Determining blowout risks for producing wells

A method for estimating the probability that a producing well will blow out uses a fault tree to analyze how each piece of completion equipment affects the well's overall integrity. The technique attempts to predict blowout frequency and to pinpoint changes that could be made to a well completion to maximize its reliability. The simplified well-completion diagram includes the Christmas tree, casing, tubing, packer, and safety valve. A basic problem in reliability analysis is the lack of accurate, universally accepted component failure rates. By properly representing the relationships that cause the top event probability, a realistic failure tree, along with a sensitivity analysis, can partially compensate for the deficiencies in the component failure rate. Also, in comparisons of similar systems having many common components, inaccuracies in three failure rates of those common components, inaccuracies in the failure rates of those common components tend to have little effect on the overall ranking. An important element of each well system's leak probability is the risk that accompanies workover procedures; when workover is included in the computation, the well completion's leak probability rises significantly due to the higher risk.