In-Situ Poisson's Ratio Determination under Different Deformational Conditions

Abstract

Abstract Knowledge of in-situ mechanical rock properties is of critical importance for well design and prediction of formation fracturing, including human-induced seismicity. Shahri and Miska (2013) proposed an innovative technique for the estimation of in situ Poisson's ratio. Under the assumption of plane strain, the interference well test was generalized to also find the average in-situ Poisson's ratio. An extension and comparison of this model to several different boundary conditions such as generalized plane stress and uniaxial strain is proposed. Firstly, the three-dimensional theory of consolidation is applied to formulate the generalized diffusivity equation for a deformable porous medium. This provides us with the coupling between deformation and flow response needed to determine Poisson's ratio from an interference well test. Generalized plane stress, simplified generalized plane stress, uniaxial strain, generalized uniaxial strain, and plane strain with constant horizontal stress assumptions are then applied, resulting in several different values of the estimated Poisson's ratio. The same field data originally analyzed are used to show the main steps of the proposed technique, and to compare its results with that derived in the earlier work. Estimation of average in situ Poisson's ratio, using different assumptions, provides a means to select the most appropriate model for accurate reservoir deformational behavior. In-situ Poisson's ratio and specific storage capacity, depending on flow-induced stress changes, can also enhance the accuracy of the estimated stress distribution resulting from production/injection. This leads to optimization of well design and formation fracturing.