Stress-dependent Biot's constant through dynamic measurements on Ekofisk chalk

Biot's constant has a significant influence on in-situ stress calculation, which is an important input in many petroleum related rock mechanics applications. It is commonly assumed, or empirically derived. Stress-dependent nature of Biot's constant is given much less attention. An experimental program was undertaken to evaluate the dynamic as well as static Biot's constant in Ekofisk chalk reservoir samples, as a function of confining pressure and differential stress in atriaxial cell. Results show that the Biot's constant for the chalk is slightly stress-sensitive, with its values decreasing with increasing deviatoric stress. Poisson's ratio was found to be more sensitive than the Biot's constant, with its values increasing with increasing differential stress. The static values of the Biot's constant were found to be greater than those obtained dynamically. From the experimental data, linear models for the variation of the above three parameters were obtained with depletion. Using these models, production induced horizontal stress changes and K_o were obtained for various field depletions.