Abstract: A steerable earth boring assembly which includes an annular collar and a drive shaft with a drill bit, where the shaft pivots with respect to the collar. An upper portion of the shaft inserts into an orientation sleeve which resides in the collar. An axial bore is obliquely formed through the orientation sleeve, and in which the upper portion inserts. An angular offset between the drive shaft and collar is changed by adjusting azimuthal positions of the orientation sleeve with respect to the collar. A brake assembly is included for applying a restraining force onto the orientation sleeve.

Abstract: A rotary steerable drilling tool with an electromagnetic steering system can include a drill collar, a bit shaft, an orientation control module, a mud tube, a mud tube coupler, a universal joint, a mud sealing device, and a drill bit. The bit shaft can be mechanically coupled to the drill collar through the universal joint and the orientation control module and rotate about the universal joint. The orientation and the inclination angle of the bit shaft against the drill collar can be controlled by the orientation control module with the electromagnetic steering system. The orientation control module can include an array of electromagnets, an array of permanent magnets, a rotor, and a set of bearings. The orientation control module can be coupled to the bit shaft through the rotor. The movement of the rotor can be driven by the interaction between the array of electromagnets and the array of permanent magnets.

Abstract: An oil-based mud formation imaging tool for measuring electrical properties of surrounding formation includes at least one base plate, a first port and a second port deployed on the base plate, surface conductors covering both sides of the base plate, and inside conductors deployed in the first port and the second ports and with gaps from the edges of the first and second ports. The first port is fed with electromagnetic signals by a waveguide and a coupling is formed between the imaging tool and the surrounding formation accordingly. Resonance signals are induced at the second port to be used to compute corresponding formation resistivity and dielectric constant. A corresponding imaging method is also provided.