Utilization of magic Lamé impedances on carbonate reservoirs' lithological and porosity characterization

The dolomite reservoir in the fourth member (Ma4) of the Ordovician Majiagou Formation is a significant gas reservoir in the Ordos Basin, China. It consists of thin layers within limestone, characterized by a mottled dolomitic limestone texture, with pores formed by complex diagenetic processes that result in low porosity values. These layers show minimal petrophysical contrast with the surrounding rock, complicating identification and property prediction using conventional elastic attributes like P- and S-impedances. To overcome this challenge, the study utilizes Lamé impedances (λρ and μρ), which expand the P- and S-impedance cross-plot space, enhancing the identification of reservoir zones. First, Lambda-rho and Mu-rho impedances were derived from logging data and cross-plotted to create a locally constrained rock physics template based on porosity and dolomite content along the vertical direction. This template was then applied to the Lambda-rho and Mu-rho attributes generated from seismic pre-stack inversion. The rock physics template (λμρ cross-plot) accurately predicted dolomite content and porosity from seismic data, achieving high precision compared to the conventional porosity and dolomite content logs. This study highlights the effectiveness of Lamé parameters (λμρ) in predicting and estimating reservoir property distributions, providing valuable insights into the geological origins of dolomite and advancing hydrocarbon exploration and development.