Formation elastic properties near a borehole may be altered from their original state due to the stress concentration around the borehole. This could result in a biased estimation of formation properties but could provide a means to estimate in situ stress from sonic logging data. In order to properly account for the formation property alteration, we propose an iterative numerical approach to calculate the stress-induced anisotropy around a borehole by combining the rock physics model of Mavko et al. (1995) and a finite-element method.We show the validity and accuracy of our approach by comparing numerical results to laboratory measurements of the stress-strain relation of a sample of Berea sandstone, which contains a borehole and is subjected to uniaxial stress loading. Our iterative approach converges very fast and can be applied to calculate the spatially varying stiffness tensor of 1 the formation around a borehole for any given stress state.2
Anisotropic elastic parameters for shales are widely needed in seismic imaging, reservoir characterization, and carbon sequestration monitoring. Unlike other elastic parameters such as vertical P and S wave velocities, anisotropy parameters are not measured directly from the acoustic well logs due to the single-directional nature of a well. We assume that shale anisotropy is induced by thin cracks that are filled with liquid in a background isotropic medium, whose bulk and shear moduli are obtained from the vertically measured P and S wave velocities, density, and porosity from corresponding well logs through a formalized inversion scheme. We show that the estimated anisotropy using the proposed method is consistent with the mineralogy and agrees with the published laboratory measurements. This framework allows us to quantify the uncertainties in the anisotropy parameters estimated from the inversion, which can be used as a measure to evaluate the validity of the chosen rock physics model.
Plain Language SummaryThe differences in the wave speeds as they propagate in different angles, defined as anisotropy, are widely needed for imaging the subsurface and understanding the tectonic processes. However, measurements made in a vertical borehole cannot provide this directional information. In this study, we assume a rock physics model for shales that adds anisotropy-inducing thin inclusions in an isotropic background, the elastic and fluid properties of which are inverted formally from the measured well logs. The proposed method generates anisotropy estimates that agree with published laboratory measurements and that are consistent with the mineralogy log. Moreover, the proposed method quantifies the uncertainties in the estimated anisotropy, which can be used to evaluate the applicability of the chosen model on a particular rock formation.
This study presents composite electrode materials based on graphene oxide (GO) and transition metal oxide nanostructures for supercapacitor applications. Electrophoretic deposition of GO on a conductive substrate was used to form reduced graphene oxide (rGO) films through chemical reduction. The specific capacitance of the rGO was calculated up to 117 F/g at 100 mV/s scan rate from KOH (1 M) electrolyte using an Ag/AgCl reference electrode. The strong interaction of GO with Co3O4 and MnO2 nanostructures was demonstrated in the self-assembled Langmuir–Blodgett monolayer composite, showing the potential to fabricate thin film supercapacitor electrodes without using binder materials. This two-step process is nontoxic and scalable and holds promise for improved energy density from redox capacitance in comparison with the conventional double layer supercapacitors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.