0:10
So the search for conventional oil
is really a search for these special oil traps
and special conditions.
Now, when did this start happening?
Well, oil has been known for a long time.
In more recent times,
oil was used during the 19th century,
primarily as a lubricant for wagon wheels,
but it was not used as an energy source
because it was very limited in supply.
The only place that people knew where they could get oil from
were what-were localities called natural oil seeps.
These are places where cracks or fractures
tap into an oil reserve underground
so the oil is able to migrate up and bubble out
at the surface of the earth.
You can actually see
some of these natural oil seeps today,
for example, the La Brea Tar Bits
that occur in a park in California
near the city of Los Angeles.
You can go there, look at the ground,
and watch oil actually bubbling out at the surface.
But that was not enough of a supply,
so in the mid 19th century
a group of investors from the eastern United States
decided to see if they could figure out how to drill a well,
like a water well,
only into an oil reserve,
and collect oil in sufficient quantities
to economically produce it and use it
as a-as a heating source or as a lighting source.
One of the reasons there was a lot of demand
and a lot of interest in this
was that the predominant lighting source
at the time was whale oil,
and whales were being hunted to extinction,
so the supply of whale oil was pretty much being overused.
Well, to make a long story short,
in 1859 these investors hired a guy named Edwin Drake,
he drilled a well in Pennsylvania, it struck oil,
and so to speak, the rest is history.
Basically, beginning in 1859
the world began to utilize oil
in vast quantities, and the oil age began.
These days, finding oil reserves
is a much more complicated and expensive process.
All the easy oil has been found.
To find oil reserves today
requires primarily the use of a technique
called seismic reflection profiling.
Specifically, geologists generate a source of energy
that sends artificial earthquakes,
basically vibrations, into the earth.
Those vibrations bounce off the layers of strata underground
come back up to the surface
where they are recorded by small seismographs.
A computer is able to take the data,
and by measuring the travel time
for the energy to go down and come back up,
can produce an artificial image of what's underground.
In effect, it's like an x-ray of the interior of the earth.
This method can be used on land,
typically by using big trucks that have a metal plate
that presses against the surface
and transmit a low-frequency vibration into the earth,
or it can be done out in the ocean
where a boat tows what's called an air gun
that sends a pulse of high-pressure air
into the water
that generates a vibration that passes through the water
into the sediment below
and down into the rock beneath that
and then gets-gets, uh, returns to the surface
and is recorded by seismographs that are towed behind the ship.
The technique is very sophisticated, very complicated.
Now it can be done in three dimensions,
so you can create cubes of information underground.
But basically, as you can see in this simple reflection profile,
the layers of strata show up as different bands,
and-and you can see their shapes
and recognize potential traps underground,
because the process of drilling is so expensive these days,
millions and millions of dollars to drill a single hole,
that oil companies do not want to drill
without being pretty sure
that they're going to strike a significant reserve underground.
4:02
What about the process of drilling itself?
Well simplistically it's done as follows.
You put a drill head,
which is composed of metal barbs
or sometimes diamond-studded barbs,
in-onto the surface of the ground,
connect it to a pipe,
and then start rotating that pipe.
The drill head will revolve
and gradually grind its way into the rock below.
Now, you can imagine that this process of grinding rock
generates an awful lot of heat,
so the drill head would melt if it weren't constantly cooled.
And the cooling is done by sending,
what's called drilling mud, a fluid,
down the pipe and out through holes in the drill head.
Not only does that fluid cool the drill head,
but it also flushes the-the cuttings,
the ground-up rock, out of the hole,
and as a consequence
you keep adding new pipe at the top,
revolving it, and it keeps drilling and drilling
deeper and deeper down into the earth.
5:00
The drilling mud serves another purpose as well.
You can imagine
that the hydrocarbons that are filling the pore space
in rocks deep down underground are under a lot of pressure.
They're feeling the weight of rock over the top
pushing down on them,
and the weight of all the overlying fluids
in the pore spaces, in the rock above pushing down on them,
so if you were to just drill an open hole
down into those rocks,
they would be under so much pressure
that they would rush out of the hole
and gusher, or vent, out at the earth surface.
We'll see that's- that's not good,
because that's not only losing the hy-hydrocarbons,
but it's contaminating the environment,
and if those hydrocarbons should spark and ignite,
it can create a disastrous fire.
So the advantage of having drilling mud
ins-is that it provides a weight
to hold those pressurized fluids underground.
So drilling mud, which is actually not pure water
it's a mixture of water and clay and iron filings
and other kinds of chemicals and so forth to add weight,
it serves three purposes.
It cools the bit,
it flushes out the cuttings,
and it counters the natural subsurface pressure
of the hydrocarbon reserves.
Once an oil well isf- been drilled,
it's not just an open hole in the ground.
The drillers have to finish or complete the hole,
and what that usually involves is sending down a casing pipe,
steel pipe,
that-that will be the main conduit for the hydrocarbons
to come back up out of the ground.
Typically that pipe is cemented into place
with concrete
so that it's-it's-it's straight and also there's no opening
between the-the rock surrounding it
and the pipe itself,
so that you can't have materials seeping out around the pipe
and coming back out to the surface.
Then at the bottom of the hole,
special charges cause perforations in the pipe
and in the-in the-in the cement and into the surrounding rock
and provide an avenue for the hydrocarbons
at the specific horizon to come into the h-into the casing
and then up the casing pipe
and then out the well at the surface.
This is what casing pipe looks like.
7:08
Once the-the process of pipe has been established,
a pump is installed at the surface
and the pump starts just going up and down
and pulling the oil out of the subsurface,
storing it in tanks or putting it into pipelines
or putting it into trucks
where it can be carried to where it's utilized.
Now, in a conventional field,
many wells had to be drilled,
because an individual well can only suck the oil or gas
out of a relatively limited area around it.
So from the air, an oil field may look like a pin cushion
with lots and lots of little platforms.
Now, each of these is not
where the drilling's taking place anymore.
These are simply the platforms where the pumps are installed.
But you can see,
as in this example that we're looking at in Texas,
there are oil wells all over the place.
These days, the search for oil has taken geologists and
taken oil companies off-shore
because the sedimentary rocks that contain oil
are not limited to the land.
Some of the major reserves are in strata
that are now underneath the continental shelf,
submerged beneath the ocean.
To get at this oil,
it's necessary to have an offshore platform.
The shallower water platforms are actually built on towers
that are anchored
in the sediment below the sea surface.
Some of these can go down 1500 feet or so.
But in really deep water,
oil companies now utilize floating platforms
that are sometimes tethered to the ground
or sometimes kept in place by precise controls.
Platforms are immensely expensive.
They may be co-they may cost in excess of a billion dollars
because of the technology involved to build them
and the amount of materials to build them.
Dr. Stephen MarshakProfessor and Director of the School of Earth, Society, and Environment
Dr. Eileen HerrstromLecturer
