Observations on dynamic tensions of drill string during drilling operations of scientific drilling vessel Chikyu

Abstract

The scientific drilling vessel Chikyu began scientific drilling at the Nankai Trough in 2007 via a system integration drilling test off Shimokita. To attain success in deep drilling and coring, one of the important issues is to ensure the strength of the drill pipes. During drilling operations, various forces are exerted on the drill pipe, such as dynamic tension due to vessel heave as well as bending stress due to vessel movement and ocean current. During the design phase, strength evaluation of the drill pipe is conducted under several assumptions. To ensure the strength of the drill pipe, it is important to utilize data acquired from actual drilling operations and to verify the analysis model. Therefore, we acquired drilling data such as vessel motion and hook load during drilling operations. By utilizing the drilling data, the dynamic tension can be estimated and the analysis model can be verified. Furthermore, with the dynamic tension estimated from the acquired data, the weight on bit variation can be estimated. In addition, the occurrence of buckling modeled with parameters such as the weight on bit and drill pipe specifications is discussed. Of course, if there are unexpected phenomena, these can be observed using the drilling data.