A Case Study: Depth Impact on Recovery of Immiscible Gas Injection in an Iranian Undersaturated Oil Reservoir

Abstract

In saturated oil reservoirs, the pressure of the reservoir is gradually reduced with oil production, which ultimately leads to gas production of the reservoir and formation of a gas cap. After the period of natural depletion from oil reservoirs, it is necessary to use secondary and then tertiary methods of enhanced oil recovery (EOR). One of the most common methods, if gas is available, is gas injection. By injecting gas while pressure maintenance and re-pressuring to the initial pressure of the reservoir, the recovery factor increases. This increase in recovery factor mainly occurs due to maintenance or an increase in pressure and a decrease in interfacial tension (IFT) and viscosity. In Iran, except in one of the fields where gas injection is done with the aim of miscible gas injection, other gas injection projects are done with the aim of pressure maintenance. In these projects, the proper place for injection is not taken into consideration, and the gas is done in the highest part of the reservoir. The question was raised at what depth the gas injection should be done to be optimal. Therefore, one of the reservoirs in the south of Iran was selected, and a feasibility study was conducted with the aim of determining the most suitable injection point. In this study, the issue of the appropriate place for gas injection, whether it is in the gas cap, in the middle of the production column, or near the water/oil contact, has been investigated, and the results have been presented. Also, it is approved that the injection in a saturated reservoir has a higher recovery factor than under a saturated reservoir. Finally, injection near water/oil contact is known as the preferred option.