Methods for characterizing asphaltene instability in reservoir fluids

Patent metadata

Field	Value
Publication number	US-9255475-B2
Application number	US-201113696780-A
Country	US
Kind code	B2
Filing date	Apr 20, 2011
Priority date	May 7, 2010
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

A methodology for reservoir understanding that performs investigation of asphaltene instability as a function of location in a reservoir of interest. In the preferred embodiment, results derived as part of the investigation of asphaltene instability are used as a workflow decision point for selectively performing additional analysis of reservoir fluids. The additional analysis of reservoir fluids can verify the presence of asphaltene flocculation onset conditions and/or determine the presence and location of phase-separated bitumen in the reservoir of interest.

First claim

What is claimed is:

1. A method for identifying instability of asphaltene in petroleum fluid within a reservoir traversed by at least one wellbore, the method comprising:
(a) at a plurality of measurement stations within the at least one wellbore, acquiring at least one fluid sample at the respective measurement station and performing downhole fluid analysis of the fluid sample to derive properties of the petroleum fluid of the reservoir as a function of location in the reservoir, wherein the properties of the petroleum fluid derived in (a) include concentration of an asphaltene fraction, the petroleum fluid comprises a solute part and a solvent part, and the solvent part comprises a bulk reservoir fluid;
(b) deriving values of a first parameter characterizing solubility of the petroleum fluid for different locations or pressures in the reservoir, wherein the values of the first parameter characterize solubility of the bulk reservoir fluid as a function of pressure or depth in the reservoir;
(c) generating values of a second parameter characterizing fluid properties of the petroleum fluid for different locations or pressures in the reservoir, wherein the values of the second parameter are based upon concentration of the asphaltene fraction derived in (a), and wherein the values of the second parameter characterize solubility of the bulk reservoir fluid at the onset of flocculation of the asphaltene fraction as a function of pressure or depth in the reservoir; and
(d) evaluating the values of the first parameter derived in (b) and the values of the second parameter generated in (c) in order to identify a location where onset of flocculation of the asphaltene fraction is likely, wherein the evaluating of (d) equates the location where the onset of flocculation of the asphaltene fraction is likely to the location at a pressure or the depth where the value of the first parameter matches the value of the second parameter.

2. The method according to claim 1 , wherein the first parameter characterizes solubility of the bulk reservoir fluid.

3. The method according to claim 2 , wherein the value of the first parameter for a given location is calculated from the density of the bulk reservoir fluid at the given location.

4. The method according to claim 3 , wherein:
the value of the first parameter for the given location is derived from an empirical correlation to density of the bulk reservoir fluid at the given location of a form
δ m =17.347ρ m +2.904,

where
ρ m is the density of the bulk reservoir fluid at the given location in g/cc, and
δ m is the first parameter at the given location in MPa 0.5 .

5. The method according to claim 3 , wherein the density of the bulk reservoir fluid at the given location is measured by one of downhole fluid analysis and/or laboratory analysis of the reservoir fluids collected from the given location.

6. The method according to claim 3 , wherein the density of the bulk reservoir fluid at the given location is derived from output of an EOS model.

7. The method according to claim 1 , wherein the second parameter characterizes solubility of the bulk reservoir fluid at the onset of flocculation of the asphaltene fraction.

8. The method according to claim 7 , wherein the value of the second parameter for a given location is based upon a number of predetermined properties of the reservoir fluid at the given location, the predetermined properties including the volume fraction of the asphaltene fraction, the partial molar volume of the asphaltene fraction, and the molar volume of the bulk reservoir fluid.

9. The method according to claim 8 , wherein:
the value of the second parameter for the given location is derived from the relation

δ

m
,
onset

=

δ
a

-

{

-

RT

v
a

⁡

[

ln
⁢

⁢

ϕ
a

+
1
-

(

v
a

v
m

)

]

}

1
/
2

,

where
φ a is the volume fraction of the asphaltene fraction at the given location,
υ a is the partial molar volume for the asphaltene fraction at the given location,
υ m is the molar volume for the bulk reservoir fluid at the given location,
δ a is the solubility parameter for the asphaltene fraction at the given location,
R is the universal gas constant, and
T is the absolute temperature of the reservoir fluid.

10. The method according to claim 9 , wherein δ a at the given location is derived from a temperature gradient relative to a reference measurement station.

11. The method according to claim 9 , wherein υ a is constant across reservoir locations and is given by a spherical model based on molecular diameter for the asphaltene fraction.

12. The method according to claim 9 , wherein ν m for the given location is provided by the solution of an EOS model.

13. The method according to claim 9 , wherein φ a for the given location is calculated from an empirical relation relating φ a to color measured by downhole fluid analysis.

14. The method according to claim 13 , wherein the empirical relation relating φ a to color measured by downhole fluid analysis is tuned such that φ a matches a solution at a particular location corresponding to estimated reservoir pressure for asphaltene precipitation onset as measured by downhole fluid analysis.

15. The method according to claim 14 , wherein:
the solution is given by

Assignees

• Zuo Youxiang
• Mullins Oliver C
• Dong Chengil
• Freed Denise
• Pomerantz Andrew
• Lehne Eric
• Zhang Dingan
• Schlumberger Technology Corp

Inventors

• Zuo Youxiang
• Mullins Oliver C
• Dong Chengil
• Freed Denise
• Pomerantz Andrew
• Lehne Eric
• Zhang Dingan

Classifications

• E21B49/0875

  determining specific fluid parameters · CPC title

• E21B49/10 Primary

  using side-wall fluid samplers or testers · CPC title

• E21B2049/085

  Fixed Constructions · mapped topic