Antonio Claudio de França Correa

Integrated Modeling for 3D Geomechanics and Coupled Simulation of Fractured Carbonate Reservoir

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. Introduction 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). This multidisciplinary project has been developed with a team of geophysicists, geologists, reservoir and geomechanics engineers. An integrated approach involving seismic inversion, structural geology, rock mechanics and multiphase flow in porous media is used to build a 3D geomechanical model of an offshore naturally-fractured carbonate reservoir, Campos Basin, Eastern Brazilian Continental Margin. The first phase of the project involves auditing the data and building 1D Mechanical Earth Models (1D-MEM). These 1D-MEMs use data observations of stress directions and magnitudes (e.g. breakout directions, induced fractures, leak-off-tests, in combination with drilling experience and employed mudweights) for creating stress models along the well trajectory and are later used as calibration tool for the 3D geomechanical model. For the second phase a 3D Mechanical Earth Model (3D MEM) is built, by gridding the reservoir as well as over-, underand sideburdens, and populating the model with mechanical properties. Rock properties such as Young’s modulus, Poisson’s ratio, density, friction angle, unconfined compressive strength are distributed using a combination of well log observations, seismic AVO inversion models and rock mechanics test data (Herwanger and Koutsabeloulis, 2011). Pore pressure is also assigned based on seismic interval velocities calibrated with pressure observations (Dutta, 2002). The properties are developed based on