Fracturing mechanism of shale gas reservoir with variable pump rates

Strengthening the interaction between hydraulic fractures and natural fractures by the adjustment of pump pressure is the key of fracture network. Longmaxi shale outcrops are selected to study the propagation of hydraulic fractures and the interaction between hydraulic fractures and natural fractures by utilizing tri-axial fracturing test system. The pump pressure increases in a step-wise manner during the tests. The experimental results indicate that the variable pump rates can gradually build the pressure, which generates many under-fracture points in weak planes around the wellbore. Hydraulic fractures will have dynamic extension along these under-fracture points when there is a sudden increase of pump rate. As the pump rate increases in a step-wise manner, the pump pressure significantly increases. Higher pump rate leads to a more fluctuant pump pressure and a more complex fracture network. The occurrence and geometric distribution of natural fractures and net pressure can influence the degree of further interaction. The results prove that the variable pump rates can activate more natural fractures, which contributes to form complex fracture network.