四川盆地北部陆相大气田形成与高产主控因素

Key controls on accumulation and high production of large non-marine gas fields in northern Sichuan Basin

基于大量样品分析测试资料和勘探实践,探讨四川盆地北部元坝、通南巴等地区陆相须家河组—自流井组天然气成藏与富集高产控制因素。四川盆地北部地区陆相层系天然气主要源自同层系烃源岩,烃源岩有机质丰度高,达到较好—好烃源岩标准,有机质类型以Ⅲ型为主,整体处于高—过成熟生气阶段。受物源影响,研究区发育多期(扇)三角洲体系,主河道砂体多期叠置、大面积分布,储集层与烃源岩形成下生上储和互层式成藏组合。根据对九龙山、马路背、元坝3个地区5口典型高产井的解剖分析,提出研究区勘探与研究的整体思路:沉积物源控制岩石类型、胶结类型、沉积微相;烃源岩控制成藏规模和气藏位置;构造类型控制裂缝发育的规模、发育的部位;裂缝和储集层的匹配控制产量的高低和稳产时间。依此模式预测元坝地区西部和剑阁地区须三段、须四段,元坝中东部地区须四段、自流井组及通南巴构造马路背、河坝场地区珍珠冲段、须二段,是天然气富集高产的主要区块。

Based on the data from multiple sample analysis and tests and exploration practice, key factors controlling gas accumulation, enrichment and high production in the continental Triassic Xujiahe--Jurassic Ziliujing formations in Yuanba, Tongnanba and other areas, northern Sichuan Basin, were discussed. Natural gas in continental strata in this part of the basin are derived from the source rocks in the same strata, which are good - very good source rocks with high abundance of organic matter （mostly type III） and generally in high mature - overmature gas generating stage. Depending on provenance, multi-period （fan） delta systems are developed in the research area, where the main fluvial channel sands are superimposed in multi periods and distributed extensively, and reservoirs and source rocks form the ＂lower generation and upper storage＂ and ＂inter-bedded＂ assemblages. Five typical high-yield wells in the Jiulongshan, Malubei and Yuanba areas are investigated and an overall concept for exploration and research in the area is proposed： sedimentary source controls rock types, cementation types and sedimentary microfacies; source rocks control the size and location of gas accumulation; structural types control the magnitude and location of fractures; the combination of fracture and reservoir determines the level and retention duration of gas production. According to this model, the following areas have enriched gas and high production： Xu-3 and Xu-4 members of Xujiahe Formation in the western Yuanba and Jiange, Xu-4 member and Ziliujing Formation in the mid-eastern Yuanba, Zhenzhuchong and Xu-2 members in Malubei and Hebachang areas in the Tongnanba structure.