2/1-8

General

Well 2/1-8 was drilled on the Cod Terrace on the margin between the southern Vestland Arch and the Central Trough in the North Sea. The objective was to evaluate the Late Jurassic Gyda member reservoir sandstone (the "2/1-3 Sand") in the south-eastern part of the field.

Operations and results

Appraisal well 2/1-8 was spudded with the jack-up installation Neddrill Trigon on 28 July 1985 and drilled to TD at 4151 m (4159 m Logger's Depth) in the Triassic Skagerrak Formation. The well was drilled with spud mud down to 635 m, and with KCl/polymer mud from 635 m to 3474 m. At this depth the drill string got stuck while pulling out of the hole. It was freed after pumping pipelax into the hole. Following the pipelax pill and down to 3888 m the mud contained 1.0 - 2.5% oil. Drilling commenced with an oil-free KCl/polymer mud from 3888 m to TD. Below 2000 m logger's depth = driller's depth + 8 m. Above this depth there is no discrepancy. In the following all quoted depths are logger's depths.

A 40 m thick Gyda member sandstone was penetrated at a depth of 3899.5 m. Cores from the reservoir proved a coarsening up sequence of very fine to medium grained sandstone. The reservoir was oil bearing throughout. Oil stain and gas bleed were observed in cores of very fine sandstones and siltstones from the underlying Farsund and Haugesund Formations. The Ula Formation at 4037 m was 26 m thick and water bearing. Traces of hydrocarbons were recorded from 3818 - 3821 m in the Early Cretaceous Åsgard Formation. These possibly result from leakage, up a minor fault, from Late Jurassic rocks. There were no significant hydrocarbon shows in any other section of the well.

Three cores w