reference will now be made in detail to embodiments of the invention , one or more examples of which are illustrated in the accompanying drawings . each example is provided by way of explanation of the invention , not as a limitation of the invention . it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention . for instance , features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment . thus , it is intended that the present invention cover such modifications and variations that come within the scope of the appended claims and their equivalents . in the description which follows , like parts are marked throughout the specification and drawing with the same reference numerals , respectively . the drawing figures are not necessarily to scale and certain features are shown in schematic form or are exaggerated in scale in the interest of clarity and conciseness . in a conventional drilling operation , a primary wellbore extends into an earth formation for the production of oil and gas . the primary wellbore includes a casing string which is inserted into the wellbore after the wellbore has been drilled . the casing string is generally installed in a wellbore when the well is drilled to target depth or when the sidewalls of the wellbore are in danger of collapsing . if the sidewalls of the wellbore collapse , the wellbore is cased and drilling continues with a smaller drillbit . once the target is reached , a smaller diameter casing or liner is installed to prevent the sidewalls from collapsing . typically , once the casing string is installed , cement is forced down the inside of the casing string and up the annulus to seal the casing to the wellbore and prevent fluids from transiting along the wellbore outside of the casing from one formation to another . a liner is installed within the casing within the primary wellbore . once a production zone has been reached , a production tubing string is installed within the liner to carry hydrocarbons to the surface where such hydrocarbons are recovered and transported to market . near the downhole end of the production tubing string , a production packer assembly is installed to seal a production annular space between the liner and the production tubing string in order to prevent fluids from escaping into other parts of the wellbore or formations and to direct the produced fluids into production tubing . additionally , the production packer assembly ensures the fluids do not flow by the tubing by liner annulus to lower portions of the wellbore . referring to fig1 , at the downhole end of the production tubing string 15 a production packer assembly 24 is utilized to ensure fluids do not flow down liner 14 to lower portions of the wellbore . at the downhole end of the production tubing string 15 and below production packer assembly 24 is a tailpipe 26 . as previously mentioned , it is sometimes desirable to drill a sidetrack well from within a wellbore . for clarity , it should be understood that conventional wells are drilled substantially vertically from the surface downward to or through the producing formation . however , wellbores may be drilled at a slanted or inclined orientation from the vertical axis . likewise , deviation may produce a horizontal orientation . sidetrack wells may extend in any direction from the original well and , in the case of a horizontal wellbore , may extend upward or downward . depicted in fig1 , tailpipe 26 , located at the downhole end of a production tubing string 15 and running below production packer assembly 24 , is interrupted by the installation of a permanent bypass whipstock assembly 62 , which is utilized to assist in the efficient and economical formation of a sidetrack or lateral well . for demonstrative purposes only , and not by way of limitation , the present illustrated embodiments provide for the use of permanent bypass whipstock assembly 62 to form a sidetrack well which exits liner 14 to the right . furthermore , for demonstrative purposes only the permanent bypass whipstock assembly is installed below the deepest production packer assembly , however , the permanent bypass whipstock assembly can be installed in the tailpipe below any production packer assembly . in one embodiment , as shown in fig2 which is a cross - section of fig1 , permanent bypass whipstock assembly 62 generally has a cylindrical shape with a relatively straight primary path 64 slightly offset from liner axis 1 extending therethrough . referring back to fig1 , permanent bypass whipstock assembly 62 preferably includes a thick robust body constructed of a durable material , such as steel , around primary path 64 and potential sidetrack path 66 to resist forces and pressures , such as drill bits , rotating equipment and other downhole insults , likely imposed as equipment is inserted therethrough . permanent bypass whipstock assembly 62 is securely connected to tailpipe 26 at a desired location within the string such that a portion of tailpipe 26 is above permanent bypass whipstock assembly 62 and an additional length of tailpipe 26 extends below permanent bypass whipstock assembly 62 . tailpipe 26 is assembled at the surface with permanent bypass whipstock assembly 62 installed in the desired location and the combined assembly is subsequently installed with the production assembly . in a preferred embodiment , permanent bypass whipstock assembly 62 replaces a section of tailpipe 26 by being screwed or otherwise secured in place . when installed , permanent bypass whipstock assembly 62 is completely open to the path of downhole production , thereby not interfering with the production from the wellbore below the installation of permanent bypass whipstock assembly 62 , as shown in fig2 . in an embodiment , permanent bypass whipstock assembly 62 includes several components , a thin - walled portion and a thick walled portion , as shown in fig1 . in an embodiment of the present invention , thin - walled portion 102 is an elongated piece running the entire length of permanent bypass whipstock assembly 62 . the interior surface of thin - walled portion 102 defines primary path 64 , while the exterior surface is in close proximity with liner 14 . in another embodiment of the present invention , thick - walled portion 104 is located along the peripheral surface opposite thin - walled portion 102 . unlike thin - walled portion 102 , thick - walled portion 104 includes sidetrack path 66 , a whipstock portion 96 , and an optional stabilizing portion 94 . sidetrack path 66 , located above whipstock portion 96 , provides an inclined path by a sidetrack well is ultimately formed . in an alternate embodiment of the present invention , sidetrack path 66 is located below optional stabilizing portion 94 and above whipstock portion 96 in an effort to provide a path for the formation of a sidetrack well . sidetrack path 66 , as shown in fig1 , 3 and 4 , appears to have an angle which is more substantial and dramatic than would perhaps be preferred . the exaggerated or more dramatic angle is drawn so that the angle may be more easily seen by the reader . in the preferred embodiment , the permanent bypass whipstock assembly is quite long and the sidetrack path is also relatively long compared to what is shown in fig3 . the preferred angle is between 1 . 5 to 3 degrees . referring to fig3 , whipstock portion 96 is a wedge shaped member with an inclined surface 95 defining the lower surface of sidetrack path 66 . the inclined surface of whipstock portion 96 follows the natural incline of sidetrack path 66 . the interior wall of whipstock portion 96 follows the natural slightly curved path of tailpipe 26 providing a guiding mechanism for the formation of sidetrack well 60 . additionally , the interior wall of whipstock portion 96 defines primary path 64 of permanent bypass whipstock assembly 62 . the exterior wall of whipstock portion 96 is in close proximity to the wall of liner 14 . in an alternate embodiment of the present invention , an optional stabilizing portion 94 , can be installed above sidetrack path 66 . optional stabilizing portion 94 can have a wedge shape with an inverted trough defined by the upper surface sidetrack path 66 , which follows the natural incline of sidetrack 66 . the interior wall of stabilizing portion 94 defines primary path 64 , following the natural curvature of tailpipe 26 which tailpipe 26 would have followed had it not been interrupted by the insertion of stabilizing portion 94 . the exterior wall of stabilizing portion 94 is also in close proximity to the wall of liner 14 . referring to fig3 , when it is desired to create sidetrack well 60 , a retrievable diverter 72 is inserted to block the primary path 64 of permanent bypass whipstock assembly 62 . retrievable diverter 72 is designed to be installed by a simple wireline tool and recovered in a similar manner a latching mechanism , such as a keyhole 73 . diverter 72 includes a sloped top surface which aligns with the desired location of the sidetrack via a sidetrack path 66 whereby tools inserted through tailpipe 26 are deflected onto sidetrack path 66 . preferably , sidetrack path 66 is a gently sloped path with a circular cross section to provide stability for any tools or rotating equipment to be restrained while in sidetrack path 66 . it is important to recognize that retrievable diverter 73 and permanent bypass whipstock assembly 62 perform completely different functions in the present invention . for example , permanent bypass whipstock assembly 62 allows for complete downhole access when installed , while retrievable diverter 72 eliminates downhole access upon installation of the diverter . after diverter 72 is inserted , a drill string is directed downhole with a milling bit suited for the slow process of milling through the steel liner 14 . bit pressure should be concentrated on the whipstock surface recognizing that diverter 72 and the corresponding surface of sidetrack path 66 of permanent bypass whipstock assembly 62 will direct the milling drillbit against the location of liner 14 where a window is desired for sidetrack wellbore 60 . once the milling bit has fully opened the window , the drillstring is withdrawn and re - installed with a conventional drillbit to drill sidetrack well 60 to its full depth . again , diverter 72 and the corresponding surfaces of sidetrack path 66 of permanent bypass whipstock assembly 62 direct the conventional drillbit to and through the window to form sidetrack 60 . likewise , bit pressure may be applied to the whipstock assembly . any portion of the diverter that encounters drilling loads should be completely separate than the portion of the diverter containing the retrieval mechanism . in an embodiment , the diverter experience limited drilling loads . in another embodiment of the present invention , only the outer circumference of the diverter experience drilling forces . referring now to fig3 & amp ; 4 , when sidetrack well 60 is completely formed , the drillstring is withdrawn and a liner pipe 80 is installed into sidetrack 60 guided downhole by diverter 72 and the corresponding surfaces of sidetrack path 66 of permanent bypass whipstock assembly 62 . upon completion of formation of sidetrack well 60 , including insertion of liner pipe 80 and perforation , if necessary , all of the necessary tools and equipment are removed whereby diverter 72 is retrieved to more fully open up downhole path 64 for further work or production . it is important to recognize that several sidetrack ( multilateral ) wells can be formed in a single primary wellbore using this technique where several permanent bypass whipstock assemblies are installed at various points in the tailpipe string . likewise , the sidetrack ( s ) and existing production can be produced selectively by including a packer and nipple below each permanent bypass whipstock assembly . in an embodiment of the present invention , the production from the sidetrack wellbore is selectively produced by including a packer above the permanent bypass whipstock assembly . in another embodiment , the packer is placed below the permanent bypass whipstock assembly . in yet another embodiment , a packer is placed above the permanent bypass whipstock assembly furthermore , the production from the sidetrack well of the permanent bypass whipstock assembly may contain multiple exit points . permanent bypass whipstock assembly 62 is substantially larger in diameter than tailpipe 26 such that permanent bypass whipstock assembly 62 is in close proximity to liner 14 , thereby reducing the clearance between tailpipe 26 and liner 14 . as such , the permanent bypass whipstock assembly is essentially restricted from lateral movement inside liner 14 due to their relative diameters or sizes . the permanent bypass whipstock assembly reduces the clearance to no more than is necessary to run an additional permanent bypass whipstock assembly and / or packer assembly into the liner , thus eliminating the need for cement by placing the permanent bypass whipstock assembly in close proximity to the liner wall for a single string exit . furthermore , by eliminating the need for cement , the original production below the tailpipe can be produced . finally , the scope of protection for this invention is not limited by the description set out above , but is only limited by the claims which follow . that scope of the invention is intended to include all equivalents of the subject matter of the claims . each and every claim is incorporated into the specification as an embodiment of the present invention . thus , the claims are part of the description and are a further description and are in addition to the preferred embodiments of the present invention . the discussion of any reference is not an admission that it is prior art to the present invention , especially any reference that may have a publication date after the priority date of this application .