Environmental Engineering Reference
In-Depth Information
While reserve densities of commercially exploited coals
and hydrocarbons overlap, ranging from 10
0
GJ to 1
TJ/m
2
, power densities of oil and gas extraction are nec-
essarily much lower when prorated over the total reser-
voir area. Coal mining will remove at least half and often
all the fuel in accessible seams while oil and gas produc-
tion exhausts the reservoir gradually, over a period of
many decades, and the best unaided recovery rates do
not surpass 35% of the original oil content. Even in the
richest fields, extraction densities rarely surpass 200
W/m
2
of total area. Al-Burk
¯
n, as delineated from satel-
lite images, rated about 250 W/m
2
in the early 2000s,
Ventura-Rincon some 130 W/m
2
since its beginnings
in 1916, Hassi Messaoud just over 30 W/m
2
, and al-
Ghaw
¯
r about 10 W/m
2
since 1948, all values much
below the typical coal extraction densities of 1-20
kW/m
2
.
Much higher power densities result when counting
only the land that is actually claimed by extraction. In
the world's richest oil fields, individual wells produce an-
nually at least 1 PJ of crude, the peak Middle Eastern
output was nearly 12 PJ/well, and al-Ghaw¯r used to
flow at up to 40 PJ/well. Only a small percentage of
these oil field areas are actually taken up by surface struc-
tures or reserved for the right-of-ways of gathering pipe-
lines. Actual extraction power densities are thus at least
10-20 kW/m
2
. In contrast, the annual production aver-
age for more than 500,000 U.S. wells operating in 2005
was just 34 TJ/well. Dominant (
>
95%) lift wells aver-
aged less than 25 TJ/well, and the best estimates avail-
able for U.S. oil fields fall within 1-3 kW/m
2
. The
typical power densities of natural gas extraction are 10-
15 kW/m
2
but are reduced by up to 1 OM by adding
the right-of-ways for gathering pipelines and space for
field gas processing.
Rapid post-WW II expansion of the oil industry, from
less than 500 Mt in 1950 to about 3.5 Gt by the year
2000 when there were almost 1 million wells in more
than 100 countries, and to about 3.9 Gt in 2005 (fig.
8.6), drove the scaling-up of all of its infrastructural ele-
ments. This was a particular challenge for offshore pro-
duction, which now supplies nearly one-third of the
world's crude oil. The first drilling from wharves was
done in California as early as 1897, and the first plat-
forms were extended into Venezuela's Lake Maracaibo
in 1924. The first well drilled out of the sight of land
(nearly 70 km from the Louisiana shore) was completed
by Kerr-McGee Corporation in the Gulf of Mexico in
just 6 m of water in 1947 (Brantly 1971). Offshore drill-
ing then progressed from small jackup rigs for shallow
near-shore waters (the first one, Offshore Rig 51,in
1954) to drill ships capable of working in up to 3000 m
of water and semisubmersible rigs.
The Transocean company pioneered self-propelled
jackups, dynamically positioned semisubmersibles, and
rigs capable of year-round drilling in extreme environ-
ments (Transocean 2003). During the 1970s the com-
pany introduced the Discoverer class of drill ships; by the
end of the twentieth century their fifth generation was
capable of working in waters up to 3000 m deep. But
Shell Oil was the first company to deploy a semisubmer-
sible rig, Bluewater I, in 1961 in the Gulf of Mexico. By
the century's end the industry's worldwide surveys listed
nearly 380 jackups (mostly for work in waters of 30-90
m), about 170 semisubmersibles (for water depths up to
300 m), and about 80 drill ships and barges for a total of
nearly 640 marine drilling rigs.
There was a concurrent increase in the size of offshore
production platforms. In November 1982, Statfjord B,a
concrete platform weighing more than 800,000 t in the
