Research on Gas Zone Identification in Tight Sand Based on the Fluid Substitution Theory

Typical tight sandstone gas reservoirs are developed in the eastern margin of the Ordos Basin. The complex pore structure leads to "non-Architic response", which makes the resistivities of oil, gas, and water layers in tight reservoirs are basically the same, and it is difficult to identify fluid properties. By analyzing the acoustic response characteristics of tight sandstone reservoirs in this area, it is found that parameters such as the P-wave velocity ratio and Poisson's ratio are sensitive to changes in gas-bearing changes. Based on the seismic rock physics Gassmann theory, combined with array acoustic wave and other logging data, a modulus model including rock porosity, skeleton, and mixed fluid was established, and finally the mixed fluid modulus was obtained. Examples of test wells in the study area show that the identification of tight sandstone gas layers based on fluid replacement methods plays an important role.