Reliability and Risk Assessment Software Development for Casing String in High-Pressure Gas Well

This paper presents eight casing failure modes and the corresponding limit state equations for casing in high-pressure gas well. The manufacture imperfections are considered by introducing the new calculation formulas of casing strength. According to the distribution regularities of casing performance properties, the casing reliability can be calculated with the known distribution of casing strength and load. The casing string is divided into several computing units for reliability calculation and the division criterion is given. Finally, the software named “safety and reliability assessment of gas well casing string in complex status” is developed with the VB6.0 as developing platform. The influencing factors and failure modes probability of casing reliability in different depth are researched and an actual casing is calculated as example. The comprehensive results show that the main influencing factors of casing reliability are collapsing strength and external collapse load, and casing collapse is the main failure mode.