Velocity Estimation of Friendswood’s Weathering Zone using Fermat’s Interferometric Principle By Chaiwoot Boonyasiriwat University of Utah

Outline Motivation Goals: Estimate Velocity Distribution Problem and Solution Results Conclusion Future work

Motivation An accurate velocity distribution of the weathering zone is very important for accurately imaging the subsurface structure.

Goals To determine the horizontal velocity distribution of the weathering zones of the Friendswood field data. To test the power of the Fermat’s interferometric principle.

Outline Motivation Goals: Estimate Velocity Distribution Problem and Solution Results Conclusion Future work

Problem Given: VSP gathers of the Friendswood field data Find: Horizontal velocity distributions of the weathering zones

Friendswood VSP Acquisition Geometry Shot Geo- phone 24 Shots 98 Geophones

0 m 92 m 2.2 km/s 2.2 km/s 3.6 km/s 3.6 km/s 4300 ft/s 6900 ft/s 30 ft 1000 ft 25 ft 600 ft CDP CDP (Sen Chen et al, 1991) (Sen Chen et al, 1991) WET WET Friendswood Tomograms RT RT

Fermat’s Interferometric Principle g” sgx Specular Rayg’x’ Diffraction Ray

Velocity Estimation where s g

Outline Motivation Goals: Estimate Velocity Distribution Problem and Solution Results Conclusion Future work

Results: Shallow Reflector 220

Numbers of Data

Results: Deep Reflector 310

Outline Motivation Goals: Estimate Velocity Distribution Problem and Solution Results Conclusion Future work

Conclusion Fermat’s interferometic principle is fast and simple Horizontal velocity distributions of two reflectors in the weathering zones have been estimated The resulting velocities might not be accurate due to the inaccurate ghost arrivals and the simple method used to compute the velocities.

Future Work Use full reflection tomography to compute the horizontal velocity distribution.