Experimental research on hydraulic fracture initiation and propagation by CT scanning

With the application of larger size tri-axial experiment system and CT scan monitoring technique, the geometries of hydraulically induced fractures in larger dimensions volcano rock outcrops can be observed intuitively and effectively, and analyze the impact of different scenarios on fracture growth such as principal stress differential, rock pores and nature fracture existence. The experimental results show that it is difficult to fracture hard volcano rock and the pumping pressure is obviously turbulent. Fracture propagation is mainly controlled by horizontal principal stress but the locations and length of nature fractures, rock pore magnitude and rock mechanical properties could also influence the fracture initiation and propagation pattern to form complexity. The fracturing fluid may open the nature fracture firstly and make the fracture propagate along the nature fracture orientation. The nature fractures at different angles around the wellbore could make fracture initiate at different pumping time, in an unsymmetrical way and eventually divert to maximum horizontal principal stress direction. If there are few nature fractures and large pores distributed around the wellbore, the fracture geometry may be like conventional bi-wing fracture, but the special volcano rock properties may cause the hydraulic fracture to propagate tortuously and go out of a planar.