Natural fracture characterization and wellbore stability analysis of a highly fractured southwestern Iranian oilfield

Wellbore stability analysis is an essential part of well planning where mechanical characteristics of rocks and the state of in-situ stresses are determined to evaluate the likelihood of borehole failure during drilling. In this study, natural and drilling induced fractures were characterized using image logs for a fractured reservoir located in Southern Iran. Mechanical Earth Modeling (MEM) and wellbore stability analysis were also carried out by the combination of wireline log data and in-situ measurements for a vertical well drilled in this field. The obtained results indicated the presence of several major/minor fractures in the studied interval but majority of them were found to be closed fractures. According to the MEM, formations would suffer from breakout (shear failure) in several intervals which might be linked to their low strengths, huge stress anisotropy and inappropriate selection of the mud weight. Give then fact that the break-out failure obtained from the Mogi-Coulomb criterion had a match with the borehole failure captured by the caliper log, the geomechanical parameters estimated through the methodology proposed should have sufficient accuracy and can be used for the stability analysis of other wells drilled in the same field.