# US 11,898,444 B2 · Contamination estimation of formation samples

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- Number: US 11,898,444 B2
- Document ID: US11898444B2
- Status: Granted
- Kind: B2
- Application number: 17/343,220
- Filed: 2021-06-09
- Published: 2021-09-23
- Granted: 2024-02-13
- Earliest claimed: 2021-06-09
- Assignees: Halliburton Energy Services, Inc.
- Applicants: Halliburton Energy Services, Inc.
- Inventors: Waqar Ahmad Khan; Mehdi Azari; Abbas Sami Eyuboglu
- Web page: https://patentgrep.com/patent/US11898444B2

## CPC

- E21B 49/081: {with down-hole means for trapping a fluid sample (E21B49/10 takes precedence)}
- E21B 49/005: {Testing the nature of borehole walls or the formation by using drilling mud or cutting data}
- E21B 49/08: Obtaining fluid samples or testing fluids, in boreholes or wells
- E21B 49/086: {Withdrawing samples at the surface}
- G01N 9/32: by using flow properties of fluids, e.g. flow through tubes or apertures
- 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}
- E21B 49/0875: {determining specific fluid parameters}
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- 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)

## Abstract

Contamination estimation of a mud filtrate or reservoir sample requires a robust handle on the properties of mud filtrate at downhole conditions. Coupling acquired data with downhole measured data provides a robust estimation of contamination by encompassing the entire available data. Downhole density of the mud filtrate sample may be estimated based on a characteristic of the mud filtrate sample. A density of a formation fluid of the reservoir may be determined using a formation tester tool. The contamination of the formation fluid may be estimated based on the clean fluid density and the estimated mud filtrate density by, for example, using a material balance equation or ratio. An estimated pump-out time for the formation fluid may be determined based on the estimated contamination and a trend of the estimated contamination of the formation fluid.

## Claims

### Claim 1

A method for contamination estimation, comprising:
collecting or extracting a mud filtrate sample at a subsurface location;
retrieving the mud filtrate sample at a surface;
determining a surface density of the mud filtrate sample at the surface;
estimating downhole density of the mud filtrate sample based, at least in part, on the surface density for a given temperature and a pressure downhole;
determining a plurality of formation fluid densities for a period of time;
determining a constant pumping rate, wherein the constant pumping rate is based on a pumping rate at which a plurality of pumping rates associated with a predetermined time interval are within a range of deviation of each other;
filtering the determined plurality of formation fluid densities based, at least in part, on the constant pumping rate;
performing an analysis of the determined plurality of fluid densities at the constant pumping rate versus an exponential function of time to determine a best fit linear regression, wherein all of the analysis is performed at the constant pump rate, wherein the constant pump rate is predetermined from a median or an average of the plurality of pump rates;
determining a clean fluid density based, at least in part, on the best fit linear regression;
estimating a contamination based, at least in part, on dividing a first calculated density by a second calculated density, wherein the first calculated density comprises subtracting from the clean fluid density from a real-time formation fluid density measurement, and wherein the second calculated density comprises subtracting the clean fluid density from the estimated mud filtrate density;
estimating a pump-out time based, at least in part, on the estimated contamination and a trend of the estimated contamination;
comparing the estimated contamination to a contamination threshold, wherein the contamination threshold is about 20%; and
collecting a reservoir fluid sample based, at least in part, on the comparison, wherein the reservoir fluid sample is collected when the estimated contamination is at or below the contamination threshold.

### Claim 2 (depends on 1)

The method of contamination estimation of claim 1, further comprising receiving one or more formation fluid density measurements from one or more sensors, wherein the determined plurality of formation fluid densities is based on the one or more formation fluid density measurements.

### Claim 3 (depends on 1)

The method of contamination estimation of claim 1, further comprising positioning a formation tester tool within a wellbore, wherein the formation tester tool collects the reservoir fluid sample.

### Claim 4 (depends on 1)

The method of contamination estimation of claim 1, further comprising determining one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or more mud filtrate characteristics.

### Claim 5 (depends on 4)

The method of contamination estimation of claim 4, wherein the one or more mud filtrate characteristics comprise at least one of type of material, chemical composition, temperature, density, viscosity, thickness, toughness, slickness, and permeability.

### Claim 6 (depends on 1)

The method of contamination estimation of claim 1, wherein determining the constant pumping rate comprises determining a pumping rate at which a plurality of pumping rates associated with a predetermined interval of time are within a range of deviation.

### Claim 7 (depends on 1)

The method of contamination estimation of claim 1, wherein the clean fluid density is determined based, at least in part, on extrapolation of the linear regression for a time that approaches infinity.

### Claim 8

A non-transitory computer-readable medium storing one or more executable instructions that, when executed, cause one or more processors to:
actuate collection or extraction of a mud filtrate sample at a subsurface location;
instruct a formation tester tool to retrieve the mud filtrate sample at a surface;
determine a surface density of the mud filtrate sample at the surface;
estimate downhole density of the mud filtrate sample based, at least in part, on the surface density for a given temperature and a pressure downhole;
determine a plurality of formation fluid densities for a period of time;
determine a constant pumping rate, wherein the constant pumping rate is based on a pumping rate at which a plurality of pumping rates associated with a predetermined time interval are within a range of deviation of each other;
filter the determined plurality of formation fluid densities based, at least in part, on the constant pumping rate;
perform an analysis of the determined plurality of fluid densities associated at the constant pumping rate versus an exponential function of time to determine a best fit linear regression, wherein all of the analysis is performed at the constant pump rate, wherein the constant pump rate is predetermined from a median or an average of the plurality of pump rates;
determine a clean fluid density based, at least in part, on a linear regression of the filtered determined plurality of formation fluid densities versus an exponential function of time corresponding to the constant pumping rate;
estimate a contamination based, at least in part, on dividing a first calculated density by a second calculated density, wherein the first calculated density comprises subtracting the clean fluid density from a real-time formation fluid density measurement, and wherein the second calculated density comprises subtracting the clean fluid density from the estimated mud filtrate density;
estimate a pump-out time based, at least in part, on the estimated contamination and a trend of the estimated contamination;
compare the estimated contamination to a contamination threshold, wherein the contamination threshold is about 20%; and
collect a reservoir fluid sample based, at least in part, on the comparison, wherein the reservoir fluid sample is collected when the estimated contamination is at or below the contamination threshold.

### Claim 9 (depends on 8)

The non-transitory computer-readable medium of claim 8, wherein the one or more executable instructions that, when executed, further cause the one or more processors to receive one or more formation fluid density measurements from one or more sensors, wherein the determined plurality of formation fluid densities is based on the one or more formation fluid density measurements.

### Claim 10 (depends on 8)

The non-transitory computer-readable medium of claim 8, wherein the one or more executable instructions that, when executed, further cause the one or more processors to position a formation tester tool within a wellbore, wherein the formation tester tool collects the reservoir fluid sample.

### Claim 11 (depends on 8)

The non-transitory computer-readable medium of claim 8, wherein the one or more executable instructions that, when executed, further cause the one or more processors to determine one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or mud filtrate characteristics.

### Claim 12 (depends on 11)

The non-transitory computer-readable medium of claim 11, wherein the one or more mud filtrate characteristics comprise at least one of type of material, temperature, density, viscosity, thickness, toughness, slickness, and permeability, and wherein the one or more mud filtrate characteristics comprise at least one of a type of material, a chemical composition, a temperature, a density, a viscosity, a thickness, a toughness, a lubricity and a permeability.

### Claim 13 (depends on 8)

The non-transitory computer-readable medium of claim 8, wherein determining the constant pumping rate comprises determining a pumping rate at which a plurality of pumping rates associated with a predetermined interval of time are within a range of deviation.

### Claim 14 (depends on 8)

The non-transitory computer-readable medium of claim 8, wherein the clean fluid density is determined based, at least in part, on extrapolation of the linear regression for a time that approaches infinity.

### Claim 15

A system for contamination estimation, comprising:
a mud filtrate sample, wherein the mud filtrate sample is collected or extracted at a subsurface location;
a formation tester tool configured to retrieve the mud filtrate sample at a surface;
a processor;
a non-transitory memory coupled to the processor, the non-transitory memory comprising one or more instructions that, when executed by the processor, cause the processor to:
determine a surface density of the mud filtrate sample at the surface;
estimate downhole density of the mud filtrate sample based, at least in part, on the surface density for a given temperature and a pressure downhole;
determine a plurality of formation fluid densities for a period of time;
determine a constant pumping rate, wherein the constant pumping rate is based on a pumping rate at which a plurality of pumping rates associated with a predetermined time interval are within a range of deviation of each other;
filter the determined plurality of formation fluid densities based, at least in part, on the constant pumping rate;
perform an analysis of the determined plurality of fluid densities associated at the constant pumping rate versus an exponential function of time to determine a best fit linear regression, wherein all of the analysis is performed at the constant pump rate, wherein the constant pump rate is predetermined from a median or an average of the plurality of pump rates;
determine a clean fluid density based, at least in part, on a linear regression of the filtered determined plurality of formation fluid densities versus an exponential function of time corresponding to the constant pumping rate;
estimate a contamination based, at least in part, on dividing a first calculated density by a second calculated density, wherein the first calculated density comprises subtracting the clean fluid density from a real-time formation fluid density measurement, and wherein the second calculated density comprises subtracting the clean fluid density from the estimated mud filtrate density;
estimate a pump-out time based, at least in part, on the estimated contamination and a trend of the estimated contamination;
compare the estimated contamination to a contamination threshold, wherein the contamination threshold is about 20%; and
collect a reservoir fluid sample based, at least in part, on the comparison, wherein the reservoir fluid sample is collected when the estimated contamination is at or below the contamination threshold.

### Claim 16 (depends on 15)

The system for contamination estimation of claim 15, wherein the one or more instructions that, when executed by the processor, further cause the processor to receive one or more formation fluid density measurement from one or more sensors, wherein the determined plurality of formation fluid densities is based on the one or more formation fluid density measurements.

### Claim 17 (depends on 15)

The system for contamination estimation of claim 15, wherein the one or more instructions that, when executed by the processor, further cause the processor to determine one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or more mud filtrate characteristics, and wherein the one or more mud filtrate characteristics comprise at least one of a type of material, a chemical composition, a temperature, a density, a viscosity, a thickness, a toughness, a lubricity and a permeability.