Abstract:

Hydraulic fracturing is not only a natural action but also an artificial method to alter rock structure. Hydraulic fracturing process, fracture propagation pattern, and influencing factors including shape and magnitude of inlet hole, stress conditions, and specimen strength were investigated by software of F-RFPA2D. The water pressure that causes occurrence of AE is named initial pressure Pis，while fracture pressure Pcs is the pressure which leads to dramatic increase of AE, and makes macrofractures propagate in instability till rock specimen failure. In the same rock specimen size, Pis and Pcs of rock specimen with circle-shaped hole are greater than those with square-shaped hole in the same hole area; and they increase when inlet hole area decreases. Pis and Pcs increase with the increase of confining pressure and strength of rock specimen; while their differences increase only with rock strength; theoretical fracture pressure Pct and simulated Pcs have almost the same change trend. Macrofractures are usually borne near angle points in rock specimen with square-shaped hole, while the positions are random in rock specimen with circle-shaped hole. Macrofracture propagating directions are random under no confining pressure, but they are in accordance with main stresses directions when confining pressure is not zero; the macrofracture along maximum principal stress direction extend until split rock specimen, while others do not grow completely. Above results are of some significance to hydraulic fracturing tests and engineering practice.

Key words: rock mechanics, single-holed rock specimens, hydraulic fracturing, influencing factors, numerical simulation