Development and genetic mechanism of complex carbonate reservoir fractures: A case from the Zanarol Oilfield, Kazakhstan

By core observation and slice analysis, two types of fractures can be identified in reservoirs of Zanarol Oilfield, including macro-fractures and micro-fractures. Macro-fractures refer to tectonic fractures and stylolites, and micro-fractures mainly refer to grain breakage fractures and micro-tectonic fractures. The development of the different scale fractures is controlled by lithology, formation texture and stress field. Macro-fractures are well developed in tight rocks such as micrite and micro-fractures are well developed in granular carbonate rocks of good porosity and permeability. The Zanarol Oilfield is a typical layered pool, with interbeds of granular carbonates and tight carbonates, and this texture controls the vertical distribution of macro-fractures and micro-fractures. Macro-fractures in the ? layer are well developed due to its tight reservoir, and micro-fractures are well developed in the ? layer because of its loose reservoir. The planar distribution of the fractures is controlled by principal stress, and fractures are well developed in zones with high principal stress.

摘 要通过岩心观察、薄片分析等方法研究让纳若尔油田储集层裂缝发育特征，发现油田发育宏观裂缝和微观裂缝两种不同尺度的裂缝，宏观裂缝包括构造裂缝和缝合线，微观裂缝主要是颗粒破裂纹和构造微缝。不同尺度的裂缝发育程度与碳酸盐岩岩性、地层结构和应力场大小有着密切的关系。宏观裂缝多发育于泥晶灰岩等胶结致密的岩石中，微裂缝多发育在孔渗性较好的颗粒灰岩中。让纳若尔油田是层状特征明显的碳酸盐岩油藏，储集层与致密隔夹层频繁间互的地层结构模式决定了宏观裂缝和微观裂缝的垂向分布模式：Д层储集层较为致密，在构造应力作用下形成宏观裂缝；Г层储集层较为疏松，在构造应力作用下多形成微观裂缝。平面上，裂缝发育与分布受主应力大小控制，在主应力场相对高值区，裂缝发育程度更高。