Steel pipe supplied in sections, which are joined together by threaded couplings to increase the total length to connect the rig surface to the BHA. The drill pipe rotates the bit and circulates drilling mud.
The total combination of the BHA, transitional drill pipe, and the drill pipe in use within the well.
Common drilling hazards are lost circulation, gas zones, fluid loss, kicks and differential sticking.
The drilling window is the range of fluid gradients between the pore and fracture pressure gradients. If pressure in the wellbore drops below the pore pressure gradient, an influx is likely to occur. If the pressure in the wellbore exceeds the fracture pressure gradient, well fluids may be lost to the formation and can cause the rock to crack.