Factors determining Poisson's ratio

Abstract

ABSTRACT Poisson’s ratio is determined by two independent factors, i.e., the solid rock and dry or wet cracks. The former is influenced by the constituent mineral composition. The higher Poisson’s ratio of the rock solid is, the higher is Poisson’s ratio of the rock. Poisson’s ratio of the solid rock may be roughly estimated from clay contents for clastic rocks. Cracks defined as flat pores of low aspect ratios lower in the dry case or heighten, in the wet case, Poisson’s ratio of the rock. The magnitude of change depends on the volume concentration and aspect ratio of cracks. The higher the pore volume concentration and the lower the aspect ratio, the larger is the amount of change in Poisson’s ratio. Cracks are also chiefly responsible for the difference between static and dynamic elastic constants and the ratio of static versus dynamic Poisson ratios approaches one when cracks occupy a smaller amount of the total volume. INTRODUCTION Poisson’s ratio is an important mechanical property and can be used to predict the geomechanical behavior during the drilling of wells and the following recovery processes. Well instability, sand production and hydraulic fracturing are greatly affected by strength parameters, which may relate to its magnitude (Kumar, 1976). Reservoir volume changes due to injection or production and subsequent surface uplift or subsidence can be substantial (Stancliffe and Kooij, 2001). Numerical modelling requires this parameter as input to forecast their influence on wells and surface installations. It is therefore necessary to make reasonable predictions for the purpose of successful oilfield operations. Conventionally there are two methods to determine this parameter. The first is a uniaxial loading test to compute the ratio of radial strain and axial strain