Abstract: A method for driving pipe into the ground, which is particularly suitable for driving conductor pipes that are commonly installed in the hydrocarbon production industry during the construction of oil wells and gas wells, more particularly offshore wells comprises, assembling at the lower end of a drill string means for supporting a conductor pipe on the drill string, a reciprocable impact driving means, means for reciprocating the reciprocable impact driving means using fluid pumped through the drill string, an anvil capable of transferring the percussive force of the reciprocable impact driving means to the conductor pipe and means for jetting fluid, positioning the assembly within a conductor such that the assembly and conductor are supportable by the drill string and the means for jetting fluid is at the lower end of the conductor, positioning the lower end of the conductor pipe on the ground into which it is to be driven, (d) actuating the reciprocable impact driving means to impact the anvil and drive th

Abstract: An apparatus is provided for the drilling of a borehole and its simultaneous lining with cement or the like by the same apparatus. The apparatus comprises a combination spray bead and reamer head, a means to drive the reamer head through a borehole and a means for delivering cement to the spray head. Cement is fed to a rotatable spray disc or arms of the spray head, which is arranged to distribute the cement substantially evenly over the internal surface of the borehole created by the reamer head. The apparatus uses lined drill rods, as well as a lined reamer core with a double walled plastic tube. An air transfer assembly is used to connect an internal air source to an air passage contained in the plastic tube, such that the external air source remains stationary during rotation of the lined drill rods and attached reamer and spray beads.

Abstract: 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.

Abstract: A method for drilling boreholes using casing as the drill string and for removing a drilling assembly from the wellbore while leaving the casing in the well bore. In the method, the drilling assembly is prepared for removal from the wellbore by launching a release tool and manipulating the drilling assembly using the release tool.

Abstract: A cement float collar is made for pumping downhole and into engagement with a groove formed in the casing, called the profile nipple. As such, no restriction is needed in the casing for accepting or latching the float collar and the portion of casing including the groove can be installed at the start of the drilling operation. In addition, the profile nipple can be used to engage other drilling tools and, therefore, can already be in place when the final well depth (TD) is reached.

Abstract: A drill bit and a single pass drilling apparatus are disclosed. The one-piece drill bit is rotatable about a drilling axis and has a connection portion, adapted to be rigidly connected to a drill steel, a pilot part and a reamer part. The reamer part has a leading and at least one trailing first rock machining means disposed on one side of the pilot part within a sector defined by sector angle ?. At least one of the trailing first rock machining means is axially spaced from the leading first rock machining means in the direction toward the trailing end of the drill bit.

Abstract: An apparatus that facilitates the insertion of a stanchion into the ground. The apparatus comprises a first side including a plurality of connection apertures, a second side including a plurality of connection apertures, and at least one connector engaging the connection apertures to removably engage the first side to the second side. The first and second sides reposition the ground and substantially separate the stanchion from the ground during insertion. Additionally, the apparatus maintains the integrity of the hole into which the stanchion is placed during insertion of the stanchion into the ground. Preferably, the first and second sides define a substantially circular opening when engaged to one another. Additionally, each side includes a length and the connector substantially spans the length and vertically connects the first side to the second side along the length.

Abstract: Embodiments of the present invention generally provide methods and apparatus for forming a tubular-lined wellbore which does not decrease in diameter with increasing depth or length. Methods and apparatus for forming a substantially monobore well while drilling with casing are provided. In one aspect, a portion of a second casing is expanded into a portion of a first casing having a larger inner diameter than the remaining portion of the first casing string. In another aspect, the portion of the second casing is expanded into a portion of the first casing having a compressible member therearound. In another aspect, a lined lateral wellbore may be constructed by forming a lateral wellbore extending from a main wellbore lined with casing. A diameter of at least a portion of the lateral wellbore may be expanded. An expandable tubular element may be run into lateral wellbore and expanded to have an inner diameter equal to or larger than an inner diameter of the main wellbore casing.

Abstract: A casing bit, which may comprise a composite structure, for drilling a casing section into a subterranean formation, and which may include a portion configured to be drilled therethrough, is disclosed. Cutting elements and methods of use are disclosed. Adhesive, solder, electrically disbonding material, and braze affixation of a cutting element are disclosed. Differing abrasive material amount, characteristics, and size of cutting elements are disclosed. Telescoping casing sections and bits are disclosed. Aspects and embodiments are disclosed including: at least one gage section extending from the nose portion, at least one rotationally trailing groove formed in at least one of the plurality of blades, a movable blade, a leading face comprising superabrasive material, at least one of a drilling fluid nozzle and a sleeve, grooves for preferential failure, at least one rolling cone affixed to the nose portion, at least one sensor, discrete cutting element retention structures, and percussion inserts.

Abstract: A method of sealing the wall of a wellbore (1) as it is being drilled through a subterranean formation using a drill string (3) having a drill bit (4) on the lower end thereof comprises fitting to the lower end of a drill string (3) a device comprising (i) a cylindrically gathered pack of flexible tubing (6), (ii) a receptacle (5) for the gathered pack and (iii) a radially expandable locking means (8) having a first end of the tubing of the gathered pack connected either directly or indirectly thereto, and drilling a first section of wellbore, expanding the locking means (8) against the wellbore wall such that the first end of the tubing that is withdrawn from the gathered pack is locked in place in the wellbore, drilling a second section of wellbore with the movement of the drill string (3) through the wellbore causing the tubing to be withdrawn from the gathered pack (6) and to be turned inside out thereby forming a liner for the second section of wellbore.

Abstract: A bit assembly is for a drill having a casing, a central axis and a hammer movably disposed within the casing. The bit assembly includes a chuck with a tubular body having first and second ends, the first end being connected with the casing such that the second end is spaced axially therefrom, and one or more openings extending generally axially from the second end toward the first end. A bit includes a body with a tubular portion having a cavity and one or more axial lugs, the lug(s) being disposable within the chuck opening(s). A retainer is coupled with the chuck, disposable within the bit cavity and engageable with the bit lug(s) so as to releasably couple the bit with the chuck. The retainer is preferably a deflectable ring sized to receive a portion of the hammer, such that the hammer prevents disengagement of the retainer from the bit.

Abstract: Apparatus and methods for drilling with casing. In an embodiment, methods and apparatus for deflecting casing using a diverter apparatus are disclosed. In another embodiment, the apparatus comprises a motor operating system disposed in a motor system housing, a shaft operatively connected to the motor operating system, the shaft having a passageway, and a divert assembly disposed to direct fluid flow selectively to the motor operating system and the passageway in the shaft. In another aspect, methods and apparatus for directionally drilling a casing into the formation are disclosed. Methods and apparatus for measuring the trajectory of a wellbore while directionally drilling a casing into the formation are also described.

Abstract: A borehole may be drilled utilizing the bottom hole assembly 10, 50 with a downhole motor 14, 110, which may offset at a selected bend angle. A bend for directional drilling may be provided by a PDM, or by a RSD. A gauge section 36 secured to the pilot bit 18 has a uniform diameter bearing surface along an axial length of at least 60% of the pilot bit diameter. The bit or reamer 16 has a bit face defining the cutting diameter of the drilled hole. The axial spacing between the bend and the bit face is controlled to less than fifteen times the bit diameter. The downhole motor, pilot bit and bit may be retrieved from the well while leaving the casing string in the well.

Abstract: A method and device for boring, particularly percussion boring or rotary percussion boring, a hole in soil or rock material and for forming an anchoring. A borehole is formed by inserting a drill bit, and a casing tube is placed inside the borehole during the boring process. Once the borehole is completed, the boring rods are detached from the drill bit and removed from the borehole. The periphery of the casing tube is provided with a number of passage openings for discharging hardenable material. A tensioning device for the anchor, particularly an anchor plate and a screw that can be screwed onto the casing tube, can be fixed to the end of the casing tube protruding from the borehole. Anchoring or fixing elements for anchoring the casing tube on the surrounding inner wall of the borehole are provided, in particular, on the end area of the casing tube oriented toward the drill bit.

Abstract: The present invention involves a method and apparatus for monitoring conditions downhole and/or manipulating downhole tools by placing electrical wire on a casing string while drilling with casing. Wire is inserted into a groove within the casing string while drilling with the casing string into a formation. The wire connects downhole equipment to surface equipment. Multiple casing strings may be drilled into the formation while wire is simultaneously inserted into a groove therein.

Abstract: A drilling assembly (2) comprises upper (4) and lower (6) drill strings with a fluid passage (80) therethrough for distributing fluid to a bottom hole assembly (10). The upper drill string (4) has an upper end (11) connectable to a drilling apparatus (13) and fluid source (16) and a lower end (18) with an attached casing expander unit (20) that communicates the fluid passage (80) of the upper (4) and lower (6) drill strings. An upper end (22) of the lower drill string (6) is formed from a casing string (24) telescoped over the casing expander unit. A constriction (31) connects the casing string (24) with the rest of the lower drill string (6). A flow restriction device (35) in the lower drill string acts to control fluid flow through the fluid passage.

Abstract: A rotatable drilling shoe attachable to a section of casing that allows for drilling and casing of a well bore in a single trip. The drilling shoe includes a fixed section and a rotatable section that has a drillable bit attached thereto. The drilling shoe further includes a mechanism for inhibiting rotation of the rotatable section after the casing is cemented into place so that the drillable bit can be drilled out by a subsequent drilling operation.

Abstract: A down-hole tool guide is disclosed for deflecting various down-hole tools having a tendency to hang or bind in uncased bore holes. The down-hole tool guide or ball guide assembly, being adaptive to the down-hole tools, extends forwardly there from and includes an eccentric rotatable ball and high-pressure jets. In cases where the guide is used to guide casing, the ball guide assembly is constructed from a drillable material thereby allowing the hole bore to be extended beyond the last set casing depth without side deviation from the original bore.

Abstract: A driving device for installing a pipe or casing, without the use of hydraulic or pneumatic means, by capturing the rotational motion of the drill string. The driving device is placed at the top end of the pipe being (42) installed and the drill string (2) passes through the center of the device. The drill string freely rotates, advances or retracts within the driving device, until the driving device is attached (4) to the drill string when required. When the driving device is attached to the drill string, the rotational force of the drill string and any downward force applied to the drill string are captured, and used to install the pipe. The driving device uses the rotation of the drill string to impact a blow to the pipe, driving the pipe downward. The driving device uses any downward force applied to the drill string to maintain downward pressure on the pipe.

Abstract: A method and associated equipment are disclosed which allow drilling at least a portion of a well and subsequently cementing casing in a single trip. The method is particularly suited for deep-water offshore operations where the drill string can be run through a section of casing leaving a bit and an under-reamer extending out below. The casing is equipped with ports through which cement can be pumped as well as an external casing packer to prevent the uncured cement in the annulus from U-tubing. Several casing sections can be run in during drilling and cemented succession using the one trip method.

Abstract: A steering head that comprises a forward pivot block and a rearward pivot block. The forward pivot block is attached to a leading edge of a casing. The rearward pivot block is attached to a trailing portion of the casing, the leading edge being separated from the trailing portion by a gap in the casing. Extending between the forward and rearward pivot blocks is a central drive shaft. The central drive shaft includes a threaded portion and is rotatable to move a drive nut away from or towards the rearward pivot block. The central drive shaft, to either side of the drive nut, is covered by a cylindrical sleeve. A second internal sleeve extends between the rearward pivot block and the drive nut to protect the threads of the drive shaft from earthen debris when the casing is being advanced or reversed to steer the forward-most casing portion during operation.

Abstract: An apparatus is provided for the drilling of a borehole and its simultaneous lining with cement or the like by the same apparatus. The apparatus comprises a combination spray head and reamer head, a means to drive the reamer head through a borehole and a means for delivering cement to the spray head. Cement is fed to a rotatable spray disc or arms of the spray head, which is arranged to distribute the cement substantially evenly over the internal surface of the borehole created by the reamer head. The apparatus uses lined drill rods, as well as a lined reamer core with a double walled plastic tube. An air transfer assembly is used to connect an internal air source to an air passage contained in the plastic tube, such that the external air source remains stationary during rotation of the lined drill rods and attached reamer and spray heads.

Abstract: In a method and device for boring or drilling, in particular percussion drilling or rotary percussion drilling, holes in soil or rock, wherein a borehole is formed by a percussive and/or rotary movement carried out by a drill bit (2) mounted on a drill rod assembly (3) and a jacket tube (6) coupled with the drill bit (2) is introduced into the borehole, it is provided that the jacket tube (6) is received in a socket (5) provided on the end facing away from the drill bit working surface, of an envelope tube (4) coupled with the drill bit (2), and that the jacket tube (6) is subjected to a percussive and/or compressive stress on its end facing away from the drill bit, whereby directionally precise boring or drilling is rendered feasible.

Abstract: A method and apparatus for holding and turning a tubular and string of tubulars, such as casing, for make-up and drilling with the tubulars are disclosed. The apparatus generally includes a spear and a clamping head, both of which are mounted to a top drive. The spear and the clamping head can be engaged to transmit torque therebetween from the top drive. In addition, an aspect of the invention provides variable height wickers positioned on slips to enable use of the slips with variable inner diameter (ID) and weight casing without deformation or rupture of the casing. Still further, a casing collar is also provided to provide reinforcement to the casing in the area of slip contact with the casing ID.

Abstract: A downhole filter comprises a tubular member having a wall defining a plurality of openings. The openings have an outer width less than an inner width. The parts of the opening defining the smaller width are defined by radially outer parts of the openings, such that particulates or sand prevented from passing through the openings will tend to be retained to the outside of the tubular member. A method comprises providing a tubular string having a non-porous tubular portion and a porous tubular portion, and installing the tubular string within a wellbore such that the porous tubular portion is located adjacent a fluid-producing formation within the wellbore. In another embodiment, an apparatus comprises a drill string comprising a non-porous tubular portion and a porous tubular portion, and an earth removal member operatively connected to a lower end of the drill string.

Abstract: A drilling apparatus comprises a casing shoe, ring bit, and center bit. The casing shoe may be connected to a casing received within the casing shoe. The ring bit is received within the casing shoe and retained at the end of the casing. The ring bit rotates relative to the casing shoe, and drills a peripheral portion of a hole. The center bit drills a central portion of the hole, and may be rotated and percussively driven to drill the hole. The center and ring bits are adapted for: engaging one another so that rotating and percussively driving the center bit also rotates and percussively drives the ring bit; engaging one another so that retracting the center bit also retracts the ring bit, casing shoe, and casing; enabling disengagement from one another and withdrawal of the center bit from the ring bit and the casing shoe.

Abstract: The present invention provides a method and apparatus for casing while drilling without the use of an underreamer. In one aspect, the invention provides a flexible drill collar that enables drilling of a large enough borehole for passage of the casing string therethrough.

Abstract: The present invention provides a global drilling system comprising a crown bit, a driver drill bit and a square drill bit. The crown bit has a tubular body with an inner surface and an outer surface, wherein the inner surface circumscribes a hollow passageway, and a pair of projections extending into said hollow passageway. The pair of projections are positioned substantially opposite one another on said inner surface. The driver drill bit has a drilling head with a pair of cut-away portions positioned substantially opposite one another and a pair of locking surfaces adapted for engaging the projections on the crown bit. The square drill bit has a drilling head with two tapered cut-away portions positioned substantially opposite one another. Each cut-away portion corresponds to one of the pair of projections such that the drilling head is able to pass through the hollow passageway of the crown bit.

Abstract: Methods of and apparatus for drilling, casing and/or completing a borehole wherein one or more portions of the borehole are drilled into a formation at a single diameter along the entire length or depth of the or each portion of the borehole. An expandable tubular member is then located within the or each portion of the borehole and radially expanded in the or each portion to line and/or case it or them. Optionally, a corrosion resistant member and/or a service string can be located in the borehole. An advantage of certain embodiments is that a single diameter borehole is formed along the entire length or depth thereof.

Abstract: The steel drill string attached to a drilling bit during typical rotary drilling operations used to drill oil and gas wells is used for a second purpose as the casing that is cemented in place during typical oil and gas well completions. Methods of operation are described that provide for the efficient installation of a cemented steel cased well wherein the drill string and the drill bit are cemented into place during one single drilling pass down into the earth. Methods are provided to selectively cause a drilling trajectory to change during drilling with casing. A one-way cement valve is installed near the drill bit of the drill string that allows the cement to set up efficiently under ambient hydrostatic conditions while the drill string and drill bit are cemented into place during one single drilling pass into the earth.

Abstract: The invention relates to a method for drilling, being carried out by a drilling apparatus, having a drilling device (1) that comprises a casing part (2) and a drilling unit (3), in the drilling head (I) of which there are first drilling means (4) for drilling a center hole and second drilling means (5) for reaming of the center hole for the casing part (2) as well as flushing flow arrangement (6) for flushing of waste, being generated. At least during the drilling situation, the first drilling means (4) are coupled by a power transmitting and, in order to enable removal of the same from the hole, removable arrangement, such as a bayonet coupling or like, with the second drilling means (5).

Abstract: A pipe handling device for mounting to use with a top drive and possibly a pipe engaging apparatus, includes a link arm having a first end pivotally connectable to move with the top drive and an outboard end pivotally connectable to a pipe elevator segment, and a drive system to drive the outboard end of the link arm at least between a lower position and a raised position. A pipe handling system and method may include or employ the pipe handling device.

Abstract: Bits for use in drilling with a well completion string having a bit body and a cutting face that includes a plurality of sets of cutter elements mounted on the cutting face. The bit body has a central longitudinal bore having an integrated female non-shouldered, standard oilfield completion string thread. The bits are designed with minimal cutter coverage, and this combined with the integrated completion string thread allows for economical completion of a well with high ROP expected from a PDC type bit. In an additional embodiment, a bit comprises a bit body and a cutting face having integrated cutting structures.

Abstract: A method includes drilling and lining a wellbore, in one aspect by mounting a drill bit on a drill string including a section of expandable tubing and providing a tubing expander in the string, rotating the drill bit and advancing the drill string through a bore, and passing the expander through the expandable tubing to expand the tubing. The apparatus comprises a drill string including a section of expandable tubing, a drill bit mounted on the string, and a tubing expander mounted on the string.

Abstract: A method of drilling and lining a bore in an earth formation comprises providing a tubular outer elongate member and an inner elongate member located within the outer member. At least one of the members is spoolable. A drill bit is mounted to one of the members and a bore is drilled by advancing the drill bit through the earth formation and advancing the members through the bore.

Abstract: The present invention generally relates to methods for drilling a subsea wellbore and landing a casing mandrel in a subsea wellhead. In one aspect, a method of drilling a subsea wellbore with casing is provided. The method includes placing a string of casing with a drill bit at the lower end thereof in a riser system and urging the string of casing axially downward. The method further includes reducing the axial length of the string of casing to land a wellbore component in a subsea wellhead. In this manner, the wellbore is formed and lined with the string of casing in a single run. In another aspect, a method of forming and lining a subsea wellbore is provided. In yet another aspect, a method of landing a casing mandrel in a casing hanger disposed in a subsea wellhead is provided.

Abstract: A method and a device for the drilling, in particular the percussive or percussive rotary drilling of a hole in earth or rock and for securing an anchorage in the hole. A bore hole is created by a drill bit mounted on a drill pipe and a sliding sleeve that surrounds the drill pipe at a distance is simultaneously introduced. A sliding sleeve configured with a longitudinal slit is introduced at least partially and rests substantially against the bore hole during the drilling, whereby a reliable anchorage can be achieved with a simple construction by the sliding sleeve with a longitudinal slit.

Abstract: A tunneling system including a tunneling apparatus including a cutting structure for forming a borehole and at least one linkage section for transmitting a force generally toward the cutting structure is disclosed. A method of disposing a casing string within a subterranean formation by applying a force generally to the trailing end of the tunneling apparatus, generally toward the leading end thereof, but without transmitting the entire force through the entire casing string is also disclosed. At least one linkage section extending within but not in contact with at least one casing section of the casing string may transmit the force. Also, a force limiting member may limit a force applied to the casing string.

Abstract: A method for drilling boreholes using casing (16) as the drill string and for advancing a casing string toward the bottom of the borehole is described. In the method, the drilling assembly (26) is used as a guide over which the drill string (16) is advanced toward the bottom of the borehole prior to removing the drilling assembly from the wellbore.

Abstract: The steel drill string attached to a drilling bit during typical rotary drilling operations used to drill oil and gas wells is used for a second purpose as the casing that is cemented in place during typical oil and gas well completions. Methods of operation are described that provide for the efficient installation of a cemented steel cased well wherein the drill string and the drill bit are cemented into place during one single drilling pass down into the earth. A stabilizer is attached to the drill string that is used to centralize the drill string in the well during cementing operations. A one-way cement valve is installed near the drill bit of the drill string that allows the cement to set up efficiently under ambient hydrostatic conditions while the drill string and drill bit are cemented into place during one single drilling pass into the earth.

Abstract: A method for the placement of subterranean electrodes is disclosed and which includes the steps of providing an earth engaging drill; forming a bore hole in the surface of the earth with the earth engaging drill; providing an electrode; and delivering the electrode into the bore hole by employing the earth engaging drill.

Abstract: In a device for sealing a bore hole and discharging drill cuttings and stripped excavation material, including a housing adapted to receive sealing elements and an opening capable of being connected to the bore hole, one side wall of the housing is provided with at least one opening for the connection of a haulage duct, wherein the housing end side facing the bore hole is equipped with a lockable, particularly screwable, sealing flange (13) for the detachable connection with a bore hole lining (11). The sealing flange (13) is rotationally and sealingly mounted within the housing and carries projections, in particular an annular brim (15) which is overlapped by a stop (14) of the housing.

Abstract: A method of lining and drilling a bore (10) comprises the steps of mounting a first section of bore-lining tubing (20) on the lower end portion of a drill string (18). The method also includes running the drill string and tubing into a bore having an unlined section and an existing tubing lined section, locating the first tubing section (20) in the unlined section, uncoupling the first tubing section (20) from the drill string (18), and drilling the bore beyond the first tubing section.

Abstract: The invention is a hoist system for a derrick with a derrick inside, a derrick outside, and a derrick top side; a splittable block connected to the derrick top side; a hoisting cable guided through the splittable block; a moveable trolley with a trolley top side and a trolley bottom side, wherein the trolley is connected to the splittable block and wherein the moveable trolley is removably secured on the derrick; and a hoist winch adapted to pull the hoisting cable over the derrick top side and through the splittable block to move the moveable trolley relative to the derrick.

Abstract: The present invention generally relates to methods for drilling a subsea wellbore and landing a casing mandrel in a subsea wellhead. In one aspect, a method of drilling a subsea wellbore with casing is provided. The method includes placing a string of casing with a drill bit at the lower end thereof in a riser system and urging the string of casing axially downward. The method further includes reducing the axial length of the string of casing to land a wellbore component in a subsea wellhead. In this manner, the wellbore is formed and lined with the string of casing in a single run. In another aspect, a method of forming and lining a subsea wellbore is provided. In yet another aspect, a method of landing a casing mandrel in a casing hanger disposed in a subsea wellhead is provided.

Abstract: A clamp system for allowing a pile driving/pulling system to be attached to a caisson to be driven into or extracted from the earth. The clamp system comprises a structural member, first and second clamp systems, first and second locking systems, and a clamp displacement system. The clamp displacement assembly is operatively connected between the structural member and the first and second clamp assembly. When the first and second clamp systems are disengaged from the pile and the first and second locking systems are disengaged from the structural member, the clamp displacement system may be operated to obtain a desired clamp distance between the first and second clamp assemblies.

Abstract: An apparatus including a support member, the support member including a first fluid passage, a mandrel coupled to the support member, the mandrel including: a second fluid passage, a tubular member coupled to the mandrel, and shoe coupled to the tubular liner, the shoe including a third fluid passage, and a drilling assembly coupled to the shoe, wherein the first, second and third fluid passages and the drilling assembly are operably coupled.

Abstract: A method is disclosed for drilling a wellbore. The method includes operating a turbine-type mud motor having a bi-center drill bit coupled to it, and applying an axial force to the bit which is selected so that the bit drills in a directionally stable manner. In one embodiment, the motor is a steerable motor operated to maintain a selected trajectory of the wellbore.

Abstract: A borehole may be drilled utilizing the bottom hole assembly 10, 50 with a downhole motor 14, which may offset at a selected bend angle. The motor housing is preferably run slick, and a gauge section 36 secured to the pilot bit 18 has a uniform diameter bearing surface along an axial length of at least 60% of the pilot bit diameter. The bit or reamer 16 has a bit face defining the cutting diameter of the drilled hole. The axial spacing between the bend and the bit face is controlled to less than fifteen times the bit diameter. The downhole motor, pilot bit and bit may be retrieved from the well while leaving the casing string in the well.

Abstract: The present invention provides a method and apparatus for setting concentric casing strings within a wellbore in one run-in of a casing working string. In one aspect of the invention, the apparatus comprises a drilling system comprising concentric casing strings, with each casing string having a drill bit piece disposed at the lower end thereof. The drill bit pieces of adjacent casing strings are releasably connected to one another. In another aspect of the invention, a method is provided for setting concentric casing strings within a wellbore with the drilling system. In another aspect of the invention, the releasably connected drill bit pieces comprise a drill bit assembly.