塔里木盆地东北部中上奥陶统致密砂岩储集性能与成因

塔里木盆地东北部中上奥陶统发育了一套巨厚的砂岩、粉砂岩与泥(页)岩互层的浊积岩,其勘探前景日益引起人们的关注.通过对库鲁克塔格露头系统采样,详细研究了中上奥陶统却尔却克组砂岩的储集性和成因.却尔却克组砂岩主要为细粒长石砂岩、岩屑砂岩、岩屑长石砂岩和长石岩屑砂岩;长石颗粒、方解石胶结物的溶蚀孔隙是主要的孔隙空间,孔隙结构以微小孔-微细喉道组合类型为主;平均孔隙度1.72%,平均渗透率4.584×10-3μm2,属于特低孔低渗的储层.近物源快速沉积作用导致的低成分成熟度和中等-差结构成熟度,是却尔却克组致密砂岩形成的内在原因;较高的塑性颗粒含量和超补偿沉积导致的强烈压实作用和晚期较强的胶结作用是储层物性差的重要因素;较弱的溶蚀作用及破裂作用未能明显地改善储层的物性条件,也是形成本组低孔低渗的砂岩储层的重要原因. 

Property and origin of tight sandstones in Middle-Upper Ordovician, northeastern Tarim Basin

In the northeastern Tarim Basin,a thick set of turbidite composed of sandstone,siltstone and mudstone (shale) was found in the Middle and Upper Ordovician,attracting more and more attentions for exploration.The reservoir property and origin of sandstones from the Querquek Formation were studied in detail through systematic sampling of Kuruktag outcrops.The sandstones from the Querquek Formation mainly included fine-grained arkose,lithic sandstone,debris feldspar and feldspathic lithic sandstone.The dissolved pores of feldspar particle and calcite cement worked as the main pore space,and the pore structure was mainly micro pore and throat.The average porosity was 1.72%,and the average permeability was 4.584×10-3μm2,indicating extra-low porosity and extra-low permeability reservoir.The low compositional and mid-poor textural maturities of sandstone resulted from near source and rapid deposition were the inherent reasons for the formation of Querquek tight sandstone.The severe compaction resulted from ultra-compensation,the high content of plastic particle and the late weak dissolution were the important factors for poor physical property reservoir.The weak dissolution and fracturing did not improve the physical property of reservoir obviously,and were the important reasons for poor reservoir with low porosity and permeability.