Fluid characterization and phase envelope prediction from downhole fluid sampling tool
Disclosed herein are methods and systems for fluid characterization of fluid samples from a downhole fluid sampling tool. A fluid characterization method may include obtaining a fluid sample of a reservoir fluid; analyzing the fluid sample to derive input parameters, wherein the input parameters comprise fluid properties obtained from measurement of the fluid sample; determining component mole fractions of the fluid sample using a mole fraction distribution function; and determining calculated fluid properties using equation of state flash calculating.
1. A fluid characterization method comprising:
obtaining a fluid sample of a reservoir fluid;
analyzing the fluid sample to derive input parameters, wherein the input parameters comprise fluid properties obtained from measurement of the fluid sample;
determining component mole fractions of the fluid sample using a mole fraction distribution function;
determining calculated fluid properties using equation of state flash calculating; and
determining updated values for molecular weight of C6+ components and density of C36+ components of the fluid sample if a difference in the calculated fluid properties are not within a tolerance error, and then repeating the steps of determining component mole fractions and determining calculated fluid properties.
2. The method of claim 1 , wherein obtaining the fluid sample comprising operating a downhole fluid sampling tool in a wellbore to obtain the fluid sample.
3. The method of claim 1 , wherein the fluid properties of the input parameters comprise a component concentration, a live oil density, and a gas-to-oil ratio.
4. The method of claim 3 , wherein the component concentration is a lumped component concentration.
5. The method of claim 1 , further comprising obtaining initial values for molecular weight of C6+ components and density of C36+ components of the fluid sample.
6. The method of claim 5 , wherein the initial values are used in the mole fraction distribution function to determine component mole fractions.
7. The method of claim 1 , wherein the component mole fractions determined using the mole fraction distribution function are delumped component mole fractions of a lumped component concentration obtained in the step of analyzing the fluid sample.
8. The method of claim 1 , wherein the mole fraction distribution function is represented by the following equation:
z
i
=
{
σ
e
-
τ
1
(
k
-
i
)
α
1
,
i
=
5
,
…
,
k
σ
e
-
τ
1
(
k
-
i
)
α
1
,
i
=
k
,
…
,
200
wherein i is single carbon number, z is mole fraction of component with single carbon number i, k is single carbon number with local maximum mole fraction, and G1, 02, T1, T2, and a are unknown parameters to be solved.
9. The method of claim 1 , wherein the step of determining component mole fractions of the fluid sample comprises solving the mole fraction distribution function for one or more unknown parameters.
10. The method of claim 9 , wherein the step of determining component mole fractions of the fluid sample further comprises determining the component mole fractions of the fluid sample based on the mole fraction distribution function.
11. The method of claim 1 , further comprising comparing the calculated fluid properties with the input parameters, the calculated fluid properties and input parameters comprising gas-to-ratio and dead oil density.
12. A system for characterizing a fluid sample, comprising:
a downhole fluid sampling tool operable to obtain fluid samples while disposed in a wellbore; and
a processing unit operable to:
analyze the fluid sample to derive input parameters, wherein the input parameters comprise fluid properties obtained from measurement of the fluid sample;
determine component mole fractions of the fluid sample using a mole fraction distribution function;
determine calculated fluid properties using equation of state flash calculating; and
determine updated values for molecular weight of C6+ components and density of C36+ components of the fluid sample if the difference in the calculated fluid propeliies are not within a tolerance error.
13. The system of claim 12 , wherein the downhole fluid sampling tool comprises an elongated tool body and a sensor.
14. The system of claim 12 , wherein the processing unit is distributed between a downhole processing unit and a processing unit disposed at a surface.
15. The system claim 12 , wherein the fluid properties of the input parameters comprise a component concentration, a live oil density, and a gas-to-oil ratio, and wherein the component concentration is a lumped component concentration.
16. The system of claim 12 , wherein the processing unit is further operable to obtain initial values for molecular weight of C6+ components and density of C36+ components of the fluid sample, wherein the initial values are used in the mole fraction distribution function to determine component mole fractions.
17. The system of claim 12 , wherein the mole fraction distribution function is represented by the following equation:
z
i
=
{
σ
e
-
τ
1
(
k
-
i
)
α
1
,
i
=
5
,
…
,
k
σ
e
-
τ
1
(
k
-
i
)
α
1
,
i
=
k
,
…
,
200
wherein i is single carbon number, z is mole fraction of component with single carbon number i, k is single carbon number with local maximum mole fraction, and 01, 02, 1\, 2, and a are unknown parameters to be solved.
18. The system of claim 12 , wherein the processing unit is further operable to compare the calculated fluid properties with the input parameters, the calculated fluid properties and input parameters comprising gas-to-ratio and dead oil density.