徐家围子断陷安达凹陷沙河子组层序四沉积相研究及勘探意义

STUDY ON THE SEDIMENTARY FACIES AND ITS EXPLORATORY SIGNIFICANCE FOR SHAHEZI FORMATION SEQUENCE SQ4 IN ANDA SAG OF XUJIAWEIZI FAULT DEPRESSION

徐家围子断陷安达凹陷沙河子组致密砂砾岩是大庆油田致密气勘探的重点层系之一。其从下至上发育4个三级层序,SQ1分布局限,SQ2、SQ3以暗色泥岩和煤层为主,最上部SQ4砂砾岩最为发育,成藏条件优越。通过砂岩成分成熟度和成像测井分析,揭示了沙河子组SQ4沉积时期受东西两大物源控制。根据古地貌形态、水体能量的控制因素分析,结合研究区9口取心井资料和28口钻测井资料,阐明了安达凹陷SQ4时期主要发育辫状河三角洲、扇三角洲和湖泊相三种类型。其中水下分流河道形成的砂砾岩体是最有利储集类型,湖退环境下形成的河口砂坝和前缘席状砂有可能成为后期湖区勘探的潜在目标。

The tight glutinite zones developed in Shahezi Formation of Anda Sag in Xujiaweizi Fault Depression are one of the important serieses in the tight gas exploration of Daqing Oilfield.From bottom to top,four third-grade sequences are developed;SQ1 is limited,SQ2 and SQ3 are mainly composed of the dark mudstone and coal,SQ4 conglomerate is most developed on the top and has excellent reservoir accumulating conditions.By analyzing the sandstone compositional maturity and imaging logging data,it is revealed that during the deposition of Shahezi Formation SQ4,the sag is controlled by two great provenances from east to west.According to the analyses of the ancient topography and controlling factor of the water energy,combining with 9-well coring data and 28-well log data within the study area,it is clarified that there kinds of the facieses are principally developed in the above period：braided river delta、fan delta and lake.Among them,the glutenite body developed in the underwater distributary channel is the most favorable reservoir accumulation type,the mouth dams and front sheet sands formed in the lake retreating environment may become the potential targets in the later exploration stage of the lake area.