# Poisson's Ratio

## Definition - What does Poisson's Ratio mean?

Poisson’s Ratio is the negative ratio between the lateral strain and the longitudinal strain (or the transverse to axial). It can also be interpreted as the change in a geometric shape that happens under uniaxial stress. This simply means that a material gets thinner from two directions when it is stretched in one direction and a uniform stress is applied. The longitudinal direction is across the breadth and the lateral strain is across the length. This situation is an elastic constant situation.

## Petropedia explains Poisson's Ratio

Poisson’s Ratio is named after Simeon Poisson. It is helpful in the oil and gas industry in the following ways:

- Prediction of Geo-mechanical behavior during well drilling.
- It is required for numerical modeling
- Well recovery processes

Strength parameters can be estimated in a way if we can correlate Poisson’s Ratio and elastic moduli. For example, in a wet rock at 10 MPa the Poisson’s Ratio varies inversely with the Youngs' modulus, which signifies that the higher the Poisson’s Ratio the lower the Youngs' modulus.

This Poisson’s Ratio can be determined by two methods:

- Uniaxial loading test
- By calculating the shear and compression velocities from sonic well logs and then calculating the poisons ratio using formula.