The Effect of Casing Wear on the Burst Strength of Casing—Part 2: Statistical Burst Strength of Worn and Unworn Casing Strings

Abstract

A theoretical analysis has been performed to determine the effects of wear on the burst strength of casing. Burst occurs either by a leakage at the casing joint or by a rupturing of the casing wall. The statistical nature of rupturing of casing is presented in this paper; joint leakage is discussed in a companion paper[1]. A method is presented in this paper that calculates the probable burst strength and confidence limits given the statistical distribution of casing properties; this method may be used for both worn and unworn casing. Using a limited set of casing properties, the analysis shows that the API methods for determining burst resistance may result in burst values that have very low probabilities of failure. In addition, the data used show that considerable casing wear can be tolerated before there is a significant probability of rupturing the casing wall under API calculated burst pressures.