30/7-3

General

Well 30/7-3 was drilled in the Fensal sub-basin south-southeast of the Hild Discovery and north of the Odin Discovery.

The main objective of the well was to test a mapped seismic anomaly below the "Ml" marker, prognosed to be a possible porous carbonate development at Cenomanian level. The location of the well gave a test of the anomaly on the western edge, according to the seismic mapping. Secondary objectives were possible Early Cretaceous sand/limestone pinch-outs and Late Jurassic sands.

Operations and results

The well 30/7-3 was spudded with the semi-submersible installation Polyglomar Driller on 6 August 1976 and drilled to TD at 4044 m in the Early Cretaceous (Albian - Aptian) Cromer Knoll Group. When drilling the 12" hole at 3001 m, a leak was discovered in the wellhead. A groove was cut in the sealing area between the wellhead and the collet connector. A wellhead extension was run in the damaged wellhead with four o-rings as seal towards the original wellhead. The drilling was continued and 9 5/8"casing was set at 3782 m. While drilling 8-3/8" hole at 4044 m circulation was lost. When the mud weight was reduced in an attempt to re-establish circulation the well started to flow. A barite plug was set at bottom, and this finally stabilized the well. The well was drilled with freshwater gel to 700 m and with lignosulphonate mud from 700 m to TD.

A comparison of the results from the seismic velocity survey and the seismic interpretations identify the interval between 3795 m and 3918 m as the target seismic anomaly. In this interval a sequence of limestone, marlstone and shale was found. The limestone is composed of mainly calcite with recognisable coccoliths. In the lower part minor terrigenous components of quartz sand and silt, and mica flakes were encountered. In places the limestone became very argillaceous grading to marlstone and shale. No visible porosity or any hydrocarbon s