MEASUREMENT OF CRUDE OIL INTERFACIAL TENSION TO … · the impact of pressure change, injection gas...

MEASUREMENT OF CRUDE OIL INTERFACIAL TENSION TO

DETERMINE MINIMUM MISCIBILITY IN CARBON DIOXIDE

AND NITROGEN

by

Ibrahim O. Awari-Yusuf

Submitted in partial fulfilment of the requirements

for the degree of Master of Engineering

at

Dalhousie University

Halifax, Nova Scotia

August 2013

© Copyright by Ibrahim O. Awari-Yusuf, 2013

ii

DALHOUSIE UNIVERSITY

PETROLEUM ENGINEERING

The undersigned hereby certify that they have read and recommend to the Faculty of

Graduate Studies for acceptance a thesis entitled “MEASUREMENT OF CRUDE OIL

INTERFACIAL TENSION TO DETERMINE MINIMUM MISCIBILITY IN CARBON

DIOXIDE AND NITROGEN” by Ibrahim O. Awari-Yusuf in partial fulfilment of the

requirements for the degree of Master of Engineering.

Dated: August 19, 2013

Supervisor: _________________________________

Reader: _________________________________

iii

DALHOUSIE UNIVERSITY

DATE: August 19, 2013

AUTHOR: Ibrahim O. Awari-Yusuf

TITLE: MEASUREMENT OF CRUDE OIL INTERFACIAL TENSION TO

DETERMINE MINIMUM MISCIBILITY IN CARBON DIOXIDE AND

NITROGEN

DEPARTMENT OR SCHOOL: Petroleum Engineering

DEGREE: MEng. CONVOCATION: October YEAR: 2013

Permission is herewith granted to Dalhousie University to circulate and to have copied

for non-commercial purposes, at its discretion, the above title upon the request of

individuals or institutions.

_______________________________

Signature of Author

The author reserves other publication rights, and neither the thesis nor extensive extracts

from it may be printed or otherwise reproduced without the author’s written permission.

The author attests that permission has been obtained for the use of any copyrighted

material appearing in the thesis (other than the brief excerpts requiring only proper

acknowledgement in scholarly writing), and that all such use is clearly acknowledged.

iv

DEDICATION

I dedicate this work to the two father figures in my life, Mr Ismaila Awari-Yusuf and Mr

Yusuf Yusuf Awari, to Mrs Taibat Awari-Yusuf and to all my family and friends who

have supported me through the course of my studies.

v

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................................... vii

LIST OF FIGURES................................................................................................................ viii

ABSTRACT ......................................................................................................................................... x

LIST OF ABREVIATIONS AND SYMBOLS ........................................................................................... xi

ACKNOWLEDGEMENTS ..................................................................................................................xiii

CHAPTER 1 INTRODUCTION ............................................................................................. 1

1.1. Background ...................................................................................................................... 1

1.2. Objective ............................................................................................................................... 3

CHAPTER 2 LITERATURE REVIEW ................................................................................... 4

2.1. Miscibility .............................................................................................................................. 4

2.2. Miscible flooding ................................................................................................................... 4

2.3. Carbon dioxide flooding ........................................................................................................ 5

2.3.1. Properties of carbon dioxide ............................................................................................. 5

2.4. Nitrogen flooding .................................................................................................................. 6

2.4.1. Nitrogen properties ........................................................................................................... 7

2.5. Miscible flooding mechanism ............................................................................................... 7

2.6. Interfacial tension ................................................................................................................. 8

2.7. Minimum miscibility pressure ............................................................................................... 8

2.8. Experimental methods for determining minimum miscibility pressure ............................... 9

2.9. Crude oil density ................................................................................................................. 10

CHAPTER 3 EXPERIMENTAL ............................................................................................. 11

3.1. The theory behind the pendant drop technique ................................................................ 11

3.2. Apparatus ............................................................................................................................ 13

3.3. Accuracy and reproducibility .............................................................................................. 16

3.4. Materials ............................................................................................................................. 17

3.5. Requirement of the drop shape analysis ............................................................................ 17

3.5.1. Crude oil density measurement ....................................................................................... 17

3.5.2. Carbon dioxide Density .................................................................................................... 18

3.5.3 Nitrogen Density ............................................................................................................... 20

vi

3.6 DSA Measurement ............................................................................................................... 22

CHAPTER 4 RESULTS AND DISCUSSION ................................................................... 24

4.1. Crude oil and carbon dioxide systems at 220C .................................................................... 26

4.2. Crude oil and nitrogen systems at 220C .............................................................................. 35

4.3 Gullfaks C using carbon dioxide at 600C ............................................................................... 44

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS ........................................ 47

1.1 Conclusions .................................................................................................................... 47

5.2 Recommendations ............................................................................................................... 48

REFERENCES ................................................................................................................................... 49

vii

LIST OF TABLES

Table 3.1: Calibration data .................................................................................................16

Table 3.2: Crude oil density data ...................................................................................... 18

Table 3.3: Carbon dioxide density data .............................................................................19

Table 3.4: Variation of nitrogen density with pressure..................................................... 20

Table 4.1: DSA measurement for Arab AH-50 using carbon dioxide .............................. 25

Table 4.2: DSA measurement of Gullfaks C using carbon dioxide .................................. 27

Table 4.3: DSA measurement of West Texas Intermediate using carbon dioxide ........... 27

Table 4.4: DSA measurement of Arab AH-50 using nitrogen.......................................... 35

Table 4.5: DSA measurement of Gullfaks C using nitrogen ............................................ 36

Table 4.6: DSA measurement of West Texas intermediate using nitrogen ...................... 37

Table 4.7: DSA measurement of Gullfaks C using carbon dioxide at reservoir

temperature ....................................................................................................................... 44

viii

LIST OF FIGURES

Figure 2.1: Pure carbon dioxide phase diagram ................................................................ 5

Figure 2.2: Carbon dioxide density as a function of pressure at 600C ............................... 6

Figure 3.1: Schematic of a pendant drop ........................................................................ 17

Figure 3.2: Drop shape analysis (DSA 100 V 1.9) and high pressure pendant drop (PD-E

1700) ................................................................................................................................. 18

Figure 3.3: Schematic of the axisymmetric drop shape analysis (ADSA) ...................... 19

Figure 3.4: Variation of carbon dioxide density with Temperature ................................. 22

Figure 3.5: Variation of Gullfaks C density with pressure .............................................. 24

Figure 3.6: Flow sheet of the PD-E1700 …………….………………………………………………….……..22

Figure 4.1: Variation of Arab AH-50 drop volume with pressure using carbon dioxide at

220C................................................................................................................................... 31

Figure 4.2: Variation of Gullfaks C drop volume with pressure using carbon dioxide at

220C................................................................................................................................... 31

Figure 4.3: Variation of West Texas intermediate drop volume with pressure using

carbon dioxide at 220C ...................................................................................................... 32

Figure 4.4: Variation of Arab AH-50 drop surface area with pressure using carbon

dioxide at 220C .................................................................................................................. 33

Figure 4.5: Variation of Gullfaks C drop surface area with pressure using carbon dioxide

at 220C ............................................................................................................................... 33

Figure 4.6: Variation of West Texas intermediate drop surface area with pressure using


Figure 4.7: Variation of Arab AH-50 interfacial tension with pressure using carbon

dioxide at 220C .................................................................................................................. 35

Figure 4.8: Variation of Gullfaks C interfacial tension with pressure using carbon

dioxide at 220C .................................................................................................................. 35

Figure 4.9: Variation of West Texas intermediate interfacial tension with pressure using


Figure 4.10: Variation of Arab AH-50 drop volume with pressure using nitrogen at 220C

........................................................................................................................................... 40

Figure 4.11: Variation of Gullfaks C drop volume with pressure using nitrogen at 220C

.......................................................................................................................................... .40

Figure 4.12: Variation of West Texas intermediate drop volume with Pressure using

nitrogen at 220C ................................................................................................................ 41

Figure 4.13: Variation of Arab AH-50 drop surface area with pressure using nitrogen at

220C................................................................................................................................... 42

Figure 4.14: Variation of Gullfaks C drop surface area with pressure using nitrogen at

220C................................................................................................................................... 42

Figure 4.15: Variation of West Texas intermediate drop surface area with pressure using

nitrogen at 220C ................................................................................................................ 43

Figure 4.16: Variation of drop interfacial tension With pressure Using nitrogen at 220C

........................................................................................................................................... 44

Figure 4.17: Variation of Gullfaks C Drop IFT With Pressure Using nitrogen at 220C.. 44

Figure 4.18: Variation of West Texas intermediate drop interfacial tension with pressure

using nitrogen at 220C ....................................................................................................... 45

ix

Figure 4.19: Variation of Gullfaks C’s interfacial tension with pressure using carbon

dioxide At 600C................................................................................................................. 47

Figure 4.20: Variation Of Gullfaks C’s interfacial tension With temperature ................ 47

x

ABSTRACT

Gas injection has been used to enhance oil recovery due to its ability to maintain

reservoir pressure, reduce oil viscosity, reduce oil interfacial tension, displace residual oil

and induce oil swelling effect.

However the type of gas used would have a considerable impact on oil recovery and the

cost incurred during injection thereby determining the economics of the process.

In this study, the axisymmetric drop shape analysis (ADSA) technique is used to assess

the impact of pressure change, injection gas type and crude oil type on the pendant drop

volume, surface area and interfacial tension. The ADSA technique is used to measure the

pendant drop parameters of the Arab AH-50, the Gullfaks C and the West Texas

intermediate crude oil pendant drops in carbon dioxide and nitrogen. It is found that in

each test, the pendant drop volume, surface area and IFT reduce linearly with pressure

increase. Reduction in the three parameters is more pronounced in the crude oil-carbon

dioxide system. The vanishing interfacial tension (VIT) technique is used to estimate first

contact minimum miscibility pressure of the crude oil-gas systems from the measured

interfacial tension and it was seen that the systems with carbon dioxide required less

pressure to achieve miscibility thereby making carbon dioxide a more favourable gas for

miscible flooding in comparison to nitrogen.

xi

LIST OF ABREVIATIONS AND SYMBOLS

= Oil density at reservoir conditions(lb/ft3)

= Fake density used in oil density calculation (lb/ft3)

= Pseudo liquid density (lb/ft3)

= Oil density at reservoir bubblepoint (lb/ft3)

= The difference in density of the two phases (Kg/m3)

= Adjustment of oil density due to pressure (lb/ft3)

= Adjustment of oil density due to temperature (lb/ft3)

Interfacial tension

= Weighted average surface gas specific gravity

= Stock tank oil specific gravity

= Separator gas specific gravity

= Interfacial tension (mN/m)

a = Capillary length

= Constants

B0 = Bond number which represents the ratio of buoyancy force to surface force

(dimensionless)

= Weighted average oil compressibility from bubble point pressure to a higher

pressure of interest, 1/psi

g = Gravitational acceleration (M/s3)

= Pressure (psia)

= Bubblepoint pressure (psia)

= Pressure difference at a reference plane (psia)

r = Characteristic radius (m)

R0 = Radius at the apex of the drop (m)

= Principal radii of curvature

xii

=Solution gas oil ratio at bubblepoint pressure (scf/STB)

mN/m = Mill-Newton per meter

= Temperature (0F)

ADSA = Axisymetric drop shape analysis

EOR = Enhanced oil recovery

IFT = Interfacial tension

MMP = Minimum miscibility pressure

PV = Pore volume

RBA = Rising bubble apparatus

VIT = Vanishing interfacial tension

xiii

ACKNOWLEDGEMENTS

I am immensely grateful to all faculty members and staff especially Mr Mumuni Amadu

and Mr. Matt Kujath for their support and motivation during this project. I will also like

to thank my supervisor Dr. Michael Pegg, for the continued assistance, guidance and

support given me through the course of this project. I am also thankful to Dr. Jan

Healssig for his acceptance to serve on the examining committee.

Finally, to my family which has been a constant source of encouragement and support, I

say thank you.

1

CHAPTER 1 INTRODUCTION

1.1. Background

As crude oil recovery from conventional reservoirs continues to decrease, enhanced oil recovery

(EOR) is increasingly becoming significant in the petroleum industry. Gas injection has been

used as an EOR process in the petroleum industry for a very long time due to its pressure

maintenance capability, its ability to reduce the viscosity of reservoir fluids, and its efficiency in

displacing reservoir fluids as well as inducing oil swelling effect which is the expansion of the

reservoir oil due to the dissolution of the injected solvent into the reservoir fluid (Sclumberger

Limited, 2013).

Interfacial mass transfer occurs between the injected gas phase and the reservoir fluid during gas

injection until an equilibrium state is achieved. As a result of this phenomenon, the physical and

chemical properties of the reservoir fluid are modified leading to a more efficient displacement

process (Danesh, 1998).

Gas flooding can be classified into miscible, semi miscible and immiscible flooding processes

depending on the temperature, pressure, type of injected gas and reservoir conditions (Ali et al.,

2013). Lake (1989) stated that fluids that mix in all proportions while still existing in a single

homogenous phase are considered to be miscible. The minimum miscibility pressure (MMP) is

defined by Johnson and Pollin as the lowest pressure at which an apparent point of maximum

curvature can be seen as recovery of oil at 1.2 pore volumes (PV) gas injected is plotted against

pressure (Johnson & Pollin, 1981) this can also be said to be the pressure at which the interfacial

tension (IFT) between two phases is zero (Green & Willhite, 1998).

2

The classification of gas flooding is based on the MMP (Wang & Gu, 2011). Hence If the

pressure of the reservoir is not maintained above the MMP of the injected gas then the injection

process would become semi miscible or immiscible (Fanchi, 2006).

Determining MMP accurately is a crucial step in the design of an economical miscible injection

program. Numerous analytical and experimental methods have been developed to predict or

estimate MMP. Traditionally, the slim tube method is considered as the standard technique for

MMP measurement in an oil/solvent system (Huang & Dyer, 1993). However, it is very

expensive and time consuming (Gu et al., 2013). High pressure carbon dioxide core flood tests

can also be used to measure MMP in a similar fashion as the slim tube method (Huang, 1992).

The rising-bubble apparatus (RBA) (Christiansen & Haines, 1987) and the vanishing interfacial

tension (VIT) technique (Rao, 1997; Rao & Lee, 2002; Rao & Lee, 2003 ; Gu et al., 2013) are

faster and less expensive methods of which MMP can be experimentally estimated.

It has been shown that IFT reduces in a linear fashion in an isotherrmal system as the pressure

reduces (Adamson & Gast, 1997) and that MMP can be estimated through the extrapolation of

the IFT linear equation till IFT is zero (Rao & Lee , 2003).

The choice of injection gas would depend on the availability of the gas, reservoir conditions and

the economic viability of the gas injection process. Carbon dioxide injection is said to be one of

the most effective methods to improve the efficiency of the oil recovery process (Alvarado &

Manrique, 2010; Farouq & Thomas, 1996).

To test the above stated statements, the axisymmetric drop shape analysis (ADSA) technique is

used to assess the impact of pressure change, injection gas type and crude oil type on the pendant

drop volume, surface area and IFT. In more detail, the ADSA technique is used in this study to

measure the DSA pendant drop parameters of the Arab AH-50, the Gullfaks C and the West

3

Texas intermediate pendant drops in carbon dioxide and nitrogen systems. The VIT technique is

then used to estimate first contact minimum miscibility pressure of the crude oil and gas systems

from the measured IFT at 220C and over a pressure of 100 to 600 psi.

1.2. Objective

This work is being carried out for the following reasons:

1) To understand the principles behind miscible gas injection as an EOR method .

2) To test the accuracy of statements from literature that state that IFT reduces linearly with

pressure increase under isothermal conditions and that carbon dioxide is a more favorable

gas for miscible flooding compared to nitrogen.

3) To generate data that can form the basis of correlations to determine MMP of the used

crude oil samples in carbon dioxide and nitrogen systems.

4) To determine the variation in pendant drop volume and surface area with pressure and

density.

5) To determine if IFT varies linearly with pressure at non reservoir conditions.

4

CHAPTER 2 LITERATURE REVIEW

2.1. Miscibility

Miscibility between two or more fluids has been defined in numerous ways by different authors

(Rao D. N., 1997; Benham et al., 1965; Lake, 1989). However all definitions acknowledge one

of the following (Mohamed, 2009): (1) Inexistence on an interface between the mixing fluids; (2)

Occurrence of zero IFT between the mixing fluids; (3) All fluid mixtures mix in all proportions

while existing in a single indistinguishable phase.

2.2. Miscible flooding

This is a branch of enhanced oil recovery (EOR) where miscible gases are injected into the

reservoir. These gases maintain the reservoir pressure as well as improve the recovery of the

reservoir fluid due to the reduction in IFT between the injected fluid and the reservoir fluid

(Schlumberger Limited, 2013). Many miscible gasses could be injected into the reservoir to

achieve the same outcome. The choice of the gas would depend on the cost and its availability. A

few gases that are currently being used are liquefied petroleum gas (LPG) such as methane and

propane, light hydrocarbon, nitrogen and carbon dioxide. Carbon dioxide is the most widely used

gas for miscible flooding because it reduces oil viscosity and is less expensive when compared to

LPG (Schlumberger, 2013).

5

2.3. Carbon dioxide flooding

Carbon dioxide has been used in oil recovery since 1952 (Stalkup, 1978). Carbon dioxide can be

used for miscible displacement (Rathmel et al., 1971), immiscible displacement (Kumar & Von

Gonten, 1973), reservoir pressure maintenance (Holm & Josendal, 1974), well stimulation

(Stright Jr., Aziz, & Settari, 1977), etc.

2.3.1. Properties of carbon dioxide

Carbon dioxide is a relatively non-toxic, non-flammable fluid (Mohamed, 2009). It has a critical

temperature and pressure of 30.9782 0C and 7.3773 MPa respectively; its triple point is -56.558

0C and 517.15 MPa (Span & Wagner, 1994). Figure 2.1 illustrates the pressure-temperature

property of carbon dioxide. It can be seen that carbon dioxide would exist in different phases

depending on its temperature and pressure.

Figure 2.1: Pure carbon dioxide phase diagram (Zhang et al., 2012)

6

Figure 2.2 show the variation in density with pressure at 600C. It can also be seen from Figure

2.2 that pressure has a large impact on density. Figure 2.2 was plotted using data from the peace

software thermodynamic data (Peace Software) and the correlation proposed by Ouyang

(Ouyang, 2011).

Figure 2.2: Carbon dioxide density as a function of pressure at 60

0C (Peace software;

Ouyang, 2011)

2.4. Nitrogen flooding

Nitrogen flooding has been used in EOR successfully for a long time in the oil industry (Koch &

Hutchinson, 1958; Hudgins et al., 1990). It has also been used for other purposes such as gas lift,

pressure maintenance and gas cycling (Clancy et al., 1985). Nitrogen is used as an alternative to

natural gas and carbon dioxide due to its low cost and non corrosive nature and since it can be

0

0.2

0.4

0.6

0.8

1

1.2

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

de

nsi

ty (

g/cm

3 )

Pressure (psia)

Density (kg/m3) at 60 degrees

7

extracted from atmospheric air via cryogenic processes, its source is largely unlimited (Lindley,

2011).

Nitrogen miscibility is favored in reservoirs that are rich in light and intermediate hydrocarbon

components at a high reservoir pressure (Hudgins et al., 1990). Due to the high injection pressure

that nitrogen flooding requires, the reservoir should be able to withstand this high pressure

without fracturing the formation (Lindley, 2011).

2.4.1. Nitrogen properties

Nitrogen is a nontoxic, non-flammable gas at atmospheric conditions. It has a critical

temperature of -147 °C and a critical pressure of 3.3999 MPa and critical density of 314.03

kg/m3. Its triple point is at -210.1 °C and 0.01253 MPa. Nitrogen makes up at least 78% of

atmospheric air by volume (Air Liquide, 2013).

2.5. Miscible flooding mechanism

Miscible gases displace reservoir fluid in very similar ways. Lindley (2011) explained that the

injected gas forms a miscible front by vaporizing light components of reservoir oil. The enriched

gas then moves away from the injection well into the reservoir, where it further enriches itself by

contacting with reservoir oil and vaporizing more light components. This enrichment process

continues until the gas becomes miscible with the reservoir fluid and a homogenous phase with

new physicochemical properties is formed. Continuous injection of the gas would push oil via

the miscible front towards the production well. The produced reservoir fluid can be separated for

oil, natural gas and the injected gas (Lindley, 2011).

8

2.6. Interfacial tension

Interfacial tension, commonly expressed in mN/m or dyne/cm, is a property of the interface that

exists between two immiscible phases. It is referred to as interfacial tension when both phases

are liquid and it is called surface tension when one of the phases is atmospheric air. However,

they both refer to the Gibbs free energy present per unit interface area at a particular temperature

and pressure (Schlumberger, 2013).

2.7. Minimum miscibility pressure

The minimum miscibility pressure (MMP) is defined by Johnson and Pollin as the lowest

pressure at which an apparent point of maximum curvature can be seen as recovery of oil at

1.2PV gas injected is plotted against pressure (Johnson & Pollin, 1981). It can also be defined

as the minimum pressure whereby the injected gas phase becomes miscible with the residual oil

in place (ROIP) after a multi-contact process at the existing reservoir temperature. (Stalkup,

1987). MMP is dependent on factors such as the composition of the injected gas, the ROIP and

the reservoir temperature and independent of the velocity of displacement and the condition of

the porous media (Alomair et al, 2011)

9

2.8. Experimental methods for determining minimum miscibility

pressure

A number of experimental methods have been developed to measure MMP. Traditionally, the

slim tube method is considered as the standard technique for MMP measurement in an

oil/solvent system (Huang & Dyer, 1993). This method reproduces the multiphase fluid flow

through a porous medium under reservoir conditions. It is however very expensive and time

consuming (Gu et al., 2013). High pressure carbon dioxide core flood tests can also be used to

measure MMP in a similar fashion as the slim tube method (Huang, 1992).

The expensive and time consuming nature of the above methods led to the development of more

favorable methods that are faster and more cost effective such as the rising-bubble apparatus

(RBA) (Christiansen & Haines, 1987). The use of the RBA to determine MMP is faster and

requires less crude compared to the slim tube method and the core flooding approach; however,

this method could overestimate MMP for some systems (Gu et al., 2013).

The VIT, which is the technique used in this study, has recently been used to measure MMP

(Rao D. N., 1997; Rao & Lee, 2002; Rao & Lee, 2003;Gu et al., 2013). The IFT between crude

oil and carbon dioxde can be accurately measured using ADSA and the MMP can be

extrapolated from IFT data at reservoir conditions.

10

2.9. Crude oil density

There are a number of correlations that can be used to estimate crude oil density. However, in

this work, the use of correlations was not feasible due to the large amount of data needed by the

correlations. Hence the measurement of crude oil density was carried out in the laboratory using

a pycnometer (purchased from VWR International) according to ASTM standard D1217 – 12.

11

CHAPTER 3 EXPERIMENTAL

3.1. The theory behind the pendant drop technique

The pendant drop technique uses axisymmetric drop shape analysis (ADSA) to determine

interfacial properties through ascertaining the profile of the liquid droplets formed. This

experimental profile is then fitted with the theoretical Laplace equation reported by Cheng,

(1990). Hydrodynamic equilibrium is a requirement for this technique, i.e. the only forces acting

on the drop should be gravity and surface tension (Neumann & Rio, 1997). Figure 3.1 below

shows the schematic of a pendant drop.

Figure 3.1: Schematic of a pendant drop (Mohammed, 2009)

12

Chiquet et al, (2007) reported that Cheng’s equation can be represented by the following

ordinary differential equations with an arc length of s:

(17)

(18)

(19)

R0

2R0 +

(20)

Where:

θ = angle between the horizontal and the tangent to the drop contour

B0 = Bond number which represents the ratio of buoyancy force to surface force (dimensionless)

r = characteristic radius (m)

= The difference in density of the two phases (kg/m3)

g = Gravitational acceleration

R0 = radius at the apex of the drop (m)

13

The ADSA determines B0 and values that minimizes the difference between the solution to

equation 20 and the digital profile of the drop. Hence, the capillary length ‘a’ is determined.

Capillary length can be expressed as:

√

√

√

(21)

The IFT can therefore be determined by solving equation 21 after the difference in density

between the two phases has been obtained. Hence:

IFT( ) =

(22)

3.2. Apparatus

The high pressure pendant drop apparatus (PD-E 1700) and the drop shape analysis (DSA 100

V1.90.0.14) are used to measure the equilibrium and dynamic IFTs of crude oil/carbon dioxide

systems at different temperatures and pressures. The PD-E 1700 was made by

EUROTECHNICA and the DSA 100V1. 90.0.14 was made by K ̈SS. The equipment is shown

in Figure 3.2.

14

Figure 3.2: Drop shape analysis (DSA 100 v 1.9) and high pressure pendant drop (PD-E 1700)

The major components of the PD-E 1700 are a high temperature and pressure cell with two

windows. 200 0C and 69 MPa are the maximum operating temperature and pressure. The DSA

100 (V1.90.0.14) consists of a light source and a high resolution CCD camera. The high pressure

cell is placed between the camera and the light source to enable illumination through the two

windows.

The IFT is determined by analyzing the shape of a pendant drop and this is considered as the

most powerful method of measuring interfacial properties because of its versatility, accuracy and

simplicity (Cheng & Neumann, 1992; Jennings & Pallas, 1988). The pendant crude oil drop is

formed within the carbon dioxide phase using a needle installed at the top of the high pressure

cell. A digital image of this drop is acquired using a digital image acquisition system.

15

This image is then fitted with the Laplace equation of capillarity and the IFT is automatically

calculated by generating an interfacial profile that best fits the actual drop. Figure 3.3 shows a

schematic of the process.

Figure 3.3: Schematic of the axisymmetric drop shape analysis (ADSA) adapted from

(Hoorfar & Neumann, 2006)

Numerical Optimization

Physical Properties

(ρ,g)

Image Analysis

Image

(

)

Interfacial tension

16

3.3. Accuracy and reproducibility

The accuracy of the pendant drop equipment was tested by calibrating with the measurement of

the IFT of deionised pure water /atmospheric air system until the typical value of 70.26 mN/m

was obtained.The calibration data are shown in Table 3.1 below . The standard deviation of the

data was calculated as 0.310289.

Table 3.1 : Calibration data

IFT [mN/

m]

Theta(L)[deg]

Theta(R)[deg]

Theta(M)[deg]

Vol [µl]

Area [mm*2]

BD [mm]

Fit-Er [um]

Method MAG

[pix/mm] Density

70.13 108.4 108.4 108.4 24.18 39.58 1.619 3.43 L-Y 82.06 0.9968

70.71 100.8 100.8 100.8 25.34 41.48 1.533 3.86 L-Y 82.01 0.9968

70.33 107.4 107.4 107.4 24.43 39.95 1.604 3.49 L-Y 82.02 0.9968

70.17 107.1 107.1 107.1 24.45 39.99 1.604 3.61 L-Y 82.04 0.9968

70.2 107 107 107 24.46 40.01 1.603 3.5 L-Y 82.01 0.9968

69.83 106.5 106.5 106.5 24.43 40.02 1.596 3.71 L-Y 82.04 0.9968

69.88 106.3 106.3 106.3 24.47 40.06 1.596 3.67 L-Y 82.01 0.9968

70.28 107 107 107 24.47 40.02 1.6 3.43 L-Y 82.03 0.9968

70.16 106.9 106.9 106.9 24.45 39.99 1.601 3.54 L-Y 82.03 0.9968

70.06 106.7 106.7 106.7 24.46 40.03 1.599 3.52 L-Y 82.05 0.9968

70.03 106.6 106.6 106.6 24.45 40.02 1.597 3.58 L-Y 82.04 0.9968

70.18 106.1 106.1 106.1 24.67 40.31 1.596 3.5 L-Y 81.99 0.9968

70.08 105.8 105.8 105.8 24.66 40.34 1.592 3.3 L-Y 81.99 0.9968

70.08 105.7 105.7 105.7 24.67 40.35 1.59 3.52 L-Y 81.96 0.9968

70.04 105.6 105.6 105.6 24.67 40.34 1.59 3.42 L-Y 81.97 0.9968

69.99 105.5 105.5 105.5 24.68 40.39 1.589 3.27 L-Y 81.96 0.9968

70.01 105.5 105.5 105.5 24.64 40.31 1.587 3.63 L-Y 81.97 0.9968

69.9 105.5 105.5 105.5 24.58 40.24 1.585 3.5 L-Y 82.01 0.9968

69.88 105.4 105.4 105.4 24.65 40.34 1.588 3.29 L-Y 81.99 0.9968

69.93 105.4 105.4 105.4 24.68 40.38 1.588 3.39 L-Y 81.96 0.9968

70.52 107.6 107.6 107.6 24.47 39.96 1.608 3.61 L-Y 82.02 0.9968

70.56 107.6 107.6 107.6 24.5 40 1.61 3.72 L-Y 82.03 0.9968

70.5 107.5 107.5 107.5 24.46 39.95 1.607 3.77 L-Y 82.04 0.9968

70.74 104.7 104.7 104.7 25.04 40.83 1.577 3.37 L-Y 82 0.9968

70.79 104.7 104.7 104.7 25.02 40.82 1.575 3.59 L-Y 81.99 0.9968

70.71 104.7 104.7 104.7 25.02 40.81 1.577 3.54 L-Y 82.01 0.9968

70.71 104.6 104.6 104.6 25.07 40.9 1.578 3.45 L-Y 82.01 0.9968

70.67 104.6 104.6 104.6 25.03 40.86 1.576 3.47 L-Y 82.02 0.9968

70.56 104.3 104.3 104.3 25 40.82 1.571 3.46 L-Y 82.05 0.9968

70.26

24.66 40.31 1.590

17

3.4. Materials

Three crude oil samples were used in this study: Arab AH-50, Gullfaks C and west Texas

intermediate. Carbon dioxide (99.5% purity) and nitrogen (99.995% purity) were purchased from

Praxair and were used without further purification. Carbon dioxide’s critical temperature and

pressure are 30.95oC and 7.38MPa. Nitrogen’s critical temperature and pressure are -240

oC and

1.30MPa.

3.5. Requirement of the drop shape analysis

The drop shape analysis software used (DSA 1.90.0.14) requires the capillary needle diameter,

the local gravitational acceleration, and the density difference between the liquid (crude oil) and

gas phase (CO2/N2).

3.5.1. Crude oil density measurement

In this work, the use of correlations was not feasible due to the large amount of data needed by

the correlation. Hence the measurement of crude oil density was carried out in the laboratory

using a Pycnometer (purchased from VWR International) according to ASTM standard D1217 –

12.

18

Table 3.2 shows the calculated density data.

Table 3.2. : Crude oil density data

Crude Oil Temperature Density (g/cm3)

Gullfaks C 22oC 0.873

Arab AH-50 22oC 0.911

West texas intermediate 22oC 0.903

Gullfaks C 60oC 0.837

3.5.2. Carbon dioxide Density

There are numerous correlations that have been generated to estimate carbon dioxide density.

However the most popular data for carbon dioxide density are does published by Span and

Wagner in 2004. Hence carbon dioxide density data at the pressure and temperature conditions

of interest i.e., 100-600 psia and 220C and 60

0C were calculated by using peace software. These

data were validated and compared with data presented by Span & Wagner, (1994) obtained from

the National Institute of Standards and Technology (NIST) website. The average density of

carbon dioxide decreases with increasing temperature and increases with pressure.

19

Table 3.3: Carbon dioxide density data

Density (g/cm3)

Temperature (0C)

Pressure (psia)

220C 60

0C

100 0.0129 0.0113

200 0.0271 0.0232

300 0.0421 0.0355

400 0.0593 0.0488

500 0.0791 0.0630

600 0.1016 0.0780

Figure 3.4 shows that the change in density of the Gullfaks C crude with temperature is more

obvious as pressure increases.

20

Figure 3.4: Variation of carbon dioxide density with temperature

3.5.3 Nitrogen Density

Nitrogen density at the pressure and temperature conditions of interest i.e., 100-600 psia and

220C were calculated by using peace software. This data was compared and validated with data

presented by Span et al., (2000) obtained from the National Institute of Standards and

Technology (NIST) website. The average density of nitrogen increases with increasing pressure.

The nitrogen densities were calculated using the ideal gas law as the as the error due to

compressibility at the highest pressure of 600 psia is 2.5 percent.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 100 200 300 400 500 600

De

nsi

ty (

g/cm

3)

Pressure (psia)

22 Degrees 60 degrees

21

Table 3.4: Variation of nitrogen density with pressure

Density

(g/cm3)

Temperature (0C)

Pressure (psia)

220C

100 0.0079

200 0.0158

300 0.0237

400 0.0317

500 0.0396

600 0.0475

Figure 3.5: Variation of nitrogen density with pressure at 22 0C

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 100 200 300 400 500 600 700

De

nsi

ty (

g/cm

3 )

Pressure (psia)

22

3.6 DSA Measurement

Figure 3.6: Flow sheet of the PD-E1700 (EUROTECHNICA, 2008)

The schematic of the pendant drop apparatus is shown in Figure 3.6. The equipment was first

calibrated using deionized water and atmospheric air until a satisfactory value of 70.26 mN/m

was obtained. The view cell was then filled with gas (CO2 or N2) until the predetermined

pressure was reached using the screw pump on the gas cylinder. About ten minutes was allowed

for the pressure in the chamber to stabilize. Finally, crude oil was then added to the liquid supply

tank (TL1) with valve A shut. Valve B was then shut and valve A opened. The screw piston

pump (PG1) was then operated anti-clockwise to suck the crude oil into the cylinder. Once the

cylinder was full, PG1 was operated clockwise with valve A open to allow some crude into TL1

and allow trapped air bubbles to be released. Valves A and B were then closed and valve C

opened. PG1 was operated clockwise again till a small amount of crude oil was released into a

glass beaker. Valve C was then closed and valve B slowly opened while PG1 was operated

clockwise till crude oil emerged at the capillary. After the crude oil pendant drop was formed in

the gas phase, a digital image of each drop was taken and stored on the computer hard drive. The

23

DSA software determined the IFT and other output parameters which were also stored on the

computer hard drive.

The IFT of each crude oil drop was measured and the drops were replaced five times as old drops

were withdrawn from the capillary and new drops were created to ensure repeatability and

accuracy of the data. The measurements were done within five to ten seconds of contact with the

gas phase. At the end and the beginning of each test, the entire system was cleaned by flushing it

with methanol three times and drying with compressed air. IFT measurements were taken for the

three crude samples at 22oC degrees and six pressures ranging from 100-600 psi. The first

contact miscibility pressure of the Gullfak C sample was measured by measuring IFT at an

assumed average temperature of 600C and three pressures ranging from 100-300 psi. The

summary of data collected is shown in Tables 4.1 to 4.7.

24

CHAPTER 4 RESULTS AND DISCUSSION

Interfacial tension was measured for the Gulffaks C, Arab AH-50 and West Texas intermediate

dead crude oil samples using carbon dioxide and nitrogen gas over a pressure of 100 to 600 psia

and 220C and IFT was also taken for the Gullfaks C dead crude at an assumed reservoir

temperature of 600C and over a pressure of 100 to 300 psia.

The DSA results are presented in Tables 4.1 to 4.7 below. These tables contain analyzed

parameters which include interfacial tension [MN/m], pendant drop volume [µl] and pendant

drop surface area [mm*2]. Other parameters also present in the tables that were not considered

includes the pendant drop left, right and middle contact angles (Theta (L,R,M ) [deg]), the drop

base diameter [mm], the fit error [µm], the method L-Y and the magnification factor [pix/mm].

Interfacial tension, pendant drop volume and drop surface area measurements were plotted

against pressure ranging from 100 to 600 Psi and at 22oC. The Gullfaks C crude sample’s

interfacial tension, pendant drop volume and pendant drop surface area measurements using

carbon dioxide gas was also plotted against pressures of 100, 200 and 300 Psi at 60oC. The DSA

measurement for this is shown in Table 4.7. Tables 4.1 to 4.3 shows the measurement data for

the three crude oil samples using carbon dioxide at 220C while Table 4.4 to 4.6 shows the

measurement data using nitrogen also at 220C.

Figures 4.1 to 4.3 shows the variation of the three crude sample’s pendant drop volume with

pressure using carbon dioxide, Figures 4.4 to 4.6 shows the variation in the pendant drop surface

area with pressure using carbon dioxide and Figures 4.7, 4.8 and 4.9 shows the variation of

interfacial tension with pressure using carbon dioxide. All of these tests were carried out at an

experimental temperature of 220C.

25

Figures 4.10 to 4.12 shows the variation of the three crude sample’s pendant drop volume with

pressure using nitrogen, Figures 4.13 to 4.15 shows the variation in the pendant drop surface area

with pressure using nitrogen and Figures 4.16, 4.17 and 4.18 shows the variation of interfacial

tension with pressure using nitrogen. All of these tests were carried out at an experimental

temperature of 220C.

DSA measurement was also carried out at an assumed reservoir temperature of 600C for the

Gullfaks C crude sample using carbon dioxide over a pressure ranging from 100 to 300 psia. Table

4.7 shows these DSA measurements and Figure 4.19 shows the variation of interfacial tension with

pressure while Figure 4.20 shows the variation of interfacial tension with temperature.

26

4.1. Crude oil and carbon dioxide systems at 220C

Table 4.1: DSA measurement for Arab AH-50 using carbon dioxide

100 Psi , 220C

Drop

No.

IFT

[mN/m] Theta(L)[deg] Theta(R)[deg] Theta(M)[deg]

Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 22.37 88.6 88.6 88.7 9.2 20.81 1.56 1.55 L-Y 112.25

2 22.47 88.4 88.4 884 9.27 20.92 1.561 1.5 L-Y 112.01

3 22.31 89.4 89.4 89.4 9.16 20.68 1.57 1.52 L-Y 112.3

4 22.44 96 96 96 8.98 19.97 1.617 1.28 L-Y 111.6

5 22.48 90.3 90.3 90.3 9.23 20.74 1.566 1.52 L-Y 111.61

Average 22.41 9.17 20.62 1.574

200 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 21.1 90.8 90.8 90.8 8.93 20.14 1.591 1.36 L-Y 110.29

2 21.23 82.1 82.1 82.1 9.22 21.13 1.579 1.69 L-Y 110.15

3 21.31 93 93 93 8.95 20.03 1.611 1.17 L-Y 109.67

4 21.06 95.4 95.4 95.4 8.95 20.03 1.611 0.99 L-Y 110.21

5 21.27 88.6 88.6 88.6 9.1 20.56 1.587 1.57 L-Y 109.85

Average 21.19 9.03 20.39 1.596

300 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 19.2 91 91 91 8.17 18.89 1.586 0.8 L-Y 110.93

2 19.26 94.3 94.3 94.3 8.04 18.45 1.589 0.87 L-Y 110.72

3 19.4 94.9 94.9 94.9 8.09 18.51 1.614 0.81 L-Y 110.23

4 19.18 89.9 89.9 89.9 8.18 18.99 1.573 0.84 L-Y 111

5 19.35 91.3 91.3 91.3 8.22 18.95 1.587 0.89 L-Y 110.53

Average 19.28 8.14 18.76 1.59

400 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 17.15 88.9 88.9 88.9 7.5 17.85 1.583 0.751 L-Y 110.733

2 17.28 96.1 96.1 96.1 7.22 16.94 1.631 0.871 L-Y 110.086

3 16.98 89 89 89 7.39 17.66 1.579 0.844 L-Y 111.234

4 17.12 90.1 90.1 90.1 7.46 17.7 1.59 0.772 L-Y 110.664

5 17 86.4 86.4 86.4 7.47 17.95 1.569 0.895 L-Y 111.102

Average 17.11 7.41 17.62 1.59

500 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 14.39 91.81 91.81 91.81 6.22 15.42 1.581 1.063 L-Y 113.82

2 14.45 87.08 87.08 87.08 6.43 16.05 1.551 0.819 L-Y 113.57

3 14.53 96.24 96.24 96.24 6.02 14.81 1.603 0.935 L-Y 113.1

4 14.5 94.8 94.8 94.8 6.09 15.01 1.593 0.96 L-Y 113.17

5 14.46 84.68 84.68 84.68 6.5 16.3 1.546 0.704 L-Y 113.49

Average 14.47 6.25 15.52 1.575

600 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 12.38 85.1 85.1 85.1 5.68 14.74 1.549 0.62 L-Y 112.955

2 12.37 88.82 88.82 88.82 5.56 14.33 1.555 0.74 L-Y 112.982

3 12.34 93.26 93.26 93.26 5.32 13.65 1.574 0.62 L-Y 112.824

4 12.31 89.77 89.77 89.77 5.48 14.14 1.553 0.67 L-Y 112.947

5 12.29 87.11 87.11 87.11 5.57 14.43 1.543 0.63 L-Y 112.973

Average 12.34 5.52 14.26 1.555

27

Table 4.2: DSA measurement of Gullfaks C using carbon dioxide

100 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 24.29 99.4 99.4 99.4 10.1 21.47 1.665 1.067 L-Y 111.345

2 24.25 102.3 102.3 102.3 9.82 20.78 1.719 1.011 L-Y 111.447

3 24.26 97.55 97.55 97.55 10.21 21.78 1.635 0.98 L-Y 111.335

4 24.25 100.66 100.66 100.66 9.98 21.17 1.691 1.052 L-Y 111.401

5

Average 24.26 10.03 21.3 1.678

200 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 22.52 96.11 96.11 96.11 9.66 21.03 1.614 0.895 L-Y 111.022

2 22.61 100.77 100.77 100.77 9.37 20.22 1.686 0.945 L-Y 111.065

3 22.54 95.34 95.34 95.34 9.73 21.18 1.616 1.012 L-Y 111.146

4 22.6 99.91 99.91 99.91 9.45 20.4 1.671 1.027 L-Y 111.079

5 22.56 97.32 97.32 97.32 9.62 20.87 1.634 0.987 L-Y 111.123

Average 22.57 9.57 20.74 1.644

300 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 20.51 94.2 94.2 94.2 9 20.09 1.603 1.303 L-Y 110.837

2 20.54 98.2 98.2 98.2 8.79 19.46 1.645 1.331 L-Y 110.84

3 20.57 99.14 99.14 99.14 8.72 19.29 1.661 1.524 L-Y 110.825

4 20.49 96.25 96.25 96.25 8.88 19.76 1.622 1.249 L-Y 110.893

5 20.53 98.05 98.05 98.05 8.77 19.46 1.641 1.364 L-Y 110.892

Average 20.51 8.83 19.61 1.634

400 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 18.25 91.53 91.53 91.53 8.32 19.09 1.597 1.225 L-Y 110.751

2 18.23 94.13 94.13 94.13 8.19 18.7 1.619 1.519 L-Y 110.647

3 18.03 90.06 90.06 90.06 8.24 19.05 1.586 1.909 L-Y 111.009

4 18.03 89.32 89.32 89.32 8.27 19.14 1.584 1.994 L-Y 110.791

5 18.02 93.4 93.4 93.4 8.1 18.61 1.607 1.545 L-Y 110.807

Average 18.11 8.22 18.92 1.599

500 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 15.7 90.78 90.78 90.78 7.31 17.39 1.595 1.028 L-Y 110.833

2 15.69 91.35 91.35 91.35 7.29 17.31 1.596 1.123 L-Y 110.813

3 15.68 94.01 94.01 94.01 7.14 16.9 1.611 1.202 L-Y 110.772

4 15.7 92.34 92.34 92.34 7.24 17.18 1.601 1.182 L-Y 110.758

5 15.72 97.07 97.07 97.07 6.92 16.36 1.634 1.088 L-Y 110.747

Average 17.7 7.18 17.03 1.607

600 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 13.35 88.82 88.82 88.82 6.45 15.92 1.587 1.226 L-Y 110.144

2 13.34 85.74 85.74 85.74 6.56 16.28 1.58 1.367 L-Y 110.072

3 13.36 84.29 84.29 84.29 6.61 16.45 1.579 1.46 L-Y 109.963

4 13.37 89.28 89.28 89.28 6.46 15.91 1.591 1.205 L-Y 109.74

5 13.39 86.03 86.03 86.03 6.61 16.33 1.588 1.241 L-Y 109.603

Average 13.36 6.54 16.18 1.585

28

Table 4.3: DSA measurement of West Texas Intermediate using carbon dioxide

100 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 24.89 100.43 100.43 100.43 9.92 21.1 1.665 2.448 L-Y 110.352

2 24.95 99.52 99.52 99.52 10.03 21.46 1.623 2.226 L-Y 110.30676

3 24.88 98.62 98.62 98.62 10.08 21.69 1.605 2.018 L-Y 110.33715

4 24.92 96.46 96.46 96.46 10.25 22.15 1.582 1.928 L-Y 110.33981

5 24.93 94.67 94.67 94.67 10.32 22.25 1.582 2.011 L-Y 110.67834

Average 24.91 10.12 21.73 1.6114

200 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 22.91 100.85 100.85 100.85 9.04 19.73 1.657 0.99 L-Y 111.264

2 22.9 101.67 101.67 101.67 8.95 19.52 1.672 1 L-Y 111.337

3 22.73 99.76 99.76 99.76 9.04 19.82 1.643 0.946 L-Y 111.726

4 22.94 102.19 102.19 102.19 8.92 19.43 1.689 0.941 L-Y 111.195

5 22.85 98.66 98.66 98.66 9.17 20.12 1.622 0.911 L-Y 111.447

Average 22.87 9.02 19.72 2

300 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 20.82 95.2 95.2 95.2 8.57 19.41 1.572 0.751 L-Y 110.197

2 20.91 97.98 97.98 97.98 8.52 19.11 1.618 0.804 L-Y 109.873

3 21.01 99.19 99.19 99.19 8.5 18.96 1.64 0.774 L-Y 109.587

4 20.95 99.24 99.24 99.24 8.47 18.92 1.651 0.763 L-Y 109.756

5 20.84 97.37 97.37 97.37 8.5 19.13 1.5959 0.683 110.179

Average 20.91 8.51 19.11 1.615

400 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 18.62 89.08 89.08 89.08 8.04 18.87 1.545 0.654 L-Y 110.067

2 18.58 90.86 90.86 90.86 7.98 18.65 1.568 0.595 L-Y 110.148

3 18.66 95.19 95.19 95.19 7.88 18.19 1.597 0.619 L-Y 109.765

4 18.67 96.78 96.78 96.78 7.81 17.95 1.617 0.759 L-Y 109.653

5 18.59 90.01 90.01 90.01 8.03 18.78 1.549 0.581 L-Y 110.059

Average 18.62 7.95 18.49 1.575

500 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 16.31 96.71 96.71 96.71 6.91 16.39 1.614 1.182 L-Y 109.284

2 16.38 93.61 93.61 93.61 7.13 16.97 1.591 1.215 L-Y 109.309

3 16.28 94.12 94.12 94.12 7.05 16.79 1.588 1.103 L-Y 109.463

4 16.3 93.41 93.41 93.41 7.05 16.86 1.58 0.889 L-Y 109.967

5 16.28 91.79 91.79 91.79 7.1 17.06 1.566 0.846 L-Y 110.111

Average 16.31 7.05 16.81 1.589

600 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 14.5 96.18 96.18 96.18 5.96 14.79 1.581 0.776 L-Y 109.715

2 14.62 98.46 98.46 98.46 5.88 14.47 1.632 0.992 L-Y 109.06

3 14.66 99.92 99.92 99.92 5.77 14.11 1.665 1.25 L-Y 108.785

4 14.62 97.61 97.61 97.61 5.97 14.66 1.611 1.01 L-Y 108.955

5 14.59 96.34 96.34 96.34 6.03 14.88 1.6 0.925 L-Y 109.285

Average 14.6 5.92 14.58 1.618

29

Figure 4.1: Variation Arab AH-50 drop volume with pressure using carbon dioxide at 22 0C

Figure 4.2: Variation of Gullfaks C drop volume with pressure using carbon dioxide at 22 0C

y = -0.0078x + 10.319 R² = 0.9706

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700

Vo

l [µ

l]

Pressure (psia)

Arab AH-50

Linear (Arab AH-50)

y = -0.0072x + 10.918 R² = 0.9894

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700

Vo

l [µ

l]

Pressure (psia)

Gullfaks C

Linear (Gullfaks C)

30

Figure 4.3: Variation of West Texas intermediate drop volume with pressure using carbon dioxide at 22 0C

The DSA measurements for the three crude oil samples using carbon dioxide gas are shown in

Tables 4.1 to 4.3. All the pendant drops formed for this study formed from the outer surface of the

capillary needle. Figures 4.1 to 4.3 above show that the pendant drop volume reduces in a linear

fashion as pressure increases. The volume of the first crude oil sample, the Arab AH-50 reduced

from 9.17µl to 5.52µl, that of the Gullfaks C sample reduced from 10.03µl to 6.54µl and the West

Texas intermediate sample’s pendant drop volume reduced from 10.12µl to 5.92µl .This occurred

due to increase in the force exerted by the carbon dioxide gas on the pendant drop. This same

phenomena explains the decrease in the pendant drop surface area as volume is directly

proportional to surface area. It can be seen that the change in volume of the three different crude

samples is approximately the same.

y = -0.0078x + 10.842 R² = 0.9825

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700

Vo

l [µ

l]

Pressure (psia)

West texas intermediate

Linear (West texas intermediate)

31

Figure 4.4: Variation Arab AH-50 drop surface area with pressure using carbon dioxide at 22 0C

Figure 4.5: Variation of Gullfaks C drop surface area with pressure using carbon dioxide at 22 0C

y = -0.0136x + 22.617 R² = 0.9693

0

5

10

15

20

25

0 100 200 300 400 500 600 700

Are

a [m

m*2

]

Pressure (psia)

Arab AH-50

Linear (Arab AH-50)

y = -0.0107x + 22.705 R² = 0.9748

0

5

10

15

20

25

0 100 200 300 400 500 600 700

Are

a [m

m*2

]

Pressure (psia)

Gullfaks C

Linear (Gullfaks C)

32

Figure 4.6: Variation of West Texas intermediate drop surface area with pressure using carbon

dioxide at 22 0C

The DSA measurements for the three crude oil samples using carbon dioxide gas are shown in

Tables 4.1 to 4.3. Figures 4.4 to 4.6 above show that the pendant drop surface area reduces in a

linear fashion as pressure increases. The pendant drop surface area of the first crude oil sample, the

Arab AH-50 reduced from 20.62 mm2

to 14.26 mm2, that of the Gullfaks C sample reduced from

21.3 mm2 to 16.18 mm

2 and the West Texas intermediate sample’s pendant drop surface area

reduced from 21.73 mm2 to 14.58 mm

2. This change in the pendant drop surface area can be

explained as due to the increased force exerted by the carbon dioxide gas on the pendant drop. It

can be seen that the change in the pendant drop surface area for the three different crude samples is

approximately the same.

y = -0.0129x + 22.917 R² = 0.9538

0

5

10

15

20

25

0 100 200 300 400 500 600 700

Are

a [m

m*2

]

Pressure (psia)

West texasintermediateLinear (West texasintermediate)

33

.

Figure 4.7: Variation of Arab AH-50 interfacial tension with pressure using carbon dioxide at 22 0C

Figure 4.8: Variation of Gullfaks C interfacial tension with pressure using carbon dioxide at 22 0C

y = -0.0208x + 25.073 R² = 0.9885

0

5

10

15

20

25

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (psia)

Arab AH-50

Linear (Arab AH-50)

y = -0.0222x + 26.849 R² = 0.9962

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (psia)

Gullfaks C

Linear (Gullfaks C)

34

Figure 4.9: Variation of West Texas intermediate interfacial tension with pressure using carbon

dioxide at 22 0C

The DSA measurements for the three crude oil samples using carbon dioxide gas at 220C are

shown in Tables 4.1 to 4.3. Figures 4.7 to 4.9 above show that the pendant drop IFT reduces as

pressure increases in a linear fashion. The IFT of the first crude oil sample, the Arab AH-50

reduced from 22.41 mN/m to 12.34 mN/m, that of the Gullfaks C sample reduced from 24.26

mN/m to 13.36 mN/m and the West Texas intermediate sample’s IFT reduced from 24.91 mN/m to

14.6 mN/m. It can be seen that the change in IFT for the three different crude samples over the

same pressure range is approximately the same.

Solving the trendline equations of the three crude oil samples for zero IFT yields a first contact

miscibility pressure of 1205 psia for the Arab AH-50, 1214 psia for the Gullfaks C sample and

1288 psia for the West Texas intermediate sample.

y = -0.021x + 27.056 R² = 0.9984

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (psia)

West Texas Itermediate

Linear (West Texas Itermediate)

35

4.2. Crude oil and nitrogen systems at 220C

Table 4.4: DSA measurement of Arab AH-50 using nitrogen

100 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 24.21 91.17 91.17 91.17 10.62 22.62 1.608 0.665 L-Y 110.69

2 24.23 100.73 100.73 100.73 10.4 22.1 1.622 0.38 L-Y 111.75

3 23.98 99.4 99.4 99.4 10.99 23.51 1.603 0.367 L-Y 112.33

4 23.94 88.4 88.4 88.4 10.84 23.14 1.598 0.449 L-Y 112.4

5 24.28 90.29 90.29 90.29 10.97 22.52 1.592 0.34 L-Y 112.36

Average 24.13 10.76 22.99 1.605

200 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 23.82 92.1 92.1 92.1 9.72 21.45 1.572 1.51 L-Y 113.197

2 23.91 93.37 93.37 93.37 9.74 21.39 1.577 1.511 L-Y 112.996

3 23.95 89.31 89.31 89.31 9.8 21.76 1.537 1.629 L-Y 112.845

4 23.88 89.53 89.53 89.53 9.77 21.72 1.55 1.506 L-Y 112.99

5 23.96 91.86 91.86 91.86 9.77 21.56 1.55 1.49 112.7173

Average 23.9 9.76 21.58 2

300 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 23.1 90.76 90.76 90.76 9.58 21.29 1.558 3.008 L-Y 111.731

2 23.15 89.23 89.23 89.23 9.62 21.46 1.549 2.57 L-Y 111.699

3 23.19 91.37 91.37 91.37 9.61 21.29 1.581 2.793 L-Y 111.627

4 23.06 88.06 88.06 88.06 9.59 21.49 1.544 2.4 L-Y 112.102

5 23.13 89.456 89.456 89.456 9.62 21.43 1.553 2.386 L-Y 111.9082

Average 23.13 9.6 21.39 1.557

400 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 22.6 90.43 90.43 90.43 9.5 21.17 1.562 3.43 L-Y 111.767

2 22.5 88.91 88.91 88.91 9.51 21.27 1.557 3.086 L-Y 112.101

3 22.57 86.58 86.58 86.58 9.56 21.51 1.55 2.678 L-Y 112.115

4 22.63 85.56 85.56 85.56 9.6 21.63 1.546 2.562 L-Y 112.02

5 22.61 84.64 84.64 84.64 9.58 21.66 1.54 2.511 L-Y 112.127

Average 22.58 9.55 21.45 1.55

500 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 22.16 87.41 87.41 87.41 9.49 21.33 1.551 2.873 L-Y 111.71

2 22.07 88.47 88.47 88.47 9.41 21.14 1.552 2.955 L-Y 112.026

3 22.21 85.61 85.61 85.61 9.51 21.49 1.547 2.511 L-Y 111.754

4 22.05 87.7 87.7 87.7 9.4 21.18 1.551 2.73 L-Y 112.215

5 22.1 84.95 84.95 84.95 9.45 21.43 1.542 2.397 L-Y 112.214

Average 22.12 9.45 21.31 1.55

600 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 21.56 90.58 90.58 90.58 9.17 20.65 1.557 3.14 L-Y 112.182

2 21.52 86.3 86.3 86.3 9.19 20.96 1.54 2.637 L-Y 112.47

3 21.5 86.67 86.67 86.67 9.19 20.92 1.541 2.656 L-Y 112.607

4 21.48 90.4 90.4 90.4 9.13 20.6 1.554 3.074 L-Y 112.555

5 21.63 85.61 85.61 85.61 9.25 21.1 1.532 2.512 L-Y 112.323

Average 21.54 9.19 20.85 1.545

36

Table 4.5: DSA measurement of Gullfaks C using nitrogen

100 Psi ,220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 24.09 96.15 96.15 96.15 10.12 21.77 1.619 2.898 L-Y 112.211

2 24.04 94.97 94.97 94.97 10.11 21.85 1.588 2.588 L-Y 112.489

3 24.2 92.25 92.25 92.25 10.3 22.33 1.577 1.97 L-Y 112.168

4 24.23 93.03 93.03 93.03 10.28 22.24 1.573 2.055 112.088

5 24.1 90.76 90.76 90.76 10.34 22.47 1.564 1.786 L-Y 112.328

Average 24.13 10.23 22.13 1.582

200 Psi , 220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 23.97 89.73 89.73 89.73 10.46 22.71 1.572 1.499 L-Y 111.486

2 23.96 89.625 89.625 89.625 10.44 22.68 1.571 1.4383

333 L-Y

111.4833333

3 23.96 90.54 90.54 90.54 10.4 22.57 1.572 1.479 L-Y 111.536

4 24 90.54 90.54 90.54 10.42 22.6 1.57 1.459 L-Y 111.498

5 23.93 89.17 89.17 89.17 10.43 22.71 1.565 1.452 L-Y 111.643

Average 23.96 10.43 22.65 2

300 Psi , 220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 23.73 95.12 95.12 95.12 10.15 21.91 1.595 1.735 L-Y 111.646

2 23.74 94.34 94.34 94.34 10.2 22.04 1.588 1.62 L-Y 111.607

3 23.61 88.98 88.98 88.98 10.33 22.58 1.557 1.701 L-Y 111.863

4 23.63 91.84 91.84 91.84 10.27 22.3 1.574 1.387 L-Y 111.821

5 23.65 90.1 90.1 90.1 10.34 22.52 1.562 1.686 L-Y 111.697

Average 23.67 10.26 22.27 1.575

400 Psi , 220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 23.22 89.83 89.83 89.83 10.32 22.48 1.576 2.367 L-Y 111.251

2 23.22 92.16 92.16 92.16 10.29 22.26 1.599 3.222 L-Y 110.915

3 22.89 83.27 83.27 83.27 10.37 22.95 1.572 1.732 L-Y 111.972

4 23.03 83.87 83.87 83.87 10.43 23 1.572 1.869 L-Y 111.644

5 23.15 84.58 84.58 84.58 10.47 23.02 1.569 1.959 L-Y 111.424

Average 23.1 10.38 22.74 1.578

500 Psi , 220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 22.78 90.69 90.69 90.69 10.21 22.24 1.578 2.525 L-Y 111.064

2 22.79 91.41 91.41 91.41 10.09 22.05 1.826 1.808 L-Y 111.044

3 22.7 92.87 92.87 92.87 10.01 21.83 1.583 2.099 L-Y 111.186

4 22.44 87.83 87.83 87.83 10 22.14 1.55 1.8 L-Y 111.858

5 22.45 86.82 86.82 86.82 10.04 22.26 1.551 1.9 L-Y 111.819

Average 22.63 10.07 22.1 1.618

600 Psi, 220C

Drop No. IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 22.29 91.74 91.74 91.74 10.02 21.89 1.586 2.672 L-Y 111.095

2 22.17 95.27 95.27 95.27 9.67 21.16 1.581 2.287 L-Y 111.353

3 22.25 89.99 89.99 89.99 10.02 22.02 1.567 2.376 L-Y 111.28

4 22.17 89.57 89.57 89.57 10.02 22.04 1.568 2.25 L-Y 111.453

5 22.26 89.92 89.92 89.92 10.05 22.05 1.568 2.376 L-Y 111.272

Average 22.23 9.96 21.83 1.574

37

Table 4.6: DSA measurement of West Texas intermediate using nitrogen

100 Psi ,220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 25.38 93.8 93.8 93.8 10.5 22.48 1.601 1.07 L-Y 110.66

2 25.59 91.2 91.2 91.2 10.74 23.01 1.606 1.1 L-Y 110.65

3 25.43 88.5 88.5 88.5 10.6 23.01 1.604 1.13 L-Y 112.71

4 25.59 92.3 92.3 92.3 10.56 22.71 1.585 1.06 L-Y 112.24

5 25.51 92.1 92.1 92.1 10.52 22.66 1.581 1.09 L-Y 112.42

Average 25.5 10.58 22.77 1.595

200 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 24.91 86.78 86.78 86.78 10.73 23.25 1.596 2.951 L-Y 111.88

2 24.83 89.24 89.24 89.24 10.53 22.83 1.584 2.914 L-Y 111.88

3 24.85 85.49 85.49 85.49 10.64 23.23 1.583 2.655 L-Y 111.88

4 24.87 87.08 87.08 87.08 10.58 23.04 1.578 2.788 L-Y 111.88

5 24.84 86.52 86.52 86.52 10.62 23.13 1.586 2.773 L-Y 111.88

Average 24.86 10.62 23.1 2

300 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 24.63 92.2 92.2 92.2 10.4 22.45 1.589 3.01 L-Y 111.88

2 24.64 92 92 92 10.41 22.48 1.587 3.01 L-Y 111.88

3 24.63 91.9 91.9 91.9 10.41 22.49 1.584 3.1 L-Y 111.88

4 24.64 90 90 90 10.5 22.76 1.579 3.2 L-Y 111.88

5 24.62 92.6 92.6 92.6 10.31 22.29 1.58 2.87 L-Y 111.88

Average 24.63 10.41 22.49 1.584

400 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 24.32 89.4 89.4 89.4 10.47 22.73 1.572 0.339 L-Y 113.068

2 24.36 88.7 88.7 88.7 10.5 22.83 1.569 0.382 L-Y 113.039

3 24.33 90.2 90.2 90.2 10.44 22.64 1.573 0.415 L-Y 113.106

4 24.28 89.7 89.7 89.7 10.42 22.66 1.571 0.327 L-Y 113.2456

5 24.35 90.2 90.2 90.2 10.42 22.62 1.572 0.322 L-Y 113.099

Average 24.33 10.45 22.7 1.571

500 Psi , 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 23.97 92.3 92.3 92.3 10.26 22.24 1.579 0.2988889 L-Y 112.85

2 23.9 93.3 93.3 93.3 10.18 22.07 1.584 0.406 L-Y 113.052

3 24.03 93.9 93.9 93.9 10.22 22.07 1.589 0.313 L-Y 112.739

4 23.99 91.2 91.2 91.2 10.31 22.39 1.573 0.2911111 L-Y 112.8533333

5 23.98 92.1 92.1 92.1 10.27 22.27 1.576 0.316 L-Y 112.852

Average 23.97 10.25 22.21 1.58

600 Psi, 220C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-Er

[µm] Method

MAG

[pix/mm]

1 23.74 95.7 95.7 95.7 10.11 21.78 1.609 0.375 L-Y 112.324

2 23.63 93.14 93.14 93.14 10.2 22.09 1.588 0.356 L-Y 112.591

3 23.59 91.39 91.39 91.39 10.26 22.28 1.579 0.571 L-Y 112.656

4 23.6 93.91 93.91 93.91 10.14 21.94 1.592 0.428 L-Y 112.621

5 23.66 96.32 96.32 96.32 10.03 21.62 1.609 0.374 L-Y 112.448

Average 23.64 10.15 21.94 1.595

38

Figure 4.10: Variation of Arab AH-50 drop volume with pressure using nitrogen at 22 0C

Figure 4.11: Variation of Gullfaks C drop volume with pressure using nitrogen at 220C

y = -0.0013x + 10.016 R² = 0.9444

9.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

0 100 200 300 400 500 600 700

Vo

l [µ

l]

Pressure (psia)

Arab AH-50

Linear (Arab AH-50)

y = -0.0016x + 10.58 R² = 0.9892

9.9

10

10.1

10.2

10.3

10.4

10.5

0 100 200 300 400 500

Vo

l[µ

l]

Pressure (psia)

Gulfaks C

Linear (Gulfaks C)

39

Figure 4.12: Variation of West Texas intermediate drop volume with pressure using nitrogen at 220C

The DSA measurements for the three crude oil samples using nitrogen gas are shown in Tables 4.4

to 4.6 . All the pendant drops formed for this study using nitrogen formed from the outer surface of

the capillary needle. Figures 4.10 to 4.12 above show that the pendant drop volume reduces in a

linear fashion as pressure increases. The volume of the first crude oil sample, the Arab AH-50

reduced from 10.8µl to 9.19µl, that of the Gullfaks C sample reduced from 10.23µl to 9.96µl and

the West Texas intermediate sample’s pendant drop volume reduced from 10.58µl to 10.15µl. The

increase in the force exerted by the nitrogen gas on the pendant drop can be used to explain this

reduction in volume. This same phenomena explains the decrease in the pendant drop surface area

as volume is directly proportional to surface area. It can be seen that the change in pendant volume

for the three different crude samples is approximately the same. However, the change in pendant

drop volume is very small compared to the change experienced using carbon dioxide.

y = -0.0011x + 10.798 R² = 0.9582

10.1

10.2

10.3

10.4

10.5

10.6

10.7

0 100 200 300 400 500 600 700

Vo

l [µ

l]

Pressure(psia)

West texas intermediate

Linear (West texas intermediate)

40

Figure 4.13: Variation of Arab AH-50 drop surface area with pressure using nitrogen at 22 0C

Figure 4.14: Variation of Gullfaks C drop surface area with pressure using nitrogen at 22 0C

R² = 0.8238

20.8

20.9

21

21.1

21.2

21.3

21.4

21.5

21.6

21.7

0 100 200 300 400 500 600 700

Are

a [m

m*2

]

Pressure (psia)

Arab AH-50

y = -0.0026x + 22.87 R² = 0.9779

21.7

21.8

21.9

22

22.1

22.2

22.3

22.4

22.5

22.6

22.7

0 100 200 300 400 500

Are

a [m

m*2

]

Pressure (psia)

Gulfaks C

Linear (Gulfaks C)

41

Figure 4.15: Variation of West Texas intermediate drop surface area with pressure using nitrogen at

22 0C

The DSA measurements for the three crude oil samples using nitrogen gas are shown in Tables 4.4

to 4.6 . Figures 4.13 to 4.15 above show that the pendant drop surface area reduces in a linear

fashion as pressure increases. The pendant drop surface area of the first crude oil sample, the Arab

AH-50 reduced from 22.99 mm2 to 20.85 mm

2, that of the Gullfaks C sample reduced from 22.13

mm2 to 21.83 mm

2 and the West Texas intermediate sample’s pendant drop surface area reduced

from 22.77 mm2 to 21.94 mm

2. This change in pendant drop surface area can attributed to the

increased force exerted by the nitrogen gas on the pendant drop. It can be seen that the change in

the pendant drop surface area for the three different crude samples is approximately the same.

However, the change in pendant drop surface area is very small compared to that experienced

using carbon dioxide.

y = -0.0026x + 23.475 R² = 0.9124

21.8

22

22.2

22.4

22.6

22.8

23

23.2

0 100 200 300 400 500 600 700

Are

a [m

m*2

]

Pressure (psia)

West texasintermediate

Linear (West texasintermediate)

42

Figure 4.16: Variation of drop interfacial tension with pressure using nitrogen at 22 0C

Figure 4.17: Variation of Gullfaks C drop interfacial tension with pressure using nitrogen at 22 0C

y = -0.0054x + 24.785 R² = 0.9826

21

21.5

22

22.5

23

23.5

24

24.5

25

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (psia)

Arab AH-50

Linear (Arab AH-50)

y = -0.004x + 24.697 R² = 0.9587

21.5

22

22.5

23

23.5

24

24.5

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (Psi)

Gullfaks C

Linear (Gullfaks C)

43

Figure 4.18: Variation of West Texas intermediate drop interfacial tension with pressure using

nitrogen at 22 0C

The DSA measurements for the three crude oil samples using carbon dioxide gas at 22 0C are

shown in Tables 4.4 to 4.6 . Figures 4.16 to 4.18 above shows that the pendant drop IFT reduces as

pressure increases in a linear fashion from 200 psia. The IFT of the first crude oil sample, the Arab

AH-50 reduced from 24.13 mN/m to 21.54 mN/m, that of the Gullfaks C sample reduced from

24.13 mN/m to 22.23 mN/m and the West Texas intermediate sample’s IFT reduced from 25.5

mN/m to 23.64 mN/m. It can be seen that the change in IFT for the three different crude samples

over the same pressure range is approximately the same. However the change in IFT is very small

compared to that gotten using carbon dioxide.

Solving the trendline equations of the three crude oil samples for zero IFT yields a first contact

miscibility pressure of 4377 psia for the Arab AH-50, 5437 psia for the Gullfaks C sample and

8232.25 psia for the West Texas intermediate sample.

y = -0.0035x + 25.714 R² = 0.9737

23

23.5

24

24.5

25

25.5

26

0 100 200 300 400 500 600 700

IFT

[mN

/m]

Pressure (Psi)

West Texas Intermediate

Linear (West Texas Intermediate)

44

4.3 Gullfaks C using carbon dioxide at 600C

The pressures required to achieve first contact miscibility using nitrogen compared to carbon

dioxide is relatively large, on this basis, carbon dioxide was found to be a more suitable gas for

miscible flooding thereby confirming numerous literature work. Hence IFT measurement was

carried out for the Gullfaks C crude oil sample at an assumed reservoir temperature of 600C over a

pressure of 100 to 300 Psi and the DSA measurement is given in Table 4.7 below.

Table 4.7: DSA measurement of Gullfaks C using carbon dioxide at reservoir temperature

100 Psi, 600C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 21.64 91.19 91.19 91.19 9.95 21.71 1.618 4.25 L-Y 113.723

2 21.7 94.14 94.14 94.14 9.72 21.21 1.612 6.43 L-Y 114.496

3 21.7 91.74 91.74 91.74 9.89 21.6 1.607 5.978 L-Y 114.312

4 21.7 92.57 92.57 92.57 9.89 21.5 1.617 4.48 L-Y 113.746

5 21.77 92.64 92.64 92.64 9.9 21.56 1.62 5.645 L-Y 113.844

Average 21.7 9.55 21.45 1.55

200 Psi, 600C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 20.6 90.56 90.56 90.56 9.42 21 1.576 3.24 L-Y 113.133

2 20.6 90.16 90.16 90.16 9.43 21.04 1.577 3.14 L-Y 113.159

3 20.61 90.72 90.72 90.72 9.42 20.97 1.577 3.255 L-Y 113.037

4 20.61 90.54 90.54 90.54 9.42 21 1.577 3.219 L-Y 113.07

5 20.62 90.89 90.89 90.89 9.41 20.96 1.577 3.217 L-Y 113.09

Average 20.61 9.42 20.99 2

300 Psi, 600C

Drop

No.

IFT


Vol

[µl]

Area

[mm*2]

BD

[mm]

Fit-

Er

[µm]

Method MAG

[pix/mm]

1 18.91 90 90 90 8.91 20.21 1.573 1.75 L-Y 105.887

2 18.91 89.9 89.9 89.9 8.92 20.21 1.573 1.716 L-Y 105.887

3 18.92 90 90 90 8.92 20.22 1.573 1.685 L-Y 105.867

4 18.92 90 90 90 8.92 20.21 1.573 1.695 L-Y 105.878

5 18.93 90 90 90 8.92 20.22 1.572 1.664 L-Y 105.858

Average 18.92 8.92 20.21 1.573

45

Figure 4.19: Variation of Gullfaks C’s Interfacial tension with pressure using carbon dioxide at 600C

Figure 19 shows the variation in IFT with pressure at 600C over a pressure range of 100 to 300

psia. Solving the trendline equations for zero IFT yields a first contact miscibility pressure of

1668Psi for the Gullfaks C sample.This is higher than the estimated pressure at 220C .

Figure 4.20: Variation of Gullfaks C’s Interfacial tension with temperature

y = -0.0139x + 23.193 R² = 0.9845

18.5

19

19.5

20

20.5

21

21.5

22

22.5

0 50 100 150 200 250 300 350

IFT

[mN

/m

Pressure (psia)

Gullfaks C

Linear (Gullfaks C)

18

19

20

21

22

23

24

25

0 50 100 150 200 250 300 350

IFT

[mN

/m

Pressure (psia)

Gulfaks C (60 Degrees)

Gullfaks C (22 degrees)

46

Figure 4.20 shows that first contact minimum miscibility pressure increases with temperature

increase which goes against the general convention that minimum miscibility pressure reduces

with temperature increase. The number of data points used in plotting the IFT versus pressure

graph at 600C could be the cause of the difference in the result; however, more data points could

not be gotten at 600C due to equipment malfunction.

49

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS

1.1 Conclusions

Minimum miscibility pressure is an essential parameter in planning minimum miscibility

flooding .This parameter depends on the type of gas used as well as reservoir temperature.

This study has determined minimum miscibility pressure of carbon dioxide and nitrogen

separate system. The following are the conclusions that can be drawn from this experimental

work.

1) First contact minimum miscibility pressure can be obtained by measuring the variation in

pendant drop IFT data with temperature and pressure.

2) At a constant temperature, Crude oil pendant drop volume and surface area decreases

with increases in pressure.

3) Besides pressure increase, other parameters such as the density of the gas used affect the

pendant drop volume surface area and IFT.

4) Crude oil pendant drop forms the outer surface of the needle regardless of the gas used.

5) On the basis of IFT reduction with pressure increase, carbon dioxide is more suitable for

miscible flooding than nitrogen by more than 100 %.

6) More than three pressure data points are required to accurately estimate miscibility

pressure at a particular temperature.

7) Data generated from this study could be used as a basis to generate correlations that

predicts first contact miscibility pressure for the Arab AH-50, the Gullfaks C and the

West Texas intermediate crude samples using Carbon dioxide and Nitrogen.

48

5.2 Recommendations

1) A gas piston pump should be added to the pendant drop apparatus so as to increase the

range of pressure that can be used on the apparatus. The current set up restricts the

pressure range to that of the gas cylinder used.

2) More data points should be gotten at increased temperature and pressure to increase the

accuracy of IFT estimation.

3) The impact of gas density on the crude oil pendant drop volume, surface area and IFT

could be further investigated.

49

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