3D spatial model of Biot's effective stress coefficient using well logs, laboratory experiments, and geostatistical method in the Gachsaran oil field, southwest of Iran

The knowledge of Biot's effective stress coefficient is of particular importance to simulate the effects of pore pressure variations during reservoir depletion and injection operations. Direct experimental evaluation of this parameter can be limited by the availability of good quality cores. The experiments can also be expensive and time-consuming particularly in low-permeability formations. This paper presents a method to evaluate a 3D spatial model of Biot's effective stress coefficient based on well logs and the empirical correlation between dynamic and static Young's modulus in the wells. To estimate static Young's modulus, uniaxial compression tests are performed on the cores obtained from Asmari reservoir in the Gachsaran oil field and the correlation between static and dynamic Young's moduli is established. The mineral volume fraction in the wells is obtained from mineralogy log and validated using thin-sections, XRD, XRF, and SEM studies. Bulk and solid bulk modulus are estimated and a 1D model was built for 47 wells in the field, which is validated using two samples in one of the wells. An empirical relation has been obtained to estimate Biot's effective stress from total porosity log. Then, a 3D spatial model of Biot's effective stress coefficient has been presented by Sequential Gaussian Simulation (SGS) in the Gachsaran oil field, southwest of Iran.