ABSTRACT:

Three highly deviated wells were drilled into the Porto Corsini Terra Field, on-shore Ravenna, Italy. The purpose of this campaign was to develop a gas bearing pinched anticline reservoir. From previous wells a detailed geological and petrophysical study was prepared prior to drilling and resulted in the identification of reservoir layers that were targeted by the deviated wells. The first two wells missed the target due to directional problems and geological uncertainties. A geosteering approach was adopted for the third well that was drilled using oil based mud and real-time Vision Azimuthal Density Neutron (VADN*) density images. The image data were compressed downhole and transmitted to the rig acquisition computer where they were decompressed and analysed. The images allowed the precise placement of the borehole relative to the geological structure, showing the exact dip of sandy layers, while drilling. Variations in between the seismic interpreted structure and the real anticline crest position were inferred from the structural dip analysis made out of the images interpretation. A team of ENI and Schlumberger specialists used these in real time to make geosteering decisions and the required changes in well section still to be drilled. The well trajectory corrections allowed new layers to be reached not originally considered in the reserves. After drilling the density images were used for the final field structural interpretation, instead of a wireline dipmeter. The quality of LWD data allowed geosteering and proper formation evaluation, saving rig time, drilling and logging costs.

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