ABSTRACT:

Up to 2015, about 5 million metric tons of CO2 have been injected into the Lower Tuscaloosa sandstone at Cranfield field, Mississippi. Pressure monitoring at one injection well shows that the bottom-hole pressure did not increase with the imposed injection rates as expected. Above the injection zone, pressure gauges measured a change of pore pressure of approximately 0.1 MPa in the absence of leaks. These two unexpected responses during the injection suggest potential geomechanical events induced by CO2 injection. We conducted triaxial tests in Tuscaloosa sandstone rock samples with CO2-acidified brine in order to understand chemo-poromechanical processes that may have contributed to these unexpected responses. Experimental results include measurements of permeability, relative permeabilities, quasi-static and dynamic elastic moduli, Biot coefficient, and chemically-induced creep at in-situ reservoir stresses. Results show a marked anisotropy in transport properties originated from features up to the scale of a few millimeters. Rock samples exhibited significant plastic strains upon loading and yield stress consistent with current burial depth. Creep rate increases more than one order of magnitude after CO2 injection. Chemically-induced creep deformation seems insufficient to cause significant reservoir compaction but may have contributed to horizontal stress relaxation.

1. INTRODUCTION
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