Integrated of inclined pilot hole core with horizontal image logs to appraise an aeolian reservoir, Auk Field, central North Sea

An inclined appraisal well, 30/16-13, drilled in 1992-3 in the north of the Auk Rotliegend oil field, Central North Sea confirmed sufficient gross rock volume to justify a horizontal appraisal/development sidetrack 30/16-13S1 to assess the viability of a horizontal well development for Auk North. Close proximity of the two wells provided an opportunity for an integrated reservoir description. Core over the entire 125 m reservoir section of 30/16-13 was orientated, and tied to dipmeter data, later reprocessed into image logs. These data, plus conventional log responses, enabled a threefold subdivision of the aeolian facies including dune slipface sandstones. The sidetrack was horizontally geosteered through 625 m of reservoir, maintaining a stand-off above the field-wide free water level, and beneath the dipping Top Rotliegend structure unconformity. Careful selection of the optimal azimuth for the horizontal well track to pass up stratigraphic section maximized the number of slipface intervals encountered and preferential permeability pathways to the wellbore. Formation MicroImager (FMI) logs in the horizontal well, calibrated with core and logs from the inclined hole, enabled the characterization of the lithofacies, faults and fractures, including orientations. This detailed reservoir characterization was much greater than could be expected from either hole.