FY2001 Oil and Gas Recovery Technology Review Meeting Diagnostic and Imaging. High Speed 3D Hybrid Elastic Seismic Modeling Lawrence Berkeley National Laboratory, GX Technology, Burlington Resources. Contacts: Valeri Korneev 510-486-7214, [email protected]; - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
LBNLLBNLGXTGXTBRBR FY2001 Oil and Gas Recovery Technology Review Meeting
Diagnostic and Imaging
High Speed 3D Hybrid Elastic Seismic Modeling
Lawrence Berkeley National Laboratory, GX Technology, Burlington Resources
LBNLLBNLGXTGXTBRBR Issues of 3D modeling performance
• Accuracy. Improves by using higher order differencing and finer gridding.
• Model size. No less then 5 grid points per shortest wavelength.
• • Acoustic code requires 3.5 *N cells, where N = Nx*Ny*Nz number of cells for model
parameters sampling. Elastic code needs 6 times more cells.
• CPU time. Acoustic code requires 5*K operations per grid cell. Elastic code requires 5 times more operations per grid cell, where K= 6*m, m - an order of differential operator.
• Stability. Requires integration time step
• Optimization. Avoid over sampling and too small time integration steps. Use parallel computing. Avoid computing in undisturbed cells.
LBNL has a fast and accurate wave propagation algorithm for moderately heterogeneous elastic media:
We are going to apply it
LBNLLBNLGXTGXTBRBR
Hybrid Ray Tracing and FD approachspeeds up computations up to 10 times
W a v e f i e l d a t p o i n t x a t t i m e t .
u x t m x sS
u g x x s t d S( , ) ( ) ( ) ( , , )
S – d a t a e x c h a n g e s u r f a c e , m – m o d e l p a r a m e t e r s ,u - i n c i d e n t w a v e f i e l d , g – G r e e n ’ s f u n c t i o n
Fast code throughslow simple media
FD code throughcomplex media
LBNLLBNLGXTGXTBRBR LBNL PC cluster
• Vendor - SGI
• 8 dual Pentium III CPU 800 MHz
• 512 SDRAM per node
• Myrinet LAN - fast net card
• Lynux based
• Price $60K
• Completion by the end of 2000
LBNLLBNLGXTGXTBRBR Year 2001 efforts
Requested budget - 250K
• Parallel 3D elastic code
• Nonuniform grid for 3D
• 4-th order in time scheme for 3D
• Hybrid (ray tracing + FD) algorithm
• Topography for 3D
LBNLLBNLGXTGXTBRBR BoxLib Parallelism
• Hybrid C++/Fortran Programming environment.
• Library supports parallel PDE solvers on rectangular meshes.
• MPI portability: distributed and shared memory supercomputers, clusters of engineering workstations.
LBNLLBNLGXTGXTBRBR Discretization
• Fourth order accuracy in space and time based on a modified equation approach.
• 2D: fourth order scheme gives 2 times the performance of conventional second order schemes.
• 3D: fourth order 4 times as efficient.
LBNLLBNLGXTGXTBRBR
Parallel Performance
0
1
2
3
4
5
6
7
8
9
1 2 4 8 16 32 64
IBM 2
IBM 4
T3E 2
T3E 4
Wall clock run time
Number of CPUs
4-th order scheme performs better as number of CPUs increases.