EXPERIMENTAL STUDY ON EFFECT OF PUMP RATE ON FRACTURE NETWORK PROPAGATION

In the field of hydraulic fracturing for shale gas production, the pump rate has a significant effect on fracture network propagation. The random natural fractures in shale reservoir lead to confusion of parametric sensitivity analysis in hydraulic fracturing. Firstly, based on the fracture characteristic in shale reservoir, concrete specimens with three sets of orthogonal pre-existed fractures are prepared. Then, with true triaxial fracturing simulation experimental system, the fluid with constant pump rate is injected into the specimens under true triaxial loading. Finally, the area of fractures per unit volume(P₃₂) is employed to analyse the effect of pump rate on fracture network propagation. The results show as follows. (1)In the specimens with small dimension of block element(high pre-existed fractures density), the phenomenon of stimulation reservoir volume is more significant. (2)The fluid with low pump rate can stimulate only pre-fractures in specimens. The fluid with medium and high pump rate can not only stimulate the pre-fractures, but also divert the direction of stimulated pre-fractures and open new hydraulic fractures in concrete, which increases the complexity of fracture network. (3)With the increase of injection rate, the P₃₂ value of specimen after fracturing increases. However, when the injection rate increases to a certain value, the P₃₂ value doesn't increase, or even decreases.