Ultrasonic Experimental Study Of Conventional Sandstone Saturated With Different Fluid

When studying oil and gas reservoirs,we usually study conventional oil and gas reservoirs,that is,light hydrocarbons(gas)whose hydrocarbons are mostly short-chain alkanes,and their properties are quite different from those of unconventional oil and gas reservoirs such as heavy oil.Different fluid types,viscosity and saturation have great influence on the elastic properties of the reservoir.The study of the relationship between the elastic properties of the reservoir and these parameters can lay a foundation for reservoir and fluid prediction.In this paper,ultrasonic experiments were carried out to study the variation of ultrasonic velocity of fluid-bearing sandstone with fluid type(water,68# white oil,glycerol),viscosity and saturation,and the ultrasonic experimental data was simulated and explained based on the two-scale model.Specifically,the six fluid sandstone samples(two artificial sandstones and four natural sandstones)are saturated with the above fluids,and the saturation is changed.The experimental measurements are carried out under different pressure conditions to obtain the longitudinal and transverse wave velocities of the rock samples.The experimental results show that the longitudinal and transverse wave velocities of the rock sample increase with the increase of pressure,but increase rapidly under low pressure conditions and increase gently under high pressure conditions.Comparing the results of different fluids saturated with the same rock sample,it can be found that as the viscosity of the fluid increases,the relative increment of the longitudinal and transverse wave velocities after the saturated fluid of the rock sample increases gradually,and the increment of the longitudinal wave velocity is higher than the shear wave velocity.In addition,the difference between saturated glycerol results and saturated water results is greater than the difference between saturated 68# white oil and saturated water,and the shear wave velocity is less affected by fluid.Comparing the experimental values with the Gassmann theoretical values,it is found that the experimental values are always higher than the Gassmann theoretical predictions,but as the pressure increases,the difference between the two decreases,and the experimental results basically accord with the Gassmann theoretical values.In order to accurately simulate and explain the performance of velocity under different pressures,we chose the two-scale model(MJGW)to fit the experimental data,and found that the model can well describe and explain the influence of fluid saturation and confining pressure on the ultrasonic velocity of sandstone.However,the prediction accuracy of fluid samples with different viscosity fluids is different.The experimental and simulation results show that the rock sample is mainly controlled by the jet flow effect at low saturation,and is controlled by the jet flow and the slab saturation at high saturation.