System and method for predicting viscosity of heavy oil formations based on nuclear magnetic resonance (NMR) measurements

Patent metadata

Field	Value
Publication number	US-10585083-B2
Application number	US-201615180246-A
Country	US
Kind code	B2
Filing date	Jun 13, 2016
Priority date	Jun 13, 2016
Publication date	Mar 10, 2020
Grant date	Mar 10, 2020

Abstract

This disclosure describes systems and methods to predict viscosity of heavy oil in a geological formation, even when the geological formation also contains water such as clay-bound water, using a downhole nuclear magnetic resonance (NMR) tool. The downhole NMR tools may obtain responses include distributions of a first relaxation time T1, a second relaxation time T2, or diffusion, or a combination of these. The responses of the NMR measurements that are due to water are separated from the responses of the NMR measurements that are due to heavy oil. The responses of the NMR measurements due to heavy oil are then related to likely values of viscosity of the heavy oil based on empirical or simulated measurements.

First claim

The invention claimed is:

1. A method comprising:
placing a downhole tool in a wellbore in a geological formation containing heavy oil and water;
obtaining nuclear magnetic resonance measurements in the wellbore, wherein the nuclear magnetic resonance measurements comprise at least T 1 and T 2 measurements;
using one or more processors to determine a viscosity of the heavy oil including by:
separating responses of the nuclear magnetic resonance measurements that are due to water from responses of the nuclear magnetic resonance measurements due to heavy oil by:
(1) arranging the nuclear magnetic resonance measurements in a matrix and decomposing the matrix as a product of a first component matrix and a second component matrix, wherein the first component matrix comprises vectors that describe various fluids in the geological formation and the second component matrix comprises corresponding proportions of the fluids in the geological formation; or
(2) partitioning a plot of T 1 and T 2 measurements into sections attributable to water and sections attributable to heavy oil; or
(3) determining a secular relaxation rate (T 2,sec ) as defined below:

1

T

2
,
sec

=

1

T
2

-

1

T
1

;

 and

relating the responses of the nuclear magnetic resonance measurements due to heavy oil to values of viscosity of the heavy oil based on empirical or simulated measurements.

2. The method of claim 1 , wherein separating the responses of the nuclear magnetic resonance measurements that are due to water from the responses of the nuclear magnetic resonance measurements due to heavy oil comprises identifying a contrast between a first distribution and a second distribution in a T 1 domain.

3. The method of claim 1 , wherein relating the responses of the nuclear magnetic resonance measurements due to heavy oil to values of viscosity of the heavy oil comprises mapping the T 1 and T 2 measurements to the viscosity of the heavy oil using a non-linear function mapping using a database of laboratory measurements, simulated measurements, or both.

4. The method of claim 3 , wherein mapping function is a linear combination of Gaussian Radial Basis Functions (RBFs) as shown below:

log
⁡

(
η
)

=

∑

j
=
1

N

⁢

c
j

⁢

exp
⁡

(

-



A
T

-

A

T
,
j



2

2
⁢

s
j
2

)

∑

j
=
1

N

⁢

exp
⁡

(

-



A
T

-

A

T
,
j



2

2
⁢

s
j
2

)

where N is the number of heavy oil samples in the database and {right arrow over (A T )} is given by:
{right arrow over ( A T )}={right arrow over ( A T )}( A ( T 1 ), A ( T 2 ), T )

where η is the viscosity of the oil in centipoise, T is temperature in Kelvin, and s is the widths of the Gaussian RBFs.

5. The method of claim 1 , further comprising constructing an interpolation function using a logarithm of the viscosity of the heavy oil.

6. The method of claim 1 , further comprising displaying the separated responses of heavy oil and water on a log.

7. A system comprising:
a downhole tool configured to obtain nuclear magnetic resonance measurements in a wellbore in a geological formation containing heavy oil and water, wherein the nuclear magnetic resonance measurements comprise at least T 1 and T 2 measurements;
one or more processors configured to determine a viscosity of the heavy oil including by:
separating responses of the nuclear magnetic resonance measurements that are

Assignees

• Schlumberger Technology Corp

Inventors

• Anand Vivek

Classifications

• G01N33/2823 Primary

  Raw oil, drilling fluid or polyphasic mixtures · CPC title

• G01N24/081

  Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity · CPC title

• G01R33/448

  Relaxometry, i.e. quantification of relaxation times or spin density (G01R33/50 takes precedence) · CPC title

• G01N11/00

  Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties · CPC title

• G01V3/32

  operating with electron or nuclear magnetic resonance · CPC title