Abstract: A drill bit for drilling through sticky formations, such as chalk or marl, comprises a plurality of waterways for transporting drilling fluid and rock flour to the gauge of the bit. These waterways have in downstream direction gradually increasing cross-sectional areas A, the increase of size of said areas along the length of a waterway being at least substantially proportional to the squared radius r thereof from the central axis. In this manner the rock flour velocity remains equal or decreases in downstream direction in the waterways so that the risk of rock flour accumulation and compaction is reduced.

Abstract: A tubular drill string element, such as a stabilizer or tool joint, comprises an outer surface having in circumferential direction a ratchetted profile. The ratched profile is preferably oriented such that provides low resistance against right hand rotation but high resistance against left hand rotation of the drill string.

Abstract: A rotary drill bit is provided with cutting elements having a front layer of interbonded abrasive particles, such as synthetic diamonds, which layer has a thickness that varies with distance from the bit body. The characteristic relation thus obtained between bit agressiveness and bit wear can be used to monitor the bit wear condition during drilling.

Abstract: A tubular drill string element, such as a stabilizer or tool joint, comprises an outer surface having in circumferential direction a ratchetted profile. The ratchetted profile is preferably oriented such that provides low resistance against right hand rotation but high resistance against left hand rotation of the drill string.

Abstract: A downhole drilling motor is disclosed in which an output shaft is allowed to translate in axial direction relative to the motor housing over a predetermined stroke. Fluid pressure of a drilling fluid pumped to a rotary drill bit driven by the motor may be used during operation of the motor to exert a predetermined axial force to the output shaft so as to control the axial force exerted to the bit during drilling.

Abstract: A drag type bit is equipped with nozzles for creating high velocity mud jets discharging into waterways in front of the wings of the bit, which nozzles are oriented such that each jet successively strikes the borehole bottom and front face of a wing at a small angle.

Abstract: A rotary drill bit is provided with a plurality of cutting elements having a front layer of abrasive particles, wherein the cutting elements located in the center region of the bit comprise a thicker abrasive front layer than those in the outer region of the bit. The bit design enables optimization of drilling characteristics.

Abstract: A rotary drill bit comprising a tubular strainer element co-axially arranged within the body of the bit and being provided with narrow axial slots arranged to prevent solid debris from passing to the nozzles of the bit. The self-cleaning ability of the strainer element is enhanced by increasing the bore of the strainer element in the region below the slots.

Abstract: The cutting elements of a rotary drill bit comprise a thin front layer of interbonded abrasive particles, such as diamonds, which layer has a thickness less than 0.45 mm.