Study of CO2 Mobility Control in Heterogeneous Media Using CO2 Thickening Agents

CO2 injection is an effective method for performing enhanced oil recovery (EOR). There are several factors that make CO2 useful for EOR, including promoting swelling, reducing oil viscosity, decreasing oil density, and vaporizing and extracting portions of crude oil. Moreover, the ease with which CO2 becomes soluble in oil makes it an ideal gas for EOR operations.

However, there are several problems associated with CO2 flooding, especially when reservoir heterogeneity exists. The efficiency of CO2 is hindered by mobility problems, which result from the unfavorable mobility ratio. In such cases, the injected CO2 leads to an early breakthrough, which means fingering through the target zone occurs while leaving most of the residual and/or trapped oil untouched. Furthermore, an increase in the CO2 to oil ratio makes the EOR project uneconomical. However, if there are techniques available to control the injected CO2 volume, the problems just mentioned can be resolved.

Nowadays, several methods are applied to control the CO2 flooding in heterogeneous porous media. In the present study, the CO2 coreflood system was integrated with a computed tomography (CT) scanner and obtained real-time coreflood images of the CO2 saturation distribution in the core sample. Throughout this study, two polymers, Polydimethylsiloxane (PDMS) and Poly (vinyl ethyl ether) (PVEE), were tested to assess their ability to increase the CO2 viscosity and therefore improve sweep efficiency. A drop-in pressure test was first conducted to evaluate the viscosifier's ability to increase CO2 viscosity; therefore, reduce its mobility. The results showed that the PDMS polymer has the greatest influence on increasing the CO2 viscosity and reducing its mobility. Also, the PVEE polymer has lower mobility than that of neat CO2. Based on the coreflood experiments, injection of viscosified CO2 using the PDMS polymer resulted in the highest oil recovery among the other injection tests have been conducted. Also, the laboratory tests show that injecting the viscosified CO2 using the PVEE polymer led to higher oil recovery than from the neat CO2 injection. This research serves as a preliminary study in understanding advanced CO2 mobility control using the thickening agents technique and will provide an insight into the future studies on the topic.