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Stress, Fracturing, Flow and Transformation in Porous Media (co-organized)
Convener: Daniel Koehn  | Co-Conveners: Renaud Toussaint , Olivier Lacombe , Bjørnar Sandnes , Nicolas Beaudoin , Damien Delvaux 
 / Wed, 20 Apr, 08:30–12:00
 / Attendance Wed, 20 Apr, 17:30–19:00

The characterization and the understanding of flow of fluids within rocks and granular media has become an ever-increasing problem in Earth Sciences, Physics, and in many industrial applications, including CO2 sequestration, hydrocarbon migration, ore deposit development, and radioactive waste disposal. One of the main problems is the understanding of flows in transforming porous media (PM), where the rocks and fluid pathways evolve spatially and temporally, for example due to chemical interactions with the flow, to changing stress or due to compaction of the solid matrix. The dynamic feedbacks between flow, destruction of permeability due to compaction or local precipitation, and creation of permeability due to dissolution, chemical reaction or fracturing, makes understanding of such complex systems a challenge. Such feedbacks between flow of fluids and PM in which they are flowing, are important in both relatively slowly deforming PM such as in naturally evolving reservoirs, and in rapidly evolving PM such as fluid-filled fault zones or soils experiencing earthquakes, rapidly flowing grain-fluid mixtures in debris flows, or industrial processes in petroleum production such as pyrolysis or hydrofracking. We invite contributions that study the feedback mechanisms and their impact on the porous media through interdisciplinary approaches.

Stress states in the Earth's crust are of fundamental importance, they determine how rocks deform, how fracture and fold patterns develop and how faults behave. In general, the access to ancient states - paleo-stresses - is allowed by different methods that give mainly reduced stress tensors, focusing on the direction of paleo-stress axes and on the stress ratio, while only few provide differential stresses, and even fewer both quantities.

Recent advances have focused on (1) separation of heterogeneous fault-slip datasets and inversion of fault-slip data with low diversity, (2) paleostress inversion using mechanical modeling and tests on the validity of the so-called Wallace-Bott hypothesis, and (3) development of new techniques for inverting calcite-twin data and roughness of stylolites to derive differential/principal stress magnitudes.

The session aims at making the point on the advances in methods of paleo-stress analysis and at evaluating how paleo-stress reconstructions contribute to tectonic studies, both in terms of orientations and magnitudes. We also would like to discuss keys and pitfalls in paleostress reconstructions, to move forward the long-lived debate on stress vs strain vs kinematic interpretation of fault-slip data and other geological indicators, and to estimate to what extent paleostresses can be compared to modern stresses in terms of distribution in time and space and of geological and physical meanings. We would also like to tackle the need for new improved techniques and the way existing ones can be more thoughtfully combined and applied in order to better constrain tectonic evolution and crustal mechanics. Our ultimate wish would be to bring together researchers who work on these topics. We welcome a wide range of contributions: methodological contributions, contributions that use paleo-stress analyses to decipher the regional polyphase tectonic history and/or to improve our understanding of reactivation mechanisms and strain partitioning in the brittle regime, as well as modeling studies of stress states at the local or regional scale.

Solicited Speaker: Christopher W. MacMinn, University College Oxford