| Based on the analysis of thin sections by microscope, measurement of porosity and density, and geological setting, we tested the rock physical parameters of sandstone, siltstone, carbonate and other transitional sedimentary rocks by the MTS system under formation conditions (temperatures, pressures and pore fluid properties). The rocks we tested are from Tertiary (including Zhujiang Formation, Zhuhai Formation, Enping Formation, Hanjiang Formation) of Zhujiangkou Basin in Southern China Sea. According to the analysis results, we studied the main ultrasonic wave velocity characters of rocks, which are compressive and shear wave velocity and Poisson's ratio under different formation conditions. By means of the results obtained, such as the quantificational relationships between the rock ultrasonic wave parameters and the important formation conditions like pressures, and the half-quantificational relationships between the rock ultrasonic wave parameters and porosity and density of those rocks, and the relationships between rock ultrasonic wave parameters and the composition of rocks, we established the corresponding relationships between the ultrasonic wave parameters and depth under the main formation conditions (indicating temperature and pressure gradient) in Tertiary of Zhujiangkou basin, which should be very useful for the geophysical exploration. By studying the above experiment, we can draw the following main conclusions.1) Under the conditions of confining pressure from 0 to 56 MPa and temperature from 25 to 170 C, the velocities of compressive wave of the samples we tested, saturated completely by air, are from 2140 m/s to 6045 m/s, with the average of 3741.5 m/s; the velocities of shear wave 1 of them are from 1407 m/s to 3181 m/s, with the average of 2322.1 m/s; the velocities of shear wave 2 are from 1430 m/s to 3197 m/s, with the average of 2330.7 m/s; the Poisson's ratio are from 0.0016 to 0.3215, with the average of 0.1751.2) Under the conditions of confining pressure from 18 to 89 MPa, pore fluid pressure from 10 to 46 MPa and temperature from 69 to 170 C, the velocities of compressive wave of the samples we tested, saturated completely by brine with 30,000 ppm NaCl, are from 2495 m/s to 6208 m/s, with the average of 4213.5 m/s; the velocities of shear wave 1 of them are from 1423 m/s to 3158 m/s, with the average value is 2341.3 m/s; the velocities of shear wave 2 of them are from 1414 m/s to 3178 m/s, with the average of 2351.2 m/s; the Poisson's ratio are from 0.1961 to 0.3461, with the average of 0.2753.3) From the samples saturated completely by air to those saturated completely by brine, the velocities of compressive wave of the rocks increase obviously, with the extent of 11.73%; the velocities of shear wave change little or decrease slightly, with the average of decreasing extent of 1.21% for shear wave 1 and 1.16% for shear wave 2. The difference of velocity between compressive wave and shear wave makes Poisson's ratio increase obviously, with the average extent of 87.25%.4) The velocity of the compressive and shear wave and Poisson's ratio for the samples saturated completely by air increase with the increasing of confining pressure, but the increasing extent of velocities of compressive wave is more than that of shear wave.5) The velocity of the compressive and shear wave for the samples saturated completely bybrine increases with the increasing of confining pressure (with the constant pore pressure), but Poisson's ratio decreases.6) Some interior factors, such as the composition of rock, porosity, density and so on. can influence directly the velocities of compressive wave and shear wave of rock. Commonly, the higher the content of carbonate in rock, the higher the velocity of compressive wave and shear wave; the higher the mud content, the lower the velocity of compressive wave and shear wave; the higher the porosity of rock, the lower the velocity of compressive wave and shear wave; the more compacted the rocks, the higher the velocity of compressive wave an...
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