Abstract: An improved technique more accurately determines pore pressure of sedimentary rock penetrated by a borehole from the earth's surface. Formation overburden is directly measured at one or more locations in the borehole, and a log of formation overburden is generated using the measured overburden pressures and conventional geophysical data. A linear relationship has been determined between the logarithm of effective stress for a specific mineral and the logarithm of solidity, which allows the maximum effective stress and the compaction exponent for that mineral to be determined. This linear relationship enables the effective stress and compaction exponent for rock comprising a combination of minerals to be precisely determined at multiple borehole intervals. The effective stress and overburden calculated according to the techniques to the present invention are particularly useful to geologist and well planners in the oil and gas industry.

Abstract: The porosity-effective stress relationship, which is a fuction of lithology, is used to calculate total overburden stress, vertical effective stress, horizontal effective stress and pore pressure using well log data. The log data can be either real time data derived from measurement-while-drilling equipment or open hole wireline logging equipment.