Wellbore stability represents a big challenge to drill vertical and horizontal wells in unconventional reservoirs. Geomechanically driven drilling events can be minimized with a robust geomechanical characterization particularly in shale formations with strong anisotropy and multiple weak bedding planes.
A mechanical earth model (MEM) is a numerical representation of the pore pressure, mechanical properties and stresses acting on the subsurface. When these types of models are combined with a failure criterion, they provide the safe mud weight window to avoid compressive and tensile failure while drilling.
In this study, the results of different types of MEMs were analyzed to determine their impact on mud weight window and how this optimization would lead to reduce nonproductive times (NPT). Based on new calibration data (e.g. pore pressure and closure pressure), there was a progress in geomechanical knowledge of the field and, as a result, more complex geomechanical models were built. The simplest case was an 1D isotropic geomechanical model in which mechanical properties were assumed equal in all directions. Then, applying a 1D anisotropic geomechanical model the impact of bedding planes in rock anisotropy were evaluated.
The results indicate that the isotropic model was only applicable to vertical wells. Horizontal wells require a stability analysis based on anisotropic model to avoid shear failures due to a mud weight underestimated, since the horizontal UCS (unconfined compressive strength) is 24% lower than the vertical direction.
La Amarga Chica is located in the center-east sector of Neuquén Province, in Argentina, into the Embayment of the Neuquen basin (Fig. 1)
It is currently one of the blocks with the biggest oil production from the Vaca Muerta shale.
The geological structure is characterized by a gently dipping monocline, which ascend progressively to the northeast. There are three major faults families: WNW and NNW en echelon faults and NS normal faults (Vittore, 2018).
