Underground compressed air energy storage (CAES) in naturally fractured depleted oil reservoir: Influence of fracture

Abstract

In the last decade, the sources of clean energy supply to meet human needs have been given much attention by researchers worldwide. Compressed air storage in underground formations is an excellent way to balance energy production and consumption. During off-peak hours, with the consumption of excess electrical energy, the air is temporarily stored at high pressure in the desired environment. The stored compressed air produces recovered electrical power during the needed hours and peak energy consumption. Compressed air energy storage in underground structures, including depleted hydrocarbon reservoirs, due to having a suitable storage capacity for air and because their geological characteristics have already been well identified, is one of the storage methods. In order to underground storage of compressed air in aquifers and salt caverns, research have been carried out, but so far, studies have yet to be carried out regarding the storage of compressed air in depleted natural fractured oil reservoirs. This study simulated the storage of compressed air in a naturally fractured depleted oil reservoir, the effect of fracture on the rate of oxidation reactions, air dissolution and air diffusion in the oil and water phases. Also, for the first time, an examination of the fracture properties, including porosity, permeability, and fracture spacing on the amount of air recovery during CAES, was numerically simulated. Significantly Increasing the fracture porosity and permeability improves the air recovery and leads to a 19% and 16% respectively increase in the air recovery factor. In the fractured reservoir, increasing the fracture porosity has the most significant effect on reducing the air recovery factor and reducing the fracture spacing has the most negligible effect on the air recovery. Finally, the results of this study showed that due to the consumption and loss of air in the fractured reservoir compared to the conventional reservoir, the air recovery factor in the fractured reservoirs is less than the conventional reservoirs.