Conversion Technologies 67
absolute quantity of the resource available. Third, most of the highest quality resources
have been already depleted, and the remaining ones are increasingly difficult to extract.
Combination of these reasons has prompted the search for alternative sources of carbon
among both renewable and fossil resources. At least in principle there are alternatives
to traditional light oil among other fossil resources. These resources are usually called
unconventional oil and might be used to supplant and possibly replace currently used
crude oil and provide carbon and energy to the economy once current fossil fuel deposits
are exhausted. The most widely considered alternatives with their short characteristics
are presented in the following sections.
3.2.3.4 Shale Oil (Tight Oil)
Shale oil is similar in structure to light oil. The difference between the two is their loca-
tion and method of extraction. Conventional oil deposits can be continuously retrieved
from the source until it is depleted. Shale oil on the other hand is much more compli-
cated to extract. Oil is entrapped in porous rock formations that need to be fractured
to release it. The fracturing is performed by drilling multiple vertical–horizontal wells
and injecting hectolitres of water with numerous chemicals often not disclosed by the
drilling companies. Created fissures make the oil flow into the surface where it can be
collected. A number of refractures needs to be performed to maintain the flow of shale
oil from the rock to surface.
3.2.3.5 Oil Sands, Bitumen Extra Heavy Oil
This group of non-conventional oil contains oxidised hydrocarbon mixtures in which
lighter fluid fractions have evaporated. These heavier hydrocarbons contained in bitu-
minous sands cannot be extracted as easily as conventional oil. First, they cannot be
pumped, hydrocarbons mixed with sands are strip mined and extracted with hot water.
Second, the extracted hydrocarbons require advanced upgrading to be transformed into
fuels. Combination of these two factors makes this technology expensive and limited to
regions with abundant water resources and cheap energy, both of which are increasingly
scarce. Additionally, the extraction process produces a lot of wastewater contaminated
with hydrocarbons that are usually stored in ponds that create environmental and health
hazards.
3.2.3.6 Shale Gas
In recent years, the advances in the extraction of the so-called shale gas gave the oil
and gas industry large hopes for significantly extending the life span of gas technolo-
gies. From the chemical point of view, there is no difference between shale gas and
‘conventional’ natural gas; they are both predominantly composed of methane. What
differs however is the method of extraction, which is very similar to the one used for
shale oil. Shale gas is entrapped in porous rock formations that need to be fractured
before the gas is released. The fracturing (fracking) is performed by drilling multiple
vertical–horizontal wells and injecting water with chemicals. Fractured rocks release the
gas into the water and ultimately to surface; secondary fracking needs to be performed
to maintain the flow of gas.
3.2.3.7 Methane (Gas) Hydrates
Gas hydrates are ice-like solids formed from water and natural gas. Natural gas is
entrapped inside the cages made of frozen water particles. These cages are stable at
