Iran is ranked second after Russia, possessing about 91 trillion cubic meters of natural gas (equivalent to 81% of the world’s reserves). The optimal use of these vast reserves requires long-term precise scientific planning and a complete study and understanding of various related aspects. With huge gas reserves, Iran is known as the second country in the world with natural gas reserves, and from this point of view, it is at the center of international attention. The privileged strategic position of Iran, which is located in the center of crucial natural gas markets in the world, on the one hand, and the massive volume of the country’s oil reserves, which are generally in their second period of exploitation and require the injection of natural gas to increase the recovery rate, on the other hand, necessitate codified and long-term planning for gas allocation to achieve maximum benefits. This research aims to check whether a reservoir undergoing gas injection is profitable to inject or export gas and generalize its results to reservoirs under the same conditions.
The development of gas reservoirs such as South Pars has increased the gas supply in the country and created 
the necessary platform for using natural gas in various industrial and export sectors. There are different options for natural gas consumption in different sectors. Among other things, natural gas can be used in the development of petrochemical and steel industries, the development of gas exports, the injection of gas into oil fields, and the increase of oil recovery. Economic evaluation is one of the most essential criteria for gas allocation and allocation volume to each sector.
According to the implementation of petrochemical industrial projects and exports in the country, there is a reliable assessment of the economic efficiency of these sectors. However, it is necessary to provide a specific model for economic evaluation due to the technical and economic complexity of gas injection into oil fields. For this purpose, presenting a financial model based on the technical models of gas injection projects can help evaluate gas injection projects in the country so that the correct policy based on economic models can be made in this sector.
At first, it was checked from a technical and reservoir point of view by modeling with standard software that each amount of gas injected into the reservoir will increase the amount of production and how much this increase in production will add value to the output. In this section, the costs for gas injection, such as equipment and gas injection costs, were also obtained. Then, the output of the modeling done in several different scenarios was used in financial modeling in the majority of an investment project to inject gas into an oil field and generate income from the increased production of the field. The results were compared in the continuation of the relevant modeling concerning different sensitivity analysis parameters. Ultimately, it tried to obtain the minimum technical and economic conditions necessary for the profitability of gas injection into oil fields using modeling and evaluating the results.
This research examined gas applications based on different scenarios and sensitivity analysis, including injection and export. Then, the economic evaluation of each scenario was done to obtain the optimal state. Also, one of the reservoirs in the south of Iran was investigated, and the obtained information could be generalized to other reservoirs in the country with similar conditions.
A detailed investigation was conducted on the gas injection process in southern oil reservoirs using a sophisticated reservoir model and a commercial reservoir simulator. The analysis focused on both technical and economic aspects. The reservoir model consisted of 4 production wells and 3 gas injection wells, operated for 15 and 10 years, respectively. The impact of different injection pressures on the final recovery factor and cumulative oil production was examined from a technical perspective. It was observed that all gas injection scenarios resulted in an improved oil recovery factor, with injection at well bottom pressures of 3750, 4000, 4250, and 4500 psi leading to respective improvements of 10%, 12%, 13.7%, and 15% compared to natural depletion (no gas injection in the reservoir).
From an economic standpoint, a sensitivity analysis is conducted on various parameters related to production and injection, such as the price of produced oil, the price of produced gas, the cost of injected gas, and the discount rate. The results revealed that higher oil and gas prices increased the economic value of gas injection projects. Additionally, a comparison between the financial benefits of gas injection projects and gas export was made, considering parameters such as the price of export gas and gas export costs (both capital and operational). As the export gas price increased, gas export projects became more favorable than gas injection. Conversely, as the cost of gas export escalated, the desirability of gas export diminished compared to gas injection in the reservoir.
Overall, this comprehensive study provides valuable insights into the technical and economic considerations surrounding gas injection in southern oil reservoirs, highlighting its potential for enhanced oil recovery and economic viability compared to gas export projects.