A review of the models to obtain the internal friction angle and cohesion during plastic behavior for weakly consolidated reservoirs
Juan Carlos Valenzuela Meza1; Edson Felipe Araujo Guerrero1; Alejandra Arbelaez Londoño1; Guillermo Alzate Espinosa1; Abel Naranjo Agudelo1
1 Universidad Nacional de Colombia
Resumo
Currently, the majority of oil reserves worldwide are stored in heavy oil reservoirs. These are characterized by having low levels of consolidation, and deforming permanently under the influence of mechanical stresses. During plastic strain, reservoir can exhibit irreversible changes in several properties, which may generate events as sand production, well instability, subsidence, and changes in petrophysical properties such as porosity and permeability or mechanical properties such as elastic modules, tension strength, uniaxial compressive strength (UCS), among others. Then, in order to make assertive predictions and prevent events like those mentioned above, it is appropriated to study the effect of the change in the rock properties during plastic strain using coupled reservoir simulation. Consequently, this paper presents a review of the basic existing models in the literature, which predict the behavior of the angle of internal friction and cohesion of the rock under a plastic strain regime. It has been found that most models propose mathematical expressions to describe the behavior of the considered properties in function of the level of plastic strain. Each model incorporates a different parameter to quantify the level of plastic strain, however these parameters are not correlated with variables of direct measurement and are only applied to certain tests, and as a result a comparative analysis is performed between the found parameters and their behavior with the total rock strain. For this analysis, a simulation of elastic and plastic regimes of rock behavior is conducted using a progressive algorithm under the basic assumptions of the plasticity theory and the failure criteria of Mohr-Coulomb with yield surface of bilinear behavior. This algorithm solves stresses and strains for each increment of axial displacement for a Uniaxial Compressive Strength Test. The performed simulations show that the accumulator parameters of plastic strain exhibit a similar behavior respect to the total strain experienced by
Palavras-chave: Plastic regime; internal friction angle; cohesion; hardening; softening