The effect of bedding plane on the hydraulic fracture growth in gas shale reservoirs: Analytical solution

In the hydraulic fracturing process, the mechanical behavior of bedding planes is known to influence the growth of fractures in the surrounding rock. An analytical investigation was conducted into the growth process of hydraulic fractures in bedded rock. The effects of the number of bedding layers, the mechanical properties of these layers, internal pressure, and confining pressure on radial displacement, radial stress, tangential stress, and the critical radii of failure were examined. In all samples, the bedding planes were oriented perpendicular to the internal pressure. It was observed that as internal pressure increased, radial stress values rose while tangential stress values decreased. When the internal uniform compressive load matched the external load, the values of radial and tangential stresses became independent of radial distance in the cylindrical specimen. It was found that hydraulic fractures (HF) may propagate within the bedding layers due to a decrease in the modulus of elasticity and strength of the rock. Shear failure in the hydraulic fractures was found to be exacerbated when cohesion and friction angle values were low. Numerical simulations indicate that four major sets of tensile fractures developed in a medium strength model, while a significant number of small cracks emerged in the weak rock. The middle layer, which had high tensile strength, remained stable. This suggests that the strong middle layer can transfer internal forces to the weaker rock after crack propagation occurs in the upper layer, resulting in small crack growth in the soft rock. Additionally, the dip angles of the large fracture sets related to the vertical axis were found to be 45 degrees. This study may contribute to the simulation of hydraulic fracturing in oil shale reservoirs.