Energy and Human Ambitions on a Finite Planet, 2021a

8 Fossil Fuels 120
barrel of crude oil contains about 6.1 GJ of energy (1,700 kWh; 5.8 MBtu).
For reference, the world consumes about 30 billion barrels a year (the
U.S. is about 7 billion barrels per year, or 20 million barrels per day).
No single country produces oil at a rate greater than about 12 million
barrels per day. 25
To provide some perspective on how special/rare oil is, the chances of
finding any by drilling a r<strong>and</strong>om spot on the planet is about 0.01%. 26
This is because many geological conditions must be met to make oil:
1. Organic material must be deposited in an oxygen-poor environment
to inhibit decomposition, like dead animal <strong>and</strong> plant remnants
settling to the bottom of a still, shallow sea;
2. The material must be buried <strong>and</strong> spend time under at least 2 km
of rock, to “crack” large organic molecules into the appropriate
size, like octane, for instance (Figure 8.3);
3. The material must not go below about 4 km of rock, or the pressure
will “overcrack” the molecules to form natural gas (still useful, if
trapped underground);
4. An impermeable caprock structure must sit atop the permeable
<strong>and</strong> porous rock (Figure 8.5) that holds the high-pressure oil to
keep it from simply escaping. 27
Oil deposits are rare <strong>and</strong> tend to be clustered in certain regions of
the world where ancient shallow seabeds <strong>and</strong> geological activity have
conspired to sequester organic material <strong>and</strong> transform it appropriately.
The process takes millions of years to complete, <strong>and</strong> we are depleting
the resource about 100,000 times faster than it is being replenished. 28
Many early oil wells were “gushers”—under enough pressure to push
up to the surface under no effort. Modern extraction is not so lucky,
having depleted the easy oil already. A combination of techniques is
used to push or pull the oil out of its porous rock, including pumps,
injecting water under high pressure, bending the drill path to travel
horizontally through the deposit, or fracturing 29 the underground rock
via pressurized fluids. More work is required to coax the oil out of the
ground as time moves forward.
25: As a consequence, the U.S. is presently
unable to support its petroleum needs from
domestic resources alone.
26: . . . based on a crude calculation of the
total resource <strong>and</strong> assuming a typical deposit
thickness of 10 m
Figure 8.5: Oil <strong>and</strong> gas embedded in porous
rock, under an impermeable caprock [42].
From U. Calgary.
27: Losing even a drop per second adds
up to 20 million barrels over one million
years, which is short on these geological
timescales.
28: A simple way to see this is that it took
tens of millions years to create the resource
that we are consuming over the course of
a few centuries: a ratio of at least 100,000
(see Box 10.2; p. 169). This is like charging a
phone for 3 hours <strong>and</strong> then discharging it
in 0.1 seconds! Viva Las Vegas! Fireworks!
29: . . . colloquially called fracking
8.2.3 Natural Gas
Natural gas is familiar to many as a source of heat in homes (stoves, hot
water, furnace), but is also a major contributor to electricity production
<strong>and</strong> industrial processes (usually for direct heat in furnaces/ovens). It
is also used extensively in the production of fertilizer via the Haber
process. 30
Natural gas is primarily methane (CH 4 ). Its formation process is similar
to that of oil, but deeper underground where the pressure is higher <strong>and</strong>
longer-chain hydrocarbons are broken down to single-carbon methane
30: The Haber process uses the energetically
cheap hydrogen in methane (CH 4 )to
produce ammonia (NH 3 ) as a chief ingredient
in nitrogen-rich fertilizers.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.