Seismic waves geometry
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Seismic waves can be reflected or refracted and are used to interpret subsurface geology. Reflection geometry uses the arrival times of waves to interpret subsurface features. For example, reflection along a horizontal reflector results in a hyperbolic travel time curve. Seismic source-well drilling (SSWD) uses reflected seismic waves to locate reservoirs before drilling and address problems like leaks during production by using relief wells. It provides advantages over wireline methods by enabling borehole seismic measurements while drilling.
![Reflection along horizontal
Reflector
• v = Average
Velocity
• v= x / t
• t = x / v
• x = ]4h2 + x2[1/2
• t =]4h2 + x2[ 1/2
/ vV2t2 = 4h2
+ x2](https://image.slidesharecdn.com/seismicwavesgeometry-171023035458/85/Seismic-waves-geometry-10-320.jpg)
![• A common mid-point (CMP)
• A common depth point (CDP)
• MOVEOUT (∆𝑡) : the variation of
travel time with offset
t =]4h2 + x2[ 1/2 / v
t0 = 2h/ v
As](https://image.slidesharecdn.com/seismicwavesgeometry-171023035458/85/Seismic-waves-geometry-13-320.jpg)
Seismic waves geometry
- 2. • Definition • Seismic waves Geometry • Reflection VS Refraction • Reflection Geometry • Actual Reflection • Reflection along horizontal Reflector • Application: SSWD Outlines
- 3. Seismic waves Geometry Relationship Between Points of Seismic Data and its Corresponding Definition and Geological and Geophysical interpretation
- 8. • Reflection Geometry Methods are based on the study of the Arrival times of waves Bear in mind: • You have a one layer ! • A one Reflector Characteristics ! • A one medium ! Reflection Geometry
- 10. Reflection along horizontal Reflector • v = Average Velocity • v= x / t • t = x / v • x = ]4h2 + x2[1/2 • t =]4h2 + x2[ 1/2 / vV2t2 = 4h2 + x2
- 11. 𝑉2 𝑡2 4ℎ2 - 𝑥2 4ℎ2 = 1 Reflection along horizontal Reflector • Thus, the travel time curve is a hyperbola 𝒚 𝟐 𝒂 𝟐 − 𝒙 𝟐 𝒃 𝟐 = 𝟏 • As hyperbola equation form is :
- 13. • A common mid-point (CMP) • A common depth point (CDP) • MOVEOUT (∆𝑡) : the variation of travel time with offset t =]4h2 + x2[ 1/2 / v t0 = 2h/ v As
- 14. Applicati on
- 16. • Safe exploration and operation is a great importance for the industry and society. • Seismic technology helps the companies to better understand the subsurface and to characterize where the hydrocarbon resources are located. • In Offshore drilling it’s a must to locate the position of drilling bit and wellbore during operations. Offshore Drilling SSWD
- 17. • Technique: Before Drilling: (To locate the Reservoir) - Seismic receivers are put on the seabed. -a wave are shot from a ship on the sea surface. - the waves penetrate the seabed and reflected to the geophones. -We can locate the reservoir from the reflected waves and know some subsurface formations which considered as obstacles like: SSWD Technique 1-Sand Layers 2- Rock Layers 3- Gas Pockets
- 18. • Knowing the position of these obstacles enables the drilling team to avoid them and reach safely to the target. SSWD Technique - Some problems may occur such as a leakage in the production line. - By using SSWD we can execute a relief well to reach the production line and pump a fluid then kill this production line. During Production
- 19. • Borehole Seismic measurements are extremely useful for correlating drilled depth with seismic depth, setting coring and casing points, avoiding drilling hazards, and identifying, over pressure zones. It is widely accepted that while these seismic surveys can be obtained while drilling, there are at least two main issues that need to be understood in order to make these seismic measurements accurately and reliably. The first issue relates to the fact that, as opposed to a wireline based measurement tool, the drilling operation may prevent direct coupling between the sensors and the formation. The coupling of the formation signal into the sensors depends on factors including the weight of the tool in combination with well deviation. Thus, in general, the quality of the coupling needs to be evaluated. In particular, the sensors which are tangential to the borehole, i.e., the nominal azimuthal and vertical sensors, need to be more thoroughly tested. It can be expected that the radial sensor may couple better than the other components for a large range of deviations. • The second issue for making accurate and reliable seismic measurement is accurate time keeping between the downhole and surface systems. Timing (a highly accurate clock) is far more complicated than the traditional wireline approaches which rely on direct cable communications to correlate the seismic source activation, and communicate it to the acquisition components. Instantaneous and direct means of communication are not currently available in the MWD environment. SSWD VS Wireline
- 20. Resources