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Line 16: − <math> Trace Seismic = \text{Wavelet}^* {Reflection Coefficient}</math>+ + + − <math> RC = \frac{\text{IA2-IA1}}{\text{IA2+IA1}}</math> − − <math> IA = \text{Density} \times {Velocity}</math> Line 38:
Line 37: + + − ''Tuning Thickness = ¼ λ − λ = wavelength of wave − '' + + − + + − <references/>+
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==Seismic Trace==
==Seismic Trace==
Seismic trace is resulted by convolution of wavelet and reflection coefficient. Wavelet is wave that represents a seismic reflector that recorded by a geophone where every source has different character of wavelet. While, Reflection coefficient (RC) is parameter that represents geological model in the subsurface. The value of RC depend on contrast of impedance acoustic (IA) where contrast of IA is proportional to RC, RC is proportional to Seismic trace and Seismic trace at specific depth is equal with amplitude. Mathematically relation all parameters are expressed by equation below:
Seismic trace is resulted by convolution of wavelet and reflection coefficient. Wavelet is wave that represents a seismic reflector that recorded by a geophone where every source has different character of wavelet. While, Reflection coefficient (RC) is parameter that represents geological model in the subsurface. The value of RC depend on contrast of impedance acoustic (IA) where contrast of IA is proportional to RC, RC is proportional to Seismic trace and Seismic trace at specific depth is equal with amplitude. Mathematically relation all parameters are expressed by equation below:
:<math>\text{Trace Seismic} = \text{Wavelet} \times \text{Reflection Coefficient}</math>
: <math>\text{RC} = \frac{\text{IA}_2 - \text{IA}_1}{\text{IA}_2 + \text{IA}_1}</math>
: <math>\text{IA} = \text{Density} \times \text{Velocity}</math>
Seismic trace has some important parameters to data interpretation that is polarity and phase. There is 2 kind of wavelet phase which is used at seismic that is zero phase wavelet and minimum phase wavelet. Commonly zero phase wavelet is used to interpretation seismic data because the wavelet has highest S/N than other, maximum amplitude coincides with spike of reflection, and the pattern of wavelet is symmetry so picking horizon become easy.<ref>Sukmono , S. and Agus, A. (2001). Karakterisasi Reservoir Seismik. Bandung: Lab. Geofisika Reservoir ITB</ref>
Seismic trace has some important parameters to data interpretation that is polarity and phase. There is 2 kind of wavelet phase which is used at seismic that is zero phase wavelet and minimum phase wavelet. Commonly zero phase wavelet is used to interpretation seismic data because the wavelet has highest S/N than other, maximum amplitude coincides with spike of reflection, and the pattern of wavelet is symmetry so picking horizon become easy.<ref>Sukmono , S. and Agus, A. (2001). Karakterisasi Reservoir Seismik. Bandung: Lab. Geofisika Reservoir ITB</ref>
==Tuning Effect==
==Tuning Effect==
In many cases the amplitude of the seismic waves cannot represent the subsurface conditions. This is due to the vertical resolution of the seismic data. The vertical resolution is referred tuning thickness that is distance of 2 pieces in a vertical objects which can be distinguished by seismic waves. At this thickness, seismic amplitude is the amplitude of the interference from many amplitude so that some subsurface geological uniqueness is lost. Tuning effects caused reservoir thickness can be at peak or trough depends on the interference that occurs <ref>Sukmono , S. and Agus, A. (2001). Karakterisasi Reservoir Seismik. Bandung: Lab. Geofisika Reservoir ITB. </ref>. ). Tuning thickness equation is
In many cases the amplitude of the seismic waves cannot represent the subsurface conditions. This is due to the vertical resolution of the seismic data. The vertical resolution is referred tuning thickness that is distance of 2 pieces in a vertical objects which can be distinguished by seismic waves. At this thickness, seismic amplitude is the amplitude of the interference from many amplitude so that some subsurface geological uniqueness is lost. Tuning effects caused reservoir thickness can be at peak or trough depends on the interference that occurs <ref>Sukmono , S. and Agus, A. (2001). Karakterisasi Reservoir Seismik. Bandung: Lab. Geofisika Reservoir ITB. </ref>. ). Tuning thickness equation is
:<math>\text{Tuning Thickness} = \frac{1}{4} \lambda</math>
::where λ = wavelength of wave
[[File:Aapg 6.png|300px|thumbnail|center|figure 6 Interference under tuning thickness<ref>Posamentier, H. 2010. Patch Reefs in Seismic: http://seismicatlas.org/</ref>]]
[[File:Aapg 6.png|300px|thumbnail|center|figure 6 Interference under tuning thickness<ref>Posamentier, H. 2010. Patch Reefs in Seismic: http://seismicatlas.org/</ref>]]
==Factors That Influences Amplitude==
==Factors That Influences Amplitude==
Factors that influences velocity of wave are porosity, density, temperature, grain size, gas saturation, frequency, external pressure, pore pressure and stress. The curve between P wave velocity and various parameters are shown in the figure below. The most influential factor on the P wave velocity changes include porosity, gas saturation, external pressure and pore pressure. The relationship between gas saturation and P wave velocity drops drastically resulting in the formation of anomalies such as DHI, AVO, and others.
Factors that influences velocity of wave are porosity, density, temperature, grain size, gas saturation, frequency, external pressure, pore pressure and stress. The curve between P wave velocity and various parameters are shown in the figure below. The most influential factor on the P wave velocity changes include porosity, gas saturation, external pressure and pore pressure. The relationship between gas saturation and P wave velocity drops drastically resulting in the formation of anomalies such as DHI, AVO, and others.
[[File:Aapg 7.png|300px|thumbnail|center|Figure 7 Some Parameter That Influence to P Wave Velocity<ref>Hilterman, F.J., (2001). Seismic amplitude interpretation: short course notes. Distinguished Instructor Series no. 4. Society of Exploration Geophysicists, Tulsa, Oklahoma</ref>]]
[[File:Aapg 7.png|300px|thumbnail|center|Figure 7 Some Parameter That Influence to P Wave Velocity<ref>Hilterman, F.J., (2001). Seismic amplitude interpretation: short course notes. Distinguished Instructor Series no. 4. Society of Exploration Geophysicists, Tulsa, Oklahoma</ref>]]
==Application==
==Application==
DHI is a seismic amplitude anomalies. DHI will appear when a seismic data has a high IA. There are three kind of DHI that is bright spot, polarity reversal and dim spot as shown in the figure below. Besides the three effects below are also indicated fluid contact with the flat spot zone as a result of contact fluid on seismic data.
DHI is a seismic amplitude anomalies. DHI will appear when a seismic data has a high IA. There are three kind of DHI that is bright spot, polarity reversal and dim spot as shown in the figure below. Besides the three effects below are also indicated fluid contact with the flat spot zone as a result of contact fluid on seismic data.
[[File:Aapg 8.png|400px|thumbnail|center|Figure 8 Kind of DHI.<ref>Bacon et.all. (2003). 3D Seismic Interpretation, Cambridge University Press. P.126</ref>]]
[[File:Aapg 8.png|400px|thumbnail|center|Figure 8 Kind of DHI.<ref>Bacon et.all. (2003). 3D Seismic Interpretation, Cambridge University Press. P.126</ref>]]
Attributes amplitude such as AVO, strong reflection, the variance is one example of an advanced interpretation used to perform reservoir characterization. The whole method is based on the basic concept of which the amplitude AVO study the amplitude variations of the offset to determine the distribution of fluid. Strong reflection calculate the square of the amplitude of real and imaginary in order to know the possibilities regions and variants studied reservoir uniformity of data where the data is not uniform can indicate patterns of fault.
Attributes amplitude such as AVO, strong reflection, the variance is one example of an advanced interpretation used to perform reservoir characterization. The whole method is based on the basic concept of which the amplitude AVO study the amplitude variations of the offset to determine the distribution of fluid. Strong reflection calculate the square of the amplitude of real and imaginary in order to know the possibilities regions and variants studied reservoir uniformity of data where the data is not uniform can indicate patterns of fault.
[[File:Aapg 10.png|400px|thumbnail|center|Figure 9. Attribute Reflection Strength. Show The Anomaly of Strong Amplitude that Indicating of Reservoir<ref>Taner, M. T and Sheriff, R.E. Application of Amplitude, Frequency, and Other Attributes to Stratigraphic and Hydrocarbon Determination. AAPG Memoir 26 Seismic Stratigraphy- Applications to Hydrocarbon Exploration</ref>]]
[[File:Aapg 10.png|400px|thumbnail|center|Figure 9. Attribute Reflection Strength. Show The Anomaly of Strong Amplitude that Indicating of Reservoir<ref>Taner, M. T and Sheriff, R.E. Application of Amplitude, Frequency, and Other Attributes to Stratigraphic and
Hydrocarbon Determination. AAPG Memoir 26 Seismic Stratigraphy- Applications to Hydrocarbon Exploration</ref>]]
Amplitude is a very important parameter to be observed. Studying deep about amplitude will provide much additional data that can be used when interpretation the seismic data. So let think big, start small.
Amplitude is a very important parameter to be observed. Studying deep about amplitude will provide much additional data that can be used when interpretation the seismic data. So let think big, start small.
==References==
==References==
{{reflist}}