A method and apparatus for conducting earth borehole operations include a reel ( 28 ) of continuous coiled casing ( 30 ), and an injector ( 20 ) for moving the coiled casing. The bottomhole assembly including at least a motor ( 54 ) and a bit ( 56 ) is connected to the free end of the coiled casing, and injected into the earth while circulating fluid through the coiled casing to form a drilled earth borehole having a borehole wall. The coiled casing drill string may be retrieved from the borehole, the bottomhole assembly removed, and the coiled casing again injected into the borehole, then suspended from a wellhead assembly. After severing the coiled casing, a bonding agent such as a cementitious material may be injected into the suspended coiled casing and into the annulus between the coiled casing and the borehole.

FIELD OF THE INVENTION 
     The present invention relates to earth borehole operations such as those involving the drilling and/or lining of earth boreholes in oil and gas wells. More particularly, the present invention relates to methods and apparatus for drilling and/or lining earth boreholes using coiled casing. 
     BACKGROUND OF THE INVENTION 
     In conventional earth borehole operations such as drilling, the casing, liner, or drill string (collectively “tubular string”) is made up of sections or joints of threaded tubular members, generally about 30-40 feet long, which are sequentially threaded together as the tubular string is advanced into an earth borehole. Accordingly, it is necessary for the drilling or casing running operations to be intermittently interrupted so that successive joints of tubular members can be attached, and the drilling or casing running operations continued. When threaded drill pipe or casing is employed and the next joint is ready to be attached, the drilling or casing running operations are stopped, and the tubular string in the earth borehole is suspended with slips or the like forming part of the wellhead assembly. The next joint is then stabbed into the suspended tubular string and made up, and the running operations then continued. Operations such as making and breaking threaded connections are time consuming and, more importantly, inherently dangerous to personnel on the rig floor. Furthermore, during the time when the next joint is being attached to the suspended string, fluid circulation operations involving drilling mud or casing running fluids are stopped. In conventional drilling or casing running operations using jointed tubular members, continuous circulation is thus not practical since, as noted above, during the period when a successive joint is being added, circulation operations are stopped. Continuous circulation is desirable to maintain the annulus between the casing string and the borehole clear and to prevent bridging. It is also desirable, during casing running operations, that the casing string suspended in the earth borehole be kept filled with fluid to prevent excessive fluid pressure differentials across the casing string, and thereby prevent collapse and/or blowouts. 
     Casing has been used as a drill string such that once the earth borehole has been drilled to the desired depth, the casing forming the drill string can be cemented in place in a conventional manner. This technique eliminates the need for separate drill strings and casing strings. Usually, when the casing string is used as the drill string, the end of the casing string in the earth borehole is attached to a disposable or retrievable bottomhole assembly which includes a motor and a drill bit. When the drilling operation is completed, the bottomhole assembly can be retrieved and the casing string in the borehole then cemented in place in a conventional manner. While drilling with casing clearly has advantages in terms of savings of time and money compared to conventional earth borehole drilling operations involving separate drill strings and casing strings, present methods for drilling with casing employ jointed casing with all the attendant problems discussed above with respect to jointed drill strings and/or casing strings. 
     Coiled tubing having a size of less than 3 inches or less has been uncoiled from the reel and inserted in threaded casing in a well. Although coiled tubing is not normally used in conjunction with cementing operations, it has been known to uncoil tubing from a reel into a well with a damaged casing, and then to cement the annulus between the tubing and the damaged casing in order to continue recovery from the well. 
     Those familiar with coiled tubing operations recognize that coiled tubing sizes conventionally extend up to about 3 inches, and that casing sizes typically extend to about 4 inches to about 7 inches or more. Coiled casing according to the present invention will thus typically have a diameter of 4 inches or more, and will commonly have a diameter of 4½ inches or 5½ inches. 
     U.S. Pat. No. 3,724,567 discloses a system for handling drill pipe or tubing for workover operations. The threaded tubular string may be a continuous piece moved from a storage position to the well U.S. Pat. No. 4,100,968 discloses a technique for running casing using a powered rotating tool. U.S. Pat. No. 5,197,553 discloses a retrievable bit and downhole motor at the lower end of a tubular drill stem, and U.S. Pat. No. 5,271,472 discloses a bit assembly including radially extendable and retractable arms with cutters that may be withdrawn through the drill stem. 
     U.S. Pat. No. 5,215,151 discloses a drilling technique with a continuous length of jointed coiled tubing. Hydraulic fluid may be pumped through the tubing string, and a wireline used to retrieve the bit. U.S. Pat. No. 5,547,314 discloses a system for storing and running jointed tubulars into a well. U.S. Pat. No. 6,250,395 discloses a system for installing and retrieving threaded pipe in a well. U.S. Pat. No. 5,641,021 discloses a well casing drill tool with closing sleeve. 
     U.S. Pat. No. 6,419,033 discloses a system for drilling a well with a bit and an underreamer. U.S. Pat. No. 6,439,866 discloses a downhole motor with a sealed bearing. U.S. Pat. No. 6,443,245 discloses a casing shoe. U.S. Pat. No. 6,513,223 and 6,585,052 disclose tubing centralizers. U.S. Pat. No. 6,564,868 disclose a tool and method for cutting a tubular. U.S. Pat. No. 6,705,413 discloses a technique for drilling with casing using a retrievable bit. 
     The prior art has not disclosed techniques for significantly reducing the cost of running casing in a well, and accordingly significant costs and risks are incurred both in running a casing in a well and in retrieving the casing string from a well. 
     The disadvantages of the prior art are overcome by the present invention, and improved equipment and techniques for running casing in a well is hereinafter disclosed. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method of drilling an earth borehole includes providing a reel of continuous coiled casing having a free hand, and an injector for moving the coiled casing. A bottomhole assembly including at least a downhole motor and a drill bit is connected to the free end of the continuous coiled casing to form a coiled casing drill string. A coiled casing drill string is injected into the earth while circulating fluid through the coiled casing to form a drilled earth borehole having a borehole wall. The coiled casing drill string is retrieved to the surface from the borehole, and the bottomhole assembly may be removed from the free end of the coiled casing, which may then be reinjected into the earth borehole and suspended from a wellhead assembly. The suspended coiled casing may be severed to form a suspended coiled casing string in the earth borehole, with an annulus being formed between the borehole wall and an exterior surface of the suspended coiled casing string. A cementitious material or other bonding agent may then be injected into the suspended coiled casing string and into the annulus. 
     In another embodiment, a retrievable bottomhole assembly is connected to the free end of the coiled casing to form a coiled casing drill string, and the earth borehole is drilled by injecting the coiled casing string into the earth while circulating fluid through the coiled casing to the bottomhole assembly. The coiled casing drill string is suspended in a wellhead assembly, and severed at a location above the suspension by the wellhead assembly. The bottomhole assembly may then be retrieved through the suspended coiled casing drill string. 
     In yet another embodiment, the free end of the coiled casing is connected to a disposable bottomhole assembly, and the coiled casing drill string is injected into the earth and suspended from a wellhead assembly. The coiled casing drill string is severed at a location above the suspension by the wellhead assembly, and a bonding agent injected into the suspended coiled casing drill string and about the bottomhole assembly, and upwardly into the annulus between the coiled casing drill string and the drill borehole. 
     In another embodiment of the invention includes an apparatus for drilling an earth borehole, including a reel of continuous coiled casing, a bottomhole assembly attached to the free end of the coiled casing and including at least a drill bit and a downhole motor, and an injector for injecting the coiled casing in the bottomhole assembly into the earth to form a drilled earth borehole with an annulus formed between the borehole wall and an exterior surface of the coiled casing. One or more pumps circulate fluid through the coiled casing and the bottomhole assembly and into the annulus between the borehole wall and the coiled casing. 
     In yet another embodiment, a method of installing a liner into a drilled earth borehole includes providing a reel of continuous coiled casing and an injector for moving the coiled casing. The coiled casing is injected into the drilled earth borehole, and an annulus formed between a wall of a drilled earth borehole and an exterior surface of the coiled casing injected into the drilled earth borehole. Fluid is circulated through the coiled casing as the coiled casing is injected, with the fluid passing upwardly through the annulus. 
     In yet another embodiment of installing a liner in an earth drilled borehole, coiled casing is injected into the drilled earth borehole while circulating fluid through the coiled casing, and the coiled casing is suspended in the borehole in a wellhead assembly. Coiled casing is severed at a length above the suspension by the wellhead assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view, partially in section, showing the use of coiled casing to drill an earth borehole using a conventional drilling rig. 
         FIG. 2  is a view similar to  FIG. 1 , but shows the use of a trailer mounted coiled casing rig to drill an earth borehole. 
         FIG. 3  is an elevational view, partially in section, showing a coiled casing bottomhole assembly being removed from a drilled earth borehole. 
         FIG. 4  is an elevational view, partially in section, showing continuous coiled casing with a cementing shoe being lowered into a drilled earth borehole. 
         FIG. 5  is an elevational view, partially in section, showing a cementing operation wherein a casing string from coiled casing has been suspended in a drilled earth borehole and is being rotated to enhance bonding between the cement and the suspended casing string. 
         FIG. 6  is a view similar to  FIG. 5  showing reciprocation for enhancing bonding between the cement and the suspended casing string. 
         FIG. 7  is an elevational view, partially in section, showing the use of a coiled casing string as a drill string with a retrievable bottomhole assembly comprising a drill bit, an underreamer and a downhole motor attached to the end of the coiled casing string. 
         FIG. 8  shows the assembly of  FIG. 7  being retrieved through the suspended string using a preinstalled retrieval line in the coiled casing. 
         FIG. 9  shows the retrievable bottomhole assembly of  FIG. 8  approaching the upper, open surface of the suspended casing string for the removal of the bottomhole assembly. 
         FIG. 10  is an elevational view showing the installation of a mud swivel and pig launcher on the upper end of the suspended casing string of  FIG. 9 . 
         FIG. 11  shows a pump down cementing shoe which has been released from the pig launcher shown in  FIG. 10 . 
         FIG. 12  is a side view showing the cementing shoe landed at the bottom of a suspended casing string and a wiper plug being pumped down to displace cement from the interior of the suspended casing string and into the annulus between the earth borehole and the casing string. 
         FIG. 13  depicts the drilling of an earth borehole with coiled casing using a disposable bottomhole assembly. 
         FIG. 14  shows a cementing operation through the disposable bottomhole assembly shown in  FIG. 13 . 
         FIG. 15  shows directional drilling with coiled casing according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts a conventional drilling rig  10  comprising a derrick  12  having a crown  14  from which is suspended a traveling block  16 , traveling block  16  being attached to bails  18  which in turn suspend a coiled casing injector head  20 . A typical wellhead assembly  22  is located on or adjacent the rig floor  24  and includes slips or other gripping devices for suspending tubular members in an earth borehole. 
     Mounted on a pad  26  is a spool  28  for housing coiled casing  30 , coiled casing  30  being played off of reel  28  through an arched guide  31  into injector head  20 , through wellhead  22  and then into a drilled earth borehole  32 . As shown, earth borehole  32  has an upper section  34  in which has been installed surface casing  36  which is cemented in place by cement  38 . As shown, the portion of the coiled casing suspended below the wellhead  22 , referred to as the suspended casing string, is provided at its free end with a casing shoe  40  through which cement or other bonding agent can be pumped in a conventional fashion to cement the suspended casing string in the wellbore  32 . Cementing fluid may thus pass down the casing string and up the annulus  42  between the suspended casing string and the wall  44  of the earth borehole  32 . Since the coiled casing  30  is unjointed, it will be appreciated that a primary borehole liner can be continuously installed into the earth borehole  32 , there being no need for intermittent stops to connect successive joints of casing as is typically done in jointed casing running operations. 
     A source  46  of commonly used fluids, such as brine, fresh water, drilling mud, etc., can be supplied to the coiled casing as desired through line  47  during the running operations to facilitate injection of the casing string into the borehole. The returns from annulus may be directed to mud pit  48  through line  50 . In this regard, connection systems used to connect coiled tubing to such fluid suspensions can also be employed in the coiled casing operations of the present invention. When the desired length of casing string is in the borehole, the casing string may be engaged by the slips in the wellhead assembly  22  and the coiled casing severed at a location above the securing of string  30  to the wellhead  22 . Thereafter, a bonding agent such as cement can be pumped down the casing string to cement the casing string in place in the borehole. 
       FIG. 2  is similar to  FIG. 1 , and shows a derrick  12  suspending the injector  20 , and a reel  28  supplied with fluid through line  47  while unreeling the coiled casing to the injector. A winch  51  is depicted for raising and lowering the injector  20  on the mast  12 . Pit  48  receives the returns from the annulus. In this application, the coiled casing reel  28  is provided on a trailer mounted unit  29 . 
     The lower portion of  FIG. 2  is enlarged to more clearly show the annulus  32  surrounding the coiled casing  30 , and also depicts a conventional mud motor  54  at the lower end of the casing string  30  for rotating the bit  56 . Fluid is thus pumped through the casing string  30  by line  47 , through the mud motor  54  and the bit  56 , then up the annulus  42  and into the pit  48 .  FIG. 2  also simplistically depicts one or more drill collars  52  and one or more stabilizers  53  provided above the motor  54  for adding weight for drilling and for stabilizing the bottomhole assembly, respectively. 
       FIG. 3  depicts further details with respect to the lower portion of the coiled casing string  30 , the mud motor  54  and the bit  56 . Motor  54  may have the same diameter or a slightly larger diameter than the diameter of the coiled casing  30 , so that the annulus  32  may be restricted in the area of the motor  54 . The retrievable bottomhole assembly, including motor  54  and bit  52 , may be periodically retrieved to the surface by powering injector  20  to move coiled casing  30  upward, thereby allowing the motor to be checked, repaired or replaced, and the bit replaced. 
     In the  FIG. 4  embodiment, the borehole  32  has been drilled to the desired depth, and the coiled casing string  30  is inserted with a conventional cementing shoe  58  provided at the lower end of the coiled casing. In an alternate embodiment, the cementing shoe may be replaced with a cementing joint. 
     In the  FIG. 5  embodiment, a bonding agent, such as a cementitious material, is injected through line  60  to a swivel-type cementing head  62 , and from there travels downward through the coiled casing string  30  to the cementing shoe  58  at the lower end of the well. During this operation, the casing string is supported by slip  64  provided within the wellhead  22 . As the hole fills with cement, fluid within the annulus  32  is driven upward and out the flowline  50  to a mud pit, as previously described. During the cementing operation, the cementing head  62  may be designed to facilitate right hand and/or left hand rotation of the coiled tubing string  30 , thereby providing a more effective bond between the coiled casing string and the borehole wall. 
     In the  FIG. 6  embodiment, an alternative cementing head  66  is suspended by bails  18 , and is fed with a cementitious material through line  60 . The cementing head  66  and the coiled casing string are suspended from an elevator, and are moved axially during the cementing operations. The bonding fluid is transmitted down the coiled casing  30  and out the shoe  58  at the lower end of the coiled casing string. Fluid in the annulus  32  flows by line  50  to the mud pit. For this operation, the coiled casing string preferably is reciprocated at a direction substantially aligned with the axis of the coiled casing to ensure a quality bond between the coiled casing and the borehole wall. After cementing, the tubular  30  may be suspended in a well from a wellhead, or from a casing hanger. 
     In the  FIG. 7  embodiment, the retrievable mud motor  68  is suspended at the lower end of the coiled tubing from a wireline  70 , which extends to the surface. The mud motor  68  rotates a pilot bit  71 , and also reamer section  72  which has a cutting diameter appreciably larger than the diameter of the coiled tubing  30 . Those skilled in the art will appreciate that coiled casing  30  may be left in the hole, and the mud motor  68 , bit  71 , and reamer  72  may be retrieved to the surface wireline  70 , with the retrieved components passing through the ID of the coiled casing  30 . Reamer  72  thus retract to a diameter slightly less than an internal diameter of the coiled casing, as shown in  FIG. 8 .  FIG. 9  shows the mud motor  68 , the reamer  72  and the pilot bit  71  adjacent an upper end of the casing string  30 , which has been severed at a location above the slips  64  of a suitable casing hanger which fixes the coiled casing with respect to the rig floor  24 . The wireline  70  may thus be retrieved through the severed coiled casing  30  and the injector  20 . When retrieved to the surface, the mud motor may be repaired or replaced, and both the pilot bit and the reamer  72  replaced with new components. In an alternate embodiment, a coiled tubing string may be used instead of wireline  70  to retrieve the bottomhole assembly. 
       FIG. 10  illustrates a cementing head  66  generally shown in  FIG. 6 , and more particularly illustrates one or more wiper plugs  76  and control members  78  for regulating the release of the wiper plugs. Cement is pumped via line  66  into the interior of the casing string  30 , and fluids in the annulus flow out the line  50  to a suitable pit or other fluid retainer. 
     As shown in the  FIGS. 11 and 12  embodiment, a pig  80  may be pumped down the coiled tubing  30  to land at the end of the coiled tubing string, with a cementitious material  82  being pumped behind the pig  80 , and the upper end of the cementitious fluid being sealed from a non-cementitious driving fluid  83  by the wiper plugs  76 . Fluid thus exits the bottom of the coiled casing  30 , passes out of the pig  80  and into the annulus  32 , filling the annulus with cement. 
     In the  FIG. 13  embodiment, the mud motor  54  at the lower end of the coiled casing cement  30  is powered by fluid passing downward through the coiled casing  30  and the mud motor to rotate the bit  56 . For this embodiment, mud motor and bit may be an expendable item, and accordingly when the desired depth is reached, the cementitious material  82  may be pumped down the coiled casing  30 , with the wiper plug  76  (see  FIG. 14 ) serving the function previously described. The cementitious material may thus fill the annulus about the coiled casing  30 , and also fill the annulus about the motor  54  and the bit  56 . 
       FIG. 15  discloses yet another embodiment, wherein the mast  12  is inclined relative to the trailer  29  so that the coiled casing  30  can be used to drill under a river. The motor  54  and the bit  56  may thus be provided with conventional directional drilling capability, and for this purpose the motor may include a relatively small internal bend (not shown) common for directional drilling equipment. 
     Circulation of fluid through the coiled tubing casing string occurs during drilling, with the circulating fluid flowing between the interior of the casing string and the annulus. Circulation when installing a liner is preferable in order to better convey the liner into the well and to provide proper hole cleaning. Circulation of a bonding agent, such as a cementitious fluid, is required if the liner is to be cemented in the open hole. 
     For each of the embodiments discussed herein, the coiled casing once installed in the well provides the primary barrier between the formation and the interior of the casing. Coiled casing may be perforated after it is installed, so that formation fluid will flow into the interior of the casing string. In other embodiments, the coiled casing is not a solid tubular, and instead may be slotted or perforated for preventing collapse of a formation wall while allowing fluid to flow into the interior of the casing string. 
     The coiled casing of the present invention may be made from various materials, including a carbon alloy steel or a carbon fiber material. Various types of guide devices, cementing stage tools, driver shoes, packers, perforating guns, correlation indicators, and cross-over tools may be used in conjunction with the coiled casing string. The bottomhole assembly may include drill collars, drill pipe, heavy weight drill pipe, shock subs, jars, hole openers, stabilizers, reamers, cross-over subs, and various types of drill bits. Whipstocks, bent subs, and various types of downhole motors with bent housings may be conveyed on the bottomhole assembly of the coiled casing string. Wellbore production tools may also be used with a coiled casing string, including side bore extensions and lateral extension placements. 
     The coiled casing may be drilled or conveyed into a wellbore vertically, directionally, or in a substantially horizontal plane. The techniques of the present invention may be used to recover various types of hydrocarbons, including oil and gas, and may also be used for geothermal applications, or to recover water. Applied internal pressure within the coiled casing may be produced with an energized fluid or gas. Air, nitrogen, natural gas, water, compatible liquid hydrocarbons, drilling muds, and other mediums may be used for pumping into the coiled casing string utilizing pumps or compressors common in the oilfield industry. 
     Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.