In recent years, the oil and gas perforation industry has seen the growth of several perforation flow laboratories to experimentally measure the flow characteristics of perforated cores. In such experiments, the determination of core flow efficiency (CFE) depends on the theoretical flow rate in addition to the measured flow rate. Usually, an average core axial/radial permeability is used to calculate the theoretical flow rate, thereby neglecting the heterogenic/anisotropic nature of the core. In this study, we examined the significance of considering the core heterogeneity/anisotropy through experiments and a computational fluid dynamics (CFD) approach.
In this study, a cylindrical Berea sandstone core sample (7-in. diameter x 30-in. length) is drilled axially using a custom drill, with a 1-in.-diameter hole and 3.25-in.-length increments through the core. Flow characteristics were measured under axial flow boundary conditions for each drilling depth of the core. Further, multiple axial/radial core plugs were extracted and routine core analysis was conducted on these core plugs to measure the localized porosity and permeability. Subsequently, the experimental data was complemented by conducting numerical simulations using commercial CFD software for each perforation length.
For the case where the average axial permeability from experiments was used directly in the CFD simulations, significant discrepancies in equivalent permeability were found between experiments and simulations. Subsequently, CFD simulations using the localized permeability of axial core plugs showed good agreement with experiments. It was also found that CFD results using the localized permeability of all axial and radial core plugs provided similar results as compared to using only the axial core plugs. It can be inferred from the above results that core axial heterogeneity is very important for perforation flow prediction and the anisotropy has minimal effect on the CFD results for this Berea core.
Therefore, this study provides insight into the importance of axial permeability heterogeneity to calculate CFE for a perforated core flow under axial flow boundary condition in the perforation flow lab. It also plays an important role in the development / validation of numerical models and more importantly evaluating shaped charge performance for perforated core /well-scale scenarios.