Environmental Engineering Reference
In-Depth Information
8.6 (a) Global crude oil production, 1900-2005 (Smil
2003; BP 2006). (b) Ursa tension leg platform operated
by SEPCo 120 km southeast of New Orleans (photograph
courtesy of SEPCo, Houston).
Norwegian sector of the North Sea, became the heaviest
object ever moved by people. By 1989, Shell's Bullwin-
kle, sited in 406 m of water and weighing about 70,000
t, became the world's tallest pile-supported fixed steel
platform (SEPCo 2004). By 1999, Shell's Ursa tension-
leg platform was the largest structure of its kind, displac-
ing about 88,000 t, rising 146 m above water, and
requiring 16 steel tendons to anchor it to 340-t piles
placed 1140 m below the surface (fig. 8.6) (SEPCo
2004). SPAR, another innovative design, is also moored
by steel lines, but its deck is supported by a single large-
diameter cylinder.
Reservoir yields increased as extended reach, horizon-
tal drilling, and improved methods of secondary and ter-
tiary oil recovery extracted more oil from parental rocks.
Directional drilling uses steerable downhole motors that
are powered by the pressurized mud flowing in cavities
between a spiral-fluted steel rotor and a rubber-lined
stator (SPE 1991; Cooper 1994). Steerable downhole
motors are also used by a new drilling technique that
was introduced during the late 1990s and that unreels
narrow (5-7 cm diameter) steel tubing, wrapped on a
large drum mounted on a heavy trailer, into a well (Wil-
liams et al. 2001). The benefits of directional and hori-
zontal drilling are clear; it can reach much larger volume
of hydrocarbon-bearing strata from a single drill site.
Even for the lightest oils, natural reservoir pressure
releases no more than 40% of the fuel originally present
in the parental rock. For heavy oils the share is below
10%, and means in most oilfields are 25%-35%. Various
