Abstract
We calculate the effective vertical and horizontal stresses in the Hejre field, North Sea with a Biot’s coefficient estimated from log data. We show that a drilling window (for a vertical well) calculated with these stresses is larger than if using a Biot’s coefficient of 1. We show a method to estimate Biot’s coefficient from logging data and find Biot’s coefficients between 0.8 and 1 for the Shetland chalk Group, 0.8 to 1 for the Tyne Group and 0.6 to 0.8 for the Heno sandstone formation. Biot’s coefficient is straight forward to estimate in formations with a stiff frame, whereas in formations such as shales caution has to be taken. We discuss the consequence of assuming "shale" to be a mineral rather than assuming shale to be composed of minerals and fluid.