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Physical Modeling: Time Lapse, 3D, and VSP Robert W. Wiley Allied Geophysical Laboratories University of Houston. Outline. Properties of Physical Modeling Fracture Model Time-Lapse Model 3D VSP Model Hardware Future Directions Conclusions. Properties that scale well.

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Outline

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  1. Physical Modeling: Time Lapse, 3D, and VSP Robert W. WileyAllied Geophysical LaboratoriesUniversity 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 Glass slides x Glass blocks 1.1 cm Resin 35.5 cm Fracture model under construction showing glass slides in situ y

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

  8. 1071 CDP 1360 2 2.5 3 Line 2151

  9. Line 2140 500 m Offset 1071 CDP 1360 2.2 Time (s) 2.4 2.6 + -

  10. Damp for 750 m offset – time slice 2430 ms – Perp. 200 Line 1 100 200 300 1 Trace Number

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

  12. Time-Lapse Model

  13. The model as constructed (Wardana, 2001)

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

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

  16. 3D VSP Model

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

  18. Preprocessing (First break pick)

  19. Hardware

  20. TRANSDUCERS Spherical Transducers Pin Transducers 3 C Transducers Shear 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. Line 2140 500 m Offset CDP 1150 1202 Curvature 2.4 2.6

  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. Line 2140 500 m Offset 1071 CDP 1360 2.2 Time (s) 2.4 2.6 + -

  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. Shear Transducer Design www.valpeyfisher-ud.com

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