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青西凹陷下白垩统下沟组是该区致密油的主要储集层,本次研究通过普通薄片和铸体薄片观察以及高压压汞等分析测试手段,从岩石学特征、储集空间类型以及孔隙结构特征等方面剖析下沟组致密泥云岩储层特征。结果表明:1)下沟组储层岩石类型以深灰色一灰色纹层状泥质白云岩和白云质泥岩为主,泥级斜长石含量较高,增大了储层岩石脆性,易于产生裂缝;2)泥云岩储层储集空间多样,既有原生孔隙,也有因构造和溶蚀作用形成的构造微裂缝和溶蚀缝洞;3)泥云岩储层的孔隙度和渗透率较低,属于低孔低渗储层,不同岩性之间储层物性差别较大;4)高压压汞测试结果显示:排驱压力和中值压力较高,孔喉半径较小,整体表现出孔隙结构差、非均质性强的特点;5)根据孔隙结构均质系数E_p将研究区储层分为3类:Ⅰ类储层E_p<1.29,储层孔喉分选好,孔隙结构非均质性弱;Ⅱ类储层,1.291.79,储层孔喉分选差。
The Lower Cretaceous Xiagou Formation in Qingxi Depression is the main reservoir of tight oil in this area. Through the observation of common thin slabs and cast thin sections and high pressure mercury intrusion analysis and testing methods, this paper analyzes the characteristics of lithology, reservoir space, Pore structure characteristics and other aspects of the Xiagou Formation tight mudstone reservoir characteristics. The results show that: 1) The lithology of Xiagou Formation reservoir is mainly composed of dark gray-gray layered muddy dolomite and dolomitic mudstone, with high content of mudstone plagioclase, which increases the rock brittleness and is easy to produce Fractures; 2) the mudstone reservoirs have diverse reservoir space, both of which have original pores and structural microfissures and dissolution cracks due to tectonism and dissolution; 3) the porosity and permeability of mudstone reservoirs are low , Which belongs to the low-porosity and low-permeability reservoirs, and the physical properties of the reservoirs differ greatly between different lithologies. 4) The results of high pressure mercury intrusion test show that the displacement pressure and median pressure are higher, the pore throat radius is smaller, Poor structure and strong heterogeneity. 5) Based on the pore structure homogenization coefficient E_p, the reservoirs in the study area are divided into three types: type I reservoirs E_p <1.29, pore-throat sorting, non-uniform pore structure Class Ⅱ reservoirs, 1.29 1.79, poor reservoir pore throat sorting.