Page 113 - Fundamentals of Enhanced Oil and Gas Recovery

CHAPTER FOUR

Miscible Gas Injection Processes

1
2
Pouria Behnoudfar , Alireza Rostami and
3
Abdolhossein Hemmati-Sarapardeh
1
Department of Petroleum Engineering, Amirkabir University of Technology, Tehran, Iran
2
Department of Petroleum Engineering, Petroleum University of Technology (PUT), Ahwaz, Iran
3
Department of Petroleum Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

4.1 ENHANCED OIL RECOVERY

Applying primary and secondary oil recovery approaches leads to approximate
remaining of 67% original oil in place (OOIP). As an example, in the known oil fields
of the United States, this remaining oil in place is approximately equal to 377 billion
barrels. Therefore, the so-called enhanced oil recovery (EOR) methods are increas-
ingly being used in the oil fields due to rapid increase of the world oil price and oil
consumption [1]. After primary and secondary recovery, a high portion of original oil
remains in place that is entrapped in the pore spaces as a result of capillary and viscous
forces [2]. Hence, the EOR processes contribute to a greater recovery efficiency from
depleted oil reservoirs.
In general, EOR methods are categorized as waterflooding, chemical flooding, gas
injection, and thermal techniques such as hot water or steam injection. Previously
developed EOR methods are chiefly proposed for heavy oils, even though the latter is
generally employed in light oil recovery [3]. By three key mechanisms of nonthermal
EOR techniques including waterflooding, chemical flooding, and gas injection,
recovery factor can be promoted. These mechanisms are as follows [4]:
• Viscosity modification of displaced and/or displacing phase,
• Reduction of interfacial tension (IFT) between the displaced and displacing phases,
• Approaching or accomplishing miscibility by diluent extraction.
Some of nonthermal EOR techniques, such as alkaline flooding, alkaline
surfactant polymer, and polymer flooding, are exposed to some operational limita-
tions, such as reservoir permeability and formation temperature. Besides, they are
costly to be conducted in field-scale operation [5].
In the midst of all EOR methods, gas injection processes have been identified as
one of the most efficient techniques. On the other hand, gas injection can enhance
oil recovery by IFT reduction due to mass transfer between the displaced and

Fundamentals of Enhanced Oil and Gas Recovery from Conventional and Unconventional Reservoirs. © 2018 Elsevier Inc.
DOI: https://doi.org/10.1016/B978-0-12-813027-8.00004-7 All rights reserved. 101