Calculation Method of Allowable Torsional Rotating Number of Compound Drill String under Axial Tension

Compound drill string is often used in deep and ultra-deep well drilling.If downhole complicate conditions as drill string sticking occurs,allowable torsional rotating number needs to be calculated when dealing with these conditions,but so far there is not a calculation method for it.Therefore,proceeding from the material mechanics theory,this paper established mathematic relationship between maximum shear stress and geometrical dimension of the combination string,and evaluted which section reaches allowable value first,then the formula to calculate allowable torsional rotating number was derived.Examples of checking calculation showed that the formula was scientific and reasonable,could provide guidance when dealing with drill string sticking in deep and ultra-deep wells.