小型含油气盆地成因类型、特征与油气赋存

Genetic Classification,Characteristics and Hydrocarbon Occurrence of Small-scale Petroliferous Basins

沉积盆地分布广、数量多,其中小型盆地数量占比居多。中国小型盆地占全国盆地总数的80%以上,虽然发现工业油气藏的小型盆地占比少于10%,远低于大—较大型盆地(>76%),但是小型含油气盆地的油气丰度(HAPUA)大多较高,“小而富”盆地远高于多数大中型含油气盆地,勘探成效较高。通过对中国16个含常规油气小型盆地的综合研究,根据盆地形成机制和动力环境的差异,将其分为残留型和原始型两大类型;进一步将后者细分为走滑、裂陷和热力成因3类。小型残留成因含油气盆地一般经历了主力烃源岩形成的原盆建造、后期改造残留和晚期覆埋生烃的演变时段,3期缺一不可。其中原盆中部分烃源岩得以残留奠定了资源基础,晚期深埋是烃源岩成烃-聚集并成藏的关键环节。原始小型含油气盆地中的走滑、裂陷和热力3种成因类型,均在较活动的动力环境中形成演化,一般具有较快沉降-沉积、较高地温场、活跃的深部背景和晚(后)期改造等特征。这类动力环境使盆地沉积了“小而厚”的地层并形成多种形式的构造圈闭,有利于生物超常勃发繁盛和优质烃源岩形成及生烃转化,有助于油气聚集成藏。盆地油气“小而富”与“小岩体成大矿”,在形成动力环境和成矿理论认识等方面有相通之处。这两大领域在科学研究和学术思想等方面可触类旁通、相互借鉴参考。

Sedimentary basins are widely distributed on Earth.Among them,the small basins account for their majority.In China,small basins account for over 80%of the total number of basins,while in aspect of the industrial oil and gas reservoirs,the small-scale basins contribute less than 10%which is far less than large and medium-sized basins(>76%).However,the hydrocarbon abundances per unit area(HAPUA)of most small-scale petroliferous basins are high;for some basins characterized by“small but enriched”,the HAPUAs are much higher than large-to medium-sized petroliferous basins,resulting in higher exploration effectiveness.A comprehensive study of 16 small-scale basins containing conventional oil and gas in China was implemented.They are divided into remnant and proto small-scale basins based on the differences in basin formation mechanisms and dynamic environments.Furthermore,the proto small-scale basins are subdivided into strike-slip basin,rift basin,and thermal basin.Remnant small-scale petroliferous basins generally undergo three imperative evolutionary stages,including the proto-basin construction stage with development of the main source rock,the reformed and remnant stage,and the late buried and hydrocarbon generation stage.The residual source rocks in the proto-basin provide a resource foundation,and the deep burial in the late stage is the key link for hydrocarbon generation and accumulation.The three subtypes of proto small-scale basins,strike-slip,rift,and thermal basins,are all formed and developed in relatively active dynamic environments.They are generally characterized by rapid subsidence and deposition,relatively high geothermal fields,active deep background,and later-stage modification.This dynamic environment results deposition of“small but thick”strata in the basin and forms various structural traps.It also benefits the extraordinary growth and prosperity of organisms,the formation of high-quality source rocks,and hydrocarbon generation and accumulation.There are similarities between the“small but rich”petroliferous basins and the“small rock bodies forming large ore deposits”in terms of the formation dynamic environment and ore-forming theory.The two fields can be compared and mutually referenced in scientific research and academic thinking.