Development and investigation of continuous circulation drilling

Continuous circulation drilling(CCD)can maintain the continuous circulation of drilling fluid when making or breaking the stands of drill pipe,which will build up the steady equivalent circulating density(ECD)and guarantee the uninterrupted blowing out of the debris.Currently,there are mainly two ways to realize continuous circulation drilling,namely continuous circulation system(CCS)and continuous circulation valve(CCV).The analysis show that compared with the conventional drilling method,continuous circulation drilling have significant technical advantages,since it can eliminate bad effect,such as surge swab,cutting settlement and gas accumulation,and improve the ECD control ability,which will effectively reduce incident and strengthen drilling safety.So it has much important practical value in many fields,such as the well with little pore/fracture pressure gradient difference,deepwater well,extended reach well,horizontal well,underbalanced well,high pressure and high temperature well,and gas hydrate exploration well.In addition,according to the status,characteristics and trends of CCD technology,and considering the technological level and operational safety,it was proposed that the main research objective in future should be to develop continuous circulation system and to solve the problems of some key technologies such as drill pipe protection,joint thread protection,dynamic seal in high pressure,and mud diverting control.