Evaluation of Wellbore Stability by Analytical and Numerical Methods; a Case Study in a Carbonate Oil Field

Abstract

The instability of the wellbore has significant effects on drilling, causing delays in operations, increasing costs, and ultimately may result in the abandonment of wells. Nowadays, it is possible to stabilize a wellbore by changing the drilling mud composition. With the help of rock mechanics and knowledge of the mechanical properties of the formation, the optimal path for the drilling of the well and the window of the mud is determined. Several features of the formation are influential in wellbore design; knowing these features is necessary for designing optimal mud weight to ensure wellbore stability. In practice, analytical methods for the calculation of the optimal mud weight are more convenient than numerical ones because the latter needs information on many samples that are usually unknown at the commencement of the project. This research investigates the wellbore stability in the Kupal carbonate oil field using an analytical method with three rock strength criteria of Mogi-Coulomb, Mohr-Coulomb, and Hoek-Brown failure. We conclude that the Mogi-Coulomb criterion predicts a minimum drilling mud pressure and is more conservative. This is due to the use of its intermediate stress.