The Spontaneous Potential Log as an Aid in Establishing Electrical—Hydraulic Conductivity Relations in Complex Sedimentary Rock Environments: A Case Study in Taiwan

Hydraulic conductivity estimation in fractured and clay-rich sedimentary rocks is often challenged by geological heterogeneity and disturbances from drilling operations. This study investigates the applicability of borehole geophysical logging, focusing on spontaneous potential (SP) and single-point resistance (SPR), to establish reliable correlations with hydraulic conductivity in sedimentary formations of Taiwan’s mountainous regions. Conventional approaches based on Archie’s law and formation factors were found to be unreliable due to inaccuracies in pore-water resistivity caused by drilling mud contamination and lithologic complexity. To overcome these issues, a two-stage SP-based screening method was developed to refine datasets by differentiating lithologic intervals and filtering heterogeneous or noise-affected samples. Regression models derived from these screened datasets demonstrated that SPR exhibited the strongest predictive performance, while SP filtering significantly enhanced correlation accuracy. Among the developed models, one provided practical predictions with broader coverage, whereas the more refined model achieved higher precision with fewer data points. The results highlight the advantages of integrating SP screening with resistivity logging to create a cost-effective and systematic approach for estimating hydraulic conductivity in complex geological settings, thereby offering valuable support for groundwater resource evaluation and engineering applications.