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Hi! My AP Environmental Science class is in the
midst of learning about renewable & nonrenewable
resources. We are also talking about oil drilling
in Santa Barbara County.We are wondering what the
main difference is between fracking and cyclic
steaming. What are the pros and cons involved
with each and what types of drilling is best for
our environment.We look forward to hearing from
you. We are hoping to get some different
perspectives on this--like from geologists,
biologists, chemists & environmentalists. Thanks!
Laura :) |
Question Date: 2014-04-11 | | Answer 1:
I really like this question! (I’m a geologist, so
you know, because you were interested in different
frames of reference) There are three basic ideas
that people need to know to understand these two
techniques.
The first is porosity. Porosity
is the amount of open space in a rock. Rocks like
granite, where crystals have grown together have
almost no porosity, but rocks like sandstone have
high porosity (20-30% of the rock), because the
sand grains don’t fit together perfectly. The
pores in a rock are where ground water, oil, and
gas exist.
The second idea is
permeability. This is how well water, oil, and gas
can flow through a rock. Sandstones are rocks with
high porosity and high permeability. This means
that they can hold a lot of water, oil, and gas,
and those fluids can flow through the rock, so
they are easy to get out. “Shales” are rocks made
mostly of mud. These rocks can have high porosity
like sandstones, but usually their permeability is
very low, meaning the fluids are “trapped” and
cannot flow out of the rock.
The third idea is viscosity.
When we are talking casually, we usually just say
“oil and gas.” In reality though, there are
dozens of different hydrocarbon molecules (chains
of hydrogen and carbon), especially in “crude
oil.” Longer, heavier hydrocarbon chains are more
viscous, meaning they flow more slowly.
Since we have been extracting
oil and gas for over 100 years, we have already
extracted most of the “easy stuff.” This is where
fracking and steam cycling come in.
“Fracking,” which is short for
“hydraulic fracturing,” is when water (with a
bunch of additives) is pumped into the ground at
high pressures in order to break the rock apart.
More fractures mean that the rock is more
permeable and so more oil and gas can flow to the
well and be extracted. With shales and sandstones
that aren’t permeable, this is the only way to get
oil and gas out, but it is also used to increase
the productivity in areas that are already
producing.
Cyclic steaming is used to
extract the heavy hydrocarbons that don’t flow
easily. The main goal of injecting steam is to
heat up the oil, because hot oil flows faster and
they can extract hydrocarbons that would otherwise
flow too slowly to be economically viable. The
viscosity analogy that people often make is honey
or molasses. They flow very slowly when they are
cold, but if you heat them up they will flow much
faster.
| | Answer 2:
Hydraulic fracturing (fracking) and cyclic
steaming are both designed to make it easier to
extract oil that is stuck in pore spaces in the
rock in which the oil is trapped. However, they
are aimed at slightly different reservoir/oil
types. Cyclic steaming is often used when the oil
is what they call 'heavy' oil. This is a type of
oil that is very viscous (resistant to flow) and
sticky, almost like tar. The oil's viscosity
decreases as its temperature goes up, allowing it
to be recovered. So with cyclic steaming, the
production company drills a well into an oil
reservoir and injects steam into the rock until
the little tendrils of steam are able to heat up
and 'liquify' the otherwise immobile oil. Then
the injector well is converted back into a
producer well, so that all the warm, runny oil can
be brought to the surface. The well is then
turned back into an injector well, and so on,
until the reservoir has been effectively depleted.
This type of oil recovery is sometimes called the
'huff and puff' method.
Cyclic steaming is usually used on sandstone
oil reservoirs, which allow fluids to flow
relatively well (as long as the fluids are not too
viscous!)
Hydraulic Fracturing is often used when the oil
reservoir is very impermeable (meaning the pore
spaces in which the oil resides are not connected,
and thus the oil cannot flow to the production
well). In these rocks, the oil need not be heavy,
but the impermeability of the rock is what limits
its ability to flow. In these cases, the
production company drills a well into the oil
reservoir, then pumps a large volume of dense
fracking fluid and sand into the well under
extremely high pressure. This pressure creates a
network of fractures in the oil reservoir that
increase its permeability, allowing the trapped
oil to flow back into the well. Fracking is most
common on reservoirs made of shale, which do not
allow fluids to flow very well.
Both methods involve using fluids to 'stimulate'
the well into production. However fracking
involves actually breaking the rocks to release
the oil, while cyclic steaming involves heating
the oil up so that it can flow. So, it is rare
for both methods to be applicable to the same oil
field.
Both methods are carried out carefully, so
that only the rock interval containing the oil
will be affected by the fracking fluids or the
steam. Usually a regulatory agency monitors the
drilling of the well and the fracking/steaming
process to make sure the injected fluids are going
where they should be going. However, not every
well is perfect and sometimes wells have to be
shut down for leaking steam or fracking fluid into
the wrong rock layers. Both methods are also very
energy-intensive. In order to generate enough
steam to heat up an oil body, an enormous amount
of natural gas is burnt...so we end up using a lot
of energy to create energy. Also, the water that
gets converted to steam must come from somewhere.
Steaming means a lot of water comes up with the
oil, and that contaminated water must be
re-injected into the reservoir to dispose of it.
Not a very efficient way to make oil, so the only
reason it works is because the price of oil is so
high! When the price drops, cyclic steaming will
slow down considerably.
Fracking requires a larger initial investment,
but is likely to be more efficient over the long
run (as long as the geologists and engineers have
done their homework!)
Hope that helps,
| | Answer 3:
This problem is complicated because your question
is really an engineering geology question, which
means that I, despite being a geologist
(specifically, a paleontologist), do not really
understand the differences between them well
enough to answer your question. Both involve
breaking up rock and then inputting something to
prevent subsidence after extraction, but the
environmental consequences of each are going to
vary depending on the circumstances, whether it's
on land or in the ocean, and possibly on the
character of the oil reservoir as well.
It also depends a great deal on the quality of
the engineering; drilling for oil is only very
locally destructive from an ecological standpoint,
unless something goes horribly wrong and you get
an oil spill. Getting an oil spill of course is
something that nobody wants, the oil companies
least of all (ethical reasons aside, they're
losing all of that valuable oil). I'll note that
it's been several decades since the last oil spill
in the Santa Barbara channel, which at least
suggests that the quality of the engineering is
fairly safe. That said, drilling oil is going to
have global environmental effects as well, in the
form of greenhouse emissions.
However, again, not being an engineering geologist
or a marine biologist who studies the effect of
oil drilling, I can't really comment on which is
better and why, especially in this specific
instance.
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