Rock and fluid interactions play a significant role in many aspects of formation evaluation and reservoir characterization studies. Most reservoir simulation studies only consider the fluid flow characteristics without any attention to the formation-fluid compatibility and interactions. The rock-fluid interaction is known to have a large impact on determination of the geomechanical and acoustic properties of the formation and may result in the misinterpretation of the logging, well testing analysis and microseismic data, resulting in inaccurate evaluation of the formation.

In this paper, the grain contact adhesion hysteresis model introduced by Tutuncu (1992) was modified to improve non-Hertzian deformation with the addition of the elastic moduli and permeability anisotropies. The dependence of the geomechanical and acoustic properties as a function of applied stress, fluid saturation and measurement frequency have been investigated in anisotropic rocks. The modified model was utilized to study the effect of the interactions between the fluid and rock and the role of the fluid chemical, electrochemical and dielectric properties on the deformation and acoustic properties of shales and tight gas sandstones. A practical methodology for modeling the anisotropy of the fluid-rock system has been added into the Tutuncu's grain contact adhesion hysteresis model for better representation of geomechanical behavior of the highly anisotropic unconventional reservoir characteristics. The effects of temperature and partial saturation are also incorporated in the model.

The model provides a quantitative evaluation of the influence of surface forces on the deformation and the micromechanics of the granular rocks and how they are influenced when they are exposed to various fluids. The results show that while the viscosity and density of the saturating fluid are the key factors in reservoir engineering studies, the rock-fluid interactions play a significant role in deformation, failure and wave propagation behavior in the tight oil and shale gas formations. Porosity, clay content, stress, saturation, frequency and anisotropy have leading roles in controlling deformation, failure, permeability, and wave velocities in shale reservoirs.

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