煤成气多层系富集机制与全含气系统模式--以鄂尔多斯盆地东缘临兴区块为例

Multilayer coal-derived gas enrichment mechanism and whole gas bearing system model:A case study on the Linxing Block along the eastern margin of the Ordos Basin

鄂尔多斯盆地发育以煤成气为主要气源的多层系常规和非常规含气系统,不断在新区、新层系、新类型和新领域中取得勘探突破。为了进一步提升盆地油气勘探效率,重新认识油气地质理论,在系统剖析盆地东缘临兴区块下古生界、上古生界和中生界含气层系分布规律基础上,探讨奥陶系—三叠系的含气序列,刻画了多层含气系统形成条件及富集特征,揭示了煤成气在源岩层系滞留、源外层系富集的成藏过程,并建立了全含气系统模式。研究结果表明:①研究区发育煤系烃源岩主控的石炭系—二叠系连续型煤层气、页岩气、铝土岩天然气和准连续型致密砂岩气,圈闭条件主控的不连续型三叠系岩性—构造气藏,输导条件主控的奥陶系马家沟组碳酸盐岩气藏;②多层系气藏垂向叠置分布,形成煤系及其上覆下伏层系全含气系统,该系统受沉积、储层和输导体系等综合控制,发育连续型、堆叠型、侧叠型、孤立型等含气层;③全含气系统形成的基础是煤系生烃持续充注,核心是天然气“生—运—聚—散”动态变化,体现为常规构造—岩性气藏和非常规连续型气藏有序共生、垂向叠置,需要立体勘探开发。结论认为:①盆地天然气勘探应从源储耦合、有序聚集的视角寻找煤系及其上覆下伏地层的滞留气、近距离充注气和远距离运移气,以期实现多层系、多类型天然气有效开发;②研究成果有效指导了临兴区块天然气立体开发,为鄂尔多斯盆地和其他含煤盆地天然气持续勘探提供了参考。

Multilayer conventional and unconventional gas bearing systems with coal-derived gas as the main gas source are developed in the Ordos Basin,and exploration breakthroughs have been achieved continuously in new areas,new layers,new types and new fields in the Linxing Block along the eastern margin of the basin.In order to further improve the oil and gas exploration efficiency in the Ordos Basin and re-understand the petroleum geology theories,this paper discusses the Ordovician-Triassic gas bearing sequence and describes the formation conditions and enrichment characteristics of the multilayer gas bearing system after systematically analyzing the distribution of Lower Paleozoic,Upper Paleozoic and Mesozoic gas bearing systems.In addition,the coal-derived gas accumulation process of retertion in the source rocks and enriching outside the source rocks is revealed and a complete gas bearing system model is established.And the following research results are obtained.First,the Carboniferous-Permian continuous coalbed methane(CBM)and shale gas and quasi-continuous tight sandstone gas controlled by coal measure source rocks,the Triassic discontinuous lithologic-structural gas reservoir controlled by trap conditions,and the Carboniferous bauxitite gas reservoir and Ordovician Majiagou Formation carbonate gas reservoir controlled by transportation conditions are developed in the study area.Second,due to the vertical superimposed distribution of multilayer gas reservoir,a complete gas bearing system composed of coal measure and its overlying and underlying layers is formed,which is under the joint control of sedimentation,reservoir and transportation systems and contains various gas bearing layers,such as continuous type,stacked type,lateral superimposed type and isolated type.Third,a complete gas bearing system takes the continuous charging of coal measure hydrocarbon as the formation foundation and the dynamic evolution of natural gas"generation-migration-accumulation-diffusion"as the core and is embodied as the orderly symbiosis and vertical superimposition of conventional structural-lithologic gas reservoir and unconventional continuous gas reservoir,so its exploration and development shall be stereoscopic.In conclusion,natural gas exploration in the Ordos Basin shall aim at searching for the residual gas,short-distance charging gas and long-distance migration gas in coal measure and its overlying and underlying layers from the perspective of source-reservoir coupling and orderly accumulation,so as to achieve efficient development of natural gas of multiple layers and multiple types.What's more,the research results provide an effective guidance for the stereoscopic development of natural gas in the Linxing Block and a reference for the continuous exploration of natural gas in the Ordos Basin and other coal bearing basins.