Patent Publication Number: US-2007107941-A1

Title: Extended reach drilling apparatus &amp; method

Description:
The present application claims the benefit of pending U.S. Provisional Patent Application Ser. No. 60/731,988 filed Oct. 27, 2005 the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF INVENTION The present invention relates to an apparatus and method for drilling an extended reach well in a formation.  
     BACKGROUND  
      In the production of hydrocarbon fluid from an earth formation, wellbores are drilled to provide a conduit for hydrocarbon fluid to flow from a subterranean reservoir to a production facility at the surface. The ability to drill longer and deeper wells at inclined angles (referred to as extended reach drilling or ERD) is becoming increasingly important to the oil and gas industry. An ERD well is generally defined as a well with a throw ratio of approximately 2:1 where the throw ratio is the ratio of horizontal depth to true vertical depth (TVD). Some extended reach wells (characterized as ultra ERD wells) may have throw ratios as high as 6:1.  
      Traditionally wellbores are formed in two phases. In the first phase, a drill string (or drill pipe) with a drill bit attached to the lower end is rotated by a kelly or rotary table located at the surface. As the drill bit creates a hole in the earth, drilling mud is circulated through the annular space between the drill string and the wellbore wall to cool the bit and transport cuttings (rock chips from drilling) to the surface. In the next phase, the drill string and bit are removed and the wellbore is lined with a string of steel pipe known as casing. The casing serves to stabilize the newly formed wellbore and facilitate the isolation of certain areas of the wellbore adjacent to the hydrocarbon bearing formations. Once the casing is cemented in the wellbore, a smaller bit is inserted through the casing and used to drill deeper into the earth. This process is then repeated and numerous sections of casing are installed until the desired depth is reached. When the well is complete, the entire string of casing resembles an extended, inverted telescope.  
      To reduce costs and drilling time, a process known as “drilling with casing” is often employed. This process involves attaching the drill bit to the same string of tubulars that will be used to line the wellbore. Because the same string is used, both phases of the wellbore formation can be completed in a single trip. However, the traditional nested arrangement of casing in a well causes the available diameter for the production of hydrocarbon fluid to decrease with depth in a stepwise fashion. This becomes a technical and economic problem for deep wells with many separate casings because drilling a small diameter deep hole becomes very challenging. To overcome this problem, the oil and gas industry has begun to experiment with new drilling and casing techniques that involve radially expanding individual casing strings as they are installed in the well in order to maximize the available diameter. One such technique is described in WO 2004/097168 A1, which is herein incorporated by reference. This technique known as “expandable” technology, eliminates the aforementioned telescoping effect, and may enable the drilling of a “monodiameter well,” a well in which every joint of casing used to line the wellbore has the same diameter.  
      Another recent development is the replacement of conventional drill pipe with “coiled tubing.” Whereas conventional drill pipe is assembled from relatively short rigid lengths of pipe, coiled tubing is a single strand of flexible pipe that is capable of handling a drilling assembly. A downhole drilling motor is used to create the mechanical energy necessary to rotate the drill bit and a tractor device that grips onto the interior of the wellbore maintains the proper amount of weight on bit and holds the reactive torque from the motor.  
      Even with these recent advancements in drilling technology, operators still encounter challenges drilling and running completions in extended reach wells. One major limitation is overcoming the friction incurred by the drill string rotating and sliding on the casing or formation. Frictional losses can reduce the weight on bit so much that it is impossible to drill with a reasonable penetration rate. Sufficient weight on bit is required to force the drill bit into the formation. Thus, the maximum drilling depth for an ERD well is often limited by the weight on bit, torque, or resistance of the drill string.  
      In addition to the frictional problem, disposal of cuttings and steering also limit drilling of ERD wells. Because ERD wells are so deep and long, cleaning the cuttings from the drill out of the hole poses a challenge. The need to steer the drill bit through three dimensional rock formations is also costly and time-consuming because the operator is often required to trip out of the hole multiple times to replace or change equipment.  
      US Pat. No. 6,467,557 B1 discloses a means to overcome the challenges associated with extended reach drilling using a rotary long reach drilling assembly. The tool described comprises an elongated conduit extending through a bore, a drill bit for being rotated to drill the bore, a 3D steering tool on the conduit for steering the bit, and a tractor on the conduit for applying force to the bit. The tractor includes a gripper which can assume a first position that engages an inner surface of the bore and limits movement of the gripper relative to the inner surface. The gripper can also assume a second position that permits substantially free relative movement between the gripper and the inner surface of the bore. A propulsion assembly moves the tractor with respect to the gripper while the gripper position is in the first position.  
      WO9909290 discloses an extended reach drilling system for drilling a borehole in an underground formation. The ERD system comprises a drill bit, a motor for driving the drill bit, a drill-pipe to surface, a hydraulic cylinder/piston arrangement for providing the required weight on bit, the drill-pipe being coupled to a selected one of the cylinder and the piston of said cylinder/piston arrangement by swivel means allowing rotation of the drill pipe relative to one of the cylinder or the piston, the drill bit being coupled to the other one of the cylinder and the piston, and locking means for locking said selected one of the cylinder and the piston against the borehole wall, the locking means being operable between an engaged and a disengaged position.  
      WO9708418 discloses a method and apparatus for propelling a tool having a body through a passage. The tool includes a gripper including at least a gripper portion, which can assume a first position that engages an inner surface of the passage and limits relative movement of the gripper portion relative to the inner surface. The gripper portion can also assume a second position that permits substantially free relative movement between the gripper portion and the inner surface of the passage. The tool includes a propulsion assembly for selectively continuously moving the body of the tool with respect to the gripper portion while the gripper portion is in the first position.  
      There are several opportunities for improving existing drilling systems to overcome the challenges associated with extended reach wells. First, there is an opportunity to overcome the problems associated with frictional losses and maintaining weight on bit. Known systems may encounter difficulty achieving the penetration rate necessary to drill extended reach wells. Although tractors and other gripping devices apply some additional force to the drill bit, a tractor&#39;s grip on the inner surface of the bore may be insufficient to overcome the frictional losses especially if a rotary system is used. In addition to the problem associated with frictional loss, there is also an opportunity to address the telescoping problem posed by conventional casing methods. Generally, the ability to drill a deep well is limited by the available diameter in the deepest segment of the nested casing. Maximizing the diameter of this segment of casing would enable the operator to drill deeper extended reach wells.  
     SUMMARY OF THE INVENTION  
      The present inventions include a method for drilling a well in a formation comprising inserting a thruster, a first conduit, and a drill bit into a wellbore lined with a previous casing and applying a force to the first conduit with the thruster wherein the thruster grips onto the previous casing.  
      The present inventions include an apparatus for drilling a well in a formation through a wellbore lined with a previous casing comprising a drilling assembly and a thruster connectable to the drilling assembly; wherein the thruster is capable of gripping onto the previous casing and providing a force to the drilling assembly.  
      The present inventions include a method for drilling a well in a formation comprising providing a wellbore lined with a previous casing, inserting a first drilling assembly comprising a drill bit at a distal end, a first conduit connectable to the drill bit, and a thruster connectable to first conduit, gripping the previous casing with the thruster, and drilling a well. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is better understood by reading the following description of non-limitative embodiments with reference to the attached drawings, wherein like parts of each of the figures are identified by the same reference characters, and which are briefly described as follows:  
       FIG. 1  illustrates a side view of an extended/ultra extended reach drilling apparatus and method.  
       FIG. 2  illustrates a side view of another embodiment of the extended reach drilling apparatus and method. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIG. 1 , wellbore  101  is shown extending through formation  102  and is lined with previous casing  103 . First conduit  104 , drill bit  105 , and thruster  106  are shown being inserted into wellbore  101 . In this embodiment, first conduit  104  is a section of drilling casing; however, other similar oilfield equipment (e.g. liner) could be used. Thruster  106  is shown in this embodiment as a tractor. Any substitute device capable of gripping or applying force could be used.  
      In operation, the drilling assembly (comprising first conduit  104 , drill bit  105 , and thruster  106 ) is inserted into wellbore  101 . In the embodiment shown, drill pipe  107  is used to perform this function; however, other oilfield equipment (e.g. coiled tubing) may be used instead. After the drilling assembly is inserted, thruster  106  applies a force to first conduit  104  causing drill bit  105  to drill a hole and extend wellbore  101 . Thruster  106  provides the necessary weight on bit for penetration by gripping onto previous casing  103 . The torque required to rotate drill bit  105  may be transferred by first conduit  104 . Although it is shown as a liner in this embodiment, first conduit  104  may also be drilling casing or other oilfield equipment. It is also possible to insert a drill pipe inside the liner to transmit the torque to drill bit  105 .  
      Once wellbore  101  is extended, first conduit  104  is removed from the drilling assembly and hung against previous casing  103 . First conduit  104  is optionally secured in place by expansion, cementing, or any other method. Drill pipe  107  is then used to remove the drilling assembly. A new drilling assembly is lowered into wellbore  101  comprising drill bit  105 , thruster  106 , and second conduit (not shown). The steps are then repeated until the desired depth is reached.  
      Turning to  FIG. 2 , wellbore  201  is shown extending through formation  202  and is lined with previous casing  203 . Drilling assembly  204  is being lowered into wellbore  201 . Thruster  205  and liner  206  are also shown being lowered into wellbore  201 . In the embodiment shown, coiled tubing  207  is used to perform this function; however, other oilfield equipment (e.g. drill pipe) may be used instead of coiled tubing. Drilling assembly  204  comprises drill bit  208 , drill motor  209 , steering mechanism  210 , mud pump  211  to drive steering mechanism  210 , and expander  212 . Additional components (not shown) such as directional assemblies, bent housings, bent subs, measurement while drilling (MWD) instruments, and other downhole tools may also be attached to drilling assembly  204 .  
      In operation, after drilling assembly  204  is inserted into wellbore  201 , the torque required to drive drill bit  208  is provided by drill motor  211 . The torque is transferred via the liner or via drill pipe or coiled tubing inserted in the liner. Thruster  205  applies a force to liner  206  causing drill bit  208  to drill a hole and extend wellbore  201  and holds the reactive torque from the drill motor. Thruster  205  provides the necessary weight on bit for penetration by gripping onto previous casing  203 .  
      Once wellbore  201  is extended, drilling casing  206  is removed from the drilling assembly and hung against previous casing  203 . Drilling casing  206  is then expanded using expander  212 . Optionally drilling casing  206  may be expanded against formation  202 . Drilling casing  206  may also be expanded to be the same diameter as previous casing  203 ; it may also be expanded so that it has a smaller diameter. Preferably drilling casing  206  is expanded so that its outer diameter is substantially equal to the inner diameter of previous casing  203 . Expander  212  may be a pig, cone, rotary expansion device, cyclic expansion device or any other expansion device. After expansion, drilling casing  206  is then optionally cemented in place. A new drilling assembly is lowered into wellbore  201  the steps are then repeated until the desired depth is reached. The subsequent drilling casings may each be expanded so that the wellbore is monodiameter.  
      Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials, and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature.