Plastic limit analysis of defective casing for thermal recovery wells

The service life of the casing is one of the technical problems affecting heavy oil recovery efficiency. Plastic limit analysis of the defective casing can effectively prevent casing failure and improve the comprehensive service life in high temperature and pressure thermal recovery wells. In this paper, the analysis of such influencing parameters as defect shape, defect depth, defect circumferential spread, defect number and defect distribution are conducted respectively and it is proven that defect depth and circumferential spread are the main controlling factor to the plastic limit load of defective casing. Furthermore, plastic limit load mathematical model of defective casing caused by the combination of high temperature and high steam injection pressure is presented through the classical formula of plastic limit load for ideal circular tube. The model is then amended by the numerical calculation results and proven to be in good agreement with the data gained from the defective casing blasting failure experiment. Hence, the presented mathematical model can accurately predict the plastic limit load of defective casing in thermal recovery wells.

► We found defect depth and circumferential spread are the most sensitive factors. ► The mathematical model of plastic limit load is simple and practical. ► We consider defect physical parameters and temperature on the plastic limit load.