地质科技通报 (Mar 2023)
Experimental investigation of the influence of pressure and temperature on the acoustic velocity and spectral characteristics of carbonate rocks
Abstract
The acoustic wave propagation characteristics of carbonate rocks have important application value. The systematic analysis of the effects of fluid type, fluid pressure, temperature and confining pressure on acoustic wave velocity and spectrum characteristics of carbonate rocks still needs to be strengthened. Carbonate rocks with pores and fractures mined from the Dengying Formation in the Hechuan and Tongnan areas, Sichuan Basin, were selected to carry out acoustic transmission experiments under different conditions. The effects of confining pressure, pore pressure, pressure difference, temperature and fluid category on the acoustic velocity of carbonate rocks and the dominant frequency characteristics of transmitted acoustic waves were analyzed. The results show that the sensitivity of acoustic velocity to pressure change in saturated formation water is lower than that in saturated nitrogen. In the process of pressure change, the variation amplitude of acoustic velocity is positively correlated with the porosity of rock samples. Within the experimental temperature range, with increasing temperature, the P-wave velocity and S-wave velocity of the saturated formation water and nitrogen samples decreases lightly. When the differential stress is low, the acoustic velocity corresponding to the way of changing the differential stress by changing the pore pressure is greater than that by changing the confining pressure, and the conclusion is opposite when the differential stress is high. Under the same differential stress condition, the acoustic velocity is more sensitive to changes in the confining pressure than the changes of pore pressure. The included angle and slope difference of the two acoustic velocity-differential stress curves corresponding to constant confining pressure and constant pore pressure can qualitatively reflect the relative size of the dynamic Biot effective stress coefficient of carbonate rock samples. With increasing differential stress, the contribution of pore pressure to effective stress decreases gradually. With increasing pore pressure, the dominant frequency amplitudes of the P-wave and S-wave gradually decrease. With increasing confining pressure, the dominant frequency amplitudes of the P-wave and S-wave gradually increase. With increasing temperature, the dominant frequency amplitudes of the P-wave and S-wave gradually increase. The research results are helpful to the theoretical research and engineering application of pore pressure predictionin carbonate formation based on logging acoustic information.
Keywords
