Research And Application Of String Mechanical Model Under Complicated Working Condition

It is of great significance to set up an appropriate string mechanical model to analyze the pipe string's security and stability under complex conditions for the guarantee of safe production in oil and gas field.The main purpose of this study was to research and develop the model and the software for string mechanics analysis and checking under complex conditions.So based on string-step theory,a set of model was put forward to analyze string mechanical in three-dimensional space,the model is applicable to any complex conditions of tubing string stress analysis.It was more simple compared to the common finite element algorithm and method of lateral force and shaft coupling algorithm,the result of model calculation is close to the actual data,and calculation results error is smaller.In this paper,the description of well track including the survey data processing,trajectory of interpolation and extrapolation,track quality assessment are analyzed in detail;At the same time the temperature field,pressure field on the basis of predecessors was improved,deduced symmetrical distributed radial the unsteady heat transfer calculation model of horizontal well;Discussed with annulus were filled with protection fluid or nitrogen cylinder and gas storage cylinder inside and outside pressure balance model is set up respectively,analyzed and calculated the string inside and outside pressure and changes of differences under two kinds of model,the results show that the same tubing pressure,temperature changes,the use of annulus nitrogen injection pressure is far less than only injection of annulus protection fluid pressure;The longer the nitrogen gas column length,the lower the annulus pressure;Tubing fluid temperature and pressure sensitivity analysis showed that temperature of annulus pressure effect is outstanding,the injection of nitrogen column length reaches a certain range,the ability to control pressure is prominent,even it exceeds the scope of the ability to control pressure,it has no obvious change;the best nitrogen column length was studied,nitrogen column length and the best combination packer running depth chart was developed.Compiled with mechanics analysis software of comprehensive functions such as borehole trajectory description,temperature stress field calculation,pipe string design,mechanical analysis and deformation analysis,check analysis,pipe tools database and so on,was widely used in oil field.