Slow Waves in Fractures Filled with Viscous Fluid

Stoneley guided waves in a fluid-filled fracture generally have larger amplitudes than other waves, and therefore, their properties need to be incorporated in more realistic models. In this study, a fracture is modeled as an infinite layer of viscous fluid bounded by two elastic half-spaces with identical parameters. For small fracture thickness, I obtain a simple dispersion equation for wave-propagation velocity. This velocity is much smaller than the velocity of a fluid wave in a Biot-type solution, in which fracture walls are assumed to be rigid. At seismic prospecting frequencies and realistic fracture thicknesses, the Stoneley guided wave has wavelengths on the order of several meters and an attenuation Q factor exceeding 10, which indicates the possibility of resonance excitation in fluid-bearing rocks. The velocity and attenuation of Stoneley guided waves are distinctly different at low frequencies for water and oil. The predominant role of fractures in fluid flow at field scales is supported by permeability data showing an increase of several orders of magnitude when compared to values obtained at laboratory scales. These data suggest that Stoneley guided waves should be taken into account in theories describing seismic wave propagation in fluid-saturated rocks

Acoustic Emission Precursors of M6.0 2004 Parkfield and M7.0 1989Loma Prieta Earthquakes

Two recent strike-slip earthquakes on the San Andreas Fault(SAF) in California, the M6.0 2004 Parkfield and M7.0 1989 Loma Prietaevents, revealed peaks in the acoustic emission (AE) activity in thesurrounding crust several months prior to the main events. Earthquakesdirectly within the SAF zone were intentionally excluded from theanalysis. The observed increase in AE is assumed to be a signature of theincreasing stress level in the surrounding crust, while the peak andsubsequent decrease in AE starting several months prior to the mainevents is attributed to damage-induced softening processes as discussedherein. Further, distinctive zones of low seismic activity surroundingthe epicentral regions in the pre-event time period are present for thetwo studied events. Both AE increases in the crust surrounding apotential future event and the development of a low-seismicity epicentralzone can be regarded as promising precursory information that could helpsignal the arrival of large earthquakes

Pressure diffusion waves in porous media

Summary Pressure diffusion wave in porous rocks are under consideration. The pressure diffusion mechanism can provide an explanation of the high attenuation of lowfrequency signals in fluid-saturated rocks. Both single and dual porosity models are considered. In either case, the attenuation coefficient is a function of the frequency

Advanced Reservoir Imaging Using Frequency-Dependent Seismic Attributes

Our report concerning advanced imaging and interpretation technology includes the development of theory, the implementation of laboratory experiments and the verification of results using field data. We investigated a reflectivity model for porous fluid-saturated reservoirs and demonstrated that the frequency-dependent component of the reflection coefficient is asymptotically proportional to the reservoir fluid mobility. We also analyzed seismic data using different azimuths and offsets over physical models of fractures filled with air and water. By comparing our physical model synthetics to numerical data we have identified several diagnostic indicators for quantifying the fractures. Finally, we developed reflectivity transforms for predicting pore fluid and lithology using rock-property statistics from 500 reservoirs in both the shelf and deep-water Gulf of Mexico. With these transforms and seismic AVO gathers across the prospect and its down-dip water-equivalent reservoir, fluid saturation can be estimated without a calibration well that ties the seismic. Our research provides the important additional mechanisms to recognize, delineate, and validate new hydrocarbon reserves and assist in the development of producing fields

Acoustic Emission Precursors of M6.0 2004 Parkfield and M7.0 1989 Loma Prieta Earthquakes

Two recent strike-slip earthquakes on the San Andreas Fault (SAF) in California, the M6.0 2004 Parkfield and M7.0 1989 Loma Prieta events, revealed peaks in the acoustic emission (AE) activity in the surrounding crust several months prior to the main events. Earthquakes directly within the SAF zone were intentionally excluded from the analysis. The observed increase in AE is assumed to be a signature of the increasing stress level in the surrounding crust, while the peak and subsequent decrease in AE starting several months prior to the main events is attributed to damage-induced softening processes as discussed herein. Further, distinctive zones of low seismic activity surrounding the epicentral regions in the pre-event time period are present for the two studied events. Both AE increases in the crust surrounding a potential future event and the development of a low-seismicity epicentral zone can be regarded as promising precursory information that could help signal the arrival of large earthquakes