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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Priority is claimed from U.S. Provisional Application No. 61/012,479, filed on Dec. 10, 2007. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to well interventions. More specifically, the invention relates to apparatus and method for guiding a downhole tool through a wellbore having wellbore restrictions. 
         [0005]    2. Background Art 
         [0006]    In the extraction of oil and gas from underground reservoirs, it is frequently necessary to insert a downhole tool or an assembly of such tools, e.g., a tool “string”, into a wellbore drilled through the reservoir. It can be difficult to push tool strings, examples of which include well completion strings, workover strings, and logging tool systems to the full depth of the wellbore due to restrictions in the wellbore. Examples of such restrictions include ledges and washouts created during the drilling of the wellbore, during well stimulation, during injection of fluids into the reservoir from the Earth&#39;s surface, or while producing fluids from the underground reservoir to the surface. Ledges and washouts may also be created as a result of collapse of the formation in which the wellbore is drilled, where the flow of fluids from within the wellbore is insufficient to move debris from the collapsed formation to the Earth&#39;s surface. 
         [0007]    When inserting a relatively stiff (“stiff” being defined in terms of bending moment) tool string, e.g., a tubular string or a stiff well logging tool string, into a wellbore, the lower end of the stiff tool string can be prevented from going further into the wellbore if it lands against a washout or ledge formed as explained above. A semi-stiff, spoolable rod, such as described in International Application Publication No. WO 2006/003477, and used to provide services under the service mark ZIPLOG, which is service mark of the assignee of the present invention, may face the same challenge as the stiff tool string when traversing a wellbore with such restrictions. Another challenge related to such spoolable rods is that the well equipment operator cannot visually or otherwise determine if the lower end of the rod is moving or not. Failure to determine such movement while the surface end of the rod is being inserted into the wellbore can cause the equipment operator to continue pushing the rod into the wellbore against a stopped lower end of the rod, causing damage to or failure of the rod. 
       SUMMARY 
       [0008]    In one aspect, a guide tool for mounting onto a downhole tool for use in a wellbore penetrating subsurface formations is provided. The guide tool has a bull nose. The bull nose has a first section with an end for sealing against and engaging a lower end of the downhole tool and a second section axially deflectably coupled to the first section. 
         [0009]    In another aspect, an apparatus for use in a wellbore penetrating subsurface formations is provided. The apparatus comprises a downhole tool and a guide tool having a bull nose. The bull nose has a first section with an end that seals against and engages a lower end of the downhole tool and a second section axially deflectably coupled to the first section. 
         [0010]    Other features and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, described below, illustrate typical examples of the invention and are not to be considered limiting of the scope of the invention, for the invention may admit to other equally effective examples. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
           [0012]      FIG. 1  shows a wellbore penetrating subsurface formations and an apparatus according to the present invention suspended in the wellbore. 
           [0013]      FIG. 2  is a diagram of a portion of the apparatus of  FIG. 1  illustrating a guide tool attached to a lower end of a downhole tool. 
           [0014]      FIG. 3  shows the downhole tool and guide tool in an open hole section of a wellbore in a stopped position. 
           [0015]      FIG. 4  shows the hole finder of the guide tool oriented outwardly in order to allow the downhole tool to continue along the wellbore. 
           [0016]      FIG. 5  shows the downhole tool hung up in a restriction in the wellbore. 
           [0017]      FIG. 6  shows the hole finder back in the neutral position, which allows the downhole tool to continue along the wellbore. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The invention will now be described in detail with reference to a few examples, as illustrated in the accompanying drawings. In describing the examples, numerous specific details may be set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or processes may not be described in detail so as not to unnecessarily obscure the invention and because they would be within the ambit of one of skill in the art. In addition, like or identical reference numerals may be used to identify common or similar elements. 
         [0019]      FIG. 1  shows a wellbore  100  drilled through subsurface formations  102 ,  104 . Subsurface formation  104  may be a hydrocarbon producing formation. The wellbore  100  typically starts with a vertical portion  106 , which can extend anywhere from hundreds to thousands of meters, and gradually or otherwise curves, for example, into a horizontal portion  108 , which can extend for lengths up to several thousand meters. This particular wellbore configuration is meant to serve as an example of possible configurations of a wellbore that may be used with the invention and is not intended to limit the scope of the invention. A pipe or casing  110  extends from the surface  112  to a selected depth in the wellbore  100  and is cemented in place in the wellbore  100 . A wellhead  114  is positioned at the surface  116 , above the wellbore  100 . The wellhead  114  includes various valves to regulate flow of fluids from within the wellbore  100 , as will be familiar to those skilled in the art. The wellhead  114  also enables access into the wellbore  100  for drilling and well intervention, for example. 
         [0020]    In the example illustrated in  FIG. 1 , a wellbore apparatus, generally identified at  118 , extends from the wellhead  114  into the wellbore  100 . The wellbore apparatus  118  includes a downhole tool  120 . In some examples, the downhole tool  120  may be a semi-stiff tool, such as a semi-stiff, spoolable rod, as described in, for example, International Publication No. WO 2006/003477, and as stated in the Background section herein is used to provide services under the service mark ZIPLOG by the assignee of the present invention. As described in the &#39;477 publication, the spoolable rod includes one or more optical fibers encased in a thin metal barrier layer, which in turn is encased in a composite layer. The downhole tool  120  may be coupled to a surface system  122 , which may include, for example, a recording unit, a communications unit, and/or a measurement unit (none of which is shown separately). In other examples, the downhole tool  120  may be a stiff tool string made of wellbore tubulars such as production tubing or drill pipe. The downhole tool  120  may be used for work or intervention in the wellbore  110 . According to the present invention, the wellbore apparatus  118  includes a guide tool  124  attached to the lower end of the downhole tool  120 . As will be explained below, the guide tool  124  guides the lower end of the downhole tool  120  through unexpected restrictions in the wellbore  100 . 
         [0021]      FIG. 2  is a simplified diagram showing the guide tool  124  and the features that enable the guide tool  124  to guide the downhole tool  120  through unexpected restrictions in a wellbore. In the diagram shown in  FIG. 2 , the guide tool  124  includes a bull nose  126  having an upper end  128  that is attached to the downhole tool  120  and a lower end  130  that is free. The shape of the lower end  130  is generally rounded and configured to guide the bull nose  126  through the wellbore and away from restrictions in the wellbore, such as, for example, liner hanger top, ledges, and/or washouts. The shape of the upper end  128  may be similar to that of the lower end  130  and may serve the same purpose as described above when the downhole tool  120  is being pulled out of the wellbore. The bull nose  126  with the rounded upper end  128  and lower end  130  has a capsule shape in a neutral position. The upper end  128  of the bull nose  126  may be attached to the downhole tool  120  via any suitable mechanical gripping arrangement, indicated generally at  135 . In some examples, the mechanical gripping arrangement  135  may be similar to what is used to seal hydraulic tubing in a wellbore, as will be familiar to those skilled in the art. In some examples, the upper end  128  of the bull nose  126  sealingly engages the lower end  125  of the downhole tool  120 , thereby providing a pressure seal barrier that prevents wellbore fluids from entering into an area between the bull nose  126  and downhole tool  120  and the interior of the downhole tool  120 . The upper end  128  may sealingly engage the lower end  125  of the downhole tool  120  via the mechanical gripping arrangement  135 . 
         [0022]    The guide tool  124  may include one or more sensors, shown generally at  132 . In some examples, sensor  132   a  may be a vibration sensor for measuring vibration of the downhole tool  120 . Vibration data from the vibration sensor  132   a  may be sent to the surface and can be interpreted to determine if the downhole tool  120  is moving in the wellbore or not, or to determine the depth of the downhole tool  120  in the wellbore. If the readout of the vibration sensor  132   a  at the surface indicates no vibration, the operator may conclude that the lower end of the downhole tool  120  is not moving and may stop insertion or retraction of the downhole tool  120  into or from the wellbore before physical damage to the downhole tool  120  or wellbore takes place. In other examples, sensor  132   b  may be a temperature sensor for measuring differential temperature in the wellbore. Such differential temperature may be correlated to the depth of the downhole tool  120  in the wellbore. In other examples, sensor  132   c  may be a pressure sensor for sensing pressure external to the guide tool  124  or downhole tool  120 . 
         [0023]    Sensor(s)  132  as described above may be fiber-optic or electrical. In some examples, the guide tool  124  may include a fiber splice, shown generally at  133 , for making connections between an optical fiber(s) in the guide tool  124  and an optical fiber(s) in the downhole tool  120 . In other examples, the guide tool  124  may include an electrical connector (not shown separately) for making electrical connections between electrical components in the guide tool  124  and electrical components in the downhole tool  120 , e.g., where the sensor(s)  132  are electrical. The seal provided at the upper end  128  of the bull nose  126 , as explained above, may function to prevent unwanted fluid from entering into an area where the fiber optic and/or electrical connections are made. 
         [0024]    The bull nose  126  has an upper section  134  including the upper end  128  and a lower section  136  including the lower end  130 . The lower section  136  may be coupled to the upper section  134  via an indexing system, identified generally at  138 . The indexing system  138  provides indexed movement or deflection of the longitudinal axis of the lower section  136  with respect to the longitudinal axis of the upper section  134 . The indexing system  138  can deflect the lower section  136  relative to the upper section  134  through a set of preset angles, e.g., 0°, 45°, 90°, 120°, without decoupling the lower section  136  from the upper section  134 . Deflection is enabled by rotation about the connection area, generally indicated at  139 , between the upper section  134  and the lower section  136 . The indexing system  138  may be, for example, mechanically-activated, pressure-activated, or electrically-activated. In some examples, a mechanically-activated indexing system  138  may be a spring-loaded indexing system that can be activated by adjustment of applied axial load. Such indexing may take the form of a set of J-slots (not shown) such as shown in U.S. Pat. No. 5,433,276 issued to Martain et al. The lower section  136  functions as a “hole finder” that will ensure that the bull nose  126  is oriented toward the continued wellbore in case the bull nose  126  is lodged against a restriction in the wellbore. A restriction in the wellbore is essentially any structure or feature that can stop the downhole tool  120  from progressing along the wellbore. 
         [0025]      FIG. 3  shows the guide tool  124  and attached downhole tool  120  in an open hole section  142  of the wellbore  100 . This example of the open hole section  142  includes a featured called a “washout”  144 . In the example of  FIG. 3 , the downhole tool  120  is stopped from moving along the wellbore  100  by the washout  144 . The well equipment operator at the surface may detect that the downhole tool  120  is no longer moving, for example, by receiving vibration data from the guide tool  124  and interpreting the vibration data. When it is determined that the downhole tool  120  is no longer moving, the operator can take actions to activate the hole finder  136 . The hole finder  136  in the present example can be activated by controlling axial load on the downhole tool  120  from the surface. In some examples, the operator can cause the downhole tool  120  to move upwardly by removing axial load from the downhole tool  120 . Removing axial load from the downhole tool  120  can cause the indexing system ( 138  in  FIG. 2 ) to orient the hole finder  136  to an outward angle with respect to the longitudinal axis of the downhole tool  120 , as shown in  FIG. 4 . In other examples, the operator can increase fluid pressure in the interior of the downhole tool  120  to cause the indexing system  138  to orient the hole finder  136  to an outward angle as described above. With the hole finder  136  oriented outwardly, the operator can move the downhole tool  120  downwardly (i.e., along the wellbore) once again, whereby the hole finder  136  overcomes the washout  144 . 
         [0026]    Referring to  FIG. 5 , orientation of the hole finder  136  after the activation described above may be such that the guide tool  124  becomes lodged in a later restriction  146  (such as a reduced-diameter section) in the wellbore  100 , thereby preventing the downhole tool  120  from advancing along the wellbore  100 . Again, the operator may determine that the downhole tool  120  is no longer moving by, for example, interpreting vibration data sent to the surface from sensors in the guide tool  124 . In some examples, the operator may release the guide tool  124  by moving the downhole tool  120  upwardly as described above, wherein removal of axial load from the downhole tool  120  causes the hole finder  136  to move to the previous angle, which in  FIG. 6  is the centered or neutral position where the hole finder  136  is aligned axially with the downhole tool  120 . In other examples, the operator may cause the hole finder  136  to return to the previous angle (or centered/neutral position) by releasing pressure from the interior of the downhole tool  120 . Once the hole finder  136  is reoriented, the operator can move the downhole tool  120  along the wellbore once again. If the downhole tool  120  hangs up once again in the wellbore  100 , the hole finder  136  can be activated as described above to orient the hole finder  136  to a next outward angle, e.g.,  450  from the previous angle. Activation of the hole finder  136  can be repeated as necessary to engage one or more of a number of different angle settings, for example, 0°, 45°, 90°, and 135° (where 0° may represent the neutral/centered position). 
         [0027]    A guide tool according to the various aspects of the invention may provide a wellbore equipment operator to avoid tool damage, and to continue operations in a wellbore having obstructions with minimum delay. 
         [0028]    While the invention has been described with respect to a limited number of examples, those skilled in the art, having benefit of this disclosure, will appreciate that other examples can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Summary:
A guide tool for mounting onto a downhole tool for use in a wellbore penetrating subsurface formations is provided. The guide tool has a bull nose. The bull nose has a first section with an end for sealing against and engaging a lower end of the downhole tool and a second section axially deflectably coupled to the first section.