Patent ID: 8452538

Claim:
A method for evaluating petrophysical properties of a subterranean formation comprising the steps of: receiving a sonic log, the sonic log having a plurality of sonic measurements at a plurality of wellbore depths; receiving an electrical resistivity log, the electrical resistivity log having a formation resistivity measurement at each wellbore depth; receiving a gamma ray log, the gamma ray log having a gamma ray measurement at each wellbore depth; receiving a neutron porosity log, the neutron porosity log having a neutron porosity measurement (N PHI ) at each wellbore depth; receiving a density log, the density log having a bulk density measurement (ρ bulk-log ) at each wellbore depth; determining a set of volumes, wherein the set of volumes comprise a hydrate volume (V hydrate ), a first water volume (V H2O-1 ), a first shale volume (V shale-1 ), and a matrix volume (V matrix ), wherein the set of volumes is determined at each wellbore depth by simultaneously solving a set of linearized tool response equations; determining a second shale volume (V shale-2 ) at each wellbore depth based on the gamma ray measurements; determining a sonic porosity (DT PHI ) at each wellbore depth based on the sonic measurements; determining a calculated bulk density (ρ bulk-calc ) at each wellbore depth based on one of the first shale volume (V shale-1 ); the second shale volume (V shale-2 ); the formation resistivity measurements; and the formation resistivity measurements and one of the first shale volume (V shale-1 ) and the second shale volume (V shale-2 ); determining a density porosity (D PHI ) at each wellbore depth based on one of calculated bulk density (ρ bulk-calc ) and bulk density measurement (ρ bulk-log ); determining an apparent water resistivity (R w ) at each wellbore depth based on the formation resistivity (R t ) and the density porosity (D PHI ); determining one of a water saturation (S w ), a second water volume (V H2O-2) , and an Archie hydrate saturation (S h-Archie ) at each wellbore depth based on the density porosities (D PHI ) and a water resistivity (R w ), wherein the water resistivity (R w ) is obtained from analysis of a formation sample or a log analysis; receiving an NMR log, the NMR log having an NMR porosity measurement (NMR PHI ) at each wellbore depth; determining an NMR hydrate saturation (S h-NMR ) wherein the step of determining the NMR hydrate saturation (S h-NMR ) at each wellbore depth is determined according to the relationship S h ⁢ - ⁢ NMR = D PHI - [ NMR PHI ] D PHI + λ · [ NMR PHI ] , wherein λ = ρ fluid - ρ hydrate ρ matrix - ρ field , wherein ρ hydrate is a hydrate density at each wellbore depth, wherein ρ matrix is a matrix density, and wherein ρ fluid is a formation fluid density; and determining a sonic hydrate saturation (S h-DT ) at each wellbore depth based on the sonic porosity (DT PHI ) and the density porosity (D PHI ).