The deep electromagnetic logging-while-drilling technology has continuously progressed during the last decade thanks to the added value it brings in helping to take real-time critical decisions.
In 2008, Eni applied the first generation of directional resistivity tools to maximize reservoir exposure, map the near-wellbore reservoir structure and avoid drilling into unstable formations, thereby ensuring wellbore stability. The outstanding results and gained experience gave Eni the confidence to take on more difficult challenges with the latest generation of these electromagnetic tools. The reservoir while-drilling mapping service has been tested more recently in Italy for three case histories to resolve and map multiple subsurface beds and fluid contacts, working in complex geological settings and more than 30 m from the wellbore. The interpretation has been enhanced with the real-time automated stochastic inversion using a cloud computing system approach. The unique features and deep measurements have enabled advances in geostopping and mapping of the reservoir structure and fluid contacts, in both different lithology and well profiles.
The first field test was performed within an underground gas storage project to map the structure of the thick reservoir section (>40 m) and the gas/water contact (GWC). Due to the good reservoir conditions and suitable resistivity contrast, an environment with multiple resistivity layers and lateral thickness variability was successfully investigated, minimizing wellbore dogleg severity. The second application was dedicated to map a thin-bed gas-bearing reservoir drilled with relatively low inclination (550). The objective was to evaluate the mapping ability of possible faults and potential bypassed reserves. The final test was in landing a well above a carbonate oil-bearing reservoir. With the benefit of the deep detection range, the application enabled drilling to be stopped prior to the entry into the reservoir zone, where total mud circulation losses were expected. In addition, unique structural information was provided to update the reservoir structural model, maximizing detection of the contacts and optimizing the completion and horizontal borehole section drilling.
Ultra deep azimuthal electromagnetic technology has evolved toward new solutions to mitigate drilling risk, and the technology represents a step-change in reservoir characterization and proactive geosteering. Our examination of three cases proved the versatility and tested the limits of the technology in different geological settings, reservoir types and well trajectories.