Q:
When do you use "in-situ" production and when
does it make more sense to mine oil sands?
A:
Using current technology and
at today's oil prices, only about 10-20% of the Athabasca
Oil Sands can be mined. Mining only makes economic and engineering
sense when the overburden is less than about 75 metres thick.
Ideally, companies look for areas with less overburden since
removing overburden and then reclaiming the land adds considerably
to the cost of mining oil sands. As a result development
of the remaining 80-90% of the Athabasca Oil Sands and all
of the Cold Lake, Peace River and Wabasca deposits depends
on something called "in-situ," meaning in-place
production. There are many different techniques which have
been developed for "in situ" production, but all
of them really depend on using energy to produce energy.
In order to begin to separate the bitumen from the sand,
and then to make the bitumen liquid enough to pump, oil
sands deposits have to be heated in some way. Although many
methods of in-situ production have been suggested, the two
techniques that have been proven to work on a commercial
scale are fireflooding and various methods of steam injection.
The
simplest form of steam injection involves drilling two parallel
wells. One well is used to get high pressure steam into
the oil sands. Like fireflooding, this begins the separation
of the bitumen from the sand and lowers the viscosity of
the bitumen enough that it can be collected from a second
well. This method has a recovery rate of about 30% of the
bitumen in the formation.
Recently,
however, a variation on this technique has been developed
which greatly improves recovery and lowers the cost of production.
This method of in-situ production is called Steam Assisted
Gravity Drainage, or SAGD. It involves drilling two horizontal
wells one above the other. The top well is used to introduce
steam into the oil sands. As the bitumen thins and separates,
gravity causes it to collect in the second parallel well
where it can be pumped to the surface for further processing.
SAGD significantly improves bitumen recovery rates and therefore
lowers costs of production. In time it may prove the most
successful of the in-situ production methods developed to
date.
