P RODUCTION O PERATIONS

 As discussed in Section 3-1, current estimates are that the Alma field will produce a maximum of 32.5 MMbbls of crude oil and 8.1 Bscf of gas. The gas to oil ratio is assumed to be 250 scf per barrel. Wells are expected to have a high water cut and will be produced with the aid of ESP’s. Reservoir pressures will be maintained by produced water reinjection supplemented with treated seawater.

The FPSO will support all production activities with crude oil offloading every two weeks. Field life is anticipated to be approximately ten years.

5.3.1

Produced Fluids Offloading

It is anticipated that a shuttle tanker will visit the FPSO initially once every two weeks to offload stored crude oil. During offloading operations the offloading hose is suspended in a free-hanging catenary configuration between the FPSO stern and the bow of the shuttle tanker. Between offloading operations, the free end of the offloading hose is hung-off from a support platform at the FPSO stern (Figure 5-8). The shuttle tanker has a maximum offloading capacity of 100,000m3 (87,000 tonnes).

Figure 5-8: Offlo ading f rom Uis ge Gorm FPSO

Source: www.oilrig-photos.com/picture/number115.asp

5.3.2

Power Generation

The FPSO will have its original three 0.9MW rated diesel engines and two new 14MW steam boilers. The steam boilers can be fuelled by diesel (fuel oil), fuel gas or crude oil. Under normal operations gas produced from the reservoir will be used to power the steam boilers. However, as gas production declines over field life there will be insufficient gas produced to power both and eventually even one of the steam boilers. When gas production proves insufficient to power a boiler it will switch to duel fuel e.g., fuel gas and crude oil will be burnt at the same time. As the boilers will run on gas augmented by crude, only

ENQUEST HEATHER LIMITED  ALMA FIELD DEVELOPMENT

part of field life where excess gas is produced that cannot be burned, this will be flared. At the peak of production it is anticipated that gas production will be in the order of 7 mmscf/d (198,200m3/d).

For the steam boilers there will be a waste heat recovery scheme in place. Waste heat will be recycled back into the boilers and turned into steam. This means less waste heat is vented to the atmosphere.

The diesel engines will be used primarily during start-up when the flow of produced gas is insufficient to run the steam boilers. Once the steam boilers are operational the diesel engines will be switched off and only used during maintenance.

The steam boilers are typically 86% thermal efficient and operate at low pressures. This means that emissions of NOx are typically low. Reservoir hydrocarbons at Alma have low sulphur content and therefore SOx emissions will also be low.

Figure 5-9 shows the monthly cumulative CO2  emissions from the installed capacity of the three 0.9MW diesel generators and one 1.5MW steam driven turbo generator on the Uisge Gorm from January 2008 to August 2008 (only data available at time of EIA preparation). The monthly CO2 emissions are well below permitted levels, with a total of 28,018 tonnes of CO2  having been generated by the end of August 2008.

Figure 5-9: Cumulative total CO2 (tonnes) f rom Uisge Gorm FPSO (Jan-Aug 2008)

Source: Bluewater 

5.3.3

Gas Flaring

The flare system provides the facilities to safely collect and dispose of normal and/or emergency hydrocarbon liquid and gas releases from all areas of the process plant. The system is designed to handle all flaring situations that could occur and to meet all the relevant environmental and safety criteria.

 As discussed in Section 5.3.2 above, the vast majority of produced gas will be used for power generation. It is expected that gas will only be flared in an emergency situation. There will be no flaring as a part of well clean-up.

ENQUEST HEATHER LIMITED  ALMA FIELD DEVELOPMENT

Over 8.138 Bscf (230.4 million m3) will be produced from the Alma Development. Of this, 7.88 Bscf (223 million m3) will be used as fuel gas for power generation on the FPSO and it is anticipated that no more than 258,500 scf (7,320m3) will be flared.

Consent to flare under the Petroleum Act 1998 will be applied for approximately three to four months before start-up. This will cover any flaring during commissioning, start-up and production. Additionally, flaring activity will be considered in applying for an allowance under the EU Emissions Trading Scheme (EU ETS).

5.3.4

Chemical Use

 A number of chemicals will be required during production operations. Initial chemical injection facilities are expected to be:

Topsides corrosion inhibitor Topsides scale inhibitor Seawater biocide

Oxygen scavenger Demulsifier

 Antifoam De-oiler

Subsea scale inhibitor

Subsea hydraulic control fluid

Chemicals will either be dosed into injection water or supplied to the wells through the chemical umbilical. The quantities required will be calculated based upon production flows, temperatures and pressures.

 All chemical use will be permitted under an Offshore Chemical (Amendment) Regulations 2011 chemical permit i.e., PON15D. The majority of chemicals will be within a closed system with no discharge to sea; however some chemicals such as control fluids may be discharged at the wellheads. These permitted discharges will be risk assessed.

5.3.5

Produced Water (PW)

Under normal operations all PW will be re-injected with treated seawater into the water injection wells. The PW system has been designed to handle up to 140,000bwpd (22,260m3/d). Production forecasts suggest that the field will produce approximately 120,000bbls (19,000m3) of fluids per day. At the start of field life the water / oil ratio will be approximately 70% e.g., 30bbls of oil and 70bbls of water for every 100bbls of total produced fluids. As the reservoir declines the water / oil ratio will increase and by the end the oil water ratio will be 95% water and 5% oil (5bbls of oil for every 95bbls of water). However, throughout field life 120,000bwpd will need to be injected to maintain the reservoir pressure and balance. Any shortfall between the volume of PW extracted and the volume to be injected will be made up with treated seawater. The PW system has been designed to achieve, as a minimum, oil in water

ENQUEST HEATHER LIMITED  ALMA FIELD DEVELOPMENT

achieving OIW concentrations of <15mgl-1 on the Flora and Fife fields (including  Angus and Fergus). EnQuest are committed to a performance standard of <30mgl-1  for all PW injected so that if the system trips there is the option to discharge PW overboard.

On arriving at the FPSO produced fluids are routed through two first stage separators. Oil from the first stage separators is passed on to a second stage separator / coalescer and routed to the cargo tanks. Water comes out of the first and second stage separators and is routed through a bank of hydrocyclones. Each separator has its own dedicated bank of hydrocyclones which typically reduce the OIW concentrations in the PW from 1000mgl-1 to <30 mgl-1. From the hydrocyclones the PW is routed through one of two degasser / settling vessels. It is not expected that much settling will occur, but the vessel can be used to increase residency times should the system trip and PW requires further processing.

PW is passed from the degasser/settling vessels to a PW pump and on to one of four water injection pumps that pump the PW into the water injection flowline and through to the water injection wells. The overboard discharge valve sits between the PW pump and the water injection pump.

The FPSO will also have a separate, but connected seawater system. Seawater is de-aerated and treated with biocide before passing through one of two booster pumps and onwards through one of two water injection pumps. The seawater is co-mingled with the PW after the PW system water injection pumps before the water enters the water injection flowline.

The seawater system booster pumps and the PW system PW pumps are connected. This ensures that during planned maintenance one pump out of the six can be switched off but the combined systems can still manage throughput, with no overboard discharges necessary.

It is possible that PW may be discharged if one of the pumps fails. During this scenario, PW will be discharged overboard until the pump is bought back online or until throughput is reduced to a level where the pump is not necessary. The maximum overboard discharge would be 20,000bwpd (3,180m3) rather than the full production quantities, because without the reinjection system working reservoir pressure cannot be maintained and the wells will stop flowing. OIW concentrations in overboard discharges would be less than 30 mgl-1.

5.3.6

Sewage Treatment and Drainage

The FPSO was built in 1985 and does not have a sewage treatment plant. All sewage and food waste is macerated before being discharged overboard. Bluewater have not found a practical method of updating the system that delivers a substantially better environmental performance.

 All fluids entering the drain system are routed to the slops treatment system, processed through the produced water system and re-injected with the produced water.

5.4

D

Field life is estimated to be ten years and therefore abandonment will occur around 2033. The arrangements for decommissioning of the subsea facilities and flowlines have been development in accordance with the current UK

ENQUEST HEATHER LIMITED  ALMA FIELD DEVELOPMENT

Government legislation and international agreements in force. The decommissioning plan is based on the following assumptions:

Plug and abandon all wells

Removal of the conductor to below the mud line Removal of the subsea xmas trees

Removal of the manifold

De-oil and remove the two production flowlines Remove the water injection flowline

Remove the power cables and control umbilicals Remove and relocate the FPSO

Third party confirmation of seabed clearance

 A pigging loop has been included in the two production flowlines so they may be joined together at the drill centre location. To de-oil the flowlines, a pipeline chemical pig will be pushed down the first flowline from the FPSO around the loop and up the second production flowline. The pig will push any oil remaining in the flowline in to the processing facilities on the FPSO.