Page 117 - Fundamentals of Enhanced Oil and Gas Recovery

Miscible Gas Injection Processes 105

where P max andT stand for maximum injection pressure in MPa and reservoir temperature
in K, respectively. IFT is defined as the energy needed to build a unit surface area at the
boundary of two immiscible phases. It is the consequence of the attraction of surface mole-
cules to the interior molecules of liquid. Hence, it is very sensitive to temperature [31].

Example 4.1: Determine the MMP and maximum injection pressure for the following
systems and then discuss about the effect of purity of carbon dioxide (assume the res-

ervoir temperature is 80 C):
1. Dead oil and pure CO 2 system
2. Dead oil and impure CO 2 system

Solution: T(K) 5 T( C) 1 273.15
T 5 80 1 273.15 5 353.15K
1. Using Eq. (4.1), MMP can be calculated as follows:

MMP 5 0:116 3 353:15 2 27:1 5 16:86 MPa
and P max can be calculated via Eq. (4.5) as follows:

P max 5 0:384 3 353:15 2 102:8 5 32:80 MPa
2. Using Eq. (4.2), MMP can be calculated as follows:

MMP 5 0:222 3 353:15 2 51:0 5 27:39 MPa
and P max can be calculated via Eq. (4.6) as follows:
P max 5 0:281 3 353:15 2 61:9 5 37:33 MPa

The surface energy alters due to the dissolution of gas into the liquid interface.
Solubility is low at low pressures, and the effect of dissolved gas is negligible at low
pressure conditions, whereas the increase of temperature can cause increase of solubil-
ity of CO 2 in the crude oil at low pressures and consequently, the IFT will decrease.
The solubility of CO 2 in crude oil decreases with increasing temperature at higher
pressures [32]. As a result, the IFT increases with increasing temperatures for the case
of CO 2 gas injection. These effects can be studied by assembling an experimental
setup similar to Fig. 4.1 [29].
The obtained results in the work of Hemmati-Sarapardeh et al. [29] are illustrated
in Fig. 4.2. Also, the derived correlations, which are used to estimate IFT of crude
oil/CO 2 system in different conditions, are inserted in Table 4.1.

Example 4.2: Calculate IFT for the following thermodynamic conditions:
1. T 5 60 C, P 5 6MPa

2. T 5 80 C, P 5 7.5 MPa
3. T 5 100 C, P 5 10 MPa