Forward and Inverse Modeling of Rock Instabilities in the Presence of Fluids

Geological structures are formed by rock deformation. This deformation is often accompanied and influenced by fluid flow, e.g., subsurface migration of hydrocarbons, contaminants and ore-rich fluids, as well as metamorphic and magmatic fluids. Traditional ly these processes have been studied separately. Hydrogeology and metamorphic petrology presume a lithostatic fluid pressure distribution within the crust, an assumption that implies that the Earth's crust is fluidized and has no strength. In the same dep th range, structural geologists recognize complex stress patterns and the development of structural instabilities, but assume hydrostatic fluid pressure distribution. Most of the complexity in studying rock deformation comes from rheology. An even great er challenge arises if a combination of several rheological types, such as brittle and ductile, is essential to describe a single process. The presence of fluids may result in dynamic switching between the rheological types. Heterogeneity and complex rhe ologies give rise to unexpected instabilities: rapidly developing, deformation paths triggered by small and normally negligible irregularities. There are several classical theories of instabilities developed for various rheologies. More recently, generali zation has been made for combinations of rheologies. Similar results have yet to be developed if fluids are involved and actively affect rheology. Finally, there is a feedback between deformational instabilities and fluid flow, which is driven by fluid p ressure gradients and controlled by permeability. The deformational instabilities cause sudden changes in both – permeability and fluid pressure distributions. New dynamic paths of the fluid flow are created as a response to the rock matrix deformation; t heir prediction requires a combined treatment of fluid flow and rock deformation. Computer modeling will be employed to study systematically the complex interplay between the above mentioned processes.