Structural and hydraulic properties of a small fault zone in a layered reservoir

Abstract

This paper focuses on a small fault zone (too small to be detected by geophysical imaging) affecting a carbonate reservoir composed of porous and low-porous layers. In a gallery located at 250-m depth in the Underground Low Noise Laboratory, hydraulic properties of a 20-m thick section of the reservoir affected by the studied fault are characterized by structural measurements and by a hydraulic injection in boreholes. Main result is that the damage zone displays contrasted permeability values (up to two orders of magnitude) inherited from the differential alteration of the intact rock layers. To characterize the impact of these hydraulic properties variations on the flow of fluids, numerical simulations of supercritical CO2 injections were performed with the TOUGH2 code. It appears, the permeability variations inside the fault zone favor the appearance of high fluid overpressure located in the layers having the highest permeability and storativity.