An Experimental Investigation of the Effect of Oil/Gas Composition on the Performance of Carbonated Water Injection CWI

The objective of this research is to analyze, for the first time to the author's best knowledge, how an oil and solution gas composition affects oil recovery and differential pressure when a whole core, saturated with live crude oil, is exposed to carbonated water injection. In the past, many authors independently conducted micro-model or small-diameter core floods to understand how carbonated water injection could affect the recovery of dead or live oil. However, only one author initiated a simple identification of the dominant role that hydrocarbon composition could play in the recovery factor of the system by using micro-models, which led to the development of this research. However, despite having partially identified the importance of this variable, and being a pioneer in this type of study, the author's analyses were limited to the mixture of methane with either C6, C10, C16, or C17, which is far from reality. Therefore, for the first time to our best knowledge, a new series of whole core flood experiments was performed, which involved the use of two types of crude oils, combined with three types of solution gases, two of which were multicomponent, to identify how compositional variability could affect oil recovery and differential pressure behavior when a whole core is exposed to carbonated water injection to displace these live crude oils. The obtained results led to the conclusion that the amount of formation of the new gas phase depends mainly on the molar percentage of the C1–C7 components in the live crude oil, which result in an increase in the oil recovery factor; more importantly, it will result in a higher differential pressure. It was also concluded that slight changes in the composition of the live crude oil do not have a significant effect on oil recovery but do have a significant effect on the behavior of the differential pressure. To our best knowledge, this significant impact has not yet been identified. Further analysis led to the conclusion that the impact on the differential pressure is not mainly due to the methane content but depends more on the content of C2–C7 components. Considering that the composition of the live crude oil is relevant for the formation of the new gas phase, and that the new gas phase can be considered as the dominant production mechanism for carbonated water injection in live crude oil, it was observed that the new gas phase has a significant effect on the oil effective permeability value, even reducing it by as much as half. In addition, the author proposed a new correlation to calculate the saturation of the new gas phase in scenarios of secondary injection of carbonated water in strongly water-wet environments. Finally, the system in which the highest recovery is achieved is the one with the richest gas, i.e., with the highest molar percentage of C1–C7 components, together with a non-water wet rock.