Abstract: Coal measure source rocks of Benxi Formation in Ordos Basin are widely developed in the central and eastern part of the basin, providing gas source for Paleozoic natural gas reservoirs in the basin. In recent years, breakthroughs have been made in the exploration of tight gas, shale gas and coalbed methane in the Benxi Formation of Ordos Basin. This reveals that there are various types of gas reservoirs in Benxi Formation, showing great resource potential. To deepen the understandings of the accumulation conditions and migration and accumulation laws of various types of natural gas reservoirs in Benxi Formation, the paper systematically analyzes the sedimentary environment, geochemical characteristics of gas source rocks and natural gas reservoir conditions of Benxi Formation, explores the enrichment and accumulation mechanism of multiple types of natural gas in Benxi Formation, and points out the direction of natural gas exploration. Research shows that:(1) No.8 coal and Zhaoxian shale are widely developed in the central and eastern Ordos Basin, characterized with stable distribution and moderate thermal evolution, which are favorable gas source rocks in the Paleozoic of the basin. (2) Various types of reservoirs are developed in Benxi Formation, dominated by Type II and Type III tight sandstone reservoirs, with the average porosity of 5.48% and good reservoir property. The pores and fractures of coal reservoirs are developed, and the reservoir space is dominated by cleats, plant tissue pores (cell pores), and bubble pores. The porosity is 0.5%-16.0%, and the content of free gas is high. The shale reservoir is relatively dense, and the reservoir space is dominated by inorganic pores, with an average porosity of 1.43%. (3) Sedimentary environment, gas source characteristics, reservoiring conditions and lithologic combination characteristics are the main influencing factors for the development of multiple types of natural gas in Benxi Formation. Based on the above understandings, the paper determines the exploration direction of natural gas in Benxi Formation of Ordos Basin, and optimizes and evaluates the favorable exploration areas of Benxi Formation, which is of important guidance and reference significance for the next hydrocarbon exploration and its deployment.

Key words: Ordos Basin, Benxi Formation, coal measures, natural gas, accumulation conditions

摘要： 鄂尔多斯盆地本溪组煤系烃源岩在盆地中东部广泛发育，为盆地古生界天然气藏提供了气源保障。近年来在鄂尔多斯盆地本溪组不断取得致密气、页岩气和煤岩气勘探突破，揭示本溪组天然气藏类型多样、资源潜力较大。为深化本溪组多种类型天然气藏的成藏条件和运聚规律等认识，系统分析了本溪组沉积环境、气源岩地球化学特征、天然气储集条件，探讨了本溪组多类型天然气富集成藏机理，并指明了天然气勘探方向。研究表明：①本溪组8号煤层和招贤页岩在鄂尔多斯盆地中—东部广泛发育、分布稳定、热演化程度适中，是盆地古生界的有利气源岩。②本溪组天然气储层类型多样，其中，致密砂岩储层孔隙度平均为5.48%，以Ⅱ类、Ⅲ类储层为主，储集性能较好；煤岩储层孔缝发育，储集空间以割理缝、植物组织孔（胞腔孔）、气泡孔为主，孔隙度在0.5%~16.0%，游离气含量高；泥页岩储层较为致密，储集空间以无机孔隙为主，孔隙度平均为1.43%。③沉积环境、气源特征、储集条件、岩性组合特征等是本溪组发育多类型天然气成藏条件的主要影响因素。研究认识明确了鄂尔多斯盆地本溪组天然气勘探方向，并优选评价了天然气有利勘探区，对下一步勘探部署具有重要指导与借鉴意义。

关键词: 鄂尔多斯盆地, 本溪组, 煤系地层, 天然气, 成藏条件