Abstract
This research provides insight into the process of pore- fluid induced absorption which is important for absorption compensation and seismic image enhancement. The absorptive property of a medium is described by the rock inverse quality factor ( ), perturbational forward modeling is conducted by varying saturation and estimating the inverse quality factor using first principles of rock inelastic properties and modeling seismic absorption in rock with partial gas saturation as commonly encountered in hydrocarbon exploration. The response of a visco-elastic rock depends on the frequency of the propagating seismic energy. The difference between modulus estimated at high and low frequencies is translated to the coefficient of absorption (or inverse quality factor). Absorption estimated at 0.4 irreducible water saturation (0.6 gas saturation) is higher than 0.8 irreducible water saturation (0.2 gas saturation). The higher the gas saturation, the higher the absorption, and the poorer the seismic image. The signature of gas induced absorption in the selected earth model are the increase time –thickness in the reservoir interval, large contrast in the top and base amplitude, pulse broadening and wavelet distortion. In hydrocarbon reservoir evaluation, seismic absorption can be used to interpret for fluid units. Information about seismic absorption can also be used, by means of absorption compensation, to enhance seismic data resolution.KEYWORDS: Saturation, Absorption, Dispersion, Inverse Quality Factor, Anelastic
Highlights
This research provides insight into the process of pore- fluid induced absorption which is important for absorption compensation and seismic image enhancement
The apparent increased time thickness in the reservoir interval, pulse broadening and wavelet distortion in addition to amplitude attenuation are the signatures of gas in the selected absorption model (Raji and Riebrock, 2009)
For a particular pore fluid, the response of a visco-elastic rock to a propagating wave depends on the frequency of the wave, the difference between high and low frequency compressional moduli is translated to the inverse quality factor
Summary
If the frequency is high, loading will be high, the oscillatory pressure between the fully liquid -saturated patch and the surrounding rock will not attain equilibrium .The patch is “unrelaxed’’ (Dvorkin and Mavko, 2006). The elastic modulus of a partially saturated rock due to attenuation changes with frequency. The difference between high and low frequencies compressional moduli is translated into inverse quality factor using Standard Solid Linear Model of Dvorkin et al (2003). The compressional moduli of a partially saturated rock containing fully liquid saturated patches is estimated from the bulk moduli of a partially saturated rock ( )
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