experimentalevaluationoflignosulfonate asa sacrificial ... a... ·...

Experimental Evaluation of Lignosulfonate as a Sacrificial

Agent in COa-Foam Flooding

by

Andy Eka Syahputra

Thesis

Submitted in Partial Fulfillment of the Requirements for the Degree ofMaster of Science in Petroleum Engineering

Department of Petroleum EngineeringNew Mexico Institute of Mining and Technology

Socorro, New Mexico 87801

August 1999

ABSTRACT

Lignosulfonates are abundant wood-based chemicals obtained as by products in

the sulfite process of wood pulping. They are relatively inexpensive compared to most

polymers and surfactants. An effort to improve the economics of tertiary oil recovery

operations by using lignosulfonates, a mixture of a lignosulfonate reagent with

surfactants was studied. Three sets of laboratory experiments were performed: (1) to

quantify interfacial tension and foam durability; (2) to quantify the sweep efficiency

when using lignosulfonate mixedwith a good foaming surfactant in COi-foam flooding

in heterogeneous core; and (3) to investigate lignosulfonate as a sacrificial agent to

minimize the loss of surfactant by adsorption on reservoir rock. All of the experiments

except the adsorption measurements were conducted at elevated pressures.

Quantification of interfacial tension and foam durability using a high-pressure

foam durability apparatus was performed as the first set of laboratory experiments to

screen lignosulfonate as a sacrificial agent in C02-foam flooding. The foam durability

test demonstrates the potential of using lignosulfonate solutions at various concentrations

as sacrificial agents to be mixed with other surfactants, such as alpha olefin sulfonate and

alkyl phenol ethoxylate for C02-foam flooding. We found that the lignosulfonate solution

was a weak foam former. When the lignosulfonate solution was added to different

surfactant solutions, foam stability was affected by the lignosulfonate concentration. The

results of the foam durability test show that a strong foam could be formed by some

lignosulfonate solutions mixed with surfactant CD1045; thus, lignosulfonate can be

tested as a sacrificial agent in CO2-foam flooding processes.

The second set of laboratory experiments was to determine the sweep efficiency

using lignosulfonate as a sacrificial agent mixed with a good foaming surfactant in CO2-

foam flooding in heterogeneous reservoirs. A noncommunicating composite core sample

of two different permeability regions (ratio 1:10) in parallel was used. The high

permeability region was located in the centerof the core and the low permeability region

in the annulus. In order to reduce mobility and increase sweep efficiency of CO2

injection, lignosulfonate mixed with surfactant CD1045 was coinjected into a C02-foam

core flooding apparatus. The results indicate that lignosulfonate mixed with surfactant

CD1045 significantly improved the nonuniformity in displacement associated with rock

heterogeneity and reduce the channeling of CO2 in a heterogeneous core. Coinjection of

CO2 and lignosulfonate as sacrificial agent at 5000 ppm mixed with two concentrations

of surfactant CD1045 (250 ppm or 500 ppm) are effective for diverting displacing fluid

into the low permeability region. Thus, oil from the low permeability region was

displaced and oil production was increased.

The third and final set of experiments was to investigate the degree of retention of

the injected components. The loss of injected surfactant is a major factor causing poor

efficiencyof C02-foam flooding. In this study, we performed experiments to investigate

lignosulfonate as the sacrificial agent to minimize the loss of the good foaming

surfactant. A single core sample of Berea sandstone was used to investigate the

adsorption by a circulation method. Solutions were circulated through the core using

surfactant CD1045 and a sacrificial agent (lignosulfonate) with different initial conditions

to establish the adsorption isotherm under equilibrium conditions with constant flow rate

at a specific confining pressure. Experimental results show that using surfactant CD1045,

the amount of adsorption onto therockincreases as concentration increases andby using

lignosulfonate mixed with surfactant reduces the adsorption of surfactant CD1045.

ACKNOWLEDGEMENTS

I would like to express my sincere appreciation and gratitude to my advisor Dr.

ReidB. Griggfor his valuable guidance, advice, patience, and encouragement throughout

the course of this study.

Many thanks are due to my coadvisor Dr. Jyun Syung Tsau for comments,

suggestions, encouragement, useful discussions and guidance in the set up of foam

durability experiments apparatus and adsorption measurement apparatus during the

course of this research. I also express my appreciation to the other members of my

advisory committee. Dr. LarryTeufel, Dr. Her Yuan Chen for their advice and time spent

on this thesis.

I wish to express my gratitude to the Petroleum Recovery Research Center

(PRRC) for the financial support through research assistantship grant.

Appreciation is also extended to Dr. Hossein Yaghoobi for his guidance in the set

up of the C02-foam coreflooding experiment apparatus. I also wish to thank Liz

Bustamante for her help in correction of the thesis manuscript. I would like to thank to

the entire staff of the PRRC for their kindness and assistance.

Finally, I am greatly indebtedto my parents, my brother Dr. Erwinsyah putra, my

wife Afrin Aulia, my beloved daughter Navira Alifa, my family and my friends for their

patience, moral support, understanding and encouragement during this study.

11

TABLE OF CONTENTS

Abstract

Acknowledgments ii

List ofTables

List of Figures ix

Chapter 1 Introduction 1

Chapter 2 Literature Review 5

2.1 Characteristics of Lignosulfonate 5

2.2 CO2 Breakthrough 6

2.3 C02-Foam Flow Behavior 8

2.4 Adsorption Effects 9

Chapter 3 Experimental Descriptions 12

3.1 Foam Durability Test 12

3.1.1 Foam Durability Apparatus 12

3.1.2 Foam Durability Experiments and Procedure 13

3.2 C02-Foam Coreflooding Test 21

3.2.1 COa-Foam Coreflooding Apparatus 21

3.2.1-a Core unit assembly 21

3.2.1-b A foam generator 26

3.2.1 -c Differential pressure transducers 26

3.2.1-d Backpressure regulators (BPR) 26

3.2.1-e Floating piston accumulators (FPA) 27

iii

3.2.1-f Positive displacement pumps 27

3.2.1-g Data acquisition system 28

3.2.1-h Effluent collection 29

3.2.2 COa-Foam Coreflooding Experiments and Procedure 29

3.3 Adsorption Measurement Test 30

3.3.1 Adsorption Measurement Apparatus 30

3.3.2 Adsorption Measurement Experiments and Procedure 30

Chapter 4 Discussion of Results 34

4.1 Foam Durability Results 34

4.2 C02-Foam Coreflooding Results 43

4.3 Adsorption Measurements Results 55

Chapter 5 Conclusions and Recommendations for Future Work 66

5.1 Conclusions 66

5.1.1 Foam Durability Experiments 66

5.1.2 C02-Foam Coreflooding Experiments 67

5.1.3 Adsorption Measurement Experiments 68

5.2 Recommendations for Future Work 68

References 70

Appendix - A Foam Durability Experimental Data 76

Appendix - B C02-Foam Coreflooding Experimental Data 82

Appendix - C Adsorption Measurements Experimental Data 101

iv

LIST OF TABLES

Table 3.1 Surfactant and Brines Properties 20

Table 3.2 Lignosulfonate Properties 20

Table 3.3 Properties of Isolated Coaxial Composite Core 25

Table 4.1 Sununary of Isolated Coaxial CompositeCore Experiments 44

Table 4.2 Cost Savings Using a Sacrificial Agent, Based on Adsorption Results

(Ib/acre-ft) 65

Table A.1 Foam Durabilty Experimental Data:

Decay of Calcium Lignosulfonate Data 77

Table A.2 Foam Durability Experimental Data:

Interfacial Tension (IFT) Calculation 79

Table B.l COi-Foam Coreflooding Experimental Data:

CO2 Displacing Oil at Center 83

Table B.2 COi-Foam Coreflooding Experimental Data:

CO2/ Brine Displacing Oil at Center 83

Table B.3 COa-Foam Coreflooding Experimental Data:

CO2 / Surfactant @500 ppm Displacing Oil at Center 84


CO2/ Surfactant @2500 ppm Displacing Oil at Center 84

Table B.5 C02-Foam Coreflooding Experimental Data:

CO2/ Surfactant @2500 ppm Displacing Oil at Annulus 85


C02 / (500 ppm Surfactant + 5000 ppm Lignosulfonate) Displacing

Oil at Center 85

Table B.7 COz-Foam Coreflooding Experimental Data:

CO2 / (500 ppm Surfactant + 5000 ppm Lignosulfonate)Displacing

Oil at Annulus 86


CO2/ (250 ppm Surfactant + 5000 ppm Lignosulfonate) Displacing

Oil at Center 86


CO2/ (250 ppm Surfactant + 5000 ppm Lignosulfonate) Displacing

Oil at Annulus 87

Table B.IO C02-Foam Coreflooding Experimental Data:

CO2/ (5000 ppm Lignosulfonate) Displacing Oil at Center 87

Table B.ll C02-Foam Coreflooding Experimental Data:

Total Oil Recovery from Both Region at CO2 / (Surfactant @2500 ppm) 88


Total Oil Recovery from Both Region at CO2/(250 ppm Surfactant

+ 5000 ppm Lignosulfonate) 88


Total Oil Recovery from Both Region at CO2/(500 ppm Surfactant

+ 5000 ppm Lignosulfonate) 89


Pressure Difference at The Core versus Time for CO2 /(500 ppm

vi

Surfactant CD1045) 90


Pressure Difference at The Core versus Time for CO2/(2500 ppm

Surfactant CD1045) 92



Surfactant CD1045 + 5000 ppm Lignosulfonate) 95



Surfactant CD1045 + 5000 ppm Lignosulfonate) 98

Table C.1 Adsorption Measurement Experimental Data:

CD1045 & Lignosulfonate Standard Curve with Different

Wavelengths 102


Adsorption of Surfactant CD1045 onto Berea Sandstone

(The core was flushed with brine followed by injecting the different con

centrations of CD1045) 102


Adsorption of Lignosulfonate onto Berea Sandstone

(The core was flushed with brine followed by injecting the different con

centrations of lignosulfonate) 103


Adsorption of Surfactant CD1045 Mixed with Lignosulfonate Using

Vll

Surfactant Strandard Curve. (The core was flushed with brine followed by

injecting the three different concentrations of surfactant mixed with ligno-

Sulfonate) 104


Adsorption of Surfactant CD1045 onto Berea Sandstone (The core was

flushed with brine prior to injecting each concentrations of surfactant) 105

Table €.6 Adsorption Measurement Experimental Data;

Adsorption of Surfactant CD1045Mixed with Lignosulfonate Using

Surfactant Standard Curve (The core was flushed with brine prior to

injecting each concentrations of surfactant mixed with lignosulfonate) 105


Adsorption of Surfactant CD1045 with Three Different Sequences of

Experiments onto Berea Sandstone (The core was flushed with brine prior

to injecting each concentrations of solutions) 106

vui

LIST OF FIGURES

Fig. 2.1 Structure of a section of lignosulfonate molecule 7

Fig. 3.1 Foam durability apparatus 15

Fig. 3.2 Sapphire tube 16

Fig. 3.3 IFTs between surfactant and dense CO2 19

Fig. 3.4 C02-Foam coreflooding apparatus 23

Fig. 3.5 Core unit assembly 24

Fig. 3.6 Adsorption measurement apparatus 32

Fig. 4.1 IFTs between lignosulfonate calcium in different brines and dense CO2 37

Fig. 4.2 IFTs between lignosulfonate solutions with surfactants and dense CO2 38

Fig. 4.3 Decay of C02-foam of lignosulfonate with brine 3 (base solution) 39

Fig. 4.4 Decay of C02-foam of lignosulfonate with 0.025 wt % CD1045 40



Fig. 4.7 Cumulative GOR observed from the high permeability (center) region 48

Fig. 4.8 Cumulative GOR observed from the low permeability (annulus) region 49

Fig. 4.9 Oil recovery through the high permeability region (center) 50

Fig. 4.10 Oil recovery through the low permeability region (annulus) 51

Fig. 4.11 Oil recovery through both regions 52

Fig. 4.12 Pressure drop profiles and oil recoveryfor the low permeability region

(annulus) with different concentrations of surfactant in CO2injection 53

Fig. 4.13 Pressure drop profiles and oil recovery for the low permeability region

ix

(aimulus) with different concentrations of surfactant mixed with 5000 ppm

lignosulfonate in CO2injection 54

Fig. 4.14 Surfactant CD1045 standard curve with wavelength 520 nm 58

Fig. 4.15 Lignosulfonate calcium standard curve with wavelength 283 nm 59

Fig. 4.16 Adsorption of surfactant CD1045 onto Berea sandstone core sample 60

Fig. 4.17 Adsorption of lignosulfonate onto Berea sandstone core sample 61

Fig. 4.18 Adsorption of surfactant CD1045 onto Berea sandstone cores sample as a

function of surfactant CD1045 concentration at lignosulfonate levels of

0 ppm and 500 ppm (The core was flushed with brine followed by

injecting the three different concentrations of surfactant) 62

Fig. 4.19 Adsorption of surfactant CD1045 onto Berea sandstone core sample as a

function of surfactant CD1045 concentration at lignosulfonate levels of

of 0 ppm and 500 ppm (The core was flushed with brine prior to injecting

each concentrations of surfactant) 63

Fig. 4.20 Adsorption of surfactant CD1045 with three different sequences of

Experiments onto Berea sandstone core sample 64

CHAPTER 1

INTRODUCTION

Despite the favorable characteristics of gas injections for displacing oil, gas injection

processes have major problems with poor sweep efficiency, due to viscous fingering,

gravity override, and reservoir heterogeneity. In CO2 injection, mobility is usually high

relative to that of other reservoir fluids because of the large viscosity contrast between the

reservoir and injected fluids. Therefore, CO2 sweep efficiency decreases and early gas

breakthrough occurs as a result of the unfavorable mobility ratio. Several alternatives

have been proposed to increase sweep efficiency of CO2 injection in the field or in

experimental work, such as injecting water alternating with gas (WAG) (Caudle and

Dyes, 1958), direct CO2 thickeners (Heller et al., 1983), and injecting surfactant solution

alternating with gas (SAG) (Bernard and Holm, 1964; Tsau and Heller, 1992). The

benefits of usingSAGto improve the efficiencyof CO2 displacement have been reported

by several investigators (Albrech and Marsden, 1970; Yang and Reed, 1989; Tsau and

Grigg, 1997; Yaghoobi etal, 1998).

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-2-

Laboratory and field studies indicate that foam potentially presents an efficient

method of reducing CO2 mobility (Yang and Reed; 1989, Tsau et al., 1992, 1996, 1997,

1998; Yaghoobi et al, 1994, 1995, 1996; Prieditis et a/., 1992; Kuehne et al., 1992;

Bernard et aL, 1964). Foam inside porous medium is defined as a dispersion of gas in

liquid such that the liquid phase is continuous and at least some part of the gas is made

discontinuous by thin liquid films called lamellae (Falls et al.^ 1988). The foam occurs as

gas dispersed within a surfactant solution and the mobilites of gas and aqueous phase are

reduced.

The inherent advantage of foam over water for mobility improvement is that it

consists of 85 to 95% gas. This means that a relatively small amount of water is used to

decrease CO2 mobility. Foam has other properties that are favorable to oil recovery,

particularly by CO2 flooding. The apparent foam viscosity is greater than the viscosity of

its components. This factor is favorable for greater oil recovery because increased

viscosity is reflected in improved mobility ratio. Foam also increases trapped gas

saturation and decreases the oil saturation. In addition, high-trapped gas saturation

usually reduces gas mobility. All of these unique properties of foam indicate that it

should be useful in CO2 flooding. Foam properties may also cause unfavorable increased

in injectivity and increased chemical costs.

It has been found that surfactants can play an important role in controlling CO2

mobility, but surfactants are expensive. In order to find solutions that are less expensive,

lignosulfonate was tested as a sacrificial agent, mixed with the good foaming to form

C02-foam. The overwhelming appeal of lignosulfonate is the relative low cost (about

$0.03/lb) for calcium lignosulfonate compared to a good foaming agent (about $1.43/lb)

-3-

for Chaser™ CD1045 and is available as a byproduct from the pulp and paper industry.

The prices of CD1045 and lignosulfonate were quoted by Chevron Chemical (1991) and

Georgia Pacific (1998), respectively.

In this work the performance of foam using lignosulfonate was investigated with

three different sets of experiments. The first set of studies used the foam durability

apparatus (Tsau et al., 1992, 1996, 1997). The purposes of the first set of studies were

threefold. The first was to determine the foaming ability and stability of foam. The

second objective was to identify the optimum concentration of a lignosulfonate/surfactant

mixture. The final objective was to provide information about interfacial tension between

CO2 and lignosulfonate/surfactant mixture.

The second set of experiment was conducted using the C02-foam coreflooding

apparatus (Tsau et al, 1998; Yaghoobi et a/., 1994, 1995, 1996). In this study, we

examined the effectiveness of COa-foam flooding with lignosulfonate at 5000 ppm

concentration mixed with two different concentrations of surfactant CD1045 (250 ppm

and 500 ppm). The solution was injected simultaneously with CO2 into saturated

heterogeneous porous media to displace oil. We used lignosulfonate mixed with certain

concentrations of surfactant CD1045 because they formed a strong foam in previous

foam durability test experiments. The experiments were performed on a

nonconmiunicating composite core sample of two different parallel permeability regions.

The purposes of this study were twofold. The first was to determine the delay of CO2

breakthrough time. The second objective was to examine the effectiveness of

lignosulfonate/surfactant mixture on diverting displaced fluid to the lower permeability

-4-

region to improve oil recovery. The results were compared with the results from using

surfactant CD1045, lignosulfonate and brine (1.5 wt% NaCl and 0.5 wt% CaCla).

The third set of studies examined adsorption by the circulation method (Tsau et al.,

1999). The purpose of the third set of study was to assess both the loss of primary

foaming agent and of lignosulfonate for economic evaluation, and to design a surfactant

injection scheme to minimize the loss of the primary foaming agent onto sandstone.

CHAPTER 2

LITERATURE REVIEW

2.1 Characteristics of Lignosulfonate

Lignosulfonates are anionic polyelectrolytes that are soluble in water, tolerate

hard water (polyvalent ions, e.g. calcium and magnesium) and are derivatives of lignin

(Kalfoglou, 1977). The use of lignosulfonates as sacrificial agents for C02-foammobility

control is desirable because they are stable at high reservoir temperatures, plentiful, and

lower cost than either polymers or other surfactants. One variety of lignosulfonate

products is the lignosulfonic acids. These are calcium, magnesium, sodium or ammonium

salts of the lignosulfonic acids that are available under various tradenames including

Marasperse™, Lignosite™, Orzan™, Toranil™, and Rayflo™ (Kalfoglou, 1977). The

organicstructureof lignosulfonate has not been completelyelucidated but the basic lignin

monomer unit is substituted phenyl propane. The complex structure of lignosulfonates

make them completely insoluble in oils. The molecular weight and degree of sulfonation

govern the extent of electrical charge of the system under consideration. The type of

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-6-

metallic ions in the lignosulfonate affects its properties. The structure of a section of

lignosulfonate can be seen in Fig. 2.1.

The lignosulfonate used in this study is Lignosite®100 calcium lignosulfonate,

which is produced by sulfonation of softwood lignin and provided by the manufacturer in

a powder form. Lignosite®100 calcium lignosulfonate is particularly effective because

alcohol fermentation and distillation purify it. This removes the hexose sugars and yields

a product with a high content of calcium lignin sulfonate. High purity calcium

lignosulfonate from softwood is the most effective composition for many applications

and is the most widely used of all lignosulfonates.

2.2 CO2 Breakthrough

Early CO2 breakthroughoccurs in most CO2 projects, especially in heterogeneous

reservoirs. Several methods have already been proposed to alleviate that problem. Rowe

et al. (1981) injected alternate slugs of water with CO2 for reducing injecting mobility.

The water decreases the relative permeability of the porous medium to CO2 and thus

lowers its mobility. When the porous medium is not strongly water-wet, this method

seems to work well, but in strongly water-wet fomations, CO2 may have difficulty in

contacting the residual oil left after the slug of injected water. Although water alternating

gas (WAG) seems to be successful in some field operations, it is not an ideal method,

because after water is injected and followed by CO2, the fronts formed around the

injection well are unstable. The CO2will tend to finger through the high water saturation

zones and may bypass regions of high oil saturation.

SOjM

IOCH,

C —C—C—

I I I ^H. H H OCH.

-7

H£OH

ICH

HiCOH

KC

HC

HC

Acs OH

OCH,

HiCOH

1

C•

1CH

MO^

H]CO

CHiOH

ICO

<1

OCH,

OCHi

HiC

KC

HjCO

OH

v4

CH

CH

HC CH,

- O

OCH,

OH

Fig. 2.1 - Structure of a section of lignosulfonate molecule.

\

-8-

Moreover, the solubility of CO2 in water would increase the overall CO2

consumption to make the CO2 project less economical.

One method to control CO2 viscous fingering is the use of C02-foam. Because the

foam has a muchhigher effective viscositythan CC)2, it tends to inhibit viscous fingering.

2.3 C02-foam flow behavior

Foam has the ability to block or minimize CO2 flow into high permeability

regions in C02-foam flooding. With an apparent viscosity greater than the CO2, foam

reduces gas mobility in a favorable way that corrects the nonuniformity flow problem in a

heterogeneous porous medium.

The flow behavior and the displacement mechanism of C02-foam were

investigated by several authors (Bernard et al, 1980; Wang, 1984). In 1980, Bernard

al. presented results of using three classes of surfactants (anionic, cationic and nonionic)

to improve the effectiveness of CO2 flooding. Oil recovery efficiency increased when

surfactant was used with CO2, and that efficiency further increased with flooding

pressure. One anionic surfactant was found to be superior for that purpose as it emulsified

CO2 well and greatly reduced CO2 mobility. Wang (1984) investigated the flow behavior

of C02-foam and the displacement mechanism in porous media glassbead pack using

SACROC and Rock Creek crude oils. He examined these models with varying CO2 slug

injection sequences and some surfactant concentration. His results showed that C02-foam

flooding slightly improved oil recovery and delayed gas breakthrough.

Several researchers have reported that some surfactants generated foams, which

selectively reduced mobility of CO2 by a greater firaction in higher than in lower

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penneability regions (Moradi et aL, 1997; Yang and Reed, 1989; Yaghoobi et ai, 1994,

1996; Lee et al, 1991; Tsau and Heller, 1996; Tsau et al, 1998). The main purpose of

injecting COa-foam is to divert the injection fluid into the lower permeability region. The

oil in lower permeability regions is often by passed and often has a higher portion of

unrecovered oil compared with high permeabilityregions.

In 1996, Yaghoobi et al. conducted COa-foam core flooding experiments in core

samples without oil present. The experiments were performed in composite core samples

with two different permeability regions in capillary contact. They found that the

displacement of C02-foam delayed CO2 production and improved sweep efficiency in

bothregions. The experiment wascontinued by Tsau et al (1998) on two composite core

systems of a known heterogeneity with oil present. The first composite core system

consisted of two coaxial permeability layers in capillary contact. The second composite

system used a barrier embedded between two different permeability regions to prevent

flow communication between two parallel zones. They observed that foam was diverted

to lower permeability regions and delayed CO2 breakthrough, thus improving oil

recovery efficiency for both regions.

2.4 Adsorption Effects

Surfactant loss due to adsorption during C02-foam flooding is considered a major

factor in the inefficiency of tertiary oil recovery. Various experimental methods have

been used to measure the adsorption of surfactants on sample cores. One of those was

conducted by Mannhardt et al. (1990). They measured adsorption onto sandstone and

limestone cores for two types of surfactants (anionicand amphoteric surfactants) found to

- lo

be effective in forming mobility control foams under extremely high salinityconditions.

Theyfound that anionic surfactant adsorbed more strongly onto limestone core than onto

sandstone core, while the opposite behavior was observed with amphoteric surfactant.

Also, they found the presence of divalent ions increased adsorption levels of both

surfactants onto both rock types.

In order to minimize the loss of injected surfactant, several studies have been

conducted to optimize the cost of application (Trogus et al, 1977; Bae et aL, 1976;

Lawson, 1978). For economic reasons, it is desirable to find sacrificial agents that are less

expensive and that minimize the loss of surfactant.

Several researchers investigated the amount of sacrificial agent needed to allow

for adsorption onto reservoir rock. In 1976, Hobbs investigated the possibility that

sacrificial agents that adsorb in place of surfactants could be used in a preflush or as a

competitive additive to the surfactant slug, but effective agents were not identified.

Similar experimental results were reported by Hurd (1976).

A process using lignosulfonates as sacrificial agents during oil recovery by

surfactant flooding was patented by Kalfoglou (1977). His results showed that the

injection of lignosulfonates into the reservoir as a preflush reduces the loss of the costly

primary surfactant (petroleum sulfonate) by adsorption onto the reservoir rock. He

asserted that since lignosulfonates have strongly ionized sulfonate groups, they are

capable of covering the potential adsorption sites of the rock by means of electrostatic

attraction or hydrogen bonding and, as a consequence, impart a negative charge to the

surface. Afterward, the surface would have little or no affinity for anionic surfactants

such as petroleum sulfonates and their loss by adsorption would be minimized.

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Novasad (1984) investigated the use of lignosulfonate as a sacrificial adsorbate in

surfactant flooding. The author found that lignosulfonate can improve oil recovery by

two possible ways. First, lignosulfonate reduced surfactant adsorption by being

preadsorbed on to reservoir rock surfaces and second, lignosulfonate acted together with

the surfactant at the liquid-liquid interface to further reduce interfacial tension between

oil and brine.

Somansundaran (1989) examined the adsorption of sodium dodecylsulfonate

(SDS) in the presence of lignosulfonate. The addition of 1000 ppm lignosulfonate

decreased sulfonate adsorption onto kaolinite by almost half an order of magnitude in the

premicellarregionbut it had no noticeable effect in the micellar region. The adsorption of

SDS onto kaolinite in the presence of varying concentrations of lignosulfonate (from

1000 ppm to 5000 ppm) was found to decrease with an increase in the lignosulfonate

level and SDS adsorption onto kaolinite was completely inhibited at an initial

concentration of 7500 ppm.

Hong et al (1987 and 1990) showed that surfactant loss could be reduced

significantly (>50% reduction) by pretreatment with a lignosulfonate preflush. However,

when the lignosulfonate was incorporated with the surfactant slug, no significant

reduction in adsorption of the surfactant was obtained. The investigation was continued

by injecting lignosulfonate as a sacrificial adsorbate in real-world situations at Glenn

Pool field. A lignosulfonate solution was injected as part of the preflush in one of the

patterns without any interruption of the surfactant flood project. Results of this

experiment testing the effect of lignosulfonate on sulfonate adsorption demonstrated that

almost half the injected lignosulfonatewas adsorbed, and more oil was produced.

CHAPTERS

EXPERIMENTAL DESCRIPTION

This chapter describes the experiments conducted in this study. Three different

sets of experiments were performed. The first set used the foam durability apparatus to

optimize the concentration of lignosulfonate mixed with surfactants. The second set of

experiments was conducted using the C02-foam coreflooding apparatus to investigate the

effectiveness of C02-foam for improving oil recovery by using lignosulfonate mixed

with surfactant for diverting displacingfluid from the high to the low permeability region

of the core. The third set investigated adsorption using a sacrificial agent such as

lignosulfonate to minimize the loss of surfactant. The adsorption experiments were

performed using a circulation method for establishing the adsorption isotherm under

equilibrium conditions with constant flow rate.

3.1 Foam Durabilty Test

3.1.1 Foam Durability Apparatus

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-13-

The foam durability apparams is a device that is used for testing surfactant

properties at high pressure, thus allowing the evaluation of these surfactants for reservoir

use. The schematic view of the entire apparatus is shown in Fig. 3.1 with an enlarged

viewof the sapphire tube high-pressure cell shownin Fig. 3.2. The apparatus consists of

a CO2 source tank, a visual cell made from a transparent sapphire tube, a buffer solution

cylinder, a Ruska pump and a cathetometer for measuring the level of bubble decay

versus elapsed time. The CO2 tank and the sapphire tube high-pressure cell are major

parts of the system that are contained in a temperature-controlled water bath. The Ruska

pump and the buffer solution tank are installed outside of the water bath and their

temperatures are maintained at the test temperature through another temperature control

systemthat consisted of Exacal Circulator, Flowthru Coolerand tubing that wrap around

the pump and buffer solution tank.

3.1.2 Foam Durability Experiments and Procedure

During the durability experiment, the sapphire visual cell is first filled with the

solution to be tested. Once the system is brought to the desired pressure by means of the

Ruska pump, the dense CO2is introduced through a needle at the lower end of the cell.

Depending on the effectiveness of the lignosulfonate and lignosulfonate mixed surfactant,

the bubbles either formed a layer of foamlike dispersion at the top of the sapphire tube or

coalesced into a clear layer of dense CO2. After a standard volume of CO2 (1.75 cc) is

introduced into the sapphire tube, the pump is stopped and the duration of formed foam is

measured. The measure of foamability is the fraction of the bubbles that stay intact as a

foam layer at the top of the cell. The durability of the foam is obtained in terms of foam

-14-

decay by measuring the change of the percentage of foam or coalescence of the bubbles.

The screening tests on lignosulfonate solutions and the Iignosulfonate/surfactant mixtures

were conducted at 77° F (25® C) and 2000 psig.

To Ruska Pump

o

Buffer

Solution

Outlet

-15-

To Isco Pump

Water Bath

Sapphire Tube

CO^ Tank

Fig. 3.1 - Foam durability apparatus

h ' '. : '

'^'y.V ;.

'•/ •

, 3-».

A«

• 'W'

...w

•

..' ''-Tf-.; -^ «••"'- s '"k ''•»

-16-

•i

Bubbles

Needle

Fig. 3.2 - Sapphire tube

-17-

The measurement techniques for calculating the interfacial tension are analogous

to those of the drop-weight method. The rate of entry of the dense CO2 is known from the

pump settmgs and number of drops are recorded against time; thus, the volume and

radius of each drop can be calculated. The radius of the needle from which the bubbles

emerge, the density of the lignosulfonate solution, and the density of the CO2 are also

known. The following equation is used to calculate IFT:

|'''̂ 'k.surf-''ooJs=2"rTf (3.1)\ J

Where

R = average radius of the bubbles, cm.

r = radius of the needle from which the bubbles emerge, cm.

Y = interfacial tension between dense CO2and lignosulfonate,

dynes/cm.

f = dimensionless correction factor.

g = gravity, cm/sec^.

The correction factor is necessary because a portion of the CO2will remain on the

tip of the needle after the bubble is released. The correction factor for the drop weight

method was reported by Harkins and Brown (1919) and summarized by A.W. Adamson

(1990).

Stock solutions of Lignosite®100 calcium lignosulfonate at a concentration of 10

wt% were prepared by dissolving the product powders into distilled water and three types

-18-

of brines. The properties of three types of brine and surfactants are described in Table

3.1. The critical micelle concentration (CMC) values for surfactant solutions using

Chaser™ CD1040, Chaser™ CD1045, and Chaser™ CD1050 were determined to be

0.06%, 0.07% and 0.07%, respectively (Fig.3.3).

Lower concentrations of lignosulfonate solution, ranging from 0.5 to 7.5 wt%,

were prepared by dilution of the 10 wt% batch solution with a brine solution. The values

of pH and density were measured for 0.5 wt% to 10 wt% concentrations of

lignosulfonate,see Table 3.2. The summaryof the foam durability test data are presented

in Tables A.1-A.2, Appendix A.

u 12

c 10

0.001

-19-

OCD1040 ACD1050 XCD1045

0.01 0.1 1

Concentration (wt%)

Fig. 3.3 - IFTs between surfactants and dense CO2.

10

-20-

Table 3.1 - Surfactants and Brines Properties

Solution Concentration

(PPM)pH Density, (p)

(gm/cc)Type Active

(wt%)Formula Manufacture

Chaser™CD1040

250 6.3 1.033 Anionic 40.0 Alpha OlefinSulfonate

Chaser Inter-

National

Chaser™CD1045

250 6.8 1.024 Not avai

lable

46.7 Not available Chaser Inter

national

Chaser™CD1050

250 5.98 1.026 Nonionic 70.0 Alkyl PhenolEthoxylate

Chaser Inter

national

Brine 1 10000 6.59 1.016 * 100.0 1.0Wt%CaC12 *

Brine 2 10000 6.92 1.017 * 100.0 1.0Wt%NaCl *

Brine 3 20000 6.72 1.013 * 100.0 1.5Wt%NaCl

&0.5Wt%

CaC12

*

(*): Not applicable.

Table 3.2 - Lignosulfonate Properties

Lignosulfonate pH Density, (p )wt% (gm/cc)

10 4.80 1.069

7.5 4.83 1.061

5.0 4.90 1.056

2.5 4.96 1.045

1.0 5.21 1.034

0.5 5.93 1.024

-21-

3.2 COi-Foam Coreflooding Test

3.2.1 C02-Foam Coreflooding Apparatus

The C02-foam coreflooding experiments were performed by using a high-

pressure coreflood apparatus, which is shown in Fig. 3.4. The major elements of this

apparatus are a core unit assembly, a foam generator, differential pressure transducers,

back pressure regulator (BPR), floating piston accumulators (FPA), positive displacement

pumps, data acquisition system and effluent collection.

3.2.1-a Core unit assembly

Thecore unitassembly comprised of a nonconmiunicating composite coresample

with a large permeability contrast of 1 to 10. A brass sleeve was used between the two

regions of the cores to prevent communication between them. The annulus was a fired

Berea core with length 6.7 cm, diameter 3.56cm and 500 md permeability. The core was

epoxied to the brass sleeve. A central hole with a diameter of 1.6 cm was drilled and

filledwith 90-120 microndiameterglassbeadshaving5000 md permeabiUty. The core

unit assembly of a heterogeneous core is shown in Fig 3.5 and the properties of the

isolated coaxial composite core are listed in Table 3.3.

The core holder consisted of one upstream distribution plate within an end cap

and a downstream dual end cap. Both ends were secured by six long bolts to sustain

pressure. The inlet distribution plate was used to share fluid across the surface of the two

sections equally. An 0-ring was put on the edge of this distribution plate to seal;

preventing fluid invasion. A dual outlet end cap was designed such that the effluent fluids

of the center and annulus sections can be collected separately. In this end cap, fluid

-22-

sealedby an 0-ring on its edge. A one millimeterseparatorbarrier machined in the center

of the end cap sat on the center hole sand pack to prevent the central effluent fluid from

beingmixed with the fluidexiting the annulus section. This dual outletendcap was added

as a special feature to the core unit assembly so that the effluent fluids from the central

and annulus sections wouldenter independently into separateoutlet paths.

-23-

Notes:

A. COi-Tank.B. Nz-Tank.C. Brine, Surfactant

<M- Lignosulfonate.

) D. Oil.

mm E. CO2.F. Distilled Water.

* B G. Foam Generator.

H. Core Holder.

I. PressureTransduco*.

3. PressureTransducer.

K. BPR for Annuius.

L. BPR for Center.

M. To Computer.N. To Temco Pump.O. To Milton-Roy Pump.P. To Dry Gas Meter.

Q- To Wet Test Meter.

R. To Strip ChartP

Q -• R

Fig. 3.4 - COi-Foam coreflooding apparatus.

-'''A.-

'''•-Mf'-. ^

"••^•5i4:. V .-• • •,0.

^ ^"T J$• -/f^••#SI:

Inlet Endcap

T

B

-24-

Core Holder

Outlet Endcap

I

Bnina

Distribution grooves O-ring

Stainless

steel sleeve

Glass beads

Fig. 3.5 - Core unit assembly.

Epoxy

Berea sandstone

-25

Table 33 - Properties of Isolated Coaxial Composite Core.

CompositeCore sample (isolated)

K

(md)Area

(cm^)

Center Region(Glass bead 90-120 mm) 5000 0.42 1.27

Annulus Region(Fired Berea sandstone) 500 0.23 7.58

-26-

3.2.1-b A foam generator

The foam generator was a 2.5-cm long, and 3.7-cm diameter consolidated, fired

Berea sandstone core, inline with the core unit assembly. It was epoxy-mounted in a 304-

grade stainless steel holder designed to sustain pressure up to 3000 psi, in a manner

similar to that described for the core itself. COa/brine, C02/surfactant, C02/lignosulfonate

and C02/lignosulfonate mixed with surfactantwere coinjected into it to generate the foam

or bubbles, which propagated to the core.

3.2.1-c Differential pressure transducers

Differential pressure transducers, Validyne models DP-215 and DP-303, were

used to measure the pressure drops between different areas of the system. Appropriate

diaphragm sizes were used in the transducers to meet the anticipated pressure range in

each location. The transducers were calibrated with a dead-weight tester before they were

used. The low-pressure diaphragms (< 5-psi) were calibrated using a mercury

manometer. A threeway testing valve was mounted for each transducer to make sure that

a zero reading can be initially achieved prior to recording the data and can be rechecked

periodically during the run.

3.2.1-d Backpressure regulators (BPR)

Backpressure regulators, modified Temco model BPR-50, were used to maintain

the system pressure. The high pressure BPRs were connected to the center and annulus

outlet ports at the core exit while the domes were both connected to a nitrogen cylinder

from which they could be pressurized simultaneously. The low-pressure outlets from the

-27-

BPRs were connected to two separator vessels. The performance of the BPRs was very

critical, as it affected the flow velocities of the two high and low permeability sections.

The BPRs-50consists of two major sectionsthat areboltedtogether on each side of a thin

stainless steel diaphragm. The first part is the dome body, in which an empty volmne of

about 40 cc canbe filled withinertgas in order to pressurize the system. The second part

is a unit in which a diaphragm and a pencilshaped piece called the stem are attached

together via a seal bar. The stem moved freely within a 5-nmi hole in the center of the

unit and allowed fluid to flow when the dome pressure is equal to the inlet fluid pressure.

The seat and stem designs were modified to improve their ability to maintain identical

backpressure.

3.2.1-e Floating piston accumulators (FPA)

Three floating piston accumulators were employed as the transfer vessels with

volumetric capacity of a few liters for oil, brine or surfactant or lignosulfonate mixed

with surfactant, and CO2. The sealed pistons in these accumulators kept the solutions and

distiUed water isolated from each other. Distilled water was used as a displacing fluid for

advancing their pistons via the pump.

3.2.1-f Positive displacement pumps

A Milton-Roy HI metering pump and a TEMCO 1000-1-10-MP pump used

distilled water to drive the fluid inputs of aqueous phase and high pressure CO2 into the

system through floating piston accumulators. When saturating the core with oil, a Milton-

Roy in metering pump was used to drive water into the floating piston accumulators of

-28-

oil. The maximum flow rates in the Milton Roy HI pump and the TEMCO pump were

200 cc/hr and 21.95 cc/hr, respectively. However, for this experiment the core was

injected with a constant injection rate with the volumetric ratio of CO2 to aqueous

solution of 4 to 1. Therefore, the constant injection rate for CO2 was 13.16 cc/hr and 3.29

cc/hr for the aqueous phase. The total flow rate for these experiments were 16.45 cc/hr or

1.3 ft/d (Darcy velocity). When CO2 was injected alone, the flow rate was 16 cc/hr or 1.2

ft/d.

3.2.1-g Data acqiusition system

The data acquisition system consisted of a PCL-711S PC-Multilab Card (B & C

Microsystem Inc., Sunnyvale, CA.) mounted in a windows operated personal computer

and a MCl-20carrier demodulator(Validyne Engineering Corporation), receiving voltage

signals from the Validyne transducers. Several channels were used for transforming the

input signal, corresponding to each transducer, into DC voltages for the PC-LabCard. In

1995, Yaghoobi wrote an interactive program in Turbo Pascal to monitor, record and

convert the raw data to a usable form such as the pressure unit (psi), and to carry out

further computations for plotting and data processing. The voltage signals, produced by

each Validyne transducer, were transformed through a designated channel into the

demodulator and then to the computer for data acquisition. These data points were

averaged with a time delay of ten seconds. Rearranged data was saved mstantaneously in

four independent data files.

-29-

3.2.1-h Effluent collection

A special dual outlet end cap was designed to collect the effluent fluid separately

from the centerand annulus sections of the composite core. The output flowed from the

two regions, which were separated by a circular barrier of the same diameter as the

central zone of the composite core. The two output regions had their own exit plumbing

so that each was lead to a modified backpressure regulator (BPR) in which the dome

pressure was maintained at the test pressure (2100 psi). The two low-pressure liquid

outputs from the BPRs flowed into receiving flasks, while the outputs of atmospheric

pressure gas flowed through a wet test meter or a dry gas meter. The oil from the core

was collected in sample vials for the elapsed time of 30, 45 and 60 minutes during each

displacement run.

3.2.2 COi-Foam Coreflooding Experiments and Procedure

The experiments were conducted on a core saturated with crude oil. The crude oil

was degassed separator oil from the Sulimar Queen field. Lea County, New Mexico. We

used CO2, C02/brine, CO2/CDIO45 at concentrations of 500 ppm or 2500 ppm, CO2/

lignosulfonate at the concentration of 5000 ppm, COyClignosulfonate @ 5000 ppm mixed

with CD1045 @ 500 ppm) or COz/Clignosulfonate @ 5000 ppm mixed with CD1045 @

250 ppm) as the displacing agents. All tests were conducted at a constant injection rate of

CO2 to aqueous phase of 4 to 1 through core that already saturated with oil. Tests were

performed at a typical Permian Basin reservoir pressure and temperature (101° F and

2100 psig). The breakthrough time and incremental oil recovery were recorded for each

-30-

nin. The summary of C02-foam Coreflooding experiments are presented in Tables B.l-

B.17, Appendix B.

3.3 Adsorption Measurement Test

3.3.1 Adsorption Measurement Apparatus

The experiments were conducted using the circulationmethod apparatus shown in

Fig. 3.6. The confining pressure of the core holder in this apparatus was 200 psi. A

minipump was used to deliver fluid at a constant flow rate. The Berea sandstone core was

cut into a single core sample with length 2.3 in, diameter 1.5 in, porosity 14.7%, pore

volume 9.75 cc and permeability of 300-md. The core was inserted into rubber sleeve to

separate core from confining fluid and then into a stainless steel core holder. The stirrer

was used to mix the solution (surfactant, lignosulfonate and lignosulfonate mixed with

surfactant) in the flask during experiments. All adsorption measurements were conducted

at 77° F and ambient outlet pressure.

33.2 Adsorption Measurement Experiments and Procedure

To allow for equilibrium, at beginning of the experiments, brine from a flask

filled with a known weight of 102.5 cc was circulated through the core for 24 hours at a

flow rate of 10 cc/hr. After 24 hours of circulation, a known weight of brine was removed

from the system and was replaced with a known amount having a known of surfactant

solution concentration. After another 24 hours of circulation, another sample was

removed from the system and more surfactant having a different concentration was

added. Each removed sample was tested to determine the concentration change.

-31-

consequently the amount adsorbed onto the core. The cycle of sampling and adding was

repeated until no significant additional surfactant was adsorbed and the surfactant

adsorption isotherm was established. In a second series of experiments, the same

circulation rate and time were applied but with a different circulation scheme. A detailed

description of the circulation sequence will be given in the results and discussions.

The concentrations ofsolution components were analyzed spectrophotometrically.

The solution preparation methods to be used in a UV/visible wavelength

spectrophotometer to determine the unknown concentrations for CD1045 and

lignosulfonate were suggested by the sample providers (Chaser International and Georgia

Pacific Corporation).

A colorimetric method was used to analyze the unknown concentrations of

surfactant CD1045. This method relies on the formation of an ion pair by the anionic

surfactant component and a cationic dye (dimidium bromide). The ion pair is extractable

into anorganic solvent (chloroform) and changes its color from transparent to pink while

the dye alone is not. The mixed solution consisted of 1 cc surfactant, 7 cc chloroform and

7 cc dimidium bromide disulfine blue indicator. The surfactant dissolved into chloroform

was extracted into a square cuvette holding about 2.5 cc and measured with the

spectrophotometer at the wavelength of 520 nm.

For determining the unknown concentration of lignosulfonate, the dye and

organic solvent were not necessary, as the unknown concentrations of lignosulfonate

were directly measured using a spectrophotometer at a wavelength of 283 nm, which is

also minimal interference from CD1045.

Pump

-32-

MagneticStirrer

ConfiningPressure

Core Holder

Stainless Steel

Rubber

^ Berea Sandstone

Fig. 3.6 - Adsorption measurement apparatus.

-33-

The amount of adsorbed substance was determined based on the following

equation:

(V.dC,+V.C„+VpvC„)' V +v +v *

^ad ^ ^tv ^ *PV

_10-^V,(C.Vb(l-^)

where

Ci* = average initial concentration of system, ppm.

Ci = concentration of flask, ppm.

Cn = equilibrium concentration after last circulation, ppm

Cn+i = new equilibrium concentration, ppm.

Vad = volume of flask, (102.5 cc).

Vtv = tubing volume, (2.5 cc).

Vpv = pore volume of rock, (9.75 cc).

Vb = bulk volume, (66.57 cc).

Vt = total system volume, cc.

Vt =Vad+Vtv + Vpv

Mad = mass adsorption onto the rock, mg/ccrock-

(|) = porosity, (14.7%).

Summary of the adsorption measurements are presented in Tables C.1-C.7,

Appendix C.

CHAPTER 4

DISCUSSION OF RESULTS

The results of the experiments conducted in this study are presented and discussed.

Three types of experiments were performed. They were foam durability, C02-foam

coreflooding and adsorption measurement experiments. The data sets discussed in this

section can be found in Appendix A through C.

4.1 Foam Durability Results

Figure 4.1 shows the results of interfacial tension (IFT) between CO2 and

lignosulfonate solutions with diflerent base solutions (distilled water. Brine 1, Brine 2,

Brine 3, see Table 3.1). The IFT values in this graph were calculated using Eq. 3.1. The

results show that the IFTs increase with decreasing concentration of lignosulfonates.

Adding monovalent or divalent cations (Na"^, Ca^^ into distilled water lower the

interfacial tension slightly.

-34-

-35-

When lignosulfonate solutions were mixed with different 0.025 wt% surfactant

solutions, the result showed that IFTs increase with the lignosulfonate concentration (as

shown in Fig. 4.2) which is different from what was observed in Fig 4.1. The IFT

measurements were terminated at a concentration of 10 wt% because the solution of

lignosulfonate was too dark to see the bubbles. The results show that the IFT of

lignosulfonate solutions mixed with CD1045 is the lowest followed by mixtures with

CD1050 and CD1040, respectively. Lower IFTs favor foam generation and bubbles

stabilization.

Figure. 4.3 presents the result of static decay of COa-foam using lignosulfonate

solution as a foam former withBrine 3 as the base solution. The percentage of foam in

this graph indicates the persistence of foam remaining inside the sapphire cell after a

standardvolumeof CO2 hasbeen injected. The percentages of foam generated from these

solutions are very small, less tiian 20%. This indicates that this solution is a weak

foaming agent. The bubbles formed at 0.5 wt% concentration of lignosulfonate coalesced

in less than a minute. At higherconcentrations, the percentage of foam increased and the

bubbles formed lasted more than five minutes.

A very different trend was found when 0.025 wt% surfactant CD1045 was mixed

with lignosulfonate solutions at different concentrations, as shown in Fig. 4.4. Very

strong bubbles were formed (100% foam) at low concentrations (0.25 and 0.5 wt%) and

did not coalesce for at least90 minutes. At a concentration of 1.25 wt% of lignosulfonate,

a lower percentage of foam was formed (72%) but the bubbles also lasted for at least 90

minutes. At concentration above 2.5 wt% of lignosulfonate, the percentages of foam

became smaller and the bubbles coalesced in less than 20 minutes.

-36-

Lower concentrations of lignosulfonate showed higher percentages of foam

formed and longer decay times. The foaming ability of a surfactant increases as the

interfacial tension between CO2 and surfactant solution decreases. At a concentration of

lignosulfonate of 0.25 and 0.5 wt% with 0.025 wt% CD1045, the system was as stable

and as good foaming agent as CD1045 alone at high concentration.

The higher percentage of foam with lower percentage of lignosulfonate

concentrations were also found when 0.025 wt% CD1050 was mixed with lignosulfonate

at different concentrations. However, the percentages of foam formed at 0.25 and 0.5

wt% were lower than CD1045 and decreased with the time; but still had some foam

remaining after 90 minutes as shown in Fig. 4.5.

Similar trends are also shown in Fig. 4.6 when 0.025 wt% surfactant CD1040 was

mixed with lignosulfonate at different concentrations. However, at concentrations of 0.25

and 0.5 wt%, the percentage of foam formed was lower than in either CD1045 or

CD1050 and the bubbles coalesced in less than 20 minutes. But it should be noted that

CD1040 with no lignosulfonate decays much faster than CD1045 or CD1050.

These results show that lignosulfonate solutions mixed with 0.025 wt% CD1045

at concentrations of 0.25 and 0.5 wt% are the most stable compared to other solution of

CD1045 as well as solutions of CD1050 and CD1040. These results support earlier

finding that the Chaser™ CD1045 is one of the best foaming agents (Tsau and Heller,

1992; Preditis and Paulett, 1992; Kuehne, etal, 1992).

27

e22o

w<uc>»

2,17

12

0.1

-37-

-O-LC+DW

-O-LC+Brinel

LC+Brine2

-O- LC-<-Brine3

I I I I 1,1, • • • ' ' i-

1 10Concentration (wt%)

I I I I I >.

Fig.4.1 - IFTs between calcium lignosulfonate

in different brines and dense CO2.

100

25

20

115CO0)c>«

T3

hIO11.

5

0.1

• • ' • • •

-38-

+-

1 10Concentration (wt%)

-0-LC+CD1045

-^s-LC+CD1050

-0-LC+CD1040

I I I 1 I 111

100

Fig. 4.2 - BFTs between lignosulfonate solutions with surfactants and dense CO2.

30

25

20

-39-

—H-10wt% -0-7.5wt%

-i!^5.0wt% -^2.5 Wt%

1.0 Wt% -X- 0.5 Wt%

5 10

Elapsed Time (minutes)

Fig. 4.3 - Decay of C02-foamof lignosulfonate with Brine3 (basesolution).

—f

15

120

100 S—9

80

.? 60

-40-

-X- -X- -x- -X

-+-5.00wt% -0-3.75wt%

-i5t-2.50wt% -X-1.25wt%

-0-0.25wt% -0-0.50 wt%

- 0.00 wt%

20 40 60


80 100

Fig. 4.4 - Decay of C02-foam of lignosulfonate with 0.025 wt% CD1045.

120

100 X—X—X ^x-

-41-

•X- —X

-+-5.00wt%

-^2.50 wt%

-O-0.25 wt%

-X-0.00 wt%

40 60


-0-3.75wt%

-X-1.25wt%

-0-0.50wt%

Fig. 4.5 - Decay ofCOi-foam of lignosulfonate with 0.025 wt% CD1050.

-42-

h- 5.00 wt% -O-3.75 wl%

-j2s-2.50 wt% -O-1.25 wt%

-•-0.25 wt% -)K-0.50 wt%

X 0.00 wt%

10 15


20

Fig. 4.6 - Decay ofC02-foam of lignosulfonate with 0.025 wt% CD1040.

25

-43-

4.2 C02-Foain Coreflooding Results

Table 4.1 summarizes observed CO2 breakthrough time in both permeability

regions. When pure COa was used as a displacing agent in the noncommunicating

composite core (run #1), breakthrough occurred in the high permeability region (center)

after 0.26 PV of CO2 was injected but no breakthrough had been observed in the low

permeability zone (aimulus) when the test was terminated after 2.78 PV of total fluid was

injected. Coinjection of CO2 with brine, CD1045 @500 ppm and lignosulfonate @5000

ppm (runs #2, #3 and #4) simulated short cycles of WAG or SAG and delayed CO2

breakthrough was observed at 0.42 PV, 0.42 PV and 0.49 PV, respectively in the center.

CO2 breakthrough had not occurred in the low permeability region (annulus) at

termination which was after 5.31 PV, 6.46 PV and 13.72 PV injected, respectively. The

CO2 channeled through the highpermeability region andcontinued to flow preferentially

due to the high permeability contrast between the two layers.

When CD1045 @2500 ppm or lignosulfonate mixed with CD1045 (runs #5

through #7) were coinjected with CO2, foam displacement diverted fluid to the low

permeability region. In C02/CD1045@2500 ppm, CO2 breakthrough occurred after 0.48

PV of fluid injected in the high permeability region and 3.32 PV fluid injected in the low

permeability region. Even though using CD1045 @2500ppm (run #5) diverts the foam to

the lower permeability region, it is more expensive than using lignosulfonate mixed with

surfactant, as seen in run # 6 and #7. CO2 breakthrough in the high permeability region

occurred at 0.35 PV and in the low permeability region at 0.86 PV and 0.75 PV,

respectively.

-44-

Table 4.1 - Summaiy of Isolated Coaxial Composite Core Experiments

Run

#

ExperimentalConditions

Flow

rate

(cc/hr)

Ratio Bieakduough inAnnulus Region

(PV)

BrealdiroughTime in

Annulus Region( minutes)

Breakthrough inCenter Region

(PV)

BreakthroughHmein

Center Region( minutes)

1 CO2displaced oil 16 1 2.78 (♦*) (*) 0.26 14

2 COi/brine displacedoil

16.45 4:1 5.31 (••) (*) 0.42 22

3 COj/suif.(@SOO ppm)displaced oil

16.45 4:1 6.46 (♦♦) (*) 0.42 22

4 COj/lignosulfonate(©SOOOppm)displac^ oil

16.45 4:1 13.72 (♦») (*) 0.49 23

5 COi/surf. (@2500ppm) displaced oil

16.45 4:1 3.32 173 0.48 25

6 C02/(sarf.-flig-nosulfonate) (@S00iq>m + @5000 ppm)displaced oil

16.45 4:1 0.86 45 0.35 18

7 C02/(surf.+lig-nosulfonate) (@2S0ppm + @5000 ppm)displaced oil

16.45 4:1 0.75 39 0.35 18

(*): No breakthrough was observed. (**): End of the experiment

-45-

The production of CO2 in the low permeability regions indicated that foam

diverted part of the injected CO2 from the high to the low permeability region. When

lignosulfonate was used with surfactant CD1045, foam displacement becomes more

uniformin the two different permeabilityregions.

Figures 4.7 and4.8show theresults ofplotting thecumulative gas oil ratio(GOR)

as a function of total pore volume injected. The highest cumulativeGOR occurred in the

high permeability region when CO2 only was used as the displacmg agent. Coinjected

CO2 with brine or foam reduced the cumulative GOR. When surfactant @2500 ppm or

lignosulfonate mixed with surfactant were coinjected with CO2, foam was displaced

through the core, substantially reducing the GOR in the high permeability region while

detectable CO2 was produced fromthe low permeability region (Fig. 4.8).

This illustrated that surfactant @2500 ppm or lignosulfonate mixed surfactant

reduces the problem of nonuniformity in a displacement associated with the rock

heterogeneity and reduce the channelingof CO2 in a heterogeneouscore.

Figures4.9 and 4.10 present the results of the amount of oil produced (fractional

oil recovery) from the high and low permeability regions as a fimction of total pore

volume of displacing fluid injected. As mentioned earlier, the low permeability region

had a higher portion of recoverable oil compared with the high permeability regions;

therefore, it is hoped that the fluid injection will displace the oil from both, the high and

low permeability regions. About 100% of the oil in the high permeability region was

produced for each displacing agents usedin this study, as shownin Fig.4.9.

However, there was no oil production from the annulus Gow permeability) region

when CO2, C02-brine, C02-surfactant @500 ppm and C02-lignosulfonate @5000 ppm

-46-

were injected, as shown in Fig. 4.10. The mixture injection systems of surfactant @2500

ppm and lignosulfonate mixed with surfactant successfully depleted the low permeability

region (annulus). The displacement efficiency of surfactant @500 ppm with

lignosulfonate @5000 ppm at about 8.0 total PV injected in this region had the highest

efficiency (97%), followed by surfactant @2500 ppm (94%), surfactant @250 ppm, and

lignosulfonate @5000 ppm (68%). The production occurred earlier for surfactant @250

ppm with lignosulfonate at 5000 ppm than CD1045@2500 ppm and was not surpassed

until after more than 3 PV of fluid had been injected.

Further evidence to support this assertion is presented in Fig. 4.11 where

fractional oil recovery is plotted through both regions. The displacement of surfactant

@2500 ppm can recover all oil left from both regions, but surfactant at this concentration

is expensive as previous explanation. In order to find the cheaper solution, lignosulfonate

@5000 ppm wasmixedwith surfactant @250 ppm and @500 ppm.The sweep efficiency

at about 8.0 total PV injected from lignosulfonate mixed with surfactant @250 ppm was

not as effective for both regions, because the foam was not strong enough to divert as

much fluid to the low permeability region. Therefore, to make the lignosulfonate mixed

with surfactant more effective and recover all oil left from both regions, the concentration

of surfactant mixed with lignosulfonate was increased to 500 ppm. This mixture

performed better than CD1045 alone at the high concentration.

Figure 4.12 shows the pressure drop profiles and oil recovery for the low

permeability region with different concentrations of CD1045. The pressure drop using

CD1045 at 500 ppm are very low. That result indicates there was no oil produced from

the low permeability region. In order to increase the sweep efficiency from this region.

-47-

the concentration of surfactant was increased to 2500 ppm. No oil was produced during

the first two hours of the test. Foam started to form in the center section and gradually

diverting displacing fluid into the annulus section; thus displacing oil from this section

and increasing the oil production.

Pressure drop profiles and oil recovery for the low permeability region (annulus)

with different concentrations of CD1045 mixed with 5000 ppm Iignosulfonate in CO2

injection can be seen in Fig. 4.13. The pressure drop of CD1045 @500 ppm and

Iignosulfonate @5000 ppm is higher than that of CD1045 @250 ppm and Iignosulfonate

@5000 ppm; hence increasing the oil recovery.

-48-

12.00 1

10.00

6.00 -

i 4.00

0.00 1.00 2.00 3.00 4.00 5.00

Total Pore Volume Injected

-X-C02

-O C02/surfactant@ 500 ppm C02/surfactant@2500 ppm-O- C02/(surf@500 ppm + lig @ 5000ppm) -O-C02/(surf@250 ppm+ lig @ 5000ppm)-X- C02/lignosulfonate@5000 ppm

C02/Brine

6.00

Fig. 4.7- Cumulative GOR observed from the high permeability (center) region.

7.00

OCOO 10.00 -

16.00

14.00 •

12.00

8.00

c 6.00

" 4.00-

0.00 1.00 2.00

-49-

3.00 4.00 5.00 6.00


7.00 8.00 9.00

-£r-C02/surfactant @2500 ppm -O-C02/(surf@500 ppm + lig @ 5000ppm)HD- C02/(surf@250 ppm + lig @ 5000 ppm)

Fig. 4.8- Cumulative GrOR observed from the low permeability (amiulus) region.

-50-

1.20

o 0.80

O 0.60CO

o 0.40

0.00 1.00 2.00 3.00 4.00 5.00


•x—ffl:

6.00 7.00

-X-C02 -l-C02/Brine

-O C02/surfactant@ 500 ppm -o- C02/surfactant@2500 ppm-O- C02/(surf@500 ppm + lig @ 5000 ppm) -A- C02/(surf@250 ppm + lig@ 5000 ppm)-X- C02/lignosulfbnate@ 5000 ppm

Fig. 4.9 - Oil recoverythrough the high permeability region (center).

1.20

^ 1.00 -

IS 0.80 ^

6 0.60 -

.2 0.40 -

0.20 -

0.00

-51-

2.00 4.00 6.00


8.00 10.00

-£s-C02/surfactant @2500 ppm -O- C02/(surf@500 ppm + Hg @ 5000 ppm)-O- C02/(surf@250 ppm + lig @ 5000 ppm)

Fig. 4.10 - Oil recoverythrough the low permeability region (amiulus).

1.20

P 0.80

O 0.60

.2 0.40

0.20

-52-

3 4 5 6


C02/surfactant @2500 ppm -o- C02/(surf@500 ppm + Iig @ 5000ppm)-•-C02/(surf@250 ppm + iig @ 5000 ppm)

Fig. 4.11 - Oil recovery through both regions.

S.

sQ

£S 10.00CO

25.00

20.00

15.00

5.00

0.00

-53-

100 200 300

Time, minute

400

—O—Pressure drop of CD1045 @ 2500 ppmA Pressure drop of CD1045 @ 500 ppm

- -O- -Oil recovery of CD1045 @ 2500 ppm

1.20

1.00

0.80 ^

0.60 S

0.40

0.20

0.00

500

Fig. 4.12 - Pressure dropprofilesandoil recovery for the low permeability region(annulus) with different concentrations of CD1045 in CO2 injection.

30.00

25.00

j£ 20.00

15.00

S 10.00

-54-

1.20

O 1.00

0.80 C

0.40 o

0.20

0.00

0 50 100 150 200 250 300 350 400 450

Time, minute

—A—Pressuredrop of C02/(CD1045@500 ppm + lig@5000 ppm)-O-Pressure drop for C02/(CD1045@250 ppm + lig@5000 ppm)- O- -Oil recovery for C02/(CD1045@500 ppm + lig@5000 ppm)- -X- -Oil recovery for C02/(CD1045@250 ppm + lig@5000 ppm)

Fig. 4.13 - Pressuredrop profiles and oil recoveryfor lowpermeabilityregion (annulus)with different concentrations of CD1045 mixedwith5000ppm lignosulfonate in CO2

injection.

-55-

4.3 Adsorption Measurements Results

The standard calibration curves of lignosulfonate and CD1045 were established (as

shown in Figs. 4.14 and4.15) to determine the concentrations of CD1045, lignosulfonate

or lignosulfonate mixed with CD1045 in the later analysis. An explanation of standard

curves relatedto using the wavelengths for lignosulfonate andCD1045 (283 and 520 nm,

respectively) has already been given in the adsorption measurement experiments and

procedure.

Figure 4.16 shows the amount of surfactant adsorbed onto Berea sandstone rock

samples. The adsorption isotherm of CD1045 indicates that the mass adsorbed onto the

rock increases as the final (equilibrium) concentration of surfactant increases. Similar

results (as shown in Fig. 4.17) were obtained when lignosulfonate wascirculated through

the core sample, where increasing the amount of final concentration of lignosulfonate

increased the adsorption of lignosulfonate. The adsorption quantity reaches a maxiiriiim

of 3 mg/ccrock at lignosulfonate concentration of 15000 ppm, then it decreases to 2.5

mg/cciock at a high concentration (20000 ppm).

The adsorption results of CD1045 in the presence of 5000 ppm of lignosulfonate

and the adsorption result of lignosulfonate (5000 ppm) are plotted as fimctions of the

final concentration of CD1045 in Figs. 4.18 and 4.19, with different initial conditions

(using brine) of the core sample. In Fig. 4.18, the core was flushed with brine followed by

injecting the three different concentrations of surfactant. For Figure 4.19, the core was

flushed with brine prior to injecting each concentrations of CD1045. Adsorption results

of CD1045 in the absence of lignosulfonate are also included in these figures. In Figures

4.18, 4.19 and 4.20 were presented the final concentrations of CD1045 that they were

-56-

based on initial concentrations of CD1045 with three different concentrations of 250

ppm, 500 ppm and 1000 ppm.

Figure 4.18 presents the adsorption results when 5000 ppm of lignosulfonate was

coinjected with different final concentrations of CD1045. The adsorption of CD1045

increases as the final concentrationincreases. However, the adsorption amount is reduced

by adding lignosulfonate into surfactant solutions from 1.28 to 0.69 mg/cc rock (46%) at

1000 ppm and from 0.61 to 0.31 mg/cc rock (49%) at 500 ppm initial concentrations of

CD1045. No significant reductionwas found at 250 ppm initial concentrationof CD1045.

Similar results were obtained using different initial conditions, as shown in

Fig.4.19. The adsorption amount is reduced from 0.97 to 0.81 mg/cc rock (17%) at 1000

ppm, 0.32 to 0.20 mg/cc rock (37%) at 500 ppm and 0.20 to 0.14 mg/cc rock (30%) at 250

ppm initial concentration of CD1045. This indicates that initial conditions are important

in the adsorption of CD1045.

Figure 4.20 depicts the adsorption of surfactant CD1045 in three different

sequences of experiments. The first sequence used CD1045, where the core was flushed

with brine before injecting the different concentrations of surfactant. The second

sequence used lignosulfonate as the sacrificial agent; the core was first flushed with

brine, then lignosulfonate was injected followed by injecting CD1045. The third

sequence coinjected lignosulfonate with CD1045, where the core was flushed with brine

before injecting the different concentration of CD1045 mixed with lignosulfonate. The

results show that coinjecting 5000 ppm of lignosulfonate with CD1045 (500 ppm and

lOOO ppm initial concentrations) reduces the adsorption of CD1045 by 38% and 17%,

respectively, whereas preflushing the core with 5000 ppm lignosulfonate reduces the

-57-

adsorption of CD1045 (500 ppm and 1000 ppm initial concentrations) by 56% and 30%,

respectively.

In order to demonstrate the cost effectiveness of using lignosulfonate as sacrificial

agent, an example calculation is presented in Table 4.2. The expense due to CD1045

adsorption was determined based on the model consisting of a 15 feet pay thickness

formation with 12% average porosity in a 25 acre field. Coinjection of lignosulfonate

with CD1045 reduced the loss of CD1045 from 870 to 544 Ib/acre-ft at 500 ppm and

from 2638 to 2203 Ib/acre-ft at 1000 ppm CD1045. The cost savings wouldbe $153,992

and $230,988, respectively. On the other hand, prefiushing the core with 5000 ppm

lignosulfonate reduced the adsorption of CD1045 from 870 to 381 Ib/acre-ft at 500ppm

and from 2638 to 1849 Ib/acre-ft at 1000 ppm CD1045. The cost savings would be

$205,323 and $372,147, respectively.

The results show that prefiushing with 5000 ppm lignosulfonate is more effective

in reducing the loss of surfactant CD1045 and more money could be saved than by

coinjecting 5000 ppm of lignosulfonate with CD1045.

« 0.08

-58-

y = 0.0006X + 0.0012

100 150 200

Concentration, ppm

250 300

Fig. 4.14 - Surfactant CD1045 standard curve with wavelength520 nm.

8CO

I 1.60^

3.50

3.00

2.50

2.00

1.00

0.50

0.00 —1—

50

-59-

y = 0.0094X + 0.0895

100 150 200 250

Concentration, ppm

300 350

Fig. 4.15- Lignosulfonate calcium standard curvewith wavelength 283 nm.

o>

Eco

e-S

<

3.50

2.50

-60-

200 400 600 800

Final concentration of surfactant CD1045,ppm

r •• i !•

1000 1200 1400 1600 1800

Fig. 4.16 - Adsorption ofsurfactant CD1045 onto Berea sandstone core sample.

9 2.50

2.00

s 1.50

•P 1.00

-61-

5000 10000 15000 20000

Final concentration of lignosulfonate, ppm

Fig.4.17 - Adsorption oflignosulfonate onto Berea sandstone core sample.

25000

1.20 -

^ 1.00

0.20 -

5 0.00

-62-

200 400 600 800

Final concentrations of surfactant, ppm

1000

-O-O ppm of lignosulfoante -^5000 ppm of lignosulfonate

Fig. 4.18 - Adsorption of surfactant CD1045 onto Berea sandstone coresample asa function ofsurfactant CD1045 concentration at lignosulfonate levels of0 ppm and 5000

ppm (The core was flushed with brine followed by injecting the three differentconcentrations ofsurfactant).

1.20

I

-63-

100 200 300 400 500

Concentrations of surfactant, ppm600

-O-O ppm of lignosulfoante -^5000 ppm of lignosulfonate

Fig. 4,19 - Adsorption ofsurfactant CD1045 onto Berea sandstone core sample asa function ofsurfactant CD1045 concentration atlignosulfonate levels of0 ppm and 5000

ppm (The corewas flushed with brine prior to injecting each concentrations ofsurfactant).

o E 0.40

-64-

Final concentration of surfactant, ppm

-O-CD1045 alone -O-Ugnosulfonate first Mixed

600

Fig. 4.20 - Adsorption ofsurfactant CD1045 with three different sequences ofexperiments ontoBereasandstone core sample.

-65-

Table 4.2 - CostSaving Using a Sacrificial Agent, Based on Adsorption Results

(Ib/acre-ft).

Adsorption results in (Ib/acre-ft) Cost saving with a sacrificial agent ($)

Initial con-. CD1045 Mixture Pie-flush with Mixture Pie-flash with

centradon 001045+ 5000 ppm CD1045+ 5000 ppm

(ppm) Ugnosulfonate Lignosulfonate Lignosulfonate lignosulfonate

500 ppm 870 544 381 $ 153,992 $ 230.988

1000 ppm 2638 2203 1849 $205^23 $ 372,147

CHAPTERS

CONCLUSIONS

AND

RECOMMENDATIONS FOR FUTURE WORK

5.1 Conclusions

Conclusions were drawn based on the three different sets of laboratory

experiments. These studies investigated the feasibility of using Ugnosulfonate as a

sacrificial agent to mix with surfactants in C02-foamflooding application.

5.1.1 Foam Durability Experiments

Based on the results of a series of foam durability experiments, the following

conclusions can be drawn:

1. Ugnosulfonate in a brine solution (1.5 wt% NaCL + 0.5 wt% CaCl2) is a weak

foaming agent for generating COa-foam bubbles.

2. Lower interfacial tension is favorable to generating more stable foam in the

mixture of lignosulfonate/surfactant mixture.

-66-

-67-

3. The BFTs of lignosulfonate solutions decrease with the increase of the

concentration of lignosulfonate.

4. The IFTs of the mixtures of surfactant and lignosulfonate increase with the

concentration of lignosulfonate.

5. When a low concentration (0.25 and 0.5 wt%) of lignosulfonate was mixed with

0.025 wt% of other surfactants, CD1045 generated the strongest foam followed

byCD1050andCD1040.

5.1.2 COi-Foam Corefloodjng Experiments

Based on COa-foam coreflooding experiments, the following conclusions were

made:

1. Lignosulfonate mixed with CD1045 could improve the problem ofnonuniformity in

displacement associated with rock heterogeneity and reduce the channeling of CO2

in a heterogeneous core.

2. Coinjection of CO2 and lignosulfonate at 5000 ppm as sacrificial agent mixed with

various concentration of surfactant CD1045 (250 ppm or 500 ppm) is effective for

delaying CO2 breakthrough time in the high permeability region and diverting

displacing fluid into the low permeability region. Thus, oil in the low permeability

region was displaced andoil production was significantiy increased.

3. The displacement efficiency ofCD1045 @500 ppm and lignosulfonate @5000 ppm

at about 8.0 total PV injected had the highest oU recovery (97%) in the low

permeability region, foUowed by CD1045 @ 2500 ppm (94%), and CD1045 @250

ppm and lignosulfonate @5000ppm (68%).

-68-

4. The pressure drop of CD1045 @500 ppm and lignosulfonate @5000 ppm is higher

than that of CD1045 @250 ppm and lignosulfonate @5000 ppm; producing a higher

oil recovery.

5.1.3 Adsorption Measurement Experiments

Based on adsorption measurement experiments, the following conclusions can be

drawn:

1. The adsorption of surfactant CD1045 on Berea sandstone increases as the

concentration of CD1045 increases.

2. CD1045 adsorption is dependent on the initial core conditions.

3. The addition of lignosulfonate reduces the adsorption of surfactant CD1045.

4. Coinjecting 5000 ppm of lignosulfonate with CD1045 (500 ppm and 1000 ppm)

reduces the adsorption of CD1045 by 17% to 38%, respectively, whereas

preflushing the core with 5000 ppm lignosulfonate reduces the adsorption of

CD1045 (500 ppm and 1000ppm) by 30% to 56%, respectively.

5. Preflushing with 5000 ppmlignosulfonate is more effective in reducing the lossof

CD1045 and more money could be saved than by coinjecting 5000 ppm of

lignosulfonate with CD1045.

5.2 Recommendations for Future Work

1. Besides using calcium lignosulfonate as sacrificial agent, other types of

lignosulfonate such as ammonium lignosulfonate and sodium lignosulfonate

mixed with different types of surfactants such as CD1045, Dowfax8390 and

CD128 should be examined.

-69-

2. Using different types of rock such as limestone and carbonate in COi-foam

corefloodingexperiments and adsorption measurement experiments are necessary

to be performed to investigate the effectiveness of lignosulfonate as a sacrificial

agent in different types of reservoir rocks.

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