In petroleum drilling technology, a drill string in an oil rig is the column, or string, of drill pipe with attached tool joints that transmits fluid and rotational power from the kelly or top drive to the drill collars and bit. Often, especially in the oil patch, the term is loosely applied to both drill pipe and drill collars.
In rotary drilling, it is typical to employ a multi-cone bit at the lower end of a drill collar string which is suspended from the lower end of a drill pipe extending upwardly to the surface.
Drilling fluid or "mud" is pumped down the drillstring and out of orifices in the bit and returns to the surface via the well annulus to cool the bit, clean the borehole bottom and to carry cuttings to the surface.
A drilling fluid is pumped down the drillstring and passes into the bottom of the borehole through orifices in the bit 11, and circulates back to the surface via the annulus between the drillstring and the borehole wall.
On lifting and rotating the drillstring, the mandrel moves upwardly relative to the housing whereupon the lugs interlock with the splines to allow rotation of the drill bit as it is lifted off bottom.
Drilling mud is circulated down the central passage through the drill collars, mandrel and couplings to the drill bit and the drillstring rotated in the conventional manner.
If a directional hole is to be drilled, the principal resistance to rotation of the drillstring may be at a midpoint, for example near or at a whipstock, and the shear sub may then be most advantageously connected in the drillstring at a midpoint.
Feeds |
Contact