Formulations of the Coupled Processes of Two-phase Fluid Flow and Deformation in Geomaterials

The State of the Art and Future Perspectives

Abstract

 A set of constitutive equations for poroelastic materials saturated by multi-phase fluid is important for modeling subsurface geoengineering activities such as carbon dioxide sequestration into subsurface formations and land subsidence related to the production of water dissolved methane. Difficulties in such modeling mainly arise from the fact that the pressures of each phase fluid differ due to the difference of wettabilities of each fluid. Thus, the contributions of each fluid pressure to bulk strain and to the increment of porosity need to be rigorously expressed in the constitutive relations. In addition, the partial porosity of each fluid should be expressed separately. In this article, existing models are reviewed to discuss how these two difficulties have been treated; then, the state-of-the-art understanding of constitutive equations and remaining problems are presented.
 In the case of poroelasticity and the two-phase fluid condition, the Bishop's effective stress parameter is considered appropriate to express the contribution of each fluid pressure to bulk strain. For the expression of increment of partial porosity, thermodynamically consistent equations expressed by experimentally determinable parameters have been proposed recently, and the importance of introducing these equations is explained.