velocity estimation of friendswood’s weathering zone using fermat’s interferometric principle by...

Velocity Estimation of Velocity Estimation of Friendswood’s Friendswood’s

Weathering Zone using Weathering Zone using Fermat’s Fermat’s

Interferometric Interferometric PrinciplePrinciple

By Chaiwoot BoonyasiriwatBy Chaiwoot BoonyasiriwatUniversity of UtahUniversity of Utah

OutlineOutlineMotivation

Goals: Estimate Velocity Distribution

Problem and Solution

Results

Conclusion

Future work

MotivationMotivation

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

GoalsGoalsTo determine the horizontal velocity distribution of the weathering zones of the Friendswood field data.

To test the power of the Fermat’s interferometric principle.

OutlineOutlineMotivation

Goals: Estimate Velocity Distribution

Problem and Solution

Results

Conclusion

Future work

ProblemProblemGiven:

VSP gathers of the Friendswood field data

Find:

Horizontal velocity distributions of the weathering zones

Friendswood VSP Acquisition Friendswood VSP Acquisition GeometryGeometry

Shot

Geo-phone

24 Shots

98 Geophones

0 m0 m 92 m92 m

2.2 km/s2.2 km/s 3.6 km/s3.6 km/s

4300 ft/s4300 ft/s 6900 ft/s6900 ft/s

30 ft30 ft

1000 ft1000 ft25 ft25 ft 600 ft600 ft

CDPCDP

(Sen Chen et al, 1991)(Sen Chen et al, 1991)

WETWET

Friendswood TomogramsFriendswood Tomograms RTRT

Fermat’s Interferometric Fermat’s Interferometric PrinciplePrinciple

g”g”

ssgg

xx

Specular Ray

gg’’

x’x’

Diffraction Ray

0diff spec

''gsx'''gg ''sg0)( ''gsx '''gg ''sg

)(min''g ''gsx''sg'''gg

Velocity EstimationVelocity Estimation

where 22 ZXL

s g

/2LV ref

OutlineOutlineMotivation

Goals: Estimate Velocity Distribution

Problem and Solution

Results

Conclusion

Future work

Results: Shallow Results: Shallow ReflectorReflector

220

23522352 23522352 576576

)(min''g ''gsx''sg'''gg

''gsx''sg'''gg

Numbers of DataNumbers of Data

Results: Deep ReflectorResults: Deep Reflector

310

OutlineOutlineMotivation

Goals: Estimate Velocity Distribution

Problem and Solution

Results

Conclusion

Future work

ConclusionConclusion• 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 WorkFuture Work

• Use full reflection tomography to compute the horizontal velocity distribution.