箕状断陷湖盆湖底扇特征及油气勘探——以二连盆地赛汉塔拉凹陷腾格尔组二段为例

Characteristics of sublacustrine fan in half-graben rift lake basin and its petroleum prospecting: Case study on the second member of Tenggeer Formation,Saihantala Sag,Erlian Basin

以二连盆地赛汉塔拉凹陷为例,通过对腾格尔组二段湖底扇砂岩体的岩石学、结构、构造等特征的分析,认为赛汉塔拉凹陷湖底扇比较发育,具有典型浊流沉积所形成的鲍马序列以及非典型浊积岩"AAA"、"ABABAB"序等沉积特征,在沉积结构上具有典型浊流沉积的粒度分布特征,并具有丰富的浊流沉积构造现象。湖底扇主要发育在凹陷缓坡带扇三角洲前缘同沉积断裂形成的断裂坡折带下部,以及陡坡带控盆边界断裂下降盘的近岸水下扇沉积前端的洼槽区。湖底扇的形成与同沉积断裂的长期活动密切相关,规模大小受断裂活动、古地貌坡度、物源供应等因素控制。湖底扇砂岩体具有毗邻烃源岩,易形成岩性圈闭,油气运移和聚集条件好等优越条件,对油气勘探具有重要的意义。

Analysis is made on petrology,texture and structure of sublacustrine fan sand bodies in the second member of Tenggeer Formation.The sublacustrine fan develops well,and it is characterized by the Bouma sequence resulted from typical turbidite deposit and the AAA and ABABAB sequences of non-typical turbidite.For depositional texture,it features grain distribution of typical turbidite deposit and contains abundant turbidite deposit structures.The sublacustrine fan mainly develops in the lower part of the fault slope break formed by synsedimentary faulting in the fan delta front of gentle slope in the sag and in the troughs in front of offshore subsea fan deposit in the down-throw of faults at boundary of the basin controlled by abrupt slope.The forming of the sublacustrine fan is closely related to the long period synsedimentary faulting activities,and the scale is controlled by the fault activity,slope gradient of palaeogeomorphology and the supply of deposit.The sublacustrine fan sand bodies are adjacent to source rocks,they are easy to form litholohic traps and favorable for petroleum migration and accumulation,which is significant for the petroleum prospecting.