A rotary drill bit (10) has a jet pump device including a plurality of jet pump assemblies (26). Each jet pump assembly (26) has an outer housing (28) secured to the bit body (14) and receiving any elongate nozzle member (46) therein in concentric relation to form an annular chamber (48) therein. A flow restriction (38) is mounted within the outer housing (28) above the nozzle member (46). The elongate nozzle member (46) has a lower nozzle port (50) and an opposed upper nozzle port (52). Drilling fluid from the central bore (20) is directed to the nozzle member (46) where the drilling fluid is divided into two streams, one stream for flow through lower nozzle port (50) against the formation and the outer stream for flow through the upper nozzle port (52) and flow restriction (38) to create a low pressure area or suction in an annular chamber (48). A low pressure cross sectional area is formed at the bottom of the bore hole (B, FIG. 4) and drilling fluid with entrained formation cuttings is drawn upwardly through the annular chamber (48) and the flow restriction (38).

A ground drilling machine comprises a controller for automatically controlling the injection of working liquid according to the output signal output as a function of the rotating condition of the pilot head 20. When the pilot head 20 is driven forward or backward, working liquid can be injected by switching the working liquid transfer valve 111 so long as the pilot head 20 is revolving in order to improve the digging efficiency, the soil delivering efficiency and the cooling efficiency of the machine. The injection of working liquid can be suspended when the direction of propelling the pilot head 20 is shifted while stopping the revolution of the pilot head 20 because no working liquid is required for delivering the dug soil and cooling the leading body. Thus, working liquid can be injected always at an optimal rate depending on the rotating condition of the pilot head 20 to suppress any waste of working liquid and reduce the construction cost.

A chip breaker for use in a fixed-cutter, rotary-type drill bit used in drilling subterranean formations is disclosed. The chip breaker includes a knife-like protrusion positioned proximate a cutting element and adjacent or in a fluid course defined by the drill bit body. As formation chips, shavings, or cuttings are generated during drilling, the chips move over the protrusion and are split or scribed by the protrusion. Drilling fluid breaks the split or scribed chips away from the surface of the fluid course adjacent the cutting element and transports them through the junk slots. Additionally, chip splitters may be positioned on ramped surfaces that further lift the formation chips away from the surface of the fluid course.

A drilling method in which a rotary drill bit is mounted on a tubular drillstring extending through a bore comprises: drilling through a formation containing fluid at a predetermined pressure; circulating drilling fluid down through the drill string to exit the string at or adjacent the bit, and then upwards through an annulus between the string and bore wall; and adding energy to the drilling fluid in the annulus location above the formation. The addition of energy to the fluid in the annulus has the effect that the pressure of the drilling fluid above the formation may be higher than the pressure of the drilling fluid in communication with the formation and that predetermined differential may be created between the pressure of the formation fluid and the pressure of the drilling fluid in communication with the formation.

The present invention generally provides apparatus and methods for reducing the pressure of a circulating fluid in a wellbore. In one aspect of the invention an ECD (equivalent circulation density) reduction tool provides a means for drilling extended reach deep (ERD) wells with heavyweight drilling fluids by minimizing the effect of friction head on bottomhole pressure so that circulating density of the fluid is close to its actual density. With an ECD reduction tool located in the upper section of the well, the friction head is substantially reduced, which substantially reduces chances of fracturing a formation.