Environmental Statement - Maersk Oil

Balloch Field Development Environmental Statement
Section 2 Proposed Development
Total fuel capacity on the NTvL is 1,373 m 3 (8,642 bbls) and on the Sedco 704 is 1, 051 m 3 (6,610 bbls).
As a worst case scenario, the spill modelling presented in Section 6 of this ES modelled the loss of
diesel from the NTvL.
The rig(s) will be towed to location with the assistance of three anchor handling vessels (AHVs), two in
front and one to the rear. Semi‐submersible drilling rigs tend to have anchor facilities using 8 (e.g.
Sedco 704 and NTvL) or 12 (e.g. NTvL) point chain wire mooring systems. For the purposes of this ES,
the worst case scenario of 12 will be assumed.
Whilst in position, a statutory 500 m exclusion zone will be established around the rig in accordance
with safety legislation. Unauthorised vessels, including fishing vessels, will not be permitted access to
the area. The drilling rigs will be equipped with navigation lights, radar and radio communications.
2.4.3. DRILL RIG AND SUPPORT VESSELS
Various support vessels will be associated with the drilling of the Balloch wells including three AHVs, a
supply vessel and a standby vessel. Table 2‐6 summarises the drill rig and support vessel activity and
fuel usage during the drilling of the proposed wells. It is possible that a reduced number of transit
days will be required for the AHVs should the second two production wells be drilled consecutively,
but as a worst case it is assumed that the rig will be moved off location between the drilling of these
two wells. No additional guard vessel will be required as the guard vessel associated with the GPIII
FPSO will meet the requirements of the drilling rigs.
Table 2‐6 Fuel consumption of vessels associated with the drilling of the first Balloch well.
Vessel type 1
Duration (days)
Working fuel
consumption (te/d) 1 Total fuel use (te)
Phase I (appraisal/ production well)
3 x Anchor handling vessels (transit) 24 2 50 1,200
3 x Anchor handling vessels (working) 6 5 30
1 x Semi‐submersible drilling rig 70 10 700
1 x Supply vessel (transit) 80 10 800
1 x Supply vessel (working) 10 5 50
Helicopter (5 hour return flight) 40 3 3 4 120
Phase II (second and third production wells)
3 x Anchor handling vessels (transit) 48 2 50 2,400
3 x Anchor handling vessels (working) 12 5 60
1 x Semi‐submersible drilling rig 140 10 1,400
1 x Supply vessel (transit) 160 10 1,600
1 x Supply vessel (working) 20 5 100
Helicopter (5 hour return flight) 80 3 3 3 240
Total 8,700
1 Source: The Institution of Petroleum, 2000.
2 Estimates it takes 4 days to transport rig to well location, therefore 2 x 4‐day trips per anchor vessel per well.
3 Duration in hours.
4 te/hr.
2.4.4. BLOW OUT PREVENTER
The NTvL is fitted with a 10,000 psi high pressure Cameron Iron Works well control system and a Blow
Out Preventer (BOP) stack while the Sedco 704 is fitted with a 15,000 psi BOP. The function of the
BOP is to prevent uncontrolled flow from the well by positively closing in the well at the seabed, as
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