Open Access

ARTICLE

Uncertainty Analysis Method of Casing Extrusion Load for Ultra-Deep Wells

Meng Li¹, Kanhua Su¹, Zijian Li², Dongjie Li³, Lifu Wan¹

1 School of Petroleum, Chongqing University of Science and Technology, Chongqing, 401331, China.
2 Memorial University of Newfoundland, St. John's, A1C5S7, Canada.
3 Engineering Technology Research Institute, PetroChina Huabei Oilfield Company, Renqiu, 062552, China.

Computer Modeling in Engineering & Sciences 2017, 113(4), 475-495. https://doi.org/10.3970/cmes.2017.113.475

Abstract

With the consideration of the randomness of complex geologic parameters for ultra-deep wells, an uncertainty analysis method is presented for the extrusion load on casing in ultra-deep wells through complex formation at a certain confidence level. Based on the extrusion load model for casing in ultra-deep wells and the prerequisite of integrity of formation-cement ring-casing, the probability and statistics theory is introduced and the sensitivity analysis on the uncertainty of extrusion load on casing is conducted. The distribution types of each formation parameters are determined statistically. The distribution type and distribution function of the extrusion load on casing are derived. Then, the uncertainty analysis of the extrusion load on casing is carried out on several ultra-deep wells in Shanqian block as case study. Several conclusions are made regarding to the field trial result. The randomness of formation elasticity modulus and formation Poisson’s ratio are the main influence factors. The equivalent density profile of extrusion load on casing in ultra-deep wells is a confidence interval with a certain confidence level, rather than a single curve; the higher the confidence level is, the larger the bandwidth of the confidence interval of equivalent density profile becomes, and the larger the range of uncertainty interval becomes. Compared with the result of uncertainty analysis, an error exists in the result of traditional single valued calculation method. The error varies with different casing program and can be either positive or negative. The application of uncertainty analysis of extrusion load on casing provides proof for the accurate determination of casing collapse safety factor. Thus, the over engineering design or under engineering design as a result of tradition casing design will be avoided.

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