Non symmetric Poison s ratio of unconventional shale
Publication Date: 2015-Nov-24
The IP.com Prior Art Database
Poisson s ratio is most used abused subject in petroleum industry It has been used to identify lithology predict pore pressure estimate strength in situ stresses and makes inferences for hydrocarbon saturations recovery factor oil gas in place extent of fractures etc However the interesting and frustrating thing is that the Poisson s ratio is not accurately known
Poisson’s ratio is most used (abused) subject in petroleum industry. It has been used to identify lithology, predict pore pressure, estimate strength; in-situ stresses and makes inferences for hydrocarbon saturations, recovery factor, oil-gas in place, extent of fractures etc. However, the interesting and frustrating thing is that the Poisson’s ratio is not accurately known.
The present work takes a look into it, defines what is Poisson’s ratio, how is it measured, why there is a discrepancies in its measurements, what are the typical measured values and finally, suggests precaution in using it for better understanding of geomechanics wherever Poison’s ratio is used.
Poisson’s ratio is an elastic parameter similar to Young’s modulus under Hook’s law. Ideally, in an environment of uniaxial loading in laboratory testing and assuming rock type to be isotropic, it is defined as the ratio of lateral strain to longitudinal strain and classified as static Poisson’s ratio. However, under the logging or seismic wave measurements, it can also be calculated by ratio of compressional or P-wave velocity (also expressed as an inverse or slowness, DTC) and shear or S wave velocity (also expressed as an inverse or slowness of DTS) and classified as dynamic Poisson’s ratio. In both the cases of static and dynamic Poisson’s ratio calculations, the uncertainty levels are much higher than that associated with Young’s modulus. In the static condition it is due to the measurements of a very low level of strains at tiny section of granular and often heterogeneous and anisotropic rocks and other uncontrollable experimental errors. In dynamic condition it is due to the complexities of DTS wave trains. The Poisson’s ratio is a calculation from ratio of DTS/DTC and a small error in DTS causes big error in Poisson’s ratio (Barree et al, 2009). Zhang & Bentley (2005) modeled and summarized that the Poisson’s ratio depends on the extent and type of cracks; flat or compliant cracks would have a pronounced effect on Poisson’s ratio. Addition...