Biot Coefficient from well logs with lab calibration: a Brazilian pre-salt case study

ABSTRACT: The Biot's coefficient influences the stress distribution in space and time along the production history of hydrocarbon reservoirs. We applied the classical method for measuring Biot's coefficient in laboratory, which involves the measurement of rock volumetric compressibility and solid matrix volumetric compressibility with stress-strain experiments, on several samples from a Brazilian pre-salt oil field. These experiments are valuable but expensive. We also measured the compressional and shear-wave velocities of the same samples under dry and saturated conditions. With the velocities and rock density we can estimate the rock "dynamic" volumetric compressibility. We observed that the dynamic compressibility is related with the direct measurement. It is possible to estimate the Biot coefficient from well logs, which is less expensive than real measurements and result in an almost continuous curve along the well path. This requires sonic and density logs, as well as calibrated compositional logs with the solid matrix mineral composition. We made estimates of Biot coefficients from wells of the oil field and observed a good agreement with the real measurements in core samples, if we consider the uncertainties in experiment and calculations.