Abstract:
The apparatus is a whipstock assembly for use in a wellbore to form a lateral wellbore therefrom. In one aspect, a whipstock is attached to a cutting tool by a shearable connection whereby the whipstock and cutting tool assembly may be run into the wellbore simultaneously. The shearable connection is designed to fail in compression while being able to withstand forces in tension brought about by the whipstock, accessories and extensions required to properly place the whipstock above a preset packer in the wellbore. The shearable connection means consists of two sets of shearable members, one set provides equal shear resistance in tension and in compression, another set provides shear resistance in tension, but not in compression. The resulting connection is stronger in tension than in compression and failure of the connection due to the weight of the whipstock assembly is less likely.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of Ser. No. 09/545,917 filed on Apr. 10, 2000 is now U.S. Pat. No. 6,464,002, issued Oct. 15, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to a downhole milling and drilling assembly, more particularly to a whipstock assembly having a shearable connection with enhanced shear strength in one direction. 
     2. Background of the Related Art 
     In the drilling of oil and gas wells, lateral wellbores are often required to form another wellbore into an adjacent formation, to provide a perforated production zone at a desired level, to provide cement bonding between a small diameter casing and the adjacent formation, or to remove a loose joint of surface pipe. To create the lateral wellbore, milling tools are used for removing a section or a “window” of existing casing from a primary wellbore. The milling tools have cutting blades and typically utilize a diverter such as a whipstock to cause the tool to be moved laterally while it is being moved downwardly and rotating in the wellbore to cut an angled opening, pocket or window in the well casing or a borehole. 
     Formation of a lateral wellbore is typically performed in a step saving manner according to the following steps: An anchoring member or packer is set in a wellbore at a desired location below the location where the lateral wellbore will be formed. The packer acts as an anchor against which tools above it may be fixed in place in the wellbore. The packer typically has a key or other orientation indicating member and the packer&#39;s orientation is checked by running a tool such as a gyroscope indicator into the wellbore. A whipstock/cutter combination tool is then run into the wellbore and landed in the packer whereby the whipstock is oriented in the direction of the desired lateral wellbore. The cutter is connected to the whipstock by a shearable member, like a bolt. In this manner, the cutter and whipstock can be run-in to the well together, saving an additional trip. Pushing on the cutter shears the bolt, freeing the cutter from the tool. Rotation of the string and the cutter can then begin the formation of the lateral wellbore. 
     Multiple lateral wellbores in a well necessitate the setting of a whipstock at various vertical locations in the wellbore. Rather than removing and relocating the packer, extensions are used between the whipstock and the packer to accurately locate the whipstock at that point in the wellbore where the next lateral wellbore will be formed. Depending upon the distance between the packer and the new wellbore, an extension member can add significant weight to the combination tool. In some instances, the weight of the whipstock, stinger, extensions and accessories can exceed the shear strength of the connection member between the cutter and the whipstock, which is designed to shear only upon the placement of weight on the connection from above. For example, in a 5½″ wellbore, a whipstock and stinger typically weighs around 1,000 lbs. and the shear value of the shearable connection between the whipstock and cutter is about 16,000 lbs. An extension and accessories, like a stabilizer, could add 16,000 lbs. to the assembly bringing the weight near the shear value of the connection between the whipstock and cutter. In another example, a 9⅝″ wellbore typically utilizes a whipstock and stinger having a combined weight of 3,000 lbs. The shear value of the connection between the whipstock and cutter in these wells is around 30,000 lbs. Extensions and accessories for a lateral wellbore can weigh as much as 30,000 lbs., bringing the total weight of the assembly over the shear value of the connection. A failure of the shearable connection from tensile force placed upon it from below could result in a loss of the whipstock assembly and/or the packer therebelow and damage to the well. Simply increasing the shear strength of the connection member is not a viable option, since compressive force from above to shear the strengthened connection may not be available, and damage to parts of the assembly may result from the increased force. 
     In addition to the need for enhanced tensile resistance to the shearable connection between the whipstock cutter, there are instances when increased compressive shear strength is needed to prevent a failure of the connection when the assembly is being pushed into a horizontal wellbore against its own weight and friction with the wellbore casing. 
     There is a need therefore for a whipstock assembly with a shearable connection between the cutter and whipstock that can withstand tensile forces applied by the weight of the whipstock assembly. There is also a need therefore for a shearable connection between a whipstock and a cutter which will tolerate greater forces in one direction than in an opposite direction but still fail upon the application of a compressive force from above. There is a further need therefore, for a shearable connection member which has greater strength in tension than in compression. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a whipstock assembly for use in a wellbore to form a lateral wellbore therefrom. In one aspect, a whipstock is attached to a cutting tool by a shearable connection whereby the whipstock and cutting tool assembly may be run into the wellbore simultaneously. Upon compressive force from above, the shearable connection fails and the cutting action can begin. The shearable connection is designed to fail in compression but to withstand forces in tension brought about by the whipstock, accessories and extensions required to properly place the whipstock above a preset packer in the wellbore. In one aspect, the shearable connection means provides a first set of shearable members with equal shear resistance to tensile and compressive forces applied between the whipstock and cutter. Another set of shearable members provide shear resistance against tensile forces between the whipstock and cutter but do not provide shear resistance against compressive forces. The resulting connection is stronger in tension than in compression and failure of the connection due to the weight of the whipstock assembly is less likely. In another aspect of the invention, a retractable finger provides additional shear strength in tension. The retractable finger is spring-loaded and is housed in a slot formed in a lug portion of the whipstock. When the shearable connection is in tension, the finger interferes with a surface formed in the cutter, adding additional shear strength to the connection. When the shearable connection is in compression, the finger folds into the slot, providing no additional resistance against the compressive force. In another aspect of the invention the shearable connection is designed to provide additional shear resistance to compression forces but not to tensile forces applied between the whipstock and cutter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a schematic view showing one embodiment of the whipstock assembly of the present invention in a wellbore. 
     FIG. 2 is a perspective view showing the cutter and whipstock and the shearable connection therebetween. 
     FIG. 3 is a front view of the lug portion of the whipstock illustrating the circular and elongated apertures formed therein. 
     FIG. 4 is a side view, partially in section of the lug portion of FIG.  3 . 
     FIGS. 5-7 are section views taken along lines  5 - 5 ,  6 - 6  and  7 - 7  of FIG.  3  and depicting the circular and elongated apertures in the lug portion. 
     FIG. 8 is a front view, partially in section of the cutter illustrating the apertures formed therein. 
     FIGS. 9-10 are section views taken along lines  9 - 9  and  10 - 10  of FIG.  8 . 
     FIG. 11 is a section view showing the shearable connection during assembly. 
     FIG. 12 is a section view showing the shearable connection prior to shearing. 
     FIG. 13 is a section view showing the shearable connection as the threaded fastener fails. 
     FIG. 14 is a section view showing the shearable connection as the pin fails. 
     FIG. 15 is a section view of an alternative embodiment of the shearable connection prior to shearing. 
     FIG. 16 is a section view of the second embodiment after the shearable connection has failed. 
     FIG. 17 is a front view of an alternative embodiment of the invention depicting apertures formed in the cutter having a horizontal orientation. 
     FIG. 18 is a front view of the outside of the lug portion of the whipstock depicting two elongated apertures and two circular apertures formed therethrough. 
     FIG. 19 is a front view of the shearable connection between the lug portion of the whipstock and the cutter. 
     FIG. 20 is a perspective view of an alternative embodiment of the invention depicting two horizontal slots formed on the inner surface of the lug portion of the whipstock. 
     FIG. 21 is a perspective view showing horizontal ridges formed in the outer surface of the cutter. 
     FIG. 22 is a section view showing the inner action between the horizontal grooves formed in the lug portion and the horizontal ridges formed in the outer portion of the cutter. 
     FIG. 23 is a section view showing the shearable connection upon failure of the threaded member. 
     FIG. 24 is a perspective view of an alternative embodiment of the invention showing a plurality of ridges formed on the inside surface of the lug portion of the whipstock. 
     FIG. 25 is a perspective view showing a plurality of ridges formed on the outer surface of the cutter. 
     FIG. 26 is a section view depicting the inner action between the ridges formed on the inside surface of the lug portion and the outside surface of the cutter. 
     FIG. 27 is a section view showing the shearable connection just after the threaded member has failed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic view of the whipstock assembly  100  of the present invention installed a wellbore  110 . The wellbore is typically lined with pipe  115  but could be an unlined borehole. The whipstock assembly includes a cutter  120  or mill which is disposed on a run in string. The run-in string will ultimately be used to rotate and advance the cutter and form the lateral wellbore. In one example, the cutter is designed to form the entire lateral opening in the wellbore including the removal of the casing and the starting hole in the formation. A whipstock  130  include a concave, slanted portion  135  which cooperates with the cutter  120  to facilitate the formation of a window (not shown) in the wellbore  110 . The whipstock  130  is connected at an upper end to the cutter thereabove by a shearable connection. In the preferred embodiment, the shearable connection is formed between the cutter and lug members  140  formed at the upper end of whipstock  130 . Below the whipstock  130  is an extension  145  having a length to accurately place the whipstock  130  at that vertical location in the wellbore where a new lateral wellbore is to be formed. The extension member extends from the whipstock to a preset packer  150  in the wellbore therebelow. The extensions can vary in length, depending upon the desired placement of the new wellbore and by using extensions of different lengths, the same packer can be used for each new lateral wellbore. 
     In the preferred embodiment, the whipstock cutter, extension and accessories are assembled at the surface of the well and run into the well as one assembly in order to save multiple trips. The extension below the whipstock ensures that the whipstock is located at the desired vertical location in the wellbore. The whipstock is rotationally set in the wellbore by cooperation of a key at the downhole end of the extension with a slot in the preset packer. Thereafter, a compressive force from above, applied upon the cutter, will shear the shearable connection between the cutter and the whipstock, separating the two and permitting the milling operation and the formation of a new lateral wellbore to begin. 
     FIG. 2 is a perspective view showing run-in string  125 , cutter  120  and lugs  140  of whipstock  130 . This shearable connection of the embodiment is made between the lug  140  and the cutter  120 . However, the sharable connection could be between any adjacent portions of the cutter and whipstock. In the embodiment illustrated in FIG. 2, two shearable members provide resistance to both compressive and tensile forces applied between the whipstock and cutter and two shearable members provide resistance only to tensile forces between the whipstock and cutter. FIG. 3 is a view of the inside surface of the lugs  140  and FIG. 4 is a side view thereof. The lugs  140  include a plurality of apertures therethrough which are designed to align with apertures in the cutting member. 
     Each lug  140  includes a first circular aperture  205  extending therethrough and another elongated aperture  210  therebelow terminating at the inside surface of the lug  140  in an elongated shape. FIG. 5, taken along lines  5 - 5  of FIG. 3, depict the circular apertures  205  extending through the lug. As shown in the Figure, the apertures are countersunk at an outside edge  206  to house the head of a threaded member. FIG. 6 depicts the upper portion of elongated apertures  210  taken along lines  6 - 6  of FIG.  3 . FIG. 7, taken along lines  7 - 7  of FIG. 3 depicts the lower portion of the elongated aperture  210  extending through the lug and terminating in an elongated shape at the inside surface thereof. 
     FIGS. 8-10 illustrate the apertures formed in the cutter that cooperate with the apertures formed in the lugs of the whipstock to make up the shearable connection. Specifically, FIG. 8 shows the upper  305  and lower  310  receiving apertures formed in the cutter  120 . In the preferred embodiment, the upper receiving aperture  305  is threaded to receive a threaded fastener and the lower receiving aperture  310  is non-threaded for receipt of a pin member therein. In the embodiment shown, the pin members are held in place by frictional forces between the pin and the aperture. However, the pins could be retained in the apertures by a latching mechanism wherein the pins lock into place through rotation. 
     FIGS. 11-14 are section views depicting the shearable connection between the cutter  120  and the lugs  140  of the whipstock and the shearing of the connection member in the well. Specifically, FIG. 11 depicts the manner in which the connection is assembled with a pin  405  inserted through elongated aperture  210  of lug  140  and into lower receiving aperture  310  of cutter  120 . 
     FIG. 12 illustrates a threaded member  410  inserted through the circular aperture  205  and the lug  140  and into the upper receiving aperture  305  in the cutter after the pin  405  has been inserted thereunder and is free to travel within the elongated aperture  210  formed in the lug  140 . FIG. 12 illustrates the shearable connection between the whipstock lug  140  and the cutter  120  as it would appear in the well prior to shearing of the connection. Specifically, when a tension force is applied between the whipstock and cutter and the lug is pulled downwards in relation to the cutter, both the threaded member  410  and the pin  405  thereunder bear the shear load. In this manner, the strength of the connection is enhanced when the assembly is being lowered into the wellbore and a tensile force is being applied between the whipstock and cutter due to the weight of the whipstock and extensions. 
     FIG. 13 depicts the shearable connection just after a compressive force has been applied to the cutter  120  from above and sheared the threaded member. Specifically, the threaded member  410  has sheared and the cutter  120  has moved down in relation to the lugs  140  of the whipstock. Because the pin  405  is free to travel in the vertical space created by the slot shape, the pin  405  adds no resistive force to the compression force applied between the whipstock and cutter. 
     FIG. 14 depicts the shearable connection after the pin  405  has moved vertically in the slot-shaped aperture and is then sheared by the force of the cutter  120  moving downward in relation to the lug  140 . In this manner, the compressive force necessarily applied between the whipstock and cutter is limited to that force needed to shear only the threaded member  410 . Thereafter, the force needed to shear the pin member is largely supplied by the kinetic energy of the moving cutter  120 . In this manner, the shearable connection strength is not enhanced against a compressive force applied between the whipstock and cutter, but only against a tensile force applied therebetween. 
     FIGS. 15 and 16 show an alternative embodiment of the present invention wherein a spring-biased finger  510  adds strength to the shearable connection against a tensile force but not against a compressive force. FIG. 16 depicts the relationship between the cutter  520 , the whipstock lug  540  and the spring-biased finger  510  prior to failure of the shearable connection. Specifically, a slot  515  is formed on the inside surface of the lug  540  of the whipstock and the spring-biased finger  510  is mounted therein. The finger  510  is biased away from the cutter  520  and prior to failure of the shearable connection, the finger  540  is held within a cutout  525  formed in the outer surface of the cutter  520 . As the whipstock assembly is lowered into the well and tensile forces are acting upon the shearable member, the finger  525  serves to enhance the strength of the shearable connection against tensile forces applied between the whipstock and cutter. 
     FIG. 16 depicts the shearable connection of the embodiment just after failure due to a compressive force applied between the whipstock and cutter. A compressive force has been applied and a threaded member  550  has sheared. Rather than resist the compressive forces, the spring-loaded member  510  has retreated into slot  515  where it no longer interferes with movement between the cutter and whipstock. 
     FIG. 17 is a front view of a cutter  600  showing an alternative arrangement of the shearable connection wherein the apertures are arranged in a horizontal fashion. FIG. 18 is a front view of the outside surface of the lug portion  602  of the whipstock depicting the horizontal arrangement of the apertures including circular apertures  605  and elongated apertures  610 . In operation, the shearable connection provides additional shear strength to tensile forces between the whipstock and cutter but not to compressive forces applied therebetween. FIG. 19 is a front view of the assembled shearable connection between the cutter  600  and the lug portion  602  of the whipstock. 
     FIG. 20 is a perspective view showing another embodiment of the invention wherein the inside surface of the lug portion  700  of the whipstock includes two horizontal grooves  705  formed therein. The grooves  705  extend the entire distance around the inside surface of the lug portion  700  and each groove includes a bottom, upper and lower surface. In the preferred embodiment, the upper surface  708  of each groove is perpendicular to the bottom surface thereof and is designed to interfere with a mating upper surface  752  of a ridge  750  formed on the outer surface of a cutter  730 . The lower surface  710  of the groove  705  is sloped downward and is likewise designed to interact with a mating surface  755  formed on the ridge  750  of the cutter  730 . A single aperture  715  extends through the lug portion  700  and aligns with a threaded aperture  745  formed in the cutter  730 . FIG. 21 is a perspective view of the cutter  730  showing the two ridges  750  formed thereon. The ridges are constructed and arranged to interact with the grooves  705  formed in the lug portion  700  and to create a connection therewith that provides shearable resistance to one force applied between the whipstock and cutter but not to an opposite force. Specifically, the grooves have an upper surface  752  that is perpendicular to the surface of the cutter and is designed to interfere with the upper surface  708  of groove  705 . The lower surface  755  of each ridge  750  is sloped to mate with the lower surface  710  of the groove  705  and minimize interference therebetween. 
     FIG. 22 depicts the shearable connection of the embodiment as it appears prior to the failure of the shearable connection. A single threaded fastener  760  extends between the lug portion  700  and the cutter  730  providing shear resistance to both compressive and tensile forces applied between the whipstock and cutter  730 . The ridges  750  formed on the outer surface of the cutter  730  are housed within the groove  705  formed on the inner surface of the lug portion  700  and the interaction of the mating perpendicular surfaces  708 ,  752  acts to add shear strength to tensile forces applied between the whipstock and cutter  730 . As the whipstock assembly is lowered into a wellbore and prior to the landing of the whipstock or extension into a packer or other anchor, tensile forces present between the whipstock and cutter are born by the groove  705  and ridge  750  members as well as the threaded member  760 . 
     FIG. 23 depicts the shearable connection of the embodiment as the connection fails due to a compressive force between the whipstock and cutter. The threaded member  760  has failed and the cutter  730  has moved down in relation to the lug portion  700 . The mating surfaces of the grooves  705  and the ridges  750  have moved across each other allowing the movement of the cutter  730  in relation to the lug portion. After failure, the cutter is rotated out of alignment with the grooves of the lug portion  700 , allowing the cutter to be raised above the whipstock prior to the commencement of the cutting action. 
     FIG. 24 is a perspective view of another embodiment of the invention showing a plurality of profiles  802  formed in the inside surface of a lug portion  800  of a whipstock. The profiles are horizontal in orientation and extend the entire distance across the inside surface of the lug. Each profile includes an upper surface  810  and a lower surface  805 . In the preferred embodiment, the upper surface  810  of each profile is substantially perpendicular to the surface of the lug portion and the lower surface  805  of each profile is sloped downward. An aperture  807  (not shown) is formed through the lug portion. FIG. 25 is a perspective view of an outer surface of a cutter  855  depicting a plurality of profiles  850  formed thereupon. A threaded aperture  851  is formed in the cutter surface. In the preferred embodiment, each profile formed on the cuter is constructed and arranged to interact with the profiles  802  formed on the lug portion  800  such that the profiles fit together to add shear resistance to a first force between the whipstock and cutter but not to an opposite force therebetween. 
     FIG. 26 is a section view showing the shearable connection of the embodiment prior to failure. A threaded fastener  870  extends through aligned apertures  807 ,  851  in the lug portion  800  and cutter  855 . The profiles  802  formed upon the inner surface of the lug portion  800  engage the profiles  850  formed upon the outer surface of the cutter  855  to create shear resistance to tensile forces applied between the whipstock and cutter as the assembly is lowered into a wellbore. The single threaded fastener  870  provides shear resistance in both directions. FIG. 27 is a section view of the embodiment showing the shearable connection just after failure. The threaded fastener  870  has failed and the cutter  855  has moved down in relation to the lug portion  800  of the whipstock. The matching profiles formed on the lug portion  800  and the cutter  855  have offered little additional resistance to the compressive force between the whipstock and cutter and the connection has failed due to force adequate only to shear the threaded fastener  870 . The design of the shearable connection in this embodiment requires both a shearing and compressive force between the cutter and the whipstock as depicted by arrows A &amp; B in FIG.  27 . 
     The novel design of the shearable connections described herein add additional shear strength to a connection between a cutter and a whipstock assembly in response to a force applied between the whipstock and cutter thereby avoiding unintentional failure of the connection member due to increased weight of the whipstock assembly. At the same time, no additional shearing force is necessary in the opposite direction to separate the cutter from the whipstock in order to begin formation of a lateral wellbore. 
     While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.