Discussion on the Design of Well Trajectories in Deepwater Relief Wells

Because there is no standard or actual design experience to serve as a reference in well trajectory design for deepwater relief wells in China,work was done to develop selection charts that would connect points(targets)in accordance with principless for deepwater relief well locations.They were developedin a way to respect the restricted conditions in drilling relief wells,they were individually evaluated for each of the four kinds of common relief well trajectories:"J" shape,parallel close connected shape,directly connected,and "pass-by" shapes.Research results showed that the well trajectory with "pass-by" shape had a great advantage in improving the measurement range and position accuracy.Consequently,it has been determined to be the preferred well trajectory for deepwater relief wells,and divided into four stages,i.e.approaching,positioning,tracking and intercepting.The key design factors as the entrance angles at all stages and well spacing,etc.,have been studied,and it was determined that when the maximum inclination angle of the relief well is less than 60°,the dogleg should be not greater than 3°/30m,which determines the basic design method of well trajectory in deepwater relief wells.The method has been used for designing well trajectories in a deepwater relief wells in the CNOOC overseas block.Research results showed the newly-developed method could provide valuable guidance for designing well trajectories in deepwater relief wells in China.