Lukman arief water column effect
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Sea water parameters, i.e. salinity, temperature and tidal are always vary in value. Variations in the water column can be divided into two categories. Firstly, tides, weather, and currents can affect the elevation of the sea surface. Secondly, changes in salinity and water temperature can induce variation in water velocity. Variations in the water column at a three-dimensional survey can induce time shift, resulting in a lateral discontinuity in crossline section. This final project is to discuss how far the changes in salinity and temperature, changes in tidal height and change of both in simultaneously (the effect of water column) can affect the continuity of crossline reflection on a acquisition survey. This study is started from the discovery of high temperature and salinity values of a sea water to determine water velocity. For the modeling, seismic velocity and tidal values are simulated randomly to simulate a sailline. From the result it can be concluded that for the marine acquisition with a depth of 1000 m, tides up to 12 meters can cause timeshift by 12 ms. Sea water velocity that varies from 1493 m/s up to 1503 m/s can cause up to 12 ms time shift, while 2 meters in tidal difference and 3 m/s in velocity variation can be ignored. Effects of water column consisting of water velocity variations and tidal variations can cause up to 25 ms time shift. If not corrected, this large time shift would cause lateral discontinuities in crossline section.
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Lukman arief water column effect
- 1. Lukman Arief Bandung Institute of Technology Water Column effect on Seismic Data
- 2. Bandung Institute of Technology Change of Sea water temperature and the effect on seismic velocity Water Column effect on Seismic Data
- 3. > Why? • Lots of marine survey nowadays, • Sea water property is complex and fluctuated. • Marine survey takes time. Water Column Effect on Seismic Data Processing
- 4. > Sea Temperature: Where & When the temperature is extreme? Water Column Effect on Seismic Data Processing Spatial: Temporal: > January - March > April - June > October - December
- 5. Water Column Effect on Seismic Data Processing Mackenzie Equation : c(D,S,T) = 1448.96 + 4.591T - 5.304 x 10-2T2 + 2.374 x 10-4T3 + 1.340 (S-35) + 1.630 x 10-2D + 1.675 x 10-7D2 - 1.025 x 10-2T(S - 35) - 7.139 x 10-13TD3 T = Temperature S = Salinity D =Depth Validity range: • Temperature : 2° - 30°C • Salinity : 25 - 45 ‰ • Depth :0 - 8000 m > How to get: seismic velocity of the sea water
- 6. > The result: seismic velocity of the sea water: 1480 m/s to 1540 m/s Water Column Effect on Seismic Data Processing
- 7. > Day Variation: Sea Water Seismic Velocity Variation per Day sailline kecepatan (m/s) B-1 1493 B-2 1495 B-3 1497 B-4 1500 B-5 1503 B-6 1500 B-7 1497 B-8 1495 B-9 1493 B-10 1495 B-11 1497 B-12 1500 B-13 1503 B-14 1500 B-15 1497 sailline kecepatan (m/s) B-16 1495 B-17 1493 B-18 1495 B-19 1497 B-20 1500 B-21 1503 B-22 1500 B-23 1497 B-24 1495 B-25 1493 B-26 1495 B-27 1497 B-28 1500 B-29 1503 B-30 1500 Avg. Velocity var iation per day : 1493 m/s – 1503 m/s speed time
- 8. > Principles: Acquisition Water Column Effect on Seismic Data Processinghttp://www.walkermarinegeo.com
- 9. > Principles : Processing seismic data Water Column Effect on Seismic Data Processing Adding the wiggles: Stacking = summing every trace to a one reflection point
- 10. Fine, that just a single line. What about coverage an area like this? Subsea World News Staff , November 22, 2011; Image: Octanex
- 11. > 3D seismic acquisition: Coverage an area Water Column Effect on Seismic Data Processing Inline Sailline 5 Sailline 2 Sailline 3 Sailline 4 Sailline 1 Sailline 6 Sailine … Sailline 30 Crossline
- 12. If the temperature of the sea water is changing, What the effect to the seismic data?
- 13. > Modelling: Create a crossline section Water Column Effect on Seismic Data Processing Sailline Sailline 5 Sailline 2 Sailline 3 Sailline 4 Sailline 1 Sailline 6 Sailine … Sailline 30 Crossline
- 14. > Modelling: Generate a reflection Water Column Effect on Seismic Data Processing
- 15. Water Column Effect on Seismic Data Processing > Modelling: Generate a reflection
- 16. > Data Processing: Generate seismic reflection Water Column Effect on Seismic Data Processing CDP gather response
- 17. > Data Processing : Normal Move Out Water Column Effect on Seismic Data Processing NMO gather
- 18. > Data Processing: Stacking to create a reflection Water Column Effect on Seismic Data Processing
- 19. > Modelling: Create a crossline section Water Column Effect on Seismic Data Processing Sailline Sailline 5 Sailline 2 Sailline 3 Sailline 4 Sailline 1 Sailline 6 Sailine … Sailline 30 Crossline
- 20. > Seismic Section: Crossline with sea water seimic velocity variation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
- 21. > Seismic Section: Crossline with sea water seimic velocity variation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
- 22. > Graph: Crossline with sea water seimic velocity variation 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1325 1330 1335 1340 1345 1350 1355 0 5 10 15 20 25 30 TWT(ms) Penampang Crossline efek kecepatan ideal 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1497 1495 1493 m/s 1495 1497 1500 1503 m/s 1500 1325 1330 1335 1340 1345 1350 1355 0 5 10 15 20 25 30 TWT(ms) Crossline efek kecepatan ideal Velocity variation
- 23. > Seismic Section: Crossline with sea water seimic velocity variation + tidal 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
- 24. > Velocity Variation: Water Colum: Tidal included Water Column Variation : Variation of sea water velocity. + Variation of Tidal (Lacombe et al, 2009) Tidal Velocity Variation sailline tidal (m) kecepatan (m/s) 1 0 1493 2 12 1495 3 0 1497 4 12 1500 5 0 1503 6 2 1500 7 10 1497 8 2 1495 9 10 1493 10 2 1495 11 4 1497 12 8 1500 13 4 1503 ….. … …. 30 10 1500
- 25. > Graph: Crossline with sea water seimic velocity variation + tidal Water Column Effect on Seismic Data Processing 1325 1330 1335 1340 1345 1350 1355 0 5 10 15 20 25 30 TWT(ms) Penampang Crossline efek pasut efek kecepatan efek kombinasi ideal Tidal velocity change both 1325 1330 1335 1340 1345 1350 1355 0 5 10 15 20 25 30 TWT(ms) Crossline efek pasut efek kecepatan efek kombinasi ideal
- 26. > Graph: Crossline with water velocity variation + tidal Water Column Effect on Seismic Data Processing 1325 1330 1335 1340 1345 1350 1355 0 5 10 15 20 25 30 TWT(ms) Penampang Crossline efek pasut efek kecepatan efek kombinasi ideal
- 27. Just 25 milisecond shifting? From a 6 second seismic image? Its it worthed?
- 28. If velocity of this layer = 4000 m/s then 25 milisecond is 100 meter
- 30. > Reference Ablitt, Justin. Technical Guides - Speed of Sound in Sea-Water. (Online) (http://resource.npl.co.uk/acoustics/techguides/soundseawater/, diakses 18 Juli 2010). Anonim. Tides and Storm Surge. (Online) (http://arekteknik.com/tides-and-storm-surge.html, diakses 24 Juni 2011). Bacon, M., Simm, R. & Redshaw, T. 2003. 3-D Seismic Interpretation. England Geological Magazine.2004; 141: 245-246. Hadi,Safwan., 2002, Oseanografi Fisis. Penerbit ITB, Bandung. Lacombe, C., Butt, S., Mackenzie, G., Schons, M., & Bornard, R. 2009. Correcting for water-column variations. The Leading Edge 28, 198. Mohite-Patil, T.B., Saran, A.K., Sawant, S.R., Chile, R.H. & Mohite-Patil, T.T. 2010 Simulation Study of Acoustic Wave Propagation in Ocean. International Journal of Computer Applications 12(8):40–44. Foundation of Computer Science. Schlitzer, Reiner., 2010. Ocean Data View 4, http://odv.awi.de. Stewart, Richard. 2008, Introduction To Physical Oseanography, Department of Oseanography, Texas A & M University.
- 32. > Perbandingan Persamaan Mohite-Patil et.al (2010)
- 33. > Perbandingan Validitas dengan Data
- 34. >>> Ekstraksi Data (5500 m)
- 35. >>> Ekstraksi Data (1000 m)
- 36. >>> Ekstraksi Data (3000 m)
Editor's Notes
- If we want to know how big the effect of sea water temperature to the seismic data,Then we have to take an extreme case. We want to know where and when the temperature is high
- Persamaanempirikdigunakanuntukmenghitungkecepatansuaradalam air laut
- Dengan rumus mackenzie
- This is the average velocity variation per day.Because of thesun,temperature in sea surface can differ up to 6 degrees celsiuxSamahalnyadenganvariasipasangsurut, kecepatan air lautjugabervariasiterhadapwaktu. Variasi yang akanditekankandisiniadalahvariasiharianakibattemperatur. Akibatpaparansinarmatahari, temperaturdipermukaan air lautdapatberbeda 6 derajatCelcius. Dalamsimulasiininilaikecepatan air lautdivariasikanantara 1493 m/s hingga 1503 m/s.
- Now we talk about seismic acquisition
- If we want to covarage an area, the acquisition ship must be make a single line survey, an turn back to make another line.So that make an area.
- This is the simplemovement of the shipAs you see, after make sailine number 1, the ship must turn back to make sailine number 2.and so on.
- So back to the problem,If the temperature of the sea water is changing,What the effect to the seismic data?
- To know this, we must simulate a seismic survey, just to get a single crossline image to know the lateral change of seismic data
- Imagine a single line acquisition Iniadalahcontoh model yang dibuatmemakai software GX-2Untukmembuatsuatupenampangcrossline, makauntuksetiapkasusvariasidibuat 30 model yang posisinya parallel satusama lain sehinggasetiap model merepresentasikamsatusailinedenganmenggunakan software GX-II. Setiap model sailinedibuatdenganpanjanglintasan 2400 meter, dengan first trace offest 100m offset increment 12,5 m danjumlah geophone 192 (akibatkomputasihanya 185 yang terekamoleh GX-II)Klik video:Untukpenyederhanaankarenahanyasatu CDP yang digunakanpadasailinemakadigunaankonfigurasipenembakankesatutitiksehinggasetiap model menghasilkansatu shot CDP gather untukkemudiandi NMO dengankecepatan yang berbeda-bedatiapmodelnyasertadi stack
- Imagine a single line acquisition Iniadalahcontoh model yang dibuatmemakai software GX-2Untukmembuatsuatupenampangcrossline, makauntuksetiapkasusvariasidibuat 30 model yang posisinya parallel satusama lain sehinggasetiap model merepresentasikamsatusailinedenganmenggunakan software GX-II. Setiap model sailinedibuatdenganpanjanglintasan 2400 meter, dengan first trace offest 100m offset increment 12,5 m danjumlah geophone 192 (akibatkomputasihanya 185 yang terekamoleh GX-II)Klik video:Untukpenyederhanaankarenahanyasatu CDP yang digunakanpadasailinemakadigunaankonfigurasipenembakankesatutitiksehinggasetiap model menghasilkansatu shot CDP gather untukkemudiandi NMO dengankecepatan yang berbeda-bedatiapmodelnyasertadi stack
- This is result of the shot response in CDP gather
- Ini adalah contoh NMO gather dari gambar di atas
- Setelah di NMO Lalu kemudian setelah di stack sehingga akan menghasilkan satu trace CDP untuk setiap modelKlik gerak:Dan cdp-cdp tersebut digabungkan untuk mencitrakan satu penampang crossline
- To know this, we must simulate a seismic survey, just to get a single crossline image to know the lateral change of seismic data
- Ini adalah hasil crossline dengan variasi kolom air
- (Variasi temporal kecepatan air laut pada kasus ini dapat menyebabkan statik hingga 12 ms untuk kecepatan 1493 m/s - 1503 m/s dan menyebabkan timeshift sebesar 4 ms untuk setiap 3 m/s perubahan kecepatan. Pada Gambar 4.2 tidak terlihat timeshift antara kecepatan 1495 m/s dan 1497 m/s sehingga dapat disimpulkan bahwa variasi dengan perbedaan kecepatan 2 m/s dapat diabaikan.)
- (Variasi temporal kecepatan air laut pada kasus ini dapat menyebabkan statik hingga 12 ms untuk kecepatan 1493 m/s - 1503 m/s dan menyebabkan timeshift sebesar 4 ms untuk setiap 3 m/s perubahan kecepatan. Pada Gambar 4.2 tidak terlihat timeshift antara kecepatan 1495 m/s dan 1497 m/s sehingga dapat disimpulkan bahwa variasi dengan perbedaan kecepatan 2 m/s dapat diabaikan.)
- (Seperti yang diketahui bahwa varisi dari efek pasang surut dan efek temporal kecepatan bergerak dengan pola yang harmonis, tetapi gabungan kedua efek tersebut pada kolom air menghasilkan timeshift yang terlihat acak. Kombinasi variasi temporal kecepatan dan variasi pasang surut ini juga menyebabkan nilai timeshift kolom air menjadi lebih besar daripada timeshift maksimum yang dihasilkan oleh variasi temporal kecepatan ataupun variasi pasang surut. Minimum TWT nya adalah 1328 dan maksimum pada TWT 1353 sehingga mempunyai selisih timeshift hingga 25 ms yang bila tidak dikoreksi akan menyebabkan diskontinuitas lateral pada penampang crossline. Variasi kolom air dengan timeshift yang besar ini perlu dikoreksi agar reflektifitas crossline lebih kontinyu. )
- Untuksimulasi kali ini, nilaiVariasikolom air didapatdarikombinasivariasipasangsurutsertavariasi temporal kecepatan air laut. Untuksimulasiini, variasikolom air didapatdenganmenggabungkanvariasipasutdanvariasi temporal kecepatan air lautsebelumnyaseperti yang dijabarkanpadaTabelberikut:
- Necessary?Well, its depent.
- But if the seismic image is converted to depth.Let say the velocity of the rock 4000 m/s. so 25 milisecond is about 100 meter difference.So its up to you, is 100 meter difference is important? And you sure you wouldn’t miss anything?Remember, it’s a static correction. Which means,every object in the seismic image is shifting with the same amount