1. A method for real-time management of sampling of formation fluids from an earth formation surrounding a wellbore, the region of the formation immediately surrounding the wellbore being at least partially invaded by wellbore fluids, comprising: withdrawing fluids from the earth formation; sensing a physical or chemical property of the withdrawn fluids; outputting a signal corresponding to the sensed physical or chemical property; using the output signal to model properties of the withdrawn fluids; and using the modeled properties of the fluid sample for the real-time management of the sampling of the formation fluids.