Method and apparatus utilizing NMR measurements to gather information on a property of the earth formation surrounding a wellbore

摘要

A method is provided for gathering information on the pore pressure in an earth formation surrounding a wellbore. The method includes the initial steps of selecting at least one suitable property (e.g., porosity, drilling fluid composition, etc.) of the drilling environment (which is defined by the wellbore and the surrounding formation) and at least one NMR parameter (e.g., T2 distribution) in an NMR measurement response. The method selects a suitable property for which values over a plurality of wellbore depths can be correlated with the characteristics or behavior of the pore pressure in the earth formation. The method further includes conducting an NMR measurement at a plurality of wellbore depths, thereby generating an NMR response from the drilling environment. The measured values of the NMR parameter in the NMR response are then correlated with values of the suitable property. Next, the values of the suitable property are compared over the plurality of depths, and then the correspondence between the property values is correlated with the behavior of the pore pressure over the plurality of depths. In this way, the characteristics of the pore pressure in the earth formation over the plurality of wellbore depths are determined.