Primarily used in the sandstone reservoir and less in limestone areas, chemical flooding can recover around 40% of the remaining oil. The working principle of chemical injection (chemical flooding) is based on mixing certain chemicals with water and injecting this solution to the reservoir, to increase the mobility of oil and reduce rock-surface tension.
Each chemical serves a different purpose and include water-soluble polymers, surfactants, polymer gels, alkaline chemicals, and biopolymers. Water-soluble polymers increase viscosity of injected water. Surfactants and alkaline work like a "soap" and reduce surface tension (also known as IFT- Interfacial tension) and allow the oil to travel more freely. Under polymer flooding, long-chain polymer molecules are mixed with water and injected into the reservoir. The major objective of polymer flooding is to shut off excess water and to improve sweep efficiency, i.e. volume of the reservoir reached by the injected solution. Microbial injection is the process of affecting the microbial environment in the reservoir. By injecting microbes into the reservoir, surface tension is reduced and oil viscosity and sweep efficiency is improved. This method is used very rarely, due to high costs and environmental concerns.
While done onshore, the logistics make it easier to conduct a chemical injection EOR project. Whereas in the offshore environment it is more complex, challenging and costly, due to the fact that existing infrastructure was not designed to accommodate it, in terms of weight, space, storage, and power. Retrofitting ageing offshore facilities may be impossible and would require new facilities.
As an alternative, a specialized vessel can be used. However, due to the technical parameters, such a vessel must be equipped with a number of technologies that would allow desalination, treatment separation, mixing and injection of the solution. Due to the size of the vessel and technical requirements, it is cost-prohibitive to build a dedicated Chemical Enhanced Oil Recovery (CEOR) vessel. Petronas in Malaysia was about to award a contract to build a first CEOPR vessel for its Angsi project, but the go-ahead was suspended.
In addition, the complex chemical processes and reactions of the reservoir are yet to be further understood and evaluated. Highly deviated wells and larger well spacing offshore makes it even more complicated.