Wellbore Stability Analysis Using Geomechanical Units in One of the Gas Fields in South of Iran

In this study, a collection of methods is used to analyze wellbore stability in the south of Iran. Elastic moduli such as Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio and UCS of the formation are calculated using compressive and shear wave velocities which are provided by DSI logging tools. Afterwards, the calculated dynamic moduli are calibrated to static values using empirical equations extracted from a neighboring Salman field. These static moduli clustered by multiresolution graph-based clustering (MRGC) method to produce geomechanical units. After establishing the geomechanical units by MRGC, the geomechanical units evaluated through correlating with the caliper, gamma ray and NPHI logs. In next step, pore pressure model of the well is determined using Eaton’s equation. In the last phase of the research, the mud window for each geomechanical unit is determined regarding to angle of breakout. The angle of breakout in each geomechanical unit must be less than 90 degrees to have a stable well. This study suggests a new procedure for borehole instability analysis in vertical and directional wellbores. Presented method in this project can be used for easy and reliable determination of critical mud weight and wellbore trajectory required to maintain wellbore stability.