Modeling of Biot’s coefficient for a clay-bearing sandstone reservoir

The exploration of unconventional reservoirs has been vigorously developed with the application of hydraulic fracturing technology in horizontal wells. The success of fracturing depends on the accuracy of the effective stress, which could be considerably influenced by Biot’s coefficient. Biot’s coefficient is mainly influenced by the clay content, porosity, and fluid saturation. Previous studies regarding the calculation of Biot’s coefficient considered only the porosity or porosity structure and are irrational for sandstones with a high clay content and low permeability. A method was conducted to estimate Biot’s coefficient from wave velocities based on the Biot and Squirt (BISQ) poroelasticity theory. It is suggested that the clay content surrounding the skeleton, rather than that in the skeleton, affects the Biot’s coefficient significantly. A clay content coefficient and fluid saturation are considered in the BISQ model. Experiments with samples from four oil fields show that the Biot’s coefficient calculated using our method matches well with those obtained from in situ experiments. It is suggested that the new method for determining Biot’s coefficient is much more suitable for sandstones with low permeability, low porosity, and high clay content, compared to the methods put forward by other studies. In addition, it is proposed to calculate Biot’s coefficient by using seismic or acoustic logging data.