arXiv subjects

Hari Viswanathan

Publications and source records attributed to Hari Viswanathan.

21 records · Page 2Linked to original sources

arXiv2018

Simulation of fracture coalescence in granite via the combined finite-discrete element method

Fracture coalescence is a critical phenomenon for creating large fractures from smaller flaws, affecting fracture network flow and seismic energy release potential. In this paper, simulations of fracture coalescence processes in granite specimens with pre-existing cracks are performed. These simulations utilize an in-house implementation of the Combined Finite-Discrete Element method (FDEM) known as the Hybrid Optimization Software Suite (HOSS). The pre-existing cracks within the specimens follow two geometric patterns: 1) a single crack oriented at different angles with respect to the loading direction, and 2) two cracks, where one crack is oriented perpendicular to the loading direction and the other crack is oriented at different angles. The intent of this study is to demonstrate the suitability of FDEM for modeling fracture coalescence processes including: crack initiation and propagation, tensile and shear fracture behavior, and patterns of fracture coalescence. The simulations provide insight into the evolution of fracture tensile and shear fracture behavior as a function of time. The single-crack simulations accurately reproduce experimentally measured peak stresses as a function of crack inclination angle. Both the single- and double-crack simulations exhibit a linear increase in strength with increasing crack angle; the double-crack specimens are systematically weaker than the single-crack specimens.

physics.geo-ph↗

arXiv2018

A generalized anisotropic deformation formulation for geomaterials

In this paper, the Combined Finite-Discrete Element Method (FDEM) has been applied to analyze the deformation of anisotropic geomaterials. In the most general case geomaterials are both non-homogeneous and non-isotropic. With the aim of addressing anisotropic material problems, improved 2D FDEM formulations have been developed. These formulations feature the unified hypo-hyper elastic approach combined with a multiplicative decomposition-based selective integration for volumetric and shear deformation modes. This approach is significantly different from the co-rotational formulations typically encountered in finite element codes. Unlike the co-rotational formulation, the multiplicative decomposition-based formulation naturally decomposes deformation into translation, rotation, plastic stretches, elastic stretches, volumetric stretches, shear stretches, etc. This approach can be implemented for a whole family of finite elements from solids to shells and membranes. This novel 2D FDEM based material formulation was designed in such a way that the anisotropic properties of the solid can be specified in a cell by cell basis, therefore enabling the user to seed these anisotropic properties following any type of spatial variation, for example, following a curvilinear path. In addition, due to the selective integration, there are no problems with volumetric or shear locking with any type of finite element employed.

physics.geo-ph↗

arXiv2014

Uncertainty quantification for CO2 sequestration and enhanced oil recovery

This study develops a statistical method to perform uncertainty quantification for understanding CO2 storage potential within an enhanced oil recovery (EOR) environment at the Farnsworth Unit of the Anadarko Basin in northern Texas. A set of geostatistical-based Monte Carlo simulations of CO2-oil-water flow and reactive transport in the Morrow formation are conducted for global sensitivity and statistical analysis of the major uncertainty metrics: net CO2 injection, cumulative oil production, cumulative gas (CH4) production, and net water injection. A global sensitivity and response surface analysis indicates that reservoir permeability, porosity, and thickness are the major intrinsic reservoir parameters that control net CO2 injection/storage and oil/gas recovery rates. The well spacing and the initial water saturation also have large impact on the oil/gas recovery rates. Further, this study has revealed key insights into the potential behavior and the operational parameters of CO2 sequestration at CO2-EOR sites, including the impact of reservoir characterization uncertainty; understanding this uncertainty is critical in terms of economic decision making and the cost-effectiveness of CO2 storage through EOR.

physics.geo-ph↗