Page 80 - Synthetic Fuels Handbook

FUELS FROM PETROLEUM AND HEAVY OIL 67

applications. Enhanced oil recovery methods using microorganisms or electrical heating
have been proposed; their current state of development is not complete.
Thermal recovery methods include cyclic steam injection, steam flooding, and in situ
combustion. The thermal methods are used to reduce the viscosity of the oil and provide
pressure so that the oil will flow more easily to the production wells.
The steam processes are the most evolved enhanced oil recovery methods in terms
of field experience. For example, steam-based processes are most often applied in res-
ervoirs containing heavy oil in place of, rather than following, primary or secondary
recovery methods.
In situ combustion, an alternate thermal process, has been field tested under a wide
variety of reservoir conditions, but few projects have proved economic and advanced to
commercial scale. In the current economic climate, in situ combustion methods are once
again being given serious consideration for the recovery of heavy oil and bitumen from tar
sand formations.
Miscible methods use carbon dioxide, nitrogen, or hydrocarbons as miscible solvents
to flood the reservoir and can produce 10 to 15 percent of the original oil in place. The
solvents mix with the oil without an interface and are very effective in displacing the oil
from the reservoir. Their greatest potential is enhancing the recovery of low-viscosity oils.
Unfortunately, these methods do not always achieve high sweep efficiency.
The chemical methods include polymer-flooding, surfactant-(micellar/polymer,
microemulsion)flooding, and alkaline-flooding processes. These methods take advantage
of physical attributes of chemicals injected along with a displacing water driver to improve
recovery. Polymer flooding is conceptually simple and inexpensive, but it produces only
small amounts of incremental oil. It improves waterflooding by using polymers to thicken
the water to increase its viscosity to near that of the reservoir oil so that displacement is
more uniform and a greater portion of the reservoir is contacted.
Surfactant flooding is complex and requires detailed laboratory testing to support field
project design, but it can produce as much as 50 to 60 percent of residual oil. Surfactants
are injected into the reservoir to reduce the interfacial tension between the residual oil and
flood water to release the oil from the reservoir rock. The surfactant causes the oil droplets
to coalesce into an oil bank that can be pushed to production wells. Improvements in dis-
placement efficiency clearly have been shown; however, sweep efficiency is a serious issue
in applying this method.
Once the oil is recovered it is transported to the refinery where conversion to various
products takes place.

3.3 PETROLEUM REFINING

3.3.1 Dewatering and Desalting
Petroleum is recovered from the reservoir mixed with a variety of substances: gases, water,
and dirt (minerals). Thus, refining actually commences with the production of fluids from
the well or reservoir and is followed by pretreatment operations that are applied to the
crude oil either at the refinery or prior to transportation. Pipeline operators, for instance,
are insistent upon the quality of the fluids put into the pipelines; therefore, any crude oil to
be shipped by pipeline or, for that matter, by any other form of transportation must meet
rigid specifications in regard to water and salt content. In some instances, sulfur content,
nitrogen content, and viscosity may also be specified.
Field separation, which occurs at a field site near the recovery operation, is the first
attempt to remove the gases, water, and dirt that accompany crude oil coming from the