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

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 composition 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 formation pressure, in situ stress and fracturing scheme, etc.