柴达木盆地北缘侏罗系沉积相类型及储集层评价

Sedimentary facies type and reservoir evaluation for the northern Qaidam basin.

柴达木盆地东部三湖地区第四纪湖相沉积面积达1× 1 0 4km2 以上 ,第四系厚度最大为 34 0 0m ,其中 ,下更新统涩北组中上段的泥岩夹粉砂岩段是该区的主力气源岩 ,也是原生构造型气藏发育层段。目前的勘探和研究成果表明 ,该区第四系局部构造属同沉积构造 ,其形成虽受深层第三纪古构造和古地形影响 ,但第四纪变形的边界控制条件不同。采用遥感解译手段 ,结合地震剖面研究 ,认为三湖地区第四系局部构造的形成受盆地北侧边界断裂的影响更大 ,变形动力主要来自盆地北缘 ,构造分布在一定程度上受盆地边界断裂、盆内主干断裂等控制 ,根据主干断裂的分布特征可推测局部构造的分布位置。柴达木盆地北缘侏罗系可划分为 3个层序。层序Ⅰ :早侏罗世盆地具明显的断陷性质 ,边界断层控制物源供给和沉积相的类型及展布 ,发育近岸浊积扇—湖泊沉积体系和扇三角洲—湖泊沉积体系 ,在湖盆中央凹陷区发育滑塌浊积扇。层序Ⅱ :中侏罗世早中期湖盆由断陷转化为坳陷 ,地势较平缓 ,陆源碎屑供给较少 ,广泛发育湖泊和沼泽沉积。层序Ⅲ :中侏罗世晚期至晚侏罗世 ,气候变干旱 ,湖盆由原先的坳陷转为挤压 ,发育冲积扇、河流和氧化滨浅湖沉积。盆地北缘侏罗系储集层总体为低孔低渗储集层 ,但在局部地区有机酸大量产生的溶解带。

The Jurassic system is divided into 3 sequences in northern Qaidam basin of China: (Ⅰ)Faulted-down obviously displayed in the early Jurassic basin, and source of material and type of sedimentary facies as well as their distributions were controlled by boundary fault activity, and nearshore turbidite fan-lacustrine and fan delta-lacustrine depositional systems developed in the early Jurassic, and slump turbidite fan developed in central depression;(Ⅱ)Lacustrine and marsh sediments widely developed in middle Jurassic. Basin changed from faulted-down to depression in this period, with a topography gent, and terrigenous clastics less and (Ⅲ)Alluvial fan, river and oxidized littoral and shallow lake developed in late period of middle Jurassic and late Jurassic, when climate changed from humid to arid, and the nature of basin changed from depression to compression. The Jurassic reservoirs are marked by low-porosity and low-permeability clastic rocks.But the quality of reservoirs is improved in areas of producing generous organic acid and nearby surface of unconformity and fracture zone.