6506/12-7

General

Well 6506/12-7 was drilled as an exploration well on the Northeast Smørbukk structure. The primary purpose was to find hydrocarbon accumulations of significant amounts in the Middle and Early Jurassic sandstone reservoirs. Secondary objectives were to check for hydrocarbon accumulations deeper than the structural closure of the main field. The well should also verify the geophysical and structural interpretation and improve the geological, paleontological and geochemical understanding of the area. Total depth was to be in rocks of Triassic age or 4000 m in order to satisfy the licence commitment.

Operations and results

Well 6506/12-7 was spudded with the semi-submersible installation Dyvi Delta on 7 April 1987 and drilled to TD at 4840 m in the Early Jurassic Tilje Formation. Drilling proceeded without significant problems. The well was drilled with spud mud down to 597 m, with gypsum/polymer mud from 597 m to 4427 m, and with a pre-hydrated Bentonite/Lignosulphonate mud system from 4427 m to TD. No shallow gas was encountered.

The first show appeared in the Lange Formation at 3791 - 3794 m. During coring there were oil shows in Garn and Ile Formations, while Ti1je only contained small traces of oil. Both cores and logs indicated that Garn and Ile Formations were hydrocarbon bearing down to ca 4538 m, while Ti1je Formation was indicated to be water bearing. The porosity was assumed to be between 8 and 12 %. Mobil wanted to test the Ti1je Formation to get a fluid sample to understand the logs better. This was a wise decision because the formation produced oil at very good rates. The Garn Formation on the other hand did not produce any formation fluid when tested. The oil/water contact in the Tilje Formation was not found because the logs did not give clear data.

Eight cores were cut in the well with a total recovery of 62.6 m core. One core was cut in the interval 4053 - 4058 m (Spekk Formation), two cores from 4