New Drilling and Steering Technologies Overcome Chalk Group Challenges in Central North Sea

Finlaggan in central North Sea is a gas condensate field. The Field is a combined structural-stratigraphic closure with the western limit constrained by a stratigraphic pinch-out of the Lower Cretaceous Britannia Sandstone reservoir onto the easterly dipping slope of the Middle Jurassic Rattray High. The eastern limit of the field is defined by dip closure and the northern and southern limits are fault bounded. The observed compartmentalization is explained by the presence of seismic and sub-seismic faults along with inter-zone shales. The improved resolution from the reprocessing and seismic inversion allowed the interpretation of the top and base of the reservoir grids. Detailed mapping delineates the field structure as having three main segments which are separated by faults strands that tip out to the east and do not fully offset the reservoir. This compartmentalization is also evident in the production data from the original two wells where performance is not in accordance with the mapped volumes. Drilling to the sand reservoir requires to go through the Chalk group, which is composed of multiple hard layers known and presence of chert to cause damages to the tool string and steering difficulties. A water standoff needed to be maintained while navigating within the best properties of the reservoir in the horizontal section while accounting for several risks such as: Uncertainty in intra-reservoir zone thicknessesImpact of segment bounding fault throwPermeability variationsBaffling / sealing across fault compartments