Experimental Study Of Seismic Rock Physics Properties Of Tight Rocks At Multi-frequency Band

Due to the influence of diagenesis and post-diagenesis,tight sandstone and carbonate form a relatively complex pore structure.When the pores are filled with fluid,the elastic parameters such as compressional and shear wave velocities are affected by pore structure and pore fluid.In the theoretical study of the dispersion and attenuation mechanism,there are few experimental data at multi-frequency band,especially at the seismic frequency band.In this paper,the multi-frequency seismic rock physics experiments(from seismic frequency to ultrasonic frequency)were carried out for the selected tight sandstone and carbonate samples.Elastic properties were measured at seismic band according to the stress-strain method.And the velocities at ultrasonic frequency band were measured by pulse transmission technique.According to the thin section,Micro CT scan images of tight rock samples,the representative pore structure types of the experimental samples were classified.The effects of pressure,pore fluid mobility and pore structure on the velocity dispersion of experimental samples are summarized.The effective pressure will affect the compressional and shear wave velocity and dispersion amplitude of the experimental sample,but the characteristic frequency does not change with the effective pressure.With the fliuid viscosity increase,the characteristic frequency of the sample velocity dispersion will move toward the low frequency.As the permeability of the samples increase,its characteristic frequency will move toward the high frequency.When the aspect ratio of microcracks increase,the compressional and shear wave velocities at ultrasonic frequency band will increase too.And the characteristic frequency of the velocity dispersion will move toward the high frequency.When the samples mainly contains stiff pores,the amplitude of velocities dispersion will decrease,but the characteristic frequency will not change too much.Based on the strict poroelastic theory,we extend the traditional squirt-flow theoretical model by gradually adding soft pores into the rock matrix.The extended squirt-flow theory model is also used to calculate the correlation between the velocity and inverse quality factor of the sample with the pore structure.Also we compare the predition results of extended squirt-flow model with the experimental results.The extended squirt-flow model can semi-quantitatively explain the results of multi-frequency seismic rock physics measurements,which greatly improves the understanding of the dispersion response of tight rocks.