Abstract: It is very difficult to diagnose the downhole condition and predict the casing failure or damage, which is caused by h factors as unclear circumstances around the wellhole, unknown loads to casing, complicated failure chanism, fuzziness of many factors, fuzzy relation between cause and effect of casing damdge, etc. On the is of analysis of these factors, this paper establishes a model to deal with the fuzzy relation, and presents a new thod—sequential fuzzy sythetic evaluation (SFSE), which can predict the down-hole condition according he given data of the well and the field. This method provides a new way for the prediction of the service-life ownhole casing.

Key words: Casing failure, Life, Prediction, Fuzzy analysis, Evaluation