Propagation criterion of hydraulic fracture in rock based on the rock micro-cracking mechanism

• A new propagation criterion for hydraulic fractures is derived from the micro-cracking mechanism at the mineral particle scale, integrating pore pressure gradients and macroscopic boundary stresses. • The disturbed skeleton stress induced by gradient pore water pressure is equal to the pore water pressure difference, and the mechanical shape factor a/b is around 1 but greater than 0.5. • Micro-cracks initiate among mineral particles, connect to form micro-hydraulic fracture surfaces, and open to form macro-hydraulic fractures, with initiation occurring at the micro-cracking initiation pressure (MCIP). • The theoretical MCIP values calculated by the proposed criterion closely match experimental measurements, validating the model.