English abstract
Many oil and gas reservoirs are characterized with complex geological conditions and thin
reservoirs. In recent years, drilling lateral and multilateral wells has become the best
option to improve the reservoir productivity due to the increase in the well contact.
However, drilling issues with high severity most often occurs, e.g., borehole washouts,
breakouts, collapses, peak-offs, stuck drill pipes and drill bits, and even losses of
boreholes which lead to a non-productive time and significant increase in drilling cost. To
avoid these problems, it is important to have a good understanding of rock mechanics and
in situ stresses, especially the maximum horizontal stress around the borehole which is
critical parameter in drilling optimization and wellbore stability modeling.
In this research, three dimensional geomechanical model is adopted to improve the
prediction of the maximum horizontal stresses of the fields from the formed breakouts in
the drilling operations. The model is based on poroelastic constitutive law in conjunction
with Mogi-Coulomb shear failure criterion that considers the impact of the intermediate
principal stress, 𝜎𝜎2. The maximum horizontal stress was estimated using both Mohr Coulomb and Mogi-Coulomb failure criterion to study the impact of intermediate stress.
The results show that considering the intermediate principal stress have a significant
impact and provide a better estimation of the maximum horizontal stress from the
observed breakouts. The developed three-dimensional geomechanical model was utilized
to study nine different field cases for different rock formations. In all the studied rock
formations, the model was able to accurately predict the maximum horizontal stress that
was compatible well with the actual field observations. Moreover, a sensitivity analysis
was conducted on shale formations in Oman in order to study the effect of each parameter
individually on the estimation of the maximum horizontal stress. It has been found that
the stability model is sensitive to the rock geomechanical properties, which are cohesion
and friction angle followed by the minimum horizontal stress and pore pressure.
