Quantitative Risk Assessment on Safety and Reliability of Casing Strength for Oil and Gas Wells

A quantitative risk assessment method of casing collapse resistance and internal pressure resistance is established in accordance with the theory of structural reliability and random theory, in terms of geometrical parameters, mechanical property and external load randomness of casing and on the basis of the analysis on shortcomings of safety coefficient and assessment methods for conventional casing design. Using Monte-Carlo random sampling method, a probability of casing failure with different pressure and a relationship between safety coefficient and probability of casing failure have been obtained by simulating a random distribution regularity of casing strength. Studies show that quantitative risk assessment methods could be adopted to perform quantitative assessment on casing safety and reliability. Casings of different types and under the effect of different external loads have similar safety coefficient and different probabilities of failure. Failure probability assessment index calculated with random theory may provide bases for the selection of conventional safety coefficient and casing design and assessment with uncertain external loads.