6407/7-1 S

General

Well 6407/7-1 S is located ca 30 km west of the Draugen field on the Njord A-structure in the southern part of the Halten Terrace. The apex of the A-structure is at about 2600 m MSL. The structure has a complex geology with dense faulting. The objective was to test for hydrocarbons in the structure, with the Middle and Early Jurassic as the primary and secondary targets. In addition, the well should obtain reservoir data from the Middle and Early Jurassic reservoir sandstones and establish a better stratigraphical, sedimentological, and structural knowledge of the area. The well should penetrate a deep reflector interpreted to be the "Top Middle Triassic Evaporite reflector". The prognosed total depth was 4025 m.

Operations and results

Wildcat well 6407/7 1 S was spudded with the semi-submersible installation Polar Pioneer 19 October 1985 and was drilled to TD at 3950 m in Triassic rocks. Ca 30 days (17%) of the rig time was down time. Major causes for this were sub sea problems with orienting the temporary guide base, bad weather, and fishing for various objects and stuck tools. In addition the section from ca 746 to 1177 m required wiper trips and a lot of reaming to clean the hole. This added several days to the drilling time. The well was vertical down to 1177 m, it built deviation angle up to maximum 9.8 deg at 1460 m, and had a deviation between 9.8 and 3.0 deg from there to TD. The well was drilled with spud mud down to 1172 m, with KCl/polymer mud from 1172 m to 2710 m, with gel/polymer mud from 2710 m to 3601 m, and with gel/lignosulphonate mud from 3610 m to TD.

The top of the reservoir came in at 2759 m, 70.5 m higher than prognosed. Oil was discovered in three separate reservoir units. The upper reservoir (2759 - 2783.5 m) consisted of sandstones belonging to the Fangst Group and Ror Formation. Relative pressure in this unit was 1.35 g/cc. The main reservoir (2839 -2988 m) consisted of sandstones be