1/3-9 S

General

Well 1/3-9 S is located on the Tambar Field on the Cod Terrace in the North Sea. The objective was to appraise the possibility of commercial quantities of hydrocarbons in the Ula Formation sandstones of the JU8 prospect (the Ula Formation is sometimes referred to as the "Gyda Sandstone Member" in this part of the North Sea). The well was planned deviated to avoid shallow gas anomalies and to fully appraise the target sand.

Operations and results

Well 1/3-9 S was spudded with the semi-submersible installation Mærsk Jutlander on 8 May 1998 and drilled to 3100 m where hole problems led to plug-back and a sidetrack (1/3-9 S T2) with kick-off at 1836 m. Final TD of the well was set at 4516 m in the Late Jurassic Ula Formation. The well was drilled with seawater and hi-vis pills down to 1050 m, with Barasilc WBM from 1050 m to 3185 m, and with Enviromul OBM from 3185 m to TD. Total Non-Productive time for the well was 40%, most of which was due to contamination of the mud system, the side-track of the well and the TD logging performance. The 12 1/4" Section was notably different from plan, after an unexpected water kick was taken at 2535 m. This not only reduced the mud systems ability to accept contaminants, with a required MW increase up to 1.7sg, but also severely reduced the ROP, due to high overbalance drilling, later in the section. This also resulted in setting the 9 5/8" casing high, leaving reactive shales open whilst drilling the 8 1/2" section.

The Palaeocene Forties sands of the 1/3-6 and 1/3-7 wells were not encountered.The target Ula Formation sandstone was encountered at 4266.3 m, 33.7 m high to prognosis. It was oil-bearing with an estimated OWC at ca 4375 m. Oil sh