Hydraulic Fracturing in a Confined Space System: Stress State, Fracture Space, and Production Enhancement Mechanism

Existing mechanical models for hydraulic fracturing technology are established based on open space systems, assuming fractures are primarily formed through tensile failure. However, the source mechanism of newly created fracture space under confined space conditions with constant total volume remains unclear. This study develops a mechanical model for hydraulic fracturing in confined space systems based on fundamental principles including volume conservation, pore volume redistribution, Newton's third law, and Pascal's law. The research demonstrates that: the formation of artificial fractures and accommodation space for proppants originates from the adjustment and redistribution of existing pore space; compressive differential deformation provides the mechanical basis for shear fracture formation; rock deformation and failure follow an evolutionary sequence of "compression (generating fracture space) → tension (controlling fracture propagation direction) → differential deformation (forming shear fractures)."Based on the newly established mechanical model and Biot's poroelastic coupling theory, a novel fracturing production enhancement mechanism is proposed. This mechanism can provide theoretical guidance for well placement, wellbore trajectory design, and hydraulic fracturing target optimization, contributing to improved reservoir utilization and recovery rates, while offering new theoretical foundations for reservoir development numerical simulation.