7120/8-1

General

Wildcat well 7120/8-1 is located in the Snøhvit Field area. It was designed to test possible hydrocarbon accumulations in a seismic closure (Alpha prime structure) located to the east of a major N-S running fault in the western part of the block. The primary target was sandstone of Middle Jurassic age.

Operations and results

Well 7120/8-1 was spudded with the semi-submersible installation Ross Rig on 28 June 1981 and drilled to TD in Late Triassic rocks ((Fruholmen Formation). The 17 1/2" hole was drilled to 1128 m when the lower marine riser accidentally unlatched and two days of rig time were lost curing this problem before drilling could continue. When plugging back the well, gas bubbles were observed in the riser. Four days of rig time were lost before this problem was cured. Apart from this no significant difficulties were encountered and the well was drilled according to schedule. The well was drilled with spud mud down to 358 m, with gel mud from 358 m to 750 m, and with gel/lignosulphonate mud from 750 m to TD.

Relatively dry gas was encountered at 2092 m in sandstone of the Middle to Early Jurassic Stø Formation. Log analysis, confirmed by RFT data, found a gas column down to a water contact at 2180 m. The reservoir sandstone showed good to excellent reservoir properties. Organic geochemical analyses showed TOC levels in the Early Cretaceous mudstones in the range ca 1.3 % to ca 5 %, generally increasing downwards to the base of the Cretaceous. Within the Late Jurassic Hekkingen Formation shales TOC increases from ca 3 % to at the top (1990 m) to more than 9 % at the base. In the Early Jurassic to Triassic below 2190 m occasional shales and thin coal beds have good potential for gas and oil, but are restricted in volume. The sediments are immature for petroleum generation down to ca 2000 m and marginally mature from this depth to TD. Kerogen is generally of Type II, with some addition of Type III in the lower