6507/7-5

General

Well 6507/7-5 is located on the northern part of the Halten Terrace off shore Mid Norway and was drilled to appraise the northern extension of the 6507/7-2 Heidrun Discovery. The primary objective was Middle and Lower Jurassic sands in a downthrown fault block located NNW of the 6507/7-2 well. Prognosed top Jurassic was at 2308 m.

Secondary objective was the Båt Group at an expected depth of 2394 m. Based on site survey, shallow gas could appear at 512, 570, 618, 746, and 799 m. Prognosed TD was 2675 m.

Operations and results

Appraisal well 6507/7-5 was spudded with the semi-submersible installation Nortrym on 16 January 1986 and drilled to TD at 2660 in the Early Jurassic Tilje Formation. The 26" hole section was drilled without marine riser to 1040 m, first as a 17 1/2" pilot hole with MWD logging, then opening up to 26". No shallow gas was recorded. The MWD quality was good, so no electric logging was performed in this section. Since no riser was used, all returns were to seafloor down to 1040 m. No significant problems were encountered during operations. The well was drilled with seawater and pre-hydrated gel down to 1040 m and with KCl/polymer mud from 1040 m to TD.

No sandstone of importance was encountered above the Middle Jurassic. A hiatus from Late Cretaceous Turonian to Late Jurassic Oxfordian/Kimmeridgian was observed at 2310 m. Sandstones of the Fangst Group were encountered at 2353 to 2424 m. Analysis of cores and logs indicated good to excellent porosity and permeability in these sandstones, with the best reservoir properties towards the top, in the Garn Formation.

Poor oil shows were observed in sandstone lenses in core no 1 from the Shetland Group (2255.0 - 2282.5 m), which consisted mainly of claystones. Visible shows of uniform light brown oil were observed on cores from top of the Garn Formation down to 2400 m. Below this depth the shows were occasionally more patchy, un