A dynamic shut-in procedure is commonly adopted after a kick incident in order to build up the wellbore pressure, obtain reservoir information, and thereby handle the gas kick. In deep-water scenarios, the hydrate growth behaviors have a significant effect on gas migration and interphase mass transfer, which has not been quantitatively analyzed during the well shut-in process. In this study, a comprehensive mechanistic model of wellbore dynamics is developed considering gas migration and phase transitions. The simulation results show that the wellbore pressure field can be built up in different trends during different well shut-in periods, governed by gas seepage from the reservoir and gas migration along the wellbore, respectively. Masking the migration of free gas, the phase transition phenomena have a significant influence on the wellbore dynamics and bottomhole pressure. This work adds further insights into quantitatively characterizing the hydrate growth behaviors and interphase mass transfer rules of gas bubbles during a dynamic well shut-in procedure.
Although Bohai oilfield is still the main force of China offshore oilfield, some blocks had run out of production and need to be decommissioned. NB field which belonged to CNPC was in this state and has been decommission. 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 platforms cutting operation. Resistance force of casing-string pulled out and platform lifted had been calculated by using soil mechanics for choosing the suitable floating crane before the lifting operation. A numerical simulation was provided for checking the max displacement of platform after pile legs were cut. Moving sequence had been made based on the results of the simulation. The operation time of single casing-string had been reduced by using optimized working flow. With assistant of 150 tons class floating crane, 7-8 hours could be saved for each casing-string. Assemblage and dismantlement operation of casing-strings and pile legs cutting except the first and last casing-string or pile leg of the platform could be saved. The results of numerical simulation showed that platforms would have enough stability for decommission operation while all the pile legs had been cut. Based on the simulation results, all the platforms had been moved used one-stop operation after they had been cut and much time and money was saved. Based on the results of calculation of pulling out resistance force, 150 tons class and 500 tons class floating crane had been chosen for lifting casing-strings and platforms. During the job, the deviation of casing-strings was bigger than pile legs. The extra pulling loading was appeared for conductors. In order to find out the reason of that phenomenon, an experiment was conducted. The results of experiment could become a guidance for the next job.
Casing pipe continuous flow cryostat system is the subsystems of liquid nitrogen freezing temporary plugging project. It is also an important supporting system which make the cooling uniform, safe and stable. The requirement analysis of cryogenic user have been carried out. The main technical specifications and requirements of the system has been defined. The process flow design and key components design have also been carried out. A verification experimental system has been built. The experimental results show that the design of continuous flow cryostat system is reasonable and the outlet temperature fluctuation is less than 0.3K, which can meet the design requirements.
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