Energy and Human Ambitions on a Finite Planet, 2021a

8 Fossil Fuels 128
rate at which it can be removed depends on the thickness of the seam,
how deep it is located, <strong>and</strong> how hard it is to dig out surrounding rock.
Even oil is not in some sloshing reservoir, but permeates porous rock,
limiting how quickly the viscous fluid can be coaxed to flow out of the
rock <strong>and</strong> into the pump tube. Gas is the quickest to escape its rocky
tomb, but at this stage the U.S. has moved to “tight gas” that does not
so easily break free—forcing a technique of fracking the rock to open
channels for gas to flow. The same technique is being used to access
“tight oil” that otherwise refuses to be pumped out of the ground by
conventional means.
In all cases, it is obvious that we would pursue the easiest resources first:
the low-hanging fruit. As time marches on, we are forced to the more
difficult resources. 57 Adding to the geological factors is the simple fact
that we do not possess unlimited extraction machinery, limiting the rate
at which fossil fuels can be delivered from the ground. It is also worth
pointing out that drilling deeper will not continue to pay dividends, as
Section 8.2.2 points out that oil buried too deep will be “cracked” into
gas.
Figure 8.6 illustrates three variants of possible trajectories for a finite
resource. The left-most panel corresponds to the R/P ratio: how long
can we go at today’s rate of use, if we locked in consumption at a steady
value? The second assumes we continue an upward trajectory, which
shortens the time compared to the R/P ratio before the resource runs out
(using it ever-faster). Both of these are unrealistic in their own ways—the
second one because of the physical constraints on extraction listed above
(not a free-flowing resource). The third case is more realistic: a peak
<strong>and</strong> somewhat symmetric decline. This is how real fossil fuel resources
behave in practice. All three scenarios could create shocks to the system,
but note that the (realistic) peak scenario brings the trauma of declining
supplies soonest—long before the R/P ratio would suggest.
57: . . . deeper underground, under deep
water, or in “tight” formations
simple growth peak
Figure 8.6: Three scenarios for a finite resource
playing out, all based on the same
initial history (the red dot is “now”) <strong>and</strong>
the same remaining amount (blue-shaded
region). The red bar over each represents
the remaining time until resource decline.
See text for details.
8.5.3 Clues in the Data
Despite the uncertainties listed above, we can say for sure that Earth is
endowed with a finite supply of fossil fuels, <strong>and</strong> that in order to consume
the resource, deposits must first be discovered via exploration <strong>and</strong> then
developed into active wells. Even in areas known to have oil, 58 only
about one in ten exploratory wells bears fruit. The chances of striking oil
at a r<strong>and</strong>om location 59 on Earth is in the neighborhood of 0.01%. Section
8.2.2 indicated the chain of events that must transpire to produce oil.
58: . . . also applies to gas
59: Think about throwing a dart at the
globe.
A plot of the discovery history of conventional oil is revealing, seen in
Figure 8.7. In it, we see that discovery peaked over 50 years ago. Since
we can’t extract oil we have not yet discovered—much like we can’t
possess an iPhone model that hasn’t even been designed yet, the area
under the consumption (red) curve must ultimately be no larger than
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.