准噶尔盆地西北缘油气藏烃源示踪研究

The oil reservoirs in northwest margin of Junggar Basin have multiple source rocks and multistage accumulation history. The physical property of crude oils vary a lot. Biodegraded heavy oils are widely distributed. Restricted by objective conditions, the typical hydrocarbon source rock is not easy to obtain. There are still problems of the study on oil source in reservoirs of this area. Biomarker compositions and carbon isotopic compositions of individual n-alkanes in crude oils have the difference. And the reason are unclear. The existing research mainly focus on the biomarker and carbon isotopic composition of whole oil and group composition. Few data of carbon isotopic compositions for individual n-alkanes are reported. Molecular compositions and carbon isotopic compositions of individual n-alkanes will be systematically analyzed on crude oils from the major reservoirs in the northwest margin, Xiayan and Mosso bay area of Junggar Basin, as well as on extractions and kerogen pyrolysates of source rocks in Fengcheng formation. The results will demonstrate the variation of oil origins for the major oil reservoirs in the different area of this region, and its relation to the source kitchen distributions. The oil sources of severely biodegraded oils will be determined by analyzing the biomarker and carbon isotopic compositions of individual n-alkanes for asphaltene pyrolysates. Furthermore, sequential extraction on oil-containing reservoir rocks will be performed to reveal the source variation of oils charging the reservoirs during different episodes and its relation to the maturation histories of the main source rocks in this region.

准噶尔盆地西北缘油气聚集区多源多期成藏，原油性质差异大，稠油分布广泛。受客观条件的限制，典型的烃源岩样品不易获取，使得西北缘及腹部油源研究仍存在一定问题。不同区块油气藏原油在分子地球化学和碳同位素组成方面存在一定差异，目前造成这种差异的原因尚不明确。西北缘已有的油源研究主要针对原油分子指标和全油及族组分碳同位素组成，很少有正构烷烃单体碳同位素组成数据报道。本项目拟对西北缘断裂带、斜坡区及腹部夏盐和莫索湾地区主要油气田原油及风城组烃源岩抽提物和金管热解组分的分子和正构烷烃单体碳同位素组成特征进行系统研究，揭示原油地球化学特征的差异性及其与主要烃源岩空间展布的关系。通过稠油沥青质金管热解及对产物精细分析确定西北缘严重生物降解原油的油源。通过含油储集岩自由态、束缚态和油气包裹体组分的系统研究，揭示不同时期充注原油油源的变化及恢复油藏充注史。

准噶尔盆地西北缘油气聚集区多源多期成藏，原油性质差异大，稠油分布广泛,其油源研究仍具有一定问题。本项目通过对西北缘中二叠和上二叠统烃源岩抽提物和金管热解组分的系统研究，确定了区分上二叠风城组和中二叠下乌尔禾组两套重要烃源岩的分子和正烷烃单体碳同位素组成指标，尤其是两套烃源岩正烷烃单体碳同位素组成具有显著差异。并通过分子和单体碳同位素指标的对比，判识了西北缘断裂带、斜坡区及腹部主要油气田代表性原油的油源及其与主要烃源岩空间展布的关系，绘制了油源判识图版及油源分区图。通过稠油沥青质金管热解及对产物精细分析，确定西北缘严重生物降解原油的油源，认为其主要来自风城组烃源岩。通过含油储集岩自由态、束缚态和油气包裹体组分的成熟度变化，推断玛湖凹陷中部三叠系百口泉组油气充注期介于晚侏罗世-白垩纪之间，盖层的封闭性是控制这类油气藏成藏的重要因素。该研究精细厘定了二叠系两套重要烃源岩生成的油气分布范围，对准噶尔盆地寻找新的油气勘探突破具有重要意义。