Reliable interpretation and prediction of mechanical stratigraphy is the cornerstone of geomechanical investigations at multiple scales and in different applications. While lithological and petrophysical facies have been used in reservoir characterization to associate with storage capacity and flow characteristics of rocks, mechanical stratigraphy and its role is less known and more complex to identify.
Mechanical stratigraphy modeling is the identification and interpretation of geomechanical rock types, which deform distinctly in response to changes in the subsurface system. These changes could occur naturally over geological time due to pore pressure buildup and plate boundary interactions or may be induced through field operations including drilling, hydraulic fracturing, water flood, production, thermal operations and depletion. The different geomechanical rock types will have a combination of lithologies and will often have overlapping petrophysical properties which together lead to variations of stiffness and strength.
In this paper, the fundamentals, significance and geomechanical workflows for mechanical stratigraphy modeling are presented and discussed. In addition, evidence of mechanical stratigraphy in the subsurface for unconventional and conventional plays are shown. Applications of mechanical stratigraphy for hydraulic fracture barrier identification, well integrity, wellbore stability and subsurface containment assurance are presented.
All subsurface operations such as drilling, injection and production lead to rock deformation and potentially failure in the reservoir and overburden intervals over the lifespan of a field. While some of these impacts are operationally manageable, in many cases it is critical to predict these changes by properly characterizing the geomechanical properties of the rock during the planning stage. This can help with appropriate design of operations such as injection pressure and mud weight design and mitigate potential geomechanical risks.
At the regional scale, mechanical stratigraphy of the rock influences the faulting and folding over geologic time. In compressive settings, the contrast between different geomechanical rock types determines the form and extent of structural features. In extensional settings fracturing is mainly controlled by the mechanical properties of the host formation .