Laboratory and field measurements often fail to identify small-scale variations in rock elastic properties. Due to limited spatial resolution, conventional laboratory methods cannot properly describe rock formations exhibiting a high degree of heterogeneity, thereby masking differences between stiff and compliant layers. Continuous sample measurements can mitigate this problem but are not widely used by the industry. We build upon our previous work and apply laboratory angle-dependent ultrasonic reflection coefficient (ADURC) measurements to achieve detailed two-dimensional descriptions of the elastic properties of complex rock samples. This method successfully yields high-resolution information on P- and S-wave velocities, as well as bulk density, across the surface of rock samples. Elastic properties are estimated using a nonlinear inversion algorithm that matches laboratory measurements with numerical simulations. ADURC data acquired at various sample locations enable detailed rock descriptions, where the effective measurement area is determined by the size of the receiver, measurement frequency, and incidence angle. Consequently, the sampling area is smaller compared with triaxial loading and acoustic transmission tests, for which the resolution is controlled by sample size. Measurements conducted on samples exhibiting different levels of spatial complexity validate the capability of the ADURC method to identify small-scale heterogeneities. For the reported experiments, variations in angle-dependent reflectivity give rise to corresponding variations in the estimated P- and S-wave velocities and density, which can exceed 60%. These small-scale variations across heterogeneous rock samples often are overlooked by conventional laboratory methods.

Stress barriers play a key role in the propagation of hydraulic fractures. They are local maxima in the stress field that constrain vertical fracture propagation. The development of stress barriers is influenced by rock mechanical properties, pore pressure and tectonic stresses. However, stress prediction models are highly sensitive to available geophysical measurements and assumptions made on rock constitutive models. We compare stress estimations performed with elastic isotropic, anisotropic and viscoplastic models using Thomsen's notation (epsilon, delta, gamma) to quantify anisotropy and its effects on hydraulic fracture geometry. Using a single depth for principal stress calibration, we compare stress distributions and simulate hydraulic fracture geometries along simple vertical and horizontal well sections. Prediction errors stemming from isotropic models along anisotropic intervals increase when tectonic stresses increase. Errors generated by either over- or underestimation of d increase for tectonically passive environments, while errors generated by either over- or underestimation of. increase for tectonically active environments. Additional corrections, but also uncertainties, can be introduced by considering viscoelastic rock behaviour. Because of stress shadowing and fracture interaction, the risk of stress barrier underestimation is higher when estimating hydraulic fracture geometries along the various stages of horizontal wells.

Due to depositional, diagenetic, and structural processes, reservoir rocks are rarely homogeneous, often exhibiting significant short-range variations in elastic properties. Such spatial variability can have measurable effects on macroscopic mechanical properties for drilling and fluid production operations. We describe a new laboratory method for the acquisition of ultrasonic angle-dependent measurements of reflected waves that delivers high-resolution, continuous descriptions of P- and S-wave velocity along the surface of the rock sample. Reflection coefficient vs. incidence angle is the main source of information about rock elastic properties. The acquired measurements are matched to numerical simulations to estimate P-and S-wave velocity and density of the porous sample and their variations within the rock specimen, hence providing continuous descriptions of sample complexity. Data collected from various locations on the rock specimen are subsequently used to construct two-dimensional (2D) models of elastic properties along the surface of the rock sample. P- and S-wave velocities estimated with this method agree well with acoustic transmission measurements for most homogeneous rocks. The spatial resolution of the method is limited by receiver size, measurement frequency, and incidence angle. At high incidence angles, the surface area sensitive to the measurements increases, and consequently, the spatial resolution of the corresponding reflection coefficient decreases across neighboring rock features.

Porous rocks are rarely homogeneous. Significant spatial variations in elastic properties are often observed in rocks due to depositional, diagenetic, and structural processes. In laminated sandstones, complex carbonates, or unconventional formations, elastic properties can vary on scales from millimeters to tens of meters. Detection of inhomogeneities and their size in rocks is crucial for fracture propagation design, height containment assessment, and for improving well/reservoir productivity. Most laboratory techniques used to measure rock elastic properties fail to distinguish mid-scale anisotropy; results are subject to spatial averaging effects. We introduce a new experimental method to measure continuous compressional- and shear-wave logs of core samples based on measurements of angle-dependent ultrasonic reflection coefficients. Simultaneously with reflected waves, we detect and interpret refracted waves as an independent way to estimate acoustic wave velocities to support the analysis. Our laboratory system is equipped with an array of receivers to continuously collect measurements. At each core location, we acquire acoustic waveforms at multiple transmitter-receiver angles using a pitch-catch acquisition mode (similar to standard sonic tools). This acquisition mode uses multiple receivers, allowing us to obtain measurements at different incidence angles without moving the sample and keeping the distance traveled by reflected waves constant, thereby eliminating the need for geometrical spreading corrections in reflection-coefficient calculations. Reflectivity-vs.-angle measurements are then matched with numerical simulations to estimate rock elastic properties. Ultrasonic reflection-coefficient measurements are successfully used to estimate dynamic elastic rock properties of homogeneous and layered rock samples. For homogenous samples, values are within a 5% range when compared to those obtained with the standard acoustic transmission method. Measurements acquired on natural and artificially constructed samples show significant departures from homogeneous behavior caused by layering. Laboratory reflection-coefficient measurements enable detection of inch-scale anisotropy within the rock, leading to improved assessment of formation elastic properties. Furthermore, continuous core measurements provide high-resolution reflection-coefficient information which is complementary to open-hole ultrasonic logs.