Abstract: A tilted drive sub is disclosed with a center line of the internal diameter (ID) offset at an angle from the center line of the outer diameter (OD) starting at a point near to a top end of the tilted drive sub. This results in the ID being at an angle to the OD, with the OD of the tilted drive sub remaining straight. The offset ID has the same threads of a mud motor without a tilted drive sub. The tilted drive sub replaces the outer bearing housing of a normal performance mud motor.

Abstract: The invention concerns a bore screen comprising a plurality of perforated rigid tubular modules (1) impermeably connected in series by ball joint means (2), allowing an extracted fluid to flow though all of the elements in series and allowing the consecutive elements to move freely relative to one another, tilting in all directions.

Abstract: A drilling stabilization system includes a power section coupled to an upper end of a transmission housing, a bearing housing coupled to a lower end of the transmission housing, and a drill bit coupled to the bearing housing, wherein the transmission housing includes at least two radially outwardly extending blades disposed on the transmission housing. A method of drilling a substantially concentric wellbore includes drilling a formation with a directional drilling bottomhole assembly coupled to a drill string, changing a direction of the drilling of the formation being drilled, removing the directional drilling bottomhole assembly from the drill string, coupling a drilling stabilization system to the drill string, and drilling the formation with the drilling stabilization system.

Abstract: A system for monitoring the position of a downhole tool assembly having multiple beacons. In a preferred embodiment first and second beacons are adapted to transmit electromagnetic signals indicative of the position of the downhole tool assembly. A receiving assembly having a single antenna arrangement detects the signals transmitted from the first and second beacons. The receiving assembly processes the signals to determine the relative position of the receiving assembly to the downhole tool assembly. The determination of the relative position comprises determining a lateral offset and a distance from the downhole tool assembly.

Abstract: The present invention provides apparatus and methods for controlled steering. One embodiment of the invention provides a bit body comprising a trailing end, a pilot section, and a reaming section. The trailing end is adapted to be detachably secured to a drill string. The pilot section is located on a leading, opposite end of the bit body. The reaming section is located intermediate to the leading and trailing ends. The pilot section comprises at least one steering device for steering the pilot section of the bit body, thereby steering the entire bit body. Another embodiment of the invention provides a wellsite system comprising a drill string; a kelly coupled to the drill string; and a bit body as described above. Another embodiment of the invention provides a method of drilling a curved borehole in a subsurface formation.

Abstract: Methods are described using resistivity ahead of a drill bit measurements obtained while drilling a subterranean well using a drilling mud. Resistivity data ahead of the bit is gathered during drilling and prior to penetrating a region of interest of a known subterranean formation using the drill bit and the drilling mud. The drill string progresses at known dip and azimuth angles toward the subterranean formation. The resistivity data is used to determine pore pressure ahead of the drill bit in the formation as a function of resistivity ahead of the drill bit in the formation while the drill bit advances toward but before the bit penetrates the formation while drilling. In certain embodiments, the methods include redirecting the drill bit while drilling toward locations in the formation where pore pressure is within an acceptable range. In other embodiments, a drilling mud parameter is adjusted based on the pore pressure in front of the bit.

Abstract: Methods are described using resistivity ahead of a drill bit measurements obtained while drilling a subterranean well using a drilling mud. Resistivity data ahead of the bit is gathered during drilling and prior to penetrating a region of interest of a target subterranean formation using the drill bit and the drilling mud. The drill string progresses at target dip and azimuth angles toward the region on interest. The resistivity data is used to determine the top of the region of interest while the drill bit advances toward but does not penetrate the region. A core bit is then installed and a whole core of the region of interest obtained. Resistivity ahead of a drill bit measurements obtained while drilling a subterranean well may also be compared with conventional resistivity measurements obtained from one or more offset wells.

Abstract: In one aspect of the present invention, a drilling assembly comprises a drill bit comprising a bit body intermediate a working face and a shank. An indenting member adapted to guide the drill bit protrudes from the working face. A flexible portion is disposed above the bit body.

Abstract: A drilling system including a drill head configured to couple to a drill string. The drill head including an offset adapter, a one-way clutch, and a drill bit. The drill head being configured to provide straight drilling along a first axis, and deviated drilling along a second axis. The drilling system further including a gearbox configured to provide selective rotational operation corresponding to the straight drilling and the deviated drilling. The drilling system also including control systems to control the selected rotational operation of the gearbox.

Abstract: A drill bit having a plurality of cutters on its lower surface, each of which can having a plurality of PDC cutter elements disposed thereon. The cutting surface on each of the cutters is mounted in in an orientation that allows drilling of oversize boreholes which enables the drill bit to be turned more easily to facilitate the boreholes being drilled on a smaller radius. The placement of the cutters on each of the blades enables the drill bit to drill both vertically and laterally.

Abstract: A drill bit is described herein, having a first bit face with a first plurality of cutters oriented to bore in a first direction, and a second bit face with a second plurality of cutters oriented to bore in one or more second directions. The pluralities of cutters enable functional articulation of the drill bit, such that the drill bit can change direction within a borehole without requiring removal of the drill bit. The drill bit can thereby drill in a downhole direction and lateral directions, can back ream through the borehole, and can provide the borehole with one or more oversized regions, as desired.

Abstract: A drill bit comprising: a cutting section comprising gage cutters, wherein in the cutting section is a first end of the bit, and wherein the cutting section has a full gage diameter; a heel section comprising a blade, wherein the heel section is at an end of the drill bit opposite the cutting section, and wherein a diameter of the heel section is a full gage diameter, wherein the blade has a high spiral around the drill bit; and a clearance section between the cutting and heel sections, wherein the clearance section comprises a diameter less than full gage, and wherein clearance section extends from the gage cutters of the cutting section to the blade of the heel section.

Abstract: This invention relates to a steering component, to a steering assembly, and to a method of steering a drill bit in a borehole. The steering component is adapted for connection to a drill string, the drill string carrying a drill bit and a motor for rotating the drill bit. The steering component comprises: a rotatable driveshaft adapted for connection between the drill bit and the motor; a drive mechanism; and an offsetting component; the drive mechanism providing a rotatable connection between the drill string and the offsetting component whereby the drill string can rotate relative to the offsetting component. The drive mechanism is adapted to drive the offsetting component to rotate in an opposed direction to the driveshaft, so as to counter the rotation of the offsetting component which is induced by friction within the componentry as the driveshaft rotates. The steering component and method are likely to have their greatest utility in steering a drill bit during drilling for oil and gas.

Abstract: Methods, systems, and apparatus that are suitable for use in production of hydrocarbons from subterranean heavy oil deposits employ a subterranean cavity in communication with a borehole. The cavity is preferably formed along a U-tube borehole by coiled tubing reaming operations and/or radial drilling and explosive blasting.

Abstract: A rotary steerable apparatus is provided having an actuator for pushing the bit or pointing the bit that includes a shape memory alloy. An elongated form of the alloy, such as a wire or rod, is employed in a mechanism that applies force in a direction transverse to the wellbore in response to a change in length of the alloy. Temperature of the alloy is controlled to change shape and produce the desired force on pads for operating the apparatus. The apparatus may be used with downhole power generation and control electronics to steer a bit, either in response to signals from the surface or from downhole instruments.

Abstract: A universal joint assembly includes an assembly housing, an assembly cap coupled to the assembly housing, a rotatable mandrel, a plurality of substantially spherical drive balls, and a floating washer. The assembly housing has a plurality of pockets formed in an interior surface of the assembly housing. The rotatable mandrel is fitted within a cavity defined by the assembly housing and the assembly cap and has a plurality of pockets configured to partially receive the drive balls. The substantially spherical drive balls are rotatable within the cavity about a central axis of the mandrel. A substantially circular groove formed in the cavity is defined by a proximal end of the assembly cap and an interior wall and a shoulder of the assembly housing. The floating washer is disposed within the substantially circular groove and configured to radially displace within the groove.

Abstract: Systems and methods for multi-lateral wellbore construction and stimulation from cased parent wellbores. Methods and apparatus are provided to facilitate the creation of casing exit openings in the casing of parent wellbores. Methods and systems are provided for azimuthally and longitudinally aligning drilling assemblies through openings in a parent wellbore casing are provided to allow for drilling multiple lateral wellbores extending outwardly from a parent wellbore. A method of stimulating one or more subterranean zones intersected by multiple lateral wellbores extending outwardly from one or more patent wellbores includes the steps of: simultaneously injecting a stimulation fluid into the lateral wellbores; and stimulating the zones intersected by the lateral wellbores in response to the stimulation fluid injecting step.

Abstract: Methods and apparatus to form a well are disclosed. An example method involves determining a reservoir fluid map associated with at least a portion of a reservoir. The first fluid map has first fluid composition data associated therewith. The example method also involves measuring a formation fluid and determining a second fluid composition data based on the measurement. The second fluid composition data is compared with the first fluid composition data associated with the reservoir fluid map, and a well trajectory is adjusted based on the comparison.

Abstract: A bottom hole assembly 10 for drilling a deviated borehole includes a positive displacement motor (PDM) 12 or a rotary steerable device (RSD) 110 having a substantially uniform diameter motor housing outer surface without stabilizers extending radially therefrom. In a PDM application, the motor housing 14 may have a fixed bend therein between an upper power section 16 and a lower bearing section 18. The long gauge bit 20 powered by the motor 10 may have a bit face 22 with cutters 28 thereon and a gauge section 24 having a uniform diameter cylindrical surface 26. The gauge section 24 preferably has an axial length at least 75% of the bit diameter. The axial spacing between the bit face and the bend of the motor housing preferably is less than twelve times the bit diameter. According to the method of the present invention, the bit may be rotated at a speed of less than 350 rpm by the PDM and/or rotation of the RSD from the surface.

Abstract: A method for forming a subsurface wellbore is disclosed. The method includes operating a drilling string in a first direction of rotation. A first motor located near the end of the drilling string is operated in a direction of rotation opposite that of the drilling string. A drill bit is rotated using a second motor that is coupled to the first motor.

Abstract: The method and apparatus can create excavation cavities suitable for drilling multilateral wellbores through the excavation using a kick-off. One embodiment of the method comprises isolating a wellbore at a determined location, excavating a downhole cavity in a wellbore above the determined location, and removing the apparatus for isolating the wellbore and the apparatus for excavating the downhole cavity from the wellbore to provide full access to the wellbore and the excavation cavity.

Abstract: Steerable drilling systems for facilitating drilling according to a prescribed, three-dimensional trajectory are described. Steering may be achieved using passive actuators which require little or no power. For example, damping elements which couple a drill bit to a drill collar can be used to tilt the drill bit with respect to the drill collar. Alternatively, rotary cutting elements disposed on the drill bit may be used to control the force between the drill bit and the formation at different axial locations. The passive elements used to control the tilt or rotation of the rotary cutting elements are actuated in a certain pattern, e.g., geostationary, in order to achieve a desired deviation of the well bore while drilling ahead. One way to achieve this is through the use of field-sensitive materials, e.g. magnetorheological (MR) fluids, that change viscosity in response to an applied magnetic field.

Abstract: A sidetracking system has a pair of serially connected mills (8,9), each having a plurality of circumferentially arranged blades having a tapered cutting portion (82,93) thereon for cutting a window in a casing and then sidetracking in a formation. A whipstock has at least three axially spaced ramps, each ramp being interspaced by a substantially axially extending portion. Each of the ramps has the same angle of inclination to a longitudinal axis and the distance between the ramps is the same as the distance between the tapered portions on the mills (8,9) so that when, in operation, load is shared between both mills. The mills have a button (83,93) of hardened material located on the tapered cutting portions so that the button abrades the whipstock ramps (31,32,33).

Abstract: A drilling apparatus controls or eliminates reaction torque from drill bits thereby preventing loss of penetration due to undesired rotation of the drilling apparatus or controls drilling direction by intentionally manipulating reaction torque thereby inducing desired drill bit walk. The drilling apparatus has a concentrically divided drill bit in which an inner drill bit rotates simultaneously in the opposite direction from an outer drill bit. The inner drill bit can be moved axially forward from or back toward the outer drill bit. Forces produced by the inner and outer drill bits are controlled to eliminate or adjust reaction torque.

Abstract: An apparatus for drilling a wellbore may include a first section, a second section, and a third section, all of which are rotatably interconnected with pivot bearings and positioned along a drill string. The second section and the third section may be configured to form a controllable bend angle in the drill string. The first section, the second section, and the third section may be configured as sleeves that surround a portion of the drill string. One or more sections may include locking pads that selectively engage a wall of the wellbore. A hydraulic locking device for controlling a direction of rotation of the second section may include one or more brake elements and a reverse spinning sleeve. A first brake element may be used engage the reverse spinning sleeve and a second brake element may be used to engage a drive shaft.

Abstract: Systems and methods for drilling a multilateral well using magnetic ranging while drilling are provided. In accordance with one embodiment, a method of drilling a multilateral well includes drilling and casing a mother wellbore, installing a multilateral junction, drilling and casing a first lateral well from the multilateral junction, and drilling a second lateral well from the multilateral junction using magnetic ranging while drilling such that the second lateral well has a controlled relationship relative to the first lateral well. The first and second lateral wells may form a SAGD well pair, in which case the first lateral well may be a producer well and the second lateral well may be an injector well.

Abstract: A downhole tool string component, having a first rotor secured within a bore of the component and connected to a gear assembly, the gear assembly being connected to a second rotor. The gear assembly has a gear ratio adapted to rotate the second rotor faster than the first rotor. The second rotor is in magnetic communication with a stator which has an electrically conductive coil, the electrically conductive coil being in communication with a load.

Abstract: A method and system for mitigating risk of well collision in a field includes receiving an anti-collision standard exemption request containing a description of risk of collision between a subject well and one or more offset wells, generating an assessment of the anti-collision standard exemption request using a stored multidimensional decision matrix, reviewing the assessment, and selectively updating the decision matrix based on the review.

Abstract: The present invention relates to a managed pressure and/or temperature drilling system (300) and method. In one embodiment, a method for drilling a wellbore into a gas hydrates formation is disclosed. The method includes drilling the wellbore into the gas hydrates formation; returning gas hydrates cuttings to a surface of the wellbore and/or a drilling rig while controlling a temperature and/or a pressure of the cuttings to prevent or control disassociation of the hydrates cuttings.

Abstract: Apparatus and methodology is provided for directional drilling which avoid the effects of static friction between the drill string and the borehole. The drill string is rotated continuously in one direction during rotating drilling and during steering. During steering, the rotary speed of the drill string is varied within a revolution and substantially similarly for each of a plurality of subsequent revolutions. The drill string is rotated very slowly when oriented at or near the desired orientation to achieve the desired change in direction and then rotated much faster during the balance of each revolution. This angular velocity profile results in drilling at or near a desired orientation for a high percentage of the time it takes for each revolution. Changes in an effective tool-face orientation can be effected by shifting the phase of the velocity profile.

Abstract: A method and device for boring a hole [5] through a material along a desired path includes an umbilical subsystem [2000] connected to a boring subsystem [3000] having a plurality of pulsejets [3100]. These pulsejets [3100] repeatedly receive and ignite a combustible fluid [7] in a combustion chamber [3230] causing a portion of the fluid [7] to be forced out of a nozzle [3260] at high speeds as a fluid slug [10] that impacts materials ahead of the pulsejet [3100]. A controller [3310] controls the amount of fluid provided to each pulsejet [3100], and the firing timing, thereby controlling the intensity in which each slug [10] impacts the material. By modulating the intensity and firing sequence of each of the pulsejets [3100], material ahead of the boring subsystem [3000] is differentially bored thereby allowing steering of the boring subsystem [3000].

Abstract: A method for determining a rate of change of longitudinal direction of a subterranean borehole includes positioning a downhole tool in a borehole, the tool including first and second longitudinally spaced surveying devices disposed thereon. The method further includes causing the surveying devices to measure longitudinal directions of the borehole at first and second longitudinal positions and processing the longitudinal directions of the borehole to determine the rate of change of longitudinal direction of the borehole between the first and second positions. The method may further include processing the measured rate of change of longitudinal direction of the borehole and a predetermined rate of change of longitudinal direction to control the direction of drilling of the subterranean borehole. Exemplary embodiments of this invention tend to minimize the need for communication between a drilling operator and the bottom hole assembly, thereby advantageously preserving downhole communication bandwidth.

Abstract: A particle impact drilling system and method are described. In several exemplary embodiments, the system and method may be a part of, and/or used with, an apparatus or system, methods, to excavate a subterranean formation. The system can including, for example, removing near-borehole damage, casing, window milling, fishing, drilling with casing, under reaming, coring, perforating, effective circulatory density management, assisted annular flow, and directional control. Embodiments of associated systems and methods are also included.

Abstract: The present invention generally relates to methods and apparatus for impact drilling. A drilling tool with a housing and a piston is provided. The drilling tool may be configured to impact while simultaneously rotating a drill head, independent from the rotation of a drill string. The drilling tool may include a rolling key assembly disposed between the housing and the piston that includes a bearing adapted to roll during a first direction of the piston and slide during a second direction of the piston. The drilling tool may include a clutch mechanism configured to rotate the drill head as the piston is directed in the first direction.

Abstract: An assembly and methods for constructing a MONOWELL includes a monodiameter casing disposed in a monodiameter wellbore having diametric efficiency with a monobore production delivery system disposed within the monodiameter casing. An assembly for constructing a monodiameter wellbore includes a bottomhole assembly having a overgauge hole drilling member, a directional steering assembly, a measurement while drilling tool, and a logging while drilling tool; a work string attached to the bottomhole assembly and extending to the surface; drilling fluids flowing through the work string and bottomhole assembly; chemical casing casing the borehole; expandable casing disposed in the wellbore; and a sealing composition disposed between the expandable casing and the wellbore.

Abstract: A method and apparatus for creating inverted laterals or drainholes having an inverted or upwardly inclining bore in a producing interval from a generally vertical wellbore and a method for drilling, completing, and producing from such a drainhole.

Abstract: This disclosure relates in general to a method and system for controlling a drilling system for drilling a borehole in an earth formation. More specifically, but not by way of limitation, embodiments of the present invention provide systems and methods for controlling dynamic interactions between the drilling system for drilling the borehole and an inner surface of the borehole being drilled to steer the drilling system to directionally drill the borehole. In another embodiment of the present invention, data regarding the functioning of the drilling system as it drills the borehole may be sensed and interactions between the drilling system for drilling the borehole and an inner surface of the borehole may be controlled in response to the sensed data to control the drilling system as the borehole is being drilled.

Abstract: This disclosure relates in general to a method and system for controlling a drilling system for drilling a borehole in an earth formation. More specifically, but not by way of limitation, embodiments of the present invention provide systems and methods for controlling dynamic interactions between the drilling system for drilling the borehole and an inner surface of the borehole being drilled to steer the drilling system to directionally drill the borehole. In another embodiment of the present invention, data regarding the functioning of the drilling system as it drills the borehole may be sensed and interactions between the drilling system for drilling the borehole and an inner surface of the borehole may be controlled in response to the sensed data to control the drilling system as the borehole is being drilled.

Abstract: A method for the directional control of a rock-drilling ma-chine, the drilling unit (1) of the rock-drilling machine, which is located in a borehole (2), comprising at least a pi-lot drill bit (6) or an underreamer drill bit (8), the drill bit(s) (6, 8) being driven by an electric motor (10) via a gearbox (12), and the drill bit(s) (6, 8) being moved into the rock (3) by means of a feeding rod (4) extending from a feeding machine at the outside the borehole (2), and the drill bit(s) (6, 8), gearbox (12) and motor (10) being pivoted in a controlled manner about a steering axis (18) which is approximately perpendicular to the center axis (26) of the feeding rod (4).

Abstract: Embodiments of the present invention generally relate to a flow operated orienter. In one embodiment, a bottom hole assembly (BHA) for use in drilling a wellbore includes: a first mud motor having a stator and a rotor; a second mud motor having stator and a rotor; a drill bit rotationally coupled to the second rotor and having a tool face and a longitudinal axis inclined relative to a longitudinal axis of the first mud motor; and a clutch. The clutch is operable to: rotationally couple the second stator to the first stator in a first mode at a first orientation of the tool face, rotationally couple the first rotor to the second stator in a second mode, change the first orientation to a second orientation by a predetermined increment, orient the tool face at the second orientation in an orienting mode, and shift among the modes in response a change in flow rate of a fluid injected through the orienter and/or a change in weight exerted on the drill bit.

Abstract: In one aspect of the present invention, a drill string has a drill bit with a body intermediate a shank and a working face. The working face has at least one cutting element. A jack element is disposed within the drill bit body and has a distal end substantially protruding from the working face. The distal end has a primary deflecting surface having an angle relative to a central axis of the jack element of 15 to 75 degrees.

Abstract: A rotary steerable tool for use in a downhole drilling apparatus for adjusting the direction of drilling is disclosed. The tool comprises a tubular outer housing and a row of steering pushers slidably mounted to the housing for movement between an extended position, in which the steering pusher engages a wall of a borehole formed by the drilling apparatus, and a withdrawn position, in which the steering pushers do not engage the wall of the borehole. A tubular sleeve is mounted inside the housing to transmit rotary drive to a drilling bit. A pressure chamber defined between the sleeve and the housing communicates with the steering pushers to move the steering pushers to the extended position.

Abstract: A closed-loop drilling system utilizes a bottom hole assembly (“BHA”) having a steering assembly having a rotating member and a non-rotating sleeve disposed thereon. The non-rotating sleeve has a plurality of expandable force application members that engage a borehole wall. An orientation sensing system associated with the rotating member and the non-rotating sleeve provides signals to determine an orientation of the non-rotating sleeve relative to the rotating member. In one embodiment, the orientation sensing system includes a first member positioned in the non-rotating sleeve and a second member positioned in the rotating member. Orientation of the non-rotating sleeve relative to the rotating member is determined from the coaction between the first and second members. The orientation sensing system can use magnetic waves, electrical signals, acoustic signals, radio waves, and/or physical contact.

Abstract: The invention concerns a drilling tool steering device, characterized in that it contains, consecutively from upstream to downstream, a main body (1) and a steerable housing (2), joined respectively by at least one connection of pivot, sliding pivot, ball joint or annular linear type forming a first bearing (4), and at least one pivot connection forming a second bearing (5), to a bendable or flexible transmission shaft (3) which crosses them longitudinally, while a connection of pivot, sliding pivot, annular linear or ball joint type forming a third bearing (6) between said transmission shaft and the main body (1) is arranged in proximity to the end of said main body situated in the direction of the steerable case, and while steering is carried out thanks to means acting as a deflection system (7) for the essentially radial relative displacement of the main body (1) in relation to the steerable housing (2) in proximity to their interface, the said main body being optionally equipped on its periphery with bear

Abstract: A communication system for a casing while drilling system is provided. The casing while drilling system is adapted to advance a bottom hole assembly into a subsurface formation via a casing. The communication system comprises a high frequency modulator and a transducer. The modulator is positioned in the bottom hole assembly and adapted to generate a mud pulse by selectively restrict mud flow passing therethrough. The transducer is adapted to detect the mud pulse generated by the modulator.

Abstract: An apparatus for controlling the direction of drill bit within a wellbore. The apparatus comprises a first housing with a first housing axis therein, and wherein the first housing has a first threaded opening having a first threaded opening axis. The first housing has a helical end. A second housing is included, and the second housing contains a second housing axis, and a second threaded opening having a second threaded opening axis configured to engage with the first threaded opening. A collar is included that has a helical collar end that engages the helical collar end and wherein the helical collar end is configured reciprocal to the helical end, and rotational displacement of the first housing relative to the collar will angularly displace the drill bit axis. The apparatus may further include spline members for locking the collar in place relative to the first and second housing.

Abstract: A well system may be provided comprising a first primary inductive coupler configured to be communicably coupled to a surface device and a first secondary inductive coupler. The first secondary inductive coupler may be further configured to be communicably coupled to one or more completion components provided in a first portion of the well. In addition, the well system may comprise a second primary inductive coupler configured to be communicably coupled to the surface device and a second secondary induction coupler. The second secondary inductive coupler may be further configured to be communicably coupled to one or more completion components provided in a second portion of the well. The flow through at least one of the first and second portions of the well may be adjusted via at least one of the one or more completion components. A method for completing a well comprising inductive couplers may also be provided.

Abstract: Drilling means for directional drilling in a bore hole comprising a drill pipe and a drilling head, including a slippable clutch device linking the drill pipe and said drilling head such that torque due to rotation of said drill pipe can be controllably applied to said drilling head through at least partial engagement of said clutch, and control means operable to sense an actual orientation angle of said drilling head and compare said actual orientation angle with a required orientation angle adjustably set in said control means and to control said slippable clutch such that when the actual orientation angle and the required orientation angle are the same, the slip torque of the slipping clutch equals the motor reaction torque, so maintaining the orientation angle of the drilling tool at said required orientation angle.

Abstract: A sidetracking system has a pair of serially connected mills (8, 9), each having a plurality of circumferentially arranged blades having a tapered cutting portion (82, 93) thereon for cutting a window in a casing and then sidetracking in a formation. A whipstock has at least three axially spaced ramps, each ramp being interspaced by a substantially axially extending portion. Each of the ramps has the same angle of inclination to a longitudinal axis and the distance between the ramps is the same as the distance between the tapered portions on the mills (8, 9) so that when, in operation, load is shared between both mills. The mills have a button (83, 93) of hardened material located on the tapered cutting portions so that the button abrades the whipstock ramps (31, 32, 33).

Abstract: System and methods for guiding the drilling of a horizontal well are disclosed. A current is provided in at least one conductor positioned in a target vertical well. A magnetic field generated by the current is measured at a drilling assembly that is drilling the horizontal well. A direction from the drilling assembly to the target vertical well is determined based at least in part on the measured magnetic field. A distance from the drilling assembly to the target vertical well is determined based at least in part on the measured magnetic field. The determination of the distance includes determining at least one gradient.