Petrophysical Analysis of Seismic Energy Attenuation In Reservoir Rocks
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Date
2015
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Faculty of pure and applied Science, Ladoke Akintola University of Science and Technology, LAUTECH, Ogbomosho
Abstract
The phenomenon controlling the mechanism of intrinsic seismic attenuation, 𝑄!"#
!! in waves travelling in earth media is still poorly understood. To give insight to the mechanism – it’s cause and effect, this paper used wave induced fluid flow in partially saturated porous rock as the candidate mechanism responsible for intrinsic attenuation (or absorption) in waves propagating in earth media. Using a hydrocarbon reservoir model containing fully water saturated patches surrounded by partially gas–saturated matrix, changes in
compressional rock modulus is estimated at high and low frequency bands as a function of saturation at known irreducible water saturation. The study shows that (i) intrinsic attenuation is saturation dependent, (ii) fluid heterogeneity is a necessary condition for intrinsic attenuation, and (iii) intrinsic attenuation estimated at 0.4 irreducible water saturation (0.6 gas saturation) is higher than the intrinsic attenuation at 0.8 irreducible water saturation (0.2 gas saturation). Numerical wave simulations show that the rock-physics-based estimated attenuation is capable of causing amplitude reduction, waveform distortion, and prolonged travel time in seismic waves traveling from a source to the receiver. Overall, the study links rock physics explanations for seismic attenuation to the waveform distortion and energy depletion commonly observed in exploration scale seismic data. The learning from this study provides insights into seismic amplitude anomaly commonly observed in seismic images of fluid-saturated units.
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Keywords
Energy attenuation, Anelasticity, Partially satuted reservoir, forward modelling, Amplitude anomally
Citation
Petrophysical Analysis of Seismic Energy Attenuation In Reservoir Rocks. Science Focus Vol. 20 (2), 2015 pp. 12 – 19.