Page 16 - Synthetic Fuels Handbook

4 CHAPTER ONE

materials and the processing options have changed in an attempt to increase the efficiency
of oil production. Various national events (for the United States) and international events
(for other countries) have made it essential that we move ahead to develop fuels from
nonconventional sources.
Voices are being raised for the establishment of an industry that produces and develops
liquid fuels from nonconventional sources but there is still a long way to go. Incentives are
still needed to develop such resources.
There is a cone of silence in many government capitals that covers the cries to develop
nonconventional fuel sources. Hopefully, the silence will end in the near future, before it
is too late.

1.1 CONVENTIONAL FUEL SOURCES

For the purposes of this book, petroleum is recognized as the prominent conventional fuel
source. Thus, in the context of the definition of an alternative fuel or synthetic fuel that is
defined in the context of substitutes for petroleum-based fuel the term conventional fuel
implies any available fuel derived from petroleum.
Petroleum and the equivalent term crude oil cover a vast assortment of materials that
consist of gaseous, liquid, and solid hydrocarbon-type chemical compounds that occur in
sedimentary deposits throughout the world (Speight, 2007). When petroleum occurs in a
reservoir that allows the crude material to be recovered by pumping operations as a free-
flowing dark- to light-colored liquid, it is often referred to as conventional petroleum.
The U.S. Congress has defined tar sands as the several rock types that contain an
extremely viscous hydrocarbon which is not recoverable in its natural state by conven-
tional oil well production methods including currently used enhanced recovery techniques
(US Congress, 1976). By inference, heavy oil, which can be recovered in its natural state
by conventional oil-well production methods including currently used enhanced recovery
techniques does not fall into the same category as tar sand bitumen and therefore is a type
of petroleum. Thus, heavy oil is a type of petroleum that is different from conventional
petroleum insofar the flow properties are reduced and a heavy oil is much more difficult
to recover from the subsurface reservoir. These materials have a high viscosity (and low
API [American Petroleum Institute] gravity) relative to the viscosity (and API gravity) of
conventional petroleum and recovery of heavy oil usually requires thermal stimulation of
the reservoir (Speight, 2007 and references cited therein).
The definition of heavy oil is usually based on the API gravity or viscosity but the
definition is quite arbitrary. Although there have been attempts to rationalize the definition
based upon viscosity, API gravity, and density (Speight, 2007) such definitions based on
physical properties are inadequate and a more precise definition should involve some refer-
ence to the recovery method.
However, in a very general sense (and not in any sense meant to indicate classifica-
tion of heavy oil), the term heavy oil is often applied to a petroleum that has a gravity
o
greater than 20 API, and usually, but not always, a sulfur content higher than 2 percent w/w.
Furthermore, in contrast to conventional crude oil, heavy oil is darker in color and may
even be black. The term heavy oil has also been arbitrarily used to describe the heavy oil
that requires thermal stimulation of recovery from the reservoir and (albeit incorrectly) the
bitumen in bituminous sand (tar sand, oil sand) formations from which the highly viscous
bituminous material is recovered by a mining operation (Chap. 4).
Petroleum varies widely in composition and variations of the composition of heavy oil
add further complexity to the use of these feedstocks in the production of liquid fuels. The
variations in composition are generally reflected in variations in the API gravity, viscosity,