Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Natural gas hydrates are solid, non-stoichiometric compounds of small gas molecules and water. They form when the constituents come into contact at low temperature and high pressure. The physical properties of these compounds, most notably that they are non-flowing crystalline solids that are denser than typical fluid hydrocarbons and that the gas molecules they contain are effectively compressed, give rise to numerous applications in the broad areas of energy and climate effects. In particular, they have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and they could play a significant role in past and future climate change.

Fundamental principles and applications of natural gas hydrates

This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

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A User’s Guide

Author(s): Doughty, C; Moridis, GJ | Abstract: The capability to conduct a rapid, near real-time model-based analysis of production data from tight/shale (TS) gas fields is important in determining fracture and matrix properties. Model-based analysis of production can range from simple analytical solutions to complex numerical models. The objective of this study is to develop a simple, Excel-based tool for the analysis of the complex problem of gas production from a fractured TS gas reservoir that is based on a robust model that is faithful to the underlying physics and can provide rapid estimates of the important system parameters. The scientifically robust model used as the basis for this tool is a significant modification and expansion of the bimodal production decline curve of Silin and Kneafsey (2012). The production period is divided into two regimes: an early-time regime before the extent of the stimulated reservoir volume (SRV) is felt, where an analytical similarity solution for gas production rate is obtained, and a late-time regime where the rate can be approximated with an exponential decline or more accurately represented with a numerical integration. Our basic model follows Silin and Kneafsey (2012) and produces the widely observed -½ slope on a log-log plot of early-time production decline curves, while our expanded model generalizes this slope to –n, where 0 l n l 1, to represent non-ideal flow geometries. The expanded model was programmed into an Excel spreadsheet to develop an interactive, user-friendly application for curve matching of well production data to the bimodal curve, from which matrix and fracture properties can be extracted. This tool allows significant insight into the model parameters that control the reservoir behavior and production: the geometry of the hydraulically-induced fracture network, its flow and transport properties, and the optimal operational parameters. This information enables informed choices about future operations, and is valuable in several different ways: (a) to estimate reserves and to predict future production, including expected ultimate recovery and the useful lifetime of the stage or the well; (b) if curve-matching is unsuccessful, to indicate the inadequacy of the mathematical model and the need for more complex numerical model to analyze the system; (c) to verify/validate numerical models, and to identify anomalous behavior or measurement errors in the data. The present approach can be adapted to gas-flow problems in dual-permeability media (hydraulically or naturally fractured) or highly heterogeneous sedimentary rock, as well as to retrograde condensation.

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The Use of the Bimodal Production Decline Curve for the Analysis of Hydraulically Fractured Shale/Tight Gas Reservoirs

LBNL-2790E 1 of 634 Proceedings of the TOUGH Symposium 2009 September 14—16, 2009 Lawrence Berkeley National Laboratory Berkeley, California Editors George Moridis, Christine Doughty, Stefan Finsterle, and Eric Sonnenthal Lawrence Berkeley National Laboratory Earth Sciences Division 1 Cyclotron Road, Mail Stop 90-1116 Berkeley, CA 94720 This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Lawrence Berkeley National Laboratory – Earth Sciences Division

Proceedings of the TOUGH Symposium 2009

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Modeling studies of mountain-scale radionuclide transport in the unsaturated zone at Yucca Mountain, Nevada - eScholarship

/pdf/the-transformational-decomposition-td-method-for-2l135ilfm2.pdf

The Transformational Decomposition (TD) Method for Compressible Fluid Flow Simulations

The objective of this multi-year, multi-institutional research project was to develop the knowledge base and quantitative predictive capability for the description of geomechanical performance of hydrate-bearing sediments (hereafter referred to as HBS) in oceanic environments. The focus was on the determination of the envelope of hydrate stability under conditions typical of those related to the construction and operation of offshore platforms. We have developed a robust numerical simulator of hydrate behavior in geologic media by coupling a reservoir model with a commercial geomechanical code. We also investigated the geomechanical behavior of oceanic HBS using pore-scale models (conceptual and mathematical) of fluid flow, stress analysis, and damage propagation. The objective of the UC Berkeley work was to develop a grain-scale model of hydrate-bearing sediments. Hydrate dissociation alters the strength of HBS. In particular, transformation of hydrate clusters into gas and liquid water weakens the skeleton and, simultaneously, reduces the effective stress by increasing the pore pressure. The large-scale objective of the study is evaluation of geomechanical stability of offshore oil and gas production infrastructure. At Lawrence Berkeley National Laboratory (LBNL), we have developed the numerical model TOUGH + Hydrate + FLAC3D to evaluate how the formation and disassociation of hydrates in seafloor sediments affects seafloor stability. Several technical papers were published using results from this model. LBNL also developed laboratory equipment and methods to produce realistic laboratory samples of sediments containing gas hydrates so that mechanical properties could be measured in the laboratory. These properties are required to run TOUGH + Hydrate + FLAC3D to evaluate seafloor stability issues. At Texas A&M University we performed a detailed literature review to determine what gas hydrate formation properties had been measured and reported in the literature. We then used TOUGH + Hydrate to simulate the observed gas production and reservoir pressure field data at Messoyakha. We simulated various scenarios that help to explain the field behavior. We have evaluated the effect of reservoir parameters on gas recovery from hydrates. Our work should be beneficial to others who are investigating how to produce gas from a hydrate capped gas reservoir. The results also can be used to better evaluate the process of producing gas from offshore hydrates. The Schlumberger PETREL model is used in industry to the description of geologic horizons and the special distribution of properties. An interface between FLAC3D and Petrel was built by Schlumberger to allow for efficient data entry into TOUGH + Hydrate + FLAC3D.

/pdf/geomechanical-performance-of-hydrate-bearing-sediments-in-3zclj6hsg3.pdf

George J. Moridis

Papers

The Use of the Bimodal Production Decline Curve for the Analysis of Hydraulically Fractured Shale/Tight Gas Reservoirs

Proceedings of the TOUGH Symposium 2009

Modeling studies of mountain-scale radionuclide transport in the unsaturated zone at Yucca Mountain, Nevada - eScholarship

The Transformational Decomposition (TD) Method for Compressible Fluid Flow Simulations

Geomechanical Performance of Hydrate-Bearing Sediments in Offshore Environments