Abandonment Decommission Practice of China Bohai Bay: Working FlowOptimized and Cost Reduction

摘要

Although Bohai oilfield is still the main force of China offshore oilfield, some blocks had run out ofproduction and need to be decommissioned. NB field which belonged to CNPC was in this state and has beendecommission. In this job, most of procedure had been optimized. For pursued the best cutting performance,Abrasive Waterjet Cutting System (AWCS) had been used for multi-layer casing-strings and platformscutting operation. Resistance force of casing-string pulled out and platform lifted had been calculated byusing soil mechanics for choosing the suitable floating crane before the lifting operation. A numericalsimulation was provided for checking the max displacement of platform after pile legs were cut. Movingsequence had been made based on the results of the simulation. The operation time of single casing-stringhad been reduced by using optimized working flow. With assistant of 150 tons class floating crane, 7-8 hourscould be saved for each casing-string. Assemblage and dismantlement operation of casing-strings and pilelegs cutting except the first and last casing-string or pile leg of the platform could be saved. The results ofnumerical simulation showed that platforms would have enough stability for decommission operation whileall the pile legs had been cut. Based on the simulation results, all the platforms had been moved used one-stopoperation after they had been cut and much time and money was saved. Based on the results of calculationof pulling out resistance force, 150 tons class and 500 tons class floating crane had been chosen for liftingcasing-strings and platforms. During the job, the deviation of casing-strings was bigger than pile legs. Theextra pulling loading was appeared for conductors. In order to find out the reason of that phenomenon, anexperiment was conducted. The results of experiment could become a guidance for the next job.