9.1. CO2 source

There are three possible sources of CO2: (1) natural hydrocarbon gas reservoirs containing CO2 as an impurity (generally less than 25%), (2) industrial or anthropogenic sources with wide variation of CO2 percentage in the effluent like power plants and so on [2], and (3) natural CO2 reservoirs [49].

#### 9.2. Surface facilities

preliminary screening, according to National Petroleum Council, the optimum reservoir criteria for CO2 miscible flooding [64, 71] are summarized in Table 4. Any deviation from these criteria would depend on the size of the reservoir and potential hydrocarbon recovery. For example when reservoir temperatures are greater than 120�F, additional pressure ranges from 200 to 500 psi is required to achieve miscibility. The density of CO2 depends on the injection depth, which controls the ambient temperature and pressure and range from 0.6– 0.8 g/cc [72]. The CO2 should be injected at depth greater than 800 m, where it is in a dense phase (either liquid or supercritical) [2]. High saline reservoirs are more susceptible to CO2

Reservoir type Carbonate reservoirs preferred than sandstone one

Criteria Optimum condition Depth, ft 2500 [73]–3000 [74]

Oil gravity Medium to light oils (27–39�API)

Reservoir temperature, �F <120 Reservoir pressure, psi >3000 Total dissolved solids (TDS) <10,000 mg/L

86 Carbon Capture, Utilization and Sequestration

Oil viscosity, cp <3

Table 4. Optimum screening criteria for CO2 miscible flooding.

Minimum miscibility pressure (MMP), psi 1300–2500 Oil saturation >20% [73] Net pay thickness, ft 75–137 Porosity >7% Permeability >10 mD

All reservoir lithology, including carbonate and siliciclastic are appropriate for CO2-EOR flooding as long as they have interconnected pore space for fluid accumulation and flow. Proper reservoir characterization leads to accurate estimates of OOIP and a convenient evaluation of reservoir behavior. The OOIP calculated volumetrically, by the following equation;

7758, multiplying factor, (barrels/acre-feet); A, reservoir area,(acres);h; average net reservoir thickness, (feet); Ø; average porosity of formation; Soi; initial oil saturation in pore space; Boi;

Before conducting a CO2-flooding, its miscibility with the reservoir is determined through measurement of MMP. After that, a pilot test is conducted to check the success of the CO2- EOR process on a small scale in the field. If all results are positive, reservoir simulation is

<sup>H</sup><sup>∗</sup>Φ<sup>∗</sup> ð Þ Soi

Boi (1)

OOIP <sup>¼</sup> <sup>7758</sup><sup>∗</sup>A<sup>∗</sup>

oil formation volume factor at initial reservoir pressure (bbl/STB).

8. CO2-miscible flooding performance and simulation

storage than low salinity reservoirs.

The facility requirements for CO2-EOR include the following items.


#### 9.3. Technological challenges

Technical challenges of CO2 flooding can be summarized in the following [80].

