三塘湖盆地火山岩油藏特征与成藏过程分析

Characteristics of volcanic reservoir and process of petroleum entrapment in Santanghu Basin

三塘湖盆地属西部典型的改造型叠合盆地,火山岩油气藏主要分布于石炭系、二叠系火山岩中。本文结合盆地构造演化史与生烃史,分析了三塘湖盆地石炭-二叠纪火山岩油气藏形成的动态过程。火山岩油气藏主要形成于二叠纪末-三叠纪海西印支期和侏罗纪末-白垩纪末期的燕山期,油气藏的形成及后期调整与构造运动密切相关。火山岩油气藏具多期运聚、多期成藏和多期调整改造成藏特征,其成藏模式为以火山岩风化壳为储集层、下覆湖相泥岩为烃源岩,油气在构造背景下,沿不整合面聚集成藏,形成下生上储地层型油藏组合模式。本文结合构造演化史分析三塘湖盆地火山岩油气成藏过程,对西部沉积盆地下组合火山岩油气藏的勘探具有良好借鉴与指导意义。

Santanghu Basin is a typical reworked superimposed basin in western China. The volcanic hydrocarbon accumulations mainly distributed at Carboniferous and Permian. Based on tectonic evolution history and hydrocarbon generation history, it analyses the volcanic accumulation process in Carboniferous and Permian formations of Santanghu Basin. The Hercynian Indo- Chinese epoch, when Late Permian to Triassic, and Yanshan epoch, when Late Jurassic to Cretaceous are the two main volcanic accumulation periods. The accumulation formation and later adjustment are closely related to tectonic movements. The accumulation model can be summarized as：Permian and Carboniferous volcanic weathering crust under the unconformity surface were the favorable reservoir, which was rich in corroded pore and fissures, the main storage space. Lacustrine mudstone under the reservoirs are the source rocks. Under the tectonic background, hydrocarbon migrated through weathering crust and fissures, then accumulated to the favorable trap which usually under the unconformity surface. We called it the stratigraphic hydrocarbon accumulation model. The accumulation process analysis is useful for reference to the petroleum exploration in lower assemblage of the western basins in China.