Experimental progress on elastic wave properties of sandstones and shales
Elastic wave properties of sandstones and shales are fundamental for interpretation seismic data in terms of physical properties of reservoirs and fluid distribution.The ultrasonic(105～106 Hz)pulse transmission technique has been widely used in velocity measurements of rock samples.Development of low-frequency rock physics technique allows us to study attenuation and dispersion of elastic waves in rocks.Here we summarized experimental techniques and laboratory-derived elastic wave properties of sandstones and shales at high and low frequency.Combining with elastic properties of minerals and theoretical models of rock physics,we analyzed the influence of pressure,temperature,modal composition,pore structure,fluid and frequency on velocity and attenuation of sandstones and shales.Due to the gradual closure of pores and microcracks with the increasing pressure,P-and S-wave velocities of dry sandstones and shales increase nonlinearly with pressure at low pressure but linearly above the critical pressure.Velocities of dry sandstones and shales decrease slowly with temperature and show an ignorable dispersion effect.By contrast,attenuation and dispersion of fluid-bearing sandstones and shales are remarkable and affected by many factors including temperature,pressure,saturation degree,fluid viscosity,pore structure and frequency.Fluid-bearing sandstones and shales show higher Poisson's ratio and the inverse quality factor Q-1 than dry samples.At low pressure,velocity and porosity of sandstones have a negative correlation,whereas the controlling factors for velocity of shales are more complex.Shales are characterized by higher anisotropy in velocity,attenuation and dispersion than sandstones.An integrated study of multi-frequency rock physics measurements and digital rock physics will provide a reliable basis for technique innovation and data interpretation in exploration geophysics.
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维普
