Description:

Poroviscoelastic Behavior of Sedimentary Rock

Abstract
The success of geo-energy applications such as petroleum recovery or geological storage of CO2 depends on properly addressing the physical coupling between the pore fluid diffusion and mechanical deformation of the subsurface rock. Constitutive models should include short-term hydromechanical interactions and long-term behavior, and should incorporate the principles behind the mathematical models for poroelastic and poroviscoelastic responses. In this work, the time-dependent response of fluid-filled sedimentary rock at room temperature and isotropic stress states is experimentally quantified. Drained, undrained, and unjacketed geomechanical tests are performed to measure the poroelastic parameters for Berea sandstone, Apulian limestone, and Opalinus clay (shale). A poroviscous model parameter, the bulk viscosity, is included in the constitutive relationships and is estimated under constant isotropic stress conditions from time-dependent deformation of rock in the drained and undrained regimes for timescales on the order of days. The bulk viscosity is found to be ~ 1015-1016 Pa•s and it decreases with an increase in pore pressure despite a corresponding decrease in the effective stress. In the long term, fluid pressure can asymptotically approach minimum principal stress, which in natural reservoirs may lead to liquefaction or rock embrittlement, causing slip instabilities and earthquakes and creating high-permeability channels in low-permeable rock.

Bio
Roman Makhnenko is an assistant professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign. Roman obtained his BS (2007) in mechanics and applied mathematics at Lomonosov Moscow State University (Russia) and his MS (2009) and PhD (2013) degrees in geological and civil engineering from the University of Minnesota – Twin Cities. From 2013 to 2016, Dr. Makhnenko worked as a postdoctoral researcher and lecturer at the Swiss Federal Institute of Technology in Lausanne (EPFL, Switzerland) on the project related to assessment of geological storage of CO2. Currently, Roman is developing a rock mechanics program at Illinois that includes modern high-pressure/high-temperature rock testing facilities and new graduate and undergraduate courses on the topic.