四川盆地“槽-隆”控制下的寒武系筇竹寺组页岩储层特征及其差异性成因

Characteristics and differential origin of Qiongzhusi Formation shale reservoirs under the“aulacogen-uplift”tectonic setting,Sichuan Basin

四川盆地寒武系筇竹寺组是继五峰组-龙马溪组后页岩气勘探开发的重要接替层位,目前在德阳-安岳裂陷槽中心和槽缘部署的Z201井和WY1井页岩气勘探取得良好效果,但裂陷槽内筇竹寺组页岩储层发育特征仍不清楚。以槽内中心Z201井和槽缘WY1井为重点,结合其他页岩气勘探开发资料,系统分析了研究区筇竹寺组页岩各小层矿物特征、有机地化特征、储层及储集空间特征、含气性特征。研究结果表明:①筇竹寺组可划分为8个小层,页岩整体以脆性矿物为主,总有机碳含量(TOC)普遍大于1%,为优质烃源岩,且槽内TOC高于槽缘,具备良好的生气条件。②筇竹寺组页岩有机孔与无机孔均发育,槽内孔隙发育更好,具有极高的含气量。1,3,5和7小层黑色页岩储层品质较好,5小层储层品质最优。③德阳-安岳裂陷槽控制了筇竹寺组页岩储层发育,槽内Z201井钻遇的筇竹寺组页岩储层优于槽缘WY1井。④乐山-龙女寺古隆起控制筇竹寺组页岩有机质演化程度,古隆起内筇竹寺组有机质热演化成熟度普遍低于古隆起外,隆起区适中的热演化程度具备大规模富气的条件。筇竹寺组页岩储层各项条件较好,是未来页岩气勘探开发的主要接替区域。

The Qiongzhusi Formation,following the Wufeng-Longmaxi formations,has been recognized as a promising target for future shale gas exploration and exploitation in the Sichuan Basin.Presently,notable achievements have been made in shale gas exploration in wells Z201 and WY1,drilled at the center and margin of the Deyang-Anyue aulacogen,respectively.However,there is a lack of clear understanding of the Qiongzhusi Formation shale reservoirs occurring in the aulacogen.Focusing on wells Z201 and WY1,coupled with other data on shale gas exploration and exploitation,we systematically analyze the mineral and organic geochemical characteristics,reservoir and storage space characteristics,and gas-bearing properties of each shale in the Qiongzhusi Formationin the study area.Key findings are outlined as follows.(1)The Qiongzhusi Formation shales in the study area can be divided into eight layers,predominantly composed of brittle minerals overall.This formation generally exhibits total organic carbon(TOC)content exceeding 1%,suggesting high-quality source rocks.Furthermore,the TOC content is higher within the aulacogen than on its margin,indicating favorable gas generation conditions.aulacogen(2)Both organic and inorganic pores are found in the Qiongzhusi Formation shales,more prevalent within the aulacogen,contributing to extremely high gas content.Black shale reservoirs in layers 1,3,5,and 7 exhibit high quality,especially the layer 5.(3)The quality of shale reservoirs in the Qiongzhusi Formation is governed by the Deyang-Anyue aulacogen.Specifically,reservoirs encountered in drilling well Z201,situated within the aulacogen,exhibit superior characteristics compared to those in well WY1 located at the margin.(4)The degree of organic matter evolution in the Qiongzhusi Formation shales is significantly influenced by the Leshan-Longnvsi paleo-uplift.The organic matter generally tends to be less mature within than outside.The moderate-degree organic matter evolution within the paleo-uplift creates conditions favorable to large-scale gas enrichment.Therefore,high-quality Qiongzhusi Formation shale reservoirs are identified as a major successor play for future shale gas exploration and exploitation.