An Integrated Approach to the Characterization of Complex Fault Zones in Fractured Siliciclastic Reservoirs

The characterization of subsurface fractured reservoirs is generally a challenging task, which can be profitably faced by a multiscale approach. The analysis was provided for a horizontal well drilled in a gas bearing field with tight matrix porosity, belonging to pre-glacial Cambrian-Ordovician sediments, from fluvial to shallow marine. The adopted workflow integrating multiscale data proved effective in selecting proper stimulation intervals even when data log acquisition is limited. The analyzed example comes from an ultra-tight gas-bearing field, where a strong relationship between classified fractured intervals and well performance was observed. The thickness of the damage zone recognized in this well is about 115 meters and shows a relevant asymmetry in length and different values of fracture densities respect to the main fault plane position. The fault displacement profile, seen at sub-seismic scale and confirmed by borehole data integration, suggested that the main seismic lineament could be formed by four main fault segments; the borehole under analysis should be located at the tip of one of them, since the field stress interaction generated between neighbouring fault segments would enhance the thickness of the damage zone.