Abstract:
A technique facilitates sidetracking by eliminating one or more trips downhole. The technique comprises delivering a sidetracking system downhole into a wellbore, and utilizing a component of the sidetracking system to grip a wall of the wellbore. The sidetracking system may comprise a whipstock assembly and a running/stinger assembly in which the stinger assembly is designed for disconnection from the whipstock assembly after delivery downhole. After disconnecting the stinger assembly, the sidetracking system enables delivery of cement slurry down through the stinger assembly to form a cement plug at a desired location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present document is based on and claims priority to U.S. Provisional Application Ser. No. 61/325,068, filed Apr. 16, 2010. 
    
    
     BACKGROUND 
     Embodiments disclosed herein relate generally to whipstocks for sidetracking from a wellbore. In particular, embodiments disclosed herein relate to whipstock systems and methods. 
     Traditionally, whipstocks have been used to drill deviated boreholes from an existing wellbore. A whipstock has a ramped surface that is set in a predetermined position to guide a drill bit or drill string in a deviated manner to drill into the side of the wellbore, which may also be called a sidetrack window or window. In operation, the whipstock is set on the bottom of the existing wellbore, the set position of the whipstock is then surveyed, and the whipstock is properly oriented for directing the drill string in the proper direction. After the whipstock is set, a drill string is lowered into the well into engagement with the whipstock causing the drill string to drill a deviated borehole through a wall of the existing wellbore. 
     Other uses for whipstocks include sidetracking from previously drilled and cased wellbores that have become unproductive. For example, when a wellbore becomes unusable, a new borehole may be drilled in the vicinity of the existing cased wellbore or, alternatively, a new borehole may be sidetracked from the serviceable portion of the existing, cased wellbore. Sidetracking from a cased wellbore also may be useful for developing multiple production zones. This procedure can be accomplished by milling through the side of the casing with a mill that is guided by a wedge or whipstock component. After a milling or drilling procedure is completed, the whipstock may be removed from the wellbore. 
     Cement plugs may be set in the wellbore in sidetracking operations to prevent hydrocarbons or other fluids from lower sections of the wellbore seeping up past the whipstock location. The cement plug is set below the whipstock to isolate lower sections of the wellbore. Typically, a cement plug may be set during a first trip into the wellbore, after which the whipstock may be run into the wellbore in a second trip. Accordingly, existing operations employ two or more trips downhole. 
     SUMMARY 
     In general, the present invention provides a system and method to facilitate sidetracking by eliminating one or more trips downhole. The technique comprises delivering a sidetracking system downhole into a wellbore, and utilizing a component of the sidetracking system to grip a wall of the wellbore. The sidetracking system may comprise a whipstock assembly and a stinger assembly in which the stinger assembly is designed for disconnection from the whipstock assembly after delivery downhole. After disconnecting the stinger assembly, the sidetracking system enables delivery of cement slurry down through the stinger assembly to form a cement plug at a desired location in the same trip downhole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a cross-sectional view of a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 2  is an enlarged cross-sectional view of a portion of the sidetracking system illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic illustration of another example of a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 4  is a schematic illustration of another example of a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 5  is a schematic illustration of another example of a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 6  is a cross-sectional view of a burst sub assembly which may be employed in a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 7  is a cross-sectional view taken generally along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is a cross-sectional view taken generally along line  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a cross-sectional view of another example of a burst sub assembly which may be employed in a sidetracking system in accordance with embodiments of the present disclosure; 
         FIG. 10  is a cross-sectional view taken generally along line  10 - 10  of  FIG. 9 ; and 
         FIG. 11  is a cross-sectional view taken generally along line  11 - 11  of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to a system and methodology designed to facilitate sidetracking operations in which one or more lateral wellbores are formed with respect to another wellbore, e.g. with respect to a vertical wellbore. According to one aspect, certain embodiments disclosed herein relate to a sidetracking system including a whipstock assembly having a central bore therethrough and an expandable anchor assembly configured to be hydraulically actuated and set at a specific depth in a wellbore. The sidetracking system also may comprise a removable flow blocking member, e.g. a burst disc, to restrict a fluid flow and to increase a pressure in the central bore to actuate the expandable anchor, e.g. expandable slips and/or packer. The sidetracking system enables setting of the whipstock and creation of a cement plug in a single trip downhole into the wellbore. 
     Referring generally to  FIGS. 1 and 2 , cross-sectional views are provided of a sidetracking system  100  having a central bore  102  therethrough in accordance with embodiments of the present disclosure. In the embodiment illustrated, the sidetracking system  100  comprises a whipstock assembly  104  having an expandable anchor assembly  106  attached below the whipstock assembly. The whipstock assembly  104  comprises a sidetracking slide or ramp  105  formed to facilitate drilling of a sidetracked window and lateral wellbore. The whipstock assembly  104  may be oriented about a central axis  101  in any direction (i.e. 360°) so that a sidetracked wellbore may be drilled in a desired direction. 
     The expandable anchor assembly  106  may be attached to the whipstock assembly  104  via a threaded connection  111 . Alternatively, other types of connections also may be used. The expandable anchor assembly  106  comprises multiple slips  107  that may be expanded radially outward to engage a surrounding wellbore wall, such as a formation wall or casing. Engagement of the slips  107  with the surrounding wellbore wall anchors the sidetracking assembly  100  at the desired location in the wellbore. The slips  107  may be hydraulically actuated by increasing the pressure on fluid within the central bore  102  to cause the slips  107  to expand radially outward. However, the slips  107  may be actuated by other techniques, e.g. mechanical actuation. 
     A sub  108  of the sidetracking system  100  may be constructed as a burst sub having a removable member, e.g. a burst disc  112 . By way of example, the sub  108  may be attached to a lower end of the expandable anchor assembly  106 . The burst disc  112  enables the increasing of pressure in the central bore  102  to actuate the expandable anchor assembly  106 . In this example, the sub  108  contains any type of burst disc  112  or other type of pressure control device having a membrane or restriction configured to fail at a predetermined pressure. As an alternative, the sub  108  can contain a piston-type shear release mechanism or other suitable mechanism to release the pressure at a predetermined level. 
     Integration of the expandable anchor assembly  106  and the burst sub  108  with the whipstock assembly  104  enables the sidetracking system  100  to be located at any depth in a wellbore because the expandable anchor assembly  106  may be set at any desired location or wellbore depth. Thus, the sidetracking system  100  is capable being disposed in a wellbore at locations other than a bottom of the wellbore and other than the top of a stationary object, e.g. a “fish”, in the wellbore. 
     Referring again to  FIGS. 1 and 2 , methods of using the sidetracking system  100  in accordance with embodiments disclosed herein include running the sidetracking system  100  into the wellbore to a specified location or depth of the wellbore. As the sidetracking system  100  is run into the wellbore, fluid is circulated above the whipstock assembly  104  through a pass valve (circulating valve) (not shown) for measurement-while-drilling (“MWD”) purposes, e.g. to find a particular desired wellbore direction for sidetracking. Physical properties of the sidetracking system, such as bore pressure, temperature, and wellbore trajectory may be measured while running the sidetracking system  100  into the wellbore. Those skilled in the art will be familiar with MWD operations and methods of using the collected data to orient the sidetracking apparatus in the wellbore. Based on the MWD data taken from the wellbore, the whipstock assembly  104  may be oriented in a wellbore so the sidetracking ramp  105  faces a direction in which the sidetracked wellbore will extend. In alternate embodiments, a gyro orienting system may be employed to orient the whipstock assembly  104  in the wellbore, e.g. in a vertical wellbore. 
     Subsequently, an operator may increase pressure in the central bore  102  of the sidetracking system  100  by pumping a fluid into the central bore  102  and/or by cycling pumps to close the bypass valve. In certain embodiments, the fluid may be a drilling fluid. In alternate embodiments, the fluid used maybe a separate actuation fluid from a separate fluid source. If a separate actuating fluid is used, the separate actuating fluid is isolated by, for example, a running tool and a running tool piston (not shown). The fluid flows down the central bore to the burst disc  112  (or other blocking member), which prevents the fluid from flowing further and thus allows a pressure increase in the central bore  102 . The pressure increase is used to hydraulically actuate the multiple slips  107  of the expandable anchor assembly  106 . For example, the pressure causes slips  107  to radially expand and engage the surrounding wellbore wall. Depending on the type of anchor assembly  106 , various hydraulic pressure increases may be applied in the central bore  102  to force the slips  107  into proper engagement with the surrounding wellbore wall and thus to set the expandable anchor assembly  106  at the desired wellbore location. 
     After slips  107  are radially expanded and engaged with the surrounding wellbore wall, e.g. formation or casing, and the sidetracking system  100  is properly set in the wellbore, the burst disc  112  in burst sub  108  may be ruptured through application of additional pressure. This allows the cementing operation to commence to form a cement plug in the wellbore below the sidetracking system  100 . In some applications, the burst disc  112  may be ruptured by exerting an axial force downward on the whipstock assembly  104  in a manner which causes shear pins  109  and  110  to fail. By way of example, shear pin  109  may be designed to fail first followed by failure of shear pin  110 . As described in greater detail below, the shearing of shear pins  109 ,  110  (or other suitable release member) may be used to release a running assembly, e.g. stinger assembly,  114  prior to pumping cement down through central bore  102 . This ensures easy retrieval of the running assembly  114  following the cementing operation. The cementing operation is designed to form and set a cement plug in the wellbore below or adjacent the sidetracking system  100  to isolate a lower section of the wellbore from the sidetracking region at which the lateral wellbore is formed. Following cementing, a drill string having a drill bit is conveyed downhole into engagement with a whipstock of the whipstock assembly  104 . Once the drill string is downhole, the drilling operation may be commenced to form a sidetracked well with the aid of the whipstock assembly  104 . 
     Embodiments of the present disclosure provide a sidetracking system that can simultaneously set a whipstock assembly and a cement plug in a single trip into the wellbore. The sidetracking system may be used at any location or depth of the wellbore, as opposed to conventional sidetracking devices that must be located either at a bottom of the wellbore or on top of a stationary object. By decreasing the number of trips into the wellbore, the time and costs associated with drilling deviated wellbores is decreased. 
     Referring generally to  FIG. 3 , another embodiment of the sidetracking system  100  is illustrated. In this embodiment, the sidetracking system  100  is illustrated as disposed in a wellbore  116 . The sidetracking system  100  comprises whipstock assembly  104  having a whipstock  118  comprising the sidetracking slide or ramp  105 . The whipstock assembly  104  also may comprise a variety of other components  120 , such as an anchor spacer  122 . The whipstock assembly  104  and the entire sidetracking system  100  may be conveyed downhole into the wellbore  116  via stinger assembly  114 . In this embodiment, stinger assembly  114  comprises a setting tool  124  coupled to whipstock  118 . The stinger assembly  114  also comprises a stinger  126  which extends down into whipstock assembly  104  to deliver a cement slurry along the central bore  102  for forming the cement plug at a desired location along wellbore  116 . The stinger assembly  114  is secured to whipstock assembly  104  or to another suitable component by a release mechanism  127 , such as the shear pins  109  and/or  110  described with reference to  FIG. 1 . However, other types of release mechanisms  127 , e.g. latches, may be employed. 
     In this embodiment, the sidetracking system  100  further comprises expandable anchor  106  which may be coupled to anchor spacer  122  beneath whipstock assembly  104 . The expandable anchor assembly  106  comprises expandable slips  107  which may be selectively expanded against a surrounding wall  128  of wellbore  116  to secure the sidetracking system  100  at a desired location along the wellbore  116 . By way of example, the expandable slips  107  may be expanded hydraulically by pressurizing fluid within central bore  102  against a flow restriction member  130  which may be positioned in a burst sub  132 . The flow restriction member  130  may comprise burst disc  112  or other suitable flow restriction members, such as a ball dropped onto a ball seat in the burst sub  132 , as discussed in greater detail below. The burst sub  132  may be located below expandable anchor  106 . 
     As illustrated, a tail pipe  134  may be positioned below expandable anchor  106  to direct cement slurry to the desired wellbore location for forming of a cement plug  136 . By way of example, the tail pipe  134  is coupled to a lower end of the burst sub  132 , although other components may be incorporated into this design. The length of tail pipe  134  may be selected according to the desired placement of cement plug  136 . It should be noted, however, that sidetracking system  100  may have a variety of configurations and utilize a variety of components to place the cement plug  136  at other desired locations along wellbore  116 . For example, sidetracking system  100  may be utilized to place the cement plug  136  at a bottom of the wellbore or at any of a variety of locations along wellbore  116  separate from the bottom of the wellbore. 
     In operation, the sidetracking system  100  illustrated in  FIG. 3  is initially run in hole to a desired setting depth. The whipstock  118  is then oriented with a measurement-while-drilling system or a gyro system, as discussed above. Once oriented, pressure is increased along the central bore  102  to set the expandable anchor  106  which secures the sidetracking system  100  at the desired location along wellbore  116 . After setting the expandable anchor  106 , the pressure in central bore  102  is increased to fracture or otherwise remove the flow restriction member  130 , thus allowing flow of cement slurry down through the sidetracking system. 
     The stinger assembly  114  is then disconnected from the whipstock assembly  104  by releasing the setting tool  124  from the whipstock  118 . The release of setting tool  124  may be achieved by separating, e.g. shearing, release mechanism  127  which may be in the form of a suitable shear member, e.g. shear pins  109 ,  110 . However, other types of release mechanisms  127  may be employed to enable selective separation of stinger assembly  114  from the portion of sidetracking system  100  which remains downhole. Following separation of the stinger assembly  114 , cement is pumped down through stinger  126  and through the sidetracking system  100  to establish cement plug  136  at the desired location within wellbore  116 . After the cement is pumped, the stinger assembly  114 , including setting tool  124  and stinger  126 , is tripped out of the hole and removed. At this stage, a drilling assembly may be conveyed downhole into engagement with whipstock  118  of whipstock assembly  104 . The ramp  105  is designed to support the drilling assembly and to direct the assembly laterally to facilitate sidetracking and formation of the desired lateral wellbore. By way of example, the ramp  105  of whipstock  118  may be concave and formed from a hard material, such as steel. The ramp  105  also may be angled at a desired angle, e.g. up to 3°, designed to achieve the planned sidetracking transition in forming the lateral wellbore. 
     Referring generally to  FIG. 4 , another embodiment of the sidetracking system  100  is illustrated. In this embodiment, the sidetracking system  100  may again be disposed in wellbore  116 . The sidetracking system  100  similarly comprises whipstock assembly  104  having whipstock  118  and sidetracking ramp  105 . The whipstock assembly  104  and the entire sidetracking system  100  may be conveyed downhole into the wellbore  116  via stinger assembly  114 . In this embodiment, stinger assembly  114  again comprises setting tool  124 , coupled to whipstock  118 , and stinger  126 . Stinger  126  extends down into whipstock assembly  104  to deliver a cement slurry along the central bore  102  for forming the cement plug at a desired location along wellbore  116 . The stinger assembly  114  is secured to whipstock assembly  104  or to another suitable component by the release mechanism  127 , e.g. a shear mechanism which may be in the form of shear pins  109  and/or  110 . 
     In this embodiment, however, the expandable anchor  106  is in the form of a packer  140 , such as an inflatable packer, positioned below whipstock assembly  104 . The packer  140  is designed to seal against the surrounding wellbore wall  128  to provide a platform on which cement plug  136  may be formed at a desired location above the bottom of wellbore  116 . In the specific example illustrated, the whipstock assembly  104  and packer  140  are separated by additional components, such as an intermediate tail pipe  142  and a circulation sub  144 . The tail pipe  142  may be selected to facilitate positioning of the cement plug at a desired location along the wellbore  116 . The circulation sub  144  comprises one or more ports  146  through which cement slurry is expelled to create the cement plug. The ports  146  may initially be blocked by suitable blocking members  148 , such as burst discs. It should be noted that expansion of packer  140  may be achieved according to a variety of methods depending on the specific type of packer selected. For example, the packer  140  may be a swell packer, a mechanically actuated packer, an inflatable packer, or other suitable seal members designed to form a seal between the sidetracking system  100  and the surrounding wellbore wall  128 . If pressurized fluid is needed to inflate packer  140 , a burst sub  132  may be positioned below the packer or a ball and ball seat may be incorporated into the inflatable packer. 
     The embodiment illustrated in  FIG. 4  provides reliable spotting of the cement plug location even when the cement plug is located significantly off-bottom. Furthermore, the packer  140  is able to provide additional isolation even if the cement plug  136  has integrity issues, e.g. honeycombing. This type of design also enables use of a shorter cement plug which, in turn, requires less tail pipe and less cement to create greater efficiencies with respect to the sidetracking operation. 
     In operation, the sidetracking system  100  illustrated in  FIG. 4  is initially run in hole to a desired setting depth. The whipstock  118  is then oriented with a measurement-while-drilling system or a gyro system. Once oriented, the packer  140  is expanded against the surrounding wellbore wall. By way of example, a ball may be dropped to block flow along central bore  102  which allows the pressure to be increased to set an inflatable packer. Pressure is then increased further to open flow through ports  146  by, for example, fracturing blocking members  148 , e.g. rupture discs. 
     The stinger assembly  114  is then disconnected from the whipstock assembly  104  by releasing the setting tool  124  from the whipstock  118 . The release of setting tool  124  may be achieved by, for example, shearing the release member  127  which may be in the form of shear pins  109 ,  110 . However, other types of release mechanisms  127  may be employed to enable selective separation of stinger assembly  114  from the portion of sidetracking system  100  which remains downhole. Following separation of the stinger assembly  114 , cement is pumped down through stinger  126  and through the sidetracking system  100  until flowing outwardly through ports  146  to a location above packer  140 . This enables the cement plug  136  to be established at a location above the packer. After the cement is pumped, the stinger assembly  114 , including setting tool  124  and stinger  126 , is tripped out of the hole and removed. At this stage, a drilling assembly may be conveyed downhole to begin the sidetracking stage of operation in which the lateral wellbore is drilled. 
     Referring generally to  FIG. 5 , another embodiment of the sidetracking system  100  is illustrated. In this embodiment, the sidetracking system  100  may again be disposed in wellbore  116 . The sidetracking system  100  similarly comprises whipstock assembly  104  having whipstock  118  and sidetracking ramp  105 . The whipstock assembly  104  and the entire sidetracking system  100  may be conveyed downhole into the wellbore  116  via stinger assembly  114  which comprises setting tool  124  and stinger  126 . The stinger  126  again extends down into whipstock assembly  104  to deliver a cement slurry along the central bore  102  to form the cement plug at a desired location along wellbore  116 . The stinger assembly  114  may again be secured to whipstock assembly  104  or to another suitable component by the release mechanism  127 , e.g. a shear mechanism which may be in the form of shear pins  109  and/or  110 . 
     In this embodiment, however, the expandable packer  140 , e.g. an inflatable packer, is combined with another expandable anchor  150 . The expandable anchor  150  may be constructed in a variety of configurations, but one suitable embodiment utilizes a plurality of slips  152  which may be expanded against the surrounding wellbore wall  128 . Expandable anchor  150  may be similar to that described above with respect to the expandable anchor assembly  106  utilized in the embodiments of  FIGS. 1-3 . The packer  140  is designed to seal against the surrounding wellbore wall  128  to provide a platform on which cement plug  136  may be formed at a desired location above the bottom of wellbore  116 . However, the additional expandable anchor  150  helps support the sidetracking system  100  at the desired location within wellbore  116 . 
     In the specific example illustrated, the expandable anchor  150  is located below whipstock assembly  104  and separated from the whipstock assembly  104  by anchor spacer  122 . The burst sub  132  with flow restriction member  130  may be positioned beneath the expandable anchor  150  and above inflatable packer  140 . The expandable anchor  150  and packer  140  also may be separated by additional components, such as the intermediate tail pipe  142  and the circulation sub  144 . The tail pipe  142  may be selected to facilitate positioning of the cement plug at a desired location along a wellbore. As described above, the circulation sub  144  may comprise one or more ports  146  through which cement slurry is expelled to create the cement plug. The ports  146  may initially be blocked by suitable blocking members  148 , such as burst discs. It should again be noted that expansion of packer  140  may be achieved according to a variety of methods depending on the specific type of packer selected. For example, the packer  140  may be a swell packer, a mechanically actuated packer, an inflatable packer, or other suitable seal member designed to form a seal between the sidetracking system  100  and the surrounding wellbore wall  128 . If pressurized fluid is needed to inflate packer  140 , a burst sub  132  may be positioned below the packer or a ball and ball seat may be incorporated into the inflatable packer. 
     The embodiment illustrated in  FIG. 5  utilizes expandable anchor  150  to provide primary support, while the packer  140  can serve as a secondary supporting member. Furthermore, the packer  140  is able to provide additional isolation even if the cement plug  136  has integrity issues, e.g. honeycombing. This type of design also provides for reliable space out of the cement plug  136  especially when setting the plug off the bottom of the well. This design also enables use of a shorter cement plug which, in turn, requires less tail pipe and less cement to create greater efficiencies with respect to the sidetracking operation. 
     In operation, the sidetracking system  100  illustrated in  FIG. 5  is initially run in hole to a desired setting depth. The whipstock  118  is then oriented with a measurement-while-drilling system or a gyro system. Once oriented, pressure is increased in central bore  102  to set the expandable anchor  150 . After setting expandable anchor  150 , the pressure is further increased to open flow through burst sub  132  by removing, e.g. fracturing, the flow restriction member  130 . The packer  140  is then expanded against the surrounding wellbore wall by, for example, dropping a ball to block flow along central bore  102  which allows the pressure to be increased to set an inflatable packer. However, packer  140  may have a variety of other configurations and may be set according to other techniques. Pressure is then increased further to open flow through ports  146  by removing port blocking members  148 , e.g. fracturing rupture discs. 
     The stinger assembly  114  is then disconnected from the whipstock assembly  104  by releasing the setting tool  124  from the whipstock  118 . The release of setting tool  124  may be achieved by, for example, shearing the release member  127  which may be in the form of shear pins  109 ,  110 . However, other types of release mechanisms  127  may be employed to enable selective separation of stinger assembly  114  from the portion of sidetracking system  100  which remains downhole. Following separation of the stinger assembly  114 , cement is pumped down through stinger  126  and through the sidetracking system  100  until flowing outwardly through ports  146  to a location above packer  140 . After the cement is pumped, the stinger assembly  114 , including setting tool  124  and stinger  126 , is tripped out of the hole and removed. At this stage, a drilling assembly may be conveyed downhole to begin the sidetracking stage of operation in which the lateral wellbore is drilled. It should be noted that in each of these embodiments, the stinger assembly  114  is separated from the whipstock assembly  104  prior to pumping cement to create the cement plug  136 . In many applications, this technique can be extremely helpful in avoiding retrieval problems with respect to the setting tool  124  and stinger  126 . 
     The design, configuration, and arrangement of components within each embodiment of the sidetracking system  100  can vary to suit the parameters or requirements of a given sidetracking operation. For example, a variety of burst subs  132  may be utilized for controlling flow of drilling fluid through the sidetracking system  100  and for controlling actuation of expandable anchors or other devices. 
     Referring generally to  FIGS. 6-8 , an alternate embodiment of burst sub  132  is illustrated. As described above, the burst sub  132  may incorporate a rupture or burst disc, such as burst disc  112 . However, the embodiment illustrated in  FIGS. 6-8  provides an alternate burst sub  132  which utilizes a ball drop shear barrel assembly  154  having an internal flow through passage  155 . The burst sub  132  comprises a sub housing  156  having an internal flow path  158  which is part of the central bore  102  through which cement slurry may be passed. 
     The internal flow path  158  is defined by an internal surface  160  which is designed with a shoulder  162 . The shoulder  162  receives a manifold  164  which carries the ball drop shear barrel assembly  154 . The manifold  164  is secured against shoulder  162  by a retention ring  166 , and the ball drop shear barrel assembly  154  is removably secured within manifold  164 . In the example illustrated, the ball drop shear barrel assembly  154  is temporarily secured to manifold  164  by a plurality of shear members  168 , as illustrated best in  FIGS. 7 and 8 . The shear members  168  may comprise shear screws threaded into ball drop shear barrel assembly  154 . 
     In the embodiment illustrated, burst sub  132  further comprises a debris screen  170  positioned in internal flow path  158 . The debris screen  170  may be sized to separate debris of a specific size. Additionally, the burst sub  132  may have a variety of connection ends designed for engagement with other components of the sidetracking system  100 . For example, an upper end of the sub  132  may be in the form of a box end  172  having an internal, threaded connector  174  designed for engagement with the lower end of expandable anchor  106 , with expandable anchor  150 , or with other system components. On an opposite end, the burst sub  132  may comprise a pin end  176  having an externally threaded connector  178  similarly designed for connection with adjacent components in a variety of embodiments of the sidetracking system  100 . 
     In operation, the internal flow passage  155  of ball drop shear barrel assembly  154  may be left open during tripping of the sidetracking system  100  downhole to allow free flow of well fluid therethrough. Once the system  100  is at the desired position and ready for increased pressure, a ball  180  is dropped onto an upper ball seat  181  of the ball drop shear assembly  154  to create flow restriction member  130  (see  FIG. 8 ), thereby enabling increased pressure along central bore  102  to actuate, for example, the expandable anchor. Subsequently, the pressure may be further increased to shear off shear members  168  so that ball  180  and ball drop shear barrel assembly  154  release and flow down through the sidetracking system to clear a path for the cement slurry used to form cement plug  136 . In other embodiments, the ball drop shear barrel assembly  154  may incorporate a burst disc or other shear mechanism which fractures at a lower pressure than the shear members  168  to enable application of two different pressure levels. 
     Referring generally to  FIGS. 9-11 , another alternate embodiment of burst sub  132  is illustrated. In this embodiment, many of the components are similar to components described with reference to  FIGS. 6-8  and are labeled with the same reference numerals. The embodiment illustrated in  FIGS. 9-11  provides an alternate burst sub  132  which utilizes flow restriction member  130  in the form of a barrel  182  which is secured within manifold  164  to block a flow path  184  through the manifold  164 . In this similar embodiment, the burst sub  132  comprises sub housing  156  which includes internal flow path  158  as part of the central bore  102 . 
     The internal flow path  158  is again defined by internal surface  160  having shoulder  162  to receive manifold  164  which is secured against shoulder  162  by retention ring  166 . The barrel  182  is removably secured within manifold  164  by a plurality of shear members  168 , as illustrated best in  FIGS. 10 and 11 . By way of example, the shear members  168  may comprise shear screws threaded into barrel  182 . 
     In this latter embodiment, burst sub  132  also may comprise debris screen  170  positioned in internal flow path  158 . The latter alternate embodiment of burst sub  132  also may have a variety of connection ends designed for engagement with other components of the sidetracking system  100 . For example, box end  172  may be located at an upper end of the burst sub  132 , and pin end  176  may be located at a lower end of the burst sub. 
     In operation, the flow passage  184  within mandrel  164  is blocked by barrel  182  during tripping of the sidetracking system  100  downhole. Once the system  100  is at the desired wellbore position, pressure may be immediately increased to set the expandable anchor and/or other components. Subsequently, the pressure may be further increased to shear off shear members  168  so that the barrel  182  is removed to provide a path for the cement slurry used to form cement plug  136 . 
     Additional types of flow control subs  132  may be incorporated into the sidetracking system  100 . Similarly, different numbers of expandable anchors and flow control subs may be employed depending on the requirements of a given application and on the number of tools to be actuated in preparing the well for a sidetracking operation. Various seal members, e.g. inflatable packers, may be employed to facilitate creation of cement plugs at many locations along the wellbore above the bottom of the wellbore. However, other sidetracking applications may benefit from creating a cement plug at the bottom of the wellbore. In some applications, the system enables cementing and drilling of the lateral wellbore at substantially the same time. By way of further example, the cement slurry may be delivered to fill a region surrounding at least a portion of the whipstock  118 . The components and configurations of the sidetracking system  100  can be adjusted accordingly to accommodate these various sidetracking applications. 
     Although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.