Research On Acoustic Velocity Model Of Loose Sandstone Based On CCT

Cementation has great influence on the elastic properties and acoustic velocities of loose sandstone, but there is great deficiency in the current research on the effect of cementation. To solve this problem, this paper carefully analyzes the effects of cementation on the elastic properties and acoustic velocities of the loose sandstone based on CCT(Contact Cement Theory). The appropriate modified model, approximations for the model and the method of calculating the key parameters are then given.Firstly, the principles and the derivation process of the Contact Cement Theory(CCT) are introduced. The deficiencies of applying the theory to the loose sandstone with large cement content and non-zero contact thickness are also analyzed. For the loose sandstone with low cement moduli, the original statistical approximation for the model will bring large errors.Therefore, the new statistical approximations are given(Chapter 2).Secondly, for the loose sandstone with pore cementation under the large cement content,the model for the calculation of elastic moduli and acoustic velocities proposed by Dvorkin(1999) is further developed by combing the Differential Effective Medium(DEM) Theory and the Gassmann Equation. Especially, a method of searching the fitting porosity automatically is proposed innovatively. The verification by real data shows that the modified model has high calculation efficiency and can search the fitting porosity automatically(Chapter 3)..Finally, the cementation radius expressions in CCT are re-derived, which stretch the application range of CCT to the loose sandstone with basal cementation. With the new cementation radius expressions, the effects of the contact thickness on the moduli of the loose sandstone are investigated. The approximation of CCT considering contact thickness is also given, the modified model is then verified using the man-made loose sandstone and the good results are obtained(Chapter 4).The Contact Cement Theory(CCT) is modified and extended through this research, the new methods of determining the key parameters are also given. The modified model can better predict the moduli and acoustic velocities of the loose sandstone, which enriches the models for the calculation of the elastic moduli and acoustic velocities of loose sandstone.