Long Barrel Coring Technology for the Well NV-3 in SakhaLin Island

Well NV-3 is on the shelf of Sakhalin Island, Russia,a location characterized by a sub-Arctic offshore climate. Every year the drilling time window is very short due to the harsh conditions. Here the coring duration must be as short as possible. In order to improve the coring efficiency and reduce the coring time of Well NV-3, the long barrel coring technology was used based on the geological features of relevant formation. Under this scheme, key tools were selected, including coring bit, core catcher and coring barrel, to form an optimal coring barrel assembly. Further, key technical measures were proposed for ensuring the operation safety. Moreover, the formulas were established to calculate the number of reverse cycles and the safe lifting height of drill tools. Practical applications showed that the formulas were satisfactory to the practical conditions, and both the coring barrel assembly and technical measures were efficient, contributing average ROP of 8.4 m/h in coring operation and the recovery rate of the core up to 99.9%. Accordingly, the long barrel coring technology could overcome the limitations caused by the short drilling time window in the sub-Arctic offshore climate and greatly improve the coring efficiency.