Prediction Methods Based On The Shear Velocity Of The Rock Physics Theories

S-wave velocity is necessary in AVO analysis, reservoir prediction and fluid discrimination. However, there is often lack of S-wave velocity which either from dipole sonic or VSP. There is also lack of rock physics measurements in oil fields.S-wave velocity is often obtained from unrealistic empirical equation or constant Vp/Vs ratio assumption in AVO analysis and reservoir parameter inversion in sandstone. These S-wave velocity statistical relations are usually inaccurate and lead to unreliable AVO attributes or elastic impedance in AVO inversion. In order to get more accurate S-wave velocites, we developed a method based on rock physics theory in which Gassmann's equation and Lee's method are used to calculate elastic modulus of dry rock in porous sandstones. Furthermore, we constructed a more realistic model which cracks and fractures are included in porous model by using Thomsen's theory. The accuracy of our method is proved by comparing predicted S-wave velocity and measured S-wave log in a coal mine.Development of a carbonate rock physics model to get S-wave velocity is necessary because pore systems are very complex in carbonate rocks. First we calculated the dry frame moduli using the measured elastic wave velocity according to the Gassmann equation. Then we used the calculated dry frame moduli to get the S-wave velocity of the carbonate with the fluid in the pores and the fluid substitution model is established. We also use the Lee's method to predict S-wave velocity in carbonate rocks. The most important method of the work is based on the DEM. A series facors such as pores shape, cementation, pressure and so on will effect the elastic wave. These factors can be reflected on the porosity and aspect ratio. We considered the porosity, aspect ratio and construct the model in which not only S-wave velocity but also the pores type could be estimated. The accuracy of our method is proved by comparing predicted S-wave velocity and measured S-wave log in actual data.