Joint inversion of borehole electromagnetic and sonic measurements
New-generation electromagnetic (EM) and sonic logging tools are capable of measuring multi-frequency multi-component data at multiple depths of investigation. This allows us to image the formation around the borehole by using an inversion method. A method is developed for directly obtaining porosity and fluid saturation distributions by simultaneously inverting borehole EM and sonic measurements. This joint inversion reduces the nonuniqueness of determining porosity and fluid saturation distributions, which can not be achieved with either sonic or EM inversion only. We show that the inversion algorithm can accurately obtain porosity and water saturation distributions around the borehole including the zones invaded by the mud filtrate, oil-water contacts, and as well as the dipping structures.