济阳坳陷古近系泥页岩岩石学特征对可压性的影响

Influence of petrological characteristics on fracability of the Paleogene shale,Jiyang Depression

济阳坳陷古近系泥页岩蕴含着丰富的油气资源,但针对性的压裂未取得预期效果。立足于岩石学特征,从脆性矿物类型、含量、产状及成因、黏土矿物组成、有机质含量、成岩作用强度、天然裂缝发育程度等方面对泥页岩可压性的影响进行了剖析,并与美国相关盆地的页岩有关参数进行了对比。研究认为:济阳坳陷古近系沙三下亚段—沙四上亚段泥页岩脆性矿物以硬度较低的方解石为主,总体抗嵌入能力较差;陆源的石英碎屑颗粒弥散状分布,影响压裂应力集中造缝,但含量仍与岩石脆性正相关;结晶形成的碳酸盐纹层导致岩石纵、横向非均质性增强,不利于压裂形成复杂网状裂缝;有机质含量与岩石脆性负相关,与源岩质量正相关,有利可压层段的选择需辩证综合分析;地层年代新、成岩时间短使岩石相对呈塑性,岩石脆性破裂难度增加。泥页岩可压性的影响因素非常复杂,既取决于岩石学特征又受围压条件及地应力差异等地质条件影响;压裂效果还受压裂液体系及施工参数的选择等方面的影响。

The Paleogene shale is rich in oil and gas in the Jiyang Depression. However, the recent fracturing effect of certain exploration wells was not as successful as expected. The influencing factors for shale fracability were analyzed based on petrological characteristics, such as the occurrence and genesis of brittle minerals, types and relative compo-sition of clay minerals, organic content, diagenesis stage and the development degree of natural fractures. The main brittle minerals in shale from the Jiyang Depression are calcites with lower hardness, which determine that the shale is brittle on the whole, but the degree of brittleness is relatively low and the shale shows the characteristics of＂plastic＂. Scattered quartz debris, higher TOC content and younger diagenesis age play a negative role in formation fracturing. The stronger heterogeneity resulting from laminated structure is not conducive to form a complex fracture system during the fracturing process. In addition to the petrological characteristics, the shale fracturing effect is also affected by for-mation pressure, in situ stress and fracturing scheme, etc.