# US 10,309,885 B2 · Method and apparatus for water-based mud filtrate contamination monitoring in real time downhole water sampling

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- Number: US 10,309,885 B2
- Document ID: US10309885B2
- Status: Granted
- Kind: B2
- Application number: 14/085,550
- Filed: 2013-11-20
- Published: 2015-05-21
- Granted: 2019-06-04
- Earliest claimed: 2013-11-20
- Assignees: Schlumberger Technology Corporation
- Applicants: Schlumberger Technology Corporation
- Inventors: Youxiang Zuo; Adriaan Gisolf; Julian Pop; Oliver Mullins; Chetankumar Desai
- Web page: https://patentgrep.com/patent/US10309885B2

## CPC

- G01N 9/00: Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
- E21B 49/08: Obtaining fluid samples or testing fluids, in boreholes or wells
- G01N 9/36: Analysing materials by measuring the density or specific gravity, e.g. determining quantity of moisture (methods of measurement in general G01N9/02 - G01N9/32)
- G01N 33/2823: {Raw oil, drilling fluid or polyphasic mixtures}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

A method for contamination monitoring includes measuring water based mud filtrate density and resistivity at downhole conditions, logging properties of a downhole fluid to find at least a resistivity and a density of a fluid sample at the downhole conditions, establishing a linear relationship between a water based mud filtrate conductivity at downhole conditions and the water based mud filtrate density at the downhole conditions, determining a density and a resistivity for native formation water, estimating a density for water based mud filtrate using the linear relationship between conductivity and density, and estimating a water based mud filtrate contamination.

## Claims

### Claim 1

A method for contamination monitoring, comprising: measuring a water based mud filtrate density and a water based mud filtrate resistivity at surface conditions;
converting via a downhole apparatus the measured water based mud filtrate density and resistivity to downhole conditions;
logging via the downhole apparatus properties of a downhole fluid to find at least a resistivity and a density of a fluid sample at the downhole conditions;
establishing via the downhole apparatus a linear relationship between a water based mud filtrate conductivity at downhole conditions and the water based mud filtrate density at the downhole conditions;
determining via the downhole apparatus an existence of a high quality pressure gradient at the downhole conditions;
fitting via the downhole apparatus at least one of a density and a resistivity data for native formation water using a power function and obtaining at least one of a density and a resistivity for native formation water when no high quality pressure gradient exists;
estimating via the downhole apparatus the density for native formation water from the pressure from the high quality gradient when the high quality pressure gradient exists;
estimating via the downhole apparatus the resistivity for native formation water, using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density;
estimating via the downhole apparatus a density for water based mud filtrate using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density; and
estimating via the downhole apparatus a water based mud filtrate contamination based on the water based mud filtrate density.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the estimating the resistivity for native formation water is performed using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the estimating the resistivity for native formation water is performed using Archie's expression
R
w
⁢
⁢
f
=
1
a
⁢
φ
m
⁢
S
w
n
⁢
R
t
≈
1
.8
⁢
φ
2
1
⁢
R
⁢
t
where
Rwf represents resistivity of native formation water;
a represents a constant;
φ represents a formation porosity;
m represents a cementation factor;
Sw represents water saturation;
n represents a saturation exponent;
Rt represents a formation resistivity.

### Claim 4 (depends on 1)

The method according to claim 1, further comprising:
estimating a time required for sampling to reach a water based mud filtrate contamination level.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the estimating the water based mud filtrate contamination is performed through an equation:
η
=
1
R
n
-
1
R
fw
n
1
R
wbm
n
-
1
R
fw
n
=
ρ
fw
-
ρ
ρ
fw
-
ρ
wbm
where
η represents the water based mud filtrate contamination;
R represents the resistivity of the fluid sample;
Rfw represents the resistivity of native formation water;
Rwbm represents the water based mud filtrate resistivity;
n represents an adjustable parameter;
ρfw represents the density of native formation water;
ρ represents the density of the fluid sample;
ρwbm represents the water based mud filtrate density.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the determining the existence of the high quality pressure gradient at the downhole conditions is performed through a downhole pretest.

### Claim 7

A method for contamination monitoring, comprising:
measuring via a downhole apparatus water based mud filtrate density and resistivity at downhole conditions;
logging via the downhole apparatus properties of a downhole fluid to find at least a resistivity and a density of a fluid sample at the downhole conditions;
establishing via the downhole apparatus a linear relationship between a water based mud filtrate conductivity at downhole conditions and the water based mud filtrate density at the downhole conditions;
determining via the downhole apparatus an existence of a high quality pressure gradient at the downhole conditions;
fitting via the downhole apparatus at least one of a density and a resistivity data for native formation water using a power function and obtaining at least one of a density and a resistivity for native formation water when no high quality pressure gradient exists;
estimating via the downhole apparatus the density for native formation water from the pressure from the high quality gradient when the high quality pressure gradient exists;
estimating via the downhole apparatus the resistivity for native formation water, using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density;
estimating via the downhole apparatus a density for water based mud filtrate using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density; and
estimating via the downhole apparatus a water based mud filtrate contamination based on the water based mud filtrate density.

### Claim 8 (depends on 7)

The method according to claim 7, wherein the estimating the resistivity for native formation water is performed using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density.

### Claim 9 (depends on 7)

The method according to claim 7, wherein the estimating the resistivity for native formation water is performed using Archie's expression
R
w
⁢
⁢
f
=
1
a
⁢
φ
m
⁢
S
w
n
⁢
R
t
≈
1
.8
⁢
φ
2
1
⁢
R
⁢
t
where
Rwf represents resistivity of native formation water;
a represents a constant;
φ represents a formation porosity;
m represents a cementation factor;
Sw represents water saturation;
n represents a saturation exponent;
Rt represents a formation resistivity.

### Claim 10 (depends on 7)

The method according to claim 7, further comprising:
estimating a time required for sampling to reach a water based mud filtrate contamination level.

### Claim 11 (depends on 7)

The method according to claim 7, wherein the estimating the water based mud filtrate contamination is performed through an equation:
η
=
1
R
n
-
1
R
fw
n
1
R
wbm
n
-
1
R
fw
n
=
ρ
fw
-
ρ
ρ
fw
-
ρ
wbm
where
η represents the water based mud filtrate contamination;
R represents the resistivity of the fluid sample;
Rfw represents the resistivity of native formation water;
Rwbm represents the water based mud filtrate resistivity;
n represents an adjustable parameter;
ρfw represents the density of native formation water;
ρ represents the density of the fluid sample;
ρwbm represents the water based mud filtrate density.

### Claim 12 (depends on 7)

The method according to claim 7, wherein the determining the existence of the high quality pressure gradient at the downhole conditions is performed through a downhole pretest.