Forward & Inverse Modeling Study (Seismic Velocity Image Reconstruction) SIRT and ART inversion methods comparisons

1. • SIMULTANEOUS ITERATIVE RECONSTRUCTION TECHNIQUE (SIRT)
• ALGEBRAIC ITERATIVE RECONSTRUCTION TECHNIQUE (ART)
EXAMPLES OF CROSSBOREHOLE & VSP
IMAGE RECONSTRUCTION
USING
by
Ramazan GÜNEY
March , 2018
Forward & Inverse Modeling

2. In this presentation I have discussed preliminary results of what appears to be a superior
implementation of the Algebraic Reconstruction Technique (ART) and Simultaneous Iterative
Reconstruction Technique (SIRT). The method is based on
1) Continuous application of the error correction terms as computed by ART for all rays in a
given projection , and error distribution over cells after all ray tracing completed for a single
iteration for SIRT,
2) weighting of the correction terms can be designed and back-distributed along the rays
(here no weighting factor used in ART , average correction factor assigned for each cell in
SIRT )
Since ART method generates a good reconstruction in only few iteration, it also appears that
ART to have a computational advantage over the more traditional implementation of SIRT ,
while ART method ıs converging faster . Potential applications of this implementation include
image reconstruction in conjunction with straight ray tracing for Walkaway VSP . Ray bending
effects in reality can cause curved rays leads to a non-uniform ray density across the image
represented by cells.

3. Figure 1e SIRT reconstruction of horst graben model with initial layered velocity model
#35 iteration
#34 iteration
#33 iteration
#32 iteration
Horst Graben model
Initial Layered model
Crossborehole Geometry

4. TRAVEL TIME EVERY 5 TH SHOT PLOTTED ( HORST GRABEN)
FORWARD MODELING
TTIME(S)
RAY NUMBER CONNECTING SHOR TO RECEIVER (EVERY 5TH

5. SIRT RECONSTRUCTION OF NORMAL FAULT MODEL wıth AVERAGED INITIAL VELO MODEL
Iteration# 35Iteration# 34Iteration# 33
Initial Model
Constant (average calculated )
Fault Model
COLORS show Velocities
Blue to Red
3 km /s- 4.5 km/s
Crossborehole Geometry

6. FAULT MODEL INITIAL LAYERED MODEL
(calculated)
SIRT RECONSTRUCTION
COLORS show Velocities
Blue to Red
3 km /s- 4.5 km/s
#35 iteration
CROSSBOREHOLE SIRT RECONSTRUCTION

7. FAULT MODEL INITIAL LAYERED MODEL
(calculated)
ART RECONSTRUCTION
#35 iteration
COLORS show Velocities
Blue to Red
3 km /s- 4.5 km/s
CROSSBOREHOLE ART RECONSTRUCTION

8. Half Walkaway VSP
HORST GRABEN MODEL

9. Slab Model
ART INVERSION (constant velocity (3.25km/s initial model)
VSP reconstruction
35th iteration for direct waves
half walkaway VSP (64x64 cells)
Walkaway VSP Geometry

10. Long offset half walkaway VSP (128x64 cells)
ART INVERSION (constant velocity (3.25km/s initial model)
Slab Model
VSP ART reconstruction
35th iteration for direct waves

11. VSP ART Reconstruction 15th iteration
10mx10m
Normal Fault Model

12. Initial Velocity Model (averaged velocity)
VSP ART Reconstruction Cell Size10m x 10m
3-Block Normal Fault Model
Walkaway VSP Geometry

13. Model
6mx6m cell size
< No Clip Walkaway VSP ART Reconstruction Clipped >
15th iteration
Walkaway VSP Geometry

14. 10M X 10 M 20M X 20 M
WALKAWAY VSP ART RECONSTRUCTION 15TH ITERATION
HORST GRABEN MODELS
Walkaway VSP Geometry

15. Wedge Model
Walkaway VSP ART inversion
34th iteration
35th iteration

16. ART 50th iteration
ART 49th iteration
High confidence
Model
No ray passed
VSP ART IMAGE RECONSTRUCTION