塔里木盆地轮古西地区奥陶系古岩溶储层特征

为了进一步挖掘轮古西区古溶岩探区潜力 ,利用常规薄片、扫描电镜、图像分析、同位素等测试手段 ,对该区古岩溶储层特征进行了研究 .结果表明 :轮古西地区下奥陶统碳酸盐岩基质具有低孔低渗特点 ,多属非有效储层 ;古岩溶储层的有效储集空间主要是溶蚀孔、洞和裂缝 .洞穴规模变化大 ,主要分布于距古风化壳面深度为 0～ 2 0 0m范围内 ,中、大型洞穴多分布于古岩溶剖面中下部 .各岩溶相带中 ,表层岩溶带的洞穴最发育 ,其次为水平潜流带和季节变动带 ,垂直渗流带洞穴较不发育 .裂缝类型以构造缝为主 ,以发育立缝和低角度缝为主 ,高角度缝和水平缝发育次之 .纵向上 ,季节变动带和水平潜流带的裂缝最为发育 ,表层岩溶带和垂直渗流带的裂缝发育程度较低 .储层类型主要包括孔洞型、裂缝型、裂缝—孔洞型及洞穴型 4种 .其中 ,洞穴型、裂缝—孔洞型储层的产能好 ,是该区的重要储层类型

Characteristics of Ordovician palaeokarst reservoir in the western region of Lungu, Talimu Basin

In order to further tap the exploration potentiality in this area, the reservoir characteristics are studied by traditional thin section, scanning electron microscope, image, isotope analyses etc. methods The results show that, in the western region of Lungu, the matrixes of lower Ordovician carbonate are characterized by low porosity and low permeability, and mostly are non-effective reservoirs. Dissolved pores, caves and fractures are the main effective storage spaces. Dissolved pores and caves distribute in the range of 0～200 m under the surface of weathering crust and their size varies greatly. Medium—large caves mainly distribute in the middle—lower part of palaeokarst profile. In all the karst belts, caves develop the best in the surface karst belts and better in horizontal undercurrent belts and seasonal variation belts, while worse in vertical vadose belts. The main fracture type is structural fracture, the most of the fractures is vertical or of low angle and a little is of high angle or horizontal. Fractures develop better in seasonal variation belts and horizontal undercurrent belts and worse in surface karst belts and vertical vadose belts. The Ordovician palaeokarst reservoirs can be classified into four types: pore—cavity type, fracture type, fracture—pore—cavity type and cavity type. Cavity type and fracture-pore-cavity type are the most important types which have good productivity.