Fracture propagation behavior via multi-cluster fracturing in sandstone-shale interbedded reservoirs

Initiation and propagation of fractures in multi-layered formations has been a topic of interest for the efficient utilization of hydrocarbon resources. Although there is a reasonable body of knowledge to facilitate the design and development of hydraulic fracture, the understanding of initiation and propagation of fracture clusters in layered formation is limited. This paper discusses the findings from controlled laboratory experiments and numerical modeling to understand the initiation and propagation of hydraulic fracturing operations. True triaxial tests were carried out on samples extracted from outcrop representative of Lianggaoshan formation in China. It was noted that the differential stress between the layers is critical for the initiation and propagation of multiple fracture. It was also noted that the viscosity of the fracturing fluid influences the propagation of fractures across lamina and interfaces. The intermediatory response of rocks due to the injected fluid was studied through numerical modeling of the physical process using modified cohesive zone model, which was then validated by the output from the laboratory experiments. It was noted that the increase in the fracture cluster has the potential to constrain the extent of fracture propagation whereas decrease in the cluster size increases the extent of fracture propagation. Compared to sandstone, the fracture height in shale is 30% lower. For sandstone, early-stage fracture flow distribution stabilizes more quickly, and higher fluid pressure within fractures significantly increases fracture height and effective stimulation volume.