Joseph P. Morris

Simulations of underground structures subjected to dynamic loading using the distinct element method

We present the preliminary results from a parameter study investigating the stability of underground structures in response to explosion‐induced strong ground motions. In practice, even the most sophisticated site characterization may lack key details regarding precise joint properties and orientations within the rock mass. Thus, in order to place bounds upon the predicted behavior of a given facility, an extensive series of simulations representing different realizations may be required. The influence of both construction parameters (reinforcement, rock bolts, liners) and geological parameters (joint stiffness, joint spacing and orientation, and tunnel diameter to block size ratio) must be considered. We discuss the distinct element method (DEM) with particular emphasis on techniques for achieving improved computational efficiency, including the handling of contact detection and approaches to parallelization. We introduce a new approach for simulating deformation of the discrete blocks using the theory of a Cosserat point, which does not require internal discretization of the blocks. We also outline the continuum techniques we employ to obtain boundary conditions for the distinct element simulations. We present results from simulations of dynamic loading of several generic subterranean facilities in hard rock, demonstrating the suitability of the DEM for this application. These results demonstrate the significant role that joint geometry plays in determining the response of a given facility.

Fracture Permeability Alteration due to Chemical and Mechanical Processes: A Coupled High-Resolution Model

Reactive fluid-flow experiments in fractures subjected to normal stress suggest the potential for either increased or decreased permeability resulting from fracture-surface dissolution. We present a computational model that couples mechanical deformation and chemical alteration of fractures subjected to constant normal stress and reactive fluid flow. The model explicitly represents micro-scale roughness of the fracture surfaces and calculates elastic deformation of the rough surfaces using a semi-analytical approach that ensures the surfaces remain in static equilibrium. A depth-averaged reactive transport model calculates chemical alteration of the surfaces, which leads to alteration of the contacting fracture surfaces. The mechanical deformation and chemical alteration calculations are explicitly coupled, which is justified by the disparate timescales required for equilibration of mechanical stresses and reactive transport processes. An idealized analytical representation of dissolution from a single contacting asperity shows that under reaction-limited conditions, contacting asperities can dissolve faster than the open regions of the fracture. Computational simulations in fractures with hundreds of contacting asperities show that the transition from transport-limited conditions (low flow rates) to reaction-rate-limited conditions (high flow rates) causes a shift from monotonically increasing permeability to a more complicated process in which permeability initially decreases and then increases as contacting asperities begin to dissolve. These results are qualitatively consistent with a number of experimental observations reported in the literature and suggest the potential importance of the relative magnitude of mass transport and reaction kinetics on the evolution of fracture permeability in fractures subjected to combined normal stress and reactive fluid flow.

Dynamic simulations of geological materials using combined FEM/DEM/SPH analysis

An overview of the Lawrence Discrete Element Code (LDEC) is presented, and results from a study investigating the effect of explosive and impact loading on geological materials using the Livermore Distinct Element Code (LDEC) are detailed. LDEC was initially developed to simulate tunnels and other structures in jointed rock masses using large numbers of polyhedral blocks. Many geophysical applications, such as projectile penetration into rock, concrete targets and boulder fields, require a combination of continuum and discrete methods in order to predict the formation and interaction of the fragments produced. In an effort to model this class of problems, LDEC now includes implementations of Cosserat point theory and cohesive elements. This approach directly simulates the transition from continuum to discontinuum behaviour, thereby allowing for dynamic fracture within a combined finite element/discrete element framework. In addition, there are many applications involving geological materials where fluid–structure interaction is important. To facilitate solution of this class of problems a smooth particle hydrodynamics (SPH) capability has been incorporated into LDEC to simulate fully coupled systems involving geological materials and a saturating fluid. We will present results from a study of a broad range of geomechanical problems that exercise the various components of LDEC in isolation and in tandem.

The Distinct Element Method — Application to Structures in Jointed Rock

This paper presents a brief review of the distinct element method (DEM) with particular emphasis on techniques for handling contact detection. In addition, various approaches for parallelization are considered. Our primary focus is on applying the DEM to simulations of the attack and defense of buried facilities. Some continuum approaches to this problem are discussed along with results from underground explosions. Finally, our DEM code is used to simulate dynamic loading of a tunnel in jointed rock and preliminary results are presented demonstrating the suitability of the DEM for this application.

DEVELOPMENT AND APPLICATION OF A FAST-RUNNING TOOL TO CHARACTERIZE SHOCK DAMAGE WITHIN TUNNEL STRUCTURES

Successful but time-intensive use of high-fidelity computational capabilities for shock loading events and resultant effects on and within enclosed structures, e.g., tunnels, has led to an interest in developing more expedient methods of analysis. While several tools are currently available for the general study of the failure of structures under dynamic shock loads at a distance, presented are a pair of statistics- and physics-based tools that can be used to differentiate different types of damage (e.g., breach versus yield) as well as quantify the amount of damage within tunnels for loads close-in and with standoff. Use of such faster running tools allows for scoping and planning of more detailed model and test analysis and provides a way to address parametric sensitivity over a large multivariate space.

Evaluation of the Relative Importance of Parameters Influencing Perforation Cleanup

Completion of cased and cemented wells by shaped-charge perforation results in damage to the formation, which can significantly reduce well productivity. Typically, underbalanced conditions are imposed during perforation in an effort to remove damaged rock and shaped-charge debris from the perforation tunnel. Immediately after the shaped-charge jet penetrates the formation, there is a transient surge of fluid from the formation through the perforation and into the well bore. Experimental evidence suggests that it is this transient pressure surge that leads to the removal of damaged rock and charge debris leaving an open perforation tunnel. We have developed a two-stage computational model to simulate the perforation process and subsequent pressure surge and debris removal. The first stage of the model couples a hydrocode with a model of stress-induced permeability evolution to calculate damage to the formation and the resulting permeability field. The second stage simulates the non-Darcy, transient fluid flow from the formation and removes damaged rock and charge debris from the perforation tunnel. We compare the model to a series of API RP43 section 4 flow tests and explore the influence of fluid viscosity and rock strength on the final perforation geometry and permeability.

Advances in discrete element methods for geomechanics

The discrete element method (DEM) dates back to the pioneering work of Cundall and Strack in 1979. This Special Issue of the Geomechanics and Geoengineering Journal is a collection of papers from the 4th International Conference on DEM (DEM 07) held in Brisbane, Australia, in August 2007. The conference itself was divided into several themes covering the spectrum of DEM applications. This issue focuses upon the mining, geomechanics and geophysics technical theme and highlights the great advances in DEM technology that have emerged over the past 30 years. Several recent advancements are featured in this special issue. First, with ever increasing computational power, the DEM is being applied to ever larger 3-D rock masses to provide more realistic predictions of in situ rock mass response. Additionally, it is becoming more common for the DEM to be combined with finite element method (FEM) technologies to simulate the transition from continuum to discontinuous material response. Finally, coupling between the DEM and computational fluid dynamics (CFD) capabilities is emerging as a robust technology for prediction of tightly coupled fluid-structural interaction. This issue presents several approaches to achieving this coupling that have advantages for specific applications. In addition to showcasing the computational evolution of DEM modelling capabilities, this issue presents a wide range of geomechanical applications that are enabled by these technologies. These include rockslides into dams, explosive loading of rock, missile penetration into boulder fields and wave loading of breakwaters. All these applications involve interactions between multiple phenomena, but are dominated by discrete material response in some manner that requires the DEM. The DEM 07 conference provided an opportunity to establish an international group which will provide support to future DEM conferences. The 5th international conference on DEM will be held in London in 2010. It will be chaired by Professor Ante Munjiza. Overall, DEM 07 was an excellent conference with strong technical input and plenty of opportunity for interactions between individuals and across different fields of application. There was also good student participation, with financial assistance to students wishing to attend provided by the Centre for Sustainable Resource Processing. Thanks are also due to the other sponsors who supported the conference. The Guest Editors wish to thank the authors for preparing their manuscripts for publication and the referees for their critical, yet constructive review of the papers.

Well Integrity for Natural Gas Storage in Depleted Reservoirs and Aquifers

Author(s): Freifeld, Barry M.; Oldenburg, Curtis M.; Jordan, Preston; Pan, Lehua; Perfect, Scott; Morris, Joseph; White, Joshua; Bauer, Stephen; Blankenship, Douglas; Roberts, Barry; Bromhal, Grant; Glosser, Deborah; Wyatt, Douglas; Rose, Kelly | Abstract: Introduction Motivation The 2015-2016 Aliso Canyon/Porter Ranch natural gas well blowout emitted approximately 100,000 tonnes of natural gas (mostly methane, CH4) over four months. The blowout impacted thousands of nearby residents, who were displaced from their homes. The high visibility of the event has led to increased scrutiny of the safety of natural gas storage at the Aliso Canyon facility, as well as broader concern for natural gas storage integrity throughout the country. Federal Review of Well Integrity In April of 2016, the U.S. Department of Energy (DOE), in conjunction with the U.S. Department of Transportation (DOT) through the Pipeline and Hazardous Materials Safety Administration (PHMSA), announced the formation of a new Interagency Task Force on Natural Gas Storage Safety. The Task Force enlisted a group of scientists and engineers at the DOE National Laboratories to review the state of well integrity in natural gas storage in the U.S. The overarching objective of the review is to gather, analyze, catalogue, and disseminate information and findings that can lead to improved natural gas storage safety and security and thus reduce the risk of future events. The “Protecting our Infrastructure of Pipelines and Enhancing Safety Act of 2016’’ or the ‘‘PIPES Act of 2016,’’which was signed into law on June 22, 2016, created an Aliso Canyon Natural Gas Leak Task Force led by the Secretary of Energy and consisting of representatives from the DOT, Environmental Protection Agency (EPA), Department of Health and Human Services, Federal Energy Regulatory Commission (FERC), Department of Commerce and the Department of Interior. The Task Force was asked to perform an analysis of the Aliso Canyon event and make recommendations on preventing similar incidents in the future. The PIPES Act also required that DOT/PHMSA promulgate minimum safety standards for underground storage that would take effect within two years. Background on the DOE National Laboratories Well Integrity Work Group One of the primary areas that the Task Force is studying is integrity of natural gas wells at storage facilities. The DOE Office of Fossil Energy (FE) took the lead in this area and asked scientists and engineers from the National Energy Technology Laboratory (NETL), Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), and Lawrence Berkeley National Laboratory (LBNL)) to form a Work Group to address this area. This Work Group is an expansion of the original “Lab Team” comprising scientists and engineers from SNL, LLNL, and LBNL which was formed to support the State of California’s response to the Aliso Canyon incident and operated under the Governor of California’s Aliso Canyon Emergency Order (1/6/2016). The Lab Team played a key role in advising the State of California’s Department of Conservation (DOC) in its oversight of SoCalGas during and after the incident.

Introduction to special section: CO2 storage and utilization

Monitoring, verification, and accounting (MVA) activities are critical to assess storage site performance and meet the regulatory requirements of the new Class VI Underground Injection Control Program for Carbon Dioxide (![Formula][1] ) geologic sequestration. MVA programs are designed and

Introduction to Selected Contributions from the 47th US Rock Mechanics/Geomechanics Symposium Held in San Francisco, California from June 23–26, 2013

This special issue of Rock Mechanics and Rock Engineering contains ten papers that are a representative sample of contributions from the 47th US Rock Mechanics/Geomechanics Symposium held in San Francisco, California from June 23–26, 2013. This multidisciplinary international annual meeting of the American Rock Mechanics Association (ARMA) is a focal event for the Rock Mechanics and Geomechanics community, bringing together professionals and students from civil, geological, mining, geophysical and petroleum engineering. The Symposium focused on recent advances in rock mechanics and geomechanics that cut across disciplines and spanned the globe with more than half of the papers from 38 countries outside the US. The technical sessions spanned a range of topics from civil, mining and petroleum engineering as well as cross-disciplinary topics that involve experts from many branches of science and engineering. The characterization and mechanics of fractures are a common theme among many of the papers in this issue with a diversity of tools and approaches being applied. While several authors focused upon experimental studies of the mechanics of fractures and coupled processes within them others utilized novel combinations of theory and computation to shed light upon the behavior of fractures all the way from laboratory to field scales. In addition, the topics discussed include everything from more familiar rock mechanics concepts such as rock mass characterization and stabilization to the application of mathematical concepts such as percolation theory to the scaling of mechanical and hydraulic properties. The papers contained in this special issue were selected by members of the Organizing Committee of the 47th US Rock Mechancis/Geomechanics Symposium based on the quality of the technical content of the symposium papers. All papers were expanded and rewritten, then re-reviewed for this special issue.