A Laboratory Study of Ionic Effect of Smart Water for Enhancing Oil Recovery in Carbonate Reservoirs

Abstract: Enhanced oil recovery by smart waterflooding represents a cheap, implementable and attractive emerging oil recovery technology. For sandstone reservoirs, smart waterflooding has shown incremental oil recovery in most laboratory and field tests while some promising experimental data have been presented from carbonates. It seems more difficult to assume a favourable performance for a reservoir a priori while dismissing the other, so more data and better understanding of the underlying mechanism in carbonates are needed.

This paper describes a series of experiments on Middle East carbonate core plugs designed to determine the impact of formation water and different versions of seawater (which has its sulphate concentration increased in ratio 0.5:1:2:4:8) on oil recovery, wettability modification and surface charge by smart water. The results obtained lead to the following conclusions:

• Coreflooding experiments at 230 ^oF and 3000 psi with formation brine and various versions of seawater coupled with spiking sulphate concentration executed on carbonate core aged show an excellent incremental recovery of about 10% OOIC;
• An increasing concentration of sulphate in the seawater makes a Crude Oil/Brine/Rock system less oil-wet;
• The higher the sulphate concentration, the greater the attractive force of smart water ions towards the oil/rock interaction, thereby forming an aggregate and detaching the oil from rock surface, while increasing the sulphate concentration beyond 4x seems ineffective as it gave a swift increase in pH and reduction in attractive force to the rock surface;

Results obtained are therefore discussed within the framework of mechanisms previously discussed for smart water ability to enhance oil recovery. The study then concluded that a relatively economical modification of injection water composition can significantly increase oil recovery.

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