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INCORPORATION BY REFERENCE  
       [0001]     The present application incorporates by reference the entire disclosures of U.S. Pat. No. 6,003,606 (entitled “PULLER-THRUSTER DOWNHOLE TOOL”); U.S. Pat. No. 6,347,674 (“ELECTRICALLY SEQUENCED TRACTOR”); U.S. Pat. No. 6,241,031 (“ELECTRO-HYDRAULICALLY CONTROLLED TRACTOR”); U.S. Pat. No. 6,679,341 (“TRACTOR WITH IMPROVED VALVE SYSTEM”); U.S. Pat. No. 6,464,003 (“GRIPPER ASSEMBLY FOR DOWNHOLE TRACTORS”); and U.S. Pat. No. 6,715,559 (“GRIPPER ASSEMBLY FOR DOWNHOLE TRACTORS”). The present application also incorporates by reference the entire disclosures of U.S. Patent Application Publication Nos. 2004/0168828 (“TRACTOR WITH IMPROVED VALVE SYSTEM”); and 2005/0247488 (“ROLLER LINK TOGGLE GRIPPER AND DOWNHOLE TRACTOR”). The present application also incorporates by reference the entire disclosure of U.S. Provisional Patent Application No. 60/781,885, filed Mar. 13, 2006 (“EXPANDABLE RAMP GRIPPER”). 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to tools for conducting operations within passages, and specifically to tools for borehole intervention and/or drilling.  
         [0004]     2. Description of the Related Art  
         [0005]     U.S. Pat. No. 6,003,606, entitled “Puller-Thruster Downhole Tool,” discloses an innovative self-propelled tool or tractor for drilling, completion, stimulation, and intervention that pulls a drill string and simultaneously thrusts itself and its payload downhole and/or into a casing or borehole formation. The &#39;606 patent discloses a tractor that includes one or more gripper assemblies (e.g., bladders or packerfeet) that grip onto an inner surface of a borehole or casing, and one or more propulsion assemblies that propel the tractor body forward when at least one of the gripper assemblies is gripping the borehole. A valve system directs a fluid (e.g., drilling mud, intervention fluid, hydraulic fluid) to and from the gripper assemblies and propulsion assemblies to power movement of the tractor.  
         [0006]     The &#39;606 patent discloses two basic types of tractor configurations—open loop and closed loop. The open loop system uses an externally provided fluid as a medium of hydraulic communication within the tractor. The open loop consists of a ground surface pump, tubing extending from the pump into a borehole, a tractor within the borehole and connected to the tubing, and an annulus between the exterior of the tractor and an inner surface of the borehole. The fluid is pumped down through the tubing to the tractor, used by the tractor to move and conduct other downhole operations, and then forced back up the borehole through the annulus. The tractor is powered by differential pressure—the difference of the pressure at the point of intake of fluid to the tractor and the pressure of fluid ejected from the tractor into the annulus. In the open loop system, a portion of the fluid is used to power the tractor&#39;s movement and another portion of the fluid flows through the tractor for various downhole purposes, such as hole cleaning, sand washing, acidizing, and lubricating of a drill bit (in drilling operations). Both portions of the fluid return to the ground surface through the annulus.  
         [0007]     The &#39;606 patent also discloses a closed loop configuration in which a hydraulic fluid is circulated through the gripper assemblies and propulsion assemblies to power the tractor&#39;s movement within the borehole. In particular, FIG. 19 of the &#39;606 patent discloses a downhole motor that powers the recirculation of the hydraulic fluid.  
         [0008]     U.S. Pat. Nos. 6,347,674; 6,241,031; and 6,679,341, as well as U.S. Patent Application Publication No. 2004/0168828, disclose alternative valve systems and methods for directing fluid to and from a downhole tractor&#39;s gripper assemblies and propulsion assemblies for moving the tractor.  
       SUMMARY  
       [0009]     In one aspect, a tool for moving within a passage is provided. The tool comprises an elongated body, at least one gripper assembly engaged with the body, a turbine, and a power transmission assembly. The elongated body has an internal fluid chamber and is configured to be secured to a fluid conduit so that a first fluid flowing through the conduit flows into the internal fluid chamber. The gripper assembly has an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface. The gripper assembly also has a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage. The turbine is configured to receive the first fluid flow through the internal fluid chamber, the turbine having an output shaft configured to rotate as the first fluid flows through the turbine. The power transmission assembly is configured to convert rotation of the output shaft into power for moving the gripper assembly to its actuated position.  
         [0010]     In another aspect, a method of moving a tool within a passage is provided. An elongated body having an internal fluid chamber is provided. The body is secured to a fluid conduit so that a first fluid flowing through the conduit flows into the internal fluid chamber of the body. At least one gripper assembly is provided and engaged with the body. The gripper assembly has an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface, and a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage. A turbine is provided, the turbine configured to receive the first fluid flow through the internal fluid chamber. The turbine has an output shaft configured to rotate as the first fluid flows through the turbine. A power transmission assembly is provided, the power transmission assembly configured to convert rotation of the output shaft into power for moving the gripper assembly to its actuated position. The first fluid is pumped through the conduit into the internal fluid chamber of the body and through the turbine.  
         [0011]     For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.  
         [0012]     All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic diagram of a conventional coiled tubing tractor system.  
         [0014]      FIG. 2  is a schematic diagram of a closed loop system for powering a downhole tractor, according to one embodiment of the invention.  
         [0015]      FIG. 3  is a more detailed schematic diagram of the closed loop system of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]      FIG. 1  illustrates a conventional coiled tubing tractor or tool for conducting downhole operations such as intervention and drilling. The illustrated system is an open loop configuration. The coiled tubing system  100  typically includes a power supply  102  for powering ground-level equipment, a tubing reel  104 , a tubing guide  106 , and a tubing injector  110 , which are well known in the art. The illustrated system includes a bottom hole drilling assembly  120  for drilling a borehole  132  with a drill bit  130 . However, other types of bottom hole assemblies  120  can alternatively be provided, such as those for intervention operations like hole cleaning, sand washing, acidizing, and the like. As known, coiled tubing  114  is inserted into the borehole  132 , and a fluid (e.g., drilling mud, intervention fluid) is typically pumped through the inner flow channel of the coiled tubing  114  towards the drill bit  130  located at the end of the drill string. Positioned between the drill bit  130  and the coiled tubing  114  is a tool or tractor  112 . The illustrated bottom hole assembly (BHA)  120  includes a number of elements known to those skilled in the art, such as a downhole motor  122  and a Measurement While Drilling (MWD) system  124 . The tractor  112  is preferably connected to the coiled tubing  114  and the bottom hole assembly  120  by connectors  116  and  126 , respectively, as known in the art. In this system, the fluid is pumped through the inner flow channel of the coiled tubing  114  and through the tractor  112  to the drill bit  130 . The fluid and drilling debris return to the surface in the annulus defined between the exterior surface of the tractor  112  and the inner surface of the borehole  132 , and also defined between the exterior surface of coiled tubing  114  and the inner surface of the borehole  132 .  
         [0017]     When operated, the tractor  112  is configured to move within the borehole  132 . This movement allows, for example, the tractor  112  to maintain a pre-selected force on the bottom hole assembly  120  such that the rate of movement or drilling can be controlled. The tractor  112  can be used to move various types of equipment through the borehole  132 . For example, it will be understood that the tractor  112  can be connected with or include, without limitation, a downhole motor (for rotating a drill bit), steering system, instrumentation sub (an instrumented package that controls various aspects of downhole operation, including shock vibration, weight on bit, torque at bit, rate of penetration, downhole motor rpm, and differential pressure across motor), Measurement While Drilling apparatus (an apparatus for measuring gyroscopic data such as azimuth, inclination, and measured depth), drill bit, mechanical and hydraulic disconnect for intervention, jetting tools, production logging tools (including apparatus for measuring and recording, without limitation, temperature, annulus pressure, and various flow rates), drilling logging tools (for measuring and recording, without limitation, resistivity measurements, magnetic resonance (MRI), sonic neutron density, density, fluid identification, and gamma ray measurements), perforation guns, casing collar locators, and torque limiting tools (for drilling).  
         [0018]     A closed loop configuration has relevant differences from an open loop system that operates on differential pressure (the difference in pressure between the bore of the tractor and the exterior of the tractor). With an open system, a restriction in the system is required to produce a pressure difference (decrease) between the interior and exterior of the tractor. Typically, the restriction is an orifice such as a fixed diameter nozzle, and is not capable of being adjusted from the surface. For typical coiled tubing rig operations, the effective means of control is to control the surface pump output flow rate. However, the differential pressure available at the tractor is a quadratic (non-linear) function of the surface pump output flow rate. Thus, doubling the surface pump output flow rate will increase the differential pressure through an in-series fixed orifice by a factor of four. This makes power control of the tractor more difficult as normal operational changes can have non-linear impact on tractor power, requiring additional features to be incorporated into the open loop powered tractor to restrict the amount of pressure delivered to the gripper assemblies, for example. Further, this has a disadvantage in that the normal operating range of the surface pump output flow rate required for various operations may have to be restricted, thus reducing cleaning efficiency during the operation.  
         [0019]      FIG. 2  is a schematic illustration of a turbine-powered pump for circulating hydraulic fluid in a closed loop for powering a downhole tool or tractor, according to one embodiment of the present invention. In this configuration, a first fluid (typically drilling/intervention fluid) that is externally pumped into the coiled tubing typically at the ground surface flows through the tractor and passes through a turbine  150  on its way to the remaining bottom hole assembly (typically secured to the distal end of the tractor). The flow through the turbine  150  produces rotation of the turbine&#39;s output shaft, which drives a pump  154  through a gearbox  152 . The pump  154  circulates a second fluid (typically a different type of fluid than the first fluid, such as, for example, hydraulic fluid) in a closed system loop  156 . Box  158  represents a valve system, gripper assemblies, and propulsion assemblies as known in the art. For example, the valve system, gripper assemblies, and propulsion assemblies can be substantially as shown and described in U.S. Pat. Nos. 6,003,606; 6,347,674; 6,241,031; and 6,679,341, as well as U.S. Patent Application Publication No. 2004/0168828. Also, the gripper assemblies can be substantially as shown and described in U.S. Pat. Nos. 6,464,003 and 6,715,559; U.S. Patent Application Publication No. 2005/0247488; and U.S. Provisional App. No. 60/781,885. The second fluid provides hydraulic force for operation of the gripper assemblies and propulsion assemblies, and in some cases the valves.  
         [0020]      FIG. 3  is a more detailed schematic illustration of the closed loop system of  FIG. 2  adapted for use with a variation of the Puller-Thruster Downhole Tool (also referred to as the “Puller-Thruster Assembly” or “PTA”) described in U.S. Pat. No. 6,003,606. As the first fluid is pumped through the turbine  150 , the turbine output shaft rotates to power the pump  154  via the gearbox  152  (not shown), and the pump  154  in turn circulates the second fluid through the illustrated valve assembly. The second fluid flows from a supply line  228  through a start/stop valve  160  (also known as an “idler valve”) into the valve system. A six-way control valve  162  shuttles back and forth to direct the fluid to and from an aft gripper assembly  180  (illustrated as a deflated packerfoot) and a forward gripper assembly  182  (illustrated as an inflated packerfoot), and also to and from an aft propulsion assembly  184  and a forward propulsion assembly  186  (each propulsion assembly comprising barrels and internal pistons, as taught in the &#39;606 patent). Valves  164  and  166  (also known as “directional control valves”) control the shuttling and position of the six-way control valve  162 . Packerfeet valves  168  and  170  regulate the flow of fluid into the packerfeet  180  and  182 . A reverser valve  172  controls the direction of tractor movement (i.e., uphole or downhole). The operation of these valves is understood from the teachings of the aforementioned patents incorporated by reference. A sump  157  is preferably provided to store a reservoir of the second fluid. The circulating second fluid returns to the sump  157  via a return line  230 .  
         [0021]      FIG. 3  shows an embodiment of a tool  200  (illustrated as a Puller-Thruster Assembly) positioned within a drilled hole  205  inside a rock formation  212 . The tool  200  includes an elongated body formed of central coaxial cylinders  207 . The aft gripper assembly  180 , aft propulsion assembly  184 , forward gripper assembly  182 , and forward propulsion assembly  186  are engaged on the central coaxial cylinders  207 . The aft propulsion assembly  184  includes annular pistons  218  secured to the cylinders  207 . Similarly, the forward propulsion assembly  186  includes annular pistons  220  secured to the cylinders  207 . The number of pistons can vary (e.g., up to 20 pistons) and depends on the desired thrust and pull loads.  
         [0022]     The tool body defines an internal mud flow passage  224  inside the cylinders  207 . The aft end of the tool body has an inlet  201  connected to coiled tubing  114  via a coiled tubing connector  206  (connection can be threaded or snapped together). While  FIG. 3  shows coiled tubing  114 , the tool  200  can also be used with rotary drill rigs instead. The forward end of the tool body is connected to a bottom hole assembly (BHA)  204 . The illustrated tool includes a female coiled tubing connector  208  and stabilizers  210 . The valve control pack  214  is positioned between the forward and aft gripper assemblies and also between the forward and aft propulsion assemblies. Splines  216  can optionally be incorporated between the central coaxial cylinders  207  and the gripper assemblies to prevent the transmission of torque from the BHA  204  to the coiled tubing  114 .  
         [0023]     In use, drilling/intervention fluid flows from the coiled tubing  114  into the inlet  201  of the tool body, and downhole (toward the bottom of the hole) through the mud flow passage  224 . The fluid flows through the turbine  150 , powering the pump  154 . The fluid continues through the passage  224  into the BHA  204 , exiting the BHA  204  through an outlet  203 . The inlet  201  and outlet  203  are also shown in relation to the turbine  150  on the bottom right hand side of  FIG. 3 . The drilling/intervention fluid that exits via the outlet  203  then flows uphole to the ground surface through an annulus defined between the tool  200  and the drilled hole  205 .  
         [0024]     The upper right hand side of  FIG. 3  includes a cross-sectional view of the inflated packerfoot  182 , taken along line A-A. The illustrated packerfoot  182  includes three inflated sections. Three mud flow return paths  222  are defined between the three inflated sections of the packerfoot. These return paths  222  allow drilling fluid that exits via the outlet  203  to flow back uphole past the inflated packerfoot. It will be understood that the aft packerfoot  180  can be substantially identical to the forward packerfoot  182 . The illustrated packerfoot cross section shows the packerfoot inflated radially beyond the outside diameter  226  of the tool  200 .  
         [0025]     A relevant advantage of using a turbine-powered pump as illustrated is that the system is flow-based, meaning that the downhole tractor can be more easily controlled by the surface pump that pumps fluid down into the coiled tubing toward the turbine. With a flow-based system, any change in the surface pump output volume flow rate linearly changes the power available to the tractor. Since the surface pump output flow rate can be relatively easily adjusted dynamically during tractor operation, the resulting adjustment of the power to the tractor provides enhanced control over the tractor&#39;s speed and pulling force. This enhanced control is available over a substantial operating range of surface pump output flow rates. This is convenient for some types of operations. For example, during sand washing it is desirable to provide a maximum amount of fluid into the borehole while the tractor continues its forward movement, usually at near-maximum pulling capacity.  
         [0026]     Another relevant advantage of this system is that the pump  154  is desirably directly powered by the rotating output of the turbine/gearbox combination, without any intermediate steps (e.g., electrical power generation from the turbine output, and use of such electrical power to drive an electric motor that drives the pump). The provision of such intermediate steps would introduce a risk of a loss of efficiency in converting the kinetic energy of the first fluid pumped into the turbine  150  into power for driving the operation of the pump  154 . The disclosed turbine/gearbox combination advantageously provides a highly efficient conversion of the first fluid&#39;s kinetic energy.  
         [0027]     Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications thereof. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above.

Summary:
A tool for moving within a passage comprises an elongated body, at least one gripper assembly engaged with the body, a turbine, and a power transmission assembly. The elongated body has an internal fluid chamber and is configured to be secured to a fluid conduit so that a first fluid flowing through the conduit flows into the internal fluid chamber. The gripper assembly has an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface. The gripper assembly also has a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage. The turbine is configured to receive the first fluid flow through the internal fluid chamber, the turbine having an output shaft configured to rotate as the first fluid flows through the turbine. The power transmission assembly is configured to convert rotation of the output shaft into power for moving the gripper assembly to its actuated position.