Evaluation of Low Resistivity Causes and Gas Potential in the Niutitang Formation Shale of Qianxi Block

ABSTRACT

The Niutitang Formation shale is a key gas reservoir in the Upper Yangtze Plate, yet in the Qianxi block it exhibits anomalously low resistivity and severe gas depletion, posing exploration risks. Integrating petrology, geochemistry, petrophysics, gas content, and well logs, this study investigates the origins of low resistivity, lithofacies‐dependent controls, and enrichment–depletion mechanisms. Results show (1) The shale has high quartz and clay contents, elevated total organic carbon (TOC), and overmaturity, but extremely low porosity, permeability, resistivity (<2 Ω m), and gas content (<0.1 cm ³ /g). (2) From mixed shale to siliceous shale to siliceous rock, TOC and Ro increase, whereas porosity, permeability, and resistivity decrease, reflecting compaction and graphitization. (3) Low resistivity is primarily governed by graphitization, porosity loss, and micropore decline; the lower limit is approached when Ro > 3.0%, clay mineral content falls to the 25th percentile, and porosity <0.5%. (4) Enrichment correlates with moderate organic matter, limited graphitization, higher clay and porosity, abundant micropores, and well‐developed bedding/microfractures. In contrast, depletion correlates with high organic matter, advanced graphitization, high brittle minerals, low clay and porosity, scarce micropores, and extensive macro‐fractures. These findings establish thresholds for high‐risk zones and provide a practical framework for exploration de‐risking and sweet‐spot selection in overmature marine shales.