The effects of coupled chemical-mechanical processes on the evolution of permeability in a carbonate fracture

The quality and producibility of fractured reservoirs is controlled by complex interactions between mechanical and hydraulic properties of both fractures and matrix. Fracture permeability is known to be sensitive to changes in effective stresses and to small changes in the topology of the aperture, which may be modified by coupled mechanical-chemical processes. We examined the evolution of fracture permeability in two carbonate rocks to study the mechanisms that control the effective aperture and the formation of wormholes. Experiments were run on cylindrical cores of Indiana Limestone and Captain Massive Limestone containing a single longitudinal fracture at constant effective confining stress (3.5 MPa) and constant fluid pressure gradient (2.0 MPa per meter of sample). Preliminary results show that rock texture and insoluble content do not significantly affect fracture permeability. On the other hand decreases in confining and effective stresses result in significant decreases in the rates of permeability evolution. Furthermore, our results suggest that using the Damkohler number as a predictor of wormholing in carbonate fractures may not be straightforward, and that the initial roughness of the fracture may have longer term effects on aperture and permeability evolution.