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GravStat™

GravStat™. A method of determining seismic statics from gravity data. An OEX Technology Registered in the U.S. Patent and Trademark Office offered through Lockhart Geophysical. What is the goal of GravStat™?.

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GravStat™

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  1. GravStat™ A method of determining seismic statics from gravity data. An OEX Technology Registered in the U.S. Patent and Trademark Office offered through Lockhart Geophysical.

  2. What is the goal of GravStat™? To determine seismic statics through the interpretation of high spatial frequency gravity anomalies caused by lateral changes in near surface geology.

  3. GravStat™ Model

  4. Datum Velocity & Bouguer Density

  5. Pb = 1.7 g/cc Pb = 2.6 g/cc Pb = 2.2 g/cc Nettleton Density Profile Pw = 2.2 g/cc; Vw = 8370 ft/sec Vw = 2550 m/sec

  6. Bouguer Density Analysis in Sandunes

  7. Density and Velocity are relatedby Gardner's Equation: V (feet/sec) P (g/cc)

  8. Weathering Layer 4000 ft/sec 1219 m/sec Sub Weathering Layer 8000 ft/sec 2438 m/sec GravStat™ Model

  9. ms/mGal Nomogram 17 ms/mGal 6000 28 ms/mGal

  10. Bouguer Density Analysis in Sandunes

  11. GravStat™ Statics in Sandunes

  12. The GravStat™ Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  13. The GravStat™ Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  14. Spatial Aliasing of Gravity Data

  15. Typical 3D Survey Designs

  16. 3D Survey Design-1 (660 feet)

  17. 3D Survey Design-2 (660 feet)

  18. 3D Survey Design-3 (660 feet)

  19. 3D Survey Design-4 (440 feet)

  20. 3D Survey Design-5 (300 feet)

  21. The GravStat™ Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  22. Bouguer Gravity Map (Delaware Basin)

  23. The GravStat™ Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  24. GravStat™ Static Map (Delaware Basin)

  25. The GravStat Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  26. Only elevation statics applied 3D Shot Record

  27. Elevation and Gravstat™ statics 3D Shot Record

  28. The GravStat Method • Acquire un-aliased gravity data coincident with the seismic source and receiver locations. • Remove elevation, topographic and regional effects from the gravity data. • Invert the high frequency residual gravity data into a surface consistent static correction. • Calculate and apply the statics optimizing the regional gravity and the GravStat™ inversion. • Analyze the processed seismic data for clarity and accuracy to known geology.

  29. Refraction Statics Section (glacial till)

  30. GravStat™ Statics Section (glacial till)

  31. Set A - Refraction Statics without Autostatics

  32. Set B - GravStat Statics without Autostatics

  33. Set C - Final Refraction Static Section

  34. Set D - Final GravStat Static Section

  35. Advantages of GravStat™ • High velocity over low. • Not dependent on the quality of the seismic first breaks. • Automatically compensates for velocity variations in the weathering and sub-weathering. • Long period statics are resolved. • Subtle features such as faults are more clearly imaged with GravStat™ reason less autostatic smear.

  36. Advantages of GravStat™ • High velocity over low. • Not dependent on the quality of the seismic first breaks. • Automatically compensates for velocity variations in the weathering and sub-weathering. • Long period statics are resolved. • Subtle features such as faults are more clearly imaged with GravStat™ reason less autostatic smear. • THE SEISMIC WILL NOW TIE TO THE WELLS

  37. A Kansas example how GravStat™ was used to tie to known well control. This example is a comparison of two interpretations; one using seismic data processed with refraction, and the other using seismic data processed using GravStat™.

  38. Refraction - Interpretation • The following three slides show a structural interpretation using seismic data processed with refraction statics. • The survey is over a producing field - well control is shown by the green dots. • Note how much the refraction velocity map must be distorted to tie to the known well control.

  39. Refraction - Time Structure Contour interval = 1ms

  40. Refraction - Velocity to Depth Contour interval = 5’/sec.

  41. Refraction - Depth Map Contour interval = 4 feet

  42. GravStat™ - Interpretation • The following three slides show a structural interpretation using seismic data processed with GravStat™ statics. • As before, the well control is shown by the green dots. • Note how well-behaved and generally-flat the calculated velocity map is compared to the refraction velocity map. • Also note the similarities between the GravStat™ Time and Depth Maps.

  43. GravStat™ - Time Structure Contour interval = 1ms

  44. GravStat™ - Velocity to Depth Contour interval = 5’/sec.

  45. GravStat™ - Depth Map Contour interval = 4 feet

  46. Refraction - Depth Map Contour interval = 4 feet

  47. GravStat™ - Depth Map Contour interval = 4 feet

  48. GravStat™ - Time Structure Contour interval = 1ms

  49. Refraction - Time Structure Contour interval = 1ms

  50. Conclusions • The GravStat™ time structure map mimics the actual well control more accurately than the refraction time structure map. • The GravStat™ velocity map is flatter, allowing for greater confidence in predicting prospects away from the existing well control. • The time structure on the refraction static interpretation in the SW corner of the survey is probably not a valid prospect.

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