Finite element analysis tool for factor of safety prediction in the tie-back (casing in casing) region for oil wells.



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Within the oil and gas field the tie-back technique is used to enhance blowout and collapse resistance within the well. Approved methods do not currently exist for analyzing the tie-back due to casing eccentricities and defects. This research performs in house experimental testing to determine cement material properties, and develops a fully three dimensional finite element analysis tool using COMSOL Multiphysics paired with MATLAB. The finite element analysis tool is used for calculating the probabilistic factor of safety in the tie-back region with stochastic material properties, eccentricities, and cement voids. Results are presented for the factor of safety over a wide range of loading and geometric scenarios. Results show that the factor of safety is dependent upon maintaining concentric casing strings, showing reduction by as much as 7%, but when including voids – in select scenarios – the reduction is nearly 35%.