--> Abstract: Low-Frequency Hydrocarbon Microtremors: Theory and Seismic Attributes, by Stefan Schmalholz, Erik Saenger, Yuri Podladchikov, and Robert Habiger; #90077 (2008)
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Low-Frequency Hydrocarbon Microtremors: Theory and Seismic Attributes

Stefan Schmalholz1*, Erik Saenger1, Yuri Podladchikov2, and Robert Habiger3
1ETH Zurich, Switzerland
2University of Oslo, Norway
3Spectraseis AG, Switzerland
*[email protected]

Narrow-band, low-frequency (1.0–6.0 Hertz) microtremor signals are observed worldwide over hydrocarbon reservoirs. These so-called hydrocarbon microtremors possess remarkably similar spectral and signal structure characteristics, pointing to a common source mechanism, even though the depth, fluid content (oil or gas) and reservoir type may be quite different. Two possible mechanisms generating hydrocarbon microtremors are acoustic resonance scattering and resonance amplification. Resonance scattering occurs on the macro-scale and the characteristic spectral anomalies in the surface particle velocities are generated due to multiple reflections and scattering of seismic background acoustic energy between the reservoir and the surface, and within the reservoir. Reflections and scattering are caused by complex impedance contrasts between a reservoir and the surrounding rock. Importantly, the effective impedance contrast can be enhanced or solely generated by abnormally high attenuation in the reservoir rocks caused by poroelastic effects. The second mechanism, resonance amplification, occurs on the micro-scale. Direct numerical simulations using Navier-Stokes equations and analytical solutions demonstrate that partially saturated pores exhibit a resonance frequency. This resonance mechanism can be approximated by a linear or nonlinear oscillator Previous HitmodelNext Hit. The spectra, spectral ratios, polarisation and time-variations of the measured surface particle velocities are considered for seismic attributes associated with hydrocarbon microtremors that may be identified and quantified. Understanding seismic attributes associated with different reservoir types enables Previous HitverificationTop for the theoretical explanations described above. Additionally, seismic attributes may provide typical reservoir-fingerprints for distinguishing different types of hydrocarbons. Reverse time modelling is applied to identify the origin of the microtremors.


AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain