| CPC G01N 21/3577 (2013.01) [E21B 49/10 (2013.01); G01N 21/85 (2013.01); G01N 33/2823 (2013.01)] | 13 Claims |
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1. A method for evaluating a formation fluid, the method comprising:
flowing formation fluid through a flowline in a downhole fluid sampling and evaluation measurement tool deployed in a wellbore;
making optical absorption measurements on the flowing formation fluid to generate a plurality of optical density spectra;
selecting at least one spectrum from the plurality of generated spectra using predetermined selection criteria, the selection criteria based on optical density values at one or more selected wavelengths in the generated spectra; and
estimating a fluid property of the formation fluid from the selected spectrum;
wherein the selected spectrum comprises a hydrocarbon spectrum and the selecting the at least one spectrum further comprises:
selecting spectra from the generated optical density spectra having an estimated water fraction less than a water fraction threshold to obtain first selected spectra;
selecting spectra from the first selected spectra having a measured optical density at a selected wavelength that is less than an estimated optical density at the selected wavelength obtained by interpolation to obtain second selected spectra, wherein the selected wavelength is between 1800 nm and 2000 nm; and
selecting the spectrum from the second selected spectra having a lowest optical density at the selected wavelength; and
wherein the spectra are selected from the first selected spectra when
[(Ω(t,λ2)]_MEAS<[(Ω(t,λ1,λ2,λ3)]_INT+ϵ_1
[(Ω(t,λ2)]_MEAS<[(Ω(t,λ1,λ2,λ3)]_INT−ϵ_2
wherein [(Ω(t,λ2)]_MEAS represents the measured optical density at a selected wavelength λ2, and [(Ω (t,λ1,λ2,λ3)]_INT represents the estimated optical density at the selected wavelength obtained by interpolation using λ1 and λ3, ϵ_2˜10ϵ_1 and 0.001<ϵ_1<0.01 in optical density units.
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