| Because the underground reservoir rock is under high pressure and high temprature ,it is very important to determine the relation between rock velocities and various pressures.In the light of the relation between rock velocities and confining pressure and pore pressure,the concept and formula of effective pressure is cleared in this thesis.On the base of large experimental data set,the influence of effective pressure on rock velocities is analyzed with regression method and the theory of crack closure. Gassmann theory is used to compute the influence of pore fluid on velocities. From the result of computing it is demonstrated that the velocities of rock filled with pore fluid can be predicted by Gassmann theroy.Considering the uneven distribution of earth stress,the influence of mono-axis pressure on rock velocities is also discussed.Unlike the effective pressure ,mono-axis pressure will cause velocity anisotropy.For the goal of geophysical exploration,the ratio of compressional wave velocity to shear wave velocities, the ratio of Poission, density, porosity, wave impedence and elastic moduli with effective pressure changes are also discussed.It can be seen from the result that the ratio of P- to S- wave velocities and the ratio of Poision and other geophysical constants of the sandstone rock sample filled with gas are very different with that filled with water or oil. The porosity reduction due to the pressure change can reach 10%.The regression results show that the velocities are linear related to porosity and clay content.Using such regression formula to sonic logging data indicates that the coefficients of the formula should be determined by statistical method about specific area, instead of fixed values.Because of the great frequency discrepancy between ultrasonic wave measurement, sonic logging and seismic exploration,velocity dispersion must be considered.The results of computing show thatvelocity dispersion are dependent of effective pressure and fluid viscosity. The wave velocities of sandstone samples within ultrasonic frequency band are explained by pore fluid local flow and elastic wave scattering mechanism.The wave velocities with water saturation are also measured. By water imbibing and drying rate experiments , it can be concluded that the velocities are not only related to water saturation, but fluid distribution of pore scale. Different saturation process can lead to different velocity change.The drillstring whirling is discussed in this thesis. The dynamics equations of collar whirling are deduced by use of nonlinear rotor dynamics. The expressions of critical rotational speed and critical whirling amplitude are obtained. Numerical solutions of the whirling equation with various initial conditions and drilling properties are also computed and analyzed.
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