柴达木盆地北缘第三系沉积体系演化模式

Sedimentary system evolution of Tertiary reservoirs in northern Qaidam Basin,China

基于柴达木盆地北缘第三系的地质背景和构造演化,结合野外露头、岩心、测井解释和地震相特征,研究了沉积相的纵横分布特征并建立了柴北缘第三系沉积体系演化模式。结果表明:盆地边缘的马北、马西和平台地区一带主要以冲积扇和辫状河沉积为主,靠近湖盆中心的南八仙、冷湖Ⅵ号和Ⅶ号、鄂博梁等地区主要发育辫状河三角洲平原或前缘相带。路乐河组(E1+2)冲积扇较为发育,辫状河相对发育;下干柴沟组(E3)主要发育辫状河和辫状河三角洲沉积,下干柴沟组下段(E13)到下干柴沟组上段(E23)是一个辫状河向辫状河三角洲演化的水进沉积序列;上干柴沟组(N1)和油砂山组(N2)发生进一步湖侵,湖盆扩张,为辫状河三角洲前缘与滨浅湖的交互沉积。在此基础上,建立了柴北缘古近纪—新近纪从物源区向盆地中心发育的冲积扇—辫状河—辫状河三角洲—湖泊沉积体系模式,并探讨了沉积体系演化过程及其油气意义。

Based on the Tertiary geological setting and tectonic evolution of the northern Qaidam Basin in China,combined with the outcrop,core,well log interpretation and internal seismic reflection structure,this paper establishes the sedimentary system evolution model of Paleogene and Neogene and studies the transversal-longitudinal distribution characteristics of the sedimentary facies.The results reveal that in the Mabei,Maxi and Pingtai regions on the edge of the basin,there mainly develop alluvial fans and braided rivers,and in Nanbaxian,Lenghu Ⅵ and Ⅶ,Eboliang near the center of the lake basin,there develop the braided river delta front and braided river delta plain.In Lulehe Formation （E1 ＋2 ）,alluvial fans relatively develop,and braided rivers comparatively develop. In Xiaganchaigou Formation （E3 ）,the braided river and braided river delta exist extensively,and from Lower Xiaganchaigou Formation （E13 ）to Upper Xiaganchaigou Formation （E23 ）,there is the sedimentary sequence from braided river evolving towards braided river delta. Then in Shangganchaigou Formation （N1 ）and Youshashan Formation （N2 ）,there occur further lake invasion and lake basin expansion,and the sedimentary system here is the braided river delta front alternating with the shallow lake.On this basis,this paper sets up the Tertiary sedimentary system model of the northern Qaidam Basin in which the alluvial fan-braid braided river-braid braided river delta-lacustrine facies develop from the source area to the basin center,and discusses the sedimentary system evolution process and hydrocarbon significance.