An Experimental Investigation of Sequential CO₂ and N₂ Gas Injection as a New EOR Method

Abstract

Typical non-hydrocarbon gases, which have been utilized in miscible and immiscible processes, are carbon dioxide and nitrogen. These gases are usually injected separately and have been rarely utilized together as a tertiary recovery process. In this article, the authors have experimentally focused on sequential carbon dioxide and nitrogen gas injection as a new enhanced oil recovery method. The periodic injections of carbon dioxide and nitrogen have been repeated for six injection pore volumes. Sensitivity analysis of injection pressure, injection volume, and injection rate has also been investigated in core flood experiments. The experimental results have revealed that a sequential miscible carbon dioxide and immiscible nitrogen gases injection have the highest oil recovery percentage than near miscible or immiscible carbon dioxide and nitrogen injections. The experimental results have shown that increasing ratio of miscible carbon dioxide to nitrogen resulted in increasing ultimate oil recovery percentage. This new method has also been compared with typical enhanced oil recovery methods, namely, water, miscible water-alternating-gas, miscible and immiscible carbon dioxide, and immiscible nitrogen injection using a commercial compositional simulator.

Keywords::

• carbon dioxide
• enhanced oil recovery
• immiscible gas injection
• miscible gas injection
• nitrogen