The Stress Analysis Of Casing Under Impact Loads

Vibration cementing is a new technology to improve cementing quality.It utilizes hydraulic pressure,mechanical vibration,air pulse and hydraulic impact means to produce vibration liquid which will act on casing pipe,drilling fluid and cementing fluid during the process of running casing,cementing,displacement and waiting-on-cement.Vibration technology was first used in the concrete pouring process of the construction industry.In this paper,Casing oscillator drew lessons from working principle of oscillator(cement concrete vibrator)in the construction industry.Casing oscillator had a periodic impact on casing which made casing vibration.We tamped cement slurry between the casing and the wall,improving the cementing strength of the interface,shortening the gelation time of cement paste,making the cement and casing and stratum closely knit combination,excluding in cement slurry bubble,eliminating cement voids and pits and achieving the purpose of improving cementing quality.This paper introduced the vibration principle of casing oscillator,and analyzed the strength for thread connection part of casing weak links under impact loads,and discussed transverse displacement of casing and pressure attenuation law of annular cement paste under impact load,the following results have been achieved:(1)Through the study of the basic structure of casing oscillator and the motion of oscillator in the casing,the vibration of the casing under the action of the oscillator and the fluctuation of paste caused by casing vibration are analyzed.(2)Through the study of API with 139.7×7.72 mm N-80 steel grade of thread connection part of conical casing,it analysed the stress and strength of casing threaded connection part and stress distribution of thread connections under impact loads.(3)It established the vibration analysis model of casing under different conditions in the borehole and made use of ANSYS finite element to analyse the transverse vibration of casing.Change regulation of casing transversal displacement under different impact load,and the frequency and analysis length of casing were gotten.(4)Through the establishment of the physical model of the annular cement paste,the pressure pulse of the annular cement paste is analyzed by FLUENT flow field.And the attenuation law of the pressure pulse is obtained for annular cement paste.