Methods for identification and quantification of multicomponent-fluid and estimating fluid gas/ oil ratio from NMR logs
A method for determining a proportion of a hydrocarbon constituent in a mixture including at least one hydrocarbon, includes determining at least one nuclear magnetic resonance (NMR) property for at least one hydrocarbon constituent in the mixture; correlating an NMR response for the property for each hydrocarbon constituent in the mixture; and from the correlating, calculating the proportion of at least the constituent. A computer program product is also provided.
1. A method for determining a proportion of a hydrocarbon constituent in a mixture comprising at least one hydrocarbon, the method comprising:
determining at least one nuclear magnetic resonance (NMR) property for at least one hydrocarbon constituent in the mixture;
correlating an NMR response for the property for each hydrocarbon constituent in the mixture; and
from the correlating, calculating the proportion of at least the constituent, wherein calculating includes calculating a gas-to-oil ratio (GOR) for the mixture, wherein calculating the GOR includes:
determining a transverse relaxation time (T 2 ) spectrum for the mixture;
calculating a proton fraction ratio of gas molecules to liquid molecules from the T 2 spectrum; and
converting the proton fraction to the GOR for the mixture.
2. The method as in claim 1 , wherein the determining a proportion comprises performing the determining in at least one of downhole and in a laboratory.
3. The method as in claim 1 , wherein the property comprises at least one of a longitudinal relaxation time T 1 , a transverse relaxation time T 2 , and a diffusivity, D.
4. The method as in claim 1 , wherein the determining at least one NMR property comprises measuring the property for the constituent when the constituent is separate from the mixture.
5. The method as in claim 1 , wherein the determining comprises learning the property by at least one of deriving the property and referring to a source of information.
6. The method as in claim 1 , wherein the determining comprises predicting a log-mean value for the property of the at least one hydrocarbon.
7. The method as in claim 6 , further comprising applying a mixing rule to determine the log-mean value.
8. The method as in claim 1 , further comprising using the NMR response to determine viscosity of a constituent and a viscosity of live oil.
9. The method as in claim 1 , further comprising obtaining an NMR response for each property for the at least one constituent.
10. The method as in claim 1 , wherein the NMR response comprises a proton fraction ratio for each of the constituents.
11. The method as in claim 1 , wherein the correlating comprises producing a two-dimensional map of the property.
12. An instrument for determining downhole a proportion of a hydrocarbon constituent in a mixture comprising at least one hydrocarbon, the instrument comprising:
a nuclear magnetic resonance (NMR) apparatus adapted for performing NMR evaluations downhole, and a processor coupled to the apparatus, the processor comprising a link to a computer program product comprising machine readable instructions stored on machine readable media, the instructions for determining the proportion, by implementing a method comprising:
determining at least one nuclear magnetic resonance (NMR) property for at least one hydrocarbon constituent in the mixture;
correlating an NMR response for the property for each hydrocarbon constituent in the mixture; and
from the correlating, calculating the proportion of at least the constituent, wherein calculating includes calculating a gas-to-oil ratio (GOR) for the mixture, wherein calculating the GOR includes:
determining a transverse relaxation time (T 2 ) spectrum for the mixture;
calculating a proton fraction ratio of gas molecules to liquid molecules from the T 2 spectrum; and
converting the proton fraction to the GOR for the mixture.
13. A computer program product comprising machine readable instructions stored on machine readable media, the instructions for determining a proportion of a hydrocarbon constituent in a mixture comprising at least one hydrocarbon, by implementing a method comprising:
determining at least one nuclear magnetic resonance (NMR) property for at least one hydrocarbon constituent in the mixture;
correlating an NMR response for the property for each hydrocarbon constituent in the mixture; and
from the correlating, calculating the proportion of at least the constituent, wherein calculating includes calculating a gas-to-oil ratio (GOR) for the mixture, wherein calculating the GOR includes:
determining a transverse relaxation time (T 2 ) spectrum for the mixture;
calculating a proton fraction ratio of gas molecules to liquid molecules from the T 2 spectrum; and
converting the proton fraction to the GOR for the mixture.
14. The computer program product as in claim 13 , wherein the property comprises obtaining at least one of a longitudinal relaxation time T 1 spectrum, a transverse relaxation time T 2 spectrum, a diffusivity D spectrum.
15. The computer program product as in claim 13 , wherein the correlating comprises associating an intensity for the NMR response with a proton fraction for each constituent.
16. The computer program product as in claim 13 , wherein the calculating comprises converting a proton fraction ratio to a volume ratio.
17. The computer program product as in claim 13 , wherein the mixture comprises oil based mud filtrate (OBMF) and oil (O).
18. The computer program product as in claim 17 , wherein the correlating comprises formulating a predicted log-mean response transverse relaxation time, log T′ 2LM , for the mixture by solving a relationship comprising:
log T′ 2LM ≈f OBMF ·log T 2OBMF +(1 −f OBMF )·log T O ;
where
f OBMF represents a fraction for oil based mud filtrate (OBMF);
T 2OBMF represents a relaxation time for the OBMF in a separate state; and
T 2O represents a relaxation time for oil in a separate state.
19. The computer program product as in claim 18 , wherein the calculating comprises computing an OBMF fluid fraction, f OBMF , for the mixture by solving a relationship comprising:
f
OBMF
=
log
T
2
LM
′
T
2
O
/
log
T
2
OBMF
T
2
O
;
where
T′ 2LM represents the mean response transverse relaxation time;
f OBMF represents a fraction for oil based mud filtrate (OBMF);
T 2OBMF represents a relaxation time for the OBMF in a separate state; and
T 2O represents a relaxation time for oil in a separate state.
20. The computer program product as in claim 19 , wherein the calculating further comprises calculating an oil fraction from the OBMF fluid fraction.