北羌塘拗陷巴贡组致密砂岩储层特征及控制因素

Characteristics and Controlling Factors of Tight Sandstone Reservoirs in Bagung Formation in North Qiangtang Depression

北羌塘拗陷的上三叠统巴贡组碎屑岩是羌塘盆地的储层重点层系,分析沉积、成岩作用对巴贡组碎屑岩储层物性的影响机制,可以为下步勘探工作提供地质依据。研究表明,巴贡组砂岩总体的成分成熟度和结构成熟度中等偏低,溶蚀孔隙是主要的孔隙类型,孔隙结构表现为分选差、喉道细和连通差。沉积因素是控制优质储层的主要因素,形成于分流河道微相的砂层在形成时的水动力强、搬运远,其厚度更大、原生孔隙更为发育,由于抗压实能力强、保留有更多粒间孔隙,因此,后期酸性溶蚀更为发育。绿泥石衬里抑制了粒间硅质胶结物的形成,裂缝发育改善了储层物性,煤系特有的酸性介质环境亦促进了次生孔隙的形成。

The Upper Triassic Bagung Formation clastic rocks in the North Qiangtang Depression are the key strata of reservoirs in the Qiangtang Basin.The study shows that the overall compositional maturity and structural maturity of the sandstone in the Bagung Formation are medium and low,the dissolution pores are the main reservoir space,and the pore structure is characteristic of small pore throat radius,poor sorting and poor connectivity.Dissolved pore space is the main pore type,and the pore structure shows poor sorting,fine roaring channel and poor connectivity.Sedimentary factors are the main factors controlling the quality of the reservoir.The sands formed in the microphase of the diversion channel are formed with strong hydrodynamic force and transported far away,and their thickness is larger and the primary pores are more developed,and the acidic dissolution is more developed in the later stage because of the strong compaction resistance and more intergranular pores are retained.The chlorite lining inhibits the formation of intergranular siliceous cement,the fracture development improves the reservoir properties,and the unique acidic medium environment of the coal system also promotes the formation of secondary pores.