Enhanced Oil Recovery (EOR)

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Abstract :

This article provides a summary and overview of enhanced oil recovery (EOR) technologies. Thermal recovery methods, gas injection and chemical techniques are the main categories of the EOR. Each category has its own criteria and conditions to improve oil recovery.

Introduction :

With declining reserves, operators have recognized that significant quantities of oil remained in their reservoirs after primary and secondary recoveries. Discovering and exploring new reserves and drilling new wells would take a long time and not be profitable and economical, so it is impossible and in order to cover worldwide energy

Consumption , scientists and operators have developed new technologies aimed at producing more hydrocarbons with less cost. These techniques, called enhanced oil recovery, have shown impressive results in the recovery of large quantities of hydrocarbons at the laboratory scale as well as at the scale of an oil field. Year after year, many types of EOR have appeared, ranging from thermal methods to gas injection to chemical techniques. Screening for EOR methods should be performed before choosing any of these techniques in order to suit the reservoir characteristics and fluid properties

Definition:

EOR stands for Enhanced Oil Recovery and refers to the application of technologies developed to increase the production of hydrocarbons, it is also called Tertiary Recovery. EOR processes involve the injection of a fluid into a reservoir, which will interact with the reservoir rock and hydrocarbons. EOR may extract 30 to 60 % or more of the oil in a reservoir.

Several EOR methods have been developed and used to improve overall oil displacement quality.

Thermal methods (tEOR) in these processes, a thermal source (Steam, Hot water…) is injected into the reservoir. The key method of thermal recovery is to reduce the viscosity of the oil by raising the temperature, allowing it to flow more easily through the porous media of the reservoir. Steam flooding, steam Huff and Puff, in situ combustion, and hot water injection are all part of the thermal recovery process. 

Source: COMSATS Institute
Source: COMSATS Institute

Gas injection method: This technique involves combining oil with a miscible gas. Carbon dioxide CO2 is the most widely used gas since it is miscible with oil at low pressures and temperatures, but nitrogen may also be used depending on availability. The process for recovering residual oil by injecting miscible gas is based on lowering the interfacial tension (IFT) between the oil and the miscible gas. The most common issues with this technique are viscous fingering caused by the poor sweep of the reservoir caused by the significant difference in viscosity and density of the fluids, on the other hand, gas injection operations such as CO2 can cause corrosion problems. Therefore, special prevention provisions must be taken into account.

Source: Expertise-academy.
Source: Expertise-academy.

Chemical injection (cEOR): Because of its higher performance, technological and economic feasibility, and rational capital cost, it has been considered the most promising method especially in mature waterflooded fields. Chemical EOR can be divided into three classes. In addition, Polymer, Surfactant and Alkaline agents. Alkali-polymer (AP), Surfactant-Polymer (SP), and alkali-surfactant-polymer (ASP) are examples of combinations of the three groups. The laboratory scale collection, formulation, and performance assessment are crucial to the success of chemical-assisted recovery.

Another type of chemical injection is Foam Flooding. Foam is described as the gas phase dispersion in the liquid phase, where the liquid phase is continuous and the gas phase is discontinuous. By forming bubbles in the liquid, gas separates from it, and a thin film called lamella forms between each bubble.

The foam is used to improve the displacement of oil from porous media by driving fluids such as gas and water. It enhances the efficiency of the displacement hence the RF (Recovery Factor) increases.

Foam generation in porous media (reservoir) occurs by three mechanisms, firstly. Capillary snap-off occurs when liquid is displaced by gas in a pore throat to form gas bubble. Secondly, lamella division occurs when thin film of foam gets splitted into two or more, resulting in the creation of new gas bubbles. The final mechanism, known as leave-behind, occurs when two gases fronts approach the same liquid-filled pore space, forcing the liquid in the pore to form a lamella.

For a gas-based injection process (CO2, N2, or hydrocarbon gas), conformance, channeling, and gravity override, these problems can be solved by foams, as well as and thief zone problem.

For an effective foam application, it is necessary to determine:

Type of problem to be solved and which injection wells are causing the problem. If foam is the right solution, and where the foam is to be injected (into a production or injection well).The selection of different surfactants should be based on laboratory experiments performed under standard prototype conditions. For optimal performance, the injection of the foams must follow on-and-off mode, for example: foam is injected for one week then stopped for the next week. Alternatively, 24 hours on and 24 hours off.

Microbial enhanced oil recovery (MEOR):

Microbial enhanced oil recovery has proven to be an economical technology to increase hydrocarbon production, it involves injecting a microbe into the reservoir, which has the capacity to produce a number of insoluble polymers, and it can be applied in a reservoir

That has the condition of spreading the microbe.

The MEOR has been efficiently developed for a simple process that is also efficient, non-polluting, and inexpensive to operate.

The control of the function of microbes and their metabolites in the reservoir, reproduction, and the conditions of transport of the microbes in the reservoir are all major challenges.

Source: Marchant and Banat (2012)
illustration-of-microbial-flooding-recovery

Conclusion:

 EOR processes are a promising and useful method for improving sweeping efficiency, hence increasing the production of hydrocarbons remaining in the reservoir after primary and secondary recovery. Several EOR categories and subcategories have been used in different places around the world and have shown remarkable results, hoping to innovate new low-cost and environmentally friendly technologies.

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