Researchers from Khalifa University investigated the geochemical mechanisms of surfactant polymer flooding in the rocks found in Middle Eastern oil reservoirs to develop a framework for choosing the most efficient mix.
Contrary to popular belief, retrieving oil from reservoirs isn’t as simple as drilling a hole and letting it flow. This is merely the first phase of oil recovery, where 5 to 15 percent of the oil reservoir’s total amount of oil flows to the surface under natural pressure. But continuous oil extraction causes the pressure gradient to drop in the reservoir, decreasing production rates. Maximizing production therefore requires additional effort to both maintain reservoir pressure and release maximum amounts of oil.
Researchers from Khalifa University have developed a novel geochemical modeling technique to study and evaluate the methods used to extract oil from carbonate reservoirs. Dr. Ilyas Khurshid, Postdoctoral Researcher, and Dr. Imran Afgan, Associate Professor, Department of Mechanical Engineering, investigated chemical flooding, a technique that encourages oil to detach from the pores of the rocks and flow to the surface. Their model looks at the chemicals and polymers used in this process and helps better forecast how they will interact with the oil in the reservoir. Most importantly, their work considers the rocks that make up the geological landscape of the Middle East: carbonate rocks like limestone and dolomite.
Their results were published in Nature Scientific Reports.
When a reservoir’s natural pressure falls too low to support oil production, water or gas can be injected into the reservoir to maintain pressure and increase the oil-recovery rate. Water displacement alone will release only an additional 15 percent of the oil in the reservoir, leaving as much as 70 percent of the original oil in place. At this point, enhanced oil recovery (EOR) processes are required.
Rather than simply trying to force the oil out of the ground using pressure, EOR seeks to alter reservoir properties to facilitate extraction. Polymer and surfactant flooding are two techniques for improving the recovery of viscous oil.
Water injection alone is insufficient because it may flow in highly permeable pathways that exist between the injection wells and the production wells, leaving several regions of the reservoir untouched by the flood of water. Additionally, water and oil don’t mix. Oil that is trapped within the rock matrix will not mix with the water and be swept toward the production wells. This is where polymers and surfactants are needed to detach the oil from rock surfaces. Surfactants reduce the surface tension of liquid, increasing its spreading and wetting properties.
In polymer flooding, polymers are added to the water injected into the reservoir. This increases the water’s viscosity and improves oil displacement. Surfactant flooding is often used in conjunction with polymer flooding, where surfactants are added to the water, acting in the same way as dish detergent to detach the oil from the rock surface.
“A surfactant/polymer chemical flooding operation cannot be considered as two independent mechanisms that occur in a reservoir at the same time,” Dr. Khurshid said. “The interaction of both chemicals affects the surfactant retention, operation economics, and oil recovery factor.”
Carbonate rock formations typically show low porosity and lead to low oil recovery. Plus, the salts and minerals in the rock cause the polymers to degrade. When the polymers degrade, oil-recovery efficiency is diminished.
“This is why it’s important to investigate the interaction or compatibility of surfactants and polymers with the rocks in the reservoir,” Dr. Khurshid said.
Dr. Khurshid and Dr. Afgan developed a comprehensive modeling approach to capture the effects of rock mineralogy as well as fluid composition on surfactant retention during surfactant polymer flooding. Their study is the first to consider the oil/surfactant effect on surfactant retention. Their work enables petroleum engineers to determine the best polymer and surfactant mixes to use in the carbonate rock formations found in the Middle East.
21 March 2023