Poisson's ratio is usually determined using well-logging, fracturing data and core samples. However, these methods provide us with a Poisson's ratio which is representative of only near-wellbore regions. In this paper, a technique is proposed by extending currently used pressure-transient testing concepts to include reservoir stresses. More specifically, the interference well test is generalized to find not only conventional flow parameters such as reservoir transmissivity and storage capacity, but also the average dynamic in-situ Poisson's ratio. This is accomplished by using the generalized diffusivity equation, which takes into account flow-induced stress changes.
Firstly, a generalized diffusivity equation is formulated by considering a deformable porous medium. The main goal of the generalized diffusivity equation is to extend current well testing methods to include both fluid flow and rock mechanics issues, and to present a way to determine the rock mechanics-related property, Poisson's ratio, from interference well testing. The line source solution to the diffusivity equation is used to modify the current interference well testing technique. Field data is utilized to show the main steps of the proposed transient well testing analysis technique.
An average in-situ value can be put in practice in different applications requiring accurate value of Poisson's ratio. Some examples of these include in-situ stress field determination, stress distribution and rock mass deformation, next generation of coupled fluid flow-geomechanical simulators, hydraulic fracturing design, wellbore stability analysis and sand production design. Using dynamic Poisson's ratio that could capture the flow-induced stress changes, we would be able to find the stress distribution due to production/injection within the reservoir more precisely. Accurate determination of stress distribution has a significant impact on wellbore stability issues in challenging wells, such as depleted and deep water reservoirs.