Changes

}}

}}

==Definition==

==Definition==

Amplitude is deviation of wave from zero crossing. Maximum positive amplitude is referred to peak and Maximum negative amplitude is referred to trough. The value of amplitude is equal to the value of seismic trace at specific depth. While, Seismic trace is parameter of seismic wave that represents contrast of acoustics impedance on the boundary of bedding rock on a geophone <ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/ . </ref>. Figure 1 show part of the wave:  

Amplitude is deviation of wave from zero crossing. Maximum positive amplitude is referred to peak and Maximum negative amplitude is referred to trough. The value of amplitude is equal to the value of seismic trace at specific depth. While, Seismic trace is parameter of seismic wave that represents contrast of acoustics impedance on the boundary of bedding rock on a geophone.<ref name=Abdullah>Abdullah, A., 2007, [http://ensiklopediseismik.blogspot.com/ Ensiklopedi Seismik]</ref>. Figure 1 show part of the wave:  

[[File:Aapg.png|300px|thumbnail|center|Figure 1 The Component of Wave]]

[[File:Aapg.png|300px|thumbnail|center|Figure 1 The Component of Wave]]

==Determination polarity==

==Determination polarity==

Polarity of seismic data is important parameter that must be known to interpretation seismic data where it can be known with studying character of seismic trace. When marine seismic data, the polarity is identified by reflector of sea water and seabed. The reflector appears from low to high AI, if red is negative amplitude and reflector between sea water and seabed is red. So, polarity is SEG Normal <ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/ .</ref>

Polarity of seismic data is important parameter that must be known to interpretation seismic data where it can be known with studying character of seismic trace. When marine seismic data, the polarity is identified by reflector of sea water and seabed. The reflector appears from low to high AI, if red is negative amplitude and reflector between sea water and seabed is red. So, polarity is SEG Normal.<ref name=Abdullah />

[[File:Aapg 4.png|350px|thumbnail|center|Figure 4 Identification Polaity Offshore Seismic Data<ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/</ref>]]

[[File:Aapg 4.png|350px|thumbnail|center|Figure 4 Identification Polaity Offshore Seismic Data<ref name=Abdullah />]]

Different trick is used to identify polarity of onshore seismic data. If target is carbonate or regional geology target has coal lithology. Polarity prediction can assume that Carbonate has strong AI than other lithology. That mean if carbonate contact to other lithology will show very strong amplitude because the contrast IA.is high. Picture below shows. If top carbonate has strong amplitude with red color amplitude. The change polarity of other lithology to top carbonate commonly from low to high IA, if red reflector is negative amplitude so polarity of this data is SEG normal <ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/ .</ref>

Different trick is used to identify polarity of onshore seismic data. If target is carbonate or regional geology target has coal lithology. Polarity prediction can assume that Carbonate has strong AI than other lithology. That mean if carbonate contact to other lithology will show very strong amplitude because the contrast IA.is high. Picture below shows. If top carbonate has strong amplitude with red color amplitude. The change polarity of other lithology to top carbonate commonly from low to high IA, if red reflector is negative amplitude so polarity of this data is SEG normal <ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/ .</ref>

[[File:Aapg 5.png|300px|thumbnail|center|Figure 5 Identification Polarity Onshore Seismic Data<ref>Abdullah, A. (2007). Ensiklopedi Seismik:  http://ensiklopediseismik.blogspot.com/</ref>]]

[[File:Aapg 5.png|300px|thumbnail|center|Figure 5 Identification Polarity Onshore Seismic Data<ref name=Abdullah />]]

==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 A. Agus, 2001, Karakterisasi Reservoir Seismik. Bandung: Lab. Geofisika Reservoir ITB. </ref>. ). Tuning thickness equation is

:<math>\text{Tuning Thickness} = \frac{1}{4} \lambda</math>

:<math>\text{Tuning Thickness} = \frac{1}{4} \lambda</math>

::where λ = wavelength of wave

::where λ = wavelength of wave

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, M., R. Simm, and T. Redshaw, 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  

[[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 R. E. Sheriff, R.E. [http://archives.datapages.com/data/specpubs/seismic1/data/a165/a165/0001/0300/0301.htm Application of Amplitude, Frequency, and Other Attributes to Stratigraphic and Hydrocarbon Determination], in Seismic Stratigraphy- Applications to Hydrocarbon Exploration, [http://store.aapg.org/detail.aspx?id=1157 AAPG Memoir 26] </ref>]]

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.