元坝地区须家河组致密砂岩气藏富集主控因素

Main controlling factors of the tight sandstone gas reservoir of Upper Triassic Xujiahe Formation in Yuanba area,Sichuan,China

四川盆地元坝地区须家河组具有良好的成藏基本条件,成藏要素时空匹配关系优越,具备多层段立体勘探的良好前景。本文充分利用钻井资料及包裹体分析结果,重建元坝地区须家河组气藏的成藏过程。其成藏经历了3个阶段:1晚三叠世-中侏罗世岩性气藏成藏阶段;2晚侏罗世-早白垩世构造-岩性气藏成藏阶段;3晚白垩世-现今的调整改造阶段。通过与川中广安须家河组大气田进行类比,认为该区须家河组天然气成藏主要受3方面控制:1源储共生、优质烃源岩"近源、短距、强充注"为须家河组气藏的大面积分布奠定物质基础;2多期砂体垂向叠置、侧向复合大面积展布为须家河组气藏的大面积分布提供足够的赋存空间;3相对优质储层和伴生裂缝网络共同控制了天然气的富集高产。

The Upper Triassic Xujiahe Formation in the Yuanba area possesses basic conditions of reservoir formation, superior space-time match of reservoir-forming factors, formation of large and middle gas field and good prospect of multilayer-section exploration. Gas reservoir accumulation process of the Xujiahe Formation in the Yuanba area is reconstructed by full use of drilling data and inclusions. It reveals that three periods of reservoir accumulation processes exist. ① Late Triassic- middle Jurassic is the accumulation stage of the lithological gas reservoirs; ② Late Jurassic-early Cretaceous is the accumulation stage of structural and lithological gas reservoirs; ③Late Cretaceous- present is the adjustment and transformation stage. The study also indicates that gas reservoir formation of the Xujiahe Formation in the Yuanba area is controlled by three aspects： ① Source and storage intergrowth, high and quality source rocks are of near source and short distance with strong gas infill; ② Several circles of overlaps and lateral exhibition of sands provide abundant space- formation of the Xujiahe Formation gas reservoir; ③ Gas accumulation with high productivity is controlled by both the relative high-quality reservoir and associated fractures.