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Survey Planning & Illumination with NORSAR-3D. Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey.

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Presentation on theme: "Survey Planning & Illumination with NORSAR-3D. Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey."— Presentation transcript:

1 Survey Planning & Illumination with NORSAR-3D

2 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

3 Introduction Simple Slope Model A simple model was used to demonstrate the technique. The model contains a variable velocity field overlying a reflector with a cosine dip region in the center.

4 Introduction Aperture Study, All Azimuth Survey Shot Pattern Receiver boundary for indicated shot The survey used here is a “Wide Azimuth” survey. In the illustration, the closely spaced shot lines are shown, together with the receiver boundary square for the shot location marked with the cross. The receiver pattern moves as the shot location moves.

5 Introduction Aperture Study: Area of Interest Having ray traced the survey, the Hit Count attribute is plotted in the reflection point domain. This shows where the reflection points are and the density. The display shows the attribute after masking it to a 4km x 2km area of interest.

6 Introduction Aperture Study: Shots Contributing Down dip extension An alternative domain for display is the shot domain. This display shows the shots that contributed only to the area of interest on the target. Clearly, the survey needs to be extended in the down-dip direction.

7 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

8 Introduction Reflection Points, 0 deg Dip Streamers associated with left shot. Shots Outer Reflection points This diagram relates the reflection point positions to the streamer locations assuming a flat, horizontally layered Earth. The reflection points and shot locations for two shots on adjacent shot lines are shown, but only the streamers for the left shot are drawn for clarity. The reflection point positions for the outer streamers are identical to the CMP positions.

9 Introduction Reflection points, 10 deg dip south This diagram is equivalent to the previous diagram except that a 10° dip to the south has been included in the reflector. This asymmetry skews the reflection points away from the CMP points as depicted.

10 Introduction Hit Map, E to W Direction Hit map for E-W The central part of the map, the attribute is striped. This is caused by the dip of the reflector.

11 Introduction Hit Map, Alternating Directions This map was made using the same model and survey parameters as the previous map except that the sail line directions alternate. This alters the hit count pattern

12 Introduction SMA 20Hz, E to W Directions Would this appear in migrated seismic data? Plot the migration amplitude using SMA The stripes persist.

13 Introduction SMA 20Hz, Alternating Directions This shows the Simulated Migration Amplitude llumination for the survey shot in alternating directions.

14 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

15 Introduction Illumination in SEG Salt Model The SEG/EAGE salt model was used to illustrate this topic. The salt model consists of a salt body in a sedimentary velocity field. A plane, horizontal target has been added.

16 Introduction Hit Map, E-W Survey, 6km Streamer This is the hit count attribute plotted for an east-west survey using a 6km streamer array. Away from the salt, the reflection count is continuous. Underneath the salt, the reflection count varies because of the focusing effects of the salt. Under the southwest corner of the salt there is an illumination hole.

17 Introduction Hit Map, N-S Survey, 6km Streamer This is the hit count attribute plotted for a north-south survey using a 6km streamer array. Under the southwest corner of the salt, the illumination hole persists but the details are different. If one had a particular prospect location in mind, a choice might be made between the east-west and north- south surveys.

18 Introduction Hit Map, N-S Survey, 10km Streamer This is the hit count attribute plotted for a north-south survey using a 10km streamer array. There is very little difference between this map and the one made with the 6km streamer array. The 10km streamer is probably not worthwhile.

19 Introduction Maximum Offset, 10km Streamer For each image point, this attribute shows the maximum offset that contributed to that image point. It confirms that for most of the target, 7km streamers are enough. Only in a few places below the salt would a longer streamer contribute to the image.

20 Introduction Shooting from target In the previous SEG/EAGE salt model examples, non of the acquisition geometries filled the illumination hole. An efficient alternative analysis for these local trouble spots is the flower plot display. A shot is placed in the illumination hole at the target. One-way rays are propagated from the shot up to an array of receivers on the surface. Shot point placed in the shadow zone Dense set of receivers.

21 Introduction Shooting from target: Flower Plot Rays with equal departure inclination and opposite azimuth are paired and plotted The figure shows that the east-west and north-south azimuths would not produce any ray pairs. However, the northwest-southeast direction produces ray pairs at long offsets. Azimuth Offset Best acquisition direction

22 Introduction Hit map for the new survey Repeating the streamer survey using a northwest southeast sailing direction does indeed fill the illumination hole. Complete illumination N125

23 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

24 Introduction Max. CMP-CRP, 10km Streamer Again using the SEG/EAGE salt model, the CMP-CRP distance attribute is plotted in the reflection point domain. Away from the salt the CMP-CRP distance is effectively zero, indicating that small apertures are required for imaging reflections. However, significant apertures are needed under the salt.

25 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

26 Introduction Total Illumination Amplitude The illumination map here was made using the SEG/EAGE salt model and a streamer survey. All rays that reflected from the target were used, no matter what part of the model they had traveled through.

27 Introduction Illumination Amplitude, No Salt This illumination map was made in the same way as the previous one, except that any ray that had passed through the salt was rejected. It shows the image that requires only sedimentary ray paths, and can be called the “high confidence” image, because it is not subject to uncertainties in the salt model.

28 Introduction Overview This short presentation gives some applications of NORSAR-3D ray tracing. Survey aperture Fold and Amplitude, Planned v Modelled Survey offset and azimuth Migration aperture Effect of Overburden S.R.M.E. Aperture

29 Introduction Surface Bounce Points Bounce Surface Bounce Points Streamer Array The SRME method estimates the multiple by using the surface bounce. The 2D SRME method can be used when the surface bounce occurs within the streamer array. Ray tracing can be used to see if this is a valid assumption.

30 Introduction Salt Top Multiple If the surfaces generating the multiple are approximately horizontal, then the bounce points will occur within the streamer array. This extreme example illustrates ray paths for the top salt multiple from a single shot.

31 Introduction Salt Multiple, Surface Bounce Points The surface bounce points for the top salt multiple from the single shot are depicted in red. Clearly the bounce points are not contained within the streamer array, indicating that a 3D SRME technique would be necessary.

32 Introduction NORSAR-3D Work Flow Surfaces Properties

33 Introduction Model Components Generated internally Imported surfaces – Depth/time grids – GoCAD trimeshes – GoCAD model Imported properties – SEGY property field

34 Introduction NORSAR-3D Work Flow Surfaces Properties Build Model Survey Depth Model

35 Introduction Surveys Simple Surveys Internally – Marine streamer – Ocean Bottom Sensor Complex surveys import – P1/90 – SPS – ASCII (for VSP)

36 Introduction NORSAR-3D Work Flow Surfaces Properties Build Model Survey Depth Model Ray Code Ray Trace

37 Introduction 3D Wavefront Construction Salt Reflected wavefront returning to surface. Direct wavefront Shot point and streamer array.

38 Introduction 3D Wavefront Construction This shows the result of the ray traced shot represented as the more conventional ray diagram.

39 Introduction NORSAR-3D Work Flow Surfaces Properties Build Model Survey Depth Model Events Map Illumination Make Seismogram Export Attributes Ray Code Ray Trace Map Seismogram ASCII Table User Format Toolkit Processing

40 Introduction Summary A variety of import formats for NORSAR-3D models and surveys. Wavefront Construction is fast and robust Variety of survey analysis tools in NORSAR- 3D

41 Ask for a demonstration to see how NORSAR-3D can benefit your project …Insight through modelling


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