Study on the Rock Physics Analysis and Dispersion Characteristics of Tight Gas-Bearing Reservoir

With the deepening and refinement of oil and gas exploration and development, the accuracy requirements for reservoir prediction are becoming increasingly high. There are significant differences in rock physical properties between conventional high permeability-porosity reservoirs and unconventional tight reservoirs, especially the rock physics of pore fluid is significantly differe. This article conducts the analysis of laboratory core low-frequency and frequency conversion test data, as well as shear wave logging data, for the Upper Paleozoic tight sandstone reservoir in the Sulige gas field and the Lower Paleozoic tight carbonate reservoir in the Jingbian gas field.of the Ordos Basin. This data was used to conduct a detailed study on the relationship between different gas saturation and seismic elastic parameters in tight reservoirs at medium to high frequencies (ultrasonic, logging frequency bands) and low frequencies (seismic frequency bands), as well as the dispersion characteristics of tight gas-bearing reservoirs in seismic frequency bands. Analysis shows that the speed of low-frequency measurement is lower than that of ultrasonic measurement; With the change of water saturation, the P-wave velocity measured by ultrasound and low-frequency for samples with larger pores and permeability shows a monotonic linear change, while the P-wave velocity of samples with low porosity and permeability shows a nonlinear change pattern, and the S-wave velocity remains basically unchanged or slightly decreases; Within the frequency band range of seismic waves, the dispersion phenomenon of partially saturated samples is enhanced, while the dispersion phenomenon of samples with high gas saturation is obvious. This article creates a mixed fluid model formula suitable for tight reservoirs and calculates the elastic modulus of pore fluid mixtures at different saturations. And based on the equivalent-medium theory, a rocks physical model of tight reservoir and a quantitative interpretation chart of elastic parameters are constructed. Optimize S-wave impedance and shear impedance to distinguish lithology, Poisson's ratio and Lame impedance to identify gas bearing reservoirs. Establish a single well rock physical model based on drilling data, further carry out work such as shear wave prediction, fluid replacement, AVO analysis, selection of sensitive elastic parameters, and frequency dispersion analysis of gas-bearing reservoirs. Provide reliable basis for optimizing reservoir prediction technology, quantitative interpretation, and fluid identification.