Geoscience Reference
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heat and cold storage and the viscosity effect causes cold injection to require more
energy than heat injection.
x
x
T
out
T
out
T
out
T
out
L
L
70=C
70=C
w
w
with dispersion
with dispersion
sharp front
sharp front
20=C
20=C
t
t
sharp front
sharp front
v
v
pressure
drop is
constant
pressure
drop is
constant
q
q
l
t
l
t
q
70=C
q
70=C
q
q
q
20=C
q
20=C
with dispersion
with dispersion
sharp heat
front reaches
outer border
sharp heat
front reaches
outer border
Equ. (14.8)
Equ. (14.8)
T
in
= 70=C
T
in
= 70=C
t
t
T
T
20=C
20=C
70=C
70=C
Figure 14.9 The viscosity effect with and without heat dispersion
E
LAND SUBSIDENCE
Fluid withdrawal from the underground induces land subsidence at the surface
above, which has effects for the surface water management and infrastructure,
particularly in lowland areas and deltas. Notorious subsidence due to extensive
groundwater withdrawal is observed in lowland cities, such as Bangkok, Djakarta,
New Orleans, Houston, San Jose, Mexico City, Shanghai, Tianjin, Osaka, Tokyo,
HoChiMinh City, Venice, Ravenna, and many others. Similar effects are known in
case of oil/gas withdrawal. Flooding is the major adverse effect of subsidence.
Other effects include tilting, well-casing failure, lowering infrastructure (roads,
bridges), faulting and (small) earthquakes. Methods to stop subsidence are control
of groundwater pumping, development of aqueducts, groundwater recharge, and
the construction of extensive networks of dikes and sea walls, locks, and pumping
stations. In the light of expected climate change and population growth, the
problem of land subsidence is aggravating. Here, a well function for groundwater
extraction induced subsidence and a Dutch protocol for mitigating oil and gas
exploitation effects are discussed.
Well systems are also in use for temporary dewatering of building pits. The
induced pore pressure decline in adjacent soil layers is a notorious culprit for
damage to the surroundings, in terms of subsidence, differential settlements of
buildings and desiccation of agricultural fields.
There is a principle difference in the physical system of water-withdrawal and
oil/gas withdrawal. Water withdrawal takes place from relatively shallow
permeable aquifers (water conveying sand layers) that are confined by less
pervious layers (aquitards). The pore pressure lowering causes effective stress
increase and volume decrease. In shallow formations the major contribution to the
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