渤海辽西凸起中北段变质岩潜山地层年代学特征和储层发育主控因素

Chronological characteristics of metamorphic buried hill strata and main controlling factors of reservoir development in the middle and northern section of Liaoxi Uplift,Bohai Bay Basin

辽西凸起中北段发育前寒武纪变质岩潜山地层,精确厘定潜山年代、岩性和储层发育主控因素是潜山精细勘探的必然要求。矿物定量分析和锆石U-Pb定年分析结果表明,辽西凸起中北段前寒武纪变质岩可进一步细分为太古宙变质花岗岩和古元古代变质花岗岩,两者在岩性、矿物组成上存在差异,其中以J25-AS潜山地层为代表的凸起中部以富长石、角闪石的变质花岗岩类为主,形成年代为太古宙2506~2529 Ma;以J20-B潜山地层为代表的凸起北部以富石英、黑云母的变质花岗岩类为主,形成年代为古元古代2477~2497 Ma。按矿物组成、裂缝发育及溶蚀程度,辽西凸起中北段前寒武纪变质花岗岩储层分为3种类型,分别为以角闪石为主的中等暗色矿物含量-裂缝发育-强溶蚀型、低暗色矿物含量-强裂缝发育-弱溶蚀型、以黑云母为主的高暗色矿物含量-裂缝充填-较弱溶蚀型,前两者有利于形成有效储层。辽西凸起中北段前寒武纪变质岩有效储层的发育程度受控于暗色矿物含量及类型、风化淋滤、构造作用3个关键因素,其中暗色矿物含量及类型是核心主控因素,风化淋滤和构造作用次之。

Precambrian metamorphic buried hill is developed in the middle and northern section of Liaoxi Uplift.Accurate age determination of buried hill,lithology and main controlling factors of reservoir development are inevitable for the fine exploration of buried hill.Results of mineral quantification analysis and zircon U-Pb dating show that Precambrian metamorphic rock in the middle and northern section of Liaoxi Uplift can be further subdivided into Archean metamorphic granite and Palaeoproterozoic metamorphic granite,which are different in lithology and mineral composition.The middle part represented by the buried hill of J25-AS is dominated by metamorphic granite rich in feldspar and hornblende,with the formation age of 2506-2529 Ma during the Archean era,and the northern part represented by the buried hill of J20-B is dominated by metamorphic granite rich in quartz and biotite,with the formation age of 2477-2497 Ma during the Paleoproterozoic era.According to mineral composition,crack development and dissolution degree,Precambrian metamorphic granite reservoir in the middle and northern section of Liaoxi Uplift can be divided into three types:medium dark mineral content dominated by hornblende-crack development-strong dissolution,low dark mineral content-strong crack development-weak dissolution,and high dark mineral content dominated by biotite-crack filling-weaker dissolution,among which the first and second types are conducive to the formation of effective reservoir.The effective reservoir development of Precambrian metamorphic rock in the middle and northern section of Liaoxi Uplift is mainly controlled by three important factors of dark mineral content and type,weathering and eluviation,and tectonism.Dark mineral content and type are the core controlling factors,followed by weathering,eluviation and tectonism.