Salt Boundary Delineation by Transmitted PS Waves David Sheley

Outline MotivationMotivation Transmission Migration TheoryTransmission Migration Theory ResultsResults –Synthetic –Gulf of Mexico VSP ConclusionsConclusions

Problem: Limited Illumination SEDIMENT Receiver Well SEDIMENT P PP SALT

Solution: PS Transmission Migration SEDIMENT PS Receiver Well SEDIMENT P SALT

Outline MotivationMotivation Transmission Migration TheoryTransmission Migration Theory ResultsResults –Synthetic –Gulf of Mexico VSP ConclusionsConclusions

Conventional PP Migration m(r) = S(z g,  sr +  rg )   sr  rg s r g

m(r) = S(z g,  sr +  rg )   sr s r g Transmission PS Migration  rg P-wave S-wave

m(r) = S(z g,  sr +  rg )   sr s r g Transmission PS Migration  rg

Outline MotivationMotivation Transmission Migration TheoryTransmission Migration Theory ResultsResults –Synthetic –Gulf of Mexico VSP ConclusionsConclusions

Depth (m) Offset (m) ds = 1 m dg = 1 m Vertical Boundary RVSP Model V = 5500 m/s P V = 5000 m/s P V = 3333 m/s S V = 3666 m/s S Source = 1500 Hz

Synthetic RVSP Data 0 One-way Traveltime (ms) Offset (m) 1000

Synthetic RVSP Data 0 One-way Traveltime (ms) Offset (m) 1000 Direct P PS Direct S SP PS PP SP

Depth (m) Offset (m) PP Reflection Migration P PP

PP Reflection Kirchhoff Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

PP Kirchhoff Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

PP Reflection Wavepath Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

PP Wavepath Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

Depth (m) Offset (m) PS Transmission Migration PS P

PS Transmission Kirchhoff Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

PS Kirchhoff Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

PS Transmission Wavepath Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

PS Wavepath Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

Depth (m) Offset (m) SP Transmission Migration S SP

SP Transmission Kirchhoff Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

SP Kirchhoff Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

SP Transmission Wavepath Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

SP Wavepath Migration: 90% Velocity Depth (m) Offset (m) Reduced-TimeConventional Depth (m) Offset (m)

SP Transmission Kirchhoff Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

SP Transmission Kirchhoff Migration Depth (m) Offset (m) True Velocity Single Gather Depth (m) Offset (m)

SP Transmission Kirchhoff Migration Depth (m) Offset (m) % Velocity Depth (m) Offset (m) Single Gather

True Velocity Depth (m) Offset (m) SP Transmission Kirchhoff Migration 90% Velocity Depth (m) Offset (m)

SP Transmission Wavepath Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) KM Single Gather True Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Ray Tracing True Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Fresnel Zone True Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Wavepath Image True Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) True Velocity 90% Velocity Depth (m) Offset (m)

SP Transmission Wavepath Migration Depth (m) Offset (m) % Velocity Depth (m) Offset (m) KM Single Gather

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Ray Tracing 90% Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Fresnel Zone 90% Velocity

SP Transmission Wavepath Migration Depth (m) Offset (m) Depth (m) Offset (m) Wavepath Image 90% Velocity

Outline MotivationMotivation Transmission Migration TheoryTransmission Migration Theory ResultsResults –Synthetic –Gulf of Mexico VSP ConclusionsConclusions

Acquisition Geometry Depth (kft) Offset (kft) SALT Depth (kft) Offset (kft) SALT

P-Wave Velocity Depth (kft) Offset (kft) Velocity (kft/s) 5 15 Depth (kft)

S-Wave Velocity Depth (kft) Offset (kft) Velocity (kft/s) 5 15 Depth (kft)

Offset 500 ft Z-Component Depth (ft) One-way Traveltime (s) SALT Direct P Reflected P

500 ft Offset: PP Reflections Depth (ft) One-way Traveltime (s) SALT

500 ft Depth (ft) ft Synthetic SALTSALT PP Reflection Migration Receivers Receivers

Offset 500 ft X-Component Depth (ft) One-way Traveltime (s) SALT Reflected PS Direct P

500 ft Offset: PS Reflections Depth (ft) One-way Traveltime (s) SALT

500 ft Depth (ft) ft Synthetic 8000 PS Reflection Migration Receivers Receivers SALTSALT

Offset 500 ft X-Component Depth (ft) One-way Traveltime (s) SALT Direct P Transmitted PS

500 ft Offset: PS Transmissions Depth (ft) One-way Traveltime (s) SALT

500 ft Depth (ft) ft Synthetic 8000 PS Transmission Migration Receivers Receivers SALTSALT

Outline MotivationMotivation Transmission Migration TheoryTransmission Migration Theory ResultsResults –Synthetic –Gulf of Mexico VSP ConclusionsConclusions

Conclusions Reduced-time is shown to reduce migration errors in PP reflection images.Reduced-time is shown to reduce migration errors in PP reflection images. The top and bottom of the salt tablet were successfully imaged using the three VSP gathers.The top and bottom of the salt tablet were successfully imaged using the three VSP gathers. PS transmission migration sucessfully imaged a tranmitting boundary above the receiver array.PS transmission migration sucessfully imaged a tranmitting boundary above the receiver array.

Implications Can vertical salt boundaries be imaged using PS transmissions.Can vertical salt boundaries be imaged using PS transmissions. VSP transmission migraion an alternative to single well imaging ?VSP transmission migraion an alternative to single well imaging ? Greater illumination using combined PP reflection and PS transmissionsGreater illumination using combined PP reflection and PS transmissions = Cheaper VSP. = Cheaper VSP.