页岩储层裂缝系统综合评价及其对页岩气渗流和聚集的影响

Comprehensive evaluation of fracture system in shale reservoir and its influence on shale gas seepage and accumulation

为了探究页岩储层裂缝系统发育特征、主控因素及其对页岩气渗流和聚集的影响,通过对页岩岩心和薄片进行观察和统计,根据其形态特征的差异,将裂缝分为层理缝、刺穿型高角度缝、内部高角度缝、低角度缝和微裂缝5种类型。通过对比分析多种参数对裂缝系统产生与发育的影响认为,其主控因素包括脆性矿物含量、构造作用、岩石内部结构、非均质性、力学性质及地层围压等,结合裂缝类型和主控因素等对页岩储层裂缝系统进行综合评价。其中,层理缝等水平裂缝的侧向扩散作用促进页岩气的渗流和聚集。尤其在中国南方构造变形强烈、褶皱发育的地区,层理缝与低角度缝造成页岩储层侧向扩散效果明显,使向斜型页岩气藏和背斜型页岩气藏兼具北美典型页岩气藏(自生自储,原地成藏)与常规气藏(油气富集于构造高部位)的复合型成藏模式。在封闭成藏的条件下,裂缝系统发育往往能够使游离气通过侧向扩散作用沿着裂缝渗流和聚集,于构造高部位形成气藏。

To study the development characteristics of shale fracture-microfracture system,the main controlling factors and their influences on shale gas seepage and accumulation,fractures were divided into five types according to their morphology based on core and thin section observation and statistics,including bedding fractures,cut-layer high angle fractures,internal high angle fractures,internal low angle fractures and microfractures. Through analyzing effects of multi-parameters on fracture-microfracture,it is considered that the main factors controlling the generation and development of reservoir fracture-microfracture system include the brittleness mineral content,tectonic action,internal structure of rock and its heterogeneity,mechanics characteristics and formation confining pressure. And then combining with the fracture types and main controlling factors,the evaluation of reservoir cracks was done comprehensively. The horizontal cracks,such as the bedding fracture,can enhance lateral diffusion effect,and thus significantly promote the shale gas seepage and accumulation. Especially for those areas that experienced strong tectonic deformation and developed fold structures in southern China region,the lateral diffusion effect caused by bedding fractures and low angle fractures is obvious. Syncline and anticline shale gas reservoirs,which combine characteristics of both the North American shale gas reservoir(self-sourced and in-situ accumu-lation)and the traditional oil and gas reservoirs(hydrocarbon enriched at the high point of the structure),belong to composite accumulation pattern. In a closed petroleum system,developed fracture network often can make free gas seepage along fracture through lateral diffusion and gas reservoir is formed at the high point of the structure.