古隆起埋藏期沟谷残丘地貌下沉积体系及油气藏发育模式——以准噶尔盆地腹部石南地区清水河组一段为例

准噶尔盆地腹部下白垩统清水河组为在大型车莫古隆起埋藏期继承性地貌背景下发育的一套沉积层系，是盆地继侏罗系和三叠系后又一油气勘探热点层位，但前期有关清水河组沉积体系及油气藏类型研究均未充分考虑古隆起埋藏期地貌演化，制约了油气的有效勘探开发。研究利用岩心、测井—录井、三维地震、野外露头和分析化验资料等，在对清水河组层序地层格架厘定基础上恢复沉积期古地貌，明确储层沉积相类型及沉积体系展布，同时结合前期相关研究成果，建立大型古隆起埋藏期地貌—沉积体系演化模式，并分析其对油气藏类型的控制作用。结果表明：清水河组为一套完整的三级层序，清一段（清水河组一段）可划分为低位及湖侵体系域，而清二段（清水河组二段）则为高位体系域。受控于研究区特有的沟谷—残丘地貌特征，低位域主体为局限于沟谷内部的砾质辫状河相沉积，而环残丘边部(沟谷边缘)可发育滑塌泥石流沉积；湖侵早期研究区发育浅水辫状河三角洲前缘沉积，而湖侵晚期全区被滨浅湖相—半深湖相所覆盖。区域上，持续性差异风化剥蚀及河流侵蚀使得古隆起在晚侏罗世可作为盆地内物源而存在并逐渐演化为不同规模的沟谷—残丘，但自白垩纪开始古隆起内物源作用消失且古隆起区逐渐被覆盖，地貌也逐渐准平原化并最终演变为盆地沉积沉降中心。而受控于埋藏期沟谷—残丘地貌，古隆起区油气藏类型可划分为侏罗系古残丘型油气藏、清水河组地层超覆油气藏及构造油气藏。

Development model of sedimentary system and reservoir under valley-monadnock paleotopography during buried stage of paleouplift:Case study of 1stmember of K1q in Shinan area,hinterland of Junggar Basin

Lower Cretaceous Qingshuihe Formation (K₁q) within hinterland area of Junggar Basin is a distinctive sedimentary sequence developed during the buried stage of large-scale Chemo paleouplift.In addition to Jurassic and Triassic,K₁q becomes another favorable target for hydrocarbon exploration within the basin.However,the geomorphic evolution during the buried stage of paleouplift is not fully taken into account in previous researches about sedimentary system and reservoir types ofK₁q,leading to the restriction of effective hydrocarbon exploration and development.Thus,using core,logging,3-D seismic data,field outcrop and assay data,this research rebuilds palaeogeomorphology of the study area based on the sequence stratigraphic classification and illustrates the sedimentary facies and distribution of depositional systems.Meanwhile,in combination with previous research results,the evolutionary model of paleogeomorphy and sedimentary system during the buried stage of paleouplift is established and its control on reservoir types is analyzed.The results show that:K₁q is a whole third order sedimentary sequence,and 1st member ofK₁q can be classified into LST and TST,while 2^ndmember ofK₁q is HST.Controlled by the distinctive valley-monadnockpalaeogeomorphology,LST gravelly braided rivers were confined within the valleys,moreover,slump debris flow deposits could occur around the edges of monadnocks.During the early period of TST,sedimentary system changed into shallow-water braided delta front in study area,however,shallow to semi-deep lacustrine covered the whole area in late period.Regionally,the paleouplift existed as an intrabasinal source area during the Late Jurassic due to the continuous and differential dynamics of weathering and river incision,and gradually turned into different scales of valleys and monadnocks.Whereas the intrabasinal source system of paleouplift disappeared since Early Cretaceous.During the deposition period ofK₁q,the paleouplift zone gradually buried and the peneplanation processes of palaeogeomorphology along with subsidence eventually turned the hinterland area into depocenter of the basin.Controlled by the valley-monadnockpalaeogeomorphology,reservoir types within the paleouplift area can be classified into monadnock reservoirs of Jurassic and stratigraphic overlap and structural reservoirs of K₁q.