富有机质页岩天然裂缝研究进展

Research Progress of Natural Fractures in Organic Rich Shale

天然裂缝是富有机质页岩油气储层的重要储集空间和主要渗流通道,影响页岩油气的富集、保存、单井产能及开发效果,天然裂缝发育规律研究对富有机质页岩油气勘探开发具有重要意义.本文在调研近年来海相和陆相富有机质页岩裂缝研究成果的基础上,综述了富有机质页岩天然裂缝的成因类型、发育特征、主控因素以及评价与预测方法等方面取得的最新进展,讨论了富有机质页岩天然裂缝今后重点研究方向.富有机质页岩天然裂缝分为构造裂缝、成岩裂缝和异常高压裂缝3大类6小类,其中层内张开裂缝、穿层剪切裂缝、顺层剪切裂缝和水平层理缝是其主要的裂缝类型.页岩构造裂缝的发育程度主要受脆性矿物含量、有机质含量、高脆性页岩层厚度、构造、地层倾角和流体压力等因素的控制,页岩水平层理缝的形成与发育程度主要受有机质含量、纹层类型、纹层数量、纹层厚度及后期构造抬升等因素的影响.由于陆相页岩与海相页岩的沉积环境不同导致的矿物组分、岩相变化及有机质热演化程度等方面的差异,使得陆相页岩与海相页岩裂缝的发育特征明显不同.与海相页岩裂缝相比,通常陆相页岩裂缝的分布型式更复杂,构造裂缝规模更小,穿层剪切裂缝和顺层剪切裂缝的发育程度低.页岩裂缝的评价与预测目前主要借助于已有的常规低渗透致密储层构造裂缝研究方法开展,如何针对页岩裂缝规模小和水平层理缝发育的特点,将地质、地球物理和机器学习相结合,形成适合不同尺度和不同类型页岩裂缝的分类评价与预测方法,对提高页岩裂缝的评价预测精度和更好地指导油气开发至关重要.深层富有机质页岩裂缝的发育规律、天然裂缝对水力压裂缝的影响以及综合多尺度、多产状和多成因页岩裂缝的复杂缝网系统三维地质建模,也将是今后页岩裂缝研究需要解决的重要问题.

Natural fracture is an important reservoir space and main seepage channel of organic rich shale oil and gas reservoir,which affects the enrichment,preservation,single well productivity and development effect of shale oil and gas.The research on the development law of natural fracture is of great significance to the exploration and development of organic rich shale oil and gas.Based on the research results of marine and continental organic rich shale fractures in recent years,this paper summarizes the latest progress in the genetic types,development characteristics,main control factors,evaluation and prediction methods of organic rich shale natural fractures,and finally discusses the key research directions of organic rich shale natural fractures in the future.The natural fractures of organic rich shale can be divided into three categories and six sub categories:tectonic fractures,diagenetic fractures and abnormally high-pressure-related fractures.The main fracture types are intraformational open fractures,transformational shear fractures,bed-parallel shear fractures and bed-parallel lamellated fractures.The development degree of shale tectonic fractures is mainly controlled by brittle mineral content,organic matter content,high brittle shale layer thickness,structure,formation dip angle and fluid pressure.The formation and development of bed-parallel lamellated fractures are mainly affected by organic matter content,lamina type,lamina number,lamina thickness and later tectonic uplift.Due to the differences in mineral composition,lithofacies changes and thermal evolution of organic matter caused by different sedimentary environments between continental shale and marine shale,the development characteristics of fractures between continental shale and marine shale are obviously different.Compared with marine shale fractures,the distribution pattern of continental shale fractures is more complex,the scale of tectonic fractures is smaller,and the development degree of cross layer shear fractures and bedding shear fractures is low.At present,the evaluation and prediction of shale fractures are mainly carried out with the help of the existing conventional research methods of tectonic fractures in low-permeability tight reservoirs.How to combine geology,geophysics and machine learning to form a classification evaluation and prediction method suitable for different scales and types of shale fractures according to the characteristics of small scale of shale fractures and development of bed-parallel lamellated fractures,It is very important to improve the evaluation and prediction accuracy of shale fractures and better guide oil and gas development.The development law of deep organic rich shale fractures,the influence of natural fractures on hydraulic fracturing fractures,and the three-dimensional geological modeling of complex fracture network system integrating multi-scale,multi occurrence and multi Genesis shale fractures will also be important problems to be solved in the research of shale fractures in the future.