Jose G. Arguello

Geomechanical Modeling of Reservoir Compaction, Surface Subsidence, and Casing Damage at the Belridge Diatomite Field

Geologic, and historical well failure, production, and injection data were analyzed to guide development of three-dimensional geomechanical models of the Belridge diatomite field, California. The central premise of the numerical simulations is that spatial gradients in pore pressure induced by production and injection in a low permeability reservoir may perturb the local stresses and cause subsurface deformation sufficient to result in well failure. Time-dependent reservoir pressure fields that were calculated from three-dimensional black oil reservoir simulations were coupled uni-directionally to three-dimensional non-linear finite element geomechanical simulations. The reservoir models included nearly 100,000 gridblocks (100--200 wells), and covered nearly 20 years of production and injection. The geomechanical models were meshed from structure maps and contained more than 300,000 nodal points. Shear strain localization along weak bedding planes that causes casing dog-legs in the field was accommodated in the model by contact surfaces located immediately above the reservoir and at two locations in the overburden. The geomechanical simulations are validated by comparison of the predicted surface subsidence with field measurements, and by comparison of predicted deformation with observed casing damage. Additionally, simulations performed for two independently developed areas at South Belridge, Sections 33 and 29, corroborate their different well failure histories. The simulations suggest the three types of casing damage observed, and show that although water injection has mitigated surface subsidence, it can, under some circumstances, increase the lateral gradients in effective stress, that in turn can accelerate subsurface horizontal motions. Geomechanical simulation is an important reservoir management tool that can be used to identify optimal operating policies to mitigate casing damage for existing field developments, and applied to incorporate the effect of well failure potential in economic analyses of alternative infilling and development options.

Mechanical properties and shear failure surfaces for two alumina powders in triaxial compression

In the manufacture of ceramic components, near-net-shape parts are commonly formed by uniaxially pressing granulated powders in rigid dies. Density gradients that are introduced into a powder compact during press-forming often increase the cost of manufacturing, and can degrade the performance and reliability of the finished part. Finite element method (FEM) modeling can be used to predict powder compaction response, and can provide insight into the causes of density gradients in green powder compacts; however, accurate numerical simulations require accurate material properties and realistic constitutive laws. To support an effort to implement an advanced cap plasticity model within the finite element framework to realistically simulate powder compaction, we have undertaken a project to directly measure as many of the requisite powder properties for modeling as possible. A soil mechanics approach has been refined and used to measure the pressure dependent properties of ceramic powders up to 68.9 MPa (10,000 psi). Due to the large strains associated with compacting low bulk density ceramic powders, a two-stage process was developed to accurately determine the pressure-density relationship of a ceramic powder in hydrostatic compression, and the properties of that same powder compact under deviatoric loading at the same specific pressures. Using this approach, the seven parameters that are required for application of a modified Drucker-Prager cap plasticity model were determined directly. The details of the experimental techniques used to obtain the modeling parameters and the results for two different granulated alumina powders are presented.

Controlled Ceramic Powder Compaction Through Science-Based Understanding

Reproducible manufacturing of ceramic components requires understanding and controlling materials and processing. Utilizing characterization and modeling to develop sciencebased understanding, significant advances have been made to better understand and control ceramic pressing powders, powder compaction, and sintering. This includes identifying some of the critical relationships between powder characteristics/properties, powder compaction behavior, and sintering. Another significant advance includes the development of computer simulation technology for compaction and sintering that provides guidance to improve process reproducibility and control. For powder compaction, a cap-plasticity constitutive model is implemented within a finite element (FE) framework. For sintering, a linear viscous sintering constitutive model is implemented within an FE framework. Both models have been tested and validated by comparing model predictions to experimental observations. The computer modeling technology developed can be used to improve and expand ceramic component designs, to help optimize powder pressing and sintering, and to anticipate and minimize defects during processing. The application of characterization and modeling technology to develop better powders and more robust processes will contribute to more reproducible, efficient, and cost effective manufacturing technology for ceramic components. Introduction Processing Particulate Ceramic Components. Ceramic component manufacturing is a multi-step process that involves beneficiating a ceramic powder (e.g., by granulation), shape-forming the powder into a green body (e.g., by dry pressing [1-2]), and sintering at elevated temperature to produce the desired size and shape ceramic body with the requisite properties for a given application [3]. Reproducible processing is critical in advanced ceramic component manufacturing, both to ensure the fabrication of a reliable product, and to achieve the process yields required for cost-effective manufacturing. Historically, traditional shape-forming processes such as dry powder pressing have been engineered empirically. This approach is typically time intensive, and often does not provide the understanding necessary design a new powder/component or to troubleshoot processing problems. Statistical process control (SPC) techniques have been used to help identify and eliminate the causes of non-random variability in processes such as dry pressing [4]; however, they also do not necessarily provide the insight required to fully optimize processing. Science-Based Processing. As a complement to empirical engineering and SPC techniques, scientific principals can be applied to better understand and control ceramic processing. Sciencebased understanding can be used to identify and control critical relationships between powder properties/characteristics, pressing, and sintering response that impact manufacturing, and finished component performance and reliability. A combination of characterization and modeling are required to develop the fundamental scientific understanding required to achieve this goal. We have characterized the physical properties and characteristics of granulated ceramic powders [57], and their behavior during dry pressing [8-9] and sintering [6-7,10-11]. Additionally, measured constitutive behavior has been implemented within predictive models for powder compaction and sintering to better understand and control ceramic powder processing. [1,12-17]. Ceramic Powder Processing and Modeling Dry Pressing. Because it is fast, simple, and well suited to high-volume production, powder pressing is commonly used to shape-form ceramic components [1-2]. Dry pressing also provides the Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 149-154 doi:10.4028/www.scientific.net/KEM.264-268.149

Nuclear Energy Advanced Modeling and Simulation (NEAMS) Waste Integrated Performance and Safety Codes (IPSC): Gap Analysis for High Fidelity and Performance Assessment Code Development

This report describes a gap analysis performed in the process of developing the Waste Integrated Performance and Safety Codes (IPSC) in support of the U.S. Department of Energy (DOE) Office of Nuclear Energy Advanced Modeling and Simulation (NEAMS) Campaign. The goal of the Waste IPSC is to develop an integrated suite of computational modeling and simulation capabilities to quantitatively assess the long-term performance of waste forms in the engineered and geologic environments of a radioactive waste storage or disposal system. The Waste IPSC will provide this simulation capability (1) for a range of disposal concepts, waste form types, engineered repository designs, and geologic settings, (2) for a range of time scales and distances, (3) with appropriate consideration of the inherent uncertainties, and (4) in accordance with rigorous verification, validation, and software quality requirements. The gap analyses documented in this report were are performed during an initial gap analysis to identify candidate codes and tools to support the development and integration of the Waste IPSC, and during follow-on activities that delved into more detailed assessments of the various codes that were acquired, studied, and tested. The current Waste IPSC strategy is to acquire and integrate the necessary Waste IPSC capabilities wherever feasible, and develop only those capabilities that cannot be acquired or suitably integrated, verified, or validated. The gap analysis indicates that significant capabilities may already exist in the existing THC codes although there is no single code able to fully account for all physical and chemical processes involved in a waste disposal system. Large gaps exist in modeling chemical processes and their couplings with other processes. The coupling of chemical processes with flow transport and mechanical deformation remains challenging. The data for extreme environments (e.g., for elevated temperature and high ionic strength media) that are needed for repository modeling are severely lacking. In addition, most of existing reactive transport codes were developed for non-radioactive contaminants, and they need to be adapted to account for radionuclide decay and in-growth. The accessibility to the source codes is generally limited. Because the problems of interest for the Waste IPSC are likely to result in relatively large computational models, a compact memory-usage footprint and a fast/robust solution procedure will be needed. A robust massively parallel processing (MPP) capability will also be required to provide reasonable turnaround times on the analyses that will be performed with the code. A performance assessment (PA) calculation for a waste disposal system generally requires a large number (hundreds to thousands) of model simulations to quantify the effect of model parameter uncertainties on the predicted repository performance. A set of codes for a PA calculation must be sufficiently robust and fast in terms of code execution. A PA system as a whole must be able to provide multiple alternative models for a specific set of physical/chemical processes, so that the users can choose various levels of modeling complexity based on their modeling needs. This requires PA codes, preferably, to be highly modularized. Most of the existing codes have difficulties meeting these requirements. Based on the gap analysis results, we have made the following recommendations for the code selection and code development for the NEAMS waste IPSC: (1) build fully coupled high-fidelity THCMBR codes using the existing SIERRA codes (e.g., ARIA and ADAGIO) and platform, (2) use DAKOTA to build an enhanced performance assessment system (EPAS), and build a modular code architecture and key code modules for performance assessments. The key chemical calculation modules will be built by expanding the existing CANTERA capabilities as well as by extracting useful components from other existing codes.

Geomechanical analyses to investigate wellbore/mine interactions in the Potash Enclave of Southeastern New Mexico.

Geomechanical analyses have been performed to investigate potential mine interactions with wellbores that could occur in the Potash Enclave of Southeastern New Mexico. Two basic models were used in the study; (1) a global model that simulates the mechanics associated with mining and subsidence and (2) a wellbore model that examines the resulting interaction impacts on the wellbore casing. The first model is a 2D approximation of a potash mine using a plane strain idealization for mine depths of 304.8 m (1000 ft) and 609.6 m (2000 ft). A 3D wellbore model then considers the impact of bedding plane slippage across single and double cased wells cemented through the Salado formation. The wellbore model establishes allowable slippage to prevent casing yield.

Model Constrained Sintering Experiments: Bi-Layers and Cylinder-Filled Rings.

When structures that consist of powders of two or more materials, such as low temperature co-fired ceramic packages or a planar solid oxide fuel cells, are sintered, the mismatch in the sintering shrinkage rates between the different materials produces stress, since the faster shrinking materials are constrained by those that shrink at a slower rate. These stresses can lead to the formation of defects such as cracks or shape distortion. Results of recent model experiments to study the constrained sintering in multi-material systems will be discussed for two model geometries. The first geometry is a simple bi-layer consisting of single layers of two different materials bonded together. Results of in situ observation of sintering bi-layers will be presented and discussed in relation to the properties of the individual layers such as their free sintering rates, uniaxial viscosities and viscous Poisson’s ratio. The second geometry studied was that of a ring of one material filled with a cylinder of a second, slower shrinking material. In this case, the results of several variations of this geometry including filling the ring either fully or partly with a rigid, nonshrinking cylinder or with rigid, non-cylindrical shapes will be presented and discussed.