Multicomponent Seismic Data API
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The document introduces multi-component seismic, which utilizes p-wave and s-wave data for better subsurface imaging, providing essential structural, lithological, and fluid information. It outlines the advantages and challenges of s-wave data acquisition and processing, highlighting the need for technological advancements in these areas. The summary emphasizes that while multi-component seismic adds value to exploration and reservoir development, further improvements in quality, cost, and interpretive understanding are needed.
Multicomponent Seismic Data API
- 1. Introduction to Multi- Component Seismic 1 Bablu Prasad Nonia Geophysicist (S)
- 2. Introduction Multi-component seismic refers to seismic data which utilise • P-wave data • S-wave data • Pure S-wave data • Mode converted S wave data 2
- 3. Why S-wave? 3 Goal of exploration is to get structural information lithological information fluid content P-wave seismic proved only partially successful. Two wave carry different information of subsurface. So it is advantageous to record both P and S wave dataMulti-component seismic offers a better solution: and where μ, ρ and k are respectively shear modulus, bulk modulus and density.
- 4. The Arriving of S-Wave Imaging Shear wave exploration did not gain popularity till late 90’s Non-availability of source to generate shear wave More number of channels required for multi-component acquisition (3 times) compared to P-wave acquisition P-wave was considered sufficient for imaging requirements, as the objective was mainly structural No clear economic benefit was seen initially Inadequate Processing knowledge of S-wave data 4
- 5. Acquisition 5 Source • Scalar source • Vector source
- 6. Acquisition Mode Conversion When Seismic wave impinges on an interface at an oblique angle, different types of waves are produced. 6
- 7. Advantage of Mode Conversion Shear source generates very strong noise Explosive used for P wave is buried so generates less surface waves Signal will travel in LVL only once, so less absorption Larger static correction for S wave source than P wave source. So chances of larger inaccuracy PP as well as PS data is acquired simultaneously Converted (P-S) Pure Shear (S-S) SOURCE Conventional Shear RECORD LENGTH Shorter Longer LVL Less Shallow Problem Larger Shallow Problem PROCESSING Special Conventional 7
- 8. Acquisition 3 FDU’s Triphone DSU 8 Sensor
- 9. Raw Shot Gather 9
- 10. LAYOUT 10
- 11. Survey Design Issues This bin size formula was suggested as a way to smoothen the high frequency variations fold due to the standard p-wave reflection point binning. (Lawton1993) Larger bins reduce lateral resolution and prevent a direct match between PP and PS data. CCP CMP Binning 50 meter CMP = 33.3 meter C11CP for Vp/Vs=2, Vs/Vp=0.5
- 12. Survey Design Issues 12 Offset • Shorter offsets in converted-wave cover the same subsurface area as P- Wave recording • Far offsets are constrained by P-Wave • Near offsets are constrained by converted wave NOTE: P-wave criteria for far offsets and converted wave criteria for near offsets are used
- 13. Major Issues in Processing of P-S Data CCP binning (mid point binning not valid) 13 Polarity issues Need for rotation of recorded components Difficulty in receiver statics estimation Problem associated with estimation of Vs
- 14. CCP Binning Sin φ1/α =Sin ψ1/β Ray path of incident P wave reflected wave is asymmetrical 14
- 15. CCP Binning Conversion Point does not fall at mid point 15
- 16. CCP Binning P-S ray path geometry for multi layer case 16
- 17. CCP Binning CCP binning is implemented over multiple layer, user defined windows 17
- 18. ACP Binning ∞ 18 In the limit z
- 19. Polarity Issues Polarity of back spread and advance spread will not be same 19
- 20. Polarity Issues advance spread back spread Z component 20
- 21. Component Rotation Y X Source Receiver 21
- 22. Component Rotation Source Y T R Receiver X θ Acquisition co-ordinates R-T co-ordinates 22
- 23. Component Rotation Radial response, r, is the horizontal ground motion in the source-reviver plane 23 r= x cosθ + y sinθ Transverse response, t, is the horizontal ground motion perpendicular to the source-reviver plane t= - x sinθ + y cosθ
- 24. Statics for Converted Wave Data Base of low velocity layer is not same for P and S waves 24
- 25. Statics for Converted Wave Data Shot statics same as P-P shot statics Receiver statics scaled from P-P receiver statics S-wave statics is far greater than P-wave’s 25
- 26. Vp/Vs Estimation No established method of estimating Vs, directly from converted wave data Vp/Vs has more geological significance in comparison to Vs alone There types of approach to estimate gamma • from SP gathers • processing baseed • interpretation based 26
- 27. Vp/Vs Estimation Initial Gamma (from SP gathers) Pick prominent reflector on PP gather and identify the same on PS gather Tpp=Tp+Tp Tps=Tp+Ts Vp/Vs=Ts/Tp 27
- 28. Importants Fracture density and orientation Shear wave polarised parallel to fractures( maximum stress) is FAST Shear wave polarises perpendicular to fracture (minimum stress) is SLOW 28
- 29. Birefringence 29
- 30. Gas Seepages 30 Lomond gas field
- 31. Lithology Discrimination 31 Alba Field - North Sea
- 32. Summary Multicomponent technology is not limited to benefiting reservoir development; additional exploration issues that can gain from multi-component seismic surveys include multiple attenuation and structural imaging Many advancements in field, processing, and interpretation methods A number of success stories for example lithology discrimination, DHI and fracture imaging However, there is still room for improvement in acquisition and processing quality, cost reduction, interpretive understanding application 32
- 33. Thank You 33