and near critical systems for oil based drilling fluid...

Application of Equation of State Based Methods to Correct for Oil Based Drilling Fluid Contamination in Condensates

and Near Critical Systems

John RatulowskiShell Exploration and Production Technology Company

Houston TX

Outline

• Sources of Error in Fluid Property Measurement• Development of EOS models for OBM

Contaminants• Dead Oil Data• Live Oil Data• A Field Example for a Condensate• Conclusions

Sources of Error from Downhole Samples

• Sampling– Phase splits due to drawdown – Contamination

• Transfer and Handling– Leaks– Lack of equilibration

• Laboratory Analysis– Poor technique– Lack of equilibration– Quantification of contamination

Philosophy of the EOS Approach

• The chemistry of the contaminants is better known than that of the oil

• Develop contaminant EOS description based on the known structure, physical properties, and available VLE data.– Actual compounds in the contaminant– Model compounds structurally similar– Pseudo-components with fixed properties

• Tune oil pseudo-component properties to match measured VLE data of the contaminated system

• This approach reduces the number of adjustable parameters

Petrofree (Not Petrofree LE)

50

100

150

200

250

300

350

400

450

Nor

mal

BP

C

4 6 8 10 12 14 16 18 20 22 24 Number of Carbons

Branched Straight Chain

Ester Boiling PointsFive fatty acid esters with carbon numbers 16 to 24 and an ethyl side chain

Boiling points extrapolated from known values

Group contribution techniques used to estimate EOS parameters

Viscosity model fit to data from 10 C to 65 C

Methane BIP’s fit to gas solubility data

Petrofree EOS Model Results

0

2

4

6

8

10

12

Visc

osity

cp

0 20 40 60 80 100 T Celcius

Model Data

Petrofree ViscosityAtmospheric Pressure

0.75

0.8

0.85

0.9

gm/c

c

0 2000 4000 6000 8000 10000 Pressure psia

75 F 150 F 300 F

Petrofree Density

0

500

1000

1500

GO

R S

CF/

BBL

1000 2000 3000 4000 5000 6000 Pressure psia

100 F 300 F

Methane Solubility in Petrofree

Escaid Mineral Oil

Refined product with low aromatic content C11 to C15 on SimDist analysis

In-house ECHO correlation used to generate pseudo-component properties This was sufficient to match stock tank density

Viscosity model to data between 4 C and 38 C

Methane BIP correlation fit to gas solubility data for mineral oils

1

10

100

wt %

5 10 15 20 Carbon Number

SimDist of Escaid Mineral Oil

EOS Results for Escaid

0

500

1000

1500

2000

2500

SCF/

BBL

2000 3000 4000 5000 6000 7000 8000 Pressure psia

100 F 200 F 300 F 250 F

Methane Solubility in Escaid

1

1.5

2

2.5

3

Visc

osity

cp

40 50 60 70 80 90 100 Temperature F

EOS Model Measured

Escaid ViscosityAvg Error 2.6%

Low Molecular Weight Olefins

Novaplus, Petrofree LE, IsoTeq, and Ultidrill are all compositionally similar

C14, C16, and C18 alpha or internal olefins. They may be branched or linear and may consist of single compounds or groups of isomers

C14, C16, C18 alpha olefins are used as model compounds

Literature data used to develop EOS description

Methane BIP correlation fit to gas solubility data

EOS Results for the Olefins

2

3

4

5

6

7

Visc

osity

cp

40 50 60 70 80 Temperature F

EOS Model Measured

IsoTeq ViscosityAvg Error 0.09%

0

2000

4000

6000

8000

Pres

sure

psi

a

0 500 1000 1500 2000 2500 3000 GOR SCF/BBL

Measured

Methane Solubility inNovaplus at 250 F

0

2000

4000

6000

8000

Pres

sure

psi

a

0 500 1000 1500 2000 2500 3000 GOR SCF/BBL

Measured

Methane Solubility inNovaplus at 200 F

Other Contaminant Models

• Aquamul– C20 alkyl ether– Approach similar to Petrofree esters– Limited success matching gas solubility data

• Novasol– Alpha-olefin isomers groups one near C20 the other near C30– Normal paraffins n-C30 and n-C40– Viscosity, density, and gas solubility matched adequately

Density of Dead Oil Blends

25

30

35

40

45

50

API G

ravi

ty

0 20 40 60 80 100 Mass % Contaminant

Measured EOS Model

IsoTeq/Oil API Gravity

25

30

35

40

45

50

API G

ravi

ty


Measured EOS Model

Escaid/Oil API Gravity

30

31

32

33

34

35

API G

ravi

ty0 20 40 60 80 100

Mass % Contaminant

Measured EOS Model

Petrofree/Oil API Gravity

•Linear mixing rule for API gravity.

•Variability in base fluid properties caused some error in the Petrofree trace

•Aquamul and Novasol results similar

Viscosity of Dead Oil Blends

0

5

10

15

20

25

30

Visc

osity

cp

0 10 20 30 40 50 60 Mass % Contaminant

EOS Model Measured

Escaid/Oil ViscosityAvg Error 6.3% All Points

10

15

20

25

30

Visc

osity

cp


EOS Model Measured

Petrofree/Oil ViscosityAvg Error 3.2% All Points

5

10

15

20

25

30

Visc

osity

cp


EOS Model Measured

IsoTeq/Oil ViscosityAvg Error 4.1% All Points

•Two oils of different gravity

•Temperature range from 40 to 100 F

•Contamination range from 5 to 60 wt %

•Novasol 3.7 % average error

•Aquamul 2.7 % average error

GOM Black Oil

• The oil was a black oil with a GOR of approximately 1200 SCF/BBL and a stock tank gravity of 27 API Gravity

• CCE’s at 130 F and 163 F run with 0, 5, and 10 wt % basis dead oil of three contaminates

• Results presented as deviations uncontaminated-contaminated

• Poor quality GOR data • In general, model and experiments compared favorably

EOS Results for the Black Oil (Live Oil)

0

200

400

600

800

1000

1200

Del

ta P

sat p

sia

0 2 4 6 8 10 Wt % Escaid

Measured 163 F EOS Model 163 FMeasured 130 F EOS Model 130 F

Petrofree Contaminated Black Oi

0

200

400

600

800

1000

1200

1400

Del

ta P

sat p

sia

0 2 4 6 8 10 Wt % Escaid

Measured 163 F EOS Model 163 FMeasured 130 F EOS Model 130 F

Escaid Contaminated Black Oil

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Del

ta V

isco

sity

cp

0 2 4 6 8 10 Wt % Escaid

Measured EOS Model

Escaid Contaminated Black OilLive Oil Viscosity 7000 psia 162 F

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

Del

ta V

isco

sity

cp

0 2 4 6 8 10 Wt % Escaid

Measured EOS Model

Petrofree Contaminated Black OilLive Oil Viscosity 7000 psia 162 F

EOS Results for the Black Oil (Flash Data)

1100

1150

1200

1250

1300

1350

1400

1450

GO

R S

CF/

BBL


Measured EOS Model

Black Oil Flash GOR Petrofree

1050

1100

1150

1200

1250

1300

1350

GO

R S

CF/

BBL


Measured EOS Model

Black Oil Flash GOR ESCAID

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Del

ta A

PI

0 2 4 6 8 10 Wt % Escaid

Measured EOS Model

Petrofre Contaminated Black Oil

-2.5

-2

-1.5

-1

-0.5

0

Del

ta A

PI

0 2 4 6 8 10 Wt % Escaid

Measured EOS Model

Escaid Contaminated Black Oil

• Volatile oil with a 1950 SCF/BBL GOR and 33.8 API tank gravity

• Mixture of Novasol contaminated and uncontaminated samples available from several wells and zones

• Question: How confident are we in our corrected PVT data from the contaminated samples?

• Minimal PVT rum for three contamination levels up to 10 %

EOS Results for a Volatile GOM Oil

1500

1600

1700

1800

1900

2000

GO

R S

CF/

BBL

0 5 10 15 20 % NOVSOL

Measured EOS Model

Flash GOR

1.7

1.75

1.8

1.85

1.9

Bo R

B/ST

B

0 5 10 15 20 % NOVSOL

Measured EOS Model

Oil Formation Volume Factor

4800

4900

5000

5100

5200

5300

Psat

psi

a

0 5 10 15 20 % NOVSOL

Measured EOS Model

Saturation Pressure

33.5

34

34.5

35

35.5

36

36.5

API

0 5 10 15 20 % NOVSOL

Measured EOS Model

Flash API GRavity

Near Critical Gas Condensate

7000

8000

9000

10000

11000

12000

Pres

sure

psi

a

0 100 200 300 400 500 600 Temperature F

Phase Envelope

Critical Point

Reservoir

•Near critical gas condensate 2300 SCF/BBL or 435 BBL/MMSCF

•31 API stock tank oil (condensate)

•Retrograde behavior at 130 F and 180 F confirmed in four experiments at two laboratories

•Uncontaminated sample available from first well drilled in water base mud

•Question: Would even small amounts of Novaplus contamination effect the phase behavior?

EOS Results for GOM Near Critical Fluid

0

0.2

0.4

0.6

0.8

1

Vol F

rac

Upp

er L

iq

0

0.01

0.02

0.03

0.04

0.05

Vol F

rac

Low

er L

iq

5000 6000 7000 8000 9000 10000 Pressure psia

Expt. Uncontaminated Expt.5 wt % NovaplusEOS Uncontaminated EOS 5 wt% Novaplus

GOM Near Critical Fluid 180 F CCEPhase Diagram

0

0.2

0.4

0.6

0.8

1

Vol F

rac

Upp

er L

iq

0

0.01

0.02

0.03

Vol F

rac

Low

er L

iq

4000 5000 6000 7000 8000 9000 10000 Pressure psia

Uncontaminated 5 wt % Novaplus

GOM Near Critical Fluid 130 F CCEPhase Diagram

• Single stage flash CGR of 37.8 BBL/MMSCF with a tank gravity of 48.4 API

• Same three contaminants as black oil study• Two different EOS characterizations were used. Results of the models

are sensitive to the detail of EOS characterization• Reasonably good agreement for flash data between experiment and

model• Contaminant-gas binary interaction parameters should be fit in the

retrograde region for accurate prediction of saturation pressure

EOS results for the Lean Condensate (Live Oil Data)

0

50

100

150

200

250

Del

ta P

sat p

sia


Measured 25 Component 3 Component

Escaid Condensate Dewpoint 160 F

-800

-600

-400

-200

0

200

Del

ta P

sat p

sia



Petrofree Condensate Dewpoint 160 F

-0.012

-0.01

-0.008

-0.006

-0.004

-0.002

0

Del

ta D

ensi

ty g

m/c

c



Escaid Condensate Live Oil Density9000 psia 163 F

-0.02

-0.015

-0.01

-0.005

0

Del

ta D

ensi

ty g

m/c

c



Petrofree Condensate Live Oil Density9000 psia 163 F

EOS Results for the Lean Condensate (Flash Data)

-14

-12

-10

-8

-6

-4

-2

0

Del

ta L

GR

BBL

/MM

SCF



Escaid Condensate LGR

-12

-10

-8

-6

-4

-2

0

Del

ta L

GR

BBL

/MM

SCF



Petrofree Condensate LGR

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Del

ta A

PI



Escaid Condensate Flash Gravity

0

1

2

3

4

Del

ta A

PI G

ravi

ty



Petrofree Condensate Flash Gravity

Field Case: Lean Condensate

• Small samples of dead contaminated condensate were available (about 33 wt % of Petrofree LE)

• No mud filtrate - uncertainties in mud EOS characterization and in the estimated contamination level

• PVT available on contaminated samples• The measured saturation pressure is the same as the bottom

hole pressure for the contaminated sample

Results of EOS Correction

Liquid Fallout Curves

0123456789

10

0 2000 4000 6000 8000

Pressure psia

% P

V Li

quid

Contaminated

Uncontaminated

Contaminated Corrected Measured

4-Stage SeparatorLGR BBL/MMSCF

55 40 32

4-Satge SeparatorAPI Gravity

50 49 47

Density at reservoirconditions gm/cc

0.2963 0.2947 0.2832

Potential Problems

1. Sample handling and transfer2. Problems in the lab3. Problems with the EOS model4. Areal and vertical variation in fluid

properties in the reservoir

Summary

• EOS models for oil based mud contaminants were constructed usingchemical, physical, and VLE data from the base fluids

• These models do a reasonable job of correcting black and volatile oil data

• Condensates are difficult to correct. The contaminant model should be fit to the retrograde region for accurate correction of dew points

• In practice, many things can cause differences between data measured on bottom-hole samples and production data these include:– Sample handling and transfer– Problems in the lab– Problems with the EOS model– Areal and vertical variation in fluid properties in the reservoir

and near critical systems for oil based drilling fluid...

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