青西凹陷下白垩统下沟组泥云岩致密油储层特征

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_p1.29,储层孔喉分选好,孔隙结构非均质性弱;Ⅱ类储层,1.29E_P1.79,孔喉分选较好;Ⅲ类储层E_p1.79,储层孔喉分选差。

The characteristics of Lower Cretaceous Xiagou Formation pelitic dolostone tight oil reservoir,Qingxi sag

The Lower Cretaceous Xiagou Formation is the main tight oil reservoir in Qingxi Sag. In this study, the reservoir characteristics including petrologic characteristics, reservoir space types, and pore structures were studied with the methods of thin sections, casting thin sections and high pressure Hg injection. The results show that: 1)The rock types of Xiagou Formation reservoir are mainly dark grey-gray lamellar shaly dolomite and dolomite mudstone with higher content of mud level plagioclase, which can improve rock brittleness and make it easier to form fractures; 2)There are various types of reservoir spaces in the pelitic dolostone reservoir, including primary pores, tectonic micro-fractures and dissolution fractures; 3)The physical properties of pelitic dolostone reservoir are low porosity and low permeability, and there are significant differences among different lithologies; 4)The results of high pressure Hg injection show that the pelitic dolostone reservoir is high in displacement pressure and median capillary pressure, low in pore throat radius. The overall feature is poor pore structure and strong heterogeneity; 5)The pelitic dolostone reservoir in the study area can be divided into three categories based on the parameter of E_p; class Ⅰ, E_p < 1.29, with best pore throat sorting and weakest heterogeneity; class Ⅱ, 1.29 < E_p < 1.79, with better pore throat sorting; class Ⅲ, E_p > 1.79, with poor pore throat sorting.