During the application of chemical enhanced oil recovery (C-EOR) floods, breakthrough of the injection chemicals periodically occurs resulting in stable emulsions. It is generally challenging to predict exactly when chemical breakthrough will occur, and flood designs try to eliminate this unwanted event from occurring. Some EOR recommendations use a combination of surfactant and polymer (SP), alkaline, surfactant and polymer (ASP), and variations on these two themes. In the event of chemical breakthrough, it is critical to have processes in place that can handle the ever changing conditions that evolve during the course of crude oil recovery. The emulsions from such floods can yield both stable water-in-oil (normal) and oil-in-water (reverse) emulsions particularly if the return of injection chemicals is higher than expected.

Chemical flooding involves injection of a predetermined volume of alkaline, surfactant and/or polymeric chemicals into the reservoir, in order to enhance oil recovery through reduction of Residual Oil Saturation (ROS) and enhancing sweep efficiency of the system. The surfactant, with its Interfacial Tension (IFT) reduction effects, reduces the ROS of the system, and the polymer, through its mobility control effects, increases sweep efficiency. Alkali protects the surfactant from being adsorbed, and also supplements the IFT reduction process, through saponification of the natural acids in the oil. ASP flooding has proved to increase oil recovery in many field trials globally. Several ASP pilots of different scales are reported to have yielded net incremental recovery factors in the range of 15% to 25% over waterflooding.

All physical factors listed previously that enhance oil recovery, can also greatly contribute to the formation of very stable emulsions which are ultimately quite different from naturally occurring emulsions which tend to be stabilized by components such as asphaltenes and resins. Traditional emulsion breakers are often not effective on emulsions created by chemical floods. Like any emulsion, these induced (i.e. basically synthetic) EOR-based emulsions need to be resolved or broken. Producing dry oil and clean water are requirements that all producers must achieve. Dry oil is needed to meet pipeline and various other transportation specifications, whilst clean water is required to meet environment regulations and operators’ own production needs.

The following paper focuses on an ASP pilot project in a mature Oilfield in Asia from the initial bottle test selection work through to field trial of the recommended Breaker chemistries.

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