if not entirely prevented. Thus, the drilling fluid flow is restricted to an ancillary flow path formed by a gap  912  between the filter head  904  and the support member  902 . The restriction of fluid flow achieved by plugging the filter head  904  creates a hydraulic pressure increase sufficient to activate the NBR  100 . 
       FIG. 10A  is a cross-sectional side view of a lower section of the bottom hole assembly  10  featuring an activation bushing  1000 .  FIG. 10B  is a cross-sectional perspective view of the activation bushing  1000 . In this example, the activation bushing is installed at the interface between the shank  1002  of the drill bit  22  and the central bore of the NBR  100 . However, it is appreciated that the activation busing  1000  could be located at any position within the bottom hole assembly  10  downstream of the NBR  100 . The activation bushing  1000  includes a flanged cylindrical base  1004  mounted and sealed against the wall of the central fluid passage  1006  in the drill bit  22 . A slotted inlet structure  1008  aligns with a main flow passage  1010  extending through the base  1004  of the activation bushing  1000 . Multiple ancillary flow passages  1012  are spaced circumferentially around the cylindrical base  1004 . As shown, the slotted inlet structure  1008  is provided with a sloped, conical tip that prevents drop balls from plugging the main flow passage  1010 . The ancillary flow passages  1012  on the other hand are oriented axially and designed to be plugged by the drop balls. 
       FIGS. 10C and 10D  are sequential diagrams illustrating operation of the activation bushing  1000 . As shown in  FIG. 10C , when the ancillary flow passages  1012  are clear of any drop balls, drilling fluid flows unimpeded through the ancillary flow passages and the main flow passage  1010 . In  FIG. 10D , when the ancillary flow passages  1012  have been plugged by the drop balls  1014 , the flow of drilling fluid is confined to the main flow passage  1010 . The reduction in flow area achieved by plugging at least some of the ancillary flow passages  1012  creates a hydraulic pressure increase in the drilling fluid sufficient to activate the NBR  100 . 
     The use of terminology such as “above,” and “below” throughout the specification and claims is for describing the relative positions of various components of the system and other elements described herein. Similarly, the use of any horizontal or vertical terms to describe elements is for describing relative orientations of the various components of the system and other elements described herein. Unless otherwise stated explicitly, the use of such terminology does not imply a particular position or orientation of the system or any other components relative to the direction of the Earth gravitational force, or the Earth ground surface, or other particular position or orientation that the system other elements may be placed in during operation, manufacturing, and transportation. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.