Low-frequency seismic rock physics measurement system can directly determine elastic parameters of rocks at seismic frequencies. This is of great importance for understanding seismic wave propagation and for exploring for oil and gas. In this paper, low-frequency experiments and rock physics model analysis were carried out based on the improved low-frequency seismic rock physics measurement system. The original system was improved by optimizing the shaker gain function and selecting an efficient signal extraction algorithm, i.e. a phase-locked loop algorithm, the measurement frequency band was extended to 1-2000 Hz and the strain signal acquisition time was reduced. Then, calibration experiments of standard samples (aluminum and lucite)verified the reliability and accuracy of the improved system. Using the improved system, low frequency experiments were conducted on a tight sandstone under dry and fully oil-saturated conditions. Different elastic parameters for the fully oil-saturated tight sandstone exhibited obvious dispersion trends in the frequency range of 1~2000 Hz. The comparison between the measured results and the modelling results of the squirt flow based on pore microstructures shows that the squirt flow is the main reason for the dispersion of the fully oil-saturated sandstone and also shows the modelled shear wave velocities are consistent with the measured ones, while there is a discrepancy between the modelled P-wave velocities and the measured ones, and the dispersion of the measured P-wave velocities is more obvious and broader. The discrepancy may be attributed to the more complicated pore structures in real rocks. The improved low-frequency seismic rock physics measurement system provides a powerful tool for quantitatively investigating the elastic dispersion characteristics of fluid-saturated rocks and can establish a quantitative relationship between reservoir parameters and seismic responses, thus building an important foundation for the development of new techniques that predict the properties of reservoirs and pore fluid.
ZHAO Liming, TANG Genyang, WANG Shangxu, DONG Chunhui, HE Yanxiao, ZHAO Jianguo, SUN Chao, HAN Xu. Low-frequency seismic rock physics measurement system improvement and experiments on tight sandstone. Petroleum Science Bulletin, 2019, 02: 111-122.
