Rock physics investigation of seismic wave absorption in reservoir rocks

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