DIRECTIONAL CORE DRILLING SYSTEM

A directional core drilling includes an outer barrel assembly with a guide sleeve that defines a tilt angle for orientating a drill bit within a hole and a drive barrel rotationally supported within the outer barrel assembly. An inner drive assembly is receivable within the outer barrel assembly and includes a torque latch assembly and an anti-rotation bearing assembly. The torque latch assembly includes latch arms configured to releasably couple a rotational drive input to the drive barrel. A core barrel is coupled to the anti-rotation bearing assembly and is rotationally fixed relative to the drive barrel.

TECHNICAL FIELD

The present disclosure relates to a directional drilling system for obtaining core samples.

BACKGROUND

Directional drilling is a process of steering a drill bit through the earth in various directions and angles relative to an entrance hole. Directional drilling is performed utilizing a directional drilling system that includes an outer barrel on which an axial force is applied, an inner assembly that includes a motor for generating rotation of a bit. The motor is located downhole and is powered by pressurized flow communicated through the outer pipe. In some applications an inner barrel assembly is included for capturing a core sample, the inner barrel assembly is disposed at an end of the drilling system and remains rotationally fixed relative to the rotating drill bit. The inner barrel is then retrieved once a core of a desired length is obtained. The directional bit may be steered to direct the drilling and obtaining of samples from specific locations.

The background description provided herein is for the purpose of generally presenting a context of this disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

A directional core drilling assembly according to an example disclosed embodiment includes, among other possible things, an outer barrel assembly including a guide sleeve that defines a tilt angle of a drill bit within a hole and a drive barrel rotationally supported within the outer barrel assembly. The drill bit is attached to a downhole end of the drive barrel and an inner drive assembly is receivable within the outer barrel assembly. The inner drive assembly includes a torque latch assembly and an anti-rotation bearing assembly. The torque latch assembly includes latch arms configured to releasably couple a rotational drive input to the drive barrel. A core barrel is coupled to the anti-rotation bearing assembly and movable into a position within the drive barrel such that the core barrel is rotationally fixed relative to the drive barrel.

DETAILED DESCRIPTION

Referring toFIG.1an example system for obtaining core samples is schematically shown and indicated at20. The system20includes a directional core drilling (DCD) assembly22that is disposed at the end of drill string24supported by a drilling rig28on the surface. The drill string24includes a plurality of drill pipes26coupled together to extend the DCD assembly22into a borehole25. The DCD assembly22includes features for steering the drill string24and to bore and retrieve a core sample.

Referring toFIG.2with continued reference toFIG.1, the DCD assembly22includes a drill bit30that cuts into the earth, stone, and rock to form the borehole25. A bit adaptor36C of a drive barrel assembly36rotating within a non-rotating outer barrel assembly34drives rotation of the drill bit30. A core barrel38is disposed within the drive barrel assembly36and does not rotate. A core sample32is received and held within the core barrel38as the drill bit30advances into the earth. Once the drill bit30has advanced a sufficient distance downhole to obtain a core sample of a desired length, the core32is pulled to the surface through the drill string24. The outer barrel34includes steering pads40that orientate the DCD assembly22within the borehole25to guide the formation of the borehole25.

Referring toFIGS.3and4with continued reference toFIGS.1and2, the disclosed DCD assembly22provides for an increased core diameter as compared to previous core drilling systems. The drill bit30includes an outer drill bit diameter226that defines a diameter of the borehole25generated during operation. An inner diameter64of the drill bit30corresponds to a diameter of a core sample captured during operation. An inner diameter228of the core barrel38is indicative of the capacity of the DCD assembly22to obtain larger diameter core samples relative to the hole's diameter generated by the drill bit30.

The features and configuration of the DCD assembly22as will be disclosed and described by way of example provide for the increased size of a core sample. The increase in size of the core sample is reflected in a relationship between the inner diameter64and the overall outer drill bit diameter226. In one example disclosed embodiment, the inner diameter64is between 58% and 70% as large as the drill bit diameter226. In another disclosed example embodiment, the inner diameter64is between 60% and 68% as large as the drill bit diameter226. In another disclosed example embodiment, the inner diameter64is about 62% of the drill bit diameter226. In still another example embodiment, the inner diameter64is about 64% of the drill bit diameter226. In another example embodiment, the inner diameter64is about 67% of the drill bit diameter226.

Referring toFIGS.5,6and7with continued reference toFIGS.1and2, the DCD assembly22is shown in sectional views to show separate assemblies that provide for the rotation of the drill bit30, steering of the DCD assembly22and capture of the core sample32. The DCD assembly22includes an outer barrel assembly34and an inner drive assembly50. The inner drive assembly50is inserted through the drill string24to the outer barrel assembly34. The outer barrel assembly34remains downhole and coupled to the drill string24. A drive barrel assembly36is supported within the outer barrel assembly34and is coupled to the drill bit30. The drive barrel assembly36includes a torque coupling36A, a drive barrel36B and a bit adaptor36C. The torque coupling36A is coupled to a downhole motor assembly commonly referred to as a mud motor46through a thrust bearing assembly44and a drive coupling assembly42.

A latch assembly48secures the inner drive assembly50within the outer barrel assembly34in a desired position that aligns drive features of the drive coupling assembly42. The latch assembly48engages an inner circumferential groove208of the outer barrel assembly34to transfer axial forces. The latch assembly48further provides for retrieval of the inner drive assembly50and a core sample.

The inner drive assembly50further includes the core barrel38that is disposed within the drive barrel assembly36. The core barrel38is isolated from rotation of the drive barrel assembly36by a double-acting anti-rotation thrust bearing assembly60(FIG.7).

Referring toFIG.8with continued reference toFIGS.5,6and7, the downhole end of the DCD assembly22is shown in a sectional view to illustrate the relative orientation of the outer barrel assembly34, the bit adaptor36C of the drive barrel assembly36and the core barrel38. The core barrel38and the outer barrel assembly34do not rotate. The latch assembly48provides for application of an axial force to the outer barrel assembly34through the drill string24in a known matter. The core barrel38is coupled to the inner drive assembly50in a manner that isolates it from rotation. The drive barrel assembly36rotates between the core barrel38and the outer barrel assembly34. The drill bit30is coupled to the bit adaptor36C through a threaded connection33. It should be appreciated that the illustrated drill bit30is disclosed by way of example and that other drill bit configurations may be utilized and are within the contemplation and scope of this disclosure.

A centralizing bearing62is disposed between the rotating bit adaptor36C of the drive barrel assembly36and a core lifter case66that is secured to an end of the core barrel38. The centralizing bearing62isolates the core barrel38from the rotation of the drive barrel assembly36. The centralizing bearing62is formed from a self-lubricating material to provide for a desired low friction surface to reduce and/or substantially eliminate transmission or rotational forces into the core barrel38.

The core lifter66comprises a plurality of back angled grooves. The back angled grooves provide low resistance to a core sample entering the inner area of the core barrel38as the drill bit30advances through the earth. However, the grooves will dig into the core sample and generate substantial forces to resist a core sample being pulled back out the end of the DCD assembly22.

The drill bit30includes the inner diameter64that provides for the size and diameter of a desired core sample. The inner diameter64corresponds with the inner diameter228(FIGS.3and4) of the core barrel38and the core lifter66. The inner diameter64may be of a smaller diameter than the inner diameter228the core barrel38, but not larger, to provide the core sample with defined path into the core barrel38. However, the inner diameter64may not be so small as to prevent a core sample from being captured and held within the core barrel38by the grooves of the core lifter66.

Referring toFIG.9, with continued reference toFIG.8, a radial bearing68is coupled to the end of the outer barrel assembly34and secures a group of steering pads40in place.FIG.9shows one of a lower set of steering pads40. A second, upper set of steering pads40are secured to the outer barrel assembly34at a defined axial distance. The steering pads40engages with inner surfaces of the borehole25to define an orientation of the DCD assembly22that is offset from an axial center of the borehole25. An offset between the upper and lower sets of steering pads40provides for generation of the borehole25at a desired angle that is different than straight. The desired offset is obtained by the number, size, and relative locations of the steering pads40along the outer surface of the outer barrel assembly34.

The pads40are held in place within slots45formed on the outer surface of the outer barrel assembly34and by the radial bearing68. A chamfer75is provided at the top and bottom of each steering pad40to aid movement through the borehole25. The radial bearing68is coupled to the outer barrel assembly34through a threaded connection67. In this disclosed embodiment, the threaded connection67includes threads that secure the radial bearing68with threads configured for securement in a direction opposite the rotational direction of the drill bit30.

Referring toFIGS.10,11, with continued reference toFIG.9, the angle that the DCD assembly22forms the borehole25is determined by the configuration of the steering pads40. The configuration of the steering pads40include a size of each steering pad40. Each steering pad40include a thickness78, an axial height76and a width80. Each of the thickness78, height76and width80may be modified to generate the desired angle and thereby the direction of the borehole25.

The pads40are held within the corresponding slots45by sides70,72that each have a back angle74. The back angle74is provided to hold the pads40in the slots45, in combination with the threaded-on radial bearing68shown inFIG.9.

The example pad40is shown by way of example and other sets of pads are located at different axial and radial locations. Moreover, pads40disposed at other locations, are secured within slots configured similar to those slots45shown inFIG.9. The pads40would be secured at a top or bottom location at another joint and radially within back angled surfaces on sides of a corresponding slot.

Referring toFIGS.12and13with continued reference toFIGS.9-11, the number of steering pads40may also be utilized to provide the desired angle and thereby direction of the DCD assembly22. In one disclosed example, two groups of steering pads40A and40B are disclosed with each group including three steering pads40. The two groups of steering pads40A and40B are spaced a circumferential distance82apart (FIG.12) and an axial distance84part (FIG.13). The distances82and84combine to provide a desired orientation of the DCD assembly22within the borehole25. In this disclosed embodiment the two groups of steering pads40A and40B are spaced 180 degrees apart. The turning radius provided by the DCD assembly22is provided by the pad height and the orientation of the turn relates to the position in which the non-rotating outer barrel assembly is held stationary within the borehole25by the drilling rig28at the surface.

Referring toFIGS.14and15with continued reference toFIGS.9-13, the groups of pads40A,40B contact the side of the borehole25at each location to generate an offset with respect to an axial center of the borehole25.FIG.14shows a general central axis84of the DCD assembly22and an offset90relative a center axis88of the borehole25.FIG.15shows an angle96of central axis84relative to the center axis88of the borehole25. The angle96and offset90are exaggerated to illustrate the difference in orientation relative to the borehole25. The offset90and angle96combine, in one disclosed embodiment, to provide a bend or bit tilt angle of less than 1° from the borehole central axis88. In another disclosed embodiment, the steering pads40A,40B provide a bend in the hole of between ⅛° and ¼° from the borehole central axis88. It should be appreciated that although example bend angles are disclosed by way of example, other angles are within the scope and contemplation of this disclosure.

Moreover, the orientation of the DCD assembly22to bend the borehole25can be modified by rotating the DCD assembly22about its axis to place the steering pads40A,40B at different positions. In this way, the DCD assembly22can be steered as desired to obtain core samples of certain portions of the earth.

Referring toFIGS.16and17, the example drive coupling assembly42is shown and includes a check ball assembly135, the anti-rotation thrust bearing assembly60and a torque latch assembly125. The torque latch assembly125transmits rotational power from the mud motor46to the torque coupling36A of the drive barrel assembly36. The anti-rotation thrust bearing assembly60isolates the core barrel38from the torque transmitted by the torque latch assembly125. The check ball assembly135controls flow of fluid during insertion and retraction of the DCD assembly22.

Referring toFIG.18, with continued reference toFIGS.16and17, the check ball assembly135is also included to control fluid flow during insertion and withdrawal of the DCD assembly22. The check ball assembly135includes a check ball134biased against a ball seat138by biasing spring136. The ball seat138is held within a housing128by a retaining ring168. A seal is provided about the ball seat138to seal against inner walls of the housing128.

During decent into the drill string24, the check ball134is pushed off the ball seat138by the fluid flow entering the downstream end of the inner drive assembly50. The fluid force overcomes the biasing force of the spring136. Fluid thereby flows around the ball and out the housing128through flow openings140. A plurality of flow openings140are provided such that fluid flows freely in a manner that does not slow the decent of the inner drive assembly50through the drill string24.

Upon withdrawal of the inner drive assembly50, with a core sample disposed within the core barrel38, downstream of the check ball134, the check ball134is closed and any fluid flow acts to maintain the check ball against the ball seat138. The check ball138thereby prevents fluid flow from acting on a core sample as the DCD assembly22is pulled to the surface. By preventing fluid flow from impacting a core sample, the core sample is not damaged, nor contaminated. Moreover, the closed check ball134prevents the application of any fluid forces on the core sample that may act to dislodge the core sample from the DCD assembly22.

Referring toFIG.19with continued reference toFIGS.16and17, the anti-rotation thrust bearing assembly60is disposed above the check ball assembly135and isolates the core barrel38from anti-rotation shaft116of the torque latch assembly125. The anti-rotation thrust bearing assembly60includes a bearing assembly94. The bearing assembly94includes a first group of ball bearings102and a second group of ball bearings100separated by a center washer115and disposed between an upper washer106and a lower washer104. A lower spherical seat108is seated on a lower spring retainer112. An upper spherical seat110is seated against an upper spring retainer114. The upper and lower spherical seats110,108share a coincident center of curvature which provides for the tilt of the anti-rotation shaft116with respect to housing128. In other words, the upper and lower spherical seats110,108combine to create a ball-joint-like operation and behavior.

A retaining nut130secures the center washer115to an end of the anti-rotation shaft116through a bushing117. A lower bias spring96is disposed between a portion of the housing128and the lower spring retainer112. An upper bias spring98is set between a nut118that is threaded into the housing128. Each of the upper bias spring98and the lower bias spring96are disposed within a corresponding one of the spring sleeves132A and132B. The spring sleeves132A-B maintain spring alignment on the corresponding spring retainers112, and114. The spring sleeves132A-B also limit the maximum amount of compression of their corresponding springs, which controls the maximum axial displacement between anti-rotation shaft116and housing128in either direction. A nut118includes a central opening that is larger than the anti-rotation shaft116to provide an annular clearance119. The annular clearance119provides for some side-to-side movement of the anti-rotation shaft116relative to the housing128.

The upper spring98and the lower spring96provide a biasing force against the bearing assembly94to maintain rolling contact of the ball bearings100,102against the corresponding upper and lower washers106,104and the center washer115. The force provided by the biasing springs96,98on the bearing assembly94assures that the ball bearings100,102roll along the bearing surfaces rather than skid or slide. Skidding or sliding of the ball bearings100,102can result in premature wear during operation. The working travel of the upper spring98and the lower spring96are provided to accommodate relative movement between an outer barrel assembly and the inner drive assembly such that the force required to break the core sample is communicated directly to the core catcher66. A grease passage166(FIG.18) is provided through the housing128to enable filling of the anti-rotation thrust bearing assembly60with grease.

The anti-rotation thrust bearing assembly60isolates rotation of the anti-rotation shaft116relative to the core barrel38supported below the housing128. The anti-rotation thrust bearing assembly60further accommodates relative axial and angular misalignments between the components of the inner drive assembly50and the core barrel38during retrieval of a core sample.

Referring toFIGS.20and21with continued reference toFIGS.16and17, the torque latch assembly125includes the anti-rotation shaft116that is attached to lower end158B of the torque latch body158. The upper end158A of the torque latch body158is coupled to a shaft of the thrust bearing assembly44. The torque latch body158supports first and second latch arms122A-B that are biased radially outward by spring124. The latch arms122A-B fit within corresponding slots160on either side of the torque latch body158. The latch arms122A-B include lower tabs154that are held within the slots160by a latch sleeve145. The upper end of the latch arms122A-B includes upper feet156that are held in place by a keeper ring126.

The latch arms122A-B are pivotal radially outward a radial distance sufficient for each latch arm122A-B to pop into a drive slot142of the torque coupling36A of the drive barrel assembly36. The drive slot142includes an axial abutment surface144and a drive surface146. Surfaces152of each of the latch arms122A-B engage the axial surfaces144and transfer axial loads to the torque coupling36A of the drive barrel assembly36. A rotational drive surface150of each latch arm122A-B engages the drive surface146of the slot to transfer torque to the torque coupling36A and ultimately to the drill bit30. Accordingly, the latch arms122A-B includes surfaces150and152that transfers torque and axial loads to the drive barrel assembly36and ultimately to the drill bit30.

The drive surfaces150and152are engaged upon rotation of the latch body158during an initial rotation. Downhole directed axial forces maintain the axial load on the latch arms122A-B during operation. The latch arms122A-B are movable within the corresponding slots160of the latch body158. When under an axial load, the latch arms122A-B abut an upper surface of each slot160. Torque loads are transmitted through surfaces of the slots160.

Once the drill bit30has advanced sufficiently through the earth to obtain a core sample of a desired length, the inner drive assembly50is pulled upward through the drill string24. Because the torque latch assembly125is not accessible by traditional overshot assemblies, the drive surfaces of the latch arms122A-B cannot be remotely unlatched. The disclosed latch arms122A-B includes a ramped surface148that drives the latch arms122A-B radially inward to disengage the drive slot142in response to axially upward movement. The latch arms122A-B are configured to includes a spacing123that accommodates inward radial movement of the latch arms122A-B as they disengage the drive slot142.

Referring toFIGS.22,23and24, portions of the inner drive assembly50are shown to illustrate how each of the assemblies are coupled together. The mud motor46is coupled to the thrust bearing assembly by an Oldham style coupling56. The coupling56includes a driven part172attached to a torque shaft176of the thrust bearing assembly44. A drive part170is coupled to a rotor175driven by the mud motor46. A center part174is disposed between the driven part172and the drive part170and includes tabs162,164on either side that ride in corresponding slots provided in the driven part172and the drive part170. The tabs162,164of the center part174are perpendicular to each other.

The coupling56accommodates axial and rotational misalignment between the rotor175and the shaft176. The driven part172includes a first transverse slot171. The drive part170includes a second transverse slot173. The center part174includes the first tab162that is received within the first transverse slot171and the second tab164that is received within the second transverse slot173. The first tab162is orientated perpendicular to the second tab164. The center part174is movable transverse to the axis or rotation of each of the drive part170and the driven part172to accommodate axial and rotational misalignment between the rotor175and shaft176. The coupling56provides for the transmission of torque in accommodation of any parallel misalignment of the axis or rotation between the rotor175and the shaft176. The coupling56transmits axial forces from rotor175to shaft176and thereby thrust bearing assembly44.

The example mud motor46is powered by a fluid flow communicated through the drill string24. Any known downhole powered mud motor46may be utilized within the scope and contemplation of this disclosure. The example mud motor46generates an orbiting eccentric movement in the rotor175. The coupling56accommodates the orbiting rotary motion and transfers the orbiting motion into an axial rotation of the shaft176and thereby the latch coupling158.

The thrust bearing assembly44supports the axial forces that are applied to the drill bit30while also transmitting torque to the torque latch assembly125. The thrust bearing assembly44includes a plurality of bearing assemblies178stacked axially in an annular space between the shaft176and a housing177. The disclosed thrust bearing assembly44is sealed such that fluid and contaminants are prevented from entering and fouling the bearing assemblies178.

The specific configuration of the thrust bearing assembly44may vary from the illustrated arrangement to include other known bearing configurations capable of accommodating and transferring the applicable axial loads. Accordingly, other thrust bearing assemblies as are known to those skilled in the art could be utilized and are within the scope and contemplation of this disclosure.

The disclosed inner drive assembly50thereby includes a core barrel38that is coupled to a housing128that includes the example anti-rotation thrust bearing assembly60. The anti-rotation thrust bearing assembly60isolates rotational forces generated by the torque latch assembly125from the core barrel assembly38. Accordingly, the housing128and the core barrel38do not rotate. The torque latch assembly125is coupled to the thrust bearing assembly44by the threaded interface between the shaft176and the upper end158A of the latch body158. The shaft176is driven by the mud motor46through the coupling56. The mud motor46is coupled to the latch assembly48. The latch assembly48includes features that cooperate with an overshot assembly (not shown) that enables release and retrieval of a core through the drill string24.

Referring toFIGS.25,26, and27, the outer barrel34includes an inner circumferential groove208and the latch assembly48includes outwardly biased lugs212. The lugs212expand radially outward into the circumferential groove208and include a top surface214that abuts a downhole shoulder210of the circumferential groove208. Abutment between the lugs212and the downhole shoulder210provide for axial forces to be exerted on the outer barrel34. The lugs212includes a downhole ramped surface215that pushes the lugs212radially inward when descending downhole through the drill string.

An outer landing ring282is secured to the outer barrel assembly34and fixes a downward limit to the axial location of the inner drive assembly50within the drill string22. An inner landing ring280is attached to the inner drive assembly50and abuts the outer landing ring282. The lugs212then fix an upward limit of the axial position of the inner drive assembly50and thereby the core barrel38within the outer barrel assembly34.

The outer barrel34further includes anti-rotation keys218disposed within openings220of the circumferential groove208to counteract rotational forces produced by the mud motor46. The lugs212rotate within the circumferential groove and abut the anti-rotation keys218to anchor the drive assembly50to the outer barrel34. The anti-rotation keys218counter rotational forces generated by the mud motor46.

The disclosed example anti-rotation keys218are inset into openings220defined through the outer barrel34within the circumferential groove208. In this disclosed example, two anti-rotation keys218are provided and spaced circumferentially apart such that each of the lugs212abuts a different anti-rotation key218.

Each anti-rotation key218includes a boss portion222and a flange portion224. The boss portion222is fit into the opening220within the outer barrel34and the flange224is disposed on an inner surface of the circumferential groove208. The lugs212include a side216that abut sides of the flange portion224to stop rotation relative to the outer barrel34.

As appreciated, although a specific configuration of an anti-rotation key is shown by way of example, other shapes and sizes could be utilized and are within the scope and contemplation of this disclosure. Furthermore, although two anti-rotation keys are shown, any number of anti-rotation keys could be utilized and are within the scope and contemplation of this disclosure. Accordingly, the disclosed latch assembly48provides for transmission of axial forces to the outer barrel34and counters rotational forces generated by the drive assembly50.

Referring toFIGS.28,29,30,31and32, the mud motor46is driven by a fluid flow that is pumped through the drill string24. Fluid flow is communicated to the mud motor46to drive the shaft175. Rotation of and the torque output through the shaft175is controlled by a pressure differential between entering and exit fluid flow through the mud motor46. Fluid flow is also utilized at the drill bit30to aid in cutting through the earth.

A portion230of the outer barrel assembly34includes an exhaust shroud236for directing fluid flow axially uphole. The portion230surrounds the mud motor46such that a portion of fluid exhausted from the mud motor46exits through flow channels246and out through a top opening238defined by the exit shroud236. In this disclosed example, two exhaust shrouds236are provided to accommodate the desired exhaust fluid flow. It should be understood that additional exhaust shrouds may be utilized and included within the contemplation and scope of this disclosure.

In this disclosed example embodiment, the exhaust shroud is assembled as two parts236A and236B around the portion230. The shroud parts236A and236B include ribs240that abut the external surface of the portion230to provide a desired rigidity and durability.

The portion230includes a first taper242that transitions from an upper part232to a reduced diameter that is covered by the exhaust shroud parts236A and236B. A second taper244is provided along a lower part234to provide a reduced diameter proximate the second, lower shroud236as shown inFIG.28. The first taper242includes a gradually decreasing diameter250(FIG.30) that extends to a shoulder270upon which the shroud236is assembled. Each of the shrouds236include an outer diameter254that corresponds with the diameter of the outer barrel assembly34. The second taper244includes a decreasing diameter252from the diameter248. The diameter248is the same as the outer diameter254of the upper shroud236as shown inFIG.30. The diameter252tapers radially inward to the shoulder272on which the lower shroud236is assembled.

Slots258are provided through the portion230and are in fluid communication with the channels246defined by each corresponding exhaust shroud236. The openings256communicate fluid to the inner surface of the portion230. In one disclosed example embodiment, the openings256are elongated rectangular slots that extend axially and are rounded at top and bottom sides. Any number of slots258and openings256may be provided within the contemplation and scope of this disclosure. The size and number of slots258and openings256provide a desired pressure differential for operation of the mud motor46. Moreover, the number of slots258and openings256are selected to minimize any back pressure that may inhibit desired operation of the mud motor46.

Referring toFIG.32with continued reference toFIGS.28,29,30and31, an enlarged cross-section is shown to illustrate fluid flow. An inner fluid flow schematically indicated at268is present within the portion230and exits radially outward through slots258. The fluid flow is responsive to fluid pressure provided to drive the mud motor46. The pressure is generated by the flow communicated from the surface to drive the mud motor46. The inner fluid flow268may include radial and axial components that are driven through the slots258. The internal pressure of the flows268drive it radially outward through the slots258.

The radially directed flows268are communicated into channels246defined by the exhaust shroud236and turned axially uphole as an axial flow schematically shown at266. The axial flow266exits along the outer surface of the portion230and along the tapered surface242in this example. The shroud236prevents the flow from radially impacting the surrounding surfaces of the bore hole. Because the flow is at an elevated pressure, radial impact of the pressurized flow could detrimentally disturb surfaces of the bore hole and complicate operation. The example exhaust shrouds236turn this pressurized flow axially uphole to reduce and/or eliminate any such impact.

In one disclosed example embodiment, the exhaust shrouds236are formed as two parts236A and236B that have a base portion262that seat on the shoulder270of the portion230. The two parts236A and236B are joined together and to the portion230by a weld schematically shown at264. The welds264are finished to provide a smooth outer surface of a diameter common to the diameter of the shrouds236. Each shroud part236A,236B includes a top taper260along an outer periphery to ease movement when removed from the bore hole. The taper260reduces and/or prevents catching on inner surfaces of the bore hole when removed.

Referring toFIGS.33,34,35,36and37, another fluid exhaust embodiment is shown and includes bypass openings188. The bypass openings188are disposed in a portion of the outer barrel assembly34. A first portion182and a second portion184of the outer barrel assembly22are shown coupled together by a threaded interface.

The bypass openings188communicated fluid flow into an outer annular channel186. The outer annular channel186is covered by a metering ring180. The size and number of the bypass openings188combine to define a flow area that is significantly larger than a calibration flow area that regulates the fluid flow.

The metering ring180is disposed within the annular channel186and includes a plurality of slots190. Each of the slots190include a height194and a width192. The height194and the width192define a flow area for calibrating and controlling the bypass fluid flow. The annular channel186and the openings188combine to provide a flow area that is much less restrictive than the combined flow areas defined by the slots190of the metering ring180.

In this disclosed example, the metering ring180is held between the first portion182and the second portion184within the annular channel186. Fluid flow from within the first and second portions182,184passes through the plurality of openings188into the annular channel186. The fluid flow then passes through the plurality of slots190and into an annular space surrounding the DCD assembly22into the borehole25. The fluid may then flow uphole and return to the drill rig at the surface. In this example, the metering ring180is disposed within the outer barrel assembly34in a location proximate to the mud motor46. Moreover, several metering rings180may be disposed at any location within the DCD assembly22that requires control of fluid pressure.

Referring toFIGS.38and39, a retrieval assembly198is shown and includes a release actuator200that engages a portion of the latch assembly48to release a latch coupling the DCD assembly22to the outer barrel assembly34. The retrieval assembly198includes a key assembly202that engages a guide slot52defined on an inner surface of the outer barrel assembly34. The key assembly202guides along the guide slot52to rotationally orientate the retrieval assembly198to the DCD assembly22. Axial withdrawal of the release actuator200causes a release from the outer barrel assembly34and a coupling of the DCD assembly22to the release assembly198such that the inner drive assembly50may be pulled to the surface.

The key assembly202includes a movable key portion204that is moveable radially inward to accommodate portions of the drill string24and the outer barrel assembly34that may be of a smaller diameter than the guide slot52. A biasing member206is provided to bias the movable key portion204outward into the guide slot52.

A first centralizer300is attached to an end of the release actuator200to center the release actuator200within the drill string24and outer barrel assembly34. A sensor assembly308is secured to the first centralizer300on a first end and to a second centralizer310at a second end. The sensor assembly308may be of any configuration known to provide information indicative of the position and orientation of the DCD22. Each of the first and second centralizers300,310includes wheels302that are supported on shafts and extend radially outward to engage an inner surface of the drill string24and the outer barrel assembly34. The wheels302and corresponding shafts are held in slot312by a ring304. The ring304is rotational secured by fasteners306and axially secured by a retaining ring. The axial distance between the first centralizer300and the second centralizer310positions the key assembly202to assure engagement.

Referring toFIGS.40,41and42with continued reference toFIGS.38and39, the guide slot52is configured as a helix that leads into an axial slot55. The movable key portion204engages the helix portion of the guide slot52upon axial movement and guides along the slot52and thereby rotate the retrieval assembly198as is best shown inFIGS.40-42. The movable key portion204then moves into the axial slot55(FIG.34) to provide the desired alignment. The axial slot55provides a circumferential reference point that is used to circumferentially locate a downhole orientation device as is commonly used in directional drilling and known by those skilled in the art. For example, the circumferential position of the axial slot55is used to orient the steering pads40in order to direct further boring into the earth in a desired direction.

Referring toFIG.43, another directional core drilling (DCD) assembly320is shown and includes a drill bit324that cuts into the earth, stone, and rock to form the borehole. An outer barrel assembly326includes an outer surface330without additional steering pads or features. The example DCD assembly320is generally disposed along a central axis322with the drill bit324disposed on a guide axis332. The guide axis332is angled relative to the central axis322and provides for generation of the borehole at a desired angle that is not straight. The example DCD assembly320may include all the internal drive, latching and retrieval features described above with regard to the DCD assembly22. Other combinations and devices could also be included in the DCD assembly320and remain within the contemplation and scope of this disclosure.

Referring toFIGS.44and45, the example DCD assembly320includes a guide sleeve334coupled to an end340of the outer barrel assembly326. In one disclosed embodiment, the guide sleeve includes external threads338that are coupled to internal threads342of the outer barrel assembly326. The guide sleeve334includes an inner guide surface336that is disposed along the guide axis332. The guide axis332is disposed at an angle352relative to the central axis322. The angle352is exaggerated inFIGS.44and45for illustration purposes.

A lower wear sleeve382and an upper wear sleeve384provide contact points for movement of the assembly320through the earth. The wear sleeves382,384are one of three defined contact points for the assembly320. The drill face is one contact point and the wear sleeves382,384define the other two contact points. The wear sleeves382,384are formed from a steel material that has been hardened to accommodate contact with sides of the bore hole. The wear sleeves382,384protect the outer surface of the barrel assembly326against excessive wear during use.

The drive barrel assembly344rides along the inner guide surface336to change the course of the drill bit324as it cuts and forms the borehole. Small changes in the angle that the drill bit324forms the borehole is used to steer the DCD assembly320and obtain core samples in a desired location. A core barrel assembly350for receiving a core sample is disposed within the drive barrel assembly344and remains fixed relative the drive barrel assembly344and drill bit324.

Referring toFIGS.46and47with continued reference toFIGS.44and45, the example guide sleeve334includes a fixed inner diameter335that is offset a radial distance355at a downhole end356as compared to an upstream end354. While the diameter335remains constant, it is tilted relative the axis322. The tilt is offset in a fixed direction to cause a corresponding tilt of the drill bit324. The guide sleeve334remains fixed relative to the rotating drive barrel assembly344. In one disclosed example embodiment, the bit adaptor328rides along the guide surface336to define the desired angle of the drill bit324.

The forward end356is shown inFIG.46in an exaggerated view to illustrate the radial offset355. At the forward end356, the guide surface336is spaced a radial distance358from the central axis322at a top center location. The guide surface336is spaced a radial distance360from the axis322at the bottom center location. At the uphole end354, shown inFIG.47, a radial distance360A and360B from the top center and bottom center locations are the same. The inner surface336is tilted relative to the axis322such that diameter remains the same to facilitate guiding of the drive barrel assembly344.

In one disclosed example embodiment, the angle352of the inner guide surface334is disposed at an angle of less than about 2° from the borehole central axis322. In another disclosed embodiment, the inner guide surface334is disposed at an angle between ⅛° and ¼° from the borehole central axis322. In another disclosed embodiment, the angle352is between ¾° and ¼° from the borehole central axis322. Other angles could be utilized and are within the contemplation of this disclosure.

Referring toFIGS.48and49, the drive barrel assembly344includes a main portion346that is coupled to a downhole end348. A coupling362between the main portion346and the downhole end348accommodates the tilt of the drill bit324while still driving rotation of the drill bit. The coupling362is a continuous gap375that extends entirely about the circumference of both the downhole end348and the main portion346. The gap375provides for the downhole end348to rotate along an axis364that is spaced apart from the central axis322. Accordingly, rotation indicated by arrow380about the axis322is translated into rotation378about the axis364. The size of the gap375provides for the flexibility to accommodate the tilt of the drill bit324. As the main portion346rotates about the axis322, it drives the downhole end348through the coupling362. The tilt remains in the same clocked position in the direction of the tilt angle352(Shown inFIG.44).

The coupling362is formed from captured drive shapes366that allow radial movement between the main portion346and the downhole end348, but maintain a driving connection. The example drive shapes366hold the axial orientation between the main portion346and the downhole end348by way of the specific shape. In one example embodiment, the gap375define the drive shapes366as a plurality of interlocked castellations. Each of the interlocked castellations include a first portion370and a second portion372. The shape is defined such that a width374of the first portion370is greater than a width376of the second portion372. Because the first portion370is larger than the second portion372, the coupling362, and thereby the main portion346and the downhole end348remain locked to each other.

Although the drive shape366is shown by way of example, other shapes that provide for transfer of torque through an angled interface could be utilized and are within the contemplation and scope of this disclosure.

In operation, rotation of the main portion346of the drive barrel assembly344is communicated to the downhole end348through driving contact between the drive shapes366. The gap375is sized to accommodate the tilting between the main drive portion346and the downhole end. A width368of the gap375therebetween is sized to enable relative tilting between the downhole end348and the main portion346that is at least as much as the angle352defined by the guide sleeve334. In one example embodiment, the gap is between 0.025 in and 0.008 in. (0.635 mm and 0.2032 mm). In another example embodiment the gap is between 0.020 in and 0.010 in. (0.508 mm and 0.254 mm). Other gap sizes could be utilized to accommodate other tilt angles.

The direction of the tilt angle of the drill bit324is obtained by aligning the tilt relative to a circumferential reference point, such as the axial slot55(FIG.42) that is used to circumferentially locate a downhole orientation device as is commonly used in directional drilling and known by those skilled in the art. For example, the circumferential position of the axial slot55is used to orientate the tilt provided by the guide sleeve334in order to direct further boring into the earth in a desired direction.

Accordingly, the disclosed DCD assemblies22,320include features for directing a drill bit30,324downhole for obtaining and safely retrieving core samples.