For years, most wells were
drilled vertically. Today, technology has allowed
for wells to be drilled directionally or
horizontally to intersect more of the producing
reservoir. However, crude oil extraction involves
more than drilling and pumping. Unlike natural gas
reservoirs, oil does not contain enough pressure to
gush to the surface, but has to be displaced from a
porous formation to the wellbore. The success of a
well depends on making a strong connection between
the wellbore and the reservoir system. Planning
before the drilling starts is vital.
When the crude oil is in the
wellbore, it can be pumped up to the surface. The
most common method uses a pump lowered down the
wellbore on a string of rods, and operated by an up
and down motion created by a pumpjack at the
surface. Other pumps use a rotary motion. This
method can recover up to 60 percent of the
recoverable oil in a reservoir. Other recovery
methods involve injecting water or natural gas to
maintain reservoir pressure. This is necessary
because the pressure drops as the resource is
produced. For heavy oil, steam is used to soften
the bitumen, or to enlarge or create channels and
cracks for the oil to flow more freely. The two most
successful methods are cyclic steam stimulation and
steam-assisted gravity drainage.
Steam Assisted Gravity Drainage (SAGD)
is a method that uses heat for recovering heavy oil. The
process utilizes twin horizontal wells drilled and
extended into the base of a reservoir with a
horizontal steam injector placed directly above the
horizontal production well. The mobilized oil drains
by gravity to the lower well and comes to the
surface. The Alberta Research Council’s Dr. Tawfik
Nasr is working on the continued development of SAGD.
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