In steam-flood projects, injected steam does not only change fluid properties, but also affects particle and porous media properties by rock surface processes such as rock wettability change. It may be described in a simple case as follows: the pore in a sandstone formation is naturally water-wet, at high temperature condition, in which the residual oil is trapped in the center of the pore. The oil is encapsulated and inhibited from contacting with the rock matrix by surrounding liquid-phase hot water. When the transition to steam-flooding occurs, the encapsulating water is vaporized allowing the residual oil to contact with the rock surface directly. This allows adsorption to happen, which in many cases, even at elevated temperature, can cause the wettability state to be altered rapidly. This phenomenon will affect the irreducible water saturation, the efficiency of immiscible displacement, and thus the efficiency of oil recovery.
The purpose of this study is to evaluate specific changes in rock-fluid interactions, which are triggered by steam, as a function of the change in wettability of the porous media/fluid system. The specific case introduced is X Field, Indonesia, where steam-flooding has been in operation for almost 3 decades. However, this field is currently struggling with its declining production.
In order to study and understand this mechanism, the contact angle between a solid and two immiscible fluids was investigated. Experiments were run at elevated pressure and temperature conditions. After that, image processing was applied to determine the contact angles of solid/oil/steam systems on the quartz surfaces from the drop profile. The results showed that the contact angle generally increases when the saturated pressure and temperature increases. The results of the experiment were very useful for understanding the mechanism.