Abstract Apart from conventional gas in the middle-shallow formation in the Xihu depression in the East China Sea Basin, low permeability gas sandstone layers in the middle-deep formation have recently been discovered. On the basis of integrated analysis of reservoir petrology and diagenesis, geochemistry of gas and source rocks, basin numerical modeling, gold-tube pyrolysis experiment of rocks and fluid inclusion, a comprehensive investigation of the characteristics of low-permeability reservoirs, gas origin, generation and charge in the sub-structural belts (West Slope Belt and West Sub Sag) has been performed. Strong mechanical compaction, filar authigenic illite, siliceous and carbonate cements are key factors for the formation of low permeability reservoirs. The comprehensive analysis of molecular components, stable carbon isotope compositions of gases and light hydrocarbons indicated that the low permeability gases in the WSB are mainly coal-derived and can be divided into two types: (1) mature gases sourced from local coal-measure rocks in the Pinghu Formation, (2) exogenous highly mature gases sourced from the coal-measure rocks in the Pinghu Formation in the WSS. Mature gases were injected into the low permeability reservoirs in the middle-lower Pinghu Formation at approximately 2.8Ma∼0Ma. In the meantime, partial highly mature gases generated from source rocks in the WSS also migrated to the WSB. On the whole, the gas charge in the WSB is characterized by dual-sourcing and late-stage. The low permeability gases in the WSS almost are highly mature and composed of most coal-derived gases generated from local coal-measure rocks in the Pinghu Formation and a small amount of oil-derived gases generated from local dark mudstones containing sapropelic-type organic matters in the Pinghu Formation. In addition, mature coal-derived gases generated from source rocks in the lower Huagang Formation are also present but very limited. The charge of highly mature gases in the low permeability reservoirs in the lower Huagang Formation in the WSS occurred at approximately 3.9Ma∼0Ma.

中文翻译：

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东海盆地西湖坳陷中西部低渗透储集层特征、气源、成因及充注

摘要 东海盆地西湖坳陷中浅层天然气除常规气外，近期又在中深层发现低渗透气砂岩层。在储层岩石学与成岩作用、气源岩地球化学、盆地数值模拟、岩石和流体包裹体金管热解实验综合分析的基础上，综合考察低渗透储层特征、气源、成因并在次构造带（西斜坡带和西子凹陷）中进行了充电。强机械压实作用、丝状自生伊利石、硅质和碳酸盐胶结物是形成低渗透储层的关键因素。分子成分综合分析，气体和轻烃的稳定碳同位素组成表明，WSB 中的低渗透气体主要是煤成气的，可分为两种类型：（1）来自平湖组局部煤系岩的成熟气，（2 )WSS 平湖组煤系岩源的外源高成熟气。成熟气注入平湖组中下层低渗透储层，约2.8Ma～0Ma。同时，WSS 烃源岩产生的部分高成熟气也向WSB 运移。总体来看，WSB 充注气具有双源、后期充注的特点。WSS中的低渗透气体几乎是高度成熟的，主要由平湖组局部煤系岩产生的煤成气和少量含有腐泥型有机质的局部暗色泥岩产生的油成气组成。在平湖组。此外，花港组下部烃源岩也存在成熟煤成气，但非常有限。WSS下花港组低渗透储层高成熟气充注发生在3.9Ma～0Ma左右。花港组下部烃源岩也存在成熟煤成气，但非常有限。WSS下花港组低渗透储层高成熟气充注发生在3.9Ma～0Ma左右。花港组下部烃源岩也存在成熟煤成气，但非常有限。WSS下花港组低渗透储层高成熟气充注发生在3.9Ma～0Ma左右。