Safety Analysis For Downhole Wellbore During Perforating

In recent years,with the development of perforation technologies,the field perforation operation effects have been greatly improved.Meanwhile,the perforation explosion will produce additional dynamic impact load in the narrow and long confined downhole space,resulting in the damage of downhole string,packer,pressure gauge and other tools.The risk of downhole perforation safety accidents greatly increases during perforating in the deep-water or ultra-deep-water wells,and deep wells or ultra-deep wells involved complex perforation technologies with the bad downhole working environment,which easily causes huge economic losses and threatens the safety of field operators and equipment.By this,this study carries out the related research work for the downhole wellbore safety problems during perforating from four aspects: perforation load output characteristics and prediction method,dynamic response law of string and packer,wellbore safety evaluation method and string system reliability evaluation,the main research achievements in this paper can be summarized as follows:(1)Based on the knowledge of multidisciplinary theory,the dynamic load output characteristics of downhole perforation are analyzed,which the formation mechanism and propagation laws of perforating shock wave in wellbore fluid are revealed.The numerical simulation calculations of downhole perforation performance under actual working conditions are carried out on the large-scale computer.The influence laws of different factors(total charge of perforation,wellbore initial pressure,downhole explosion effective space,detonation time interval of perforating bullets and formation pressure)on perforating impact pressure is discussed,and the peak value prediction model of which is established and verified by field cases.(2)By the finite element dynamic analysis,several sets of simulation models including hundreds of perforating bullets are established.The dynamic mechanical behavior,vulnerable links and key parts of the perforated string are acquired by extracting the dynamic data of that in different directions,positions,and times.The dynamic response laws of perforated string and packer under various working conditions are obtained,such as different perforating gun centering conditions,loading forms,perforation operation parameters,perforation technologies,string conditions and wellbore conditions and formation conditions are obtained.(3)The movement mechanism of the perforation fluid is described by establishing the motion equations.The safety distances calculation model of the packer is proposed by combining the theoretical method with the numerical simulation.The safety discrimination methods of different types of packers are formed.According to the statics and dynamic check of perforated string,the optimized combination design of which is carried out.On this basis,the downhole perforation safety optimization scheme is set up by optimizing the installation positions and number of shock absorbers,combing with safety distances optimization measure and others.The above research results are applied to field examples,which the proposed research methods are verified,and the downhole perforation safety analysis software is developed.(4)The reliability evaluation model of perforated string system under random perforating impact load is established by adding delay time and competition failure modes,which can accurately describe the degradation process of system.The reliability of string system before and after shock absorption is studied based on the dynamic data of the random shock loads on the perforated string by simulation.The results show that the degradation-based failure is more likely to occur than the duration-based failure.The shock absorber should be performed in the defective stage to improve the safety of downhole perforated string.The damage time node of perforated string system is delayed after shock absorption,and the reliability is significantly improved.