| Oil sands
consist of bitumen (soluble organic matter) and host sediment with
associated minerals, excluding any related natural gas. Most of the
oil sand deposits in the world are found in Venezuela and Canada.
1 -- Location of the Alberta oil sands in Canada: (A) regulatory
areas of oil sands development; (B) surficial expression of
the Athabasca, Peace River and Cold Lake deposits.
oil sands occur in Cretaceous fluvial-estuarine deposits of northeastern
Alberta, covering an area greater than140,000 kilometers2 (figures
1A, 1B). Bitumen also is hosted in carbonates in Alberta but, to
date, these are not commercially produced.
Alberta's reserves estimates of remaining established oil reserves
is 174.5 billion barrels, comparable with the oil reserves of Saudi
Arabia. In 2001, Alberta's production of raw bitumen and synthetic
crude oil exceeded that for conventional crude oil, accounting for
53 percent of Alberta's oil production. This trend is expected to
increase to be about 80 percent of Alberta's oil production by 2013.
2 -- Archival photograph of a Geological Survey of Canada field
party hauling a scow up the Athabasca River, Alberta, in 1914.
of the Canadian oil sands industry has a history of over 90 years.
In 1913 Sidney Ells organized the first field parties to work on
oil sands, hauling out over nine tons of oil sands by scows up the
Athabasca River valley (figure 2).
near Fort McMurray, oil sands are recovered in open-pit mines by
truck-and-shovel operations in which the world's largest Caterpillar
797 and 797B trucks have payloads of 380 tons. Oil sand is transported
to processing plants, where hot or warm water separates the bitumen
from the sand, followed by dilution with lighter hydrocarbons and
upgrading to synthetic crude oil (SCO) -- a mixture of pentanes
and heavier hydrocarbons.
field trip at the 2005 AAPG Annual Convention in Calgary will visit
the McMurray oil sands in the Athabasca area.)
percent of the oil sands reserves in Alberta are recoverable by
surface mining; in-situ technologies need to be used for the remaining
80 percent of the oil sands that are buried at depth (greater than
oil sands are unconsolidated, held together by the pore-filling
bitumen. The bitumen is a natural, tar-like mixture of hydrocarbons
that when heated has a consistency of molasses.
natural state, bitumen (density range of 8-12° API; at room temperature
viscosity greater than 50,000 centipoises) will not flow to a well
other heavy oil in sand is also considered as "oil sands" if it
is located within the oil-sand application areas (figure 1A). However,
because the pore-fluid is heavy oil and will flow to a well, these
deposits are referred to as "primary in-situ crude bitumen." The
major challenge of recovering bitumen from depth is to overcome
its high viscosity to allow it to flow to the well bore.
3A: Cyclic Steam Stimulation (CSS)
Figure 3B: Steam-Assisted Gravity Drainage (SAGD)
Sketches of common
in-situ technologies for recovery of bitumen
To do this,
thermal (or other non-primary) in-situ methods are used -- most
commonly Cyclic Steam Stimulation (CSS) and Steam Assisted Gravity
Canada's largest in-situ bitumen recovery project
uses CSS at Cold Lake. Steam injected down the well bore into the
reservoir heats the bitumen; followed by a soak period; and then
the same well bore is used to pump up fluids (figure 3A).
Lake about 3,200 wells are currently operating from multiple pads,
with two aboveground pipelines -- one to deliver steam and the other
to transport fluids back to the processing plant.
At Athabasca, the SAGD technology is used.
well pairs (700 meters long with five-meter vertical separation)
are drilled from surface pads to intersect bitumen pay (figure 3B).
Steam from the upper injector well expands, reducing the viscosity
of the bitumen, allowing the bitumen to flow. A shell forms at the
cold interface with the unheated reservoir, along which bitumen/condensate
drain by gravity to the lower producing well (figure 3B).
submersible pumps (ESPs) may assist in lift.
challenges for economic in-situ recovery involve water and gas requirements
for steam generation, reclamation and emission controls of greenhouse
gases. Generally, it takes 28 meters3 (1,000 feet3)
of natural gas and from 2.5 to four barrels of water to produce
one barrel of bitumen. Reclamation of mining sites is done to a
standard to at least the equivalent of their previous biological
in the mid-1970s, the North American energy crises have made the
Canadian oil sands a more strategic resource for North American
energy needs, accelerating industry's interest and efforts to tap
these vast bitumen reserves.