Biosteering - A Biostratigraphic Application to Horizontal Drilling in the Eldfisk Field, Norwegian North Sea: ABSTRACT

Abstract

Biosteering is an application of biostratigraphy that monitors drilling through and along the reservoir interval (horizontal section). Traditionally, biostratigraphy has provided information regarding the age, zonation, and paleoenvironment at the time of sediment deposition. This data can be used to identify and correlate a particular stratigraphic level. Wellsite biostratigraphic information can rapidly identify stratigraphic horizons. This information can then assist in steering the well through the reservoir, and predict anticipated sections ahead of the drill-bit. The primary target reservoir in Eldfisk Field is the upper part of the Tor Formation (TA layer). Prior to development drilling, a detailed biostratigraphic framework was established which provided sufficient stratigraphic resolution to identify the reservoir layers. This framework utilized micropaleontological and nannoplankton index species, reworked elements, changes in relative abundance, and assemblage associations. The age of the Tor to Ekofisk Formations ranges from late Campanian to early Paleocene Danian. Nine combined zones are recognized in the Tor to Ekofisk Formations. A number of allochthonous units are suggested in the Ekofisk Formation which represent the facies of reworking. The lowermost layer is generally missing. A total of five horizontal wells have been successfully drilled in the Eldfisk Field through January 1995. Although the original objectivemore » was to continuously remain in the upper part of the Tor Formation, local pinchouts and thinning hamper this effort in some wells. However, this biosteering technique is critical to drilling horizontal wells, and yet represents a minute portion of the total expenditure.« less