**4. EOR methods**

**3. Carbon capture and storage**

phase diagram [2].

244 Carbon Dioxide Chemistry, Capture and Oil Recovery

CO2

**Figure 2.** CO2

new project around the world that should help mitigate CO2

fuel power plant), transportation of the captured CO2

cumulated anthropic emissions of carbon dioxide [3].

from the atmosphere [5] (**Figure 3**).

behind CCS is simple and can be divided into three steps: capture of CO2

by 2050, and without the application of CCS, the overall costs to halve CO2

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

geological formations (e.g., saline aquifer and oil and reservoirs), with the aim of isolating

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

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

emissions significantly. The idea

, and permanent storage into different

(e.g., from a fossil

emissions by 2050

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 includes some individual processes [7].

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.

Gas methods, particularly carbon dioxide (CO2 ), recover the oil mainly by injecting gas into 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 especially for the reservoirs with low permeability, high pressure, and lighter oil [9].

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,

**Figure 4.** The VAPEX heavy oil recovery process [11].

reduction, viscosity reduction, wettability alteration, and mobility control. Meanwhile, there are many researchers on the background of EOR process; for a detailed review of enhanced oil recovery, we refer the interested reader to Thomas [7], and general classifications of these

A Review on the Application of Enhanced Oil/Gas Recovery through CO2 Sequestration

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247

mental Panel on Climate Change stresses the need to control anthropogenic greenhouse gases in order to mitigate the climate change that is adversely affecting the planet. Moreover, in some fields, the hydrocarbon gases produced along with the oil are re-injected into the reservoir to enhance oil production. Nevertheless, in some fields, the hydrocarbon gas is sold, and

remain unrecoverable [13]. Typically, only around one-third of the oil is produced after primary and secondary oil recovery methods. Much of the remaining oil are trapped by capillary forces as disconnected drops, surrounded by water, or as a continuous phase at low saturation with gas occupying the larger fraction of the pore space. EOR operations

is an attractive oil recovery process that involves the

to oil reservoirs and produce petroleum substances that would otherwise

the gas itself is considered as a source of energy. An attractive option is the use of CO<sup>2</sup>

. The Intergovern-

as one

 **injection**

of the main components of the solvent mixture for EOR process.

The combustion and flaring of fossil fuels produce large quantities of CO<sup>2</sup>

**-EOR: definition and advantages**

methods are shown in **Figure 6**.

**Figure 6.** Classification of EOR methods.

**5. Oil recovery by CO2**

Enhanced oil recovery using CO2

injection of CO2

**5.1. CO2**

**Figure 5.** Mechanism involved in the VAPEX process [12].

such as steam-assisted gravity drainage (SAGD), cannot be applied. In the VAPEX process, a pair of horizontal injector-producer wells is employed. The gaseous hydrocarbon solvent (propane, butane, or a mixture of them) is injected into the deposit from the top well, and the diluted oil drains are gravitated downward to the bottom producing well. Recently, an attractive option was developed using CO2 as a solvent in the VAPEX process. The high solubility and viscosity reduction potential of CO2 could provide improvement to VAPEX performance. It also creates new opportunities for CO2 sequestration [10].

Chemical methods include polymer floods, surfactant flooding, alkaline flooding, and so on. The mechanisms of chemical methods are dependent on the chemical materials added into the reservoir. The chemical methods may provide one or several effects: interfacial tension A Review on the Application of Enhanced Oil/Gas Recovery through CO2 Sequestration http://dx.doi.org/10.5772/intechopen.79278 247

**Figure 6.** Classification of EOR methods.

reduction, viscosity reduction, wettability alteration, and mobility control. Meanwhile, there are many researchers on the background of EOR process; for a detailed review of enhanced oil recovery, we refer the interested reader to Thomas [7], and general classifications of these methods are shown in **Figure 6**.

#### **5. Oil recovery by CO2 injection**

#### **5.1. CO2 -EOR: definition and advantages**

such as steam-assisted gravity drainage (SAGD), cannot be applied. In the VAPEX process, a pair of horizontal injector-producer wells is employed. The gaseous hydrocarbon solvent (propane, butane, or a mixture of them) is injected into the deposit from the top well, and the diluted oil drains are gravitated downward to the bottom producing well. Recently, an attrac-

sequestration [10].

Chemical methods include polymer floods, surfactant flooding, alkaline flooding, and so on. The mechanisms of chemical methods are dependent on the chemical materials added into the reservoir. The chemical methods may provide one or several effects: interfacial tension

as a solvent in the VAPEX process. The high solubility

could provide improvement to VAPEX performance.

tive option was developed using CO2

and viscosity reduction potential of CO2

**Figure 5.** Mechanism involved in the VAPEX process [12].

**Figure 4.** The VAPEX heavy oil recovery process [11].

246 Carbon Dioxide Chemistry, Capture and Oil Recovery

It also creates new opportunities for CO2

The combustion and flaring of fossil fuels produce large quantities of CO<sup>2</sup> . The Intergovernmental Panel on Climate Change stresses the need to control anthropogenic greenhouse gases in order to mitigate the climate change that is adversely affecting the planet. Moreover, in some fields, the hydrocarbon gases produced along with the oil are re-injected into the reservoir to enhance oil production. Nevertheless, in some fields, the hydrocarbon gas is sold, and the gas itself is considered as a source of energy. An attractive option is the use of CO<sup>2</sup> as one of the main components of the solvent mixture for EOR process.

Enhanced oil recovery using CO2 is an attractive oil recovery process that involves the injection of CO2 to oil reservoirs and produce petroleum substances that would otherwise remain unrecoverable [13]. Typically, only around one-third of the oil is produced after primary and secondary oil recovery methods. Much of the remaining oil are trapped by capillary forces as disconnected drops, surrounded by water, or as a continuous phase at low saturation with gas occupying the larger fraction of the pore space. EOR operations using carbon dioxide have been practiced for more than 50 years; the results revealed that 6–15% of original oil in place can be recovered by these kinds of processes [14].

Mehrotra and Svrcek [32–34] during the 1980s reported extensive experimental data on the dissolution of carbon dioxide on different bitumen samples in Alberta reservoirs. Their experimental data confirm a higher solubility of carbon dioxide in bitumen, and they found that

A Review on the Application of Enhanced Oil/Gas Recovery through CO2 Sequestration

saturated with oil and was surrounded by an artificial fracture at reservoir conditions. These authors observed the production of gas enriched with methane at an early stage. Next, the amount of intermediate components increased in the production stream, and during the end of the experiments, the heavier components were recovered. Their results were also confirmed

Malik and Islam [37] conclude that in the Weyburn field of Canada, horizontal injection wells

different well control techniques including completion equipment for both injection and pro-

Recently, Li-ping et al. [39] conducted an evaluation study around Ordos Basin in Yulin city of China; this Basin was divided into 17 reservoirs and is considered as the first largest lowpermeability proliferous onshore basin in China with proved reserves more than 10<sup>9</sup> t. These authors conclude that Ordos Basin has good geographical and geological conditions for CO2

The booming development and production of shale gas largely depend on the extensive application of water-based hydraulic fracturing treatments. Hence, high water consumption and formation damage are two issues associated with this procedure. More recently, Pei et al. [40]

(EGR) in order to reduce water usage and resource degradation, guarantee the environmental sustainability of unconventional resource developments, and create new opportunity for CO2

ful in the Barnett shale reservoir, but there are some scientific and engineering questions that need to be further investigated to push the proposed technology to be applicable in practice. Song investigated the effect of operational schemes, reservoir types, and development param-

numerical simulator. The author's study shows that the five-spot pattern is more suitable for WAG flooding. Appropriately expanding well spacing improves the economic efficiency, even though the recovery factor decreases slightly. In addition, oil price, rather than CO2 injection cost, is considered as the parameter that impacts the economic efficiency of WAG

micro-scale fractured system saturated by normal decane (n-C10). The authors concluded that

duction wells, at the same time improving the amount of injected and stored CO2

storage potential. Besides employing horizontal wells, Jessen et al. [38] have applied

miscible flooding. The average incremental oil recovery ratios for immiscible and

water-alternating-gas (WAG) flooding by running a compositional

injection in an outcrop chalk core

http://dx.doi.org/10.5772/intechopen.79278

as well as

249


immiscible flooding and eight reservoirs suit-

for reservoir fracturing and enhanced gas recovery


stored in high water cut oil

on oil recovery using synthetic

this solubility increases as the injection pressure increases. Darvish et al. [35] performed a set of experiments of CO2

by simulation study performed by Moortgat et al. [36].

storage, and it has nine reservoirs suitable for CO2

miscible flooding are 6.44 and 12%, respectively.

storage. This study shows that this proposed CO2

eters on both the amount of incremental oil produced and CO2

Er et al. [42] investigated the effect of injection flow rate of CO<sup>2</sup>

investigated the feasibility of using CO2

have showed to be efficient for CO<sup>2</sup>

enhancing oil recovery.

reservoirs during CO2

flooding more significantly [41].

the CO2

able for CO2

The low saturation pressure of CO2 compared to CH4 or N2 and its low price compared with other hydrocarbon solvents are the incentives for the use of CO2 in the EOR process. Moreover, a mixture of hydrocarbon solvents with CO2 may be less likely to precipitate asphaltene, which is a great problem in enhanced oil recovery [15]. Furthermore, at high pressures, CO2 density has a density close to that of a liquid and is greater than that of either nitrogen (N2 ) or methane (CH4 ), which makes CO2 less prone to gravity segregation compared with N2 or CH4 [16].

#### **5.2. Oil recovery mechanisms by CO2 dissolution**

When CO<sup>2</sup> is injected into the reservoir, it interacts physically and chemically with rocks and fluids that are present in the reservoir, creating favorable mechanisms that can make enhancement in oil recovery. Among these mechanisms include a high dissolution of CO2 into crude oil via mass transfer followed by the following aspects: an increase of oil density, a reduction of the viscosity of the original crude oil, vaporization of intermediate components of the oil, a reduction of CO2 -oil interfacial tension, oil swelling, a reduction of water–oil interfacial tension, and an improvement of reservoir permeability [17].

The main scenario followed by CO2 sequestration is the mechanism of fluid density increasing caused by the dissolution and mixing of injected CO2 into fluid. In the past, there are a set of studies that have not taken the effect of density increase from mixing into account; this mechanism in the modeling of CO2 injection has been ignored [18–21]. However, as shown in other studies, this may not be true; CO2 has an effect on the density of fluid that is present in the reservoir [22, 23]. Its dissolution and mixing leads to density increase followed by density-driven natural convection phenomena. There are several published studies which reported that this phenomenon has a significant enhancement in hydrocarbon recovery and sequestration potential [24–27].
