Advances in Enhanced Oil Recovery (EOR) technology
By Assoc. Prof. Hisham Khaled Ben Mahmud
Crude oil is one of the commonly used fossil fuels which the world’s economies and development depend on. It includes hydrocarbon components and other organic materials that can be purified to produce various petrochemical products. This process of petroleum recovery is divided into three stages – primary, secondary, and tertiary.
Primary recovery uses the oil reservoir’s natural sources of energy, such as water drive and gas cap, to recover hydrocarbons. This technique produces about 25 per cent of the Original Oil In Place (OOIP).
The secondary recovery method is applied when the reservoir pressure is depleted and unproductive. This technique can involve injection of either gas or water to improve oil production and stabilise reservoir pressure. Recovery efficiency using this method is between 10 to 40 per cent of OOIP.
After the primary and secondary recovery stages, Enhanced Oil Recovery (EOR) – the tertiary stage – is implemented.
The use of these recovery methods demonstrates the huge potential in recovering oil trapped in the porous medium scale by capillary pressure‐driven snap‐off. EOR is an increasingly crucial area of petroleum engineering, improving oil production from subsurface formations using the principles of physics and diverse engineering techniques. EOR can also involve the injection of materials that are not naturally found in the reservoir, for example, chemicals, supercritical fluid (CO2) or steam.
EOR approaches can recover over 50 per cent of total OOIP which is significantly higher than primary and secondary recovery. Thus, the impact of EOR on oil production is massive as a growth in the recovery factor by one per cent can produce 70 million barrels of conventional oil without utilising unconventional resources.
However, offshore applications of tertiary recovery methods are not viable unless certain conditions are overcome simultaneously. In contrast to onshore applications, injecting CO2, steam or miscible fluid displacement is successfully implemented cost-effectively in only a small number of projects. Offshore EOR projects are thus relatively rare worldwide, and those carried out are mainly short-term pilot projects.
This was substantiated by a study that revealed that only 19 offshore projects have been successfully completed and are in operation, indicating that the high cost of installation and implementation of such technologies remains a significant barrier to wider adoption.
Despite the hurdles, experimentation in offshore projects has been increasing in oil-rich nations like Russia and in South East Asia and the Middle East since the mid-2000s. These nations have made some headway and it has helped them enhance their global market dominance. Countries like Norway and the United Kingdom have also been investigating EOR and carbon-capture solutions to keep to their traditionally-high production targets and at the same time minimise greenhouse gas emissions.
Such advances have spurred innovation in other energy industries that can help the petroleum sector. This includes the recapturing of gas emissions (CO2) from power plants and other sources that generate large quantities of CO2. These human-made sources can be used to not only assist offshore facilities improve production recovery, but also help lower carbon emissions globally in the future.
As mentioned earlier, employing CO2 injection techniques in offshore wells remains a challenge. One major issue in gas-injection EOR, which is best utilised in offshore reservoirs, is the mobility of gas which is extremely high compared to other fluids that might exist in reservoirs. It is hard to control the fluid movement direction. During the injection process, CO2 can end up bypassing most of the reservoir formation as a result of its ultra-low viscosity and flow into other formations that have good permeability, causing these unruly amounts of carbon to miss their specified target.
To offset this, a foam can be developed and injected with CO2, trapping the bubbles within the formulation, enhancing its viscosity, and subduing any unwanted movement streams.
Studies have also shown that CO2 injection has the highest potential of improved recovery in unconventional reservoirs, followed by produced gas injection and surfactant injection. Further research and field trials are necessary to bridge the gap and improve the scaling from laboratory to field.
To improve our understanding of the complex mechanisms of EOR in conventional and unconventional oil reservoirs, more research needs to be conducted into advanced gas injection strategies, effective fracture placement utilising technologies to differentiate brittle verses ductile rock, smart injection technologies, variations in rock properties, and moving from equally spaced wells and fractures to more efficient well spacing and fracture placement.
Hisham Khaled Ben Mahmud is an Associate Professor of Petroleum Engineering in the Department of Chemical and Energy Engineering at Curtin Malaysia. He is a Professional Engineer registered with Engineers Australia and holds a PhD in Chemical Engineering from Curtin University, Master of Science in Engineering Studies from Sydney University, Graduate Diploma in Oil and Gas from Western Australia University, and Bachelor of Science (Hons) in Chemical Engineering from Tripoli University. His research foci are in enhanced oil recovery and CO2 sequestration from/in conventional and unconventional reservoirs, well stimulation using acidising approach, well production optimisation, and managing hydrate formation risks in subsea systems. He has published over 40 peer-reviewed journal articles, book chapters, and conference publications based on his research. Assoc. Prof. Hisham can be contacted via email at firstname.lastname@example.org.