The effect of geological features on hydraulic fracture propagation guided by radial boreholes in the thin interbedded reservoirs

High-strength interlayers and lithological interfaces limit vertical fracture height and stimulation efficiency in the thin interbedded reservoir. This paper proposes a novel radial borehole fracturing approach to enhance hydraulic fracture cross-layer ability. A multilayered model was developed to simulate radial borehole fracturing based on the discrete lattice method. Under different geological features, the mechanism of hydraulic fracture cross-layer propagation was determined by analyzing the evolution of in-situ stress and rock displacement around radial boreholes. Research indicates that the radial borehole effectively reduces the effect of the minimum principal stress around the near-wellbore zone, thereby decreasing the interlayered stress difference and promoting hydraulic fractures to propagate in straight paths across interlayers. When the radial borehole penetrates across lithological interfaces, rock displacement readily facilitates cross-layer propagation, thereby significantly alleviating constraints on the vertical fracture height. Furthermore, multiple pay zones could achieve effective skip-layer stimulation when radial boreholes connect multiple interlayers. The ability of hydraulic fractures to propagate across interlayers increases significantly with higher interlayered horizontal stress difference, interlayered fracture toughness difference, interlayered elastic modulus difference, interlayered tensile strength difference, and natural fracture density, or with reduced interfacial shear strength. Among these, the interlayered tensile strength difference predominantly controls the vertical fracture height based on the Spearman correlation algorithm. A propagation criterion was established for identifying a hydraulic fracture crossing a lithological interface in radial borehole fracturing under various geological factors. If the thin interbedded reservoir exhibits interlayered horizontal stress differences exceeding 10 MPa, interfacial shear strengths below 4 MPa, or natural fracture densities greater than 1 fractures/m, radial boreholes should be extended into adjacent barrier layers to stimulate outer pay layers. When radial boreholes interconnect multiple pay layers, hydraulic fracture skip-layer initiation could achieve overall reservoir stimulation and mitigate the constraints of formation conditions. This study provides theoretical foundations and engineering implementation guidelines for radial borehole fracturing in thin interbedded reservoirs.