Environmental Engineering Reference
In-Depth Information
0
10
20
30
water eq. 1 cp
water eq. 1 cp
water eq. 1 cp
water eq.+sea water
sea water 1.4 cp
kerosene (3.5 cp)
paraffin 20 cp
paraffin 100 cp
paraffin 120 cp
40
50
60
70
80
1
10
100
effective axial stress (MPa)
Figure 7.8.
Compression curves of a chalk
with different pore fluids
As oil in chalk and air in unsaturated soils play the same role as non-wetting
fluid, an extended notion of suction in a body submitted to a total stress
p
, is
proposed.
This is equal to the difference between the non-wetting fluid pore pressure
p
a
(
p
a
being the common “pore pressure”) and the wetting fluid (water) pressure
p
w
.
Suction,
S
o
, is equal to (
p
o
- p
w
). In the same fashion, the mean net stress is equal to
(
p - p
a
).
The compaction, and thus subsidence, of the Ekofisk field can easily be modeled
using the BBM model. Indeed, the framework proposed by this model allows a
comprehensive description of the hydro-mechanical history of the reservoir, from
chalk deposition on the sea floor about 80 million years ago, to today's depletion
and water injection in the reservoir.
Considering the
S
o
/(
p
' -
p
o
) plan in Figure 7.4, the oil field process is composed
of the following successive phases.
