四川盆地龙岗气田雷四~3亚段风化壳气藏特征及其主控因素

龙岗气田雷四3亚段气藏是四川盆地中三叠统雷口坡组新发现的与印支期剥蚀和岩溶作用有关的气藏,弄清该气藏的特征及控制因素,将极大地拓展四川盆地雷口坡组的勘探领域。为此,基于区域地层对比、小层划分、沉积相、储层特征及气藏特征等综合研究成果,分析得出以下结论性认识:1雷四3亚段的储层发育于其顶部a小段,风化剥蚀作用控制了a小段储层的分布及溶蚀孔洞的发育;2a小段储层岩性以泥、粉晶角砾云岩为主,次为泥粉晶针孔云岩,物性为低—特低孔隙度、特低渗透率,孔隙类型主要为基质孔隙、裂缝和溶蚀洞穴,台内滩沉积微相控制了储层的发育;3在大型地层尖灭的背景下,受构造、断层和岩性变化的影响,发育地层—构造、岩性—构造等多种圈闭类型;4气藏烃源以上三叠统须家河组为主,生储盖组合以侧生侧储和上生下储为主,次为下生上储,其气水关系复杂,存在多个水动力系统;5雷四3亚段a小段尖灭带附近的次级岩溶斜坡是寻找工业气井的最有利区。

Characteristics and major controls of weathering crust gas reservoirs in T2l43 in the Longgang Gas Field,Sichuan Basin

Gas reservoirs inT₂l₄³ (the third interval of the 4^th member of Middle Triassic Leikoupo Fm) in the Longgang Gas Field of the Sichuan Basin are new discoveries related to the erosion and karstification during the Indosinian period. A clear understanding of the characteristics and controlling factors of the gas reservoirs will greatly broaden the exploration domain of the Leikoupo Fm in the Sichuan Basin. In view of this, a comprehensive study was performed on regional stratigraphic correlation, layer subdivision, sedimentary facies, reservoir characteristics and gas reservoir features, which led to the following conclusions. (1) TheT₂l₄³ reservoirs are developed in its upper most “a” interval. The distribution of the reservoirs and development of dissolution pores and caverns are controlled by weathering and erosion. (2) The reservoirs in the “a” interval are dominated by micritic to powder crystalline breccia dolomites, followed by muddy pinhole dolomites. They have low ultralow porosity and ultralow permeability. The pore types are dominantly matrix pores, fractures and dissolution cavities. Sedimentary microfacies of intra platform beaches control the reservoir development. (3) In a large scale stratigraphic pinchout setting, various types of traps such as stratigraphic and lithologic structural traps are developed under the joint influences of structures, faults and lithologic variations. (4) The source rocks of gas reservoirs are dominated by the Upper Triassic Xujiahe Fm. The source reservoir cap rock combinations are mainly lateral generation & lateral accumulation and upper generation & lower accumulation, followed by lower generation & upper accumulation. The gas water contact is very complex and there are several hydrodynamic systems. (5) The secondary karst slopes near the pinchout zone of the “a” interval inT₂l₄³ is the most favorable area for gas exploration.