关键词: 塔里木盆地, 奥陶系, 碳酸盐岩, 台缘相带, 油气藏, 形成条件, 油气富集规律

Abstract: The largest Ordovician reef-type oil and gas reservoir discovered in China is distributed along the Upper Ordovician carbonate platform margin in the northern of central uplift of Tarim Basin.It is an unconventional hydrocarbon reservoir with complicated oil-gas-water distribution and without obvious edge water and bottom water.The analyses on forming condition and enrichment law of the reservoir showed that a large rimed carbonate platform margin system was formed,and multi-phases depositions of reefs,banks and limemud mounds were developed in the early stage of the Late Ordovician along the northern margin of central uplift.The vertically superimposed and laterally connected reef-type reservoir was distributed widely along the platform margin of Tazhong No.1 structural belt and has many kinds of secondary corrosion voids characterized by low porosity and low permeability.Three major stages of hydrocarbon activities were accountable for the abundant hydrocarbon accumulation.The low-abundance reef-bank type lithologic reservoirs were distributed along the margin tectonic zone.The carbonate platform margin controlled the hydrocarbon migration and accumulation,and a large hydrocarbon-enriched belt was formed.The oil-gas enrichment was mainly controlled by reservoirs.The difference of oil and gas occurrence was caused by multi-stage hydrocarbon accumulation and heterogeneity of reservoirs.

Key words: Tarim Basin, Ordovician, carbonate rock, platform margin, oil-gas reservoir, forming condition, oil-gas enrichment law