Parallel Seismic Data Processing

The International Lithosphere Program is a new international interdisciplinary research program in the solid earth sciences that has been established by the International Council of Scientific Unions (ICSU) at the joint request of the International Union of Geodesy and Geophysics (IUGG) and the International Union of Geological Sciences (IUGS). Its goal is a better understanding of the development of the earth, particularly those aspects upon which human society depends for its well‐being.The International Lithosphere Program (ILP) is a natural sequel to a series of international cooperative projects in the geosciences that began with the International Geophysical Year in 1957–58 and continued with the Upper Mantle Project in the 1960's and the International Geodynamics Project (IGP) in the 1970's. In 1977, IUGG and IUGS established an inter‐union task group to consider the possibility of a successor to the IGP for the 1980's. The task group, under cochairmen Carl Kisslinger (Cooperative Institute for Research in Environmental Sciences, University of Colorado), foreign secretary of the American Geophysical Union, and J. Henning Illies (Geophysical Institute, University of Karlsruhe, Federal Republic of Germany), invited suggestions and comments from the two unions and the national committees in the member countries. Their report, which was completed late in 1978, proposed a new project on the dynamics, origin, and evolution of the lithosphere. This proposal was approved by the IUGS Executive Committee in December 1979 and by the IUGS Council in June 1980. An inter‐union steering committee, established in 1979 under the joint chairmanship of Kisslinger and Illies, developed the organizational framework and constitution of the new program. These were approved by resolution of the ICSU Governing Board in September 1980, and the Inter‐Union Commission on the Lithosphere (ICL) was established to implement the program. National members of ICSU were urged to establish national committees and to develop internal programs for the new International Lithosphere Program.

Authors

The time‐dependent Maxwell equations are one of the most important approaches to describing dynamic or wide‐band frequency electromagnetic phenomena. A sequential finite‐volume, characteristic‐based procedure for solving the time‐dependent, three‐dimensional Maxwell equations has been successfully implemented in Fortran before. Due to its need for a large memory space and high demand on CPU time, it is impossible to test the code for a large array. Hence, it is essential to implement the code on a parallel computing system. In this paper, we discuss an efficient and scalable parallelization of the sequential Fortran time‐dependent Maxwell equations solver using High Performance Fortran (HPF). The background to the project, the theory behind the efficiency being achieved, the parallelization methodologies employed and the experimental results obtained on the Cray T3E massively parallel computing system will be described in detail. Experimental runs show that the execution time is reduced drastically through parallel computing. The code is scalable up to 98 processors on the Cray T3E and has a performance similar to that of an MPI implementation. Based on the experimentation carried out in this research, we believe that a high‐level parallel programming language such as HPF is a fast, viable and economical approach to parallelizing many existing sequential codes which exhibit a lot of parallelism. Copyright © 2003 John Wiley & Sons, Ltd.

Solid Earth Physics, including Seismology, Physics of the Earth, Earth Magnetism to name a few more topical disciplines, strongly relies on mathematical and numerical possibilities of modeling very complex physical processes ongoing in the Earth interior. Tremendous progress in geophysical instrumentation and still increasing quality and quantity of observational data also prompts for advanced processing methods in order to get more reliable interpretations. The goal of this chapter is to review some contributions from the Institute of Geophysics, Polish Academy of Sciences (IGF PAS) to physical and mathematical concepts used in Solid Earth Physics. We have selected some topics which are general enough to be interesting for a wide range of readers, leaving many topical issues uncovered in this review.

High temperature superconductor current leads for fusion machines

This paper derives analytical estimates for the rates of convergence of numerical first and second derivative operators involved in flux reconstruction (FR). These estimates yield the rate of convergence for steady-state advection-diffusion problems when error is measured in the vector seminorm induced by the advection-diffusion operator. This serves to rigorously quantify the effect of polynomial order, correction functions, and upwinding coefficients on the accuracy of FR schemes. We prove that for centered fluxes, the derivative operator exhibits superconvergence for a special class of correction functions, designated “SFR, which includes the nodal DG scheme. Finally, we also show that the rate of convergence of the vector $\ell^2$ norm of error for such steady-state problems is identical to the short-time rate of convergence for time-dependent problems derived in [K. Asthana et al., Analysis and Design of Optimal Discontinuous Finite Element Schemes, Ph.D. thesis, Stanford University, Stanford, CA, 2...

TOUGH2 is a widely used reservoir simulator for solving subsurface flow related problems such as nuclear waste geologic isolation, environmental remediation of soil and groundwater contamination, and geothermal reservoir engineering. It solves a set of coupled mass and energy balance equations using a finite volume method. This contribution presents the design and analysis of a parallel version of TOUGH2. The parallel implementation first partitions the unstructured computational domain. For each time step, a set of coupled non-linear equations is solved with Newton iteration. In each Newton step, a Jacobian matrix is calculated and an ill-conditioned non-symmetric linear system is solved using a preconditioned iterative solver. Communication is required for convergence tests and data exchange across partitioning borders. Parallel performance results on Cray T3E-900 are presented for two real application problems arising in the Yucca Mountain nuclear waste site study. The execution time is reduced from 7504 seconds on two processors to 126 seconds on 128 processors for a 2D problem involving 52,752 equations. For a larger 3D problem with 293,928 equations the time decreases from 10,055 seconds on 16 processors to 329 seconds on 512 processors.

Direct Numerical Simulation (DNS) of turbulence requires many CPU days and Gigabytes of memory. These requirements limit most DNS to using supercomputers, available at supercomputer centres. With the rapid development and low cost of PCs, PC clusters are evaluated as a viable low-cost option for scientific computing. Both low-end and high-end PC clusters, ranging from 2 to 128 processors, are compared to a range of existing supercomputers, such as the IBM SP nodes, Silicon Graphics Origin 2000, Fujitsu AP3000 and Cray T3E. The comparison concentrates on CPU and communication performance. At the kernel level, BLAS libraries are used for CPU performance evaluation. Regarding communication, the free implementations of MPICH and LAM are used on fast-ethernet-based systems and compared to myrinet-based and supercomputer networks. At the application level, serial and parallel simulations are performed on state of the art DNS, such as turbulent wake flows in stationary and moving computational domains.

A novel two-dimensional inverse differential quadrature method is proposed to approximate the solution of high-order system of differential equations. A critical aspect of the proposed scheme is to circumvent the error arising from high sensitivity to noise associated with high-order numerical differentiation operations during direct approximation. A general framework for approximating arbitrary functions from high-order partial derivatives is developed and a comprehensive insight for the implementation of different orders of the analysis within the context of first-order shear deformation theory kinematical assumptions governing laminated plates bending and buckling behaviours is presented. Concerning buckling analysis, a Moore–Penrose pseudo-inverse preconditioning procedure is further proposed to formulate the eigenvalue problem, since the developed algebraic expressions constitute an underdetermined system. According to the numerical tests for bending and buckling analyses of laminated plates under different loading and boundary conditions, the accuracy of current solutions compares satisfactorily with Navier’s solution, differential quadrature method and commercial finite element analysis models. Furthermore, the developed method demonstrates the potential for improved convergence in comparison with differential quadrature solutions highlighting its computational merits.

Time-lapse (4D) seismic inversion is the leading method to quantitatively monitor fluid-flow dynamics in the subsurface, with applications ranging from enhanced oil recovery to subsurface CO2 storage. The process of inverting 4D seismic data for reservoir properties is a notoriously ill-posed inverse problem due to the band-limited and noisy nature of seismic data and inaccuracies in the repeatability of 4D acquisition surveys. Consequently, ad-hoc regularization strategies are essential for the 4D seismic inverse problem to obtain geologically meaningful subsurface models and associated 4D changes. Motivated by recent advances in the field of convex optimization, we propose a joint inversion-segmentation algorithm for 4D seismic inversion that integrates total variation and segmentation priors as a way to counteract missing frequencies and present noise in 4D seismic data. The proposed inversion framework is designed for poststack seismic data and applied to a pair of seismic volumes from the open Sleipner 4D seismic data set. Our method has three main advantages over state-of-the-art least-squares inversion methods. First, it produces high-resolution baseline and monitor acoustic models. Second, it mitigates nonrepeatable noise and better highlights real 4D changes by leveraging similarities between multiple data. Finally, it provides a volumetric classification of the acoustic impedance 4D difference model (4D changes) based on user-defined classes (i.e., percentages of speedup or slowdown in the subsurface). Such advantages may enable more robust stratigraphic/structural and quantitative 4D seismic interpretation and provide more accurate inputs for dynamic reservoir simulations. Alongside presenting our novel inversion method, we introduce a streamlined data preprocessing sequence for the 4D Sleipner poststack seismic data set that includes time-shift estimation and well-to-seismic tie. Finally, we provide insights into the open-source framework for large-scale optimization that we used to implement the proposed algorithm in an efficient and scalable manner.

Summary Partial differential equation solvers based on the finite-difference method have for many years been a keystone of seismic processing and modelling applications, commonly found in practical migration and full-waveform inversion methods. Sharp density contrasts within the computational domain have potential to introduce numerical error: problematic when introducing topography to a seismic model. Including a simple step change in density to approximate an air layer compromises both stability and numerical accuracy, often requiring smoothing of the contrast, and inducing both first and second order errors in space. Topography can instead be implemented via an immersed boundary conforming to the surface. This is achieved by extrapolating the wavefield across the boundary to find solution values at necessary external nodes. As this process is confined to the pre-processing step, it has negligible effect on the computational cost of the simulation. Devitoboundary is a tool in its early stages of development, intended to compliment Devito as a user-friendly means of including immersed boundaries in practical applications. 3D immersed boundaries can be constructed from irregularly sampled topography point clouds, via Delaunay triangulation coupled with a 1D extrapolation scheme. The result is a stable, error-free boundary which can be readily integrated with Devito models.

Few-mode fibers provide a number of independent channels in a single strand of optical fiber. Therefore they have potential for increasing channel capacity and data throughput, stabilizing coherent systems, simplifying and miniaturizing fiber optic circuits, and multiplying the number of functions and operations which can be performed. However, due to the difficulties associated with the control of guided modes in such fibers, their multi-channel capacity has not yet been fully exploited. Recently, we have been attempting to better understand the modal and polarization characteristics of few-mode optical fibers, and to utilize these fibers for the major application areas of fiber optics. This paper reviews some of the early work, and describes the current development of few-mode fiber optic devices at Stanford University.

Laser scanning and digital outcrop geology in the petroleum industry: A review

Discrete event simulation model reduction: A causal approach

One of the major problems in the modeling and inversion of marine controlled-source electromagnetic (CSEM) data is related to the need for accurate representation of very complex geoelectrical models typical for marine environment. At the same time, the corresponding forward-modeling algorithms should be powerful and fast enough to be suitable for repeated use in hundreds of iterations of the inversion and for multiple transmitter/receiver positions. To this end, we have developed a novel 3D modeling and inversion approach, which combines the advantages of the finite-difference (FD) and integral-equation (IE) methods. In the framework of this approach, we have solved Maxwell’s equations for anomalous electric fields using the FD approximation on a staggered grid. Once the unknown electric fields in the computation domain of the FD method are computed, the electric and magnetic fields at the receivers are calculated using the IE method with the corresponding Green’s tensor for the background conductivity model. This approach makes it possible to compute the fields at the receivers accurately without the need of very fine FD discretization in the vicinity of the receivers and sources and without the need for numerical differentiation and interpolation. We have also developed an algorithm for 3D inversion based on the hybrid FD-IE method. In the case of the marine CSEM problem with multiple transmitters and receivers, the forward modeling and the Fréchet derivative calculations are very time consuming and require using large memory to store the intermediate results. To overcome those problems, we have applied the moving sensitivity domain approach to our inversion. A case study for the 3D inversion of towed streamer EM data collected by PGS over the Troll field in the North Sea demonstrated the effectiveness of the developed hybrid method.