Integration of Borehole Image Logs and Rock Mechanics for Critically Stressed Fractures Analysis in Weak Carbonates

This paper presents the 3D coupled geomechanics analysis of the weak carbonate section within the Shu’aiba Formation in eastern Saudi Arabia. The target interval is composed of limestones with a high matrix porosity and several layers of anhydrite.

A geomechanical model was built to analyze critically stressed fractures using calibrated 1D mechanical earth models for 29 wells, pore pressures, conventional logs and geostatistical modeling to allow propagations of rock mechanics properties into the geological framework.

The ductile/brittle zones were established on the basis of Poisson’s ratio and Young’s modulus analysis integrated with the fracture density from borehole images. These zones show that the barriers, lagoon and slope shallow facies were the most brittle.

A critically stressed fracture analysis technique was utilized to identify hydraulically-conductive and nonconductive fractures. The analysis shows that the north-western flank of the unit consists of permeable fractures and these have direct association with the circulation losses while drilling.

The geomechanical model was coupled with the reservoir dynamic model to predict changes in total stress due to reservoir pressure changes in time. Modeling was enhanced using an empirical relationship between the effective stress and permeability, with results that clearly show permeability variation at pre-production conditions.