Laboratory Investigation of the Effect of Solvent ...West Sak is a viscous oil reservoir located within the Kuparuk River Unit on the North Slope of Alaska and part of a larger viscous

LABORATORY INVESTIGATION OF THE

EFFECT OF SOLVENT INJECTION ON

IN-SITU COMBUSTION FOR VISCOUS OILS

A THESIS

SUBMITTED TO THE DEPARTMENT OF PETROLEUM

ENGINEERING

OF STANFORD UNIVERSITY

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREE OF

MASTER OF SCIENCE

By

Jean Cristofari

March 2006

I certify that I have read this thesis and that in my opin-

ion it is fully adequate, in scope and in quality, as partial

fulfillment of the degree of Master of Science in Petroleum

Engineering.

Prof. Anthony Kovscek(Principal Advisor)

I certify that I have read this thesis and that in my opin-

ion it is fully adequate, in scope and in quality, as partial

fulfillment of the degree of Master of Science in Petroleum

Engineering.

Dr. Louis Castanier(Co-Advisor)

ii

Acknowledgments

This thesis was prepared with the support of the U.S. Department of Energy, under

Award No. DE-FC26-03NT15405. However, any opinions, findings, conclusions, or

recommendations expressed herein are those of the author and do not necessarily

reflect the views of the DOE. Additionally, funding was provided by the Industrial

Affiliates of the Stanford University Petroleum Research Institute for Heavy Oil and

Thermal Recovery (SUPRI-A). This support is gratefully acknowledged. We espe-

cially thank ConocoPhilips for providing us with the West Sak oil.

I wish to express my deepest gratitude to my academic and research advisor Dr.

Anthony R. Kovscek for his guidance, support and confidence throughout my work.

I would also like to specially thank Dr. Louis M. Castanier for his guidance, time,

and strong encouragements, without which this work could not have been completed.

I wish to acknowledge Dr. Tom Tang who was always available to help me with my

experiments and all the professors from the department for their valuable support,

especially Dr. Kristian Jessen.

Special thanks to all SUPRI-A members who contributed in bringing friendliness

and an excellent work atmosphere. I would like to thank my classmates, friends and

officemates for their friendship and encouragements to give the best of myself and

made my stay at Stanford a wonderful and unforgettable experience.

Finally, I would like to thank my family for their countless support.

iii

Abstract

This thesis presents an experimental scoping study of cyclic application of solvent

injection and in-situ combustion aimed at production and upgrading of viscous and

heavy oils. In-situ combustion is an effective thermal recovery process that suffers

from fewer limitations than steam injection, but is not applied as widely. Combustion

of heavy oil generally tends to upgrade the oil because the heaviest fraction of the

crude is consumed as fuel. Solvents are also useful to reduce oil viscosity in situ and

facilitate production. Liquid solvents are usually expensive and the price of the oil

recovered low. Both solvent injection and in-situ combustion are technically effective

in a variety of reservoirs. The combination of the two methods has, however, never

been tried to our knowledge.

Two different crude oils were employed: Hamaca from the Orinoco Belt of Venezuela

and West Sak from the North Slope of Alaska. First, “Ramped Temperature Oxida-

tion” studies were conducted to measure the kinetic properties of the oil prior to and

following solvent injection. Pentane, decane, and kerosene were the solvents of inter-

est. As expected from the literature, pentane proved to be the best solvent. Second,

combustion tube experiments were conducted. Solvent was injected in a cyclic fashion

and then the tube was combusted. In both types of experiments, effluent gases were

analyzed and temperature measured. Hamaca oil presented good burning properties

that were not affected when one cycle of pentane injection preceded combustion. The

pentane extracted lighter components of the crude preferentially depositing effective

fuel for combustion. West Sak oil, however, did not exhibit stable combustion prop-

erties following solvent injection, even when metallic additives were added to enhance

the combustion. We were unable to propagate a burning front within the combustion

iv

tube. Nevertheless, experimental results show that this combined method may be

applicable to a broad range of oil reservoirs.

v

Contents

Acknowledgments iii

Abstract iv

Table of Contents vi

List of Tables viii

List of Figures ix

1 Introduction 1

1.1 Problem statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Literature review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.1 Asphaltenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.2 Solvent injection . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.3 In-situ Combustion . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3 Heavy Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2 Experimental apparatus 13

2.1 Experimental objectives . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 General equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.2.1 Electronic equipment . . . . . . . . . . . . . . . . . . . . . . . 16

2.2.2 Properties of the oils . . . . . . . . . . . . . . . . . . . . . . . 16

2.2.3 Sand mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3 Kinetic experiment description . . . . . . . . . . . . . . . . . . . . . . 18

vi

2.3.1 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.3.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4 Tube experiment description . . . . . . . . . . . . . . . . . . . . . . . 20

2.4.1 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.4.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3 Results 24

3.1 Kinetic experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.1.1 Hamaca Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.1.2 West Sak Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.2 Data analysis for kinetic experiments . . . . . . . . . . . . . . . . . . 38

3.3 Tube experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.3.1 Hamaca Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.3.2 West Sak Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4 Discussions and Recommendations 52

Conclusion 56

Bibliography 57

Appendix A 61

Appendix B 63

vii

List of Tables

1.1 Distribution of heavy oil and bitumen resources . . . . . . . . . . . . 12

2.1 Experiments with Hamaca oil. . . . . . . . . . . . . . . . . . . . . . . 13

2.2 Experiments with West Sak oil. . . . . . . . . . . . . . . . . . . . . . 14

2.3 Properties of the Hamaca Oil. . . . . . . . . . . . . . . . . . . . . . . 17

2.4 Properties of the West Sak Oil. . . . . . . . . . . . . . . . . . . . . . 17

2.5 Sand mixture composition. . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1 Increase in temperature during HTO reactions for Hamaca oil. . . . . 28

3.2 Increase in temperature during HTO reactions for West Sak oil. . . . 36

3.3 Activation Energies and critical temperatures for the Hamaca oil. . . 39

3.4 Activation Energies and critical temperatures for the West Sak oil. . . 39

viii

List of Figures

1.1 Polycyclic structures for asphaltene molecules. . . . . . . . . . . . . . 4

1.2 In-situ combustion schematic temperature profile. . . . . . . . . . . . 8

1.3 Schematic of oxygen uptake rate showing the effect of temperature. . 10

2.1 Schematic of a kinetic cell . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2 Schematic of the kinetic experiment’s procedure. . . . . . . . . . . . . 20

2.3 Schematic of a combustion tube. . . . . . . . . . . . . . . . . . . . . . 21

2.4 Schematic of the solvent injection procedure for the tube experiment. 22

2.5 Schematic of combustion procedure for the tube experiment. . . . . . 23

3.1 Concentration and temperature profiles during in-situ combustion with

Hamaca oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2 Temperature profiles after injecting different solvents. . . . . . . . . . 27

3.3 Temperature profiles after injecting different amounts of pentane. . . 29

3.4 Temperature profiles after injecting pentane at different pressures. . . 30

3.5 O2 profiles after kerosene injections. . . . . . . . . . . . . . . . . . . . 31

3.6 Temperature profiles for emulsified and de-emulsified oils. . . . . . . . 32

3.7 Concentration profiles during West Sak’s kinetic combustion. . . . . . 34

3.8 Temperature profiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.9 Concentration profiles after pentane injection. . . . . . . . . . . . . . 36

3.10 Temperature profiles during combustion with metallic additives. . . . 37

3.11 Concentration profiles during combustion after injecting 500 ml of pen-

tane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.12 Temperature profiles during combustion after injecting 500 ml of pentane. 42

ix

3.13 Sand after the tube experiment with Hamaca oil. . . . . . . . . . . . 43

3.14 Burned sand from the tube experiment with Hamaca oil. . . . . . . . 43

3.15 “Coke” from the tube experiment with Hamaca oil. . . . . . . . . . . 44

3.16 Unburned sand from the tube experiment with Hamaca oil. . . . . . . 44

3.17 Concentration profiles during West Sak’s tube combustion. . . . . . . 45

3.18 Temperature profiles during West Sak’s tube combustion. . . . . . . . 46

3.19 Sand after West Sak’s tube combustion. . . . . . . . . . . . . . . . . 47

3.20 Sand after West Sak’s tube combustion. . . . . . . . . . . . . . . . . 48

3.21 Concentration profiles during combustion after injecting 500 ml of pen-

tane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.22 Temperature profiles during combustion with metallic additives. . . . 50

3.23 Concentration profiles during combustion with metallic additives. . . 51

x

Chapter 1

Introduction

This thesis investigates the effect of solvent injection on the subsequent performance

of in-situ combustion. The work is based on experimental results obtained with a

combination of these two successful in-situ upgrading processes for viscous oils. By

mixing with oil, the solvent decreases the oil viscosity and upgrades the crude by

depositing in-situ the heavy ends. A large part of the oil’s valuable fractions (light

ends) are recovered and the heavy ends that are markedly less interesting are left.

The solvent injection is then followed by an in-situ combustion. The latter burns

the heavy ends remaining after the solvent injection and enhances the production by

decreasing the oil viscosity, due to high temperatures. The combustion also upgrades

the oil through thermal cracking. For our experiments, two oils of particular interest

within the scope of our study were used. The first set of experiments were done

with Hamaca oil from Venezuela and the field location requires important costs of

transporting to the refinery. The second set was conducted with West Sak oil from

Alaska where steam injection is unsuitable.

While the presence of oil in the Orinoco heavy-oil belt, in Central Venezuela,

has been known since the 1930’s, the first rigorous evaluation of the resources was

made in the 1980’s and the region was divided into four areas: Machete, Zuata,

Hamaca, and Cerro Negro. It contains between 1.2 and 1.8 trillion recoverable barrels

(Kuhlman, 2000) of heavy and extra-heavy oil. There are four government-approved

joint venture projects between Petroleos de Venezuela S.A (PdVSA), the state oil

1

CHAPTER 1. INTRODUCTION 2

company, and foreign partners: Petrozuata, Cerro Negro, Sincor and Hamaca. The

9-11◦ API density crude is processed at the Jose refinery complex on the northern

coast of Venezuela. The cost of transporting heavy oils to the northern coast provides

an incentive to investigate how in-situ upgrading can decrease these downhill costs.

In 2003, the total production from these projects was about 500,000bbl/d of synthetic

crude oil (this is expected to increase to 600,000bbl/d by 2005) (Acharya et al., 2004).

West Sak is a viscous oil reservoir located within the Kuparuk River Unit on the

North Slope of Alaska and part of a larger viscous oil belt that includes Prudhoe

Bay. The estimated total oil in place ranges from 7 to 9 billion barrels with an

oil gravity ranging from 10◦ to 22◦ API. The reservoir depths ranges from 2,500 to

4,500 feet with gross thickness of 500’ and an average net thickness of 90’. The

temperature is between 45 and 100◦F and there is a 2,000 ft (600m)-thick Permafrost

layer. In March 2005, 16,000 BOPD were produced and 40,000 BOPD are planned

for 2007 (Targac et al., 2005). Within the scope of this study, West Sak reservoir is of

particular interest because technical difficulties make steam injection unsuitable for

the following reasons (Gondouin and Fox, 1991):

• Steam would have to go through a thick Permafrost layer that would cause the

well to sink if it happened to melt,

• The reservoirs consists in thin and medium permeable layers,

• The formation contains some swelling clays that reduce the rock permeability

when exposed to steam condensate,

Solvent injection and in-situ combustion are effective in a variety of fields and

both upgrade the oil directly in the reservoir thereby making heavy resources easier

to exploit. The combination of these two processes is applicable at large scale to

recover viscous oil or in-situ combustion could only be applied on an ad hoc basis to

clean the wellbore region, increase the permeability, and thus to act as a stimulation

process (Castanier and Kovscek, 2005).


1.1 Problem statement

With the growing need to extract the heaviest and most viscous crude oils to face the

continuous rise in the world’s energy demand, the incentive to improve current tech-

nologies to make heavy-oil production profitable is great. Recovering viscous and low

API gravity crude oils requires improved recovery processes such as steam injection

(e.g. (Prats, 1986)), electrical heating (e.g. (Rangel-German et al., 2003)), solvent

injection (e.g. (Mokrys and Butler, 1993)) or in-situ combustion (e.g. (Burger and

Sahuquet, 1972)). Steam injection is today’s most widely applied enhanced recovery

technique (Moritis, 2004) but it can be unsuitable in many heavy oil reservoirs such as

deep or thin reservoirs, or in reservoirs overlaid by permafrost. The heat losses to the

surroundings (the overburden and underburden) can make the process uneconomic

and unsuitable. The rates at which steam upgrades the oil are very slow. In fact, it

is only after several years of steam pressures above 6.9 MPa (1,000 psi) that the oil

is noticeably pyrolyzed into a greater API crude oil (Kuhlman, 2000). Furthermore,

steam injection requires great capital investment for the steam equipment and the

insulation of pipes.

In the case of solvent injection, liquid solvents are expensive and the loss of solvents

in the reservoir is a limiting factor. Although in-situ combustion is considered as

the most profitable tertiary recovery process, it is not widely applied because of

the difficulty to control the process at large scale. Combustion fronts propagate

more erratically than steam fronts and it may be difficult to obtain good sweep

of the reservoir. The combination in a cyclic fashion solvent injection with in-situ

combustion overcomes these difficulties. A limited amount of solvent is injected to

recover the oil’s light ends and then in-situ combustion burns the crude’s heavy ends

that deposited on the rock with the solvent. the combustion helps to remove reservoir

damage and stimulate recovery.


1.2 Literature review

This report studies the combination of solvent injection and in-situ combustion. First,

solvent is injected to recover the valuable ends in the oil and precipitate the as-

phaltenes. Second, in-situ combustion oxidizes the heavy ends left in the media during

the solvent injection process and creates energy. Thus, the literature review begins

by presenting asphaltenes and solvent injection and carry on with in-situ combustion.

1.2.1 Asphaltenes

Asphaltenes are present in all crude oils, varying from 1% in light oils to 15%, or more,

in heavy oils. Asphaltene are molecules with the largest molecular weight in crude

oil (ranging from approximately 900 to 500,000) (Storm and Sheu, 1994) depending

on the method used for measurement and they have the most polar constituents.

They are formed of aromatic ring structures with oxygen, nitrogen and sulfur. Their

detailed structure is poorly understood but fragments presented in Figure 1.1 are

typical of asphaltenes molecules. The oil’s viscosity is strongly related to asphaltene

concentration and its nature (Speight, 1994) and they are directly responsible for the

high viscosity of heavy crude oils.

Figure 1.1: Polycyclic structures for asphaltene molecules (Speight, 1992).

Asphaltenes are usually defined in the literature as the fraction of crude oil that

is insoluble in n-pentane. Thus when light hydrocarbon solvents are added to crude


oil, asphaltenes tend to precipitate. Also, a drop in pressure or pH (further to acid

jobs or CO2 injection for instance) leads to asphaltene deposition. The presence

of ferric iron FE3+ also enhances asphaltene precipitation. The iron is assumed to

change the polarity of the rock and thus attract the most polar fractions of the crude

oil. Asphaltene aggregates recovered from wells were mostly low hydrogen and high

aromatic molecules (Murgich et al., 2001). Deposits occur mostly in the near wellbore

area, but also in the reservoir. In both cases, asphaltene deposition causes a decrease

in the production and it is very hard to prevent precipitation and to remedy the

situation. Unlike paraffin, they do not melt.

Resins are defined as the second heaviest molecules in crude oil and they differ

from asphaltenes mainly by a greater H/C ratio because they have less aromatic

carbons. Both have a high tendency for forming coke during visbreaking and cracking

processes, as described subsequently. They are soluble in liquids that precipitate

asphaltene, such as n-pentane, but insoluble in propane. Hence, resins coprecipitate

with asphaltenes in propane deasphalting procedures but do not precipitate in pentane

deasphalting.

The mechanism of producing asphaltene precipitates is modeled in the literature

on the basis of different theories (Islam, 1994):

Continuous thermodynamic model (CT) The continuous thermodynamic model

explains asphaltene precipitation by an upset in the balance of the chemical

composition of the petroleum. The ratio of polar to non-polar molecules and

the ratio of high to low molecular weight molecules are the two factors that

determine asphaltenes’ solubility. Mixing a miscible solvent with petroleum

changes these ratios. Asphaltenes are considered to be dissolved in the oil and

the phase behavoir depends on the thermodynamic conditions of temperature

pressure, and composition.

Steric colloidal model (SC) This model assumes that asphaltenes exist in oil as

suspended colloidal molecules. They are stabilized in hydrocarbon liquids by

the presence of resins. In fact, the interaction between resins and asphaltenes

is preferred over asphaltene-asphaltene or resin-resin interaction. Asphaltenes


are thus peptized and dispersed by resins that are always greater in number

(approximately 3 to 40 times). The micelle formed is thus much richer in resins.

The micelle is formed from a polar asphaltene core, surrounded by one or more

resin molecules that mask asphaltene’s polar functions and the macromolecule

is then soluble in crude oil. It is unlikely to have more than one molecule of

asphaltene per micelle and the number of surrounding resins is approximately

controlled by the number of aromatic centers Speight (1994). Stability depends

on the concentration of resins as compared to the amount of asphaltenes.

Fractal aggregation model (FA) The fractal aggregation model combines the idea

of the two previous models, accounting for both solubility and colloidal effects.

This model considers the asphaltenes to be partly dissolved and partly in the

colloidal state. The solubility of asphaltenes in the oil depends not only on the

peptizing effect of resins but also the resin concentration in the oil.

Thus, resins play a key role in the solubilization of asphaltenes. In the presence

of light saturated hydrocarbon such as pentane in which resins are soluble, resin

concentration will then vary and asphaltenes are supposed to undergo dissociation

with resins and precipitate. In presence of propane, asphaltene and resins precipitate

together whereas mixing the oil with a heavier solvent such as decane, leads to less

precipitation.

1.2.2 Solvent injection

Vaporized or liquid hydrocarbon solvents are useful for the recovery of highly viscous

heavy oil and bitumen. When injected in the reservoir, they finger into the oil and

decrease viscosity of the oils by dilution. The production is thus enhanced and the

solvents are recovered and recycled. The solvent should have the maximum solubility

in the oil to ensure a sizeable extraction rate. Solvent may be chosen, however, to

dilute more light ends that are of greater value than heavy ends. If the concentration

of the light hydrocarbon solvent in the diluted oil is great enough, then it leads to

a deasphalting procedure and reduces the viscosity to an even greater extent. It has

been shown that that the amount of asphaltene deposition decreases as the molecular


weight of the solvent increases. While mixing with a low molecular weight solvent, the

average molecular weight of an oil decreases and because asphaltenes are less stable

in low molecular weight environment, they tend to precipitate more.

The produced diluted oil is in-situ upgraded and has a greater API gravity than

the initial crude oil and more market value. This process can be applied in a great

variety of reservoirs, in particular in environments that are troublesome for steam

injection such as thin or deep reservoirs. For instance, the presence of an aquifer or

a gas cap will not cause significant trouble in the case of the solvent injection. The

main advantages of the process are the in-situ upgrading of oil and negligible heat

loss. Also, solvent injection has lower initial capital requirements compared to steam

injection that needs very expensive steam generation equipment. The oil upgraded

directly in the reservoir via solvent is believed to be worth 2 dollars/bbl more than

the original oil (Mokrys and Butler, 1993).

Along with asphaltene deposition, the amount of organometallic compounds (con-

taining Ni and Va) and sulfur in the crude is reduced (Mokrys and Butler, 1993).

Because they are poisons for refinery catalysts, the upgraded oil should be cheaper to

process. Moreover, asphaltene aggregates have a tendency to clog drainage channels

and to reduce the permeability; in-situ combustion will then remove these deposits

along with the organometallic compounds.

1.2.3 In-situ Combustion

In-situ combustion (or fire-flooding) consists in generating heat by oxidation of a

small fraction of the oil. The oxidation is observed by injecting air into the reservoir.

Heat is created by burning coke formed previously: it reduces oil viscosity and cracks

the medium components into light ones. With the temperature profile through the

reservoir, seven different zones are defined, as presented in Figure 1.2.

Zone 1 is the burned zone where the combustion has already taken place. Imme-

diately ahead is the combustion front where the fuel is burned with oxygen and where

heat is generated. The combustion is where the high temperature oxidation (HTO)

reactions occur and produce H2O, CO, and CO2.


Figure 1.2: In-situ combustion schematic temperature profile (Moore et al., 1995).

“Coke” + O2 → CO + CO2 + H2O

The fuel is “coke” which is formed by thermal cracking in the region ahead of the

combustion front. The temperature reached in this zone depends essentially on the

nature and quantity of fuel consumed. Just ahead, zone 3, is the cracking/vaporizing

region. Light components are vaporized and transported downstream by combustion

gases. The heavier components are pyrolyzed (thermal cracking) into lighter compo-

nents and produce some gas and solid organic residue called “Coke”. “Coke” refers

to an hydrocarbon with low H/C ratio in solid state.

heavy ends → Coke + lighter ends + Gas(CH4)

If asphaltenes precipitate in the reservoir during the solvent injection phase, they


can be transformed afterwards into fuel with the in-situ combustion process. Just

downstream, zone 4 is the condensation zone. The lighter components that evaporated

earlier, condense and dissolve in the crude oil; this region is usually referred to as the

steam plateau because temperature is approximately constant throughout the region

and controlled by the saturation conditions of water. Then, there is the water bank

(zone 5) and the oil bank (zone 6). Beyond is the unaffected oil (zone 7) that is

affected later by the combustion process.

During in-situ combustion, the various oxidation reactions are grouped into two

types, depending on the prevailing temperature (Mamora, 1993):

• low temperature oxidation (LTO) reactions that occur at temperature below

350℃. These are considered to be oxygen addition reactions. The end products

are water and partially oxygenated hydrocarbons (carboxylic acids, aldehydes,

ketones, alcohols and hydroperoxides) (Burger and Sahuquet, 1972) LTO reac-

tions increase the oil’s viscosity, boiling range, and densities.

• high temperature oxidation (HTO) reactions that result in the combustion of

coke. The heat generated during these reactions provides the energy to sustain

the entire in-situ combustion process. The products are CO, CO2, and H2O.

“Coke” + O2 → CO + CO2 + H2O

One must keep in mind that the temperature range is very oil dependent. LTO

reactions occur at temperatures below 350℃ and consume less oxygen compared to

HTO reactions, as shown in Figure 1.3. Because LTO reactions increase the oil’s

viscosity and density, temperature in the combustion front should always be higher

than 350℃ to be assured that HTO reactions are occurring and to provide energy

to the process.

Fuel deposition during in-situ combustion

Fuel (coke) deposition determines the feasibility and economic success of a combustion

project and coke is usually formed from the decomposition of heavy ends, in particular


Figure 1.3: Schematic of oxygen uptake rate showing the effect of temperature (Mooreet al., 1995).

asphaltenes. In-situ combustion is not very efficient with light oils because usually

not enough fuel is deposited. In this case, not enough heat is created in the front to

sustain the combustion. Water soluble metallic additives can then be injected. Salts

of common metals including iron, tin, zinc, and aluminium are known to increase the

amount of fuel laid down (Castanier et al., 1992) and thus are of particular interest

for light oils. Iron made in-situ combustion successful under conditions where it had

failed without any additives (Razc, 1985). Metallic additives change the kinetics of

the combustion reactions and act as catalytic compounds for these reactions.

Excessive fuel deposition would either reduce the rate of advance, increasing the

heat losses to the surroundings and decreasing the thermal efficiency or keep a normal

rate of advance with only partial burning of the fuel. Furthermore, the increase in the

volume of gas required for the combustion also increases expenses. (Abu-Khamsin,


1984)

The effect of pyrolysis on viscosity and API gravity has been quantified(Kuhlman,

2000). The viscosity of the altered oil decreases by 75% to 90% after 24 hours above

300◦C; its density decreases by 10% to 15%; and 20% to 50% of the heavy components

and asphaltenes are converted to light oil.

1.3 Heavy Oil

Heavy oil is defined in the literature as any petroleum crude that has an API gravity

lower than 20 degrees. It is dark black, viscous, does not flow well and has a high

carbon to hydrogen ratio along with a large amount of carbon residues, asphaltenes,

sulphur, nitrogen, heavy metals, aromatics and/or waxes.

Heavy oil is usually young in age because it is usually found at shallow depths in

the earth where there is not so much heat and pressure. Because of its closeness to

the earth’s surface, heavy oils have usually undergone biodegradation from exposure

to water and air so that its lighter parts or fractions are evaporated away leaving

behind its heavier parts or fractions making it a heavier crude oil.

While viscosity at reservoir temperature is the key indicator of how easily oil

flows, density is more commonly used for categorizing crude oils because it is easier to

measure. Thus, in some reservoirs, oil as low as 7 or 8 API is considered heavy rather

than extra-heavy because it can be produced by heavy-oil production methods. From

the viscosity standpoint, crude oils having viscosities higher than 100 cp at reservoir

conditions are considered as heavy (Briggs et al., 1998). For instance, in this study,

some experiments were conducted with West Sak oil that is 21◦ API degree, but has

a viscosity of 105 cp at reservoir conditions. It is not considered as a heavy oil even

though it is as viscous as heavy oils and requires improved recovery processes.

The current oil in place estimates of heavy oils are about six trillion barrels. This

figure is triple the amount of combined world reserves of conventional oil and gas.

With the continuous growth in energy demand, the incentive to develop innovative

techniques and technologies to make heavy-oil reservoirs profitable is great and the

huge amount of almost immobile hydrocarbon resources offers unlimited challenges


and opportunities to researchers.

Heavy oil Natural bitumenRegion Recovery Technically Recovery Technically

factor recoverable BBO factor recoverable BBONorth America 0.19 35.3 0.32 530.9South America 0.13 265.7 0.09 0.1W. Hemisphere 0.13 301.0 0.32 531.0Africa 0.18 7.2 0.10 43.0Europe 0.15 4.9 0.14 0.2Middle East 0.12 78.2 0.10 0.0Asia 0.14 29.6 0.16 42.8Russia 0.13 13.4 0.13 33.7E. Hemisphere 0.13 133.3 0.13 119.7World 434.3 650.7

Table 1.1: Distribution of heavy oil and bitumen resources Meyer and Attanasi (2003).

Chapter 2

Experimental apparatus

For this study, two types of experiments were conducted. Kinetic experiments, refer-

enced as “kin” in the tables, were done prior to tube experiments, referenced as “tub”.

Table 2.1 presents the experiments (tests from 1 to 11) conducted with Hamaca oil

and Table 2.2 (tests from 20 to 42) the experiments with West Sak crude.

Test Oil Type Experiment Comment1 H kin Combustion only2 H kin pentane3 H kin kerosene4 H kin 100 ml kerosene5 H kin 25 ml kerosene Failed/Plug6 H kin 100 ml C5 Failed/Plug7 H kin 50 ml C58 H kin 100 ml C109 H kin 100 ml C510 H kin Combustion only11 H tub 500 ml of C5

Table 2.1: Experiments with Hamaca oil.

The column “Experiment” describes the type of experiment conducted. “Com-

bustion only” means that no solvent was injected prior to the combustion. When

“C5” or “kerosene” are indicated, then solvent was injected prior to the combustion.

13

CHAPTER 2. EXPERIMENTAL APPARATUS 14

Test Oil Type Experiment Comment20 W1 kin Combustion only21 W1 kin 100 ml C522 W1 kin 25 ml kerosene23 W1 kin Combustion only Failed/Leak24 W1 kin Combustion only25 W1 kin 25 ml kerosene26 W1 tub Combustion only Failed/Leak27 W1 tub Combustion only28 W1 tub 500 ml C529 W11 kin Combustion only30 W11 kin 25 ml C531 W11 kin Combustion only Pb in gas measurements32 W2 tub Combustion only33 W2 kin Combustion only34 W2 kin 25 ml C535 W2 tub 500 ml C5 Failed/Short circuit36 W2 kin Combustion with metallic additives Failed/Plug37 W2 kin Combustion with metallic additives Failed/Plug38 W2 tub 500 ml C539 W2 kin Combustion with metallic additives40 W2 tub Combustion with metallic additives41 W2 kin Coke combustion42 W2 kin Combustion only

Table 2.2: Experiments with West Sak oil.

“W1” refers to an emulsified oil, “W11” refers to a de-emulsified oil obtained with

an emulsion breaker and “W2” refers to a de-emulsified oil that was provided by West

Sak operator. More explanations are given in section 3.1.2.

At the beginning of my research, we did several fuel lay down experiments where

the kinetic cell was heated while nitrogen was flowed through it and the effluent gasses

were then burned separately. However, we did not manage to have a regular inflow

of oxygen and there was also a plug in the pipe that biased the concentrations in the

effluent gases. The results from these experiments were not suitable for interpretation.


In tests 5, 6, 36, and 37, the flow tubes got plugged with sand grains during

the experiment and the flow rates decreased. Oxygen was no longer in excess in the

kinetic cell and the concentration in the effluent gas were thus biased. In test 23 and

26, a leak appeared during the experiment that made the experiment impossible to

interpret. In test 35, there was a short circuit in the band heater that created a hole

in the tube while oxygen was injected.

2.1 Experimental objectives

This study is based on experimental work and investigates the effect of preceding an

in-situ combustion process by slugs of solvent injection. Under no circumstances, did

we try to reproduce the reservoir conditions related to the oils we were working with.

This thesis focuses only on the feasibility of combining solvent injection with in-situ

combustion and representative porous media were created to conduct the experi-

ments. Our interpretations were developed by comparing results from combustions

with previous solvent injection and combustions without solvent injection.

First, kinetic experiments were conducted to understand oil’s behavior between 0

and 700℃ and the effect of three different solvents (pentane, decane and kerosene)

on the combustion was investigated. Even though propane or butane are supposed

to lead to larger asphaltene precipitation, pressure limitation of the physical model

available was the main reason for using pentane instead. Prior to combustion, different

amounts of solvent were injected through small samples of mixture of oil, sand, clay

and water at different pressures. Then, the residue was heated as air flowed through

the kinetic cell. This latter technique is often referred to as “Ramped Temperature

Oxidation” (RTO) experiments.

Second, combustion tube experiments were conducted in physical laboratory mod-

els: solvent was injected in the tube and a solvent/oil mixture was then recovered.

Next, the deposits from solvent extraction in the tube were combusted.


2.2 General equipment

2.2.1 Electronic equipment

Gas flows before and after the kinetic cell or combustion tube were measured by

separate electronic mass flow controllers. All electronic devices were permanently

switched on to allow the instruments to stabilize. The gas analyzer was a Xentra gas

analyzer (model 4200, 0.1% error) and was calibrated at the beginning of experiments

as it was subject to instrument drift. Standard gases were used to calibrate the gas

analyzer. All analyzers were first zeroed using nitrogen. Then air was flowed and the

O2 analyzer was calibrated to 20.7%. Finally, a mixture of 10% of CO2 and 10% of

CH4 was flowed to calibrate the CO2 and CH4 analyzers.

Gases were supplied from gas cylinders to the kinetic cell or combustion tube.

Pressure was maintained constant with back-pressure regulators. Produced fluids

passed first through a condenser to separate liquids from gasses. Produced gasses

would then flow through a tube containing Drierite (anhydrous calcium sulfate)

to remove water. Then, these gasses passed through another tube with Purafil II

Chemisorbant to remove acid. Finally, dry gas flowed through the gas analyzer where

carbon monoxide, carbon dioxide, methane and oxygen concentrations were measured.

The PC recorded the gas analyzer readings approximately every minute.

2.2.2 Properties of the oils

Hamaca Oil

The reservoir properties are excellent, with porosity values of up to 36% and perme-

ability values of up to 30 darcies. Hamaca crude is considered foamy and is generally

saturated with gas at reservoir conditions. Table 2.3 presents the properties of the

oil given by PDVSA.


API Gravity 10.5◦

Viscosity 8,394 cpAsphaltenes 11.3%H/C ratio 0.12

Table 2.3: Properties of the Hamaca Oil.

West Sak Oil

Table 2.4 presents properties for the West Sak crude. Data were reported by the

operators and the viscosity was measured with a rotating viscometer.

API Gravity 21◦

Viscosity 105 cpAsphaltenes 3%

Table 2.4: Properties of the West Sak Oil.

2.2.3 Sand mixture

Table 2.5 presents the composition of the sand mixture used in the experiments. The

sand used was clean and unconsolidated Ottawa sand and clay was Kaolin. Sand and

clay were first weighed and put in a basin. The mixture was stirred by hand until

a homogeneous medium was obtained. Clays often contribute to increased fuel lay

down (Burger and Sahuquet, 1972). Then water was added and the mixture was once

again stirred until it became homogeneous. Finally, oil was poured in and the total

mixture was stirred until an even texture was obtained. When packed either in the

kinetics cell or the combustion tube, the medium had a porosity of 33-35%.

When combustion with metallic additives were conducted, 0.6 g of Fe(NO3)3 were

dissolved in water and mixed. The components were uniformly distributed across the

whole combustion tube or kinetic cell. In Appendix A is presented the calculation

for the amount of iron used. Iron was used because it had already made several


Component WeightSand 8500 gKaolin Clay 450 gWater 400 gOil 450 g

Table 2.5: Sand mixture composition.

combustion processes successful under condition where combustion alone had failed

(Castanier et al., 1992).

2.3 Kinetic experiment description

2.3.1 Equipment

The schematic of the kinetic cell used in the experiments is presented in Figure 2.1.

It consists of thick-walled stainless steel cylinder measuring 12.3 cm (5-1/4 in.) long

with an O.D. of 4.8 cm (1.9 in.). Top and bottom of the cylinder were sealed with

stainless steel caps that were tightly screwed and copper gaskets.

A stainless steel tubing, referenced as a thermowell, was placed in the middle

and anchored to the top cap. A thermocouple was inserted in the thermowell and

enabled us to measure temperature in the kinetic cell. Temperature measurements

were collected manually every 2 minutes. The lower end of the kinetic cell was

connected to 1/8 in. coil tubing where gas feed was preheated during the experiment.

Two stainless steel cups were housed in the kinetic cell, both with perforated bottoms.

The lower cup was filled with clean sand and distributed uniformly the gas feed. The

upper cup was packed with the oil-water-sand mixture and was right on the top of

the lower cup. The upper cup was 7.1 cm (2.8 in.) long with an O.D. of 2.7 cm (1.049

in.).

A transfer vessel filled with solvent was used to inject the solvent. The vessel was

then connected to the top of the kinetic cell with a plastic tubing. A back pressure

regulator was added to the bottom of the kinetic cell in order to establish a 40 psi

pressure in the kinetic cell while injecting the solvent.


Figure 2.1: Schematic of a kinetic cell (Sarathi, 1999).

2.3.2 Procedure

The experiment began by packing about 50 grams of the sand/oil mixture into a

kinetic cell placed vertically to minimize the effect of gravity. The kinetic cell was

connected at its end by a back pressure regulator to pressurize the cell at 40 psi during

the solvent injection phase. The desired volume of solvent was injected at the top

of the cell with nitrogen at atmosphere temperature and upgraded oil was recovered.

Air was then injected through the kinetic cell placed in a furnace and temperature

was programmed to increase linearly with time (approximately 180℃ per hour) up

to 700℃. Air was supplied by high pressure cylinders and preheated in a coil tubing


Figure 2.2: Schematic of the kinetic experiment’s procedure.

before it entered the kinetic cell at its lower end. The pressure at the entrance of the

cell was about 120 psi and exit pressure was maintained at 90 psi by a back-pressure

regulator. Gas flows before and after the cell were measured by separate electronic

mass flow controllers. Concentrations of O2, CO, CO2, and CH4 from the effluent

gas were measured by a gas analyzer. Temperature was also recorded approximately

at two minute intervals by hand. When the sample reached 650℃ , the system was

turned off and left to cool down to room temperature.

2.4 Tube experiment description

2.4.1 Equipment

A typical combustion tube is presented in Figure 2.3. They are used to investigate

the performance of in-situ combustion processes by simulating the combustion front

in conditions close to those in a reservoir. The combustion tube is 3-4 ft long and

made of thin corrosion resistant stainless steel. The wall is 0.016 in. thick to avoid

heat conduction along the tube and tube diameter is approximately 3 inches. The


tube was placed in a jacket in the vertical position during the experiment in order to

avoid gravity segregation. During the experiment, the jacket was filled with a porous

insulator to minimize the heat losses. However, one must keep in mind that there is

less heat loss in a reservoir due to the presence of the overburden and underburden

than in the tube. A thermowell is placed in the center of the tube and spans from top

Figure 2.3: Schematic of a combustion tube (Sarathi, 1999).

to bottom. It is attached at the bottom and top caps. A thermocouple is introduced

in the thermowell and enables us to measure temperature at different positions. This

moving thermocouple provides temperature profiles via time and distance.


Pressure was measured and the back pressure set to 80 psi. Air injection rate was

constant at 2.5 l/min. Finally, concentrations in the effluent gases were measured

with the gas analyzer as described earlier. A separator collected the produced liquids

at the outlet of the tube.

2.4.2 Procedure

A typical combustion run begins by placing the thermowell in the middle of the

tube and anchoring it to the bottom flange. Roughly, 2 cm height of clean sand were

added at the bottom of the tube. The tube was packed by increments of sand mixture

prepared previously. After each increments, the sand in the tube was tamped with a

plunger that was perforated in the middle to let the thermowell pass. The tube was

Figure 2.4: Schematic of the solvent injection procedure for the tube experiment.

then pressurized with nitrogen to check for leaks. After, being pressure tested and

placed into the jacket, the top of the tube was gradually heated up to 450℃ with a

band heater placed at the top of the tube. Nitrogen was injected through the tube

to establish permeability. When the desired temperature in order to trigger HTO

reactions was attained, nitrogen injection was stopped and air was injected at 2.5

l/min. The band heater was at the same time turned off and the porous insulation was

poured into the jacket containing the tube. Ignition was always observed immediately


upon switching to air injection. The thermocouple always recorded a significant

increase in temperature when switching from nitrogen to oxygen and confirmation

that the combustion had started was also obtained with effluent gas composition.

The produced gas composition was continuously monitored and the displaced liquids

Figure 2.5: Schematic of combustion procedure for the tube experiment.

were collected through the separator. Temperature measurements made during a tube

run were used to establish temperature profiles and to monitor the propagation of

the combustion front. A typical temperature distribution is presented in Figure 1.2.

Particular attention was attached to the temperature in the combustion front. If it

was roughly below 350℃, then the combustion front was no longer creating any heat

and the experiment was stopped. Also the CO2 and CO concentrations in the effluent

gas were used to confirm whether the high temperature combustion reactions were

active or not.

Chapter 3

Results

3.1 Kinetic experiments

3.1.1 Hamaca Oil

In-situ combustion

Figure 3.1(a) represents effluent gas compositions profiles for a “pure” in-situ com-

bustion with the Hamaca oil, without any previous solvent injection. Figure 3.1(b)

presents O2 and temperature profiles. In agreement with the literature, LTO reac-

tions were first observed at 350℃. A small consumption of oxygen took place. Heavy

oils are in fact less susceptible than light oils to LTO (Sarathi, 1999). Then, HTO

reactions began at 400℃ and the temperature increased by 290℃. HTO reactions

were characterized by a great consumption of oxygen and produced CO, CO2, and

CH4 that appeared in the effluent gas. These reactions are very exothermic and create

the heat necessary to sustain the combustion.

CO, CO2, and CH4 did not react during both LTO and HTO reactions and are

less easy to interpret than O2. Thus, our further interpretations will be based on O2

and temperature profiles.

24

CHAPTER 3. RESULTS 25

(a) Concentration profiles during in-situ combustion.

(b) O2 concentration and temperature profiles during in-situ combustion.

Figure 3.1: Concentration and temperature profiles during in-situ combustion.


Solvent effect

In the following experiments (test 9, test 8, and test 4), a different solvent was used

for each experiment and the results were compared to test 10 where no solvent was

injected.

Figure 3.2 represents the temperature profiles during the combustion phase; sol-

vent has already been injected previously for test 9, 8, and 4.

During HTO reactions, the fuel is burned and CO, CO2, and CH4 are produced.

The fuel is formed previously with the crude’s heavy ends, in particular asphaltenes

and while fuel is burned during HTO reactions, the temperature increases. The more

heavy ends present in the oil, the more fuel is deposited and so the more exothermic

the HTO reactions are

large amount ⇒ large amount ⇒ significant exothermicof heavy ends of fuel HTO reactionsin the kinetic cell deposited

Because oxygen is always in excess in our experiments, the limiting factor for

the temperature to rise is the amount of fuel. The increase in temperature during

HTO reactions is directly related to the amount of heavy ends present in the kinetic

cell before combustion. We compare the rise in temperature during HTO reactions

in order to evaluate the amount of fuel deposited in the kinetic cell after injecting

different kind of solvents. It then helps us understand whether solvents extract more

heavy ends or light ends and estimate if in-situ combustion can still be successfully

applied after solvent injection. The heat created during HTO reactions is the energy

necessary to sustain in-situ combustion. If the HTO reactions do not create enough

heat, then no fuel is deposited and the combustion extinguishes itself.

The most exothermic HTO reactions occur for the pure combustion. Because no

solvent has been previously injected, nothing has been extracted and so it is coherent

to have the maximum amount of fuel deposited in the kinetic cell. All the other tests

have less exothermic HTO reactions and thus less fuel has been deposited. However,

there is a difference between the three solvents. When pentane is previously injected,

HTO reactions are more exothermic compared to kerosene or decane injection. The


Figure 3.2: Temperature profiles after injecting different solvents.

temperature increases by 250℃ as HTO reactions start. In the case of kerosene or

decane, the increase in temperature is smaller. It is insignificant for kerosene and

temperature rises only by 150℃ in the case of decane. Thus, the amount of heat

created may not be sufficient in these two latter cases to sustain an in-situ combustion

process.

All four experiments were done with the same amount of sand/oil mixture at the

beginning, but the HTO reactions are different. Because HTO reactions of deposits

remaining after pentane extraction are more exothermic than deposits from decane

and kerosene injection, more fuel is deposited during the combustion after pentane

injection than during the combustion after decane or kerosene injection. Pentane is a

lighter hydrocarbon solvent and has extracted a greater fraction of light components


than heavy components from the kinetic cell whereas kerosene and decane, heavier

hydrocarbon solvents, dissolved more heavy components than pentane. Recalling also

that pentane dissolves resins but not asphaltenes, more asphaltenes thus precipitate

when pentane is injected and thus more fuel is deposited in the kinetic cell. Whereas

asphaltenes are slightly soluble in decane and kerosene, there is less precipitate when

decane or kerosene are injected. Asphaltenes, however, are still less soluble in decane

than in kerosene, and reactions with decane are more exothermic then with kerosene,

as shown in Table 3.1

Experiment Solvent injected Asphaltenes solubility Increasein solvent in temperature

Test 10 No solvent 0 290℃Test 9 Pentane C5 ≈ 0 250℃Test 8 Decane C10 + 150 ℃Test 4 Kerosene C9-C16 ++ ≈ 0 ℃

Table 3.1: Increase in temperature during HTO reactions for Hamaca oil.

Two different amounts of C5

In test 5 (50 ml of pentane injected) and test 9 (100 ml of pentane injected), the

amount of solvent injected in the kinetic cell varied. From the temperature profiles

presented in Figure 3.3, HTO reactions are equivalently exothermic: so approximately

the same amount of fuel has been burned in the two experiments. Injecting more

than 50 ml of pentane does not dissolve additional heavy ends. With the Hamaca oil,

pentane injection still results in vigorous in-situ combustion because the heavy ends

necessary for the fuel deposition are present in significant amounts. The amount of

pentane to inject is thus closer to 50 ml than 100 ml for the kinetic cell.

Pressure dependance

In the two following experiments (test 2 and 7), the back pressure applied at the end

of the kinetic cell changed. In test 2, pentane was injected at atmospheric pressure


Figure 3.3: Temperature profiles after injecting different amounts of pentane.

whereas in test 7 the kinetic cell was pressurized with a back pressure regulator at

40 psi similar to the previous experiments. Examining the temperature profiles in

Figure 3.4, HTO reactions are more exothermic when the kinetic cell is pressurized.

Thus, with the same arguments in the previous section, pentane at 40 psi has pre-

cipitated more asphaltenes, leading to greater fuel deposition and more exothermic

HTO reactions. It is consistent with the literature (Hirschberg et al., 1984): below

the oil’s bubble point, when the pressure increases, the dissolving power of the crude

decreases. When pressure increases, pentane’s dissolving power decreases and so more

fuel is left in the kinetic cell. This result is confirmed with test 3 where 100 ml of

kerosene were previously injected at atmospheric pressure and test 4 where 100 ml

were injected at 40 psi. According to the oxygen concentration in the effluent gas


Figure 3.4: Temperature profiles after injecting pentane at different pressures.

presented in Figure 3.5, very little O2 was consumed when kerosene was injected at

atmospheric pressure. All the crude oil had been extracted by the kerosene. When

kerosene was injected at 40 psi, oxygen was consumed during HTO reactions and so

there was more fuel in the kinetic cell. Kerosene dissolves less asphaltic components

at 40 psi than at atmospheric pressure.


Figure 3.5: O2 profiles after kerosene injections.


3.1.2 West Sak Oil

Emulsified Oil versus de-emulsified Oil

Experiments with West Sak oil began in fact with an emulsified oil (referenced as

“W1” in Table 2.2) that did not burn correctly. HTO reactions were only a little

exothermic compared to Hamaca oil and not enough energy seemed to be created

in order to sustain the process. However, these results were not coherent with a

report of the US Department of Energy on Schrader Bluff (Strycker et al., 1999).

Schrader Bluff oil is believed to be very similar to West Sak oil and they had found

the oil would burn very well. An excess of emulsion breaker (DOW CORNINGR

Q2-3183A ANTIFOAM) was added to separate the water from the oil and obtained

an oil referenced as “De-emulsified oil 1” (referenced as “W11” in Table 2.2). HTO

Figure 3.6: Temperature profiles for emulsified and de-emulsified oils.


reactions turned out to be more exothermic with this de-emulsified oil 1 than with

the original oil, as shown in Figure 3.6. Later on, we received a second sample of

West Sak oil that had been de-emulsified by the provider. This latter oil is called

“De-emulsified oil 2” (referenced as “W2” in Table 2.2). The results with this latter

oil were similar to the emulsified oil and thus disappointing because little energy was

created as we can notice on Figure 3.6. We found out later that the Schrader Bluff

oil used in the US Department of Energy report was different than ours.

All further experiments were conducted with the second barrel of West Sak, the

“De-emulsified oil 2”. West Sak oil is a lighter oil than Hamaca oil and contains

only 3% asphaltenes. Thus, it will form less fuel for the HTO reactions that are less

exothermic compared to the Hamaca oil.

In-situ combustion

Figure 3.7 presents the composition of the effluent gas in O2, CO, CO2 and CH4

during test 33, a combustion without any previous solvent injection. Compared to

Hamaca oil, the concentration in O2 decreases not only during the HTO reactions

but also during the LTO reactions: light oils differ from the heavy oil by dissolving

a lot more oxygen during LTO reactions (Sarathi, 1999). LTO reactions are believed

to transform low molecular weight fraction into higher molecular weight products.

Pentane effect

Although West Sak did not seem to burn efficiently, pentane should only extract the

light ends and leave the heavy ones involved in the fuel formation for HTO reactions.

Thus, we should then obtain a heavier oil in the kinetic cell. In test 35, we injected

25 ml of pentane at 40 psi prior to the combustion. From Figure 3.8 and Table 3.2,

the HTO reactions were in fact less exothermic when we injected pentane. And, if

we look at O2’s concentrations in the effluent gas in Figure 3.9(a), we notice that a

lot less oxygen was consumed after injecting pentane. According to Figure 3.9(b),

roughly one quarter of the CO2 was produced relative to the case without solvent

injection. Pentane dissolved a large part of the oil and there was enough remaining


Figure 3.7: Concentration profiles during in-situ combustion.

heavy ends to be transformed into fuel for HTO reactions. From the results of prior

injection of pentane, we decided not to try either decane or kerosene because they

would have dissolved even more heavy ends and lead to less exothermic reactions.

Combustion with metallic additives

Because we know that metallic additives enhance combustion, we did an in-situ com-

bustion experiment with metallic additives in test 40. The metallic additives enhance

the fuel deposition by creating activated sites on the rock for the fuel deposition (He

et al., 2005). HTO reactions were more exothermic as expected, but the temperature

increase is still little compared to Hamaca oil.

Metallic additives (iron in our case) did greatly enhance the combustion; the heat


Figure 3.8: Temperature profiles for combustion after pentane injection.

created during the kinetic experiments was 3 times larger as shown in Table 3.2.


(a) O2 profiles. (b) CO2 profiles.

Figure 3.9: Concentration profiles after pentane injection.

Experiment Comment Increasein temperature

Test 32 No solvent 82℃Test 34 Pentane C5 56℃Test 39 Combustion with metallic additives 225℃

Table 3.2: Increase in temperature during HTO reactions for West Sak oil.


Figure 3.10: Temperature profiles during combustion with metallic additives.


3.2 Data analysis for kinetic experiments

A major piece of information that is obtained from the kinetic experiments, is the

temperature at which the media has to be in order to trigger HTO reactions. They

are very useful for the tube experiments in order to make sure that HTO reactions

are occurring in the combustion front rather than LTO reactions. They are presented

in Table 3.3. One must recall that HTO reactions provide energy by creating heat

whereas LTO reactions increase the oil viscosity and density (Sarathi, 1999).

Activation energies for HTO reactions are also derived from the kinetic experi-

ments by modeling them as first order reactions (Abu-Khamsin, 1984). The calcula-

tion procedure is presented in Appendix B. This calculation has strong assumptions

and the experiments induced some uncertainty. Thus the activation energy results

should be considered with caution. The calculation assumes the flow rates to be con-

stant, but during our experiments, we noticed that flow rate varied, especially during

HTO reactions. Unfortunately, we did not record steadily the flow rates. Moreover,

there is a time shift between temperature and gas measurements. Temperature is an

immediate measure because there is not any delay between actual temperature in the

kinetics cell and the temperature read. For the gas measurements, the gas has to

flow from the kinetics cell to the gas analyzer passing through several security tubes,

as explained in section 2.2.1. There is thus a delay between the gasses flowing out

of the kinetics cell and the gas concentrations being recorded. We observed that it

takes approximately 2 minutes for the gas to flow from the kinetics cell to the gas

analyzer but this delay varies when the flow varies, especially when HTO reactions

occur. Thus, when we combine temperature measurements with concentration mea-

surements at given times, some adjustments may be required to obtain a coherent

value. It was the case for the combustion with metallic additives.

Nevertheless, the calculation gave us coherent results for several tests and we

decided to present them but they should be considered with caution.

The activation energies for the different kinetic experiments with the Hamaca oil

are presented in Table 3.3. Injecting solvent prior to combustion seems not only

to increase the temperature at which HTO reactions start, but also to increase the


HTO reactionsTest Experiment Ea Ea/R Temperature

kJ/mol K K10 Combustion only 83 10,000 390℃9 100 ml of C5 + Combustion 100 12,000 402℃8 100 ml of C10 + Combustion 105 12,500 420℃4 100 ml of kerosene + Combustion 150 19,000 443℃

Table 3.3: Activation Energies and critical temperatures for the Hamaca oil.

activation energies. In fact, the solvent dissolves the light ends and depending on

the solvent some of the heavy ends. The remaining oil is thus heavier and the fuel

deposited is then heavier than when no solvent has been previously injected.

The equivalent data for West Sak is presented in Table 3.4. Injecting pentane

does neither induce a considerable change in the activation energies nor in the HTO

critical temperature. First, the amount of pentane injected is 4 times less than in

the case of Hamaca. Since West Sak did not burn correctly, we only injected a small

amount of pentane. Second, the amount of asphaltenes in West Sak is considerably

smaller than in the Hamaca oil. Thus the data is less affected by pentane. For the

combustion with metallic additives, the values are similar to the “combustion only”

experiment.

HTO reactionsExperiment Ea Ea/R Temperature

kJ/mol K KCombustion only 62 7,500 382℃25 ml of C5 + Combustion 60 7,000 391℃Combustion with metallic additives 58 7,000 385℃

Table 3.4: Activation Energies and critical temperatures for the West Sak oil.

Injecting solvent before combustion seems to increase the temperature at which

HTO reactions start. In fact, the solvent dissolves the light ends and some of the


heavy ends. The fuel deposited is then heavier than without solvent injection.


3.3 Tube experiments

3.3.1 Hamaca Oil

Figure 3.11 presents O2, CO, CO2 and CH4 concentrations during test 11: it consisted

in injecting 500 ml of pentane, recovering most of it and then launching an in-situ

combustion process. The combustion was very successful because O2 appeared very

late and CO and CO2 were produced throughout the experiment. These observations

are consistent with effective combustion. The high content of CH4 in the effluent gas

is due to the presence of pentane in the tube it has been cracked into methane.

Figure 3.11: Concentration profiles during combustion after injecting 500 ml of pen-tane.

From Figure 3.12, temperature profiles during the combustion show very well the


front’s propagation; we notice also the formation of the steam plateau at 130℃ ahead

of the front. According to the steam tables, the saturation temperature is 160℃ at

80 psi. Light components dissolved in the water are responsible for decreasing the

saturation temperature.

Figure 3.12: Temperature profiles during combustion after injecting 500 ml of pen-tane.

The tube was unpacked the day after the combustion experiment and Figure 3.13

is a picture of the sand. The top sand was the burned sand (Figure 3.14)and stretched

over 60 cm. Then, just below, there was 10 cm of dark sand which was coke residues

(Figure 3.15). Below was 30 cm of unburned sand (Figure 3.16) because the combus-

tion was stopped before it reached the end the tube.


Figure 3.13: Sand after the tube experiment with Hamaca oil.

Figure 3.14: Burned sand from the tube experiment with Hamaca oil.


Figure 3.15: “Coke” from the tube experiment with Hamaca oil.

Figure 3.16: Unburned sand from the tube experiment with Hamaca oil.


3.3.2 West Sak Oil

Combustion only

Test 32 consisted in a combustion without solvent injection. The measurement started

when we switched from nitrogen to air injection. Based on the results, the experiment

can be divided in three parts: first from the beginning until approximately twenty

minutes, second from twenty minutes to approximately seventy minutes, third until

the end of the experiment.

Figure 3.17: Concentration profiles during West Sak’s tube combustion.

Air injection started a t = 0. In the first part, methane was produced due to the

cracking of the oil during the pre-heating phase. Injected air had not yet reached the

gas analyzer. A rapid increase in temperature however was observed at the top of


the tube immediately after injecting air. The second part started when CO appeared

in the effluent gas. It confirmed that the oil had been correctly ignited. Only a few

minutes later, O2 appeared and was not being consumed in the combustion front. The

oxygen flowed then through the entire tube and some of it dissolved in the unaffected

oil and as a result, oxidized it. LTO reactions were then occurring in the tube and

we assume that it increased the oil viscosity and density. After seventy minutes,

the third phase began. CO and CO2 concentration decreased steadily whereas O2

increased twice as fast as previously. The oxygen was no longer being dissolved in the

unaffected region because the media was fully saturated. Furthermore, the decrease

in CO and CO2 reflect that the combustion front was extinguished. The combustion

did not propagate and the combustion was not self-sustainable.

Figure 3.18: Temperature profiles during West Sak’s tube combustion.


From the temperature profiles presented in Figure 3.18, we notice that after 27

minutes of air injection, the highest temperature was 420℃ which is high enough

to trigger HTO reactions. The requirements in order to sustain the combustion were

then satisfied that is, oxygen was present and the temperature was high. However, at

75 minutes, the front temperature was only 412℃, which is very close to the minimum

required to launch HTO reactions. This minimum has been determined in test 20

with the kinetic experiments as shown in Table 3.4. At 120 minutes, the front went

out and only LTO reactions took over. We then stopped the reaction by injecting

nitrogen.

Figure 3.19: Sand after West Sak’s tube combustion.

The tube was disassembled the day after the combustion experiment and the

sand mixture was examined. From top to bottom, we had approximately 10 cm of

burned sand followed by 5 cm of coke, as shown in Figure 3.19. Then, in Figure 3.20,

below these two regions, there was 85 cm of unburned sand and to the naked eye, we

distinguished two regions. The top one was clearer than the bottom. We assume that

the clear sand represents the steam plateau whereas the dark sand represents the oil

bank.


Figure 3.20: Sand after West Sak’s tube combustion.

500 ml of pentane + combustion

In test 38, we injected 500 ml of pentane before the combustion. Air was injected

at the same time as we started to measure gas concentrations. The concentration

profiles are presented in Figure 3.21. The results are consistent with the kinetic

experiments. Pentane injection worsened the oil’s combustion properties. In test 32,

after 55 minutes of air injection, there was only 3% of oxygen in the effluent gasses.

Whereas in this test, after 55 min of air injection, there was already approximately

10% of oxygen in the effluent gas. The combustion front went out 3 times faster than

when no solvent was injected. No front propagation was even noticed so we did not

record any temperature profiles.

The tube was also disassembled the next day and the sand mixture was examined.

From the top to the bottom, we hardly had 5 cm of clean sand followed by 5 cm of

coke. Then, the media did not seem affected. We saw with the kinetic experiments


Figure 3.21: Concentration profiles during combustion after injecting 500 ml of pen-tane.

that HTO experiments with West Sak oil were not very exothermic. From the sand

analysis after the combustion, we noticed that coke was formed inside the tube but

there was no front propagation.

Combustion with metallic additives

In test 40, we dissolved metallic additives in the test water. The kinetic experiments

showed that 3 times more heat was created with metallic additives than without. We

injected air at the same time as we started to measure gas concentrations. From

Figure 3.22, we notice that higher temperatures were reached during this experi-

ment with metallic additives and the characteristic temperature profile exposed in


Figure 1.2 was formed. The combustion front and the steam plateau were well de-

fined whereas nothing comparable happened in test 32 (Figure 3.18) for the “pure

combustion”. Although the combustion was enhanced, the combustion front did not

Figure 3.22: Temperature profiles during combustion with metallic additives.

propagate through the entire tube. The front extinguished at 20 cm from the top but

still propagated twice as far as the front in the “pure combustion” experiment. By

comparing the times in the temperature profiles (Figure 3.23 and Figure 3.18), we

notice that they are very similar. Thus the combustion front with metallic additives

propagated approximately twice as fast as the front in the “pure combustion” exper-

iment. In both cases, the heat losses were equal since the procedure was identical.

But, from the kinetics experiment, we saw that 3 times more heat was created with

the metallic additives. Thus the combustion front was able to propagate further. Not


enough heat, however, was released from the front to sustain the process through the

entire tube. One ought to keep in mind that heat losses are more important in tube

combustion experiment than on the field (Sarathi, 1999).

From the composition profiles presented in Figure 3.23, similar to the “pure com-

bustion” experiment, we distinguish three different phases occurring during the ex-

periment. The first one started at t = 0 and finishes at t = 60 min; the second phase

stretched from t = 60 min to t = 107 min and finally the third one from t = 107

min to the end of the experiment. More oxygen was consumed since it appeared

later in the experiment; this suggests that more fuel had been deposited and the

metallic additives operated as they were supposed to. The combustion was still not

self-sustaining.

Figure 3.23: Concentration profiles during combustion with metallic additives.

Chapter 4

Discussions and Recommendations

Fuel deposition

The major limiting factor for applying in-situ combustion is the amount of fuel de-

posited ahead of the combustion front. If insufficient fuel is formed, as is common

with light oils, the process is not self-sustaining. On the contrary, if an excess of

fuel is deposited, the combustion front is slowed down and the amount of oxidizing

gasses required to sustain the combustion becomes uneconomical. We saw earlier that

metallic additives act as catalytic compounds in the kinetics. It is then possible to

increase the amount of fuel formed. When an excess of fuel is deposited, a suitable

solvent can be chosen to dissolve part of the fractions that produce coke during the

combustion.

Hamaca oil burns very well and many successful tube experiments have already

been conducted (Mamora, 1993). A fair amount of fuel is always deposited and it leads

to exothermic HTO reactions that create enough energy to sustain the combustion.

Pentane injection does not affect the efficiency of subsequent in-situ combustion, and

thus the combination of solvent injection with in-situ combustion was successfully

applied. However, injecting decane or kerosene that are heavier hydrocarbon solvents

than pentane, led to less exothermic HTO reactions during the combustion. They

dissolved a bigger fraction of the oil’s heavy ends than pentane and less fuel was

available for the HTO reactions. These latter reactions were then less exothermic,

compared to when no solvent was injected. However, these results were intensified

52

CHAPTER 4. DISCUSSIONS AND RECOMMENDATIONS 53

with kerosene. After injecting 100 ml of kerosene, the HTO reactions were hardly

exothermic, whereas injecting decane resulted in decreasing the heat created by two

times. Heavy hydrocarbon solvents ought to be considered in order to decrease the

fuel deposition. A major criterion is then to choose the right solvent. It can range

from CO2 up to a heavy hydrocarbon solvent depending the amount of fuel deposited

by the oil.

Simulating process

West Sak oil did not burn efficiently: the kinetics experiment showed that the HTO

reactions were not substantially exothermic and the tube run confirmed that in-situ

combustion was not self-sustaining. In agreement with the results found with Hamaca

oil, pentane slightly reduced the heat created during HTO reactions. In the tube run,

when we injected pentane, the combustion front went out 3 times faster than when no

solvent was injected. No front propagation was even noticed. Metallic additives (iron

in our case) did greatly enhance the combustion; the heat created during the kinetic

experiments was 3 times bigger and the combustion front went out 112

later than

when no metallic additives were added. Furthermore, the front propagated faster

and further in the tube. The in-situ combustion, however, was not self-sustaining.

In the case of West Sak, asphaltene precipitation has been noticed during CO2

flooding (DeRuiter et al., 1994). In fact, asphaltenes have a high tendency to deposit

near the wellbore region leading to a decrease in the production. Since in-situ com-

bustion cannot be sustained with West Sak, the combination of solvent injection and

in-situ combustion ought to be considered near the wellbore to clean it and increase

the permeability (Castanier and Kovscek, 2005). The valuable ends in this latter

region would be recovered and the heavy deposits affecting the production would

then be burned. One of the main reason for asphaltenes precipitation near the well-

bore region, is the change in pressure (Wang et al., 2004). If they do not deposit

far from the wellbore, then they will flow with the crude and precipitate near the

wellbore. The concentration of asphaltenes is then greater in this latter region than

in the unaffected region. There is more fuel deposition leading to a more exothermic

combustion process. The combustion cleans the sand and increases the permeability

CHAPTER 4. DISCUSSIONS AND RECOMMENDATIONS 54

near the wellbore.

Simulation

We tried to simulate asphaltene precipitation using the pure solid model in the Com-

positional Simulation software WinProp, from the Computer Modelling Group Ltd.

However we were unable to comment our results. The molecular weight of asphaltenes

varies with the solvent used (Speight, 1994) and it is believed that heavy organic sub-

stances consist in many particles with different molecular weights. Distribution func-

tions are usually used to represent their molecular weight. As the solvents advances

in the tube and thus mixes with fresh oil, the solvent will not have the same compo-

sition. The asphaltene deposits will not have the same molecular weight whether it

precipitated at the top or middle of the tube. However, in the pure solid model used

with WinProp, a pure solid with a single molecular weight is simulated.

Future work

We did not measure the upgrading of the oil that we recovered after the solvent

injection. It requires us to separate the solvent from the oil in order to know the API

gravity of the upgraded oil. A fuel lay down calculation could be conducted, especially

for West Sak oil. One could try to model analytically the solvent effect on the fuel

deposition and implement with fuel lay down calculation. Further investigation is

required to understand why West Sak oil does not burn correctly. What are the

characteristics of the fuel deposited? Is the fuel deposition too slow?

Conclusion

The aim of this study is to propose an efficient process to upgrade heavy oil directly

in the reservoir and to recover a greater API gravity crude oil. At first, solvent

injection enables us to recover most of the light fractions of the oil by dissolving

them into the solvent. We also make sure that these valuable ends are not degraded

by the combustion. In-situ combustion burns the heavy ends that are less markedly

interesting and creates energy in the reservoir in order to upgrade the oil through

thermal cracking (by pyrolisis).

In agreement with the literature (Mamora, 1993), in-situ combustion was success-

fully applied with the Hamaca oil. During the kinetics experiment, in-situ combustion

created approximately the same amount of heat whether a large amount of pentane

(10 times the volume of crude oil) was previously injected or not. The tube runs

showed that we were successfully able to:

• inject as much pentane as there was crude oil

• recover the diluted oil and thus the crude’s light ends

• transform the heavy ends left in the media into coke (fuel) and to ignite them.

With Hamaca oil, injecting pentane was not harmful to the subsequent in-situ com-

bustion.

Decane injection affected the subsequent combustion by decreasing the fuel depo-

sition and thus reducing by two times the amount of heat created during the HTO

reactions. Decane, a heavier hydrocarbon solvent than pentane, dissolved more of

the crude’s heavy ends that are involved in the fuel deposition process. This effect

55

Conclusion 56

was increased with kerosene. The HTO reactions were not significantly exothermic

because kerosene dissolved most of crude oil. Fuel deposition was strongly affected by

these two latter solvents. In the case of an excess fuel deposition during the in-situ

combustion, solvents such as decane or kerosene injection should be considered before

the in-situ combustion.

West Sak oil did not burn efficiently. The kinetic experiments showed that little

heat was created and the combustion front in the runs only propagated 10 cm before

extinguishing. Prior pentane injection worsened the effect because no front propaga-

tion was noticed and the combustion went out twice as fast. On the opposite, metallic

additives enhanced the combustion by creating twice as much heat as the“pure com-

bustion” process, but the combustion front was only sustained over 20 cm in the tube

before extinguishing.

An economic attractive feature inherent to this combination is the in-situ upgrad-

ing of heavy oil, not only by deasphalting due to the solvent injection but also by

thermal cracking during the combustion. The viscosity of the oil is reduced in both

cases since the oil recovered has less heavy components. This results in producing a

better oil quality and potential savings during transport and further processing of the

oil, especially in refineries. This process could make heavy oil much more attractive

by reducing the gap of the price differential between heavy and light crude and by

enhancing production rates. If this combination cannot be successfully applied at

large scale du to inefficient combustion, it can definitely be considered to clean the

near wellbore region where asphaltenes precipitate preferentially.

Bibliography

Abu-Khamsin, S. A. (1984). The Reaction Kinetics of Fuel Formation for In-Situ

Combustion. Ph.D. thesis, Stanford University.

Acharya, U. K., Kent, A., Waite, M. W., Tankersley, T., Johansen, S., and Robertson,

C. (2004). Subsurface Challenges in Reservoir Modeling for Hamaca Project. SPE

86971. Presented at the SPE International Thermal Operations and Heavy Oil

Symposium and Western Regional Meeting held in Bakersfield, California, U.S.A.,

16-18 March.

Briggs, P. J., Baron, R. P., Fulleylove, R. J., and Wright, M. S. (1998). Development

of Heavy-Oil Reservoirs. Journal of Petroleum Technology February. Original paper

(SPE 15748) first presented at the 1987 SPE Middle east Oil Show held in Bahrain,

March 7-10.

Burger, J. G. and Sahuquet, B. C. (1972). Chemical Aspects of In-Situ Combustion

- Heat of Combustion and Kinetics. Soc. Pet. Eng. October, pp 410–22.

Castanier, L. M. and Kovscek, A. R. (2005). Heavy Oil Upgrading In-Situ via Sol-

vent Injection and Combustion: A ”New” Method. Proceedings of the EAGE 67th

Conference and Exhibition, Madrid Spain, 13-16 June.

Castanier, L. M., Baena, C. J., Holt, R. J., Brigham, W. E., and Tavares, C. (1992).

In Situ Combustion with Metallic Additives. SPE 23708. Presented at the Second

Latin American Petroleum Engineering Conference, II LAPEC, of the Society of

Petroleum Engineers held in Caracas, Venezuela, March 8-11.

57

BIBLIOGRAPHY 58

DeRuiter, R. A., Nash, L. J., and Singletary, M. S. (1994). Solubility and Displace-

ment Behavior of a Viscous Crude with CO2 and Hydrocarbon Gasses. SPE 20523.

Gondouin, M. and Fox, J. M. (1991). The Challenge of West Sak Heavy Oil: Analysis

of an Innovative Approach. SPE 22077. Prepared for presentation at the Interna-

tional Arctic Technology Conference held In Anchorage, Alaska, May 29-31.

He, B., Chen, Q., Castanier, L. M., and Kovscek, A. R. (2005). Improved In-Situ

Combustion Performance With Metallic Salt Additives. SPE 93901. Prepared for

presentation at the 2005 SPE Western Regional Meeting held in Irvine, CA, USA,

30 March - 1 April.

Hirschberg, A., deJong, L. N. J., Schipper, B. A., and Meijer, J. G. (1984). Influence

of Temperature and Pressure on Asphaltene Flocculation. SPE 11202 June.

Islam, M. R. (1994). Role of Asphaltenes on Oil Recovery and Mathematical Modeling

of Asphaltenes Properties, volume Asphaltenes and Asphalts, 1, chapter 11, pp

249–298. Elsevier science B.V.

Kuhlman, M. (2000). The benefits of In Situ Upgrading reactions to the Integrated

Operations of the Orinoco Heavy Oil Fields and Downstream Facilities. SPE 62560.

Presented at 2000 SPE/AAPG Western Regional Meeting held in Long Beach,

California, 19-23 June.

Mamora, D. D. (1993). Kinetics of In-Situ Combustion. Ph.D. thesis, Stanford

University.

Meyer, R. F. and Attanasi, E. D. (2003). Heavy Oil and Natural Bitumen - Strategic

Petroleum Resources. USGS Fact Sheet FS-070-03 August.

Mokrys, I. J. and Butler, R. M. (1993). In-Situ Upgrading of Heavy Oils and Bitumen

by Propane Deasphalting: The Vapex Process. SPE 25452. Prepared for presenta-

tion at the Production Operations Symposium held in Oklahoma City, OK, U.S.A.,

March 21-23.

BIBLIOGRAPHY 59

Moore, R. G., Ursenbach, M. G., Laureshen, C. J., Belgrave, J. D. M., and Mehta,

S. A. (1995). Ramped Temperature Oxidation Analysis of Athabasca oil Sands

Bitumen. Presented at the 46th Annual Technical Meeting of the Petroleum Society

of CIM, Banff, Alberta, May 14-17.

Moritis, G. (2004). Special Report: EOR Continues to Unlock Oil Ressources. Oil

and Gas Journal, pp 45–65.

Murgich, J., Rogel, E., Leon, O., and Isea, R. (2001). A Molecular Mechancs-Density

Functionnal Study of the Adsorption of Fragments of Asphaltenes and Resins on

the (001) Surface of FE2O3. Petroleum Science and Technology.

Prats, M. (1986). Thermal Recovery, volume 7. SPE of AIME.

Rangel-German, E. R., Schembre, J., Sandberg, C., and Kovscek, A. R. (2003).

Electrical-Heating-Assited Recovery for Heavy Oil. Journal of Petroleum Science

and Engineering August, pp 213–231.

Razc, D. (1985). Development and Application of a Thermocalytic In-situ Combus-

tion Process in Hungary. Proceedings European Meeting on Improved Oil Recovery

Rome, Italy, April 16-18.

Sarathi, P. S. (1999). In-Situ Combustion Handbook - Principles and Practices.

Technical report.

Speight, J. G. (1992). A Chemical and Physical Explanation of Incompatibility during

Refining Operations. Proceedings 4th International Conference on the Stability and

Handling of Liquid Fuels, US Department of Energy.

Speight, J. G. (1994). Chemical and Physical Studies of Petroleum Asphaltenes,

volume Asphaltenes and Asphalts, 1, chapter 2, pp 7–65. Elsevier.

Storm, D. A. and Sheu, E. Y. (1994). Colloidal Nature of Petroleum Asphaltenes,

volume Asphaltenes and Asphalts, 1, chapter 6, pp 125–155. Elsevier.

BIBLIOGRAPHY 60

Strycker, A., Sarathi, P., and Wang, S. (1999). Evaluation of In Situ Combustion for

Schrader Bluff. Technical report.

Targac, G. W., Redman, R. S., Davis, E. R., Rennie, S. B., McKeever, S. O., and

Chambers, B. C. (2005). Unlocking the value in West Sak Heavy Oil. SPE. Prepared

for presentation at the 2005 SPE International Thermal Operations and Heavy Oil

Symposium held in Calgary, Alberta Canada, 1-3 November.

Wang, J. X., Buckley, J. S., Burke, N. E., and Creek, J. L. (2004). A Practical Method

for Anticipating Asphaltenes Problems. SPE 87638.

Appendix A

In order to calculate the amount of iron to dissolve in the water, we did a mass balance

calculation. With the molecular weight of water MH2O = 18 g.mol−1, we calculate

the water’s molecular density dH2O = 1/18 = 55.56 mol.m−3 and we thus obtain the

number of moles of H2O in 400 g of water.

nH2O = dH2O ∗ VH2O = 2.22 ∗ 10−2 mol

Because the metallic additive is [Fe(NO3)3, 9H2O], 9 moles of H2O can dissolve

1 mole of Fe(NO3)3 and we calculate the number of moles of iron.

nFe(NO3)3 =nH2O

9= 2.47 mol

We just have to multiply by the molecular weight of the metallic additive

MFe(NO3)3 = 241.8 g.mol−1

to obtain the mass to dissolve into the water.

mFe(NO3)3 = MFe(NO3)3 ∗ nFe(NO3)3 = 0.60 g

61

Appendix B

The rate equation is:

R =q ∗ δγ

AL= −α

dCf

dt(4.1)

where:

• q is the volumetric flow rate

• A is the cross sectional area

• L is the length of the kinetic cell

• δγ is the change in molar oxygen concentration

• α is a proportionality factor equal to the number of moles of oxygen that reacts

with one gram of fuel

We assume the rate to be constant. So integrating equation refL1 and simplifying

it gives:

α ∗ Cf =

∞∫

t

q ∗ δγ

ALdt =

q

AL

∞∫

t

δγdt (4.2)

Because HTO reactions can be modeled as first order reactions, the rate is also:

R = ArPmO2

Cnf exp− E

RT(4.3)

where n in our case is equal to 1.

So:

62

Appendix B 63

R

Cf

= ArPmO2

exp− E

RT(4.4)

and

R

Cf

=q∗δγAL

1α

qAL

∞∫t

δγdt= α

δγ∞∫t

δγdt(4.5)

thus

δγ∞∫t

δγdt=

ArPmO2

αexp− E

RT(4.6)

The left hand side of equation 4.6 is called the relative reaction rate RR. By taking

the logarithm of 4.6, we obtain:

ln(RR) = ln(ArP

mO2

α) − E

RT(4.7)

E/R is then the slope of ln(RR) versus 1/T and we obtain the activation energy

by plotting ln(RR) versus 1/T.

Documents

Laboratory Investigation of the Effect of Solvent ...West Sak is a viscous oil reservoir located within the Kuparuk River Unit on the North Slope of Alaska and part of a larger viscous