海-塔盆地塔南凹陷南屯组一段沉积体系特征

Depositional system characteristics of the first member of the Nantun Formation in Tanan sag,the Hai-Ta Basin

塔南凹陷是海拉尔-塔木察格盆地最重要的油气勘探地区之一。利用岩心、测井和三维地震等资料,对塔南凹陷南屯组一段层序地层格架和沉积体系特征进行了深入研究。结果表明,南屯组一段顶、底及内部可以识别出3个不整合面和2个湖泛面,最终将其划分为3个三级层序。进而在等时地层格架的基础上,对沉积相类型和沉积体系展布特征进行了分析,确定南屯组一段主要发育扇三角洲、湖底扇和湖泊3种沉积体系。南屯组一段中、下部沉积时期,受盆地被动裂谷期"泛盆"沉积特征震荡式沉降影响,研究区主要发育西部缓坡物源控制下的扇三角洲沉积体系;南屯组一段上部沉积时期,受盆地主动裂谷期快速沉降影响,研究区主要发育湖泊沉积体系,此时盆内部次级控陷断层受北西-南东向拉张发生翘倾形成大规模反向正断层。源-储互层组合高效排烃特征、扇三角洲前缘高孔-高渗分流河道砂体和断层翘倾形成上升盘构造高部位共同决定西部次凹中洼槽反向断层下盘为油气富集主要部位。

Tanan Depression is one of the most important oil and gas exploration areas in Hailaer-Talmud Zagat Basin. Various data including cores, logs and 3 D seismic data were integrated to study in detail the sequence stratigraphic frame- work and sedimentary system characteristics of K1 nl（ the 1st member of Nantun Fm）in Tanan Sag, Haita Basin. Three un- conformites and two lake flooding surfaces were identified in K1 n1 ,according to which K1 n1 was divided into three third- order sequences. The types of sedimentary facies and distribution characteristics of sedimentary system were analyzed on the basis of isochronous stratigraphic framework. Three sedimentary systems namely fan delta, sublacustrine fan and lake were identified in the Kx n~. Fan delta sedimentary system under the control of provenance on the western gentle slope dominated in the study area during the deposition of the middle-lower part of K1 nI due to the influences of oscillatory sub- sidence of＂ flood basin＂ during passive rifting. In contrast, lake deposition system was predominant in the study area dur- ing the deposition of the upper part of KI n1 due to the rapid subsidence in the process of active rifting. At the same time, the secondary depression-controlling faults experienced NW-SE extension and tilted, forming large-scale reverse normal faults. Efficient hydrocarbon expulsion characteristics of interbeded source rock and reservoir combination, high porosity and permeability of distributary channel sands of fan delta front facies and structural high in the upthrown block of fault jointly determined the footwall of antithetic fault in the western subsag to be the main location of oil accumulation.