The torque of a rotating bit has a close relationship Le couple d'un trépan en rotation est en rapport to the movement of teeth of the bit and to the drilling - étroit avec le mouvement des dents du trépan et aussi rate. Under loads of 500 9,000 kilograms with - avec la vitesse de forage. Sous une charge allant de rotary speeds of 22 168 rpm, the torques of 29-in., 500 kg à 9,000 kg avec une vitesse de rotation allant 33411. and 4 - in. bits were measured accurately at de 22 à 168 tours/minute, on a mesuré avec précision atmospheric pressure. In these measurements both le couple de trépans de 23, 3+ et 43 inch à la pression three-cone bits and two-cone bits were used. With atmosphérique. Dans ces essais, on a utilisé des trépans constant rotation of a bit the torque varies periodi- tricônes et bicônes. A vitesse de rotation constante du cally affected by a height and shape of a tooth and also trépan, le couple varie périodiquement en fonction de by a spacing of teeth. As a bit rotates with constant la hauteur et de la forme des dents et aussi de leur speed, each cone does not necessarily rotate with espacement. Lorsque le trépan tourne à vitesse constant speed, but partly slips occasionally. This constante, chaque cône ne tourne pas nécessairement de phenomenon is influenced by bit weight, rotary speed façon constante, mais est soumis à des glissements and also by rock characteristics. momentanés. Ce phénomène est influence par le poids (qui s'exerce sur) le trépan, par la vitesse de rotation et par les caractéristiques de la roche.
Mechanical factors Main mechanical factors influencing drilling rate Factors affecting drilling are
weight on bit,
rotating speed, and
drillingfluid hydraulics and properties.
At constant rotating speed, bit condition and hydraulics, the drilling rate Some of the recognizable variables affecting drilling increases as weight on bit increases, if hydraulics are rate are practically divided into three groups as sufficient to remove cuttings. Similar to bit weight, follows :
Formation characteristics,
Mechanical rotating speed affects the drilling rate linearly as long factors,
Bit selection. as sufficient hydraulics is maintained.
At a given bit weight and rotating speed, the drilling rate increases Formation characteristics with the increase in hydraulic horse power until a point Generally penetration rate varies inversely with the where no regrinding occurs under a bit reaches. compressive strength of the formation being drilled.
The compressive strength, however, is not always a Bit selection reliable guide to drillability. Hardness and abrasive In drilling a well the effect of bit type on drilling properties of rocks affect teeth of a bit, and therefore, rate is an important consideration. Bit selection is the penetration rate is also influenced by these pro- governed primarily
