A New Approach in Casing Collapse Design Using the Geomechanical Model and Heaviest Drilling Fluid

Abstract

Few industries and undoubtedly no other resources have played such a significant role in modern world development as petroleum. Nowadays, access to geological formations bearing petroleum is slightly difficult due to most shallow reservoirs being close to the end of their economic life. Meanwhile, drilling operations have to get access to deeper reservoirs with more harsh conditions, leading to a considerable rise in instability potential. The consequences of failure are severe, and even simple bore hole instability may lead to the loss of millions of dollars in equipment and natural resources. The bore hole instabilities are not particular, and can happen in simple and very sophisticated drilling operations. In addition, these instabilities are not restricted to the drilling operation, and maybe happen even after many years that the completed well is subjected to the production. The authors intended to develop a new model for the collapse strength analysis of the casing design based on the geomechanical model and heaviest fluid used to drill the well and set the casing. This is based on the hypothesis that indeed the geomechanical in situ stresses and drilling fluid (used to drill the well and set the casing) in the annulus between the drilled well and casing exert radial stresses to the outside of the casing that may collapse the well. This survey leads to the easily computed equation to design the casing collapse strength based on the reality of the well and casing characteristics. This research is used and verified against a numerical model and field data in the South Pars gas field (Phases 6, 7, and 8 and well number SPDG-8) in the Persian Gulf and Cheshmeh Khosh oilfield in southwest of Iran. The results indicate that the proposed model is optimum and possesses satisfactory accuracy and precision.