7 POTENTIAL IMPACTS RELATED TO UNPLANNED ... spills (e.g. during bunkering), vessel accidents or...

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EIA for proposed Deep Water Exploration Well Drilling in Petroleum

Exploration Licence 39 off the coast of southern Namibia

Final EIA Report & EMP

December 2017

7 POTENTIAL IMPACTS RELATED TO UNPLANNED ACTIVITIES

This chapter assesses the impacts from unplanned events and is structured as follows:

• Section 7.1: Accidental release of oil;

• Section 7.2: Dropped objects / loss of equipment; and

• Section 7.3: Impact summary.

Section 7.1 and 7.2 deal with unplanned events, which are unintended but may occur as a result of accidents

or abnormal operating conditions. The most significant unplanned event being loss of well control (blow-out)

during drilling leading to an oil spill. Impacts may result from other unplanned events including small

operation spills (e.g. during bunkering), vessel accidents or loss of equipment offshore.

7.1 ACCIDENTAL RELEASE OF OIL

7.1.1 INTRODUCTION

Offshore drilling operations carry an inherent risk of oil entering the marine environment as a consequence of

an unplanned oil spill event. Depending on the location and severity of an incident, oil could reach the coast.

EIAs should assess the likely effects of both planned and unplanned events associated with the proposed

project. This section considers the potential impacts of an unplanned accidental oil release (upset condition).

Reservoir hydrocarbons, of which the exact composition is unknown, are a possible source of oil. Other

possible oil sources include; various oil derived materials stored and used in bulk on board the drilling unit

and support vessels. The most relevant of these materials are diesel or marine gas oil (MGO), lubricating

oils and hydraulic oils.

7.1.2 OIL SPILL MODELLING

It is important to understand the main risks of oil spills associated with exploration drilling and the

consequences if any spills were to occur. Identifying the consequence of a spill requires understanding of

what is likely to happen to the oil in the marine environment. Oil spill trajectory modelling quantifies the

probable fate of spilt oil and hence in quantifying environmental risk from oil spills. Oil spill modelling has

been used in this EIA to predict the consequences of a range of spill scenarios. The full oil spill modelling

report prepared by RPS ASA is attached as Appendix 4.1.

All modelling scenarios have been run with the assumption that no oil spill response measures (e.g. use of

dispersants, skimmers, booms, etc.) would be implemented and that no mitigating actions would be taken at

the point of spillage (e.g. pumping oil out of ruptured tanks). Therefore, the results of the modelling present

the ‘worst case’ that could result from any particular oil spill (this is standard practice). If an oil spill occurred,

Shell would initiate response measures to limit the extent and impact of a spill. The model does not take into

account the (low) likelihood of a spill occurring.

7.1.2.1 Modelled oil spill scenarios and parameters

Table 7.1 details the oil spill sources and types that could arise during drilling operations. From the list of

potential spill sources and types identified, a representative range of credible (albeit unlikely) spill scenarios

were selected to inform the oil spill modelling study.


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Table 7-1: List of spill sources and spill type

No. List of Potential Spill Sources Spill Type

1 Loss of well control and blow-out. Large release, long duration, offshore – oil.

2 Drilling unit grounding, collision or structural failure

resulting in the total loss of diesel inventory and other

oil inventory.

Medium release, short duration, offshore –

diesel/oil and/or synthetic based mud.

3 Dumping of riser content due to loss of station keeping

or collision.

Medium release, short duration, offshore –

synthetic mud.

4 Leak from base oil, hydraulic oil, diesel or lube oil

storage, or inadvertent opening of master dump valve

and discharge of one pit of mud to sea.

Limited release, short duration, offshore –

diesel, oil or synthetic based mud.

5 Grounding, collision, structural failure of support vessels

resulting in the total loss of diesel inventory and other

oil inventory.

Medium release, short duration, near-shore –

diesel/oil and/or synthetic mud.

6 Loss of containment during transport to / from drill site

resulting in the release of synthetic based muds or

other oil products.

Limited release, short duration, onshore,

potentially to sea – synthetic based mud or oil

The modelling study considered three spill scenarios - one surface and two seabed spills. The two seabed

(blow-out) scenarios included an 8-day spill and a 90-day spill of light crude oil. The shorter duration

corresponds to the time to control the blow-out via a capping device and the longer duration corresponds to

the time it would take to drill a relief well. The surface spill of marine diesel represents an instantaneous spill

of the largest fuel tank. The spill scenarios parameters used in the modelling study are presented in Table 7-

2 and the seabed release (blow-out) parameters are summarised in Table 7-3.

Table 7-2: Parameters of the spill scenarios

No. Spill

location Oil type Spill type Spill rate

Spill

duration

Total spilled

Volume / Mass

Simulation

duration

1 Drilling

unit

Marine

diesel

Surface loss of

largest fuel tank n/a

Instant

(simulated

over 4 hrs)

10 000 L 10 days

2 Well Light crude Seabed loss of well

control to capping

50 000

bbl/day 8 days 400 000 bbl 15 days

3 Well Light crude

Seabed loss of well

control to drilling of

relief well

50 000

bbl/day 90 days 4 500 000 bbl 90 days

Table 7-3: Summary of blow-out parameters

No. Water depth of the release Gas to oil ratio Pipe diameter Discharged oil temperature

2 & 3 2 000 m 190 m3/m

3 13.375 in 105

oC


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7.1.2.2 Model description

Blow-out modelling was performed in two steps:

1) Near-field analysis

The near-field modelling was completed using RPS ASA’s OILMAP/Deep model. The results of the near-

field model provide a description of the behaviour of the blow-out plume, its evolution within the water column

and the expected initial dilution (concentration decrease) with distance from the wellhead (seafloor).

This analysis provides information about the termination (“trap”) height of the plume and the oil droplet size

distribution(s) associated with the release. These results are used as initial conditions of the far-field fate

and trajectory modelling.

2) Far-field analysis

The far-field simulations were performed using RPS ASA’s 3-D oil spill modelling system, OILMAP. The far-

field simulations describe the long-term transport and weathering of the released oil mixture that typically

evolves as a horizontal process due to currents and winds. The modelling system uses a 3D Lagrangian

model where each component of the spilled oil (floating, dispersed, shoreline, etc.) is represented by an

ensemble of independent mathematical particles or “spillets”. Each spillet comprises a subset of the total

mass of hydrocarbons spilled and is transported by both currents and surface wind drift.

The far-field model initialises these particles at the trap depth, calculated by the near-field model, which are

then transported by both currents and surface wind drift. Additionally, horizontal and vertical dispersion

coefficients in the oil spill model provide for:

a) the horizontal spreading of the oil slick due to its natural tendency to thin out (balance of inertial,

gravity and interfacial tensions), and

b) the vertical mixing within the upper mixing layer of the ocean.

While these coefficients are important to reproduce the micro-scale processes (emulsion water-in-oil,

sediment trapping, minimum thickness), other macro-scale factors play a much larger role in the overall

transport of the oil spill, such as winds, currents or interaction with the coastline.

Additional information on the modelling system is contained in Appendix A of the modelling report.

7.1.2.3 Oil properties

The transport and weathering of spilled oil are dependent on oil properties. Table 7-4 summarises the

characteristics of the hydrocarbon products used in the modelling study.

Table 7-4: Summary of the oil properties used in the modelling

Oil type API

gravity

Density

(g/m2 at 15.55oC)

Viscosity

(cP at 25oC)

Interface tension

(Dyne/cm)

Emulsion Maximum

Water Content (%)

Light crude 30.0 0.8840 27.60 28.00 79

Marine diesel 34.8 0.8309 3.34 28.00 0

Viscosity and interfacial surface tension affect the degree of spreading of the oil, which in turn influences the

rates of evaporation, dissolution, dispersion, and photo-oxidation. The maximum water content is a

laboratory measurement of the tendency of the oil to form emulsions. Oils that form water-in-oil emulsions

tend to be more persistent in the marine environment, as they are less likely to be dissolved and/or

evaporated; this increases their potential for reaching the shoreline. Light products, such as marine diesel

and condensate, have no tendency in forming an emulsion, thus they are less persistent on the water


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surface relative to heavier oils (such as crude). The crude used in the modelling study was relatively light

and thus does not exhibit strong persistence on the water surface.

To classify oil products from a weathering point of view, crude oils and hydrocarbon mixtures can be broken

down into distillation cuts based on their boiling points. Total Hydrocarbon Concentrations (THC) in the oil

weathering model include both aromatic (soluble) and aliphatic (insoluble) components. In general, the

lighter aromatic compounds such as Monocyclic and Polycyclic Aromatic Hydrocarbons (MAHs and PAHs,

respectively) tend to rapidly evaporate to the atmosphere unless the product gets mixed into the water

column. If oil is released below the water surface or gets entrained before it has weathered and lost the

lower molecular weight aromatics to the atmosphere, dissolved MAHs and PAHs can reach concentrations

where they can affect water column organisms or bottom communities.

Residual oil fractions are composed of non-volatile and insoluble compounds that remain in the “weathered

whole oil” and can spread on the water surface, become stranded on shorelines and disperse into the water

column as oil droplets. This is the fraction that composes black oil, mousse and sheen. The percentages of

the components of the oils used in this modelling study that fall into each distillation category are presented

in Table 7-5.

Table 7-5: Chemical components of the four oil types used in the modelling study

Distillation

cut

Boiling

point (oC)

Chemical characteristics of

soluble (aromatics) and

insoluble (aliphatic) compounds

Fraction by Weight (including both

aromatic and aliphatic compounds)

Aromatics

(MAH and PAH) Aliphatics Light crude Marine diesel

THC – 1 < 180 Volatile and Highly

Soluble Volatile 13.7% 16.4%

THC – 2 180 – 265 Semi-volatile and

Soluble Semi-volatile 14.1% 49.0%

THC - 3 265 – 380 Low Volatility and

Slightly Soluble Low volatility 21.5% 31.9%

Residue - 4 > 380 Residual oil fraction (non-volatile and very

low solubility) 50.7% 2.7%

Total aromatics (incl

both MAH and

PAH)

49.3% 97.3%

7.1.2.4 Oil weathering

To understand weathering of the light crude oil once released into the marine environment (see Box 7-1),

several test cases were simulated assuming different representative environmental conditions expected in

the area of interest.


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Box 7-1: Oil weathering process

There are eight main weathering processes:

• Spreading - The speed at which spreading over the sea surface takes place largely depends upon the

viscosity of the oil, which in turn depends both on the oil composition and the ambient temperature. Low

viscosity oils spread more quickly than those with a high viscosity.

• Evaporation - the rate of evaporation and the speed at which it occurs depend upon the volatility of the oil. An

oil with a large percentage of light and volatile compounds will evaporate more than one with a larger

proportion of heavier compounds.

• Dispersion - Waves and turbulence at the sea surface can cause some or all of a slick to break up into

fragments and droplets of varying sizes. These become mixed into the upper levels of the water column.

• Emulsification - Emulsification of crude oils refers to the process whereby sea water droplets become

suspended in the oil to forma water-in-oil emulsion. This occurs by physical mixing promoted by turbulence at

the sea surface.

• Dissolution - Water soluble compounds in an oil may dissolve into the surrounding water. Components that

are most soluble in sea water are the light aromatic hydrocarbons.

• Oxidation - Oils react chemically with oxygen either breaking down into soluble products or forming persistent

compounds called tars. This process is promoted by sunlight, but is very slow and even in strong sunlight, thin

films of oil break down at no more than 0.1% per day.

• Sedimentation and sinking - When floating oil is getting close to the shore, sedimentation can occur. This is

when floating, semi submerged or dispersed oil comes into contact with suspended sediment, and the

sediment binds to it.

• Biodegradation - Sea water contains a wide range of micro-organisms that use hydrocarbons as a source of

energy and can partially or completely degrade oil to water soluble compounds and eventually to carbon

dioxide and water.

As a general rule, each process can be put into one of two chronological categories in terms of when their effect is

most significant:

• Early stage of a spill: spreading, evaporation, dispersion, emulsification and dissolution; and

• Later stage of a spill: oxidation, sedimentation and biodegradation.

The diagram below represents the fate of a typical crude oil spill, showing changes in the relative importance of

weathering process with time (from hours to years). The width of the band indicates the importance of the process.

Source: http://www.itopf.com/knowledge-resources/documents-guides/fate-of-oil-spills/weathering; ITOPF 2002


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Based on the results of these test cases, the following conclusions were made for this assessment:

• The light crude oil tends to evaporates quickly within the first 24 hours; the evaporative loss ranges

from 20 to 31%;

• The amount of crude oil entrained in the water column is very sensitive to the wind speed and the

properties of the oil. At the lowest wind speeds (3 m/s), there is no oil entrained into the water column

and nearly all the oil either evaporates or remains in the surface slick at the end of the 5- day test

simulation. At the highest wind speed (13 m/s), there is almost no surface oil, slightly less

evaporation, and much more entrainment in the water column. At lower wind speeds (0-5 m/s), when

vertical entrainment is limited, evaporation is the key factor to remove oil from the water surface.

However, at mid-high wind speeds (5-10 m/s) evaporation and vertical entrainment are two competing

processes to remove floating oil from the water surface;

• Formation of emulsion depends on the remaining floating oil and the wind intensity.

7.1.2.5 Simulations

Oil spill modelling was performed in two steps:

1) Stochastic analysis

Stochastic simulations provide insight into the probable behaviour of potential oil spills in response to

temporally- and spatially-varying meteorological and oceanographic conditions in the study area. The

stochastic analysis provides two types of information:

• the footprint of sea surface areas that might be oiled and the associated probability of oiling; and

• the shortest time required for oil to reach any point within the areas predicted to be oiled.

The areas and probabilities of oiling are generated by a statistical analysis of all the individual stochastic runs

(see Box 7-2). It is important to note that a single run will encounter only a relatively small portion of this

footprint.

Results from the stochastic analysis are presented in Section 7.1.2.6.1.

2) Deterministic analysis

A deterministic analysis that identifies the worst-case scenario. For each spill scenario, one deterministic

trajectory / fate simulation was run to investigate a specific “worst-case” spill event that could potentially

occur using the same combination of winds and current forcing used in the corresponding stochastic

simulation from which it was identified.

The worst-case scenario is selected based on the degree of shoreline oiling. As there was no shoreline

oiling in this study, the trajectory that came closest to the shore with the highest volume of oil in the shortest

amount of time for the 90-day blow-out scenario was chosen as the worst-case scenario.

Results from this modelling step are presented in Section 7.1.2.6.2.

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Box 7-2: Stochastic modelling approach - an ensemble of individual trajectories creates the

stochastic probability footprint

Examples of four individual spill trajectories predicted by OILMAP for a particular spill scenario. The frequency of

contact with given locations is used to calculate the probability of impacts during a spill. Essentially, all 100+ model

runs are overlain (shown as the stacked runs on the right) and the number of times that a trajectory reaches a given

location is used to calculate the probability for that location.

Probability of surface oil exceeding a given threshold for the example scenario. This figure overlays 100+ individual

model runs to calculate the percentage of runs that caused oiling above the threshold in a given area. This figure

does not depict the areal extent of a single model run / spill.


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7.1.2.6 Oil Spill Modelling Results

7.1.2.6.1 Stochastic analysis

Based on the stochastic modelling results, the following conclusions can be highlighted:

No. Scenario Conclusions

1 Instantaneous release

of 10 000 litres of diesel

• The stochastic footprint is very small and slightly oriented to the north-west of

the spill site.

• Spill trajectories are not predicted to reach shore.

• All diesel spill trajectories remain in the Namibian EEZ.

• Zone of highest probability (75-100%) is isolated to within about 1 km to the

north-northwest of the spill site with slightly lower probabilities (50- 75%)

reaching up to 2 km in the same direction.

• Probabilities greater than 1% are seen out as far as 12.5 km from the spill

site.

Refer to Figure 7-1.

2 8-day blow-out of

400 000 bbl of crude oil

• The stochastic footprint is oriented towards the north-west of the spill site due

to the dominant winds and currents in the region.

• No trajectory is expected to reach the shore.

• The footprint is mostly contained in the Namibian EEZ. However, spill

trajectories can leave the Namibian EEZ in about 7 days.

• The zone with the highest surface oiling probability (75-100%) is confined

within 125 km to the north-west of the spill site.

• Few trajectories (less than 5%) travel as far as 500 km from the spill site.

• Surface waters with high oiling probability (>50%) can be reached within the

first 3 to 4 days from the spill.


3 90-day blow-out of

4 500 000 bbl of crude

oil

• The stochastic footprint is oriented mainly towards the north-west of the spill

site due to the dominant winds and currents in the region.

• No trajectory is expected to reach the shore.

• The stochastic footprint goes beyond Namibian EEZ. Spill trajectories can

leave the Namibian EEZ in about 7 days.

• The zone with the highest oiling probability (75-100%) is confined within

200 km to the north-west of the spill site.

• Only few trajectories (less than 5%) can travel as far as 1 000 km from the

spill site.



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Figure 7-1: Stochastic analysis - Instantaneous surface spill: Surface oiling

probabilities (top) and minimum travel times (bottom)


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Figure 7-2: Stochastic analysis – 8-day blow-out: Surface oiling


Figure 7-3: Stochastic analysis – 90-day blow-out: Surface oiling



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7.1.2.6.2 Deterministic analysis

Based on the deterministic modelling results, the following conclusions can be highlighted:

No. Scenario Conclusion

1 Instantaneous release of

10 000 litres of diesel

• Released diesel oil travels to the north-west for about 4 km, staying

within the Namibian EEZ.

• The trajectory does not form a diesel slick with thickness above the

0.01 mm threshold and it is not predicted to reach the shore.

• Approximately 66% of the released diesel evaporates and no diesel

remains on the surface.

• At the end of the simulation, 30% of the marine diesel remains

entrained in the water column and 4% is removed by biodegradation

and photo-oxidation.


2 8-day seabed blow-out of

400 000 bbl of crude oil

• The trajectory travels north-west, with surface floating oil exceeding the

thickness threshold (0.01mm) up to 625 km from the spill site, leaving

the Namibian EEZ and reaching international waters.

• Due to the spill location and the predominant wind and current

conditions no oil is predicted to reach the shoreline.

• Approximately 31% of the released oil is evaporated to the atmosphere

and about 50% remains on the sea surface after 15 days.

• At the end of the simulation, 12% of the spilled oil remains entrained in

the water column and 7% of the oil is removed by biodegradation and

photo-oxidation.


3 90-day seabed blow-out

of 4 500 000 bbl of crude

oil

• The trajectory travels north-west, with surface floating oil exceeding the

threshold up to 3 000 km from the spill site, well beyond the Namibian

EEZ.

• Due to the spill location and the predominant wind and current

conditions no oil is predicted to reach the shoreline.

• Approximately 29% of the released oil is evaporated to the atmosphere

and 44% remains on the sea surface after 90 days.

• At the end of the simulation, 21% of the spilled oil remains entrained in

the water column and 6% of the oil is removed by biodegradation and

photo-oxidation.



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Figure 7-4: Deterministic analysis - Instantaneous surface spill: Maximum mass of surface oil that passed a

given location during the simulation

Figure 7-5: Deterministic analysis – 8-day blow-out: Maximum mass of surface oil that passed a given location

during the simulation


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Figure 7-6: Deterministic analysis – 90-day blow-out: Maximum mass of surface oil that passed a given

location during the simulation

7.1.3 POTENTIAL IMPACTS OF AN ACCIDENTAL OIL SPILL

Description of the source of impact

The table below summarises the project activities that could potentially result in oil spills during the project.

These would all be unplanned activities that could potentially occur during all phases of the project.

Activity phase Activity

Mobilisation Bunkering of fuel

Hydraulic pipe failure / rupture

Vessel accident

Operation Bunkering of fuel


Vessel accident

Loss of well control during drilling

Demobilisation Bunkering of fuel


Vessel accident

These activities (or event) are described further below:

• Small instantaneous spills of marine diesel and/or hydraulic fluid at the surface of the sea can

potentially occur during all project activity phases, both from the drilling unit or from support vessels.

Such spills are usually of a low volume and occur accidentally during fuel bunkering or as a result of

hydraulic pipe leaks or ruptures.

• Larger volume spills of marine diesel would occur in the event of a vessel collision or vessel accident.


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• The greatest environmental threat from offshore drilling operations is the risk of a major spill of crude

oil occurring either from a blow-out or loss of well control. A blow-out is the uncontrolled release of

crude oil and/or natural gas from a well after pressure control systems have failed.

Description of the environmental aspects

The project activities described above would result in a release or discharge of oil (including fuel and

hydraulic fluid) into the marine environment, which would result in a reduction of water quality, with the extent

being depending on the nature of the spill.

Description of the potential impact

Diesel, hydraulic fluid and/or oil spilled in the marine environment would have an immediate detrimental

effect on water quality, with the toxic effects potentially resulting in mortality (e.g. suffocation and poisoning)

of marine fauna or affecting faunal health (e.g. respiratory damage). Sub-lethal and long-term effects can

include disruption of physiological and behavioural mechanisms, reduced tolerance to stress and

incorporation of carcinogens into the food chain. If the spill reaches the coast, it can result in the smothering

of sensitive coastal habitats.

An oil spill can also result in several indirect impacts on fishing. These include:

• Exclusion of fisheries from polluted areas and displacement of targeted species from normal feeding /

fishing areas, both of which could potentially result in a loss of catch and / or increased fishing effort;

• Mortality of animals (including eggs and larvae) leading to reduced recruitment and loss of stock (e.g.

mariculture); and

• Gear damage due to oil contamination.

Oil contamination could potentially have the greatest impact on commercial fisheries for rock lobster and

sessile filter feeders (e.g. mussels) and grazers (e.g. abalone). Mortality is expected to be high on filter

feeders and, to a lesser extent, grazers. These species have low mobility and no means to escape

contamination and ultimately mortality. Thus, mariculture facilities (e.g. in Lüderitz) could be impacted if a

spill extended into these areas. For a large oil spill, fishing / mariculture activities and revenues could be

affected over a wide area until such time as the oil has either been dispersed or broken down naturally.

Potential oils spills or other major marine pollution events may also have an indirect impact on tourism by

compromising the attractiveness and amenity of coastal areas.

Receptors

Drilling activities would be located in the offshore marine environment, more than 200 km offshore, far

removed from the NIMPA, coastal islands and any sensitive coastal receptors (e.g. key faunal breeding /

feeding areas, bird or seal colonies and nursery areas for commercial fish stocks), and as spills are not

expected to reach the shore these receptors would unlikely be affected by a spill at the drill site. However, a

fuel spill from an unlikely vessel collision en route to the onshore supply base could result in some fuel

reaching the shore, potentially having major environmental effects to the sensitive coastal environment.

A spill in the area of interest would negatively affect any marine fauna it comes into contact with. In the

offshore environment, the taxa most vulnerable to spills are pelagic seabirds, although turtles, large

migratory pelagic fish and cetaceans may also be affected. Many of these are considered globally ‘Critically

Endangered’ (e.g. leatherback turtle), ‘Endangered’ (e.g. black-browed and yellow-nosed albatross, fin, blue

and sei whales) ‘Vulnerable’ (e.g. short-fin mako shark, whitetip shark and sperm whale) or ‘Near threatened’

(e.g. blue shark).


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Although the benthic fauna at the water depths encountered in the area of interest (1 500 m to 2 000 m) is

poorly known, deep water fauna inhabiting unconsolidated sediments is expected to be relatively ubiquitous,

usually comprising fast-growing species able to rapidly recruit into areas that have suffered natural

environmental disturbance. In contrast, the benthos associated with hard substrata is typically vulnerable to

disturbance due to their long generation times. Such sensitive communities would only be expected to occur

at Tripp Seamount and in the adjacent submarine canyon, which are located some 85 km south-east from

the middle point of the of the area of interest, and are unlikely be affected by a spill at the drill site.

Spills within the area of interest could also impact key fish spawning areas, which are mostly located

between the coast and the 200 m depth contour. Modelling results, however, show that there is a low

probability of oil from a large spill extending to the 200 m water depth.

From a tourism perspective, the key receptors would include those directly or indirectly reliant on the tourism

industry especially in Lüderitz.

Project Controls

The primary mitigation measure for avoiding the impacts of an accidental oil spill is to prevent any such spill

from taking place. This is done through both technology applications, as well as operational controls. In the

event of a spill incident, the project would implement an emergency response system to mitigate the

consequences of the spill. Shell would ensure all the required measures are in place to deal with very

unlikely blow-out event.

Shell manages potential impacts (consequences) of an incident (as a result of their activities) using the Bow-

Tie Risk Model (see Figure 7-7). The model involves knowing and understanding the risks/hazards (by

identifying the hazards and potential effects) and managing the risks/hazards (by preventing, mitigating and

recovering from the incident/event). The objectives of the Bow-Tie Risk Model are to assure that hazards

are managed to an acceptable level (called “As Low As Reasonably Practicable” - ALARP). This method

creates a clear differentiation between proactive (creating barriers to minimise likelihood of incidents) and

reactive (responses to mitigate consequences after an incident occurring) risk management. Barriers

interrupt the unwanted scenarios (upset condition) so that the threats do not result in a loss of control or do

not escalate into an actual impact (the consequences). The Bow-Tie Risk Model for Oil Spill Prevention,

Response and Planning for the proposed exploration drilling in PEL39 is shown in Figure 7-8.

Further details on Shell’s standard controls and responses are provided in Table 7-6.

Figure 7-7: Bow-Tie Risk Model

Incident

Minimize Likelihood

Mitigate

Consequences

Prevention

BarriersHA

ZA

RD

C

ON

SE

Q

UE

NC

E

RecoveryControls


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Figure 7-8: Proposed Bow-Tie Risk Model for Oil Spill Prevention, Response and Planning for the

proposed exploration drilling in PEL39, illustrating the high level controls and

responses

Table 7-6: Description of the barriers and controls (for avoidance/prevention) and response and

recovery (mitigation) to deal with oil spills

Barriers and Controls (Avoidance/Prevention Actions)

Design and

Technical

Integrity

The Shell wells standard defines HSSE and technical requirements for wells. It also details

assurance and competency requirements for well engineering and completion and well intervention

personnel. This covers the well design, procurement of materials and identification of risks.

Barriers and Controls (Avoidance/Prevention Actions)

Multiple

Barriers

Casing:

Casings would be designed to withstand a variety of forces, such as collapse, burst or tensile failure,

as well as chemically aggressive brines. They would be run to prevent caving-in of formations and

to provide strong foundations for continued drilling operations.

Wellbore pressure:

Subsurface pressures above and within the hydrocarbon-bearing strata would be controlled by the

use of weighted drilling mud. The hydrostatic pressure of the drilling mud in the well would be

adjusted to ensure that it is greater than the formation pressure to prevent the undesired influx of

fluids into the wellbore (known as a ’kick’). Pressure monitoring would be undertaken during drilling

to ensure that kicks are avoided or managed to prevent escalation into a blowout.

Blow-out Preventer (BOP) stack:

BOP stacks are used to control the pressure of a well through mechanical devices designed to

rapidly seal the well (or “shut in”) in an emergency.

Competent

Staff

Shell has competent and certified staff who would design the well and conduct independent sign-off

for its design. During operations Shell can transmit real-time information, such as pressure and

temperature, back to operations centres around the world for additional quality control and advise

when needed.

� Technical and HSSE

Standards & Procedures

� Equipment testing,

certification

� Competent Staff

� Contractor requirements

� Rig Safety Case

� Multiple barriers

� Blowout Preventer

� Blowout Contingency

Plan

� Oil Spill Response Plan

� Cap and Contain

Equipment

� Relief Well Plan

� Technical Expertise

� Emergency Response

Team

KEEP WITHIN CONTROL LIMITS REDUCE LIKELIHOOD

MITIGATE CONSEQUENCES PLAN FOR RECOVERY –

RE-INSTATE

� Technical and HSSE standards and procedures

� Equipment testing and certification

� Competent staff

� Contractor requirements

� Drilling unit safety case

� Multiple barriers, e.g. Blow-out Preventer

� Oil Spill Response Plan

� Well Control Contingency Plan

� Cap and contain equipment

� Relief well plan

� Technical expertise

� Emergency Response Team


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Testing and

Certification

Safety critical equipment would be subject to testing and certification to ensure that it meets design

specifications. The well design, drilling and completion plans would go through several stages of

review involving experts from Shell and the drilling contractor prior to the commencement of drilling

operations.

Response and Recovery (Mitigation Actions)

Oil Spill

Response

Plan

Despite the prevention measures and management procedures built into the design of the project

there is always a risk that a spill can occur. Thus, as standard practice, an Oil Spill Response Plan

is prepared and put in place at all times during the drilling operation. There are three principal

components underpinning an Oil Spill Response Plan:

• Crisis management (Emergency Command and Control Management);

• Spill response, containment and clean-up; and

• Well control.

Oil spill response planning is based on the principal of a tiered response (refer to Box 7-3).

The project’s Oil Spill Response Plan would be aligned with the national Namibian Marine Pollution

Contingency Plan which sets out national policies, principles and arrangements for the management

of maritime environmental emergencies including oil spills. It provides for a comprehensive

response to all oil and chemical pollution emergencies in the marine environment regardless of how

costs might be attributed or ultimately recovered.

Emergency

Command

and Control

Management

Emergency Command and Control Management arrangements range from the On-scene

Commander, normally at the source of the incident, to the main Emergency Control Centre (ECC)

Incident Commander who takes over control. As each level is activated the level of response would

equally escalate.

Well Control Whilst the Oil Spill Response Plan defines the approach and strategy required to manage the

containment, removal and clean up following a major spill, the well control process is focussed on

stopping the source of the leak. A Well Control Contingency Plan (WCCP) would be put in place for

each well.

Cap and

Containment

Equipment

If the BOP does not successfully shut off the flow from the well, the drilling rig would disconnect and

move away from the well site while crews mobilise a capping system. The capping system would be

lowered into place from its support barge and connected to the top of the BOP to stop the flow of oil

or gas. Shell is a member of OSRL, which operates advanced well intervention and capping

equipment from Saldanha Bay for deployment in the event of a subsea well control incident. This

would significantly reduce the spill period. All of Shell’s wells are designed to allow for capping.

Response and Recovery (Mitigation Actions) cont.

Containment

and clean-up

equipment

Project vessels would be equipped with appropriate spill containment and clean-up equipment, e.g.

booms, dispersants and absorbent materials. All relevant vessel crews would be trained in spill

clean-up equipment use and routine spill clean-up exercises. Logistical arrangements for the

integration of additional support would be in place (e.g. from OSRL).

Performance objectives

Zero loss of hydrocarbons to the marine environment.

Impact assessment

Potential impacts associated with small operation spills and large well blow-outs are assessed separately in

Sections 7.1.3.1 and 0 below.


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Box 7-3: Tiered Preparedness and Response

Shell uses the Tiered Preparedness and Response concept which ensures the appropriate resources are considered for

all potential scenarios identified in the plan.

Tiered Preparedness and Response gives a structured approach to both establishing oil spill preparedness and

undertaking a response. It allows potential oil spill incidents to be categorised in terms of their potential severity and the

capabilities that need to be in place to respond (IPIECA, 2007). Conventionally the concept has been considered as a

function of size and location of a potential oil spill, with three tiers typically defined (see table and figure below).

Tier categories

Tier 1 Minor spills that are quickly controlled, contained and cleaned up using local (onsite or immediately

available) company/contractor owned equipment and personnel resources. For offshore facilities, local

resources could include those at the facility, on nearby support vessels or at a designated shore support

base or staging area. A Tier 1 spill would typically be resolved within a few hours or days.

Tier 2 Tier 2 events are more diverse in their scale and by their nature involve potentially a broad range of impacts

and stakeholders. Moderate spills, controlled or uncontrolled, requiring activation of significant regional oil

spill response resources and all or most of the Spill Management Team. Tier 2 response resources are

varied in their provision and application. Management responsibilities are usually shared in a collaborative

approach and a critical feature is the integration of all resources and stakeholders in the response efforts. A

Tier 2 spill response may continue for several days or weeks.

Tier 3 Major spills, controlled or uncontrolled, requiring activation of large quantities and multiple types of response

resources including those from out of the region, and possibly international sources. Tier 3 events are rare

but have the potential to cause widespread damage and affect many people. Tier 3 response resources are

concentrated in a relatively few locations, held in readiness to be brought to the country when needed.

Such significant events usually call for the mobilisation of very substantial resources and a critical feature is

their rapid movement across international borders and the integration of all resources into a well-organized

and coordinated response. The entire Spill Management Team would be required and would likely be

supplemented by outside organisations. A Tier 3 spill response may continue for many weeks or months.

The framework for Tiered Preparedness and Response (IPIECA, 2007)


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7.1.3.1 Small operational spills

The probability of a minor accidental oil spill due to normal operations is a far greater than for a blow-out

scenario.

Based on the anticipated weathering of lighter fuel oil fractions, a small diesel spill would be relatively short-

lived on the water surface (< 10 days) and would have a relatively small footprint with the zone of highest

probability (75-100%) being isolated within 1 km of the spill site. Probabilities greater than 1% are predicted

to be restricted to approximately 12.5 km from the spill site. Thus, a small spill in the area of interest is not

predicted to reach the shore, the sensitive nearshore environment or the vicinity of Tripp Seamount

(see modelling results in Section 7.1.2.6).

Smaller spills from vessels in or on route to port pose a far greater risk to the nearshore environment. A spill

with the port limits during bunkering / loading could, however, be easily managed and contained, and is less

likely to pose a risk to the nearshore environment. A spill outside the port near the coast (e.g. in the unlikely

event of a vessel collision) could reach the shore through wave action and tidal currents.

Marine fauna

The impact of a small operational spill at the well site or near the coast on marine fauna is considered to be

regional and of zero (e.g. benthic) to high (e.g. birds) intensity depending on the faunal group in the short-

term. Collectively this impact on marine fauna is considered to be of low significance before mitigation.

Commercial fishing

A small operation spill could affected most fishing sectors depending on where the spill occurs (e.g. at drill

site or en route to onshore logistics base). However, a spill close to shore would be most significant, e.g. a

spill near Lüderitz or in the Lüderitz lagoon could impact mariculture activities, which are highly sensitive to

water quality variability. The potential impact on the fishing is considered to be of to be localised, of low

intensity in the short-term. Thus this impact is considered to be of very low significance before mitigation.

Tourism

In terms of risks to tourism, a small operational spill at the drill site is not predicted to reach the coast and

would thus not have an impact on tourism. However, a spill in the nearshore environment near Lüderitz

could impact tourism that is reliant on the marine environment (e.g. boat trips, recreational fishing trips, etc.).

This potential impact is considered to be localised, of high intensity in the short-term. Thus this impact is

considered to be of low significance before mitigation.

A summary of possible impacts related to a small operational spill are provided in Tables 7-7 to 7-9.

Mitigation

In addition to the best industry practices and Shell’s project standards, the following measures will be

implemented to manage the impacts associated with small operational spills:

No. Mitigation measures Classification

Oil spills

1 Implement Oil Spill Contingency Plan and Shipboard Oil Pollution Emergency Plan

(SOPEP). Reduce at source

2 Ensure personnel are adequately trained in both accident prevention and immediate

response.

Avoid / reduce at

source

3 Inspect and maintain all chemical / fuel containers including the vessels fuel tanks and

mud tanks. Avoid


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No. Mitigation measures Classification

4 Attempt to control and contain the spill at sea, as far as possible and whenever the sea

state permits, using suitable recovery techniques to reduce the spatial and temporal

impact of the spill.

Abate on and off site

5 Use low toxicity dispersants cautiously and only with the permission of MET/MFMR. Abate on and off site

6 Ensure adequate resources are provided to collect and transport oiled birds to a cleaning

station. Restore

Collision prevention and mitigation

7 Prepare and implement an Emergency Response Plan. Reduce at source

8 Notify relevant local authorities and fisheries associations regarding proposed activities,

including details on timing and location. Avoid

9 Enforce the 500 m safety/exclusion zone around the drilling unit. Support vessels with

appropriate radar and communications would be used during the drilling operation to

warn vessels that are in danger of breaching the safety/exclusion zone.

Avoid

10 Notify any fishing vessels at a radar range of 24 nm from the drilling unit via radio

regarding the safety requirements around the drilling unit. Abate on site

11 Request, in writing, the HydroSAN to broadcast a navigational warning via Navigational

Telex (Navtext) and Lüderitz radio for the duration of the activity. Avoid

Residual impact

With the implementation of the project controls and mitigation, the residual impacts associated with a small

operational spill on marine fauna would be INSIGNIFICANT. The residual impact on commercial fishing and

tourism are both considered to be of VERY LOW significance.

Table 7-7: Impact of a small operational spill on marine fauna

CRITERIA WITHOUT MITIGATION WITH MITIGATION

Extent Local Local

Duration Short-term Short-term

Intensity Zero to High Zero to Medium

Probability Probable Possible

Confidence High High

Significance Low INSIGNIFICANT

Reversibility Fully reversible

Mitigation potential Very Low

Table 7-8: Impact of a small operational spill on commercial fishing


Extent Local Local


Intensity Low Low


Confidence Medium Medium

Significance Very Low VERY LOW


Mitigation potential Very Low


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Table 7-9: Impact of a small operational spill on tourism


Extent Local Local


Intensity High Medium

Probability Improbable Improbable


Significance Low VERY LOW

Reversibility Partially reversible

Mitigation potential Low

7.1.3.2 Large well blow-outs

The planned activity is to drill one or possibly two exploration wells in the northern portion of the licence area.

The greatest environmental threat from an offshore drilling operation is the risk of a major spill of crude oil

occurring either from a blow-out due to, inter alia, a loss of well control and equipment failure (such as the

BOP).

The impact of a blow-out on the marine environment is largely dependent on the quantity and physical state

of the hydrocarbons released. A blow-out would result in a jet release of two-phase material (gas and

liquids). Gaseous components would be released to the atmosphere while liquid components would form a

slick on the sea surface. A seabed blow-out would form a crater as a result of the escape of high pressure

gas. Escaping hydrocarbons would form a plume of bubbles, liquids and re-suspended sediments as the

gas and liquids are ejected through the water column. The potential hazards to the marine ecosystem are

associated with the toxicity of the hydrocarbons, damage to the benthic community, the effects of increased

turbidity generated by the rising gas / sediment loaded plume and impacts associated with a hydrocarbon

slick on the sea surface.

Oil spilled in the marine environment would have an immediate detrimental effect on water quality. Most of

the toxic effects are associated with the monoaromatic compounds and low molecular weight polycyclic

hydrocarbons, as these are the most water-soluble components of the oil. Oil is most toxic in the first few

days after the spill, losing some of its toxicity as it begins to weather and emulsify.

Based on the results of the oil spill modelling study (see Section 7.1.2.6), oil is predicted to travel in a north-

westerly direction up to 3 000 km from the spill site (based on the 90-day deterministic modelling) and no oil

is predicted to reach the shoreline. No differentiation between seasons (summer and winter) is evident from

the modelling.

Possible impacts related to a large oil spill are described below and summarised in Tables 7-10 and 7-11.

Marine fauna and ecology

• Plankton (comprising phytoplankton and zooplankton): Heavy loss of pelagic eggs and fish larvae can

occur if they are present in the area of oil spill. The time of year during which a large spill takes place

would greatly affect the degree of impact that would result. Should it coincide with a major spawning

peak, it could result in severe mortalities and hence a reduction in recruitment. However, spawning

and recruitment success is subject to variability in environmental conditions that have a far greater

impact than would be posed by a single large spill. A large-scale pollution event in nearshore nursery

areas would potentially have a critical impact on juvenile commercial and other fin fish species. These


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species (juveniles) are unlikely to be able to move out of the area and depending on the scale of the

event, finfish mortality is expected with a resulting impact on the fishery (see fisheries impact below).

The peak nursery period for juvenile finfish occurs from December through to March. Thereafter, most

juvenile small pelagic species migrate southwards out of the bays.

There is, however, a low probability of oil from a large spill extending into key fish spawning areas in

water depths less than 200 m and nearshore nursery areas.

• Benthic fauna: Oil in sediments as a result of accidental spillages can result in physical smothering of

the benthos and chronic pollution of the sediments. Tolerances and sensitivities between species vary

greatly and generalisations cannot be made confidently. Some burrowing infauna (e.g. polychaetes

and copepods) show high tolerances to oils, as the weathered product serves as a source of organic

material that is suitable as a food source. Polychaetes in particular can take advantage of bioturbation

and degradation of oiled sediments. This results in highly modified benthic communities with

(potentially lethal) ‘knock-on’ effects for higher order consumers. Sessile and motile molluscs (e.g.

mussels and crustaceans) are frequent victims of direct oiling or coating. Filter-feeders in particular

are susceptible to ingestion of oil in solution, in dispersion or adsorbed on fine particles. Chronic oiling

is known to cause a multitude of sub-lethal responses in taxa at different life stages, variously affecting

their survival and potential to re-colonise oiled areas.

Fauna inhabiting unconsolidated sediments is expected to be relatively ubiquitous, usually comprising

fast-growing species able to rapidly recruit into disturbed areas. Whereas, benthic fauna associated

with hard grounds (possibility occurring at Tripp Seamount) is typically more vulnerable to disturbance

due to their long generation times. Oil is predicted to travel in a north-westerly direction away from

Tripp Seamount.

• Fish: Impacts of oil on juvenile and adult fish can be lethal, as gills may become coated with oil. Sub-

lethal and long-term effects can include disruption of physiological and behavioural mechanisms,

reduced tolerance to stress, and incorporation of carcinogens into the food chain. However, being

mobile, fish are likely to be able to avoid a large spill.

• Birds: Birds, both at sea and along the coast, are vulnerable to oil spills. Individual pelagic seabirds,

which become oiled, will almost certainly die as a result of even moderate oiling which damages

plumage and eyes. Even if oiled seabirds are collected for cleaning and rehabilitation the success

rate is low. Ingestion of oil in an attempt to clear oil from plumage can also result in anaemia,

pneumonia, intestinal irritation, kidney damage, altered blood chemistry, decreased growth, impaired

osmoregulation, and decreased production and viability of eggs.

• Turtles: The impact of oil spills on turtles is thought to primarily affect hatchling survival. Turtles

encountered in the project area would mainly be migrating adults and vagrants.

• Seals: Little work has been done on the effect of an oil spill on fur seals, but they are expected to be

particularly vulnerable as oil would clog their fur and they would die of hypothermia (or starvation, if

they had taken refuge on land).

• Cetaceans (dolphins and whales): The impact of oil pollution on local and migrating cetacean

populations would obviously depend on the timing and extent of the spill. In particular, oil pollution in

areas of cetacean critical habitat (areas important to the survival of the population), such as the

extreme near-shore calving / nursing grounds of the Southern Right whale (e.g. Elizabeth Bay and


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Hottentot Bay where calving and nursing activities are known to occur) or summer feeding grounds in

the Cape Columbine – Yzerfontein area (off the coast of South Africa), would be the most likely to

impact populations. In extreme circumstances a large spill could impact a whale or dolphin population

where the spill impacts critical habitat of that population. It is assumed that the majority of cetaceans

would be able to avoid oil pollution, though effects on the population could occur where the region of

avoidance is critical to population survival. Although adult whales have been noted to swim, and even

feed through heavy concentrations of oil, Southern Right whale calves have a far higher surfacing rate

than adults and could possibly be affected by inhalation of volatile hydrocarbons.

• Coastal environments: Sandy beaches on exposed coasts with high wave and solar energy would be

the least impacted and recover most rapidly. Similarly exposed rocky shores after initial mortalities

would recover relatively rapidly. The most sensitive coastal areas are coastal lagoons and estuaries.

Should oil enter these systems in any quantity the impact would be severe. Secondary impacts on

lagoon- and estuary-dependent biota would be equally severe. However, since oil from a spill at the

drill site is expected to head in a north-western direction, impacts on the sensitive coastal environment

is unlikely.

While the probability of a major spill happening is extremely small, the impact nonetheless needs to be

considered as it could have devastating effects on the marine environment. Assuming the worst-case

scenario of a 90-day blow-out, the potential impact on the marine environment would be of low to high

intensity depending on the faunal group and would likely persist over the short- to medium-term.

Results of the oil spill modelling study indicated that the spill would spread in a north-westerly direction

(there is no differentiation between seasons), extending over 3 000 km out of Namibian waters thus

being of international extent. In the unlikely event of an oil spill due to a well blow-out, the impact on

marine fauna is considered to range from insignificant (benthic macrofauna) to medium (larvae,

pelagic fish, marine mammals and turtles) to high (seabirds) significance before mitigation.

Collectively, the impact on marine fauna is assessed to be of high significance (see Table 7-9).

Commercial and recreational fishing

In the event of a large oil spill, fishing may have to be temporarily suspended through having to avoid fishing

in oiled waters and may suffer gear damage due to oil contamination. Although a large spill from a well blow-

out would cover a large area, only those sectors that operate in the spill area may be directly affected. Thus,

based on the results of the oil spill modelling, those sectors operating inshore of the 200 m water depth

(including rock lobster and mariculture) and those operating in the north-eastern Namibian waters (including

mid-water trawl, traditional line-fish and deep-sea crab) are unlikely to be affected due to the north-western

trajectory of an oil spill. As mentioned earlier, fish are likely to be able to avoid a large spill and in doing so

be displaced from normal fishing areas. Thus, fishing operators would also be able to avoid areas of large

scale contamination and continue fishing, albeit in different areas, resulting potentially in increased fishing

effort.

Mortality of fish eggs, larvae and juveniles may lead to reduced recruitment, which may in turn impact fishing

in the longer-term. Although modelling results show that there is a low probability of oil from a large spill

extending to the 200 m water depth, mortality to some degree would be expected on eggs and larvae and

this would ultimately impact the biological resources upon which the commercial fisheries in the area

depend. Mortality would be more significant if the spill event occurred at peak periods of larval drift and

settlement into nursery areas (most likely from November through to March). The effect on the different

fisheries can occur over a number of years depending on the life cycle of the targeted species. Anchovy, for

example, recruit to the commercial fishery in their first year, sardine in their second year and hake in their

third year.


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The potential impact on the fishing industry is considered to be regional to national in extent, and of high

intensity and short- to medium-term duration depending on whether future recruitment is affected.

The significance of this impact is, therefore, assessed to be medium without mitigation (see Table 7-10).

Tourism

There would be a low probability (i.e. 0 to 10% probability) that a large oil spill at the drill site would come

within 50 and 75 km from shore between Lüderitz and Oranjemund. Moving north from Lüderitz this distance

increases gradually and is greater than 200 km from the shore at the latitude of Walvis Bay.

In terms of the receiving tourism environment, sea-based tourism activities in the area tend to be focused on

half-day boat trips / cruises leaving from Lüderitz and Walvis Bay harbours, as well as recreational fishing

trips. The majority of boats trips take place within 5 to 10 km of the shore taking in offshore islands and other

landmarks (e.g. Halifax Island in Lüderitz and Pelican Point in Walvis Bay). In the case of Walvis Bay,

specialised pelagic bird tours go as far as the continental shelf (35 km to 45 km offshore from Walvis Bay).

These activities are not likely to be affected by the 90-day blow-out scenario. Recreational fishing also tends

not to extend to the areas at risk from a major spill. Major passenger cruise liners also pass through the

study area. However, with adjustments where needed, those travelling between South Africa and Namibia or

between Namibia and countries to the north, should be able to largely avoid spill areas.

The potential impact on tourism from a large spill at the drill site is considered to be of to be regional, of high

intensity in the short-term. Thus this impact is considered to be of low significance before mitigation

(see Table 7-11).

Mitigation

The measures that would be implemented for as large spill are the same as for operational spills (refer to

Section 7.1.3.1).

Residual impact

With the implementation of the project controls and mitigation, the residual impacts associated with a well

blow-out on marine fauna and commercial fishing would be of MEDIUM significance, while the impact on

tourism would reduce to VERY LOW significance.

Table 7-10: Impact of a large oil spill on marine fauna


Extent International Regional

Duration Medium- to Long-term Short- to Medium-term




Significance High MEDIUM


Mitigation potential Medium


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Table 7-11: Impact of a large oil spill on commercial fishing


Extent Regional to National Regional to National

Duration Short- to Medium-term Short- to Medium-term

Intensity High High



Significance Medium MEDIUM


Mitigation potential Very

Table 7-12 Impact of a large oil spill on tourism


Extent Regional Regional



Probability Improbable Improbable


Significance Low VERY LOW


Mitigation potential Low

7.2 DROPPED OBJECTS

Description of the source of impact

Materials and supplies during all phases of the project would be transported by supply vessels to the drilling

unit. As with any transfer operation there is a risk of dropped objects. Dropped objects may include drums /

containers of oil, fuel, chemicals, paint, sacks, pallets, equipment, skips, garbage, etc.

Description of the environmental aspects

The accidental loss of objects or equipment to the seabed would result in the physical disturbance of the

seabed. In addition, it would increase the hard substrata available for colonisation on the seabed.

Description of the potential impacts

Any benthic fauna present on the seabed and in the sediment in the disturbance footprint would potentially

be disturbed or crushed, resulting in injury or mortality. The availability of hard substrata on the seabed

provides opportunity for colonisation by sessile benthic organisms and provides shelter for demersal fish and

mobile invertebrates thereby potentially increasing the benthic biodiversity and biomass in the continental

slope region.

Receptors

Depending on the item dropped, the contents and the location where the event occurs impacts of particular

concern from such an incident would be those occurring in the coastal areas and the NIMPA, which have

more sensitive receptors (e.g. key faunal breeding / feeding areas, bird or seal colonies and nursery areas

for commercial fish stocks). In the case of containers lost to sea, should the inventory be inert materials then

there is little risk of harm to the marine environment. However, drums / containers of chemicals, fuel, oil or


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other environmentally hazardous materials pose a potential pollution hazard unless they can be retrieved.

This has the potential to impact the seabed and benthic communities.

Disturbance of seabed sediments would result in direct damage to, and disturbance of, the invertebrate

benthic communities living on the seabed or within the sediments. The benthic fauna inhabiting

unconsolidated sediments of the outer shelf and continental slope are expected to be relatively ubiquitous,

varying only with sediment grain size, organic carbon content of the sediments and/or near-bottom oxygen

concentrations. These benthic communities usually comprise fast-growing species that are able to rapidly

recruit into areas that have suffered disturbance. Epifauna living on the sediment typically comprise urchins,

burrowing anemones, molluscs, seapens and sponges, many of which are longer-lived and therefore more

sensitive to disturbance. No rare or endangered benthic species are known to occur in the project area. In

contrast, the benthos of deep water hard substrata are typically vulnerable to disturbance due to their long

generation times. Such sensitive communities would be expected to occur at Tripp Seamount and in the

adjacent submarine canyon, which are located some 50 km south-east of the area of interest at its closest

point.

Project Controls and Industry Practice

Shell has no project controls specifically governing the disturbance of seabed habitats during hydrocarbon

exploration. However, it is the intention of Shell to ensure that the proposed drilling operation is undertaken

in a manner consistent with good international industry practice. In this regard, Shell would assess safety

and metocean conditions before performing any retrieval operations.

Performance objectives

Protection and conservation of the marine environment, marine fauna and sensitive seabed habitats.

Impact assessment

Even with the consideration and application of the highest standards of safety, dropped objects still occur.

The accidental loss of objects or equipment to the seabed could potentially disturb and damage seabed

habitats and crush any benthic fauna within the disturbance footprint. The physical disturbance would be of

medium intensity and extremely localised. The duration of the impact would depend on whether or not the

item can be retrieved. Assuming the worst-case scenario and the non-retrieval of the item, the duration

would be permanent. Thus, the impact on benthic macrofauna is considered to be of low significance.

If a lost object / equipment is left in place on the seabed, it would effectively increase the availability of hard

substrate for colonisation by sessile benthic organisms in an environment otherwise dominated by

unconsolidated sediments, thereby locally altering the community structure by increasing biodiversity and

biomass of marine species. While this may have positive implications to certain fish species (e.g. kingklip

and jacopever), which show a preference for structural seabed features, it may enhance colonisation by non-

indigenous species thereby posing a threat to natural biodiversity. Due to the water depths in the area of

interest, colonisation by invasive species is unlikely to pose a significant threat to natural biodiversity in the

deep sea habitats. The increase in biodiversity due to accidental loss of objects or equipment would be

highly localised and of low intensity. This permanent impact on community structure, assuming the object

cannot be retrieved, is considered to be of very low (neutral) significance.

Mitigation

The following measures will be implemented to manage accidental loss of equipment.

No. Mitigation measure Classification

1 Ensuring that loads are lifted within the maximum lifting capacity of

crane system. Avoid


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No. Mitigation measure Classification

2 Minimise the lifting path between vessels. Avoid

4 Undertake frequent checks to ensure items and equipment are stored

and secured safely on board each vessel. Avoid

3 Retrieve of lost objects / equipment, where practicable, after assessing

the safety and metocean conditions. Repair / restore

Residual impact

The only mitigation measure that would reduce the significance of the residual impact is the retrieval of the

loss object / equipment; however, in some instances after assessing the safety and metocean conditions, it is

important to note that equipment may not be retrieved. The proposed measures would merely reduce the

likelihood of the impact occurring. Thus, if the object is retrieved the benthic community would be able to

recover form disturbance, with full recovery expected within 2 to 5 years. The short-term nature of this

impact would reduce it to INSIGNIFICANT.

The retrieval of equipment would eliminate the neutral impact on benthic community structure as a result of

increased hard substrate. Thus, there would be NO IMPACT on the benthic community structure.

A summary of possible impacts related to the loss of objects or equipment to the seabed are provided in

Tables 7-12 and 7-13.

Monitoring

Establish a hazards database of all lost equipment, including date of loss, location and, where applicable, the

dates of retrieval.

Table 7-13: Impact on benthic fauna due to disturbance or crushing from lost objects / equipment


Extent Local Local

Duration Permanent Short-term

Intensity Medium Low

Probability Possible Possible


Significance Low INSIGNIFICANT


Mitigation potential Medium

Table 7-14: Impact on benthic community structure due to increased hard substrate as a result of

lost objects / equipment


Extent Local

NO IMPACT

Duration Permanent

Intensity Low

Probability Possible

Confidence Medium

Significance Very Low (neutral)


Mitigation potential High


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7.3 IMPACT SUMMARY

A summary of the assessment of potential environmental impacts associated with unplanned events is provided in Table 7-14.

Table 7-15: Summary of the significance of the potential impacts associated with unplanned events

Note: VL = Very Low; L = Low; M = Medium; H = High; VH = Very High; Insig. = Insignificant

No. Activities Aspects Impacts Probability with

mitigation

Significance

Without

mitigation

With

mitigation

7.3 Unplanned events:

7.3.1 Small operational spill Reduction of water quality

Toxic effect on faunal health (e.g. respiratory damage) and

mortality (e.g. suffocation and poisoning) Possible L INSIG.

Impact on commercial fishing through exclusion from polluted

areas and reduced recruitment Probable VL VL

Exclusion of sea-based tourism activities Improbable L VL

7.3.2 Large well blow-outs Reduction of water quality

Effect on faunal health (e.g. respiratory damage) or mortality

(e.g. suffocation and poisoning) Improbable H M

Impact on commercial fishing through exclusion from polluted

areas, reduced recruitment and fishing gear damage Improbable M M

Impact on tourism through the exclusion of sea-based tourism

activities Improbable L VL

7.3.3 Dropped objects Physical disturbance of the seabed Physical damage to and mortality of benthic species / habitats Possible L INSIG.

Increased hard substrata available for colonisation Increased the benthic biodiversity and biomass Possible Insig. NO IMPACT

7 POTENTIAL IMPACTS RELATED TO UNPLANNED ... spills (e.g. during bunkering), vessel accidents or...

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