An Experimental Study Of Seismic Wave Velocity Of Sandstones In Hulesitai,Inner Mongolia

Oil and gas are often stored in sandstones,so the research about sandstone's physical properties is of significant importance in the exploration of oil and gas.Seismic wave velocity plays a vital role in physical properties of sandstone.However,there are three deficiencies in the previous study of pioneers:?i?unreliable results of seismic wave velocity tests due to insufficient accuracy of experimental instruments,?ii?no investigation on the relationship between seismic wave velocity and multiple variables,and?iii?no study on the relationship between fluid and seismic wave velocity in oil and water environment.To solve the problems above,focusing on the sandstones samples in the region of Hulesitai,Inner Mongolia,the experimental study was carried out as follows by utilizing sophisticated experimental instrument under different pressure?0²00MPa?:investigations on?i?the relationships among pressure,porosity,density and seismic wave velocity,?ii?the relationships among pressure,seismic wave velocity and water saturation,?iii?the relationship between pressure and seismic wave velocity under dry,water saturated and oil saturated environment respectively,and the relationship between pressure and sandstone's anisotropy in three orthogonal directions X,Y and Z,?iv?the relationship between dynamic elastic parameters and pressure under different water saturation and?v?on the bases of textural constituents and chemical components study of sandstones,the theoretical seismic wave velocity are calculated by applying four models,and the theoretical as well as experimental values are compared.The results are shown as follows.Firstly,seismic wave velocity and density are positively correlated,while there is a negative correlation between seismic wave velocity and porosity.Both P-wave velocity and S-wave velocity increase notably with the increasing pressure which denotes a strong logarithmic relationship.The degree of linear relationship between density or porosity and P-wave is higher than that of S-wave.Secondly,there is a positive linear relationship between P-wave velocity and water saturation under different pressure,but there is a negative correlation between S-wave velocity and water saturation in high pressure.S-wave velocity in low pressure is generally not affected by the water saturation.Thirdly,P-wave velocity under saturated condition are bigger than that in dry condition.Although under various pressures,the seismic anisotropies with different properties show a certain order which is,A_dry>A_{oil saturated}>A_{water saturated}.The anisotropy of shear wave is smaller than that of compressional wave.Fourthly,both Young's modulus and Poisson's ratio increase with the increasing confining pressures under the same water saturation.Poisson's ratio increases with the increasing water saturation under the same confining pressure,while the variation of Young's modulus does not show an obvious variation trend.Finally,the error of average velocity model of Voigt is the biggest and the error of geometric average velocity model is the smallest among four average velocity models.