1.1 Background of the Study
An average hydrocarbon field project is expected to move from the exploration stage up until the production stage before abandonment. While still at the production stage, which is the most critical and important stage, it comes to a point where there is a drastic drop in production as the rate fall subsequently. In conventional oil recovery projects, the decline of primary production to an uneconomic level led to the development of various schemes to improve the oil recovery efficiency before abandonment of a reservoir. The term enhanced oil recovery (EOR) principally refers to the recovery of oil by any method beyond the primary stage of oil production. It is defined as the production of crude oil from the reservoirs through processes taken to increase the primary reservoir drive. These processes may include pressure maintenance, injection of displacing fluids, or other methods such as thermal techniques. Therefore, by definition, EOR techniques include all methods that are used to increase cumulative oil produced (oil recovery) as much as possible (Al-Anazi, 2007).
Enhanced oil recovery can be divided into two major types of techniques: thermal and non-thermal recovery. Non-thermal recovery methods can be split into: water flooding, gas injection (including: LPG miscible slug, enriched gas miscible process, high pressure lean gas miscible process, carbon dioxide process) and chemical processes (including: micellar polymer flooding, caustic flooding, polymer flooding). Thermal recovery refers to oil recovery processes in which heat plays the principal role. The most widely used thermal techniques are in situ combustion, continuous injection of hot fluids such as steam, water or gases, and cyclic operations such as steam soaking (Taber, et al., 1997).
In gas injection processes there are two main types of gas injection, miscible gas injection and immiscible gas injection. In miscible gas injection, the gas is injected at or above minimum miscibility pressure (MMP) which causes the gas to be miscible in the oil. On the other hand, in immiscible gas injection, flooding by the gas is conducted below MMP. This low-pressure injection of gas is used to maintain reservoir pressure to prevent production cut-off and thereby increase the rate of production (Selamat, et al., 2008).
Thus, reservoir pressure is decreased by exploitation and production, leading to reduction in production. And since the role of oil and crude oil in International market and the world economy non-negligible, the adoption of appropriate contraptions and optimum enhanced oil recovery methods to improve efficiency and increase production have been a priority in Oil and gas industry.
1.2 Statement of the Problem
Primary recovery or natural production is applied for oil extraction under natural driving mechanisms in a reservoir without the use of external energy. As earlier mentioned, a reservoir has a natural economic production short span, hence it is obvious natural energies can’t provide appropriate power for optimum recovery of oil to the surface. Thus, the need to explore enhanced recovery methods such as gas-injection.