Units of Conoco Inc. have drilled their first two horizontal wells in the U.K. and Dutch North Sea, achieving good flow rates at both.
The wells used the medium radius technique, employing specially designed motor systems to achieve angle build rates of 6-20/100 ft.
In Block 49/16 off Britain, the well by Conoco (U.K.) Ltd. in North Valiant gas field was the first horizontal drilling in the southern gas province of the North Sea. It also was the first time the medium radius technique was used in the British sector.
The horizontal well drilled by Conoco Netherlands effectively doubled production to 25,000 b/d from Kotter oil field in Block K18.
Conoco said the build rates with medium radius are much higher than those achieved by long radius drilling using conventional steerable motors. The technique also provided greater accuracy and certainty in positioning the horizontal section of the hole.
In the Norwegian North Sea, Amoco Norway Oil Co. has the first of two projects under way to boost recovery in Valhall field.
NORTH VALIANT WELL
Conoco's 49/16-PO5/03 North Valiant well flowed 47 MMcfd through a choke, more than three times the rates reported for other wells in the field. The company expects an even larger volume when the well goes on production.
Conoco dubbed the well Dunehunter because the horizontal section was targeted to penetrate several large dunes in the Rotleigendes sandstone formation.
The company said the angle of deviation, built at an average rate of 12/100 ft, was more than five times the rate achieved by standard directional drilling. Conoco used specially designed steerable motors supplied by Sperry Sun Drilling Services, Great Yarmouth.
The Penrod 92 jack up drilled the well to 8,100 ft true vertical depth.
Total cost of the well was not disclosed, but Conoco said it was only 35% greater than previous conventional wells in North Valiant field.
North Valiant is part of the Valiant area production complex which produced an average 330 MMcfd during 1989. Gas moves through Conoco-British Petroleum's Loggs pipeline to Theddlethorpe on the east coast of England.
Conoco plans to drill more horizontal wells this year. Included in the program is one well in Vulcan gas field, which adjoins the Valiant area. A horizontal well from the Murchison oil field platform in the East Shetlands basin is a possibility.
KOTTER SIDETRACK
Conoco sidetracked its K8/1A horizontal well in Kotter field from the abandoned K8/1 producer using the Penrod 81 jack up. Stabilized flow was 12,000 b/d following 1 month of gradually increasing the rate.
Rate of angle build was 8-11.5/100 ft. The hole reached horizontal at 6,280 ft measured depth, 5,760 ft true vertical depth, and continued horizontally for 620 ft.
Conoco said -sidetracking from an existing well cut drilling/completion costs about 50%, compared with a new conventional well.
Although it is normal industry practice to number North Sea wells with the block designation first, Conoco has a different numbering system for its wells off Netherlands. The horizontal well is in Block K18, but it carries a K8/1A designation, meaning K for Kotter, eight for well No. 8, 1 for slot 1, and A for reentry.
Kotter is part of a two oil field complex operated by Conoco, where production has been progressively declining. The company said horizontal drilling offers the best opportunity to boost oil production without increasing water production or impairing ultimate recovery from the relatively thin, heavily faulted, Vlieland sandstone reservoir.
Conoco Netherlands Pres. John Lung said performance of the horizontal well will be monitored very closely. The company is investigating whether Kotter or nearby Logger field could benefit from further horizontal drilling.
VALHALL PROJECTS
Amoco's $10 million pilot waterflood will test the feasibility of a full scale flood in its Valhall field, currently producing 81,000 b/d of oil and 80 MMcfd of gas.
In addition, Amoco will add six well slots to the field's drilling and production platform to allow further drilling into the flank of the field structure.
Platform expansion will begin immediately, aiming for completion by mid-1990 at a cost of $7 million. Drilling through the new slots will start in second half 1990.
The waterflood pilot into the Valhall chalk started Jan. 11 at a rate of 3,200 b/d. The project will last 6-18 months, depending on results.
Valhall oil and gas moves by pipeline to the Ekofisk complex for transport through Norpipe's oil and gas system to Britain and West Germany.
Amoco, Amerada Hess Norge AS, and Enterprise Oil Norge Ltd. each own a 28.1 % interest in Valhall. Norwegian Oil Consortium AS & Co. owns the remaining 15.7%.
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