塔里木盆地碎屑岩优质储层特征及成因分析

塔里木盆地碎屑岩储层发育,主要分布于石炭系底部的东河砂岩,三叠系、侏罗系底砂岩和白垩系、下第三系底砂岩等。碎屑岩储层以孔隙型占绝对优势,少量裂缝型;孔隙有两种类型,中生界以上地层以原生孔为主;古生界则以次生孔为主,次生孔中以粒间溶孔和粒内溶孔为主。成岩作用类型多,但以表生淋滤作用、低成熟有机释放酸的溶蚀作用和深层热化学硫酸盐还原反应产生部分酸的溶蚀和沉淀作用对储层物性影响最大。对塔里木盆地碎屑岩深埋优质储层成因进行了探讨。认为塔里木盆地具特殊的地质条件,低的地温梯度,新第三纪后的快速沉降短期深埋,酸性地层水对岩石颗粒和基质的溶蚀,多次构造运动形成不整合面和断裂系统改善了储集层的性能,有利的沉积相带为优质储层发育提供了良好的物质基础。

High-Quality Reservoir Features and Genetic Analysis of Clastic Rocks in the Tarim Basin

Reservoirs of clastic rocks are well developed in the Tarim basin and distributed mainly in the Donghe sandstone at the base of the Carboniferous, Triassic and Jurassic basal sandstone and Cretaceous and Eogene basal sandstone. The opening spaces of the reservoirs are dominantly of pore type and, in a few cases, of fracture type. Pores may fall in two types, with primary pores predominating in Mesozoic and Cenozoic strata and secondary pore in the Paleozoic. The secondary pores are dominated by intragranular and intergranular pores. There are several types of diagenesis, of which supergene leaching, dissolution caused by acid released by low-mature organic matter and dissolution and precipitation caused by acid produced by deep-seated thermo-chemical sulfate reduction are the most important factors affecting the physical properties of reservoirs. The paper discusses the origin of high-quality reservoirs produced under the conditions of deep burial of clastic rocks in the Tarim basin. The authors consider that the Tarim basin is characterized by special geological conditions, i. e. low geothermal gradients, rapid subsidence and short-term deep burial of the rocks after the Neogene, dissolution of rock grains and ground-mass by acid formation water and unconformities and fracture systems formed by multiple tectonic movements, which have improved the performance of the reservoirs. The favorable sedimentary facies belt has provided a good material basis for the develop of the high-quality reservoirs.