Page 30 - Fundamentals of Enhanced Oil and Gas Recovery

18 Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi

steamflood, in which steam is injected into the injection well, moves toward the pro-
duction well, and oil is produced from production well. By heat loss near the steam
front, steam condenses to hot water. Consequently, oil swells, viscosity is decreased,
and oil displacement is improved.
In fire flooding method heat is supplied by in situ combustion in the reservoir. Air
or a mixture of light hydrocarbon and oxygen is continuously injected into the reser-
voir to maintain the combustion near the well. The fire front moves through the
production well, and heat is transferred to the reservoir fluid, including oil and water.
The reservoir water evaporates to steam, light hydrocarbons are vaporized, and oil
viscosity drops. Different mechanisms including steam drive, hot water, and light
hydrocarbon solvent help oil movement.

1.11.5 Chemical Injection
Chemical injection includes a vast range of chemicals to help oil movement with dif-
ferent mechanisms. Three major mechanisms can be considered for chemical injection
surface tension reduction, water shut-off, and wettability alteration. Although many
chemicals are developed to EOR, the classifications can be limited to ASP and
Polymer flooding. The objective of ASP injection is interfacial tension reduction
between oil and water to improve movement of trapped oil after waterflooding.
Alkaline chemicals react with reservoir oil and create in situ surfactant. This surfactant
is relatively cheaper than commercial surfactant. Also synthetic surfactant is injected
with the alkaline. Another component of ASP is polymer, which is used to increase
the viscosity of injected slug. This chemical controls the mobility of the ASP to
increase efficiency. The polymer flooding process is used in high permeable reservoirs
with high watercut. Polymers that are soluble in water are injected to the water
sources in reservoirs to control the mobility of the water by viscosity thickening.
Polymer injection is usually used in the first stages of the waterflooding to postpone
the water breakthrough.

1.11.6 Screening Criteria
The applicability of different EOR processes depends on reservoir condition, rock,
and fluid properties. Many technical screening criteria are suggested based on the res-
ervoir properties. The ranges proposed in these criteria are not absolute. Today, some
artificial intelligence (AI) methods are developed to describe the applicability of differ-
ent EOR process more realistically. Taber has gathered data on EOR projects all over
the world and suggested a table in which the applicability of different EOR methods
is investigated. Table 1.1 shows the Taber screening criteria.
As it can be seen, there are restrictions on the feasibility of processes. For example,
because of heat losses in the wellbore, thermal methods have depth limitation. On the