15/12-10 S

General

The well is positioned on the western flank of the northern segment of the Varg Field, on a horst mapped at Top Sleipner level. Thick Intra Heather sandstones present in the southern and eastern segments of Varg were expected also in the northern segment. Over the horst, Draupne/Heather shales were assumed eroded so that Intra Heather sandstones were present between BCU and Top Sleipner. These two horizons could be mapped seismically, but the extent of sandstones could not be mapped. The well was drilled to determine the extent and thickness of the Intra Heather sandstone reservoir over the northern segment of Varg and, if oil was encountered, to determine fluid characteristics and depth to the OWC.

Operations and results

Appraisal well 15/12-10 S was drilled from the S4 slot on the Varg subsea template using the semi-submersible installation Deepsea Bergen. It was spudded on 2 October 1996 and drilled deviated to TD at 3550 m in the Triassic Skagerrak Formation. The deviation started at 250 m, building angle to 35 deg at 960 m and was then kept between 28 deg and 38 deg down to TD. No significant problems were encountered in the operations. The well was drilled with seawater down to 207 m, with seawater/PAC/CMC from 207 m to 1396 m, and with Ancovert oil based mud from 1396 m to TD. No shallow gas was predicted and no shallow gas was found in the well.

Down to Top Shetland, the well was within prognosis, and penetrated the expected lithology. Below this level, the Shetland limestone was thicker than expected, and Top Cromer Knoll and Base Cretaceous was penetrated considerably deeper than prognosed (55 and 58 metres, respectively). Below BCU, the well encountered Late Jurassic shales and siltstones, and only 13 metres T