Reservoir navigation and evaluation using shallow to 'deep' resistivity devices has been routine practice in logging-while-drilling operations. In recent years azimuthal components have been added to significantly improve reservoir definition and to increase net sand drilled by reducing or avoiding reservoir exit. The established methods of geosteering with these tools allowed operators to successfully develop challenging reservoirs, but often the true structure of the geology, position of reservoir boundaries and channel shapes remained unknown, because of the limited depth of investigation of the tools.

Recent developments have allowed the desired expansion of knowledge while drilling in horizontal wells by enhancing the depth of detection of propagation resistivity tools beyond the range of conventional tools. This presentation will show how new inversion techniques applied to extra deep resistivity measurements can help to build a more accurate description of the geology of the reservoir and provide a link between real-time measurements in the well bore and seismic models. The new techniques were applied to the Peregrino Field, a complex reservoir located offshore Brazil, with geology comprised of high energy sand deposits and reserves held in a combination structural and stratigraphic trap.

The geologic information, i.e., bed boundaries and resistivities derived from the extra-deep resistivity data are on a similar scale to seismic data, and thus, they can be combined to better image the reservoir architecture. Hence, nowadays, it is possible to delineate sand thickness, reservoir continuity, sand pinch-outs, sub-seismic faults and interpret sand sheets, sand lobes and channelized sands, improving reservoir understanding and geo-steering decisions in complex heterogeneous reservoirs.