柴达木盆地英雄岭构造带古近系湖相碳酸盐岩沉积模式、演化与分布

基于野外露头、钻井、岩心、岩石薄片及实验数据,对柴达木盆地英雄岭构造带古近系下干柴沟组上段湖相碳酸盐岩的类型、演化规律和沉积模式进行了系统研究,并结合井-震资料分析和古地貌恢复,对其岩相古地理的平面分布特征进行了刻画,指出了下一步的有利勘探方向。研究表明:英雄岭构造带下干柴沟组上段主要发育藻灰岩、颗粒灰质白云岩、泥晶灰质白云岩3类碳酸盐岩,多具有混积特征,从早至晚经历了半咸化、咸化和盐湖3个沉积演化阶段;由于矿物组分及岩石结构的差异,湖相碳酸盐岩的储集性能呈现较强的非均质性,其中,藻灰岩的储集性能相对最好;储层的岩相组合在垂向上主要存在3种类型,分别发育于湖盆的不同位置。研究建立了凹隆型和缓坡型2种沉积发育模式,指出湖平面的升降频率及陆源碎屑输入量控制不同岩相的单层厚度,微古地貌控制不同岩相组合的平面分布。恢复的下干柴沟组上段沉积早、晚期的岩相古地理特征显示,泥晶灰质白云岩+颗粒灰质白云岩组合主要分布在英西—干柴沟—游园沟缓坡沿岸区和隆起区,其平面叠合面积约为600 km²,是下一步寻找常规油气藏的有利勘探方向;纹层泥晶灰质白云岩主要分布在游园沟及其以东地区的半深湖相凹陷区,其平面叠合面积可达2 500 km²,是下一步寻找非常规源内油气藏的有利勘探方向。

Sedimentary model,evolution and distribution of Paleogene lacustrine carbonate rocks in Yingxiongling structural belt,Q aidam Basin

Based on field outcrops, boreholes, cores, thin sections and experimental data, this paper systematically studies the type, evolution and sedimentary model of lacustrine carbonate rocks from the Upper Member of Paleogene Xiaganchaigou Formation in Yingxiongling structural belt of Qaidam Basin and characterizes the lithofacies paleogeographical distribution combined with borehole-seismic data analysis and paleogeomorphology restoration, and points out the next favorable prospecting direction. The study shows that the Upper Member of Xiaganchaigou Formation in Yingxiongling structural belt is dominated by three types of carbonate rocks, i.e., algal limestone, granular calcareous dolomite and micritic calcareous dolomite, most of which have hybrid sedimentation characteristics, and have undergone three sedimentary evolution stages from early to late, namely brackish water, saline water and salt lake. Lacustrine carbonate reservoirs present the strongly heterogeneous properties due to the difference of mineral composition and rock texture, among which algal limestone has the best reservoir performance. There are three types of vertical lithofacies assemblages in reservoirs, which are developed in different positions of the lacustrine basin. Two sedimentary models, namely sag-uplift and gentle slope, were established. It is revealed that the lake level fluctuation and input of terrigenous detritus controlled the single layer thickness of different lithofacies, and the micro-paleogeomorphology controlled the distribution of different lithofacies assemblages. The early and late lithofacies paleogeographic characteristics of the Upper Member of Xiaganchaigou Formation show that the assemblage of micritic calcareous limestone and granular calcareous dolomite is mainly distributed in the coastal area and uplift area of Yingxi-Ganchaigou-Youyuangou gentle slope, with a superposition area of about 600 km², indicating a favorable exploration direction for the next prospect for conventional oil and gas reservoirs. Laminated micritic calcareous dolomite is mainly distributed in the semi-deep lacustrine sag of Youyuangou and its east area, with a superposition area of up to 2 500 km², providing is a favorable exploration direction for the next prospect for unconventional intra-source oil and gas reservoirs.