Basic measurements required for a proper staticdynamic rock properties determination were presented in a previous paper by the same presented in a previous paper by the same authors. Blot's theory and Walsh's microcrack analysis are combined to study static-dynamic property relations. In the absence of property relations. In the absence of microcracks, Blot's relations are used to compute static "uncracked" rock properties using density, porosity, and the travel times of longitudinal and porosity, and the travel times of longitudinal and shear wave velocities. When microcracks are present, relations derived from Walsh's microcrack present, relations derived from Walsh's microcrack analysis along with Blot's relations are used to obtain the static properties from dynamic measurements.
Times are gone when Hall's bulk compressibility correlation was more than enough to satisfy the need for rock behavior description in petroleum engineering. Designs now require accurate representation of rock behavior using characteristics such as Young's modulus (E), Poisson's ratio (v), and bulk compressibility Poisson's ratio (v), and bulk compressibility (cb). Application of rock mechanics ranges from hydraulic fracture design, sand production control, casing design, reservoir depletion studies, and subsidence.
Rock properties were originally described assuming the rock was linearly elastic; for example, the properties were independent of any external properties were independent of any external factors. Refined analysis demonstrated that rock properties are a function of many external factors properties are a function of many external factors such as temperature, stress, rate of stress change, and stress history.
Using the rock bulk density (b), the compressional (also called longitudinal or 'P') wave velocity (vL), and the shear (also called transversal of 'S') wave velocity (v S), rock properties can be calculated using elastic properties can be calculated using elastic wave-theory for a solid medium.
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Stress systems are applied to a core in a pressure cell. Static properties are derived from the instananeous slope of the measured stress-strain curves.
A literature survey indicates that numerous researchers report differences between static and dynamic properties. Differences up to a factor of ten are reported for bulk compressibilities. Often these researchers compared elastic properties of different cores, or of the same core properties of different cores, or of the same core but at different periods in the core's stress history.
