被动裂陷盆地油气分布规律及主控因素分析——以塔木察格盆地塔南坳陷为例

The law of oil and gas distribution and mainly controlling factors of the passive rift basin:The Tanan depression of Tamuchage Basin

塔南凹陷为典型的被动裂陷盆地,构造演化历经了4个阶段:即被动裂陷阶段、主动裂陷阶段、断一坳转化阶段和坳陷阶段,形成两套含油气系统:即被动裂陷含油气系统和主动裂陷含油气系统,油气主要富集在被动裂陷含油气系统中。油气分布的主控因素概括为3个方面:1)是区域性盖层和长期发育的断层控制油气聚集的层位,盆地发育南一段上部和大一段两套泥质岩区域性盖层,厚度大,泥地比高,控制了两套含油气系统油气富集,长期发育的断层在盖层段形成剪切型泥岩涂抹,当SSF值大于5时,泥岩涂抹失去连续性,油气穿越区域性盖层垂向运移,在大二段聚集,形成次生油气藏。2)是有效烃灶和优质储层控制油气分布范围,主动裂陷阶段和被动裂陷阶段均发育一套烃源岩,被动裂陷阶段烃源岩为砂泥互层结构,排烃效率高,为优质烃源岩。大气水的淋滤作用和有机酸溶解作用分别在反向断层下盘和洼槽内部形成优质储层,油气短距离侧向运移,油气分布具有典型的"源控"和"优质储层控制"的特征。3)是反向断层、低隆起和扇体控制油气聚集,被动裂陷阶段构造沉降和翘倾作用形成大量反向断层,具有"三期同步造储"、"三面组合成藏"和"三类复合控油"成藏优势,成为被动裂陷油气系统典型的成藏模式。被动裂陷阶段形成反向断层下盘低隆,主动裂陷阶段形成中央背斜带,盆地回返阶段形成反转构造带,分别为两套含油气系统和次生油气系统油气富集提供有利场所。近岸水下扇在洼槽中心聚油,形成岩性油气藏。

Tanan depression is a typical passive rift basin,and has four tectonic evolution stages：passive rift stage,active rift stage,faultdepression conversion stage and depression stage,as well as two petroleum systems：the passive rift petroleum system which oil and gas mainly occur and active rift petroleum system.The major controlling factors of oil and gas distribution have three aspects.First of all,the regional cover and longterm development of fault control the layer of oil and gas accumulation.The Basin has two mudstone regional covers： Nan1 section and Da1 section,which has high thickness and mud ratio,controlling the oil and gas accumulation of two petroleum systems.The longterm development of fault forms shale smear of shearing type at the cover.When the SSF is greater than 5,shale smear losts the continuity and oil and gas which through the regional cover occur vertical migration,accumulating at Da2 section,as well as forming secondary reservoir.Second,the effective hydrocarbon kitchen and good reservoir control the scale of oil and gas distribution,while active and passive rift stage both develop a set of hydrocarbon source rock.The passive rift stage of hydrocarbon source rock has interbedded sand and mud structure,so the expulsion efficiency of hydrocarbon is high,which is highquality source rock.The role of atmospheric water washout filter and organic acid dissolution is that forms a highquality reservoir,respectively,at the footwall of antithetic fault and trough,so oil and gas occur a short distance lateral migration.Oil and gas distribution has typical characteristics,such as “source control” and “highquality reservoir control”.The third is the antithetic fault,the lower uplift and the fan complex control the gas accumulation.There are many antithetic faults resulting from the tectonic subsidence and the tilting at the stage of passive rifting,and they have the advantages as “three phases the synchronous productresevoir”,”three aspects compose the play” and“three types compoundly control the gas”are favour of forming the reservoir,so they are the typical reservoir model for the passive rift basin.The passive rift stage resut in the bottom wall of the antithetic fault low upward,the initiative rift stage result in the central anticlinal zone,and the reversion stage of the basin result in the reverse structure zone,and they provide place for two different hydrocarbon and secondary gas system to accumulate gas respectively.The onshore subsea apron accumulate gas in the central of depression,and formed the lithologic hydrocarbon reservoirs.