II. ENVIRONMENTAL IMPACTS AND RISKS EVALUATION OF OFFSHORE DRILLING
_____________________________________________________________________________
63
II.3.6 Contribution scores of well sections on the risk to ecosystem quality
The graph in Figure 25 (a, b) shows the impact of toxic substances on marine species that are
emitted during drilling fluid losses. It can be seen that section 36 has the highest load
contributing to marine sediment ecotoxicity and marine aquatic ecotoxicity with respectively
3.11E+06 and 1.83E+06 [pdf.m2.yr]. This is due to the use of barite for technical reasons at this
depth level. The 26" section has the second highest score in the same impact categories with 1
and 2 respectively. This is due to the contribution of diesel and chemical additives composing
the fluids at this level of the well. On the other hand, for acidification and eutrophication, it is the
26" section which contributes the most; even if the scores in these impact categories remain
much lower than those of the marine ecotoxicity of the 36" phase (water column and sediment).
It should be noted that the contributions in these two categories of acidification and
eutrophication impact are essentially linked to other stages of the life cycle of the systems such
as the manufacture of the chemical additives used in the fluids and consequently, the
environmental targets of eutrophicating and acidifying emissions are other aquatic environments
from other regions where these industries exist.
0 .0 0 E + 0 0
5 .0 0 E + 0 5
1 .0 0 E + 0 6
1 .5 0 E + 0 6
2 .0 0 E + 0 6
2 .5 0 E + 0 6
3 .0 0 E + 0 6
3 .5 0 E + 0 6
Freshwater aquatic
ecotox.
Marine aquatic ecotox.
Terrestrial ecotoxicity
Marine sediment
ecotox.
Freshwater sediment
ecotox.
PDF*m2*yr
Section 8 1/2"
Section 12 1/4"
Section 17 1/2"
Section 26"
Section 36"
Section 8 1/2"
4.04E+04
5.04E+04
1.22E+01
9.21E+04
1.03E+05
Section 12 1/4"
2.89E+04
7.23E+04
4.84E+00
1.39E+05
7.49E+04
Section 17 1/2"
2.13E+04
1.22E+05
5.27E+00
2.24E+05
5.48E+04
Section 26"
1.80E+04
3.32E+05
4.65E+00
6.68E+05
4.60E+04
Section 36"
8.63E+03
1.83E+06
8.79E+00
3.11E+06
2.13E+04
Freshw ater
aquatic ecotox.
Marine aquatic
ecotox.
Terrestrial
ecotoxicity
Marine sediment
ecotox.
Freshw ater
sediment ecotox.
a
_____________________________________________________________________________
63
II.3.6 Contribution scores of well sections on the risk to ecosystem quality
The graph in Figure 25 (a, b) shows the impact of toxic substances on marine species that are
emitted during drilling fluid losses. It can be seen that section 36 has the highest load
contributing to marine sediment ecotoxicity and marine aquatic ecotoxicity with respectively
3.11E+06 and 1.83E+06 [pdf.m2.yr]. This is due to the use of barite for technical reasons at this
depth level. The 26" section has the second highest score in the same impact categories with 1
and 2 respectively. This is due to the contribution of diesel and chemical additives composing
the fluids at this level of the well. On the other hand, for acidification and eutrophication, it is the
26" section which contributes the most; even if the scores in these impact categories remain
much lower than those of the marine ecotoxicity of the 36" phase (water column and sediment).
It should be noted that the contributions in these two categories of acidification and
eutrophication impact are essentially linked to other stages of the life cycle of the systems such
as the manufacture of the chemical additives used in the fluids and consequently, the
environmental targets of eutrophicating and acidifying emissions are other aquatic environments
from other regions where these industries exist.
0 .0 0 E + 0 0
5 .0 0 E + 0 5
1 .0 0 E + 0 6
1 .5 0 E + 0 6
2 .0 0 E + 0 6
2 .5 0 E + 0 6
3 .0 0 E + 0 6
3 .5 0 E + 0 6
Freshwater aquatic
ecotox.
Marine aquatic ecotox.
Terrestrial ecotoxicity
Marine sediment
ecotox.
Freshwater sediment
ecotox.
PDF*m2*yr
Section 8 1/2"
Section 12 1/4"
Section 17 1/2"
Section 26"
Section 36"
Section 8 1/2"
4.04E+04
5.04E+04
1.22E+01
9.21E+04
1.03E+05
Section 12 1/4"
2.89E+04
7.23E+04
4.84E+00
1.39E+05
7.49E+04
Section 17 1/2"
2.13E+04
1.22E+05
5.27E+00
2.24E+05
5.48E+04
Section 26"
1.80E+04
3.32E+05
4.65E+00
6.68E+05
4.60E+04
Section 36"
8.63E+03
1.83E+06
8.79E+00
3.11E+06
2.13E+04
Freshw ater
aquatic ecotox.
Marine aquatic
ecotox.
Terrestrial
ecotoxicity
Marine sediment
ecotox.
Freshw ater
sediment ecotox.
a