HuldraProsPect

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Huldra

Huldra field production started on November 21st, 2001 and it’s expected to continue until 2014/2015. Cessation plans indicate removal of the installation in 2015/2016. The original design life of the Huldra structure was 20 years. The field was developed as a “normally unattended” (NUI) wellhead platform with a simple process separating gas and liquid (condensate and water) for export in dedicated pipelines. The installation was specially designed to be remotely operated and is controlled from Veslefrikk which is one of the tie-in hosts. Figure 1 shows the original Huldra wellhead platform.

Figure 1: Huldra Wellhead Platform

Since the original start-up a compression module and an additional living quarters module have been installed. Figure 2 shows a picture from the 3D model the platform with the compression module and additional living quarters.

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Figure 2: Huldra (from 3D model)

Topsides

The topsides are a single wellhead module comprising three decks with a 20 person living quarters, helideck and a cold vent boom. The original operating weight of the topsides was about 4700t; however provision was made in the design for the addition of a future compression module and the imposition of a skidded drilling derrick and associated drilling loads on the weather deck. The compression module was installed in 2007.

The topsides module has overall dimensions of approximately 32.5m (North South) by 60m (East West).

Process facilities

The original wellhead platform was equipped with a production separator, wet gas coolers and a wet gas scrubber; additionally export metering and pigging facilities are also installed. In 2006 a booster compressor and aftercooler module was installed.

The production separator is currently operated in a 2-phase mode although provision has been allowed for 3-phase operation by utilising a removable weir. The gas originally free flowed to export via wet gas coolers and a scrubber, however now a compressor is utilised due to declining wellhead pressures. The gas is exported via a 22” diameter pipeline (currently gas export is to Heimdal); MEG is also injected into the export gas for hydrate inhibition.

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The liquids are currently exported without the use of a pump, although pumps are due to be installed in 2011/2012 due to the declining wellhead pressure. The current configuration exports liquids (commingled condensate and water) to Veslefrikk via an 8” pipeline.

The process facilities were originally designed with the following capacities:

• Design pressure process facilities: 150 barg • Design pressure wellhead systems: 690 barg • Export rate gas: 10.8 MSm³/d • Export rate condensate: 7160 m³/d • Export rate water 650 m³/d • Production rate each well: 3.0 Msm³/d (gas)

The booster compressor allows approximately 5 MSm³/d of gas to be exported with a suction pressure of 30 bar absolute and a discharge export pressure of 116 bar absolute.

Figure 3: Process Facility at Huldra

Booster Compressor The booster compressor was installed in 2007 and comprises a General Electric LM2500 DLE gas turbine with an ISO rating of 23200 kW. The gas turbine is installed with a double helical type split gear which has one inlet axle and two outlet axles, one for the compressor and one for an electrical generator. The compressor is of a standard centrifugal type and can be utilized as fixed speed or variable speed (note - variable speed can only be used if the electrical generator is not in use). The maximum compression power is approximately 17.5MW and the maximum electrical generation load is approximately 11 MW.

Major Equipment

Production Separator (20-VA50)

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The Production Separator is a horizontal vessel (ID = 2650mm, Tan/Tan = 9000mm) which can be configured for either 2-phase or 3-phase operation using a removable weir. The vessel has a cyclonic inlet device and the gas outlet has a vane pack. A de-sanding system is also installed in the vessel. Wet Gas Coolers (20-HA50A/B) The Wet Gas Coolers are shell and tube heat exchangers with a design duty of 2 x 14930 kW; the two coolers are arranged in parallel. They are designed to cool the gas from the Production Separator to 35°C prior to export using seawater as the cooling medium. Wet Gas Scrubber (24-VG50) The Wet Gas Scrubber is a vertical vessel (ID = 2100mm, Tan/Tan = 4235mm) designed to remove liquids from the cooled gas stream prior to export. When the compressor is in operation the scrubber is utilised as a suction scrubber. The vessel contains a vane type inlet distributor and outlet demisting device consisting of a mist mat and hydrocyclones. Compressor Aftercooler (27-HA50) The aftercooler is shell and tube heat exchangers with a design duty of 13200 kW which is designed to cool the gas from the compressor to 40°C prior to export using seawater as the cooling medium. Seawater Lift Pumps/Firewater Pumps (50-PS50A/B) The cooling system on Huldra utilises seawater as the cooling fluid. The system uses 2 x 100% seawater lift pumps (rated capacity = 1391m³/hr at 88.6m differential head) which are electrically powered and installed in the two 36” caissons (50-TG50A/B). These pumps are also utilised as firewater pumps and in this mode the pump is directly connected electrically to its related Diesel Generator (82-EG50A/B), bypassing the main switchboard and the VSD. Main Generator Drives (82-EG50A/B) The original electrical power source for the platform was via two diesel driven generators. These are Caterpillar model 3606TA drives rated at 1730 kW. The two AC generators are AvK model ANL-99L2-8W and are each rated for 1650 ekW. Production Separator Condensate Pump (20-PA001) and Wet Gas Scrubber Condensate Pump (24-PA001) As the wellhead pressure has declined additional pumps have been installed to maintain export of the condensate and water to Veslefrikk. The Production Separator Condensate Pump is an HMD seal-less pump (model HPGSP 3x1.5x13 EA17) rated for a flow rate of 65 m³/hr with a 155.8m head. The Wet Gas Scrubber Pump is a Sundyne Pump (model LMV-801) with a rated flowrate of 7m³/hr with a head of 195m.

Jacket

The Huldra WHP jacket has four legs and was designed to support a topsides weight of 9200 tonnes. X-bracing connects the legs on all four faces and on all horizontal plans except the plan at elevation + 22 m. Horizontal face members are provided all around at elevation +7 m for collision protection. Additional horizontal members on row A act as conductor guide supports. The north side of the jacket is vertical to give access to the jack-up rig. MSL is 125m. The jacket was also designed to support the following items:

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12 x 30” conductors (arranged in a 4 x 3 rectangular grid, internal guide diameter = 840mm)

1 x 22” gas riser

1 x 8” condensate riser

1 x 10” future riser (not physically installed)

2 x 20” J-tubes

2 x 12” J-tubes

1 x 10” J-tube

2 x 36” seawater lift caissons (El – 67.875m MSL)

1 x 30” seawater dump caisson (El – 20.0 MSL)

1 x 5” drain outlet caisson (El -5.0 MSL)

Additionally there is permanent access at El. +22.5 MSL to all jacket legs and an escape ladder running from the top of the jacket and down to El. –4.0 MSL along leg A2.

The structure was analyzed for all environmental and accidental load conditions that may occur throughout the 20-year design life of the platform and was designed to satisfy the company requirement for no inspection (safety factor of 10).

Operation and Maintenance

The normally unattended concept was given high attention in the selection of technical solutions and equipment, the design of the installation and the prioritization of maintenance and inspection during the operational phase. Equipment and systems were chosen to minimize maintenance activities.

Statoil’s requirement for safety, regularity & maintenance has been applied for the NUI concept. Planned maintenance has been performed by the periodic manning of the platform with a multidiscipline team from the host organisation. On average approximately 10-12 persons have been shuttled to the installation on each visit.

Drilling

The wellhead installation is adapted to allow drilling with a jack-up rig cantilevered over the installation. This is illustrated in figure 4.

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Figure 4: Jack-up drilling at Huldra

The jacket has 12 slots, arranged in a rectangular pattern, although only 6 have been used for the Huldra development.

Technical Condition

The installation has been well maintained and the general technical condition for Huldra is assessed to be good. The installation was designed for a life of 20 years. The compression module was installed on 24th September 2006 and was designed with a life of 15 years. Based on operational experience it is likely that the operational life can exceed the design life by several years without major investments beyond regular maintenance.

Capacities

Table 1 ‐ Indicative Processing Capacities for the Huldra Platform Facilities  

Gas-

Condensate Light Oil Heavy Oil

Production Separator Pressure (1, 2) bara (psia) 133 (1915) 50 (725) 10 (145)

Gas Processing Capacity MSm³/d (MMscfd) 10.8 (381) 6.5(3) (228)(3) 1.7(3) (61) (3)

Liquids Processing Capacity (2, 4) Sm³/d (kbpd) 10200 (64) 10200 (64) 10200 (64)

Notes 1. In an oil processing mode, the operating pressure of the Production Separator, 20-VA50, is reduced to

align with typical values used for the processing of light and heavy oils.

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2. The Production Separator can be reconfigured for 3-phase operation. New facilities for the treatment of produced water and its subsequent re-injection or overboard disposal to sea, can be accommodated.

3. The maximum gas capacity is limited by the power of the compressor driver based on achieving a notional gas export pressure of 100 bara.

4. The maximum liquid capacities are based on a liquids residence time of 3-minutes, and on the geometry constraints of the existing Production Separator.

5. The platform features a GE LM2500 gas turbine with an ISO rating of 23,200 kW. Currently, this power may be used for gas compression (up to 17.5 MW) and/or for electrical power generation (up to 11 MW).

6. A WHRU could be retrofitted to the gas turbine to provide inlet heating, and up to 23 MW of heat is potentially available.

Huldra Field Information

The Huldra field was discovered by well 30/2-1 in 1982. It is a gas-condensate field, located in the blocks 30/2 and 30/3 of the Norwegian sector of the North Sea, about 15 km north-west of the Veslefrikk field and 28 km north of the Oseberg field. The sea depth in the area is 125 meter. Production started on November 21st, 2001 with a plateau rate of 10.3 MSm3/d (wet gas to Heimdal). The Huldra field is operated by Statoil and the Huldra owner group comprises the following partners:

Petoro 31.95% Total E&P Norge 24.3% Norske ConocoPhillips 23.33% Statoil 19.88% Talisman Energy Norge 0.49% The Huldra field was originally defined as a “high pressure, high temperature” (HPHT) field, with an initial reservoir pressure of 675 bar and reservoir temperature of 146°C. Six producers have been drilled at Huldra. Following installation of the booster compressor, a decrease in the Production Separator pressure from 98 to 33 bara was achieved. A further decrease in the Production Separator pressure has been made possible by carrying out modifications at the Heimdal host (i.e. gas routing to the LP system) and by installing pumps on the Huldra platform for the export of condensate and water.

Further Information

Additional information on Huldra can be provided upon request. Please contact the Operators representative on Huldra.