泌阳凹陷东南部核桃园组近岸水下扇与扇三角洲沉积特征比较及控制因素分析

摘要

Coarse-grained clastic deposits are widely developed in the Hetaoyuan Formation of the steep slope belt in southern Biyang Sag of Nanxiang Basin .They together with nose-like structures in the sag form many high-quality oil and gas reservoirs .However ,the genesis of these deposits is still uncertain .The bone of contention is whether they are fan del-ta genesis or nearshore subaqueous fan genesis .To answer the question and get a better look at how they are distributed horizontally ,we compared and summarized the two geneses and discussed their controlling factors in a stratigraphic se -quence framework and from the following 6 perspectives of sedimentary settings ,subfacies and microfacies categorization , drilling and logging data,core analyses,grain size distribution features and seismic response characteristics .The results show that the steepness difference of faults caused by large boundary faulting activities controlled their genesis .Horizon-tally,fan deltas are developed in the west area with gentle faults (55°-75°) while nearshore subaqueous fans are deve-loped in the east area with steep faults(75°-90°)nearshore.Seismic profiles also show that early faults are steeper and favorable for the deposition of nearshore subaqueous fans;while later faults are more gentle and good for fan delta to be formed.%南襄盆地泌阳凹陷南部陡坡带核桃园组发育大量的砂砾岩体。这些砂砾岩体与鼻状构造配置形成该凹陷重要的油气藏。但是，前人对砂砾岩体成因的研究一直存在较大的争议，主要争论集中于砂体成因是扇三角洲成因还是近岸水下扇成因。为了明确砂砾岩体的成因及平面展布，在高精度层序地层格架建立的基础上，主要利用对比的方法，从沉积相发育背景、沉积亚相及微相划分、钻测井特征、岩心特征、粒度分布特征及地震反射特征6个方面，对这两种相类型进行了总结对比，并对控制因素进行了初步的探讨。研究结果表明，边界大断裂的活动造成的断层陡缓程度的差别对工区砂体成因类型起着重要的控制作用。在平面上，断层较缓（55°～75°）的西部地区发育扇三角洲；而在断层较陡（75°～90°）的东部地区，则发育近岸水下扇。在地震剖面上，早期断层比较陡，易沉积近岸水下扇；晚期断层比较缓，易沉积扇三角洲。