The oil reservoir accumulation patterns of the Yanwu and Hongde research areas in the Ordos Basin

Abstract

With the aim of elucidating hydrocarbon accumulation patterns and determining favorable exploration targets in the Hongde and Yanwu study areas, systematic research was carried out in this study. On the basis of prior research results, multiple datasets including structural features, fault systems, paleogeomorphic conditions and aquifer distribution data were comprehensively integrated. The research results indicate that, oil and gas accumulation is governed by four key factors: Paleogeomorphic characteristics—sandbody development and migration pathways are mainly controlled by the paleogeomorphology of the Fuxian Formation, with paleovalleys serving as the primary migration conduits; High-altitude areas and inherited nasal structures (such as slopes and residual hills) facilitate the formation of local traps, and the tectonic evolution process—The eastward migration of the Tianhuan Sag axis and the uplift of the Ordos Basin have led to a sedimentary pattern characterized by thicker deposits in the west and thinner ones in the east, formation of two-phase filling mechanism. The eastern region has become the primary concentration area; fault system—Deep-seated large faults, strike-slip extensional zones, and the intersections of multi-stage fractures all serve as effective vertical migration pathways, connecting the source rocks to the trap areas and facilitating hydrocarbon accumulation; Reservoir-cap combination—The synergistic effect of high-quality reservoir and good cap conditions is the key to effective oil and gas accumulation. Enrichment follows a “fault-guided migration, paleogeomorphic relay, micro-structure and reservoir-controlled trapping” model. Favorable zones are located at paleo-highs, fault-developed areas, and regions with high-permeability reservoirs. Reservoirs in the study area are dominated by structural and structural-lithologic composite traps. The lower Yan 10 Member and Fuxian Formation intervals are dominated by paleogeomorphology, the upper interval Yan 9 and above) is structured by folding induced by tectonic stress. Using the “four-control method” for stratified target selection yielded successful drilling outcomes.