Geology Reference
In-Depth Information
Chapter13
The Exergy Evolution of Mineral Wealth
13.1 Introduction
The aim of this chapter is to include a new dimension in the exergy evaluation of
mineral wealth: time. To do this, the authors use the Hubbert Peak Model, which is
a way of forecasting when a commodity is expected to reach maximum production.
The model is applied first for a single country (Australia) and then extended to the
entire globe. In this topic specifically, the production data input into Hubbert's
model relates to a commodity's exergy rather than its tonnage, thereby introducing
the concentration factor. This novel approach also allows for simplified illustrative
comparisons among results.
13.2 The Hubbert Peak Model applied to exergy
Hubbert (1956, 1962), a geoscientist working for Royal Dutch Shell in Texas, found
in the mid-fifties that trends in fossil fuel production almost always followed an
identical pattern. All curves, regardless of the fuel's exact specification, started
slowly before rising steeply and tending towards an exponential increase over time,
until an inflection point was reached, upon which the shape became downward con-
cave. The observed trends that Hubbert saw were and remain to this day based
on the fact that no finite resource can sustain beyond a brief period such a pro-
duction growth rate; therefore, although production rates tend initially to increase
exponentially, physical limits prevent their continuing to do so.
So for any production curve of a fixed amount finite resource, two points on
the curve are known on the outset, namely that at t = 0 and again at t = 1.
The production rate will be zero when the reference time is zero and the rate will
return to zero when the resource is exhausted, after passing through one or several
maxima. The second consideration is that the area under the production curve
must equal the quantity of the resource available (R). In this way, the production
curve of a certain resource throughout history takes the ideal form of the bell as
shown in Fig. 13.1.
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