3D Numerical modeling of the effect of in-situ stress ratio on mud weight window in the drilling of the Zagros sedimentary basin

The study of factors affecting wellbore stability has become very important in the oil and gas industry because they will save time and costs. In studying the stability of oil and gas wells, different factors such as mechanical properties, in-situ stresses, and pore pressure can be used. Consequently, knowing and calculating these parameters will be helpful in analyzing the wellbore stability. This study evaluated the effects of changing stresses on the wellbore stability and drilling mud weight window using a ratio of different stresses for the first time in one of the wells of the Zireh gas field, located in the southwest of Iran. Due to the lack of laboratory data, each of the parameters of the geomechanical model were determined by empirical correlation. Using Mohr-Coulomb and Mogi-Coulomb criteria, the drilling mud weight window was determined to be 76.99-128.17 (pcf) and 67.56-128.17 (pcf), respectively; however, Mogi-Coulomb provided better results. The wellbore stability is also investigated by using 3D numerical modeling using ABAQUS software and the Mohr-Coulomb criterion. According to the results of the numerical and analytical methods, the well is completely stable. Ultimately, five different in-situ stress ratios were examined to determine how in-situ stress distribution affected wellbore stability. According to the results, the mud weight window range decreases as the stress changes from an isotropic to an anisotropic state, indicating wellbore instability.