Abstract Recently there has been an increasing interest in simultaneous water-alternating-gas (SWAG) in oil recovery operations. This method involves the simultaneous injection of water at the top of the reservoir formation and injecting gas at the bottom of the formation. The difference in water and gas densities will provide a sweeping mechanism in which water tends to sweep hydrocarbons downward and the gas tends to sweep the hydrocarbons upward. It is expected that the two displacement mechanisms will work on establishing a flood front, which will increase the sweep efficiency and thus the oil recovery. This study investigated the performance of SWAG in oil recovery operations.
A three-dimensional finite-difference black oil reservoir simulator has been used to determine the reservoir management strategies in order to optimize the oil recovery using SWAG injection technique. A specific strategy that was studied includes the use of horizontal injectors in conjunction with vertical producers. This well configuration has been shown to yield the best oil recovery compared to other well configurations. The management strategies involved studying different design parameters to maximize the recovery performance. Such parameters include; mobility ratio between oil and water phases, viscosity ratio between gas and oil phases, location of the water and the gas injectors, and injection rates of water and gas. Results showed the investigated parameters are critical in the success of the proposed injection SWAG scheme. The study provides the conditions under which this SWAG injection technique may yield higher recovery performance.
Introduction Oil is considered the main source that provides energy to consumers around the world. The proper utilization of oil resources is a vital issue among world nations. The reservoirs, where oil is trapped, are natural occurring geological structures with mechanisms that move oil toward production wells. These mechanisms are depleted as oil production continues. The need for maintaining or enhancing these mechanisms plays a significant role in keeping the flow of oil. Injection of external fluids into oil reservoirs is a very well known practice in the oil industry that is aimed to sweep oil toward production wells. Water and gas are the most injected fluids into oil reservoirs. The careful design of the flooding operation is a key factor in achieving the objectives of the injection operations. Many injection settings have been followed in the industry with varying degrees of success. An injection technique in which gas and water are injected into reservoirs simultaneously is considered in this study. Gas is injected at the bottom of reservoir while water is being injected at the top. This technique makes advantages of the difference in water and gas densities to increase the hydrocarbon recovery. In primary recovery methods, oil is displaced toward production wells by the natural reservoir energy. Sources of natural reservoir energy are fluid and rock expansion, solution gas drive, gravity drainage and the influx of water from aquifers. When this natural energy of the reservoir is depleted and the drive mechanism is no longer can displace the oil toward production wells, improved oil recovery techniques are introduced to increase the oil recovery.
Several methods have been tried to improve the recovery from hydrocarbon reservoirs. Most of these methods use vertical wells, however, horizontal wells shows some advantages in improved oil recovery operations. The primary reason for utilizing horizontal wells is that a horizontal well provides a large contact area with the reservoir under considerations, and therefore enhances well productivity/injectivity and hence the recovery efficiency. In addition, the costs of drilling horizontal wells, nowadays, are achieving those for the conventional vertical wells due to the advancement of horizontal well drilling technology.