Oil sands are mixtures of sand,
water, clay, and crude bitumen. Oil sand grains have
layers of water surrounding a grain of sand, and a
film of bitumen surrounding the water. The
extraction process involves removing the sand from the
crude oil. This is not an easy process. As early as
the 1860s, hard, tight oil sands were being shot
with gunpowder and then nitroglycerin to shatter the
rock at the bottom of the wellbore. The practice of
shooting explosives increased flow but was
temporary, as it destroyed the well and was dangerous.
The more popular and safer method was open pit
mining. Mine equipment from the early years was
scaled up significantly when large commercial
operations started to develop. The first large
scale commercial operation, Great Canadian Oil Sands
(Suncor Energy), introduced bucketwheels from the
coal mining industry when they opened in 1967.
Syncrude Canada Limited opened in
1978 and introduced gigantic draglines sixty times as
large as the bucketwheels. However, the use of
draglines and bucketwheel re-claimers in the mining
process is being phased out, because about 80
percent of the oil sands in Alberta are buried too
deep below the surface for open pit mining. This oil
must be recovered by in situ techniques. The phrase,
"in situ" is Latin for "in place." Using drilling
technology, steam is injected into the deposit to
heat the oil sand thereby lowering the viscosity of the
bitumen. The hot bitumen migrates towards the
producing wells, which, in turn, brings the oil to the surface while
the sand is left in place. Steam Assisted Gravity
Drainage (SAGD) is a type of in situ technology that
uses innovation in horizontal drilling to produce
bitumen. Two parallel horizontal wells are drilled
through the oil sand deposit. Steam is then injected
into the top well and loosens the crude oil from the
sand. The oil flows to the lower well where it is
pumped to the surface. The technology is expensive
and requires certain conditions like a nearby water
source. However, due to the high oil recovery rates, SAGD is the most popular enhanced oil recovery
system used in Canada.
There are other in situ ways of
recovering oil sands. Cyclic Steam Stimulation (CSS)
injects high pressure and high temperature steam
into the sand deposits. The pressure and heat
separate the sand and bitumen, where the bitumen
flows to a producing well and is pumped to the
surface. The Vapour Extraction Process (VAPEX) is
similar to SAGD, but uses solvents such as ethane or
propane, which creates a vapour chamber that the oil
flows through with the help of gravity.
|