Bahman Bohloli - Norwegian Geotechnical Institute, Sognsveien ۷۲, Oslo, Norway
Lars Grande - Norwegian Geotechnical Institute, Sognsveien ۷۲, Oslo, Norway
Joonsang Park - Norwegian Geotechnical Institute, Sognsveien ۷۲, Oslo, Norway
Guillaume Sauvin - Norwegian Geotechnical Institute, Sognsveien ۷۲, Oslo, Norway

This paper presents results of rock physical-mechanical tests to assess geomechanical response of formations to the variation of pore pressure and stress. Further, it presents microseismic-geomechanics analyses of formations during fluid injection at two field cases to demonstrate significance of geomechanical studies for reservoir engineering operations. The rock physical tests include injection of a reactive fluid (CO2) into sandstone and shale samples under in-situ stress conditions in a triaxial cell while measuring resistivity, acoustic velocity and monitoring with X-ray CT scan. Acoustic emission tests were also carried out on sandstone and shale to explore potential of the tested rocks for generation of acoustic events and thus selection of monitoring method during injection or production. Field cases include microseismic monitoring from two projects where geomechanical performance of target formations were assessed during water and CO2 injection.Results of the triaxial CT scan tests showed the type of mechanisms for replacement of fluids in the cores under drainage and imbibition, and the impact of injected fluid on the velocity and resistivity. A small drop in axial velocity and a slight rise in resistivity was observed for the pre-fractured shale sample, while for the sandstone samples the ratios were higher. Acoustic emission studies in triaxial compression revealed the potential of sandstone samples in generating large quantity of acoustic emission events. Shale samples, on the other hand, displayed very few emissions. Results of the microseismic monitoring from the both field cases (In Salah and Svalbard) showed that accurate interpretation of injection datasets can determine the actual matrix and fracture injection and thus the fracture gradient of formation. Based on the laboratory and case studies, we propose and demonstrate the geomechanics and rock physics bases for the selection of reservoir monitoring methods and their importance for successful reservoir operations.

Rock physics, Geomechanical tests, Acoustic emission, Microseismic monitoring, Direct shear test