With the depletion of light oil, heavy oil is becoming one of the most promising resources to meet future energy consumption. It is estimated that total resources of heavy oil are 3396 billion barrels worldwide. Water flooding can only achieve less than 20% of heavy oil recovery. Thermal recovery has been proven as a feasible method to recover heavy oil. But it is not suitable for thin layers and deep reservoirs due to excessive heat loss. Polymer flooding and CO2 flooding are potential EOR techniques for the heavy oil reservoirs not suitable for thermal recovery. However, polymer degradation and high costs seriously hinder its field applications. Carbon Dioxide immiscible flooding effectively recovers heavy oil thanks to several mechanisms, such as oil swelling, viscosity reduction and blow-down recovery. This paper discusses the developments in CO2 immiscible flooding at laboratory scale as well as field scale. Laboratory tests show that CO2 can significantly improve heavy oil recover by 30%. Several field cases in USA, Turkey and Trinidad are reviewed. Field experiences show that CO2 flooding is a successful EOR method for heavy oil fields. However, some issues are encountered in field applications, including early gas breakthrough, corrosion, CO2 availability and high costs.
Many successful field cases of microbial enhanced oil recovery (MEOR) method have been reported for sandstone reservoirs. The objective of this study is to investigate the potential of MEOR method in UAE carbonate reservoirs. Two Bacillus strains were incubated at temperatures from 35 to 55°C, and their effects on crude oil properties and recovery were tested. It was discovered that neither strain could effectively reduce crude oil viscosity. Bacteria solutions were subsequently injected into a glass Hele-Shaw model to simulate microbial flooding in a fracture. It was observed that both strains grown under 45°C achieved maximum enhanced recovery of over 13%. Core flooding tests were conducted at elevated temperature of 70°C with limestone core. The two strains achieved enhanced oil recovery of more than 4.5%, respectively. The observation on core flooding test indicated selective plugging as the dominant recovery mechanism. Even though the recovery test results were positive, an analysis shows that MEOR method is not cost-effective. Therefore, MEOR technology may have limited potential in UAE carbonate reservoirs.
Even after secondary recovery, large amount of residual oil is held in reservoir rocks by capillary force. It is estimated that more than 50% of original oil remains underground at field abandonment. Tertiary recovery methods, or enhanced oil recovery (EOR) methods have to be employed to produce the residual oil. Most common EOR methods include thermal recovery methods, polymer flooding, and CO2 flooding.