Rotary drill bits

A rotary drill bit, for drilling wells in subsurface earth formations, and designed for rotation in a given direction comprising:

• a bit body having an internal passageway for drilling fluid, an operating end face, and at least one opening through said operating end face communicating with said passageway;
• cutting means on said bit body forming at least one elongate cutting region extending generally radially along a substantial portion of said operating end face, said cutting region having cutting surface means facing in a forward direction with respect to said direction of rotation and generally continuous cutting edge means at the outer extremity of said cutting surface means;
• said cutting means comprising a plurality of cutting elements arranged in a row along said cutting region, each of said cutting elements having an outer cutting edge, said outer cutting edges jointly forming said cutting edge means and the total combined length of said outer cutting edges in said row equalling at least 80% of the overall length of the row;
• an elongate fence carried on said bit body, extending generally parallel to said cutting region, and spaced from said cutting region in a leading direction, said fence being adapted to ride loosely over the earth formation in use and in the absence of a positive pressure differential across said fence rear-to-front, and to more tightly engage said earth formation in the presence of such positive pressure differential, the tightness of engagement increasing with said pressure differential;
• said at least one opening being positioned to deliver drilling fluid from said passageway to the area between said cutting region and said fence.