Design of casing drilling is similar to the conventional drilling design.Considering the main factors is the casing drliing.casing drilling bear more stress than conventional drilling.
The first factor to consider is the engineering design of bending.When the moment of the compression load and casing/wellbore geometry generated was big enough to make the casing buckling,then the casing bending can occur.if it bending,which may cause wear,high torque and high stress.The second factor to consider is the fatigue failure.Fatigue damage is caused by the stress is far less than the elastic strength of the material when the alternating load.Under repeated loading,withstand high stresses the beginning part of the small crack,the crack will extend to the casing body. The cross section until the rest of the static load far enough to withstand.
During drilling, the drill collar from the lower part of the eye, reaming drill the borehole enlargement to greater than the outer diameter of the sleeve. The cannula into the mud, returned by the annular space between casing and borehole. The drill bit is fixed in a specially designed tool group front, tool set to lock in the end of the casing, and through the wire rope and a special for the next drill winch is connected.