P Omidvar - Petroleum University of Technology
S.R Shadizadeh - Petroleum University of Technology

The successful production of oil and gas depends on the proper perforation of casing, which serves as a structural retainer in the well, excludes undesirable fluids, confines and conducts oil or gas from surface strata to ground level. Casing must be capable of withstanding external collapsing pressure from fluid surrounding the casing. Internal pressure encountered in conducting oil or gas from the productive formation, and tension loads resulting from its own suspended weight. Conventional collapse design is based upon uniform external pressure loading, and considers porepressure but dose not account for the effects on casing stresses from the external environment. In addition, the conventional design dose not predict the collapse load of non uniform loaded casing that arises from imperfect cement job, formation voids and casing perforation. This paper describes the result of study on easing subjected to external noon-uniform loading. These loads include the effects cement channels, surrounding formation voids and perforation. Finite element analysis is used for effect of cementing and Elasto-Plastic model for effect of perforation. Using above methods, the results of collapse strength are compared with available collapse test data (e.g. API’s) and other analytical equations.

Casing collapse strenght, Finite Element Analysis, Elasto-Plastic Method, External nonunform pressure, Four-hinge collapse mechanism, Excessive ovality