库车坳陷迪北地区下侏罗统天然气富集机制

库车坳陷迪北地区下侏罗统致密砂岩气藏广泛发育, 对其富集机制的研究具有重要意义.通过岩心和薄片观察、激光共聚焦扫描、排替压力测试、包裹体岩相学观察、显微测温等方法, 探讨了迪北地区下侏罗统天然气富集机制.研究表明: (1)迪北地区气源条件优越, 天然气快速充注; (2)迪北地区裂缝-孔隙型储层广泛发育, 储集性能优越; (3)迪北地区上覆多套厚层泥岩和膏泥岩盖层, 天然气保存条件好; (4)迪北地区断裂-砂体复合输导体系发育, 天然气高效捕获成藏; (5)迪北地区具有"早油晚气"的油气充注特征, 天然气在库车期到现今(5~0 Ma)大量充注, 储层在前康村期(约8 Ma)致密化, 即储层致密化时间早于天然气大量充注时间.因此, 在构造活动控制下, 天然气聚集成藏经历了中新世早中期原油充注、上新世以来致密深盆气藏叠加和西域期以来的致密气藏调整改造再富集3个阶段.对迪北地区天然气富集机制的研究, 有利于进一步寻找有利区, 指导致密砂岩气勘探. 

Enriched Mechanism of Natural Gas of Lower Jurassic in Dibei Area,Kuqa Depression

Tight sandstone gas of the Lower Jurassic is widely developed in Dibei area in the Kuqa depression. Therefore, the research of its enriched mechanism is of great significance. The data of the cores, rock slice, laser confocal scanning, displacement pressure, fluid inclusion petrological observation and microthermometric analysis are utilized to explore the enriched mechanism of the natural gas. Results show that: (1) the gas-source condition of Dibei area is superior and natural gas charged in short time; (2) fracture-pore type reservoir is widely developed and reservoir property is superior; (3) several thick mudstones and gypsum mantles cover the natural gas reservoirs and the conservation condition of the natural gas is superior; (4) composite fault-sand body pathway system is well developed and the natural gas accumulated with high-efficiency; (5) Dibei area is characterized by "early-stage accumulation of oil and late-stage accumulation of gas". The natural gas charged in the period of Kuqa age (5-0 Ma) and reservoir desificated in the period of early Kangcun period (8 Ma), which means that the period of reservoir desification was earlier than the period of bulk natural gas charging. Controlled by tectonic movement, the accumulating processes of the natural gas are separated into three phases: charged with oil at the early-middle periods of the Miocence; charged with the superposition of deep basin gas reservoir in Pliocene; charged with adjustment, modification and re-enrichment in Xiyu period. The study of enriched mechanism of the natural gas in Dibei area can facilitate the exploration for potential tight sandstone gas.