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吐哈盆地水西沟群致密砂岩气成藏机制新理论——近生近储和自生自储

A new gas-accumulation theory of tight sandstone gas accumulationin Turpan-Hami Basin-proximal-generation and proximal-storage type and self-generation and self-storage type

  • 摘要: 吐哈盆地侏罗系水西沟群是一套典型的地洼型沉积建造,以反映活动型沉积的分选、磨圆很差的长石岩屑砂岩为代表,广泛发育煤层、炭质泥岩和深灰色泥岩,煤系烃源岩的广泛发育为致密砂岩气藏的形成创造了条件。为明确吐哈盆地水西沟群致密砂岩气成藏模式,通过源储配置关系及气藏特征,提出了3种成藏模式:近生近储、自生自储和复合生储。近生近储指的是砂砾岩与煤层直接接触形成天然气藏,自生自储指的是砂砾岩中的碳屑排烃形成天然气藏,而复合生储指的是有前述2种作用叠加形成的天然气藏。研究区致密砂岩气藏甜点形成受控于源储三维空间的良好匹配,在源储配置成藏时间与构造圈闭形成时间上,两者具有“源-储-圈闭-藏”完美的对应关系。成藏物质体系在相同沉积体系下通过“近生近储”生排烃及短距离运移的成藏机制下运聚成藏,甜点区在决口扇发育的沉积区和构造活动强烈的北部山前带最为发育,分布在凹陷中心边缘优质砂体发育的构造高点或圈闭褶皱中心部位,揭示了构造活动对致密砂岩气成藏也有影响,形成地洼盆地天然气成藏的一个优势。“自生自储型”成藏机制在沉积不稳定的决口扇发育区广泛分布,也是一种重要的成藏机制。此外,在盆地尚有由上述两者叠合形成的复合成藏机制。这3种成藏机制是由地洼活动型构造沉积特点所决定的,反映了地洼在成藏上的独特性,非地台所能有。

     

    Abstract: The Turpan-Hami basin is a typical basin of Diwa-type sediments in the Jurassic Shuixigou Group. The Shuixigou Group is composed of structural movement type light to black gray,poorly sorted,poorly rounded,amalgamated,fine-to coarse-grained massive grawach sandstone and fine conglomerate rock. The coal,carbonic mudstone and dark gray-black mudstone is widely developed. The objectives of this article are to document three gas-accumulation models: “proximal-generation and proximal-storage”type,“self-generation and self-storage” type and “composite type”. The gas trap of “proximal-generation and proximal-storage” type is explained to that the gas-bearing sandstone and conglomerate rock is directly contacted with coal and consequently,the natural gas formed by coal could be easily charged into the sandstone and\\or conglomerate rock overlain on the coal; The gas trap of the "self-generation and self-storage" type is explained to that the gas-bearing sandstone and conglomerate rock has more carbonic debris and consequently,the carbonic debris could directly discharge natural gas into the sandstone and\\or conglomerate rock; And the “composite-type gas” trap is that one that has the gas-accumulation features of the above two types.Tight sandstone gas reservoir in the study area controlled by source reservoir matching of three-dimensional space in the source storage configuration accumulation time and structural trap formation,possessing “the source-reservoir-trap-hidden” perfect correspondence relationship.In the same sedimentary system,the accumulation material system transported and accumulated through the mechanism of hydrocarbon generation and expulsion by near generation and near reservoir and short distance migration. between the accumulation of material system born under the same sedimentary system through nearly close to store raw under thereservoiring mechanism of hydrocarbon expulsion and short distance migration accumulation. As a main accumulation mechanism,the “proximal-generation and proximal-storage” type developed well in flood-fan-well-developed sediment units in the north piedmont belt,which have relatively good physical properties and sometimes correspond wonderfully with coal seam thickness; whereas the “self-generation and self-storage” type is also widely distributed in those sedimentary unstable splay areas where the flood-fan-well-developed sediment units,it is a kind of supplementary accumulation mechanism; Otherwise,there is still another gas-accumulation model that is formed by overlaying of the above two gas-accumulation models. These three natural gas accumulation mechanisms are decided by the structure-sediments features of Diwa-active-type and reveals that Diwa-type gas trap has itself features of the gas-accumulation that platform-type gas trap does not have.

     

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