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Center for Nonlinear Studies |
The nonlinear elastic behavior of a rock sample is studied with a hybrid finite element model in both quasi-static and dynamic states. This model has application to a large number of materials. The model represents the elasticity of a consolidated material as an assembly of unit cells each of which has a simple elastic structure. In the two dimensional example developed a unit cell contains 4 elastic units, one of which is elastically stiff, two of which are elastically soft, and a single pore space. Fluid forces (pressure) are delivered to assembly by the pores. The primary parameters in this model are the elastic constants assigned to the elastically soft units, the mortar, Km. The assignment of Km is made by fitting the model to stress-strain data on rock sample. This data covers an extensive region of the pore pressure - stress space. Among the results obtained are (a) determination of the evolution of the elastic properties of the soft material with applied load with pore pressure and (b) calculation of modal frequencies as a function of elastic properties from the quasi-state (QS) study in pore pressure - stress space. Such an approach could be used to simulate other materials that may contain damage that is distributed or localized. (As the further perspectives to define the effect of (saturated and unsaturated) fluid on the nonlinear behavior of a rock, the numerical study on multiphase flow based on diverse physics will be discussed in the talk.)
Host: Chris Neale