Asphaltene gradient modeling methods

Patent metadata

Field	Value
Publication number	US-10345481-B2
Application number	US-201414571660-A
Country	US
Kind code	B2
Filing date	Dec 16, 2014
Priority date	Dec 30, 2013
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

The present disclosure relates to methods and systems for developing an equation of state model for petroleum fluids. In one embodiment, formation fluid from a plurality of depths within a wellbore may be analyzed to determine a change in a gas oil ratio with respect to depth. The change in the gas oil ratio may be employed to determine a ratio of solubility and entropy terms to a gravity term. The resulting ratio can be used to develop the equation of state model.

First claim

What is claimed is:

1. A method comprising:
taking a plurality of samples of formation fluid, via a downhole tool, at a plurality of stations;
analyzing the formation fluid within a fluid analyzer of the downhole tool at the plurality of stations to determine a change in a gas oil ratio with respect to depth;
employing the change in the gas oil ratio with respect to depth to determine a ratio of a solubility term (SOL) and an entropy term (ENT) to a gravity term (GRAV), represented by a formula:

R

SOL
+
ENT

GRAV

=

SOL
GRAV

+

ENT
GRAV

;

developing an equation of state model based on the ratio; and
applying the developed equation of state model in a production or exploration of the formation fluid.

2. The method of claim 1 , wherein analyzing the formation fluid comprises measuring an absorption spectra of the formation fluid.

3. The method of claim 1 , wherein analyzing the formation fluid comprises determining a first gas oil ratio at a first depth within a wellbore and determining a second gas oil ratio at a second depth within the wellbore.

4. The method of claim 1 , wherein analyzing the formation fluid comprises determining concentrations of carbon components within the formation fluid.

5. The method of claim 1 , wherein employing the change comprises determining a first ratio of the solubility term to the gravity term and a second ratio of the entropy term to the gravity term.

6. The method of claim 1 , wherein the equation of state model represents a change in solute concentration with respect to depth.

7. The method of claim 1 , wherein the ratio is represented by an equation:

R

SOL
+
ENT

GRAV

=

-
A

⁢

∂

ϕ

C
⁢

⁢
1

∂
h

+

kTB

g
⁡

(

ρ
a

-

ρ
m

)

⁢

∂

ϕ

C
⁢

⁢
1

∂
h

where k represents the Boltzmann constant; ϕ cl represents a volume fraction of methane in the formation fluid; g represents the gravitational constant; T represents a temperature of the formation fluid; ρ a represents a partial density of asphaltenes in the formation fluid; ρ m represents density of the formation fluid; and A and B are constants determined based on the type of formation fluid.

8. The method of claim 1 , wherein applying the developed equation of state model in a production or exploration of the formation fluid comprises:
determining a rate at which samples are to be collected to avoid entering a two-phase state of the formation fluid based at least in part on the equation of state model; and
taking an additional sample at the determined rate via the downhole tool.

9. A method comprising:
analyzing formation fluid sampled from a plurality of depths within a wellbore to determine properties of the formation fluid;
employing the properties to determine a ratio of a solubility term (SOL) and an entropy (ENT) term to a gravity term (GRAV), represented by a formula:

R

SOL
+
ENT

GRAV

=

SOL
GRAV

+

ENT
GRAV

;

developing an equation of state model based on the ratio; and
applying the developed equation of state model in a production or exploration of the formation fluid.

10. The method of claim 9 , wherein employing the properties comprises determining a change in a volume fraction of methane with respect to depth.

11. The method of claim 9 , wherein analyzing the formation fluid comprises analyzing a first sample of the formation fluid taken at a first depth, analyzing a second sample of the formation fluid taken at a second depth, and determining a weight fraction of methane in the first sample and the second sample.

12. The method of claim 9 , wherein employing the properties comprises determining a change in a gas oil ratio with respect to depth.

13. The method of claim 9 , wherein the equation of state model represents a change in asphaltene concentration with respect to depth.

14. The method of claim 9 , wherein the gravity term comprises:

(

v
a

⁢

g
⁡

(

ρ
m

Assignees

• Schlumberger Technology Corp

Inventors

• Freed Denise E
• Mullins Oliver C
• Zuo Youxiang

Classifications

• G01N33/2823 Primary

  Raw oil, drilling fluid or polyphasic mixtures · CPC title

• E21B43/00

  Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells (applicable only to water E03B) · CPC title

• G01V11/00

  Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00 · CPC title

• G06F17/5009

  Physics · mapped topic

• G01V99/005 Primary

  Physics · mapped topic