The interpretation of rock fracture requires an understanding of the physical controls on fracture growth. Several limiting factors are currently being studied, including fluids, bedding thickness, effective elastic properties, and the relationship between effective stress and fracture growth rates. For example, given the generally compressive state of stress in the subsurface, the formation of open fractures is only possible if fluid pressure is sufficient to offset the compression. However, the opening of a joint or dilation associated with shear failure reduces the fluid pressure within the fracture, limiting further fracture growth. In previous work we have modeled the complex coupling between the fluids and joint growth.
Current work is focused on similar models for shear failure.
Research on the mechanics of rock fracture is collaborative and includes joint experimental studies with the Engineering School. The distribution of openings, or aperture, within a fracture controls the pathways available for fluid flow. Although the importance of apertures in understanding flow in fractured rock is well established, little is currently known about the spatial distibution of apertures in natural fractures. Because even the slightest movements can dramatically change the aperture distribution within a fracture, direct measurement of aperture distributions in the field is exceedingly difficult. We are exploring methods to indirectly determine the aperture distribution of in situ fractures using geostatistical estimation.