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Using multidimensional scaling and kernel principal component analysis to interpret seismic signatures of thin shaly-sand reservoirs Piyapa Dejtrakulwong1, Tapan Mukerji2, and Gary Mavko1 1Stanford Rock Physics Laboratory (SRB), Department of Geophysics, 2Stanford Center for Reservoir Forecasting (SCRF), Department of Energy Resources and Engineering, Stanford University
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Motivation Limitation in seismic resolvability
Interpretations of the sub-resolution layers Goal: To investigate seismic signatures of thin shaly-sand reservoirs with statistical attributes multidimensional scaling (MDS) and kernel principal component analysis (KPCA)
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Thin sand-shale sequences
Workflow Markov Chains Rock Physics Sand/shale model Thin sand-shale sequences Interpretation Net-to-gross ratios Saturations Attributes MDS/KPCA Seismic Responses
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Markov chain for lithologies
Discrete states: sand, shaly sand, sandy shale, shale Transition probability matrix: 100 m
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Properties from rock physics
Sand Shaly-sand Sandy-Shale Shale Dvorkin and Gutierrez (2001)
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Properties from rock physics
Marion (1990) and Yin (1992)
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Generate Seismic Response
Full waveform, normally-incident, reflected seismograms are simulated using the Kennett algorithm (Kennett, 1983) with a 30-Hz, zero-phase Ricker wavelet
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Generate Seismic Response
Multiple realizations (Monte Carlo simulation)
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Multidimensional scaling (MDS)
transforms the dissimilarity matrix into points in lower dimensional (Euclidean) space configures points such that their Euclidean distances (dij) in the space match the original dissimilarity (δij ) of the objects as much as possible
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Multidimensional scaling (MDS)
Atlanta Chicago Denver Houston Los Angeles Miami New York San Francisco Seattle Washington DC Kruskal and Wish 1978
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Kernel principal component analysis (KPCA)
Perform linear PCA Map from 2D to 3D 2-D 3-D Linearly separable
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Distance Functions General Minkowski metric r = 2: Euclidean distance
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Dynamic Distance Function
Li et al. (2003) Dynamic Partial Function Dm : set of smallest m d’s from {d1,…,dn} The features for measuring similarity depend on the objects being compared pairwise
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Dynamic Similarity Kernel function
Dynamic similarity kernel (Yan et al., 2006) (Li et al., 2003) and Δm = {the smallest m δ’s of (δ1,…, δn)}
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Kernel functions Gaussian kernel
Dynamic similarity kernel (Yan et al., 2006) Inverse multi-quadric kernel Polynomial kernel (Li et al., 2003) and Δm = {the smallest m δ’s of (δ1,…, δn)}
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Projections of seismograms
MDS/KPCA Results from MDS and KPCA: projections of input seismograms onto selected principal components Measure of dissimilarity among seismograms Dissimilarity matrix or kernel matrix Configuration of points color-coded by net-to-gross ratios or other properties
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Investigate net-to-gross ratios and saturations
Effect of net-to-gross ratios: we study a set of aggrading-type transition matrices with various net-to-gross ratios. (Sw=0.1 for sand layers and 1 for the others) Effect of saturations: we generate sequences from the same transition matrix but now vary saturation (in the sand layers only)
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Net-to-gross ratios (MDS)
Classical MDS Metric MDS Non-metric MDS Classification success rate 56% 74% 73%
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Net-to-gross ratios (KPCA)
Kernel Gaussian Dynamic similarity Inverse multi-quadric Polynomial Classification success rate 81% 90% 79% 59% Classification of 3 NTG classes Stratified 10-fold cross validation
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Saturations (MDS) (A) (B) (C) Non-metric MDS Classical MDS Metric MDS
Classification success rate 65% 66% 53% 67% 57% 69% 58%
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Saturations (KPCA) Different transition matrices Same nominal NTG
More blocky sands
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Saturations (KPCA) Dynamic similarity kernel (A) (B) (C) Brine sand
Oil sand
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Inverse multi-quadric
Saturations (KPCA) (A) (B) (C) Kernel Gaussian Dynamic similarity Inverse multi-quadric Polynomial A B C Classification success rate 62% 73% 61% 88% 87% 84% 64% 67% 60% 65% 52% 3 saturation classes; stratified 10-fold cross validation
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Selecting components (KPCA)
Parallel coordinates plot Use 1st and 2nd components: success rate = 60% Use 1st and 6th components: success rate =73% Use the first 10 components: success rate = 82%
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Conclusions Dynamic Similarity Kernel (DSK) best differentiates both the net-to-gross classes and the saturation classes. The features for measuring similarity depend on the objects being compared Increasing coordinates improves classification. In addition a subset of most relevant coordinates for the property of interest can also be chosen. Similar workflow using MDS and KPCA can be applied to real seismic data to characterize thin shaly-sand reservoirs.
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Interpreting seismic signatures
?? Time Coordinate 2 X ?? Coordinate 1 well unknown N/G
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Acknowledgements Stanford Rock Physics and Borehole Geophysics project (SRB)and the Stanford Center for Reservoir Forecasting (SCRF)
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