Experimental Study On Dynamic Buckling Of Oil And Gas Well String When Hitting The Bottom Of Well

Oil and gas,as a non-renewable energy source,plays an important role in the national economy.in oil and gas drilling operations,the buckling problem of a tubular string in wellbore has always been the focus of petroleum engineering research.Most scholars study the static buckling of the tubular string through simplified model.However,the string occasionally breaks off or slips during drilling and production operations,which causes the string to slide down along the wellbore and eventually hits the bottom of the well.Under this condition,the string is subjected to transient impact loads,which may lead to dynamic sinusoidal buckling,helical buckling,and even plastic deformation or fracture,affects oil and gas production or downhole operations.The pipe string hitting the bottom of the wells is an issue of tubular string impact dynamics in oil and gas wells,in view of this problem,this paper carried out research by means of laboratory test.A dynamic buckling test rig was developed for tubular string hitting bottom hole.With high elastic silicon rods as a string,the dynamic buckling experiments was conducted when string hits bottom of the vertical well and the directional well.The dynamic displacement value,strain value,velocity value of the tubular string were measured when the simulation tubular strings with different diameters,or different mass weights hit the bottom of vertical wells and inclined vertical wells with different inclination angles by digital image related technology.Several conclusions were obtained.A string falling to the bottom of the well can cause multiple impacts,the peak of the axial strain is the largest during the first impact on the bottom of the well,and then gradually decrease in the subsequent impacts,and eventually become stable.The bottom end of the tubular string is compressed first,and then the compression wave in the tubular string propagates upward along the tubular string during the process of the tubular string hitting the bottom of the well.The tubular string bounces upwards when the compression of the tubular string reaches the maximum,and the tubular string will have tensile deformation after leaving the bottom of the well.The maximum value of velocity,compression,and strain of each point on the tubular string when the tubular string hits the bottom of a well filled with water are much smaller than the corresponding values of the tubular string hitting the bottom of a well filled with air.With the increase of the inclination angle of the wellbore,the maximum value of velocity,compression,and strain of each point on the tubing string decrease,and the impact force on the bottom of the string also decreases when the tubing string impacts the bottom of a deviated vertical well.The test results have a certain reference effect for theoretical research and field practice.