COMPARATIVE ANALYSIS OF ELASTIC PROPERTIES OF ROCKS FORMING THE GEOLOGICAL SECTION OF A DRILLED WELL

Abstract

This study presents a comprehensive comparative analysis of the elastic properties of rocks forming the geological sections of drilled wells, with particular emphasis on Poisson’s ratio as a key geomechanical parameter governing rock deformation behavior under in-situ stress conditions. Elastic properties of reservoir and non-reservoir formations play a decisive role in wellbore stability, fracture initiation, drilling safety, and the efficiency of completion and stimulation operations. Among these properties, Poisson’s ratio occupies a central position, as it directly reflects the ratio between lateral and axial strain and serves as an indicator of rock compressibility, shear rigidity, and mechanical integrity.

Poisson’s ratio is widely used in practical geomechanics for determining fracture pressure gradients, estimating minimum horizontal stress, and evaluating the susceptibility of formations to shear or tensile failure. Accurate determination of this parameter is therefore critical for predicting borehole collapse, lost circulation zones, and fracture propagation during hydraulic fracturing. In this context, the present study provides a detailed review and comparative assessment of classical laboratory-based methods and modern well-logging-based approaches for determining Poisson’s ratio in heterogeneous geological sections.

The methodology integrates data from acoustic logging (monopole and dipole sonic tools), density logs, and gamma-ray measurements to achieve reliable lithological differentiation and elastic characterization. The use of compressional (Vₚ) and shear (Vₛ) wave velocities allows Poisson’s ratio to be derived continuously along the wellbore, enabling high-resolution analysis of elastic property variations with depth. Gamma-ray logs are employed to distinguish clay-rich intervals from clean sandstones and carbonates, which is essential for interpreting elastic responses in mixed lithological sequences.

Building on an extensive body of published research and original datasets, the study systematically analyzes the relationships between Poisson’s ratio, elastic wave velocities, and key petrophysical parameters, including bulk density, porosity, mineral composition, fluid saturation, and cementation degree. The theoretical framework of the analysis is grounded in established rock physics models, such as Gassmann’s fluid substitution theory, Hertz–Mindlin contact mechanics, and effective medium approximations. These models provide insight into how changes in pore fluid, grain contacts, and confining stress influence elastic moduli and deformation behavior.

The comparative analysis reveals that Poisson’s ratio is a highly sensitive indicator of mechanical heterogeneity within geological sections. Clay-rich formations and shales typically exhibit elevated Poisson’s ratio values due to their reduced shear modulus, higher compressibility, and pronounced anisotropy. In contrast, well-cemented sandstones and carbonate rocks display lower Poisson’s ratio values, reflecting stronger grain frameworks, higher elastic moduli, and greater resistance to deformation. Fluid saturation effects are also significant: gas-bearing formations tend to show reduced Poisson’s ratio compared to water-saturated intervals, owing to the decrease in bulk modulus and changes in elastic wave velocities.

Special attention is given to the influence of elastic anisotropy, particularly in laminated shales, where Poisson’s ratio may vary depending on wave propagation direction. The study demonstrates that conventional isotropic interpretations of sonic logs can lead to substantial errors in Poisson’s ratio estimation in such formations. To address this limitation, the application of dipole sonic logging, azimuthal measurements, and advanced inversion techniques is emphasized as a means of improving the accuracy of elastic property evaluation.

The results of this study have important practical implications for drilling and reservoir engineering. Improved characterization of elastic property distributions enhances the reliability of geomechanical models used for well design, mud weight selection, casing program optimization, and hydraulic fracture planning. By integrating multi-source logging data with rock physics modeling, the proposed approach enables more accurate prediction of formation behavior under operational loads and stress changes.

Overall, the findings confirm that a comparative analysis of elastic properties—centered on Poisson’s ratio—provides a robust framework for assessing the mechanical behavior of complex geological sections. The study underscores the necessity of integrating petrophysical, geophysical, and geomechanical data to achieve a holistic understanding of subsurface formations and to support safe, efficient, and economically optimized drilling operations