关键词: 鄂尔多斯盆地, 杭锦旗地区, 北缘过渡带, 上古生界, 天然气, 勘探新发现, 成藏特征与模式

Abstract: Gas accumulation conditions in the Hangjinqi area of the northern marginal transition zone of the Ordos Basin are highly complex, and exploration concepts have undergone a major evolution—from “local structural gas control” to “large-scale lithologic trap–controlled gas accumulation,” and from “single low-saturation lithologic gas reservoirs” to “ordered distribution and differential enrichment of multiple reservoir types.” In particular, since the “14^th Five-Year Plan” period, significant discoveries have successively been made in the Xinzhao play, the Shilijiahan play, and a newly recognized Mesoproterozoic stratigraphic interval, leading to the formation of a trillion-cubic-meterscale gas province.Based on new exploration achievements in the northern marginal transition zone of the basin, and through comprehensive utilization of newly acquired drilling, seismic, and geochemical analytical data, this study further refines the understanding of differentiated gas accumulation and enrichment processes, yielding the following new insights: (1) two high-quality Carboniferous–Permian coal-measure source rock systems, the Taiyuan and Shanxi formations, are distributed around the paleo-uplift and constitute the fundamental resource basis for the formation of large gas fields in the basin-margin transition zone; (2) the widespread development of near-source, gravelly braided-river channel-bar sand bodies in the Taiyuan–Shihezi formations, superimposed on differential tectonic evolution, controls the ordered distribution of tight and conventional reservoirs along the basin margin; (3) an advantageous migration and transport framework composed of faults and sand bodies during key accumulation periods governs gas adjustment and enrichment; and (4) on the basis of these accumulation conditions, four dynamic gas accumulation models are established by integrating static and dynamic accumulation elements of major gas provinces, namely near-source–middle-stage accumulation, far-source–multi-stage accumulation, intra-source–late-stage accumulation, and rejuvenated paleoreservoir basement-hosted accumulation.These results further extend and enrich theories of hydrocarbon accumulation and enrichment within the total petroleum system of largecratonic basins, and provide important guidance for oil and gas exploration in the Ordos super basin.

Key words: Ordos Basin, Hangjinqi area, northern marginal transition zone, Paleozoic, natural gas, exploration discoveries, accumulation characteristics, and accumulation models