Analysis On Distribution Of Load Uncertainty And Safety And Reliability Of Casing In Ultra-deep Well

Geologic structure of ultra-deep well is complex, it is difficult to get a lot of data, so theuncertainty is bigger．In order to ensure casing work safely, the evaluation on the safety andreliability is of great significance．First of all, based on existing research at home and abroad,through the analysis on the geological factors of Xinjiang X Oilfeild and its mechanism ofinfluence of casing load, the calculation model under non-uniform load of well casing loadare established, the geological factors, drilling fluid performance, the performance ofparameters of the casing are carried on the analysis of probability and statistics, Monte-Carlosimulation method is used to determine the distribution of external load under the variouscondition, and they generally obey the normal distribution, then the influence law of therandomness of various parameters on the uncertainty of casing load for ultra-deep well isanalyzed. Second, the calculation model under non-uniform load, high temperature and thelining abrasion of ultra-deep well casing strength are established Monte-Carlo simulationmethod is also used to determine the distribution of casing strength under the variouscondition, and they generally obey the normal distribution as same as load, then the influencelaw of the randomness of various parameters on the uncertainty of casing strength forultra-deep well is analyzed. Third, introducing the principle of "stress-strength interferencemodel" method, according to the distribution of ultra-deep well casing load and strength, thesafety and reliability model of casing is established, the reliability under normal distributionfor casing load and strength are calculated. Finally, Matlab programming language based on the results of the study is used to analyze Well DB104and Well DB6in this area. Accordingto layer upon layer, wellbore structure and distribution of various parameters, calculating thereliability of external, internal tensile pressure of the two Wells for each layer, and with theengineering practice for reference, proves the feasibility of this method. And lists outcoefficient between the reliability and safety and obtain safety and reliability indicators forultra-deep well in Xinjiang X Oilfeild. The results show that when the reliabilities arebetween0.5to1.0, safety factors are generally between1.0and1.25, and the change ofreliability is less than that of safety. When the safety coefficient is greater than1.25, casingreliability is1.0. Reference to the Drilling history, when Casing reliability is greater than orequal to0.8, Safety factor is large enough, and casing can be thought of as safe, which canprovide reference for ultra-deep well casing strength design.