鄂尔多斯盆地延长组长7_(3)亚段页岩油特征及勘探方向

Characteristics and exploration targets of Chang 7 shale oil in Triassic Yanchang Formation,Ordos Basin,NW China

通过对鄂尔多斯盆地三叠系延长组7段3亚段(简称长7_(3)亚段)岩心观察、实验分析测试、测-录井等资料分析,揭示长7_(3)亚段多类型页岩油发育的地质特征及富集规律,探讨多类型页岩油勘探潜力及攻关方向。研究表明:①长7_(3)亚段发育运移-滞留复合型和滞留型2类页岩油,运移-滞留复合型储集层为砂质碎屑流、低密度浊流成因的砂质纹层和半深湖—深湖富有机质泥页岩纹层频繁互层叠置的组合段,滞留型页岩油储集层为页理及显微纹层频繁发育的黑色页岩,运移-滞留复合型页岩油品质略好于滞留型页岩油。②优质烃源岩提供大量高势能富烃优质流体;源储压差为渗流条件较好的贫有机质砂岩类薄夹层和页岩中的长英质纹层、凝灰质纹层及页理缝原油聚集提供动力;生烃增压缝-页理缝-微裂缝为原油微运移提供高速通道;频繁发育的砂岩夹层及长英质纹层不仅为烃类规模聚集提供有效的储集空间,还能有效提高烃类的可动性。③环洼富砂区是运移-滞留复合型页岩油规模勘探的主要方向,成熟深洼区是中高成熟度滞留型页岩油风险勘探的主要方向,围绕低熟深洼区积极推进原位转化研究和现场实施是中低成熟度滞留型页岩油勘探的主要攻关方向。

The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 73)in the Ordos Basin were analyzed by using the information of core observations,experiments and logging,and then the exploration potential and orientation of the Chang 73 shale oil were discussed.The research findings are obtained in three aspects.First,two types of shale oil,i.e.migratory-retained and retained,are recognized in Chang 73.The former is slightly better than the latter in quality.The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty–sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep–deep lacustrine organic-rich shale laminae.The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae.Second,high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy.The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina,tuffaceous lamina and bedding fractures in shales.Hydrocarbon generation-induced fractures,bedding fractures and microfractures provide high-speed pathways for oil micro-migration.Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation,and also effectively improve the hydrocarbon movability.Third,sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil.Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity.Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.