A method comprises determining a value of at least one oppositional force for a drillstring at multiple depths in the wellbore, determining a value of hook load for the drillstring at the multiple depths based on the value of the at least one opposition force at the multiple depths, and determining a calibrated drillstring weight based on a change in the value of the hook load over the multiple depths of the wellbore. The change in the value of the hook load can be determined based on a change in a measured hook load and/or a change in an estimated hook load. From the calibrated drillstring weight, an adjusted estimated hook load can be determined.

A method comprises determining a value of at least one oppositional force for a drillstring at multiple depths in the wellbore, determining a value of a drag force for the drillstring at the multiple depths, determining a value of hook load for the drillstring at the multiple depths based on the value of the at least one opposition force and the value of the drag force at the multiple depths, and determining a calibrated drillstring weight based on a change in the value of the hook load over the multiple depths. From the calibrated drillstring weight, an adjusted estimated hook load can be determined. The drag force can be calculated based on a drag per centralizer and the number of centralizers in the wellbore. A centralizer friction factor can be determined and used to calibrate the value of the drag per centralizer.

A method comprises determining a value of at least one oppositional force for a drillstring at multiple depths in the wellbore, determining a value of a drag force for the drillstring at the multiple depths, determining a value of hook load for the drillstring at the multiple depths based on the value of the at least one opposition force and the value of the drag force at the multiple depths, and determining a calibrated drillstring weight based on a change in the value of the hook load over the multiple depths. From the calibrated drillstring weight, an adjusted estimated hook load can be determined. The drag force can be calculated based on a drag per centralizer and the number of centralizers in the wellbore. A centralizer friction factor can be determined and used to calibrate the value of the drag per centralizer.

An inductive transmission element comprising a magnetically conductive electrically insulating, MCEI, annular core. The core comprises an outer wall and an inner wall apart from the outer wall. The respective walls are joined by a planar top surface. The inner wall and the outer wall form an annular trough opening adjacent the top surface. The open annular trough comprises opposed diagonal walls that intersect the top surface and a circular region at the distal end of the opposed diagonal walls. The annular trough opening may be wider or narrower than the planar top surface between the diagonal walls and outer surface. The annular core may be disposed within an annular housing comprising a polymeric block. The diagonal walls may intersect the top surface at an angle greater than 93°. The diagonal walls may intersect the circular region at an angle greater than 93°. The top surface may be polished.

A combination of a pullback adaptor and a drill bit includes a pullback adaptor having a first end, a second end, a body extending between the first end and the second end, and a protrusion extending from the body adjacent the second end. The protrusion has a threaded aperture defining an adaptor mounting axis, and the protrusion defines an annular planar mount surface generally perpendicular to the adapter mounting axis. A drill bit has a body with a steering surface, an aperture extending through the body at the steering surface, and an adaptor mount surface adjacent the aperture. The pullback adaptor is mounted to the drill bit with a fastener that extends through the aperture in the drill bit and into the threaded aperture of the pullback adaptor such that the annular planar mount surface of the protrusion engages the mount surface of the drill bit.

A combination of a pullback adaptor and a drill bit includes a pullback adaptor having a first end, a second end, a body extending between the first end and the second end, and a protrusion extending from the body adjacent the second end. The protrusion has a threaded aperture defining an adaptor mounting axis, and the protrusion defines an annular planar mount surface generally perpendicular to the adapter mounting axis. A drill bit has a body with a steering surface, an aperture extending through the body at the steering surface, and an adaptor mount surface adjacent the aperture. The pullback adaptor is mounted to the drill bit with a fastener that extends through the aperture in the drill bit and into the threaded aperture of the pullback adaptor such that the annular planar mount surface of the protrusion engages the mount surface of the drill bit.

A multi-impeller passive-rotating-stirring-type rotary drilling rig for open caissons includes a hollow main drill pipe, a drill bit, four cutting edges, four impeller shafts, four passive impellers and a rotation bracket. Through being uniformly distributed at a peripheral of the drilling rig, four passive impellers contact with a hole wall of a borehole during the drilling process for passively generating relative rotation opposite to the rotation direction of the drill bit, so as to accelerate sufficient mixing of silt and water for forming mud during the drilling process, thus enhancing the stirring effect of the drill bit on the mud. The present invention is able to improve the mud discharge efficiency without adding additional power, thus avoiding the blockage of the mud suction pipe and blockage or even breakage of the drill bit due to poor mud discharge during the drilling process.

A multi-impeller passive-rotating-stirring-type rotary drilling rig for open caissons includes a hollow main drill pipe, a drill bit, four cutting edges, four impeller shafts, four passive impellers and a rotation bracket. Through being uniformly distributed at a peripheral of the drilling rig, four passive impellers contact with a hole wall of a borehole during the drilling process for passively generating relative rotation opposite to the rotation direction of the drill bit, so as to accelerate sufficient mixing of silt and water for forming mud during the drilling process, thus enhancing the stirring effect of the drill bit on the mud. The present invention is able to improve the mud discharge efficiency without adding additional power, thus avoiding the blockage of the mud suction pipe and blockage or even breakage of the drill bit due to poor mud discharge during the drilling process.

An apparatus for use in maintaining a desired orientation of an implement is provided. The apparatus includes orientation sensing equipment operable to sense the orientation of the implement, and an orientation indicator operable to be mounted relative to the implement, the orientation indicator having a plurality of indication portions, and when the orientation indicator is mounted relative to the implement, the indication portions are positioned so as to be visible from different locations around the implement. In use, when the orientation of the implement deviates from the desired orientation, one or more indication portions provide a visible indication of a direction in which the implement has deviated from the desired orientation.

An apparatus for use in maintaining a desired orientation of an implement is provided. The apparatus includes orientation sensing equipment operable to sense the orientation of the implement, and an orientation indicator operable to be mounted relative to the implement, the orientation indicator having a plurality of indication portions, and when the orientation indicator is mounted relative to the implement, the indication portions are positioned so as to be visible from different locations around the implement. In use, when the orientation of the implement deviates from the desired orientation, one or more indication portions provide a visible indication of a direction in which the implement has deviated from the desired orientation.