A new method of rock physics modeling and its application in low permeability reservoirs of Z Gasfield, East Sea Basin

Low-permeability reservoirs have complex pore structure characteristics for which conventional petrophysical modeling methods are not suitable for detection. In addition, physical properties among different layers of low-permeability reservoirs vary considerably, so it is difficult to use unified petrophysical model to characterize the relationship between reservoir parameters and elastic parameters. We proposed a new technical approach to stratified rock physics modeling of low permeability reservoirs: for medium-low porosity and medium-low permeability reservoirs, the fluid uniform saturation model based on DEM theory was adopted; for extra-low porosity and extra-low permeability reservoirs, the fluid non-uniform saturation model based on KT theory was adopted. The predicted P-wave and S-wave velocities based on stratified rock physical modeling were in good agreement with the real logging data, which verified the reliability of the method. Based on the accurate petrophysical models, the laws of elastic parameters variations with shale content, porosity, and pore shape were further analyzed, to guide the prediction of lithology and "sweet spot" in low permeability reservoir.