**3. Carbon capture and storage**

Carbon dioxide is the most important greenhouse gas, because it is emitted into the atmosphere in large quantities [4]. Carbon capture and storage (CCS) has been recognized as a new project around the world that should help mitigate CO2 emissions significantly. The idea behind CCS is simple and can be divided into three steps: capture of CO2 (e.g., from a fossil fuel power plant), transportation of the captured CO2 , and permanent storage into different geological formations (e.g., saline aquifer and oil and reservoirs), with the aim of isolating CO2 from the atmosphere [5] (**Figure 3**).

**4. EOR methods**

includes some individual processes [7].

**Figure 3.** A schematic diagrams of possible CCS projects [5].

Gas methods, particularly carbon dioxide (CO2

Many EOR methods have been used in the past, with varying degrees of success, for the recovery of light and heavy oils, as well as tar sands. There are two main categories of EOR: thermal and non-thermal methods (include gas and chemical methods). Each main category

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Thermal methods are primarily intended for heavy oils and tar sands; these methods recover the oil by introducing heat into the reservoir. Thermal method is based on a set of displacement mechanisms to enhance oil recovery. The most important mechanism is the reduction of crude oil viscosity with increasing temperature [8]. However, the viscosity reduction is less for lighter crude oil. Therefore, thermal methods have had limited success in the field of light crudes.

Non-thermal methods (gas and chemical methods) are normally used for light oils <100 cp. In a few cases, they are applicable to heavy oils <2000 cp, which are unsuitable for thermal methods.

the reservoir. Gas methods sometimes are called miscible process or solvent methods. The reservoir geology and fluid properties determine the suitability of a process for a given reservoir. Currently, gas methods account for most EOR production and are very successful

Vapor extraction (VAPEX) is among the gas methods (**Figures 4** and **5**). It is a promising technique for the recovery of heavy oils and bitumen in reservoirs where thermal methods,

especially for the reservoirs with low permeability, high pressure, and lighter oil [9].

), recover the oil mainly by injecting gas into

Several scenarios describing the emission of greenhouse gases and models for the estimation of their influence on the global climate have been examined by the members of several association interests by this subject like the Intergovernmental Panel on Climate Change (IPCC) and the International Energy Agency (IEA). Based on the assumptions of IPCC, the climate model global temperature increases between 1 and 6°C were predicted by the year 2100, while some regions might benefit from higher temperatures [6]. The IEA Agency estimates that CCS projects should contribute to about 15–20% of the total greenhouse gas emissions mitigation by 2050, and without the application of CCS, the overall costs to halve CO2 emissions by 2050 would rise by 70% [5]. It has been estimated that geological formations worldwide are able to store more than 10,000 Gt of carbon dioxide; this huge quantity is large compared to the cumulated anthropic emissions of carbon dioxide [3].

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**Figure 3.** A schematic diagrams of possible CCS projects [5].
