High-Resolution Evaluation of Elastic Properties and Anisotropy of Unconventional Reservoir Rocks via Thermal Core Logging

Unconventional reservoir rocks frequently exhibit considerable degrees of anisotropy, heterogeneity, and high variability of physical rock properties, reflecting the variety of their geological origins. The anisotropy and heterogeneity can have a pronounced impact on sonic log readings, which poses problems since compressional and shear borehole sonic data are traditionally used both as a data source for geomechanical modelling and also for seismic calibration. Sonic logging and acoustic tests in the laboratory use different frequencies due to the small sample sizes in the laboratory, which, along with known complexities in the measurement/interpretation procedure, complicates the characterization of reservoirs in terms of their elastic properties. This paper proposes a new approach to high-resolution evaluation of the elastic properties and anisotropy of unconventional reservoir rocks, based on continuous non-contact, non-destructive high-resolution (0.2–2 mm) thermal profiling of core samples. Variations in measured thermal characteristics (principal thermal conductivity tensor components, volumetric heat capacity, thermal anisotropy coefficient and thermal heterogeneity coefficient) reflect variations in the rock fabric and composition, which also result in the variability of other properties of the rock. More than 100 m of full-diameter cores along three wells drilled in the Bazhenov formation in West Siberia (Russia) have been profiled. The results were combined with sonic well logging data, and correlations between components of thermal conductivity, density and acoustic velocities were established, as well as correlations between thermal anisotropy, Young’s modulus anisotropy and Thomsen’s parameters. Examples of high-resolution prediction of velocities, density, elastic modulus, and anisotropy parameters based on the results of thermal core logging are given, together with the respective verification.