Influence of reservoirs/interlayers thickness on hydraulic fracture propagation laws in low-permeability layered rocks

Abstract

In this study, the hydraulic fracture propagation mechanism in low-permeability layered rocks was investigated using the true triaxial hydraulic fracturing test system and the Continuum-based Discrete Element Method. Firstly, the mechanical properties of natural cores in reservoirs and interlayers were determined using uniaxial and triaxial testing machines. Secondly, the Kaiser stress effect method was employed to calculate the in-situ stress. To characterize the thickness distribution characteristics of reservoirs/interlayers in layered rocks, the concept of reservoir thickness ratio kδ was proposed. The influence law of kδ on the fracture pressure Pf of layered rocks was explored. The fracture elongation r was proposed to describe the extension state of fractures in reservoirs and interlayers, and the effect of kδ on fracture elongation r were analyzed. The spatial morphology and geometrical characteristics of fractures were characterized based on the 3D fractal dimension and fracture opening. The 3D damage variable DV was defined to reveal the damage evolution law of layered rocks during fracture propagation. The research results reveal the fracture propagation mechanism in hydraulic fracturing of layered rocks and provide theoretical guidance for the effective implementation of hydraulic fracturing technology. This study is important for the efficient reconstruction of low-permeability reservoirs with layered media and improving oil and gas recovery.