Page 234 - Fundamentals of Enhanced Oil and Gas Recovery

222 Mohammad Ali Ahmadi

Also, the following assumptions have been made for developing Buckley Leverett
approach:
• A circular reservoir with constant height
• Reservoir is homogeneous in all rock properties
• The dip angle of formation is zero
• Oil and water two-phase flow in reservoir, no gas present in the reservoir
• Compressibilities of oil and water are negligible
• Constant reservoir temperature is applied
• All rock properties do not change as pressure changes
• Constant oil and water viscosities during displacement

7.6 LOW-SALINITY WATERFLOODING

Injection of low-salinity (LS) water has widely been practiced because the water
sources are available and relatively cheaper among other practical advantages.
However, the EOR potential was not recognized until Morrow et al. [34 40] found
that changing the composition of the injected water results in changing the oil recov-
ery factor.
Yildiz and Morrow [40] supported that the injection water composition could
affect the oil recovery factor; however, the maximum recoverable oil using water
injection process occurs in a particular conditions of brine/rock/oil system.
There are different studies that have been done to evaluate the machanisms con-
tributed in low salinity water injection [41 44].

7.6.1 Effect of Rock and Fluid Properties on Low-Salinity
Waterflooding Performance
7.6.1.1 Effect of Connate Water Saturation
Tang and Morrow [37] carried out experimental tests to evaluate the effect of initial
water saturation on both high salinity and low salinity water flooding processes. They
concluded that in a case of zero connate water saturation the oil recovery achieved
from both high salinity and low salinity water flooding was almost the same. Zhang
and Morrow [46] realized that the more oil can be produce using low salinity water
injection in a case of connate water existence; as a comparison, presence of initial sat-
uration is crucial for success of such an EOR method.

7.6.1.2 Effect of the Salinity of Connate Water
Sharma and Filoco [47] found that the salinity of connate water was the primary fac-
tor controlling the oil recovery. They concluded that decreasing in salinity of connate