海拉尔盆地乌尔逊凹陷南部大磨拐河组油气来源及成藏机制

Oil-gas source and reservoir-forming mechanism of the Damoguaihe Formation in the southern Wuerxun Sag,Hailar Basin

自近年在海拉尔盆地乌尔逊凹陷大磨拐河组发现工业油流以来,其油气来源、成因机制及资源潜力倍受关注。系统油-油对比、油源对比表明,乌尔逊凹陷南部(简称乌南)大磨拐河组和南屯组原油物性特征、正构烷烃分布、母质类型和沉积环境相似,南屯组原油的成熟度稍高于大磨拐河组,但均属于成熟原油,并且这两个层位的原油均主要来自南屯组烃源岩。大磨拐河组油藏与南屯组油藏不具伴生性,以及储层含油包裹体颗粒指数(GOI)分布、包裹体均一温度和原油成熟度变化表明,乌南大磨拐河组油藏形成时期晚于南屯组油藏,为南屯组古油藏调整而形成的次生油藏。乌南原油具有"两期成藏、早聚晚调"的成藏特征,在伊敏组沉积中期,南屯组烃源岩生成的油短距离侧向运移,受断层遮挡聚集在同层的储层中;伊敏组沉积末期—青元岗组沉积时期盆地抬升回返,乌南次凹发生褶皱式反转作用,东翼断层活动强烈,南屯组油藏破坏,原油被调整到大磨拐河组形成次生油藏,故大磨拐河组油主要富集在反转构造上。

Since the commercial oil flow was discovered in the Damoguaihe Formation（K1d） in the Hailar Basin recent years,the hydrocarbon source,genesis mechanism and resource potential of this formation have been a focus of attention.The present paper discussed the oil genesis mechanism by making oil-source correlation and combining the gas and oil inclusions with homogenization temperature and alteration of maturity.Oil-oil correlations indicated that physical properties of crude oils,distribution of n-alkanes,parent material types and sedimentary environments of the K1d and the Nantun Formation（K1n） were very similar in the southern Wuerxun Sag.The maturity of crude oils in the K1n was a bit higher than that in the K1d,while they were both mature crude oils and might be derived from the same source.Oil-source correlations demonstrated that crude oils from these two layers mainly originated from the source rock of the K1n.The distribution of grains with oil inclusions（GOI）and maturity variations of these oils indicated that oils in K1n and K1d were not associated and the formation of oil pools in the K1n occurred earlier than that in the K1d.Oil pools in the southern Wuerxun Sag were secondary reservoirs that accumulated due to the regulation of paleo-oil pools of the K1n.Crude oils in the southern Wuerxun Sag were characterized by ＂the hydrocarbon accumulation of two periods＂ and ＂the early accumulation and the late regulation＂.During the middle period of the Yimin Formation（K1y） sedimentation,oils derived from the source rock of the K1n migrated laterally for a short distance and accumulated in reservoirs of the same layer because of the sealing of faults.At the end of the K1y and Qingyuangang Formation（K2q） sedimentation,inversion occurred in the basin and a folding inversion was generated in the sub-sag of the southern Wuerxun Sag,resulting in a strong movement of faults in the east limb,the destruction of the K1n reservoirs and the regulation of the oil from the K1n to the K1d to form secondary oil pools later,therefore,oils of the K1d were mainly accumulated on inversion structures.