Mechanisms of hydrated ion bridges in the development of low and ultra-low permeability reservoirs

This study focuses on the hydrated ion bridge (HIB) effect at the oil-rock interface in low- to ultra-low-permeability oil reservoirs. It systematically summarizes the research methodologies, formation mechanisms, interaction strength, and disruption mechanisms of HIB, and discusses the influencing mechanisms of HIB on the occurrence state and mobility of crude oil. On this basis, the key challenges inherent in the current HIB research are analyzed, and prospective directions for future development are proposed. Currently, research in this field primarily relies on experimental characterization techniques and molecular simulation methods. The microscopic interactions involved in HIB formation mainly include electrostatic interactions, hydrogen bonds and van der Waals forces. Notably, the hydrogen bonds between polar molecules in crude oil and hydrated ions serve as the primary sites for disrupting the HIB effect. The interaction strength of HIB is collectively modulated by ion type and concentration, reservoir solution environment, mineral type of reservoir rocks, and polar components in crude oil, which subsequently influence the occurrence state and mobility of crude oil. Systematic challenges persist in HIB-related research across three dimensions: research methodologies, scale integration and geological complexity. Specifically, the dynamic evolution mechanism of HIB remains inadequately elucidated; a discontinuity exists in the connection of spatiotemporal cross-scale modeling and prediction; and the reproducibility of actual geological environments in experimental settings is insufficient. Future research may pursue breakthroughs in the following three aspects: (1) developing in-situ dynamic experimental characterization techniques and machine learning-augmented simulation strategies; (2) establishing a framework for cross-scale model fusion and upscaling prediction; and (3) conducting in-depth studies on HIB under the coupled effects of complex mineral systems and multi-physical fields.