Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Sand barrier for a level 3 multilateral wellbore junction The following statement is a full description of this invention, including the best method of performing it known to us: 1A SAND BARRIER FOR A LEVEL 3 MULTILATERAL WELLBORE JUNCTION CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of an earlier filing date from U.S. Provisional 5 Application Serial No. 60/264,371 filed January 26, 2001, the entire disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION A multilateral wellbore system by definition includes at least a primary wellbore and a lateral wellbore extending therefrom. The junction between the primary wellbore and 10 the lateral wellbore in some cases is an avenue for sand and other particulate matter infiltration into the wellbore system which generally results in the entrainment of such particulate matter with the production fluid. Clearly, it is undesirable to entrain particulate matter in production fluid since those particulates would then need to be removed from the production fluid adding expense and delay to a final release of a product. The reasons for 15 particulate infiltration through a junction in a multilateral wellbore are many, including the not entirely controllable window size and shape which is generated by running a milling tool into the primary wellbore and into contact with a whipstock whereafter the mill tool mills a window in the casing of the primary wellbore. The milling process itself is not precise and thus it is relatively unlikely that a precise window shape and size can be 20 produced. Lateral liners run in to extend through a milled window and into a lateral borehole are constructed with regular patterns and sizes at the surface. When a regular pattern at the top of such a liner is seated against a milled window in the downhole environment, it is relatively unlikely that the liner flange will seat correctly in all regions of a milled window. This leaves gaps between the flange of the liner and the milled casing in 25 the primary wellbore resulting in the aforesaid avenue for infiltration of particulate matter to the wellbore system. A device and method capable of reducing the amount of particulate matter infiltrating the wellbore system at a junction in a multilateral wellbore will be beneficial to downhole arts.
2 SUMMARY OF THE INVENTION In one aspect of the invention there is provided a running tool having a dog thereon adapted to automatically move outwardly upon reaching a window in a casing of a wellbore and orient itself by finding a downhole vee in said window. 5 In an advantageous application of the invention, sand and other particulate matter is significantly excluded from junctions in level 3 multilateral wellbore systems by employing a thin walled sleeve having a pre-machined window therein in conjunction with the conventional milling of a window in the primary wellbore casing. The pre-machined window exhibits a known and easily controlled shape and size which 10 lends itself to assurance that a commercially available liner hanger will seal thereagainst since the liner hanger and the sleeve are machined in controlled conditions at the surface for the purpose of sealing with one another. The installation of the sleeve with the pre machined window ensures that at the ID of the wellbore casing, the window surface "seen" by the liner hanger system is one against which the liner hanger system is 15 sealable. The seal of the liner hanger may be by any number of methods, two preferred methods being by an elastomeric seal placed between the flange of the liner hanger and the sleeve, and a metal-to-metal interference fit resulting in deformation of the window sleeve outward during installation of the liner. In addition a hook liner hanger embodiment is disclosed. All of these alternate methods of providing a seal are effective 20 and each has benefits which are attractive for certain applications. The sleeve is preferably swaged at an uphole end thereof, a downhole end thereof, both or in its entirety depending upon the application and desires of the operator. In one embodiment, the casing itself of the primary wellbore is provided with a cylindrical recess capable of receiving the sleeve such that the ID of the sleeve is substantially the same diameter as 25 the ID of the casing. BRIEF DESCRIPTION OF THE DRAWINGS Referring now to the drawings wherein like elements are numbered alike in the several Figures: 3 Figure 1 is a cross-section view of a thin walled sleeve with pre-machined window according to a preferred embodiment; FIG. 2 is a cross-section view of the thin walled sleeve installed on a running tool which is illustrated schematically, the running tool including a locating dog; 5 FIG. 3 is a schematic illustration of the thin walled sleeve installed with the uphole and downhole sections of the sleeve swaged against the ID of the casing; FIG. 4 is an illustration in cross-section of the thin walled sleeve installed in a fully swaged condition against the ID of the casing wherein an alternate casing segment is employed having a recess to accept the thin walled sleeve; 10 FIG. 5 is an illustration similar to FIG. 4 with the lateral liner installed; FIG. 6 is a view of a section of a primary casing with a whipstock installed therein prior to milling the primary casing; FIG. 7 is an illustration similar to FIG. 6 but illustrating the drill bit being run downhole; 15 FIG. 8 illustrates the primary casing after drilling creating a window in the primary casing and a lateral borehole; FIG. 9 illustrates the view of FIG. 8 after the whipstock is removed; FIG. 10 is an illustration of the sleeve being located at the junction interface with a running tool; 20 FIG. 11 illustrates the running tool swaging and uphole end of the thin walled sleeve against the casing ID; FIG. 12 illustrates the sleeve in position within the wellbore; FIG. 13 is a similar view to FIG. 12 with the lateral liner installed therein; FIG. 14 is a schematic view of an alternate embodiment of the sleeve employing an 25 orientation anchor; FIG. 15 is a view of the FIG. 14 embodiment after swedging of the uphole end; and 4 FIG. 16 is a schematic section view of an embodiment employing a hook liner hanger. DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a thin walled sleeve 10 is illustrated having a premachined 5 window 12. Sleeve 10 is preferably constructed of steel with a thickness of from 0.125 inch to 0.250 inch. A preferred thickness of 0.197 inch is selected to facilitate relatively easy swaging yet provide sufficient resiliency in the sleeve to ensure a close proximity of a liner extending therethrough to said sleeve sufficient to facilitate bridging of a particular matter which would otherwise pass between said sleeve and said liner to contaminate produced 10 fluids. In another preferred embodiment the liner is sealed against said sleeve. In a preferred embodiment, bands 13 are positioned around sleeve 10 to aid in sealing and anchoring sleeve 10 against casing 20. Bands 13 are preferably elastomeric. It should be understood that one or more bands 13 may be employed as desired. The bands are visible in FIGS. 1, 2 and 10 but are not visible in other figures because they are compressed 15 between sleeve 10 and the casing of the borehole. FIG. 2 schematically illustrates a running tool 14 on which sleeve 10 is mounted for being run into the hole (not shown). Running tool 14 may be any one of several commercially available running tools capable of releasably retaining a sleeve to be run downhole. Running tool 14 does however include a schematically illustrated locating dog 20 16 unique to applications of the thin walled sleeve 10. Locating dog 16 preferably is mounted on pin 18 which includes a torsional spring (not shown). Locating dog 16 follows an ID of a casing 20 until it reaches a milled window 22 whereat locating dog 16 automatically protrudes through window 22 while running tool 14 proceeds farther downhole. As locating dog 16 reaches a lower vee 24 of window 22, it will orient itself 25 both linearly and rotationally to window 22. Because sleeve 10 is carefully oriented on running tool 14 at the surface to place locating dog 16 in a selected position relative to premachined window 12, the action of locating dog 16 in vee 24 linearly and rotationally orients sleeve 10 to the milled window 22. Once sleeve 10 is oriented properly within the hole, running tool 14 is used to 30 swage an uphole end 26, a downhole end 28 or both 26 and 28 into contact with an ID 30 5 of casing 20. One preferred method for swaging sleeve 10 is to employ an inflatable swaging device incorporated into the running tool. If both uphole end 26 and downhole end 28 are intended to be swaged then preferably two inflatable tools will be utilized simultaneously. FIG. 3 illustrates, schematically, sleeve 10 swaged at uphole end 26 and 5 downhole end 28. Referring to FIG. 4, an alternate construction for new wells is disclosed wherein casing 32 is premachined with a window and includes recess 34 which is of sufficient dimension and configuration to receive a preinstalled sleeve 10 while providing an ID 36 of sleeve 10 which substantially equals ID 38 of casing 32. By employing such casing 32 10 there is no restriction at the junction which might otherwise be problematic with respect to tools passing through the junction. As best illustrated in FIGS. 3 and 4, window 12 in sleeve 10 is preferably of smaller dimension than the window 22 (in FIG. 3) and 42 (in FIG. 4) so that a lateral liner being urged into a sealing engagement at the junction will seal against the ID 36 of sleeve 10 at window 12. 15 Referring to FIG. 5, the depiction of FIG. 4 has been repeated but with a lateral liner installed. Thus, it is illustrated that flange 44 of lateral liner 46 is seated against the window 12 in sleeve 10 and is sealed thereto. It should be noted that at the interface (arrow 48) may be an elastomeric sealing material such as polyurethane or a metal sealing material such as bronze or steel. It should also be noted that it is possible to machine the 20 premachined window 12 slightly smaller than liner 46 to provide an interference fit with the liner 10. Because of the proximity of the sleeve to the liner in the area of the premachined window, sand and other particulate matter from the area of the junction 50 is substantially excluded from the wellbore system. This can be by one of bridging or sealing depending upon the tightness of the liner against the sleeve. 25 Referring to FIGS. 6-13, a sequential illustration of one embodiment for installing the sand device is illustrated. In FIG. 6, casing 20 is illustrated with a whipstock 52 therein oriented and maintained in place by anchor 54. In FIG. 7, a drill string 56 is illustrated being introduced to the downhole environment just prior to contact with whipstock 52. Referring to FIG. 8, a milled window 22 and lateral borehole 58 are illustrated. Referring 30 to FIG. 9, the whipstock 52 has been removed from the wellbore leaving anchor 54 in 6 place. It should be noted that anchor 54 is not required for installation of the sand exclusion device described herein but could be used if desired as a locating device. Referring to FIG. 10, a running tool 14 as described hereinabove has been introduced to the downhole environment and into the vicinity of lateral borehole 58. Dog 16 orients linearly and 5 rotationally to milled window 22. Once dog 16 has landed in vee 24, as described above, the sleeve 10 is swaged with inflatable packer 60 which is illustrated in FIG. 11. Referring to FIG. 12, the swaged sleeve 10 is left in position within the wellbore and anchored to casing 20 with window 12 oriented linearly and rotationally to borehole 58. FIG. 13 illustrates a lateral liner 60 installed with flange 62 firmly seated against sleeve 10 and 10 creating a seal thereagainst with either an elastomeric sealant such as polyurethane, metal to-metal seal or other suitable seal. The above discussed method for orienting rotationally and linearly using dog 16, while a preferred embodiment, is but one embodiment. Another preferred embodiment referring to FIGS. 14 and 15 is to stab into anchor 54 with a running tool 80 having an 15 orientation anchor 82 so that sleeve 10 is orientable to the milled window (not shown in subject figure) based upon the original whipstock anchor 54 and not the vee 24 of the window. The orientation anchor 82 further seals the downhole end and thus removes the need to swage the downhole end of sleeve 10. The uphole end therefore is the only end needing swaging. FIG. 15 illustrates the uphole end swaged as has been previously 20 described herein. In another embodiment referring to FIG. 16, a schematic illustration carrying identical numerals for identical components is provided for understanding of another preferred arrangement where the sand exclusion sleeve 10 is employed in connection with a hook hanger liner 70 having hook 72 to engage with vee 24. Although a flange 44 is not 25 available in this embodiment, an interference fit between liner 70 and sleeve 10 is nevertheless crated which causes the bridging of particulates and thus their exclusion from the junction. It should be noted that while the foregoing method for creating a sand excluding junction is effective, it is only necessary to place the sleeve 10 at a desired location, and 30 run a liner through the premachined winds and into close enough proximity therewith to 7 facilitate bridging of particulate matter. Swaging the sleeve in place is a preferred operation as well. Milling of a window in the primary casing and drilling a lateral borehole may have been accomplished as part of an earlier operation. While preferred embodiments of the invention have been shown and described, 5 various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation. It will be understood that the term "comprises" or its grammatical variants as used herein is equivalent to the term "include" and is not to be taken as excluding the presence 10 of other elements or features.