柴达木盆地西部大风山地区古近系下干柴沟组下段物源方向研究

目前普遍认为柴达木盆地西部大风山地区古近系下干柴沟组下段(E13)只发育向西南方向流动的牛鼻子梁物源所形成的冲积扇-河流-辫状河三角洲-湖泊沉积体系,对于物源方向的这种认识难以解释以下事实:第一,风2井在E31发育厚层辫状水道砂岩,而位于上倾方向碱1井的对应层位则发育薄、中厚层河口砂坝砂和分流水道砂;第二,在E13沉积时,牛鼻子梁地区是阿尔金山向东南方向延伸的古鼻梁,该古鼻梁是牛鼻子梁以北地区物源向西南方向流动的屏障;第三,牛参1井位于长期继承性发育的一里坪凹陷的西北边缘,大风山地区的古地貌要高于一里坪凹陷;第四,坪东F1断层与坪东F2断层所夹持的区域在E31时是一个继承性发育的小型断陷。在综合研究该地区的钻井、测井、二维地震资料和古地理背景的基础上,首次提出在E13沉积时,大风山地区的物源来自红三旱一号以北地区,而一里坪坳陷是牛鼻子梁物源汇聚区的新认识。这一新认识对于重新认识大风山地区的沉积体系及寻找优质有效碎屑岩储层具有重要的勘探实践意义。

Study on sedimentary provenances of the lower segment of Ganchaigou formation at Dafengshan area,Qaidam basin

It is universally accepted that there is only Niubiziliang sedimentary provenance in the lower segment of Ganchaigou formation(E13) at dafengshan area.Provided however,there are some problems not be resolved in this viewpoint.Firstly,in the E13,there is thick braided river sand in well F2,but in well J1 in the upper of well F2,there are folium bar sands and distributary river sands;secondly,in E13,Niubiziliang area is a old heave in the southeast Aerjin mountain.It is this old heave that hinders the water flows to the southwest.Thirdly,well NC1 lies in the northwest edge of Yiliping de-pression,whose position is higher than that in the east.Fi-nally,the area between the faults of Pingdong No.1 and No.2 is a depression in the E13.Because analysis data is poor in the study area,it is pointed out at the first time that the sed imentary provenances at Dafengshan area come from the north of Hongsanhanyihao and Yiliping depression.This new viewpoint is helpful to recognize sedimentology system at Dafengshan area and to search for high quality clastic rocks.