Cross-band rock physics measurement and theoretical modeling of carbonate rocks - Study on the effect of different pore structures on the dispersion and attenuation of carbonate rocks

Carbonate rocks often exhibit complex pore structure characteristics, and the different pore structure of rocks with fluid saturation have different impacts on dispersion and attenuation of the seismic wave, which provides a possibility to invert the pore structure of rocks, the type of the pore fluid, etc. from the response of the seismic wave. In this work, we carried out cross-band rock physics measurements (ultrasonic and low frequency) and theoretical modeling for dolomite, limestone, and artificial carbonate, to clarify the dominant mechanism of the pore structure and pore fluid properties of the carbonate rocks on the dispersion and attenuation of seismic waves. We first classified rock samples into three types (crack, crack-pore, and pore) according to pore structures from images of thin sections and scanning electron microscopy. Then, we measured modulus dispersion and attenuation of each type of sample with fully fluid-saturated condition under different confining pressures. At low confining pressure, when fully saturated with glycerol, only one attenuation peak occurs at the frequency around 1 Hz and 100 Hz for each sample of crack-type and pore-type, respectively, whereas two attenuation peaks are observed for crack-pore-type samples (i. e. , below 1 Hz and about 100 Hz). The magnitude of attenuation peak related to the crack-type sample (crack-dominating) exhibits larger under low confining pressure and is more pressure-sensitive than that of the pore-type sample (intermediate-pore-dominating). Based on the experimental data, the squirt flow model considering the compliant pore aspect ratio distribution and intermediate pores are built and compared with results, which can help to interpret the dispersion phenomenon corresponding to different pore types in the measurement frequency range to some degree. The above research deepens the understanding of the seismic response of carbonate reservoirs dominated by different pore types and is of significance for making a more comprehensive reservoir prediction.