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60 F. Rahnama et al.
their feedstock. Many energy-producing companies are predicting a profitable
future through investment in these unconventional reserves.
Crude bitumen, a type of extra heavy oil, is a viscous mixture of hydrocarbons
that in its natural state does not flow very easily. In Alberta, crude bitumen
occurs in sand (clastic) and carbonate reservoirs in the northern part of the
province. While the bitumen found in both types of deposit are categorized as
oil sands, bitumen found in carbonate formations are not considered recoverable
at this time and with current technology.
The ‘ in-place ’ bitumen resources in Alberta amount to 1700 � 10 9
2 barrels.
The bitumen accumulations in Paleozoic carbonates hold approximately onequarter
of the in-place resource, nearly 450 � 10 9 barrels. Although the carbonatehosted
bitumen deposits are not considered in reserve estimates at this time,
recent experimental developments indicate that some of this bitumen may
become commercially viable within the next few years.
Clastic-hosted bitumen deposits are widespread accumulations of sand grains,
finer-grained clay or shale, water and extra heavy crude oil. The sand grains in
the oil sand deposits are covered with a thin layer of water, with bitumen filling
the pore space between the grains. The bitumen content of these deposits range
up to 18 mass percent. Of the 70 or more countries in the world, containing bitumen
deposits, Canada and Venezuela have the largest share.
The viscosity of bitumen prevents it from flowing naturally to a well and as
a result it cannot be produced using conventional technologies. In Alberta, two
distinct recovery methods are used to recover bitumen. Where bitumen deposits
lie closer to the surface (generally less than 70 m), the bitumen can be extracted
by mining, removing the overburden and accessing the oil sands deposit
directly. The oil sands are excavated and then washed with hot water in extraction
plants to recover the bitumen. The bitumen recovery factor, for mining
techniques, is generally over 80% of the ‘ in-place ’ resource. For deposits that are
located in deep reservoirs (between 70 and 800 m), which constitute over 90% of
the initial in-place resource, bitumen is produced using a variety of in situ technologies
where steam and, in some experiments, solvents are injected into the
reservoir to lower the viscosity and mobilize the bitumen, allowing it to flow
to the producing well. These latter techniques have recovery factors that range
between 15% and over 50% of the in-place resource.
Small portions of hydrocarbon deposits in Alberta’s three oil sand areas also
contain heavy oil with low enough viscosity to flow naturally and be recovered
similarly to conventional crude oil (primary recovery), with recovery factors of
5–10% of the in-place resource. For administrative and accounting purposes this
heavy oil is deemed to be part of the oil sand deposits and is categorized as primary
in situ bitumen production.
2 In this chapter volumes are expressed in barrels. Barrel is an imperial unit widely used in the
energy industry and is equivalent to 0.15891 m 3 . References are also made to ‘ barrels per day ’ (bpd),
‘ thousand barrels per day ’ (Mbpd) or ‘ million barrels per day ’ (MMbpd) throughout this chapter.