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The diagram above shows the acoustic impedance relationship that results in a dim spot. In reflection seismology , a dim spot is a local low-amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons [ 1 ] and is therefore known as a direct hydrocarbon indicator .
The first attributes developed were related to the 1D complex seismic trace and included: envelope amplitude, instantaneous phase, instantaneous frequency, and apparent polarity. Acoustic impedance obtained from seismic inversion can also be considered an attribute and was among the first developed. [3]
r is the specific acoustic resistance in the time domain; g = r −1 is the specific acoustic conductance in the time domain (r −1 is the convolution inverse of r). [citation needed] Specific acoustic impedance, denoted z is the Laplace transform, or the Fourier transform, or the analytic representation of time domain specific acoustic ...
The diagram above shows the acoustic impedance relationship that results in a bright spot. In reflection seismology, a bright spot is a local high amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator. It is used by geophysicists in hydrocarbon exploration.
Diagram showing the acoustic relationship that results in a seismic polarity reversal. In reflection seismology , a polarity reversal or phase change is a local amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator .
Acoustic impedance is used to produce more accurate and detailed structural and stratigraphic interpretations than can be obtained from seismic (or seismic attribute) interpretation. In many geological environments acoustic impedance has a strong relationship to petrophysical properties such as porosity, lithology , and fluid saturation.
A flat spot can result from the increase in acoustic impedance when a gas-filled porous rock (with a lower acoustic impedance) overlies a liquid-filled porous rock (with a higher acoustic impedance). It may stand out on a seismic image because it is flat and will contrast with surrounding dipping reflections. [2]
The rayl is also used for the characteristic (acoustic) impedance of a medium, which is an inherent property of a medium: [6] = Here, is the characteristic impedance, and and are the density and speed of sound in the unperturbed medium (i.e. when there are no sound waves travelling in it).