准噶尔盆地中央坳陷西部下组合油气成藏模式及勘探前景

准噶尔盆地中央坳陷西部下组合具备形成大油气田的有利条件，勘探程度较低，是重要的战略勘探领域。通过系统梳理中央坳陷西部下组合构造、源岩、储层及成藏要素配置关系，建立成藏模式，优选有利区带。研究认为：中央坳陷西部发育石炭系、下二叠统佳木河组和风城组、中二叠统下乌尔禾组3套规模烃源岩，其中风城组是优质碱湖烃源岩，生烃潜力大，与伸入玛湖凹陷内的下组合构造圈闭直接接触，源-储配置关系好。下组合发育火山岩、泥质白云岩和碎屑岩3类储层，在风城组区域性云质泥岩盖层的遮挡下形成有利储-盖组合。下组合普遍发育超压，埋深6 200 m以深油气相态以凝析油和天然气为主，易于形成高产。根据源-储对接关系，建立了源边披覆型、源边侧接型和源内叠覆型3种成藏模式，其中源边侧接型和源内叠覆型圈闭目的层与烃源岩之间发育大型供烃窗，成藏条件优越。评价优选盆1井西凹陷东北环带、莫索湾凸起、玛中构造带、沙湾凹陷西环带和达巴松鼻凸带等5个有利勘探区带，是下组合油气勘探获得战略突破的重要区带。

Hydrocarbon accumulation pattern and exploration prospect of the structural traps in lower play of the western Central Depression in the Junggar Basin

The lower play of the western Central Depression in the Junggar Basin is of favorable conditions to generating large-scale oil/gas fields. Given its low exploration maturity， the zone is a key to strategic exploration. Hydrocarbon accumulation models are established and play fairways are selected by systematically studying the structures， source rocks and reservoirs and sorting out the play element combinations of the lower play. The study shows that there are three suites of source rocks developed in the zone： the Carboniferous， the Lower Permian Jiamuhe and Fengcheng Formations and the Middle Permian Xiawuerhe Formation. Among others， the Fengcheng Formation is of high-quality source rocks deposited in alkali lake environment with great hydrocarbon generation potential and is in direct contact with the structural trap of the lower play that reaches into the Mahu Sag， indicating a good source-reservoir configuration. Reservoirs of volcanic rock type， argillaceous dolomite type and clastic rock type are well developed in the lower play， and a favorable reservoir-caprock combination is formed under the shelter of regional dolomitic mudstone seal in the Fengcheng Formation. Overpressure is generally seen in the lower play， where gas condensates and natural gas dominate the hydrocarbon phase at a burial depth below 6 200 m， prone to be of high productivity. In terms of source-reservoir configuration， three hydrocarbon accumulation models are established， that is， of source-edge draping type， source-edge juxtaposition type and intra-source overlapping type. Among others， the structural traps of the last two types have large hydrocarbon supply window developed between target reservoir and source rocks， favorable for hydrocarbon accumulation. Five play fairways are selected and evaluated， namely， the northeast ring belt of Penyijingxi Sag， Mosuowan Uplift Mazhong structural belt， west ring belt of Shawan Sag， and Dabasong nose-like salient zone， for strategic breakthroughs in oil/gas exploration in the lower play.