On the Development of Reliability-Based Design Rules for Casing Collapse

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe API design rules for casing collapse 1 give widely varying predicted failure probabilities over the D/t range for well tubulars. For low D/t, they give unconservative designs (excessive risk); and for moderate D/t, over-conservative designs (excessive safety).This paper describes the development of improved design equations, calibrated using structural reliability methods to obtain a uniform predicted failure probability. The new design rules are simpler to use than the existing API equations, and give either safer or more economic design, depending on D/t ratio.

Quantitative Risk Assessment of Oil Well Casing Strings under Non-Uniform External Loadings

“…For uncertainties are difficult to avoid, the traditional design method is difficult to deal with a lot of unknown factors and parameters change. In recent years, many scholars at home and abroad have developed a series of related studies on the reliability of casing strength [1][2][3][4][5][6][7][8], but have not yet established a systematic method of safety and reliability evaluation for oil well casing strings. Based on the theory of strength-load interference model and the Monte-Carlo method, the article analyzes the factors of casing safety and reliability in random distribution, obtains the probability distribution of casing collapse strengths under non-uniform external loadings, and simultaneously the relationship between the reliabilities and safety factors by means of different casing types in a designated region.…”