Originally, shallow water flow was severely hindering further drilling in a North Sea exploration well. The water depth was 111.5m. The 20" casing was set at 590m; above a shallow gas zone. After mounting the Blow Out Preventer (BOP), drilling the 17 ½" section started and continued for a few 100 meters. The wellhead was routinely inspected using an ROV (Remotely Operated Vessel). After some time, a tiny flow was observed around the wellhead. The flow increased in strength and later a large wash out area was observed, and further drilling had to be terminated. Most likely, the water flow originated from a zone at a depth of 172m MSL.

To cure the shallow water flow it was decided to grout cement on the outside of the casings. Regular well cements was not desirable to use since these cements are somewhat retarded in itself by mineralogical composition. It was decided to use standard construction industry cement with a very short curing time. Before the grouting could start the BOP had to be removed. Because of the shallow gas zone underneath the 20" casing, two barriers had to be included in the well for well control. Two packers were used, one drillable and one retrievable. The BOP was removed and the grouting operation was performed successfully. No water flow or gas flow were observed while the cement was setting. After the flow was cured drilling resumed, first by drilling and retrieving the packers, then continuing to drill the 12 ¼" section.

The lessons learned from this particular well are to focus on using rapid hardening industry cement when cementing the conductor and a foamed cement system around the surface casing. Furthermore, a riserless mud return system has been used on later wells to be able to drill with weighted drilling fluid prior to setting the riser. These solutions to prevent shallow water flow are further discussed and experiences from later wells are presented in the following paper.

You can access this article if you purchase or spend a download.