Chevron Corp. is putting more emphasis on U.K. North Sea operations.
Chevron U.K. Ltd. increased its stake in Ninian area developments after license partner Enterprise Oil plc opted to sell its 18.52% interest. That puts Chevron in the position of expanding operations there.
Meantime, Chevron U.K. started up production from Alba oil field in the U.K. North Sea.
In other U.K. North Sea action, a combine of Shell U.K. Exploration & Production and Esso U.K. Ltd. has won U.K. Department of Trade & Industry approval to develop two southern North Sea gas reservoirs in a 175 million ($260 million) program.
NINIAN INTEREST SALE
Enterprise made $75 million on the Ninian sale, effective Dec. 31, 1993, pending U.K. government approval.
Chevron and Ninian partners Murphy Petroleum Ltd. and Oryx U.K. Energy Co. exercised their preemptive rights to secure Enterprise's share of interests before other companies could move in (OGJ, Jan. 17 p. 29).
The deal takes operator Chevron's interest in Ninian from 17.1% to 23.63%, while Murphy's share rises from 10% to 13.82% and Oryx's from 21.37% to 29.54%. Other interests are Lasmo North Sea plc 17.25%, Neste North Sea Ltd. 4.25%, and Ranger Oil (U.K.) Ltd. 11.5%.
Ninian field lies on Blocks 3/3 and 3/8. Chevron began production there in 1978, reaching a peak of 300,000 b/d of oil in 1982. Current production averages 65,000 70,000 b/d of oil.
SATELLITE DEVELOPMENTS
Ninian's three production platforms are increasingly being used in third party developments as Ninian field production declines.
Ninian is the gathering point for oil entering the pipeline to Sullom Voe terminal from Heather field operated by Unocal U.K. Ltd., North Alwyn held operated by Total OH Marine plc, and Magnus field operated by BP Exploration Operating Co. Ltd. Total's Dunbar field is expected to send oil via Ninian to Sullom Voe starting in 1993. Three subsea satellite fields use some of Ninian's spare processing capacity: Lyell field operated by Conoco (U.K.) Ltd., Staffa field operated by Lasmo, and Strathspey field, which operator Texaco Ltd. brought on stream in late December 1993 (OGJ, Jan. 10, p. 32).
Late last year Ninian partners also announced plans for fast track development of other Ninian satellites. Four have been identified with total reserves estimated at 100 million bbl of oil (OGJ, Dec. 13, 1993, p. 24).
NINIAN POTENTIAL
Charles Smith, managing director of Chevron U.K., said, "We believe there is still tremendous potential not only in the field itself, but also through its strategic position as the entry point for the Ninian pipeline to Sullom Voe for further satellite and third party business."
Enterprise will receive an extra $2 million from the Ninian group if one of these four prospects, known as Northeast Flank, gains separate development approval from government before July 1, 1996. An appraisal well on this prospect was spudded Dec. 15, 1993. Graham Hearne, chairman and chief executive of Enterprise said, "As a result of this sale and the disposal last year of the mature Hutton and Northwest Hutton fields, we have relinquished our remaining interest in the Sullom Voe oil terminal and the associated Brent and Ninian pipeline systems."
ALBA ON STREAM
Chevron said Alba production began Jan. 14.
Start up had been delayed since Nov. 28, 1993, when Chevron originally received approval to begin production.
The delay was caused by a software fault in fire and gas detection and emergency shutdown systems aboard the field's storage tanker.
During the wait, Chevron continued with development drilling from Alba Northern platform, setting the stage for early production of 50,000 b/d from two wells.
Production from the 655 million ($985 million) Phase I of Alba development is expected to peak at 70,000 b/d later this year.
Alba development entails an oil production platform linked by a 3 km subsea pipeline to a floating storage unit (FSU). A shuttle tanker is used to offload oil for export.
ALBA DETAILS
The field, discovered in 1984, holds an estimated 400 million bbl of 19 200 gravity oil reserves. Phase II plans, covering Alba's southern portion, are under discussion.
Chevron noted Alba, which produces from relatively shallow Eocene pay at about 6,000 ft, is the first of a new generation of North Sea fields likely to yield significant production from zones about half as deep as most in the North Sea.
Development of the shallow reservoir called for advanced horizontal and high angle drilling. And Alba crude at 19 200 gravity is relatively low gravity compared with typical North Sea crudes.
All Phase I production is from a single platform in 450 ft of water. Crude moves via a 3 km pipeline to a permanently moored floating storage vessel that is offloaded via shuttle tanker.
Interests in Alba are Chevron 33.17%, Oryx 15.5%, Fina Petroleum Development Ltd. 12.65%, Santa Fe Exploration (U.K.) Ltd. 11.75%, Conoco (U.K.) Ltd. 9.33%, Unilon Oil Explorations Ltd./Baytrust Oil Explorations Ltd. 8%, Aran Energy Exploration Ltd. 5%, Conoco Petroleum (Alba) Ltd. 2.35%, and Amerada Hess Ltd. 2.25%.
ALBA SECOND PHASE
Chevron has submitted a plan to Department of Trade & Industry for Phase II development covering the southern portion of the field, with start up scheduled within 5 years of approval.
Choice of second phase development options will depend on reservoir performance under production from a single platform and the success of extended reach drilling into the southern section.
"We are optimistic about how far we can reach into the southern section, but we know we cannot reach the extremities of the field from the northern platform, given expected advances in drilling technology," said a Chevron official.
Chevron is currently studying second phase options. It is thought likely that a second platform or a subsea development will be chosen for southern Alba development.
Another consideration is that Alba overlies Britannia gas field, which holds lower Cretaceous reserves spread over five blocks and estimated at 2.5 tcf of gas and as much as 200 million bbl of condensate and natural gas liquids. Britannia, currently planned for development with a platform plus subsea tiebacks by joint operators Chevron and Conoco Inc., is scheduled for start up in 1998 (OGJ, May 31, 1993, p. 21). Field development was originally scheduled for completion in October 1997, but the date was postponed a year to give license partners more time to trim costs.
Partners in the two projects considered simultaneous development of Alba's southern portion and Britannia. A joint plan was deemed unlikely because of contrasting requirements of oil and gas/condensate developments.
Chevron designed Alba facilities to enable handling of third party oil production from nearby future developments. The company recently announced plans for further developments through Ninian field facilities (OGJ, Dec. 13, 1993, p. 24).
In October 1993 Chevron completed the 16/26 25 new pool wildcat, which discovered a potential satellite to Alba. Parliament prospect flowed 4,269 b/d of 32.80 gravity oil from two of several Paleocene zones.
ALBA PLATFORM, TANKER
Alba Northern platform consists of a conventional eight legged steel jacket and 20,200 metric ton topsides. The deck contains wellhead and processing equipment, drilling and accommodation modules and a flare boom. Maximum crew is 144.
Because Alba oil is relatively low gravity and lies in unconsolidated sand with an underlying water zone, Chevron said it had to use advanced techniques to achieve production.
These included horizontal and high angle drilling, as well as use of prepack screens and gravel packing, electric submersible pumps, and continuous water injection.
The 45,700 ton platform has 24 well slots: 15 for producers, five for water injectors, and four spares. Peak oil productive capacity is 70,000 b/d, while water injection rate is 242,000 b/d.
The nearest producing field is Block 16/21 Balmoral field 10.5 miles away, operated by Sun Oil Britain Ltd.
Alba FSU was the first purpose built storage tanker in the U.K. North Sea, Chevron noted. It stores crude oil in seven central tanks, protected against collision by water ballast wing tanks.
The FSU weathervanes around an internal turret, which is moored to the seabed by 12 anchors. During offloading, a shuttle tanker is positioned 80 m astern of the FSU.
Alba's FSU is a 125,000 dwt vessel with storage capacity of 825,000 bbl of oil. It can load at 3,125 bbl/hr from the platform and offload at 37,500 bbl/hr. The FSU can accommodate a maximum crew of 56.
The 78,000 dwt Polyclipper shuttle tanker is used to export on to refineries in Northwest Europe. The shuttle tanker will call every 5 7 days at the FSU.
Chevron said the FSU has sufficient risers and capacity to handle oil from future developments in the area by third party operators.
SOLE PIT EXPANSIONS
The Shell/Esso combine intends to exploit reserves estimated at almost 700 bcf of gas within the Sole Pit area of Quadrant 48.
The project will mainly use existing facilities in Block 48/13a Barque field and Block 48/19a Clipper field to develop:
- South Barque field, a separate reservoir 1.6 km south of Barque field, with estimated reserves of 35 bcf of gas.
- The southeastern extension of Barque field, with estimated reserves of 520 bcf of gas.
- Gas reserves at the extremities of Barque and Clipper reservoirs, estimated at 140 bcf.
Operator Shell Expro said the reserves from this project would increase by 48% the 1.45 tcf of gas of reserves accessed by Barque and Clipper field developments.
SOUTH BARQUE
Production is scheduled to begin from South Barque field in October 1994. The discovery well, drilled from the platform in 1992, will be side tracked and completed as a producer.
Development will also involve drilling two extended reach wells from the Barque platform. These win have a horizontal reach of 2,700 m from the platform and reach a true vertical depth of 490 m.
Subsea development was considered for South Barque and Barque Extension but deemed more expensive than the chosen options.
BARQUE EXTENSION
The Barque Extension lies 14 km northwest of the Clipper complex. It will be developed with an unmanned platform operated from Clipper, with first gas scheduled for October 1995.
The Barque Extension PL platform will be a four legged steel wellhead structure. It will have 15 well slots and weigh 2,000 tons. Initially eight wells will be drilled from the platform.
Shell Expro expects gas compression will ultimately be required to maintain gas production from Barque Extension. This will be provided from the Clipper compression platform, which started up in October 1993.
Shell let a 25 million ($37.5 million) contract to Heerema Havnbedrijf BV, Vlissingen, Netherlands, for engineering, procurement, fabrication, and installation of the Barque PL platform.
BARQUE/CLIPPER FRINGES
Three extended reach wells will be drilled from existing platforms to recover gas from the outer fringes of the Barque and Clipper reservoirs.
Shell said one will be drilled from Barque and two from Clipper.
About half the total investment on the overall project was said to be earmarked for drilling.
Shell let the drilling contract to Santa Fe Drilling Co. (North Sea) Ltd., Aberdeen, as a continuation of existing contracts managed from the company's Great Yarmouth base.
OTHER SOLE PIT PLANS
Shell noted the Sole Pit area lies northwest of the main Shell/Esso southern North Sea developments, which include Leman and Indefatigable fields.
Since 1966 a total 23 exploration and appraisal wells have been drilled in the Sole Pit area. Nine gas reservoirs have been discovered to date.
Clipper field facilities have spare capacity to handle further developments by Shell/Esso and other operators. Development of other Sole Pit structures is currently being studied.
In the meantime, Shell Expro plans to drill 29 exploratory, appraisal, and development wells in the U.K. southern gas basin the next 6 years. These will include wells in Sole Pit, Galleon, and Sean fields.