The characteristics of hydraulic fracture morphology in glutenite reservoirs: An experimental investigation

Hydraulic fracturing efficiently unlocks the vast energy potential of glutenite, a crucial unconventional tight oil/gas reservoir. However, the characteristics of the hydraulic fracture (HF) morphology is complex and remains unclear in highly heterogeneous glutenite reservoirs. It is challenging to design fracturing schemes effectively. In this work, rock mechanics experiments and ten groups of true triaxial hydraulic fracturing experiments were carried out to investigate the HF morphology. Critical factors such as horizontal stress difference (HSD), injection rate, fluid viscosity, gravel volume content, and gravel size were investigated. Based on computed tomography (CT) scanning technology, this work innovatively established a three-dimensional fracture characterization method in glutenite samples to observe fracture morphology. The results indicate that in glutenite reservoirs, the initiation positions of HF typically exhibit randomness, often occurring at multiple asymmetric points. The propagation directions of HF are influenced by both HSD and formation heterogeneity, frequently deviating from the direction of the maximum principal stress. The propagation behavior of HF encountering gravel mainly manifests as penetration and deflection. These behaviors are co-controlled by the penetration capability of HF and the shielding effect of gravel. Furthermore, under conditions of low HSD, high injection rate, low fluid viscosity, and large gravel size, HF morphology is more complex, with a high tendency to generate branched fractures. The initiation pressure is positively correlated with HSD, injection rate, and fracturing fluid viscosity, and negatively correlated with gravel content. This study provides a theoretical basis for the optimization of fracturing designs in glutenite reservoirs.