Experimental Study on Logging Evaluation of Matrix Mineral Modulus of Tight Sandstone Reservoir

Abstract

Porosity has an important influence on the elastic properties of tight sandstone. Using acoustic models to study the matrix mineral modulus of tight sandstone reservoirs can provide an important reference for tight sandstone reservoir evaluation. In this paper, taking tight sandstone as an example, starting from the microscopic pore scale and considering the heterogeneity of the rock skeleton, the effect of the effective stress coefficient of porosity (n) on the elastic properties of tight sandstone was discussed. In addition, the acoustic model was used to construct the calculation method of the matrix mineral shear modulus. The research results showed that the porosity disturbance model can better describe the change law of the elastic properties of the tight sandstone. As the value of n decreases from 1 to 0, the bulk modulus (K_φ) of the unencapsulated rock gradually decreases. In the process of increasing from n=0 to n=4, the rock Kud has a slight increase trend. The fluid pressure does not produce a reverse stress effect on the movement of the rock pore boundary, that is, the fluid pressure does not have any effect on the change of the rock porosity. When n>0, the pore fluid pressure will affect the movement of the rock pore boundary to a certain extent. When the porosity disturbance is not considered, the K_φ value of the formation rock will be overestimated. The Ko of tight sandstone can be obtained using Gassmann fluid substitution equation. The calculation results of modulus parameters accord with the internal mineral composition and structural characteristics of tight sandstone, which shows the effectiveness of the method.