7. Screening criteria for CO2 flooding

Screening criteria for miscible CO2 flooding comprise reservoir depth, pressure and temperature, minimum miscibility pressure (MMP), residual oil saturation, net pay thickness, crude oil gravity, and viscosity in addition to permeability, porosity, and reservoir heterogeneity [40]. In


Table 4. Optimum screening criteria for CO2 miscible flooding.

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 storage than low salinity reservoirs.

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;

$$\text{COIP} = \frac{(7758^\* A^\* H^\* \Phi^\* \text{Soi})}{\text{Boi}} \tag{1}$$

carried out to (a) scale-up the EOR process to an entire oil field and (b) define the optimum design of the WAG ratio and hydrocarbon pore volume injection volumes for maximum oil recovery [75]. The performance of a flooding process evaluated by exploring the slug of CO2 and water, the performance of oil-production wells, gas-oil ratio and water cut, and the injection wells for fluid distribution among various reservoir layers, since these parameters

CO2 Miscible Flooding for Enhanced Oil Recovery http://dx.doi.org/10.5772/intechopen.79082 87

In order to implement a successful CO2-miscible flooding several parameters are considered;

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

i. CO2 extraction: it is extracted from the separator gas, which begins to show increasing

ii. CO2 processing: it is purified to specification after its extraction from the separator gas

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

and is dehydrated before compression [78].

quantities of CO2 after its breakthrough in producing wells [77].

iii. CO2 compression: it is compressed to raise its pressure for injection [79].

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

2. Optimizing flood design and well placement for extracting more of the residual oil,

3. Improving the mobility ratio by increasing the viscosity of water by use of polymers, and 4. Extending miscibility by reducing the miscibility pressure through the use of liquefied

The primary and secondary oil recovery produces about 20–40% of the OOIP [48]. Consequently, there is a huge amount of potentially unrecovered oil left in the reservoir, which becomes the

greatly effect on the recovery factor [76].

9. Operational aspect

9.1. CO2 source

reservoirs [49].

9.2. Surface facilities

9.3. Technological challenges

petroleum gas (LPG).

10. Conclusion

1. Increasing CO2 injection volumes,

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