Study Of The Mechanism And Identifying Of Borehole Ballooning During Deepwater Drilling Operation

The phenomenon of borehole ballooning is gradually catch the attention of petroleum industry because it has the same feature with well kick,and workers then may treat it the same as well kick,thus will result in the waste of time and money or the blowout.Therefore,it is necessary to establish an effective method to identify and prevent the borehole ballooning.This paper will study this phenomenon from four aspects: mechanism,causes,identification and prevention.The research shows the ultimate cause of this phenomenon is that the annular ECD is easy to reach or exceed the fracture pressure(leakage pressure),because of the narrow safe density window caused by the poor compaction of shallow stratum.This paper establishes a transient calculation model to forecast the annular ECD under the special temperature field in deepwater formation to keep the ECD stay in the window.Use the FMEA method to divide the deepwater drilling system into three parts: environment,wellbore,platform,and get 15 fault directions may cause the borehole ballooning,then draw the fault tree which contains 5 floors to show the development of this phenomenon.Use AHP to build hierarchy according to the fault directions and get 17 causes from 3 aspects of process equipment,formation and ocean circumstance,human factors and management,then calculate each cause' weight to analyze and sort,and specially control the higher weight causes.Compare the borehole ballooning with well kick and get their essential difference is whether the formation fluid flow in.Take overflow at wellhead as the initial event and draw an event tree which contains four judgement events to preliminary establish a judge method to distinguish the borehole ballooning and well kick,and at last get 5 reasons for the initial event.With considering the special temperature field of deepwater and pressure loss,establish a method to calculate the kick tolerance during deepwater drilling operation,and use this parameter and this method to quantify the wait-observed time to avoid the unwanted shut-in operation caused by borehole ballooning.According to the causes got above,establish a preventive safety barrier for borehole ballooning which contains 6 sub barriers.Evaluate the reliability of this barrier by multi-level fuzzy evaluation method and the result shows that this preventive safety barrier has a high reliability.This paper preliminary establishes methods to distinguish and prevent the borehole ballooning,which can provide a theoretical and technical guidance for dealing with the borehole ballooning in onsite deepwater drilling operation.