A COMSOL Multiphysics study on block-to-block interactions in naturally fractured reservoirs

In fractured reservoirs, block-to-block interactions (re-infiltration and capillary continuity) significantly affect gravity drainage performance. Re-infiltration controls the drainage rate. This process may significantly delay oil production. Despite the numerous attempts to study the re-infiltration process, there is still much controversy about the factors that affect this phenomenon. This work focused on designing two sets of 2D models aimed at improving the simulation and visualization of multiphase flow in fractured porous media while providing a more realistic understanding of the pore-scale phenomena and flow communication between matrix-fracture and matrix-matrix. The simulation was performed in COMSOL Multiphysics in the single-porosity model. Moreover, the impact of different parameters such as rock type, physical properties of the fluids, tilt angle, matrix block height and area, fracture opening, and matrix blocks porosity-permeability on gravity drainage performance, especially block-to-block interactions, has been examined. Besides investigating the effect of each parameter, combined effects of those parameters have likewise been investigated. To rank the most critical observed parameters on the re-infiltration process, the grey relational analysis was applied. The results of this analysis showed the physical properties of the fluids have the most influence on re-infiltration. In addition, it was demonstrated that tilt angle reduces the degree of re-infiltration in deviated blocks. Also, a combination of oil-wet rocks and high irreducible water saturation results in a decrease in oil recovery, a delay in production, and a decrease in the degree of re-infiltration. Additionally, fractures with small openings and taller blocks promote greater re-infiltration; however, their impact on ultimate recovery is not significant. The findings of this study can help for a better understanding of the relative influence of different reservoir parameters on gravity drainage performance and block-to-block interactions.

Automated summary

This research focused on improving the simulation and visualization of multiphase flow in fractured porous media and studying the impact of different parameters on gravity drainage performance. The grey relational analysis revealed that the physical properties of the fluids have the most influence on re-infiltration, while tilt angle reduces the degree of re-infiltration. These findings provide insights into the relative influence of different reservoir parameters on gravity drainage performance and block-to-block interactions.