F Abazari - MSc student of Drilling Engineering, Shahid Bahonar University of Kerman, Iran,

Analysis of wellbore instability includes estimation of formation mechanical properties and the state of in situ stresses. In this analysis, the only controllable parameter during production operation is the bottom hole pressure. If the bottom hole pressure is larger than anticipated, the wellbore is stable and the failure of the matrix formation results from the reduction of reservoir pressure and the increase of existing stresses is created, to be prevented and also prevents sand production. On the other hand, a lower pressure can result in shear failures of rock, which is known as borehole and matrix formation breakouts can result sand production. To predict the potential for failures around the wellbore during production, one should use a failure criterion to compare the rock strength against induced tangential stresses around the wellbore at a given pressure to boundary hole with modelling and simulation is one of the analyses methods. The analysis was carried out using COMSOL software by applying the two failure criteria of Hoek-Brown and Mohr-Coulomb. The input parameters which were considered into account prepared from the Copal oil field. Finally based on the analyzed results the optimum bottom hole pressure was obtained for prevent from falling out, shear failure and sand production. In the well and brunched well for all different diameter and angle junctions, Hoek-Brown predicate minimum bottom hole pressure greater than the Mohr-Coulomb. Therefore, the bottom hole pressure should be higher than these values and in brunched well, the most unstable part is oil wells.

wellbore stability, COMSOL software, brunched well, failure criteria, bottom hole pressure