taken through a digital pressure gauge attached to the reservoir. We performed the measurements at a constant rate and continued until the pressure is stabilized. The optimal operation capacities for the pump and the pressure gauge used in this study were taken into consideration in the selection of the flow rate range. Qian et al. (2005) applied a wide range of flow rates to observe the transitions between different flow regimes.
Fig. 3a. Experimental set-up used in single and multiphase flow experiments.
They reported that it was not an easy task performing a laboratory flow test in a fracture at especially low hydraulic gradient and flow rate values due to the requirement of more precise sensors for the measurements of very small values of these parameters. However, we applied a very wide range of the flow rates, which covers the possible velocity spectrum at the field scale considering typical flow/injection rates in the field and fracture apertures.
This process was repeated for each model fracture under four different normal load (N) conditions applied perpendicularly on top of the model as well as non-loading condition. We preferred to work with low level normal