Environmental Statement - Maersk Oil

5.2.2. DISCHARGES TO SEA
5‐ 8
Balloch Field Development Environmental Statement
Section 5 Assessment of Potential Impacts and Controls
Routine discharges from vessels such as sewage are considered to have a negligible environmental
impact and are therefore not considered here. Discharges assessed during the installation of the
subsea infrastructure are associated with pipeline hydrotesting.
Hydrotesting
After installation and prior to being stabilised the lines will be flushed and hydrotested. It is
anticipated that the lines will be tested using potable water and chemicals of the lowest possible
Hazard Quotient (HQ). At the end of the testing operations, the hydrotest fluids will be discharged to
sea.
Concern over the impact of hydrotest water is due to the volume and types of chemicals discharged
and the potential impact of chemicals on the marine environment. It is anticipated that only a single
pipeline volume will be required for hydrotesting and, as such, chemical discharge will be a one‐off
discharge; therefore, any effects from the discharge will be temporary. Based on the infrastructure
listed in Table 2‐9 and assuming a tie‐in spool length of 20 m, a production spool inner diameter of 6”
and a gas lift spool inner diameter of 3”,< 3m 3 of hydrotest water will be discharged during the testing
operations of the production and gas lift jumpers and tie‐in spools at each well.
The chemicals to be used are yet to be finalised; however, the dose and quantities will be in
accordance with the manufacturer’s specifications and chemical permits will be sought prior to any
chemical use or discharge using the relevant PON15 applications. Given the small volumes, the
hydrotest fluids are expected to rapidly dilute in the marine environment.
Proposed control measures for impacts associated with discharges to sea during the installation
phase
Control measures to mitigate impacts from discharges to sea associated with the installation phase
are presented below.
5.2.3. PHYSICAL PRESENCE
The physical presence of the subsea infrastructure was assessed as being of low environmental risk;
however, given the potential for impacts on other sea users and the seabed it was further assessed.
Section 5.1.3 discusses the potential environmental impacts associated with the physical presence of
vessels on other sea users and the marine environment. This section will therefore concentrate on
the physical impacts of the subsea infrastructure.
Subsea infrastructure
Proposed Control Measures
Chemicals of the lowest possible HQ will be used.
Chemical use and discharge will be regulated under PON15C.
The subsea infrastructure is likely to disturb the mobile benthic fauna and smother the mixed flora
and fauna beneath. The structures could also cause a nuisance to fishing operations because of the
potential snag risk. To mitigate against this, the X‐mas trees and cooling spools will be of a fishing
friendly design.
Table 5‐6 shows the area impacted by the subsea infrastructure using a worst case of three wells,
with each at least 80 m from the DC2 manifold. The option chosen means that the area impacted is
minimised as the only additional flow lines are the short jumpers required to connect the wellheads
to the DC2 manifold. The maximum area impacted is anticipated to be 0.0008 km 2 .