Microfluidics study of free fall and forced gravity drainage in single- and multi-block fractured porous media: Implications on matrix-fracture interactions

Abstract

Naturally fractured reservoirs are of significant importance in global oil production. One of the main production mechanisms from these reservoirs is gravity drainage. Previous researches have focused on understanding the effective factors on the oil recovery from blocks and the degree of capillary continuity (block to block interaction). However, the results from these studies have not been consistent in some cases and there are ambiguities in the influence of some of the effective parameters on the dynamic discharge of oil from the matrix block. The purpose of the present study is to comprehensively investigate the impact of the main affecting parameters on oil recovery from the fractured porous media with the implications on the degree of capillary continuity through analysis of the stability of the oil bridges, along with addressing the reason of reported inconsistencies in previous studies. With this aim microfluidics experiments on a realistic rock-based single-block and three-block systems are performed and different parameters including the tilt angle of the blocks, injection rate and aperture of the transverse fracture are investigated. In addition, the realistic approach of aging micromodels allowed to examine the effect of degree of oil-wetness on capillary continuity in different multi block systems, an aspect that had not been explored in previous studies. In the case of multi-block systems, the location, number and stability of the formed liquid bridges and the effect on capillary continuity were examined. It was found that oil recovery from single block decreases at higher tilt angles, while in multi-block systems different trends are observed based on the range of injection rate which is attributed to the number and stability of formed liquid bridges. It was also found that in multi-block systems the increase in injection rate can establish capillary continuity through forming liquid bridges. Furthermore, new analytical relationships are developed in the case of single block porous media under free fall gravity drainage, to predict the downward flow of the liquid level within the fracture and matrix. The findings of this study can be used for enhancing the performance of gas injection strategies in fractured systems.