Study On The Force Of Casing In Deep Well Cementing

This thesis is part of the project "Mechanics Analysis and Software Study of Downhole Tools" funded by Downhole Services Company of CNPC Chuanqing United Drilling&Exploration Engineering Company.The features of long tubular strings, heavy hanging load, high pressure and long flowing section are especially obvious in ultra-deep wells. As a consequence, many safety issues and failure problems that do not even exist in shallow wells happen frequently in ultra-deep wells, which has a strong impact on the safe and economical operation of ultra-deep wells. At present there are two ways including the well cementing and liner cementing for ultra-deep wells. It remains difficult to determine the safety issues of cementing strings in ultra-deep wells directly by measuring instrument or laboratory tests. At present, the most effective method is to establish accurate mechanical and mathematical models based on the loading features of cementing strings under different conditions, and then complete calculation through software. Massive related literatures were collected, investigated and studied. The research status at home and abroad regarding downhole tools mechanics analysis and calculation software is analyzed. And the existing problems in safety evaluation of cementing strings in ultra-deep wells are discussed and concluded. Then,the main results and the research contents are presented as follows.(1) In the cementing operation of ultra-deep wells, the completion pipe string length, the U-tube effect and the flow rate changes have significant influence on the ultra-deep well cementing pipe string. Three-dimensional tubular string buckling differential equation including the well cementing and liner cementing is established with overall consideration of gravity, friction and fluid pressure inside and outside strings.(2) The mathematical model is established and solved to calculate the fluid velocity under U-tube effect. According to impact dynamics principle, the main causes of pipe vibration is the velocity changes in ultra deep well cementing. The impact loading mathematical model is established at different fluid velocities, which can provide an impact loading theory that agrees better with the actual conditions.(3) The dynamic friction effect model is established under different pumping pressures, displacements and cementing fluid densities. Based on this model, the influence of cementing parameters on the safety evaluation of tubular strings is analyzed.(4) Based on the established mechanics and mathematics models of cementing strings and fluids, a mechanical analysis software is developed. This software contains many mechanical strength databases and tool databases of cementing tubular strings. Therefore, a more convenient and reliable method is proposed for mechanical strength calculation and safety evaluation of cementing tubular strings.