Elastic–Electrical Analysis for Low-Resistivity Pay Reservoirs

Low-resistivity pay (LRP) reservoirs pose significant challenges for hydrocarbon identification due to subdued resistivity responses caused by conductive minerals, dispersed clays, or saline formation water, which obscure fluid and lithology contrasts. Conventional elastic parameters such as acoustic impedance (AI) and the Vp/Vs ratio are widely used for lithology discrimination and reservoir characterization, but their application is often limited by the absence of shear-wave velocity (Vs) data and by reduced resistivity contrast in LRPs. This study introduces two novel parameters derived from porosity-resistivity relationships: Poro-Resistivity (PR), an AI-equivalent, and EPR (Exp[Porosity/Resistivity]), a Vp/Vs-equivalent. Using well logs from three wells in the Northern Gulf of Mexico, we demonstrate that PR correlates strongly with AI (correlation up to ۰.۸۵) and exhibits enhanced sensitivity to subtle lithological variations, while EPR maintains a near-linear relationship with Vp/Vs, enabling reliable elastic property substitution in the absence of Vs measurements. Rock physics modeling validates the lithology interpretations and confirms the robustness of PR and EPR in differentiating clean sands, shaly sands, and non-reservoir intervals. The results indicate that PR and EPR can effectively replace AI and Vp/Vs for lithology discrimination and reservoir detection in LRP settings, offering a practical, data-driven solution for improved characterization in wells with incomplete log suites or ambiguous resistivity responses.

کلیدواژه ها:

Low-resistivity pay ، acoustic impedance ، Vp/Vs ratio ، porosity-resistivity ، lithology discrimination