30/6-10 A

General

Well 30/6-10 A is a sidetrack to appraisal well 30/6-10 on the Alfa structure on the Oseberg Field in the North Sea. The primary well found oil and gas all through the Brent Group with a gas/oil contact at 2520 m, but no oil water contact. The main objective was to further define the gas/oil contact and to perform drill stem tests over the reservoir. The well was planned to penetrate the Brent reservoir approximately 300 m west of the original hole.

Operations and results

Appraisal well 30/6-10 A was sidetracked on 2 December 1982 through a milled window in the 13 3/8" casing at 1788 to 1803 m in the primary well bore. The sidetrack was drilled with the semi-submersible installation Treasure Scout to 2665 m (2577 m TVD) in the Early Jurassic Drake Formation. At 2657 m bad weather came up and caused some problems and down time. The pipe got stuck at TD but was worked free after 32.5 hrs using pipe lax, Imco spot and diesel. Otherwise the sidetrack was drilled with KCl/polymer mud from kick-off to TD.

First oil shows were seen in cuttings from limestone stringers in the Balder Formation at 2015 m. Oil shows on limestone cuttings continued down through the Shetland Group to top Heather Formation at 2448 m. The Brent Group interval from 2480 - 2608.5 m (2429 - 2531 m TVD) was found hydrocarbon bearing over the entire interval with the free gas/oil contact based on RFT pressure gradients at 2594 m (2520 m TVD) in the Ness Formation. No oil/water contact was found. The net pay in the Brent Group was calculated to be 58 m with average porosity of 24.4% and average water saturation of 27%. The net/gross ratio in 30/6-10 A is higher than in 30/6-10 due to a better sand development in the Ness Formation.

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