Geomechanical models have multiple uses in reservoir management and field development planning. In this case study from a producing deepwater fractured carbonate reservoir (water depth approx. 1500m) we use the same geomechanical model to understand (i) why hydraulic stimulation failed to open a hydraulic fracture due to high minimum principal stress, (ii) what the limits of mud weights for drilling horizontal wells into the pressure depleted reservoir are, and (iii) investigate what the effect of pressure depletion and associated stress changes are on fault permeability, thereby providing an explanation for an observed early water-breakthrough. Multiple data sources, including structural seismic interpretation and Amplitude-versus-Offset (AVO) inversion, well-log measurements and rock-mechanics laboratory tests were combined in building a mechanical property model, and the computed stress state was calibrated with wellbore observations of breakouts directions, induced fractures and leak-off tests.
Reservoir geomechanics has become an accepted technology for the petroleum industry during last decades. There are many benefits on improving geomechanical understanding, including:
A better characterization of reservoir volume deformation and impact on rock permeability (compaction and dilation);
Prediction of surface subsidence;
Reducing of risks of fault reactivation and out-of-zone hydraulic fracture propagation during waterflooding or other improved oil recovery process.
In Petrobras, Reservoir Geomechanics is a fundamental tool for development of fields with large number of faults/fractures, which is the case of several offshore sandstone reservoirs in Campos Basin, as well as some carbonates fields. Here we discuss the development of a comprehensive reservoir geomechanics study in an actual field of the Campos Basin. The presented technology has been developed as part of the Technology Cooperation Agreement on Reservoir Geomechanics between Petrobras and Schlumberger. A similar study has been carried out for a sandstone field and presented at a SPE Conference (Souza et al, 2012).