An Elastic–Electrical Analysis Method for Identifying Reservoirs and Lithology and its Application in the Northern Mexico Gulf Sedimentary Basin

Abstract

The elastic–electric properties of rocks play a crucial role in enhancing our understanding of subsurface rock properties and reservoir characteristics. The purpose of investigating the elastic–electric properties of subsurface rocks is to effectively identify reservoir units and separate sand from shales in geological structures. Acoustic impedance (AI) and the Vp/Vs ratio are crucial parameters in geophysics and reservoir characterization. These parameters are employed to distinguish between fluid and lithology types, and to detect the presence of sand reservoirs. These analyses elucidate the anticipated range of the Vp/Vs ratio for reservoir units and other formations within the study area. In this research, we propose two novel equations based on porosity–resistivity relationships, namely Poro-resistivity and Exp (porosity/resistivity) (EPR). These equations serve as equivalents to AI and the Vp/Vs ratio, respectively, and better define the subsurface rock properties in the absence of S-wave velocity data in wells. Poro-resistivity functions similarly to an AI equivalent and exhibits a strong correlation with density, Vp, and AI. However, Poro-resistivity is more sensitive to lithology variations. Our findings indicate that Poro-resistivity is an effective criterion for distinguishing shale from porous sand. We employed rock physics models to assess the performance of Poro-resistivity, and the results confirmed its effectiveness. Furthermore, we compared the scatter plot of AI and the Vp/Vs ratio, a well-established rock physics template for lithological and fluid analysis, with the scatter plot of AI and EPR. The results were strikingly similar, leading us to conclude that EPR is a suitable equivalent for the Vp/Vs ratio.