A Novel Insight into the Effect on the Differential Pressure of the Formation of the New Gas Phase in Carbonated Water Injection and its Comparison With Conventional CO2 Injection
Authors: Castañeda Jaime Orlando , Alhashboul Almohannad , Farzaneh Amir , Sohrabi Mehran 
Published: February 2022

The aim of this research is to analyze how the novel formation of the new gas phase caused by the injection of carbonated water affects differential pressure behavior and, at the same time, to compare carbonated water and immiscible CO2 injection results under the same experimental conditions.

Considering that, up to now, oil displacements by carbonated water injection were mainly focused on understanding production mechanisms and on how much recovery factor is achieved, to the author's best knowledge, the behavior of differential pressure had not been evaluated in depth, as only a few authors identified abnormal behavior in differential pressure; of such authors, only a few hypothesized that differential pressure increases are possibly caused by the formation of the new gas phase. However, such hypothesis was never proven. Therefore, considering the high increase in differential pressure observed in the experiments developed by the author, a new experiment is designed to validate such a theory.

In this test, dead Oil-2 is fully saturated with CO2, and no hydrocarbon solution gas was added. The purpose of this test is to identify how differential pressure behaves when there is no mass transfer of CO2 from carbonated water to live crude oil. It is stated that there is no mass transfer of CO2 because the crude oil is fully saturated with CO2 at the experimental conditions and would not have the capacity to receive any additional mole of CO2 from carbonated water.

The results proved that the formation of the new gas phase is in fact responsible for the considerable increase in differential pressure caused by carbonated water injection. In addition, when live crude oil is fully saturated with CO2 as gas in the solution, it has been proven that, when carbonated water is injected, there is no formation of the new gaseous phase, whereby the naturally dissolved CO2 content in the crude oil in any oil field would have a relevant impact on the success of carbonated water injection as an enhanced oil recovery option.

On the other hand, it is determined that, at the experimental conditions, i.e., 1200 psi and 140°F, CO2 secondary injection behaves as an immiscible process. The results obtained after comparing both CO2 secondary injection and secondary carbonated water injection under the same experimental conditions led to the conclusion that, for the experiment, where CO2 is injected, differential pressure throughout the flood is significantly low, i.e., less than 1 psi. However, for carbonated water, differential pressure is immediately increased after injecting a few cubic centimeters until reaching values approaching 11 psi, which reveals a strong contrast between both methods of enhanced oil recovery. Behavior in differential pressure is reflected in oil recovery performance, where the CO2 injection experiment with lower differential pressure achieved a lower oil recovery factor by about 20% less.

Finally, under the experimental conditions, CO2 immiscible injection required 1314 cc of CO2 to recover 44% of the oil at four porous volumes injected. On the other hand, the injection of carbonated water only required 342 cc of CO2 to recover 64% of the oil at the same four porous volumes injected, which means a savings of 74% of CO2 at experimental conditions. The above shows, on an experimental level, that carbonated water injection is indeed much more beneficial than CO2 injection.