Envelope
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Envelope attributes also show reflection to strong acoustic impedance contrast. It is measured from complex trace of seismic signal used to locate significance seismic features. for instance, lithology variation, faults and discontinuities. Gas and sand layer will give response to envelop attributes as bright spot in corresponding to acoustic impedance changes.
As said above, envelope attributes response to acoustic impedance. It produces a bright spot in the data after applying it. From Figure 2, the upper part has bright spots which indicates the presences of gas in study area. Moving on, the horizon 3 which shows sand lithology is known by the presence of bright spots in seismic data. At the bottom part of the data which is facies 3, there is no bright spots due to the absents of sand.