Application of Equation of State Based Methods to Correct for Oil - - PowerPoint PPT Presentation

Application of Equation of State Based Methods to Correct for Oil Based Drilling Fluid Contamination in Condensates and Near Critical Systems

John Ratulowski

Shell 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
• f 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 Normal BP C 4 6 8 10 12 14 16 18 20 22 24 Number of Carbons Branched Straight Chain

Ester Boiling Points

Five 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

2 4 6 8 10 12 Viscosity cp 20 40 60 80 100 T Celcius Model Data

Petrofree Viscosity Atmospheric Pressure

0.75 0.8 0.85 0.9 gm/cc 2000 4000 6000 8000 10000 Pressure psia 75 F 150 F 300 F

Petrofree Density

500 1000 1500 GOR SCF/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

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 Viscosity cp 40 50 60 70 80 90 100 Temperature F EOS Model Measured

Escaid Viscosity

Avg Error 2.6%

Low Molecular Weight Olefins

Novaplus, Petrofree LE, IsoTeq, and Ultidrill are all compositionally similar C14, C16, and C18 alpha or internal

• lefins. 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 Viscosity cp 40 50 60 70 80 Temperature F EOS Model Measured

IsoTeq Viscosity

Avg Error 0.09%

2000 4000 6000 8000 Pressure psia 500 1000 1500 2000 2500 3000 GOR SCF/BBL Measured

Methane Solubility in Novaplus at 250 F

2000 4000 6000 8000 Pressure psia 500 1000 1500 2000 2500 3000 GOR SCF/BBL Measured

Methane Solubility in Novaplus 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 Gravity 20 40 60 80 100 Mass % Contaminant Measured EOS Model

IsoTeq/Oil API Gravity

25 30 35 40 45 50 API Gravity 20 40 60 80 100 Mass % Contaminant Measured EOS Model

Escaid/Oil API Gravity

30 31 32 33 34 35 API Gravity 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

5 10 15 20 25 30 Viscosity cp 10 20 30 40 50 60 Mass % Contaminant EOS Model Measured

Escaid/Oil Viscosity

Avg Error 6.3% All Points

10 15 20 25 30 Viscosity cp 10 20 30 40 50 60 Mass % Contaminant EOS Model Measured

Petrofree/Oil Viscosity

Avg Error 3.2% All Points

5 10 15 20 25 30 Viscosity cp 10 20 30 40 50 60 Mass % Contaminant EOS Model Measured

IsoTeq/Oil Viscosity

Avg 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)

200 400 600 800 1000 1200 Delta Psat psia 2 4 6 8 10 Wt % Escaid Measured 163 F EOS Model 163 F Measured 130 F EOS Model 130 F

Petrofree Contaminated Black Oi

200 400 600 800 1000 1200 1400 Delta Psat psia 2 4 6 8 10 Wt % Escaid Measured 163 F EOS Model 163 F Measured 130 F EOS Model 130 F

Escaid Contaminated Black Oil

• 0.04
• 0.03
• 0.02
• 0.01

0.01 0.02 0.03 Delta Viscosity cp 2 4 6 8 10 Wt % Escaid Measured EOS Model

Escaid Contaminated Black Oil Live Oil Viscosity 7000 psia 162 F

• 0.12
• 0.1
• 0.08
• 0.06
• 0.04
• 0.02

Delta Viscosity cp 2 4 6 8 10 Wt % Escaid Measured EOS Model

Petrofree Contaminated Black Oil Live Oil Viscosity 7000 psia 162 F

EOS Results for the Black Oil (Flash Data)

1100 1150 1200 1250 1300 1350 1400 1450 GOR SCF/BBL 2 4 6 8 10 Mass % Contaminant Measured EOS Model

Black Oil Flash GOR Petrofree

1050 1100 1150 1200 1250 1300 1350 GOR SCF/BBL 2 4 6 8 10 Mass % Contaminant Measured EOS Model

Black Oil Flash GOR ESCAID

• 1.4
• 1.2
• 1
• 0.8
• 0.6
• 0.4
• 0.2

Delta API 2 4 6 8 10 Wt % Escaid Measured EOS Model

Petrofre Contaminated Black Oil

• 2.5
• 2
• 1.5
• 1
• 0.5

Delta API 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 GOR SCF/BBL 5 10 15 20 % NOVSOL Measured EOS Model

Flash GOR

1.7 1.75 1.8 1.85 1.9 Bo RB/STB 5 10 15 20 % NOVSOL Measured EOS Model

Oil Formation Volume Factor

4800 4900 5000 5100 5200 5300 Psat psia 5 10 15 20 % NOVSOL Measured EOS Model

Saturation Pressure

33.5 34 34.5 35 35.5 36 36.5 API 5 10 15 20 % NOVSOL Measured EOS Model

Flash API GRavity

Near Critical Gas Condensate

7000 8000 9000 10000 11000 12000 Pressure psia 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

0.2 0.4 0.6 0.8 1 Vol Frac Upper Liq 0.01 0.02 0.03 0.04 0.05 Vol Frac Lower Liq 5000 6000 7000 8000 9000 10000 Pressure psia

• Expt. Uncontaminated

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

GOM Near Critical Fluid 180 F CCE Phase Diagram

0.2 0.4 0.6 0.8 1 Vol Frac Upper Liq 0.01 0.02 0.03 Vol Frac Lower Liq 4000 5000 6000 7000 8000 9000 10000 Pressure psia Uncontaminated 5 wt % Novaplus

GOM Near Critical Fluid 130 F CCE Phase 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)

50 100 150 200 250 Delta Psat psia 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Escaid Condensate Dewpoint 160 F

• 800
• 600
• 400
• 200

200 Delta Psat psia 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Petrofree Condensate Dewpoint 160 F

• 0.012
• 0.01
• 0.008
• 0.006
• 0.004
• 0.002

Delta Density gm/cc 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Escaid Condensate Live Oil Density 9000 psia 163 F

• 0.02
• 0.015
• 0.01
• 0.005

Delta Density gm/cc 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Petrofree Condensate Live Oil Density 9000 psia 163 F

EOS Results for the Lean Condensate (Flash Data)

• 14
• 12
• 10
• 8
• 6
• 4
• 2

Delta LGR BBL/MMSCF 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Escaid Condensate LGR

• 12
• 10
• 8
• 6
• 4
• 2

Delta LGR BBL/MMSCF 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Petrofree Condensate LGR

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Delta API 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

Escaid Condensate Flash Gravity

1 2 3 4 Delta API Gravity 5 10 15 20 25 Mass % Contaminant Measured 25 Component 3 Component

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

1 2 3 4 5 6 7 8 9 10 2000 4000 6000 8000 Pressure psia % PV Liquid Contaminated Uncontaminated

Contaminated Corrected Measured 4-Stage Separator LGR BBL/MMSCF 55 40 32 4-Satge Separator API Gravity 50 49 47 Density at reservoir conditions gm/cc 0.2963 0.2947 0.2832

Potential Problems

• 1. Sample handling and transfer
• 2. Problems in the lab
• 3. Problems with the EOS model
• 4. Areal and vertical variation in fluid

properties in the reservoir

Summary

• EOS models for oil based mud contaminants were constructed using

chemical, 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
• n 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