Seismic Facies Analysis

Seismic facies analysis Seismic facies represent a group of seismic amplitude variations with characteristics that distinctly differ from those of other facies. A seismic facies is the manifestation of the underlying geologic facies or structural feature in the seismic amplitude data. These can be searched and identified from the seismic data by different approaches. These could be based on analysis of either the seismic waveforms or the seismic attributes. Seismic facies analysis consists of the parameters and reflection configuration studies, which determine a seismic sequence. The main idea behind the facies analysis is to interpret reflections with respect to lithology, stratification,

In seismic data, depth is normally measured in two-way travel time in milliseconds or seconds. This is the time the sound waves use from it leaves the source until it hits the reflector and returns to the receiver. With the increase in depth, the frequency of the signal will decrease while the velocity and wavelength will increase. This means that with an increase in depth the seismic resolution gets poorer. The high frequencies are reflected from shallow reflectors, while the low frequencies reach further down. The velocity of the sound increases with increasing depth as the sediments are gradually more compacted with increasing depth. The seismic resolution can be categorized in two types, such as vertical resolution and horizontal resolution. Both vertical and horizontal resolution depends on the signal bandwidth) Rafaelsen et al.,

Seismic waves that originate from a point source are spherical in nature, and when incident on a plane reflector, they sweep through it by producing a succession of contact zones. Nonetheless, the limited planar area, which ‘effectively’ comes into contact at the interface and collectively contributes to produce a coherent reflection, is called the first Fresnel zone (Figure 2.16).The quality of a reflection depends not only on the area defined by Fresnel zone but also on the type of the reflecting surface. The lateral changes in reflectivity of planar widths less than a Fresnel zone tend to deteriorate the reflection quality. Modeling has demonstrated that interfaces having width less than λ/4 cannot be viewed clearly and thus defines the limit for spatial resolution (Niranjan,