Experimental investigation of matrix wettability effects on water imbibition in fractured artificial porous media

Spontaneous water imbibition into the matrix blocks is known as the main mechanism for increased oil recovery from naturally fractured oil reservoirs. The rate of oil recovery and its ultimate value is mostly affected by wettability of the rocks and their pore structure. Oil viscosity also greatly influences the rate of oil recovery. A novel experimental model was utilized to study the imbibition mechanism under different wettability conditions. Matrix blocks made from different grain types and size distributions of glass beads were saturated with two different types of synthetic oil, to mimic the oil-saturated matrixes. The wetting characteristic of the models used in this study were altered by a standard chemical treatment process. Wettability, grain type and size distribution, as well as oleic phase properties, were changed to find the effect of these parameters on oil recovery efficiency. The results revealed that presence of a small fraction of oil-wet grains drastically affects oil recovery by capillary imbibition. A criterion was obtained to describe the effects of wetting property of the matrix blocks on oil recovery efficiency by capillary imbibition. The effect of gravity force, resulting from the density difference between oil in the matrix block and the water in the fracture, was also analyzed using inverse Bond number (N _B ^-1). Application of this dimensionless number was found to be limited by the height of the porous medium. The results also confirm that oil production rate during imbibitions is greatly influenced by oil viscosity.