Guntis Moritis
Production Editor
This second in a series of two-dimensional schematics illustrates the evolving complexity, as gas field development continues, of production facility infrastructure in the U.K. southern North Sea gas sector.
The first part in this series covered facilities in the northern North Sea (OGJ, Oct. 4, 1993, p. 51).
These schematics are not to scale but illustrate approximate platform orientation and main facility components. Complexity has increased because many new projects depend on tie-ins to existing infrastructure.
To make these projects economical, development typically includes unmanned platforms, subsea completions, and extended-reach wells. New gas marketing opportunities also have improved economics for developing smaller gas accumulations.
Some discoveries awaiting development and possible date of production are as follows:
- Alison, 1994
- Barque South, 1994
- Barque Extension, 1995
- Bessemer, 1995
- Davy, 1996
- Excalibur, 1994
Galleon, 1994 - Gawain, 1995
- Johnston, 1994
- Jupiter fields
- Keith
- Schooner, 1996
- Trent, 1996
- Tyne
- Viking Jx Fs, and WX 1996
- Wollaston, 1995
- York.
Recoverable reserves, from these fields, are about 4 tcf and development will require an investment of about $3 billion.
The schematics break the southern U.K. North Sea gas sector into three areas as shown on the map (Fig. 1). Area 1 (Fig. 2) includes Leman, Hewett, and Indefatigable. Area 2 (Fig. 3) is around Viking. Area 3 (Fig. 4) covers West Sole to Caister/Murdock.
Gas production is mostly from Permian Rotliegendes sands, at about 9,000 ft, although the Bunter and Zechstein intervals produce in some fields. The recently developed Caister/Murdock platforms are the first to produce gas from the Carboniferous.
Water depths in the sector are relatively shallow, generally less than 100 ft.
All production from the southern U.K. North Sea flows to terminal facilities at Bacton, Theddlethorpe, and Dimlington/Easington.
AREA 1
The Leman field was one of the first North Sea fields to go on production. Discovered in 1966, production started in August 1968. Peak production has been as much as 3.1 bcfd. Recent peak production is about 800 MMcfd. Leman, at the time of discovery, was considered the world's largest offshore gas field with reserves of about 10 tcf. About 3.5 tcf remain.
Shell U.K. Ltd. operates the west side and Amoco U.K. Petroleum Ltd. the east. As production has declined more compression has been added.
Also operated by Shell and Amoco is Indefatigable. But in this field, Shell operates the east side and Amoco the west. Discovered in June 1966, the field produces from a depth of 8,500 ft. Original reserves were 4.5 tcf. Production started in September 1971. Recent peak production is about 500 MMcfd.
In 1993, a deviated well was drilled from the Indefatigable D platform to produce the Baird field, with reserves of about 50 bcf. Baird went on stream in December 1993.
Restructured gas sales contracts now allow for sale of incremental volumes of gas from new fields around Indefatigable. Also, reconfiguration of compression will allow export of wet gas.
A number of small fields are proposed to be developed with slimline monotower platforms. One is Amoco's Davy.
Davy contains about 150 bcf and should go onstream by 1995. Another, the Bessemer/Beaufort, will probably be a horizontal well development from a monotower. Reserves are about 120 bcf and 1995 is the expected start-up.
The proposed monotowers are three-pile structures with wellheads, pig launcher, small test separator, helideck, small emergency shelter, and emergency generator.
The Phillips Petroleum Co. U.K. Ltd.-operated Hewett was another early discovery, October 1966. The field has produced almost 4 tcf since 1969. Gas flows to shore through a 20-in. sweet line and a 30-in sour line to Bacton. The Hewett ties in the Dotty Deborah, and Della fields. Della was tied-in in 1988.
Shell-operated Sean North and South were discovered in May 1969. Initial recoverable gas was 450 bcf. Production started in 1986 from three platforms. A fourth platform for compression was added in 1990. The 30-in line goes to Shell's Bacton plant.
The field was brought on stream under a peak shaving contract under which British Gas can nominate between zero and maximum daily rate whenever needed during the 6 month winter period.
Mobil North Sea Ltd.'s Camelot, discovered in June 1987, sits in 49-ft of water, and recoverable reserves are about 250 bcf. Production started in 1989 with a peak of 70 MMcfd. Production initially was from one unmanned steel platform. A second unmanned platform was set and began producing in early 1993.
Mobil's Tristan field came onstream in 1992 and is a deviated well development from Arco British Ltd.'s Welland platform. Production from the unmanned Welland platform started in 1990. The Welland is tied into Thames.
Another Thames tie-in is Arco-operated Orwell (previously named Raleigh). It began production in August 1993. The start-up was only 1 year after Annex B approval and 18 months after conceptual design began. The three-well subsea development has the longest umbilical in the world, 34 km. The umbilical transmits power, signals, and injection chemicals. Gas production, plateau of 120 MMcfd, is sold to National Power. Reserves are 250 bcf, and proposed field life is 10 years.
The Gawain field is another Arco-operated field that will be tied into Thames. Production is expected to start in October 1995 at about 80 MMcfd. Estimated reserves are 200 bcf.
The Arco-operated Thames, Yare, and Bure were discovered in 1969 and production started in 1988. Water depth is 110 ft, and production is from reservoirs at 8,000 ft. Peak production is 144 MMcfd.
Arco is planning to reduce manning on Thames by 1995. Control then will be from shore with 50% manning.
AREA 2
Conoco Ltd.'s Viking field, discovered in December 1965, lies in 99 ft of water. Reservoir depth is about 9,000 ft and initial recoverable reserves were 2.8 tcf. Production started in August 1972, and peaked in 1974-75 at 630 MMcfd. Recent peak production has been about 130 MMcfd.
The Viking A facilities were closed down in 1991 and now serve only as a pipeline terminal. Satellite development of Jx, Fx and Wx are targeted for 1996 or 1997 and these may use the Viking A facilities.
In the Viking B, a new accommodations platform was commissioned on Jan. 4, 1992. The new quarters were prompted by safety considerations for separating accommodations from production facilities.
The Victor field, discovered in 1972, went on production in 1984. Recoverable reserves are 980 bcf. Peak production is about 250 MMcfd. Production flows to Viking.
The North and South Valiant, Vanguard, and Vulcan fields are connected to Loggs (Lincolnshire Offshore Gas Gathering System) that goes to Theddlethorpe.
The Loggs system includes Conoco-operated V fields (North Valiant 1 and 2, Vanguard, South Valiant, and Vulcan 1 and 2), Ranger Oil U.K. Ltd-operated Anglia, and Phillip's Audrey and Ann.
Conoco's five V fields are unmanned and controlled from the Loggs complex. Production started in 1988.
The Ann gas field was discovered in 1965 but production only started in October 1993. The subsea template has two horizontal wells. The template is tied into Loggs platform with a 26-mile, 12-in. gas line. Drilling two horizontal wells eliminated the need to drill three vertical wells. Contract deliverability is 70 MMcfd. Estimated reserves are 127 bcf.
Audrey started production in 1988 from an unmanned wellhead platform and a subsea well. A second platform was added in 1990. The platforms are linked by a 10.5-mile, 20-in. line to the Loggs pipeline. Production is controlled from the Loggs complex.
The Anglia field started producing in 1991. Recoverable reserves are 235 bcf, and production rate is 50 MMcfd. The field has a tripod platform not normally manned.
Other potential development projects are in Conoco's Jupiter area, Blocks 49/16, 49/17, and 49/??. The prospects are called after Jupiter's moons Ganyvmede, Callisto, Thebe, and Europa. Combined reserves are about 600 bcf and, development is expected by 1995.
In 1993, Mobil started production from the Lancelot and Guinevere using an unmanned platform. Production capacity is 200 MMcfd. Lancelot reserves are 210 bcf, and Guinevere has 75 bcf. Gas from the field joins a 20-in. pipeline to the Bacton terminal operated by Phillips.
Two deviated wells from the Lancelot platform also drain the Cador reservoir.
Mobil's Excaliber is slated to start production in 1994.
Shell's Clipper was discovered in 1969 and Barque in 1971, but production did not start until October 1990. The fields are in 72-ft water and produce from a reservoir at 8,200 ft.
A compression platform was added to Clipper in 1993.
Galleon will come on stream in 1994 and be produced from two unmanned platforms about 7 miles from the Clipper fields. Target production rate is 130 MMcfd.
AREA 3
BP Petroleum Development Ltd.'s West Sole was the first discovery of commercial hydrocarbons in the North Sea. Discovered in December 1965, initial gas reserves were 1.8 tcf. Production started in March 1967. Recent peak production has been 160 MMcfd.
The adjacent Hyde field went on production in September 1993 through two horizontal wells. Gas sales are to an independent gas marketing company, Alliance Gas, at a rate of 45 MMcfd and a peak winter rate of 77 MMcfd. A 14-in., 7-mile pipeline connects Hyde with West Sole.
Britoil-operated Amethyst West and East fields, discovered 1972, are in 66-88 ft of water. Reservoir depth is about 9,000 ft. Estimated initial recoverable gas was 800 bcf. Production started in 1990 with peak production of 180 MMcfd in 1991. Production facilities are four unmanned platforms. Onshore compression will be required in 1995.
A simplified facility design allowed development of Amethyst. The initial plans were unattractive because of both capital and operating expense requirements. The facilities now allow for wet pipeline operations, onshore compression 5-years after start of production, and remote control. operator visits are required only once per week.
The Hyde facilities used the Amethyst platforms for a design basis.
The Arco-operated Pickerill field started producing in 1992. Production is from two normally unmanned platforms. The platforms are in about 70 ft of water, and estimated reserves are 750 bcf. Peak production is 200 MMcfd.
Pickerill's gas is sold to the U.K. electric utility Powergen. This was the first sale of an entire field's production, from a U.K. gas field, that went to a purchaser other than British Gas.
BP's Villages development includes Cleeton and South Ravenspurn. The fields have been producing since 1988 with peak production of about 250 MMscfd. A new compressor platform is planned for the Cleeton field in 1996.
Hamilton Oil Great Britain plc.'s North Ravenspurn, discovered in 19&4, started producing in 1991 from the only gravity-based concrete platform in the southern U.K. gas sector. Gas goes to Cleeton.
A new satellite platform and additional compression facilities were installed in 1993. Plateau production is about 290 MMcfd.
Hamilton's Johnston is a three-well subsea development that in 1994 will be tied back to the Ravensport North field. The field's recovery is about 170 bcf.
BP's Rough was discovered in 1968 and produced through two platforms. Now the field is used for gas storage and has three additional platforms. British Gas developed the depleted reservoir for storage to meat peak demand.
Hamilton's Forbes gas production platform was removed in 1993. It sat in 80 ft of water and was installed in 1985. Esmond, Forbes, and Gordon started production in 1985.
Conoco (U.K.) Ltd. and Total Oil Marine Caister-Murdock are the first Carboniferous fields to be developed in the U.K. sector. Production started in October 1992, and flow is expected to peak at 280 MMcfd in 1994. The pipeline capacity of 750 MMcfd will allow future developments to be tied in (such as Ketch Block 44/28b and Schooner Block 44/26a) to the 26-in line to Theddlethorpe.
The fields hold about 620 bcf and 5.7 million bbl of condensate. Water depth is about 400 ft. Caister also has a Bunter interval, discovered in 1967. The Carboniferous was found with the field's fourth well in 1985. The Bunter is at 4,600 ft and the Carboniferous at 11,200 ft.
Kinetica will buy Murdock production, Kinetica is a joint-venture independent gas supplier formed by Conoco and the U.K. electric utility Powergen. Caister gas will 90 to National Power for its planned 600 megawatt power station.
Arco Trent in Block 43/24 and Tyne in Block 44/18 are other discoveries that might be developed.
