Genesis and Implications of High-Resistivity Water Zones in Jurassic Reservoirs of Huanjiang Area, Ordos Basin

The oil–water relationship in the Jurassic reservoirs of the Huanjiang area in the Ordos Basin is complex, with similar resistivity values for oil- and water-bearing zones, making effective identification challenging. This ambiguity hinders a clear understanding of hydrocarbon accumulation patterns and constrains petroleum exploration efforts. Through integrated study—including high-resolution seismic structural interpretation, formation water type analysis, and the distribution characteristics of discovered hydrocarbon shows—the genesis of high-resistivity water layers was analyzed. The results indicate that tectonic activity exerts a dual influence on hydrocarbon accumulation. During the Yanshanian tectonic phase, the formation of various types of traps provided favorable storage spaces for large-scale hydrocarbon accumulation. Additionally, a set of nearly north-south trending faults and associated fractures developed at this stage facilitated vertical migration by connecting source rocks with overlying and underlying strata, thus promoting hydrocarbon accumulation. Conversely, the Himalayan tectonic phase introduced NE–SW-trending faults with significant displacement and lateral extension, which disrupted or restructured pre-existing hydrocarbon reservoirs, adversely affecting their preservation. The destruction and redistribution of hydrocarbons in some areas led to residual hydrocarbons contributing to high-resistivity water signatures and making some oil and water layers difficult to distinguish. Two main types of large-scale reservoirs have been identified: structural-lithologic reservoirs and anticlinal trap reservoirs. Favorable traps formed by the alignment of tectonic structures and sand bodies are expected to be the primary targets for future Jurassic reservoir exploration in the study area. These findings provide valuable insights for the evaluation and exploration of similar Jurassic reservoirs across the Ordos Basin.