Patent ID: 7176682
Filing Date: 2007-02-13
Classification: G01N,G01R,G01V

Abstract:
1. A method for estimating the type of hydrocarbons in a formation surrounding a borehole drilled with an oil-based mud, comprising: (a) providing a mathematical model for a fluid mixture of native hydrocarbons and oil-based mud in the formation; (b) providing NMR signals from one or more locations in the formation; and (c) estimating the type of native hydrocarbons in said one or more locations in the formation based on the provided mathematical model and the provided NMR signals; wherein the mathematical model is based on T2 relaxation and effective diffusion D, and the step of estimating comprises generating, based on the NMR signals, an apparent T2 decay time and an effective diffusion constant to construct a T2-diffusion constant crossplot; and comparing the mathematical model with the constructed crossplot.