A Laboratory Study of Multiple Fracture Initiation from Perforation Clusters by Cyclic Pumping

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Hydraulic fracturing using cyclic pumping is a potential method for effective stimulation of unconventional oil and gas reservoirs. In our study, the laboratory-scale hydraulic fracturing experiments using cyclic pumping were conducted using cuboid concrete specimens with multiple perforation clusters. The results showed that by cyclic pumping more fractures were created from perforation clusters when compared to non-cyclic monotonic pumping. This trend was shown to increase when using high-viscosity fracturing fluids. In our cyclic pumping experiments, the maximum pressure in the first pumping cycle reached the breakdown pressure and at each subsequent cycle the maximum pressure increased. The increased maximum pressure likely acted to generate more fractures initiating from the given perforation clusters even under greater fracture height to spacing ratios and more acoustic emission (AE) events were generated by cyclic pumping compared with those by monotonic pumping. Well compliance was examined and showed a negligible change in the system compressibility among cycles. This suggests that the fractures formed by previous injection cycles were isolated from the wellbore at the start of this cycle and at least their near-well portions are closed. There are a few possibilities contributing to the difficulty in reopening the existing hydraulic fractures in subsequent injection cycles. Detailed discussion is provided based on the varying features of injection pressure. This cyclic injection method could deliver an alternative for multi-stage fracturing treatments in field applications.