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三塘湖盆地石炭系火山岩中几乎所有的油气藏都聚集在断层圈闭中,体现了断层对火山岩油气成藏具有很强的封闭能力。研究认为三塘湖盆地石炭系火山岩中断层具有垂向和侧向两种封闭性。垂向封闭性主要取决于断裂中充填物的排替压力,而排替压力大小主要与充填物的成分和充填程度相关。在火山岩中断裂充填物无非是火山岩自身破碎的岩屑和泥岩两种,泥岩充填在一定条件下具有很好的封闭性,而单纯的火山岩自身碎屑充填一般不具封闭性。但由于石炭系火山岩受到烃碱流体作用,碱交代所形成的“上硅下碱”的结果使SiO2在局部层段将火山岩自身破碎的岩屑胶结起来,形成垂向封闭。因此,火山岩中断层垂向封闭存在泥质充填和SiO2胶结2种机理。在断层两盘对应火山岩储层内,油气通常呈现“此消彼长”的现象,这是断层侧向封闭性的体现。从引起差异渗透的因素来看,火山岩中侧向封闭存在岩性对接、泥岩涂抹和胶结封闭3种机理。每种机理在不同的地质情况下对火山岩中油气聚集发挥作用。
Almost all of the oil and gas pools in the Carboniferous volcanic rocks in the Santanghu Basin are gathered in fault traps, indicating that the fault has a strong sealing ability for volcanic hydrocarbon accumulation. The study shows that the faults in the Carboniferous volcanic rocks in the Santanghu Basin have both vertical and lateral sealing. The vertical seal depends mainly on the displacement pressure of the fill in the fracture, while the displacement pressure is mainly related to the composition and degree of filling. In volcanic rocks, the fracture fillings are nothing more than rock fragments and mudstones that volcanic rocks themselves are broken. Mudstone filling has good sealing properties under certain conditions, while pure volcanic rock itself is generally not closed with its own debris filling. However, due to the hydrocarbon-alkali fluid effect on the Carboniferous volcanic rocks, the result of alkali-base formation by alkaline metasomatism results in the cementation of the fragmentary volcanic rock fragments in the local intervals and the formation of a vertical seal. Therefore, there are two mechanisms of mudstone filling and SiO2 cementation in the vertical sealing of volcanic fault. In the two volcanic reservoirs corresponding to the faults, oil and gas generally show a phenomenon of “shifting away from each other”, which is an indication of the lateral sealing of faults. From the perspective of the factors causing differential infiltration, there are three mechanisms of lateral sealing in volcanic rocks, such as lithology docking, mudstone smearing and cementation sealing. Each mechanism plays a role in the accumulation of hydrocarbons in volcanic rocks under different geological conditions.