Abstract: A logging tool capable of making different types of measurements is provided, and a plurality of measurements on a formation are obtained. Certain mineral properties of the formation are assumed and a mixed properties theorem for the formation is invoked. Upper and lower velocity limits for sonic waves traveling through the formation are determined using the above information. Biot's constant is also computed using the above information. LWD data on the formation is obtained and an effective stress is determined. A total stress is determined and, from that and the other information, a pore pressure is determined.