31/2-2

General

Well 31/2-2 was drilled some 4 km east of the discovery well 31/2-1 on seismic line 79-416 at SP 200. The concession requirement for the wells were complete penetration of the prospective Jurassic sequence and terminate in Triassic or older. The particular objectives of well 31/2-2 were: to evaluate lateral variation of reservoir parameters eastwards on the flank of the structure: to test the zone of oil shows seen in 31/2-1 in better reservoir conditions, to test the gas accumulation in a down-dip location: to evaluate the nature of the seismic flatspot, and to provide geological calibration of seismic reflectors above the reservoir for improved regional evaluation.

Operations and results

Well was spudded with the semi-submersible installation West Venture on 27 February 1980 and drilled to TD at 1857 m in the Middle Jurassic Krossfjord Formation. The 36" hole was drilled without incident to 433 m using seawater with viscous pills spotted on connections. From 422 m to 433 m hard drilling was experienced. This was interpreted as a boulder bed similar to that found at a comparable depth in the previous 31/2-1 well. Problems were encountered with the stability of the temporary guide base, and the well had to be abandoned. The rig was moved NE 25 m and re-spudded on 29 February. The well was drilled with seawater and hi-vis pills down to 800 m, and with gypsum/lignosulphonate mud from 800 m to TD.

Top reservoir (Sognefjord Formation) came in at 1544 m and was gas bearing down to a gas/oil contact at 1579 m, and oil-bearing from 1579 m down to an oil/water contact at 1591 m. Both contacts were clearly defined on logs, the gas/oil contact was confirmed by RFT pressure gradients, and moveable oil was confirmed by RFT sampling at 1587.5 m and 1590 m. Gas samples were obtained from 1548 m and 1571 m. Weak oil shows began at 1561 m in the gas zone, strong shows with stained and bleeding cores and a paraffinic smell were obs