Abstract:
An apparatus for mechanically engaging and releasably coupling two tubular members may include a first housing member, a second housing member and a piston member, wherein, in a first position, the first and second housing members are fixed relative to each other by the piston, and wherein, in a second position, the second housing member is rotatable relative to the first housing member. Certain embodiments include matingly engaged axially disposed and axially offset splines. Other embodiments include first and second interlocking mechanisms that are in an opposed relationship to couple first and second tubular members in a fixed position. Some embodiments include a method of reacting a first rotational coupling against a second axial coupling to resist both axial and rotational movement between first and second tubulars. Other embodiments include displacing a moveable member to both axially and rotationally release first and second tubulars.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to a releasable connection for a downhole assembly. More particularly, the present disclosure relates to a mechanically engaged and releasable connection that may be disposed between a tool string and a downhole tool and actuated to disconnect the downhole tool from the tool string upon application of an axial load. 
         [0002]    To form an oil or gas well, a bottom hole assembly (BHA), including components such as a motor, steering assembly and drill bit, is coupled to an end of a drillstring and then inserted downhole, where drilling commences. When forming a substantially straight borehole, the drillstring typically includes a number of pipe joints threaded end to end. Circumstances may arise in which it is desirable to disconnect the drillstring from the BHA, for example, when the BHA becomes stuck in the borehole during drilling. At such times, the drillstring is disconnected from the BHA by applying torque to the drillstring and uncoupling a threaded connection between the drillstring and the BHA. Once disconnected from the BHA, the drillstring may be extracted from the borehole and the stuck BHA subsequently retrieved via fishing, jarring or another operation. 
         [0003]    When forming a deviated, lateral or upwardly sloping borehole, it is not economically feasible or practical to use a drillstring made from jointed pipe. Instead, the BHA may be coupled to coiled tubing, which includes one or more lengths of continuous, unjointed tubing spooled onto reels for storage in sufficient quantities to exceed the maximum length of the borehole. Because the coiled tubing cannot be disconnected from the BHA by the application of torque to the coiled tubing, an axial disconnect is positioned in the tubing string between the BHA and the coiled tubing prior to insertion of the tubing string downhole. The axial disconnect facilitates decoupling of the coiled tubing from the BHA in the event that it becomes desirable to do so, such as when the BHA becomes stuck during drilling. To decouple the BHA from the coiled tubing, the disconnect is actuated to allow the BHA to disconnect from the coiled tubing upon application of an axial load to the coiled tubing. Once disconnected from the BHA, the tubing string may be extracted from the borehole and the stuck BHA subsequently retrieved via fishing, jarring or another operation. 
         [0004]    A variety of conventional axial disconnects have been used to decouple a coiled tubing string from a downhole tool, such as a BHA. Some conventional disconnects include locking dogs, interlocking fingers, grapples or similar devices which are actuated, such as by application of a hydraulic pressure load, to release the tool coupled thereto. One shortcoming of these disconnects is that the locking dogs, interlocking fingers, and grapples are relatively weak components, in comparison to the other components of the disconnect. Another shortcoming is that the disconnects are usually thin-walled. Both design characteristics limit the loads which may be safely applied to the disconnects. Other conventional disconnects may be capable of handling higher loads. However, those disconnects are typically very sophisticated tools, having many working parts, each representing a potential failure point and increased manufacturing cost. These disconnects may also include expensive high strength materials, also increasing costs. 
         [0005]    Increased downhole operating loads and costs are pushing the limits of current axial disconnects. Therefore, a stronger axial disconnect that does not resort to expensive materials is desirable. Stronger axial disconnects that also have few working parts, and thus ease manufacturing, installation, or operational complexities and related costs, would likewise be desirable. 
       SUMMARY 
       [0006]    The embodiments described herein provide an apparatus for mechanically engaging and releasably coupling two tubular members, such as for disconnecting a tool from a tool string. In some embodiments, the apparatus includes a first housing member having a first throughbore and a first flowbore in communication with the first throughbore, a second housing member coupled to the first housing member, the second housing member having a second throughbore in communication with the first throughbore, and a piston member disposed within at least a portion of the first and second throughbores, the piston member having a second flowbore in fluid communication with the first flowbore and moveable from a first position to a second position, wherein, in the first position, the first and second housing members are fixed relative to each other by the piston, and wherein, in the second position, the second housing member is rotatable relative to the first housing member. 
         [0007]    In certain embodiments an apparatus includes a first tubular member having a first set of axially disposed splines and a first set of axially offset splines, a second tubular member having a second set of axially disposed splines and a second set of axially offset splines matingly engaged with the first set of axially offset splines, and a moveable member having a third set of axially disposed splines matingly engaged with the first and second sets of axially disposed splines. 
         [0008]    In other embodiments an apparatus includes a first tubular member, a second tubular member moveably disposed in the first tubular member, a first interlocking mechanism disposed between the first and second tubular members, and a second interlocking mechanism disposed between the first and second tubular members, the second interlocking mechanism including a moveable member, wherein the first and second interlocking mechanisms are in an opposed relationship to couple the first and second tubular members in a fixed position. 
         [0009]    In some embodiments a method includes rotationally coupling a first tubular member into a second tubular member at a first location, aligning the first and second tubulars, translating a moveable member into the first and second tubular members to couple the first and second tubular members at a second location, and reacting the first coupling against the second coupling to resist both axial and rotational movement between the first and second tubulars. Other embodiments include displacing the moveable member to release the second coupling, rotationally disengaging the first tubular from the second tubular member, and removing the first tubular member from the second tubular member. 
         [0010]    In certain embodiments, the axially disposed interlocking engagements are in an opposed relationship with the axially offset interlocking engagement such that the anti-rotation of the axially disposed interlocking engagements reacts with the anti-translation of the axially offset interlocking engagement to couple the disconnect such that the primary tubular members are fixed both rotationally and translationally. The axially disposed interlocking mechanism may be moved or disengaged to then remove the opposing reaction forces, and disengage or decouple the axially offset interlocking mechanism. The axially disposed and offset mechanisms may be axially displaced from each other, but interact to provide the opposing reaction forces for coupling and selective release. 
         [0011]    The features and characteristics mentioned above, and others, provided by the various embodiments will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic view of a tubing string including a tri-lock disconnect system in accordance with the principles described herein in a deviated well; 
           [0013]      FIG. 2  is a perspective, cross-sectional view of the tri-lock disconnect system of  FIG. 1 ; 
           [0014]      FIG. 3  is a perspective view of the lower housing member of  FIG. 1  in partial cross-section; 
           [0015]      FIG. 4  is a perspective view of the upper housing member of  FIG. 1 ; and 
           [0016]      FIG. 5  is a perspective view of the piston of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus are to be interpreted to mean “including, but not limited to . . . ”. 
         [0018]    Unless otherwise specified, any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. 
         [0019]    A tri-lock disconnect system in accordance with the principles described herein may be generally described as a releasable connection for coupling a rotating tool string to a tool, transmitting loads from the tool string to the tool during normal operations of the tool string, and decoupling the tool string from the tool when so desired. While the preferred embodiment of a tri-lock disconnect system is described below in the context of a tool string consisting of a coiled tubing coupled by the disconnect to a BHA, one having ordinary skill in the art will readily appreciate that the disconnect lends itself to other applications as well. For example, a tri-lock disconnect may be inserted into a conventional drillstring between the jointed drill pipe and a downhole tool, such as a BHA. In such applications, actuation of a tri-lock disconnect to decouple the drill pipe from the BHA may be more time and cost effective than decoupling these components using traditional methods, e.g., applying a torque load to the drill pipe to unthread the drill pipe from the BHA. 
         [0020]    Referring now to  FIG. 1 , an operating environment for a coiled tubing string  105  and an operating tool  115  is shown schematically. An embodiment of a mechanically engaged and releasable connection system  100  is depicted at the lower end of the length of coiled tubing  105  disposed in a well  110 . The operating tool  115 , such as a bottom hole assembly (BHA), is coupled below disconnect  100 . Coiled tubing  105 , disconnect  100  and BHA  115  form a tool or tubing string  120 , wherein coiled tubing  105  and BHA  115  form an upper portion  125  and a lower portion  130 , respectively, of tool string  120 . Tool string  120  is positioned in a well casing  135  intersecting a downhole formation or zone of interest  140 . An annulus  160  is formed between tool string  120  and well casing  135 . Coiled tubing  105  is stored on a reel  145  at the surface  150  and is run into casing  135  and well  110  by a tubing injector  155 . Other conventional components of well  110  at the surface  150  are omitted for clarity. 
         [0021]    Referring next to  FIG. 2 , an embodiment of the tri-lock disconnect system  100  as assembled includes three working parts, specifically, a first tubular or lower housing member  205  coupled to a second tubular or upper housing member  210  and a piston  215  disposed therein. Lower housing member  205  has two ends  220 ,  225  with an annular body  230  extending therebetween. End  220  of lower housing member  205  is the downhole end of disconnect  100 . As such, end  220  of lower housing member  205  may be coupled to a first tubular member, such as lower tubing portion  130  of tool string  120  ( FIG. 1 ). In this exemplary embodiment, disconnect  100  is coupled to lower tubing portion  130  by a plurality of threads  305  (best viewed in  FIG. 3 ) located on an outer surface  310  of lower housing member  205 . To provide a fluid-tight coupling at this location, lower housing member  205  further includes two grooves  255  in outer surface  310  proximate threads  305 . Each groove  255  is configured to receive a sealing element, such as an O-ring, (not shown) prior to the coupling of lower housing member  205  with lower tubing portion  130 . End  225  couples to upper housing member  210 , as will be described. 
         [0022]    Lower housing member  205  further includes a flowbore  235  extending therethrough from end  220  of body  200  and an increased diameter throughbore  240  extending therethrough from end  225  to flowbore  235 . The size of flowbore  235  is selected to allow fluid flow therethrough at a desired rate during normal operations of tool string  120 . The size and shape of throughbore  240  is selected to receive upper housing member  210  and piston  215 , as shown in  FIG. 2  and described below. 
         [0023]    Flowbore  235  of lower housing member  205  is smaller in cross-section than throughbore  240 . Thus, a shoulder  260  is formed in body  230  at the transition between flowbore  235  and throughbore  240 . Shoulder  260  limits the depth to which piston  215  may translate into lower housing member  205 . 
         [0024]    Referring now to  FIG. 3 , throughbore  240  of lower housing member  205  includes a first portion  315 , a second increased diameter portion  320 , and a third increased diameter portion  325 . First and second portions  315 ,  320  are configured to receive piston  215 , while third portion  325  is configured to receive upper housing member  210 . First portion  315  is bounded by a generally cylindrical inner surface  330  of body  230  configured to sealingly engage piston  215  when piston  215  is inserted into first portion  315  of throughbore  240 , as shown in  FIG. 2 . Second portion  320  is bounded by a generally cylindrical inner surface  335 . The cross-section of first portion  315  is smaller than that of second portion  320 . Thus, a shoulder  340  is formed in body  230  surrounding throughbore  240  at the transition between first and second portions  315 ,  320 . 
         [0025]    A first plurality of splines  345  is formed over a portion of inner surface  335 . Each spline  345  has a length extending substantially parallel to a longitudinal axis  365  through lower housing member  205  and a height that extends substantially radially inward from inner surface  335 . Thus, the splines  345  may also be referred to as longitudinally or axially disposed splines. A recess  346  is formed between each pair of adjacent splines  345 . Splines  345  are configured to matingly engage and interlock with another set of splines formed on the outer surface of piston  215 , as will be described. When the axially disposed interlocking splines are so engaged, they form an interlocking mechanism between lower housing member  205  and piston  215  to prevent relative rotation therebetween. 
         [0026]    Still referring to  FIG. 3 , third portion  325  of throughbore  240  is bounded by a generally cylindrical inner surface  350  of body  230  configured to sealingly engage upper housing member  210  when upper housing member  210  is inserted into third portion  325  of throughbore  240 . The cross-section of second portion  320  is smaller than that of third portion  325 . Thus, a shoulder  355  is formed in body  230  surrounding throughbore  240  at the transition between second portion  320  and third portion  325 . Shoulder  355  limits the depth to which upper housing member  210  may be inserted into lower housing member  205 . 
         [0027]    To enable coupling of upper and lower housing members  210 ,  205 , as shown in  FIG. 2 , a first plurality of axially offset or spiral splines  360  are formed over a portion of inner surface  350 . Each spline  360  has a length that extends circumferentially over a portion of inner surface  350  and is angularly offset relative to longitudinal axis  365 . Thus, the splines  360  may also be referred to as longitudinally or axially offset splines. Each spline  360  also has a height that extends substantially radially inward from inner surface  350 . A recess  361  is formed between each pair of adjacent splines  360 . Spiral splines  360  are configured to matingly engage and interlock with a set of spiral splines formed on the outer surface of upper housing member  210 , as will be described. Upper and lower housing members  210 ,  205  are coupled together by engaging and interlocking spiral splines  360  with matching spiral splines on upper housing member  210  to form an interlocking mechanism, as will be described. The interlocking mechanism prevents relative axial displacement between the members  210 ,  205  when combined with the other components described herein. 
         [0028]    Lower housing member  205  further includes a recirculation port  245  (best viewed in  FIG. 2 ) with a burst disc  250  seated therein. Burst disc  250  is configured to rupture when fluid pressure in flowbore  235  significantly exceeds the expected pressure range of fluid passing through flowbore  235  during normal operations of tool string  120 . For example, assuming that the pressure of fluid passing through flowbore  235  during normal operations of tool string  120  is expected to be no greater than 3,000 psi, burst disc  250  may be configured to rupture at fluid pressures in excess of 5,000 psi. Once burst disc  250  ruptures, recirculation port  245  provides fluid communication between flowbore  235  and annulus  160  ( FIG. 1 ). 
         [0029]    Turning now to  FIG. 4 , upper housing member  210  has two ends  420 ,  425  with an annular body  430  extending therebetween. End  420  of upper housing member  210  is the uphole end of disconnect  100 . As such, end  420  of upper housing member  210  is coupled to a second tubular member, such as upper tubing portion  125  of tubing string  120  ( FIG. 1 ). In this exemplary embodiment, disconnect  100  is coupled to upper tubing portion  125  by a plurality of threads  405  located on an outer surface  410  of upper housing member  210 . To provide a fluid-tight connection at this location, upper housing member  210  further includes two grooves  455  in outer surface  410  proximate threads  405 . Each groove  455  is configured to receive a sealing element, such as an O-ring, prior to the coupling of upper housing member  210  with upper tubing portion  125 . End  425  couples to lower housing member  205 , as will be described. To provide a fluid-tight connection at this location, upper housing member  210  further includes two grooves  455  in outer surface  410  proximate end  425 . Each groove  455  is configured to receive a sealing element, such as an O-ring, prior to the coupling of upper housing member  210  with lower housing member  205 . 
         [0030]    Referring also to  FIG. 2 , body  430  includes a throughbore  435  extending therethrough. Throughbore  435  includes a first portion  415  and an increased diameter second portion  460 . First portion  415  is bounded by a generally cylindrical inner surface  465  of body  430 , while second portion  460  is bounded by a generally cylindrical inner surface  470  of body  430 . A second plurality of splines  450  is formed on inner surface  465 . Each spline  450  has a length extending substantially parallel to a longitudinal axis  444  through upper housing member  210  and a height that extends substantially radially inward from inner surface  465 . Thus, the splines  450  may also be referred to as longitudinally or axially disposed splines. A recess  451  is formed between each pair of adjacent splines  450 . Splines  450  are similar to splines  345  formed on inner surface  335  of lower housing member  205 . Further, splines  450 , like splines  345 , are configured to matingly engage and interlock with the set of splines formed on the outer surface of piston  215 , as will be described. When the axially disposed interlocking splines are so engaged, they form an interlocking mechanism between upper housing member  210  and piston  215  to prevent relative rotation therebetween. 
         [0031]    The cross-section of first portion  415  is smaller than that of second portion  460 . Thus, a shoulder  475  is formed in body  430  surrounding throughbore  435  at the transition between first portion  415  and second portion  460 . When upper housing member  210  is decoupled from lower housing member  205  and extracted from well  110  ( FIG. 1 ), shoulder  475  retains piston  215  within throughbore  435  of upper housing member  210  so that piston  215  is removed from well  110  with upper housing member  210 . 
         [0032]    Upper housing member  210  further includes a second plurality of axially offset or spiral splines  440  formed over a portion of outer surface  410  proximate end  425 . Each spline  440  has a length that extends circumferentially over a portion of outer surface  410  and is angularly offset relative to longitudinal axis  444 . Thus, the splines  440  may also be referred to as longitudinally or axially offset splines. Each spline  440  also has a height that extends substantially radially outward from outer surface  410 . A recess  441  is formed between each pair of adjacent splines  440 . Spiral splines  440  are configured to matingly engage and interlock with the first plurality of spiral splines  345  formed over a portion of inner surface  335  of lower housing member  205 . Upper housing member  210  and lower housing member  205  are coupled by engaging or interlocking spiral splines  440 ,  345 , as will be described below. 
         [0033]    Upper housing member  210  further includes a recirculation port  480  through body  430  and a plurality of recesses  485  formed in inner surface  470  proximate end  420 . Recirculation port  480  provides fluid communication between flowbore  435  and annulus  160  ( FIG. 1 ). Each recess  485  is configured to receive a shear pin or screw  490 . Shear pins  490  engage a shear groove located on the outer surface of piston  215  when piston  215  is disposed within upper housing member  210 , as shown in  FIG. 2  and described in more detail below. 
         [0034]    Turning finally to  FIG. 5 , piston  215  has two ends  520 ,  525  with an annular body  530  extending therebetween. A flowbore  540  extends through body  530  from end  525  to end  520 . Proximate each end  520 ,  525 , piston  215  further includes a pair of grooves  510  formed in an outer surface  505  of piston  215 . Each groove  510  is configured to receive a sealing element, such as an O-ring. When end  520  of piston  215  is inserted into first portion  315  of throughbore  240  of lower housing member  205 , as shown in  FIG. 2 , end  520  of piston  215  sealingly engages inner surface  330  of lower housing member  205 . Similarly, when disconnect  100 , or more specifically, end  420  of upper housing member  210 , is coupled to upper portion  125  of tubing string  120 , end  525  of piston  215  sealingly engages the inner surface of upper portion  125 . 
         [0035]    Piston  215  further includes a shear groove  515  adjacent grooves  510  proximate end  525 . When end  520  of piston  215  is inserted through upper housing member  210  and into throughbore  240  of lower housing member  205 , as shown in  FIG. 2 , shear pins  490  extending from recesses  485  in lower housing member  205  engage shear groove  515 , whereby piston  215  is suspended by shear pins  490  within upper and lower housing members  210 ,  205  and prevented from further translation relative to upper and lower housing members  210 ,  205 . The size and quantity of shear pins  490  supporting piston  215  in this manner are selected to ensure piston  215  remains suspended when exposed to the full range of fluid pressures expected during normal operations of tool string  120 . However, when piston  215  is exposed to significantly higher pressures, such as when flowbore  540  is blocked and fluid may not pass therethrough, the pressure forces acting on piston  215  cause pins  490  to shear, thereby allowing piston  215  to displace in the downhole direction, or further into lower housing member  205 . 
         [0036]    Piston  215  further includes a third plurality of splines  535  over a portion of outer surface  505  that were previously referenced regarding interlocking engagement with first and second pluralities of splines  345 ,  450 . Each spline  535  extends substantially radially outward from outer surface  505 . Each spline  535  has a length extending substantially parallel to a longitudinal axis  555  through piston  215 . Thus, the splines  535  may also be referred to as longitudinally or axially disposed splines. A recess  536  is formed between each pair of adjacent splines  535 . Further, the axial length of splines  535  is selected such that they extend into, engage, and interlock simultaneously with both sets of first and second splines  345 ,  450  of lower and upper housing members  205 ,  210 , respectively. When piston  215  is inserted into lower and upper housing members  205 ,  210  and suspended by shear pins  490 , as shown in  FIG. 2 , splines  535  of piston  215  interlock with splines  345 ,  450  of lower and upper housing members  205 ,  210 , respectively. Once interlocked, upper and lower housing members  210 ,  205  are prevented from rotating relative to or about piston  215 , as well as relative to each other. 
         [0037]    Piston  215  further includes a flanged portion or stop ring  545  extending from outer surface  505 . Stop ring  540  is configured such that its cross-section is larger than that of first portion  415  of throughbore  435  of upper housing member  210 . When upper housing member  210  is decoupled from lower housing member  205  and extracted from well  110 , piston  215  is retained with upper housing member  210  by virtue of contact between shoulder  475  of upper housing member  210  and stop ring  545  of piston  215 . The interaction between shoulder  475  and stop ring  545  prevents piston  215  from translating out of throughbore  435  and instead allows piston  215  to be removed from well  110  along with upper housing member  210 . 
         [0038]    In order to decouple upper portion  125  of tubing string  120  from BHA  115 , disconnect  100  must first be actuated. After actuation, upper housing member  210  may be decoupled from lower housing member  205 . The exemplary embodiment of a tri-lock disconnect system depicted in  FIGS. 2-5  and described herein is hydraulically actuated. For this purpose, piston  215  further includes a ball seat  550  at end  525 . Other embodiments of a tri-lock disconnect system, however, may be actuated in other ways, such as by mechanical or electrical means. 
         [0039]    To actuate disconnect  100 , a ball is dropped from the surface  150  through tool string  120  to disconnect  100  where it lands on ball seat  550  and prevents further fluid from passing into flowbore  540  of piston  215 . As a result, fluid pressure builds upstream of piston  215  until the pressure load on piston  215  causes shear pins  490  to sever. Once shear pins  490  sever, piston  215  translates downward into lower housing member  205  until abutting shoulder  260  of lower housing member  205 . When piston  215  comes to rest against shoulder  260 , splines  535  of piston  215  are fully disengaged from splines  450  on upper housing member  210 , and upper housing member  210  is free to rotate relative to lower housing member  205 . 
         [0040]    The assembly and operation of disconnect  100  will now be described with reference to  FIGS. 1 through 5 . To assemble disconnect  100 , sealing elements, such as O-rings, are inserted into grooves  455  on upper housing member  210 , grooves  510  on piston  215 , and grooves  255  on lower housing member  205 . Upper and lower housing members  210 ,  205  are then coupled. End  425  of upper housing member  210  is inserted into throughbore  240  of lower housing member  205 . When spiral splines  440  on outer surface  405  of upper housing member  210  contact spiral splines  360  on inner surface  350  of lower housing member  205 , a compression load is then applied to end  420  of upper housing member  210 . Due to the angular nature of spiral splines  440 ,  360 , the applied compression load causes upper housing member  210  to rotate into lower housing member  205 . As upper housing member  210  rotates into lower housing member  205 , spiral splines  440  engage and interlock with spiral splines  360 . More specifically, spiral splines  440  thread into recesses  361  between spiral splines  360 , and spiral splines  360  thread into recesses  441  between spiral splines  440 . Rotation of upper housing member  210  in this manner continues until end  425  of upper housing member  210  abuts shoulder  355  of lower housing member  205  and spiral splines  440 ,  360  are fully interlocked, as shown in  FIG. 2 . In some embodiments, upper housing member  210  need only be turned ¾ of a rotation to fully couple within lower housing member  205 . Further, when spiral splines  440 ,  360  are fully engaged, longitudinal splines  345  on inner surface  335  of lower housing member  205  are adjacent to and align with longitudinal splines  450  on inner surface  465  of upper housing member  210 . 
         [0041]    Next, piston  215  is inserted into upper and lower housing members  210 ,  205 . End  520  of piston  215  is inserted through throughbore  435  of upper housing member  210  and into throughbore  240  of lower housing member  205 . Once end  520  of piston  215  passes into throughbore  240 , piston  215  may be rotated relative to the assembly of upper and lower housing members  210 ,  205 , if necessary, to align longitudinal splines  535  on outer surface  505  of piston  215  with recesses  451 ,  346  between longitudinal splines  450 ,  345  on inner surfaces  465 ,  335  of upper and lower housing members  210 ,  205 , respectively. When longitudinal splines  535  align with recesses  451 ,  346 , end  520  of piston  215  may be further inserted into throughbore  240  until shear pins  490  extending from recesses  485  of lower housing member  205  engage shear groove  515  of piston  215 , thereby preventing further translation of piston  215  within upper and lower housing members  210 ,  205 . 
         [0042]    Once shear pins  490  engage shear groove  515  and piston  215  ceases to translate, longitudinal splines  535  of piston  215  are fully interlocked with longitudinal splines  450 ,  345  of upper and lower housing members  210 ,  205 , respectively, as shown in  FIG. 2 . When splines  535  are interlocked with splines  450 ,  345 , rotation of upper and lower housing members  210 ,  205  relative to piston  215  is prevented, as previously described. As long as upper and lower housing members  210 ,  205  cannot rotate relative to each other, spiral splines  440  on upper housing member  440  cannot disengage or unthread from spiral splines  345  on lower housing member  205 . 
         [0043]    Disconnect  100  is now fully assembled. Due to the engagement of longitudinal splines  535  on piston  215  with longitudinal splines  345 ,  450  on lower and upper housing members  205 ,  210 , respectively, lower and upper housing members  205 ,  210  cannot rotate relative to piston  215 . Since such rotation is prevented, spiral splines  440  on upper housing member  210  cannot disengage or unthread from spiral splines  360  of lower housing member  205  upon application of a tension load to upper housing member  210 . Thus, disconnect  100  includes three interlocking engagements, one between piston  215  and lower housing member  205 , another between piston  215  and upper housing member  210 , and the third between upper and lower housing members  210 ,  205 . Hence, disconnect  100  is also referred to as a tri-lock connection system or a tri-lock disconnect. The axially disposed interlocking engagements are in an opposed relationship with the axially offset interlocking engagement such that the anti-rotation of the axially disposed interlocking engagements reacts with the anti-translation of the axially offset interlocking engagement to couple the disconnect  100  such that the primary tubular members are fixed both rotationally and translationally. The axially disposed interlocking mechanism may be moved or disengaged to then remove the opposing reaction forces, and disengage or decouple the axially offset interlocking mechanism. The axially disposed and offset mechanisms may be axially displaced from each other, but interact to provide the opposing reaction forces for coupling and selective release. It is understood that the term “splines” as used herein does not merely include those shown in the drawings, but also other surfaces which effect the interlocking engagements described herein. The interlocking mechanisms between the various tubular members may also include teethed arrangements, tongue and groove arrangements, ridge and valley arrangements or other surfaces providing mating and interlocking engagement. 
         [0044]    Disconnect  100  is next coupled between BHA  115  and coiled tubing  105  to form tubing string  120 . Tubing string  120  is then inserted into well  110 , and BHA  115  is operated to form well  110 . During normal operations of tubing string  120 , fluid is injected downhole through coiled tubing  105  to disconnect  100 . Fluid passes through disconnect  100  via flowbore  540  of piston  215 , throughbore  240  of lower housing member  205 , and flowbore  235  of lower housing member  205  ( FIG. 2 ). From disconnect  100 , the fluid passes through BHA  115  and then returns to the surface  150  ( FIG. 1 ) via annulus  160 . Also during normal operations, interlocked spiral splines  440 ,  360  and interlocked longitudinal splines  345 ,  450  allow significant loads to be transferred through disconnect  100 . Specifically, tension loads applied to disconnect  100  by coiled tubing  105  are carried by spiral splines  440 ,  360 , while any torsional loads are borne by longitudinal splines  345 ,  450 ,  535 . These loads as well as pressure fluctuations in fluid passing through tubing string  120  during normal operations will not inadvertently actuate disconnect  100  and/or decouple upper housing member  210  from lower housing member  205 . 
         [0045]    Actuation of disconnect  100  requires severance of shear pins  490 . Their quantity and size have been selected such that their combined strength is capable of suspending piston  215  within upper and lower housing members  210 ,  215 , as shown in  FIG. 2 , under the full range of fluid pressures expected during normal operations of tubing string  120 . Fluid pressure fluctuations acting on piston  215  during normal operations are insufficient to cause piston  215  to sever shear pins  490 , and thus actuate disconnect  100 . At the same time, any load applied to disconnect  100  by coiled tubing  105  acts on upper housing member  210 , not piston  215 . Hence, piston  215  is unaffected by the applied loads, and shear pins  490  remain intact. 
         [0046]    Decoupling of upper housing member  210  from lower housing member  205  requires actuation of disconnect  100  and a tension load subsequently applied to upper housing member  205 . Due to the angled nature of spiral splines  440 ,  360  on upper and lower housing members  210 ,  205 , respectively, a tension load applied to disconnect  100  through coiled tubing  105  will cause upper housing member  210  to rotate relative to lower housing member  205  and spiral splines  440  to disengage from spiral splines  360 , unless rotation of upper housing member  210  relative to lower housing member  205  is prevented. Until disconnect  100  is actuated, longitudinal splines  535  on piston  215  remain fully interlocked with longitudinal splines  345 ,  465  on lower and upper housing members  205 ,  210 , and rotation of upper housing member  210  relative to lower housing member  205  is prevented. Hence, spiral splines  440  cannot disengage from spiral splines  360 , and upper housing member  210  cannot be decoupled from lower housing member  205 . Thus, loads applied to disconnect  100  during normal operation of tubing string  120  will not cause actuation of disconnect  100  and decoupling of coiled tubing  105  from BHA  115 . 
         [0047]    In the event that BHA  115  becomes stuck during operation of tubing string  120  and fluid flow through BHA  115  is prevented, fluid pressure within disconnect  100  begins to rise in response. When the pressure of fluid contained within flowbore  235  of disconnect  100  exceeds the burst pressure rating of disc  250 , disc  250  ruptures. Fluid within disconnect  100  is then allowed to flow from flowbore  235  through recirculation port  245  to annulus  160 . Should it become desirable to decouple coiled tubing  105  from BHA  115  so that coiled tubing  105  may be removed from well  110  and the stuck BHA  115  subsequently retrieved, disconnect  100  may be actuated to allow upper housing member  210  to decouple from lower housing member  205  upon application of a tension load to upper housing member  210 . 
         [0048]    To actuate disconnect  100 , a ball is dropped from surface  150  into tubing string  120 . Fluid passing through tubing string  120  carries the ball to disconnect  100  where the ball lands on ball seat  550  of piston  215 . Once seated, the ball prevents further fluid flow into flowbore  540  of piston  215 . As a result, fluid pressure upstream of piston  215  begins to build. When the fluid pressure acting on piston  215  causes piston  215  to exert loads on shear pins  490  in excess of their combined strength, pins  490  shear. Piston  215  then translates in the downhole direction, or further into throughbore  240  of lower housing member  205 , until end  520  of piston  215  abuts shoulder  260  on lower housing member  205 . 
         [0049]    When piston  215  comes to rest against shoulder  260 , longitudinal splines  535  on piston  215  are fully disengaged from longitudinal splines  465  on upper housing member  210 , but remained interlocked with longitudinal splines  345  on lower housing member  205 . Upper housing member  210  is then free to rotate relative to lower housing member  205  and piston  215 , while lower housing member  205  is still prevented from rotational movement due to the engagement of longitudinal splines  345  on lower housing member  205  with longitudinal splines  535  on piston  215 . 
         [0050]    A tension load is then applied to disconnect  100  via coiled tubing  105 . In response, upper housing member  210  is pulled in the uphole direction. Due to the angular nature of spiral splines  440 ,  360  on upper and lower housing members  210 ,  205 , respectively, upper housing member  210  rotates relative to lower housing member  205  until spiral splines  440 ,  360  disengage. Once spiral splines  440 ,  360  disengage, upper housing member  210  is decoupled from lower housing member  205  and returned to the surface  150 . Due to interaction between stop ring  545  on piston  215  and shoulder  475  of upper housing member  210 , piston  215  is retained within throughbore  435  of upper housing member  210  and returned to the surface  150  along with upper housing member  210 . As these components are lifted to the surface  150 , fluid contained within coiled tubing  105  flows through flowbore  435  and recirculation port  480  of upper housing member  210  to annulus  160 . After upper housing member  210 , piston  215  and coiled tubing  105  have been removed from well  110 , BHA  115  with lower housing member  205  coupled thereto may be retrieved via fishing, jarring or other operation. 
         [0051]    The above discussion is meant to be illustrative of the principles and various embodiments of the disclosure. The disclosure is susceptible to embodiments of different forms. It is to be fully recognized that the various teachings of the embodiments discussed may be employed separately or in any suitable combination to produce desired results. Many variations and modifications of the apparatus and methods disclosed herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.