1. Physical Modeling: Time Lapse, 3D, and VSP Robert W. Wiley Allied Geophysical Laboratories University of Houston

2. Outline Properties of Physical Modeling Fracture Model Time-Lapse Model 3D VSP Model Hardware Future Directions Conclusions

3. Properties that scale well Distance (typically we use 1km = 10 cm) Time (typically we use 4 ms = 0.4  s) Frequency (typically we use 30 Hz = 300 kHz) P and S velocity –For acoustic propagation we scale vp by 0.5 –For elastic propagation we do not rescale Viscosity –Gas by air –Water by water –Oil by glycerol

4. Properties that do not scale well Source and receiver size Pore size (other physics takes place for extremely small pores) Frequency dependent attenuation mechanisms (which we don’t yet understand anyway!) Soft sediments and weathering zones Other limitations A model 1 m by 1 m by 0.5 m (corresponding to 10 km x 10 km by 5 km) weighs more than one metric ton! Models take months to build We needed bigger, stronger, and more patient graduate students!

5. Fracture Model

6. Fracture Construction 1.1 cm Glass slides 35.5 cm Glass blocks Resin x Fracture model under construction showing glass slides in situ y

7. HTI model y x 63.5 cm 50.8 cm Fracture zone

8. 2.5 3 2 1071 CDP 1360 Line 2151

9. + + - 2.2 2.4 2.6 10711360 Time (s) CDP Line 2140 500 m Offset

10. Trace Number 200 1 1 100300 Line Line Damp for 750 m offset – time slice 2430 ms – Perp.

11. Positive Amplitude Most Positive CurvatureMost Negative Curvature Principle Comp Filter

12. Time-Lapse Model

13. The model as constructed (Wardana, 2001)

14. Time lapse modeling (Wardana, 2001) wet half wet dry nearmid far Amplitude

15. Time lapse modeling (Wardana, 2001) wet half wet dry nearmid far Coherence

16. 3D VSP Model

17. Physical model 6 layer alternate blue and black & a salt body ρ blue = 2.4 g/cc ρ black = 1.34 g/cc V black = 2586.9 m/s V blue =3264.3 m/s

18. Preprocessing (First break pick)

19. Hardware

20. 3 C TransducersShear Transducers Pin TransducersSpherical Transducers TRANSDUCERS

21. Old System (Backup System)

22. NI 2 Source 4 Receiver System Dry Tank

23. NI 8 Source 16 Receiver System Wet Tank

24. Initial Configuration Data Configuration

25. NI System Control- LabView Based Main Window Position Control Window

26. Future Directions Bring the two new systems on line Develop a 16 receiver system Develop a multiple source system Collect porous model data Test additional transducers Investigate other materials

27. Conclusions We are able to build reasonably complex physical models Results are similar to seismic data This is an excellent approach to acquiring controlled data for testing algorithms Physical modeling is cost effective compared to field experiments

28. Thank You

29. Curvature 2.4 2.6 CDP Line 2140 500 m Offset 11501202

30. Pinducer

31. Physical Limitations Inaccurate construction of actual model Limited selection of velocity and density parameters

32. Some Limitations Limited bandwidth with strong resonance at one frequency Limited to materials with specific elastic parameters Difficult to build lateral velocity variations Labor intensive Cannot model all real earth materials/layers

33. Source and Receiver Issues Inaccurate location of source and receiver with respect to the model Source and receiver resonate at one frequency Source and receiver dimensions are large Source and receiver have pronounced radiation patterns

34. + + - 2.2 2.4 2.6 10711360 Time (s) CDP Line 2140 500 m Offset

35. Properties that do not scale well Source and receiver size Pore size (other physics takes place for extremely small pores) Frequency dependent attenuation mechanisms (which we don’t yet understand anyway!) Soft sediments and weathering zones Other limitations A model 1 m by 1 m by 0.5 m (corresponding to 10 km x 10 km by 5 km) weighs more than one metric ton! Models take months to build We needed bigger, stronger, and more patient graduate students!

36. Why Run Models To test interpretation – Salt dome, coal seam To test algorithm – Migration, Multiple removal To test interpretation tools – fracture identification, fluid content To test theory – Lamb’s problem, Kirchhoff diffraction, anisotropy

37. Why Physical Modeling No simplifying mathematical assumptions No approximations to mathematical functions No round-off errors No a priori mathematical understanding required

38. Limitations Limited selection of velocity and density parameters Difficult to build lateral velocity variations Labor intensive Inaccurate construction of actual model Limited to frequency response of transducers Source and receiver dimensions

39. Benefits of Physical Modeling Experimental repeatability and controlled conditions Very cost-effective compared to field work Physics of elastic energy propagation through physical models is same as real world Arbitrary earthlike conditions closer to real earth data than numerical modeling

40. Spherical Transducer

41. 3C Transducer

42. www.valpeyfisher-ud.com Shear Transducer Design