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Author

Dongxiao Zhang

Bio: Dongxiao Zhang is an academic researcher from Southern University of Science and Technology. The author has contributed to research in topics: Monte Carlo method & Porous medium. The author has an hindex of 49, co-authored 289 publications receiving 9301 citations. Previous affiliations of Dongxiao Zhang include University of Oklahoma & University College of Engineering.


Papers
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Journal ArticleDOI
TL;DR: In this article, an ensemble-based closed-loop optimization method that combines a novel ensemblebased optimization scheme (EnOpt) with the ensemble Kalman filter (EnKF) was proposed.
Abstract: Summary With the advances in smart well technology, substantially higher oil recovery can be achieved by intelligently managing the operations in a closed-loop optimization framework. The closed-loop optimization consists of two parts: geological model updating and production optimization. Both of these parts require gradient information to minimize or maximize an objective function: squared data mismatch or the net present value (or other quantities depending on financial goals), respectively. Alternatively, an ensemblebased method can acquire the gradient information through the correlations provided by the ensemble. Computation of the optimal controls in this way is nearly independent of the number of control variables, reservoir simulator, and simulation solver. In this paper, we propose an ensemble-based closed-loop optimization method that combines a novel ensemble-based optimization scheme (EnOpt) with the ensemble Kalman filter (EnKF). EnKF has recently been found suitable for sequential data assimilation in large-scale nonlinear dynamics. It adjusts reservoir model variables to honor observations and propagates uncertainty in time. EnOpt optimizes the expectation of the net present value based on the updated reservoir models. The proposed method is fairly robust, completely adjoint-free and can be readily used with any reservoir simulator. The ensemble-based closed-loop optimization method is illustrated with a waterflood example subject to uncertain reservoir description. Results are compared with other possible reservoir operation scenarios, such as wells with no controls, reactive control, and optimization with known geology. The comparison shows that the ensemble-based closed-loop optimization is able to history match the main geological features and increase the net present value to a level comparable with the hypothetical case of optimizing based on known geology.

346 citations

Journal ArticleDOI
TL;DR: In this article, a higher-order solution of the means and variance of hydraulic head for saturated flow in randomly heterogeneous porous media was obtained by the combination of Karhunen-Loeve decomposition, polynomial expansion, and perturbation methods.

342 citations

Journal ArticleDOI
TL;DR: In this study, the ensemble Kalman filter (EnKF) approach is used for continuously updating model parameters such as hydraulic conductivity and model variables such as pressure head while simultaneously providing an estimate of the uncertainty through assimilating dynamic and static measurements, without resorting to the explicit computation of the covariance or the Jacobian of the state variables.

337 citations

Book
17 Oct 2001
TL;DR: Stochastic Methods for Flow in Porous Media: Coping with Uncertainties as discussed by the authors explores fluid flow in complex geologic environments and provides an overview of stochastic methods used by researchers in the community.
Abstract: "Stochastic Methods for Flow in Porous Media: Coping with Uncertainties" explores fluid flow in complex geologic environments. The parameterization of uncertainty into flow models is important for managing water resources, preserving subsurface water quality, storing energy and wastes, and improving the safety and economics of extracting subsurface mineral and energy resources. This volume systematically introduces a number of stochastic methods used by researchers in the community in a tutorial way and presents methodologies for spatially and temporally stationary as well as nonstationary flows. The author compiles a number of well-known results and useful formulae and includes exercises at the end of each chapter. As never seen before, this book includes key features such as: balanced viewpoint of several stochastic methods, including Greens' function, perturbative expansion, spectral, Feynman diagram, adjoint state, Monte Carlo simulation, and renormalization group methods; tutorial style of presentation will facilitate use by readers without a prior in-depth knowledge of Stochastic processes; practical examples throughout the text; and exercises at the end of each chapter which reinforce specific concepts and techniques. For the reader who is interested in hands-on experience, a number of computer codes are included and discussed.

328 citations

Journal ArticleDOI
TL;DR: In this paper, the existence and size of the representative elementary volume (REV) can be quantified at the pore-scale with lattice Boltzmann simulations on pore geometries reconstructed from computed microtomographic images.
Abstract: Flow in porous media is studied at the pore-scale with lattice Boltzmann simulations on pore geometries reconstructed from computed microtomographic images. Pore scale results are analyzed to give quantities such as permeability, porosity and specific surface area at various scales and at various locations. With this, some fundamental issues such as scale dependency and medium variability can be assessed quantitatively. More specifically, the existence and size of the well known concept, representative elementary volume (REV), can be quantified. It is found that the size of an REV varies spatially and depends on the quantity being represented. For heterogeneous media, a better measure may be the so called “statistical REV”, which has weaker requirements than does the deterministic REV.

269 citations


Cited by
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01 May 1993
TL;DR: 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.
Abstract: 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.

29,323 citations

Reference EntryDOI
31 Oct 2001
TL;DR: The American Society for Testing and Materials (ASTM) as mentioned in this paper is an independent organization devoted to the development of standards for testing and materials, and is a member of IEEE 802.11.
Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

3,792 citations

01 Apr 2003
TL;DR: The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it as mentioned in this paper, and also presents new ideas and alternative interpretations which further explain the success of the EnkF.
Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

2,975 citations

Journal ArticleDOI
TL;DR: This work reviews many significant developments over the past decade of the lattice-Boltzmann method and discusses higherorder boundary conditions and the simulation of microchannel flow with finite Knudsen number.
Abstract: With its roots in kinetic theory and the cellular automaton concept, the lattice-Boltzmann (LB) equation can be used to obtain continuum flow quantities from simple and local update rules based on particle interactions. The simplicity of formulation and its versatility explain the rapid expansion of the LB method to applications in complex and multiscale flows. We review many significant developments over the past decade with specific examples. Some of the most active developments include the entropic LB method and the application of the LB method to turbulent flow, multiphase flow, and deformable particle and fiber suspensions. Hybrid methods based on the combination of the Eulerian lattice with a Lagrangian grid system for the simulation of moving deformable boundaries show promise for more efficient applications to a broader class of problems. We also discuss higherorder boundary conditions and the simulation of microchannel flow with finite Knudsen number. Additionally, the remarkable scalability of the LB method for parallel processing is shown with examples. Teraflop simulations with the LB method are routine, and there is no doubt that this method will be one of the first candidates for petaflop computational fluid dynamics in the near future.

1,585 citations

Journal ArticleDOI
TL;DR: Pore-scale imaging and modelling is becoming a routine service in the oil and gas industry as discussed by the authors, and has potential applications in contaminant transport and carbon dioxide storage, which has been shown to transform our understanding of multiphase flow processes.

1,421 citations