LABORATORY INVESTIGATION OF THE EFFECT OF SOLVENT INJECTION ON IN-SITU COMBUSTION FOR VISCOUS OILS

Transcription

1 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

2 I certify that I have read this thesis and that in my opinion 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 opinion 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

3 Acknowledgments This thesis was prepared with the support of the U.S. Department of Energy, under Award No. DE-FC26-03NT 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 especially 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

4 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 Oxidation 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 interest. 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 properties 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

5 tube. Nevertheless, experimental results show that this combined method may be applicable to a broad range of oil reservoirs. v

6 Contents Acknowledgments Abstract Table of Contents List of Tables List of Figures iii iv vi viii ix 1 Introduction Problem statement Literaturereview Asphaltenes Solvent injection In-situCombustion HeavyOil Experimental apparatus Experimental objectives General equipment Electronic equipment Propertiesoftheoils Sandmixture Kinetic experiment description vi

7 2.3.1 Equipment Procedure Tube experiment description Equipment Procedure Results Kinetic experiments HamacaOil WestSakOil Data analysis for kinetic experiments Tube experiments HamacaOil WestSakOil Discussions and Recommendations 52 Conclusion 56 Bibliography 57 Appendix A 61 Appendix B 63 vii

8 List of Tables 1.1 Distribution of heavy oil and bitumen resources Experiments with Hamaca oil Experiments with West Sak oil PropertiesoftheHamacaOil PropertiesoftheWestSakOil Sandmixturecomposition IncreaseintemperatureduringHTOreactionsforHamacaoil Increase in temperature during HTO reactions for West Sak oil Activation Energies and critical temperatures for the Hamaca oil Activation Energies and critical temperatures for the West Sak oil viii

9 List of Figures 1.1 Polycyclic structures for asphaltene molecules In-situ combustion schematic temperature profile Schematic of oxygen uptake rate showing the effect of temperature Schematic of a kinetic cell Schematic of the kinetic experiment s procedure Schematic of a combustion tube Schematic of the solvent injection procedure for the tube experiment Schematic of combustion procedure for the tube experiment Concentration and temperature profiles during in-situ combustion with Hamacaoil Temperature profiles after injecting different solvents Temperature profiles after injecting different amounts of pentane Temperature profiles after injecting pentane at different pressures O 2 profiles after kerosene injections Temperature profiles for emulsified and de-emulsified oils Concentration profiles during West Sak s kinetic combustion Temperature profiles Concentration profiles after pentane injection Temperature profiles during combustion with metallic additives Concentration profiles during combustion after injecting 500 ml of pentane Temperature profiles during combustion after injecting 500 ml of pentane. 42 ix

10 3.13 Sand after the tube experiment with Hamaca oil Burned sand from the tube experiment with Hamaca oil Coke from the tube experiment with Hamaca oil Unburned sand from the tube experiment with Hamaca oil Concentration profiles during West Sak s tube combustion Temperature profiles during West Sak s tube combustion SandafterWestSak stubecombustion SandafterWestSak stubecombustion Concentration profiles during combustion after injecting 500 ml of pentane Temperature profiles during combustion with metallic additives Concentration profiles during combustion with metallic additives x

11 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 Petróleos de Venezuela S.A (PdVSA), the state oil 1

12 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).

13 CHAPTER 1. INTRODUCTION 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 technologies 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.

14 CHAPTER 1. INTRODUCTION 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 asphaltenes. 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 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

15 CHAPTER 1. INTRODUCTION 5 oil, asphaltenes tend to precipitate. Also, a drop in pressure or ph (further to acid jobs or CO 2 injection for instance) leads to asphaltene deposition. The presence of ferric iron FE 3 + 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

16 CHAPTER 1. INTRODUCTION 6 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 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

17 CHAPTER 1. INTRODUCTION 7 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 (containing 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 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. Immediately 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 H 2 O, CO, and CO 2.

18 CHAPTER 1. INTRODUCTION 8 Figure 1.2: In-situ combustion schematic temperature profile (Moore et al., 1995). Coke +O 2 CO+CO 2 +H 2 O 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 components 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(CH 4 ) If asphaltenes precipitate in the reservoir during the solvent injection phase, they

19 CHAPTER 1. INTRODUCTION 9 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 reactions 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, CO 2, and H 2 O. Coke +O 2 CO+CO 2 +H 2 O 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

20 CHAPTER 1. INTRODUCTION 10 Figure 1.3: Schematic of oxygen uptake rate showing the effect of temperature (Moore et 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,

21 CHAPTER 1. INTRODUCTION ) 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

22 CHAPTER 1. INTRODUCTION 12 and opportunities to researchers. Heavy oil Natural bitumen Region Recovery Technically Recovery Technically factor recoverable BBO factor recoverable BBO North America South America W. Hemisphere Africa Europe Middle East Asia Russia E. Hemisphere World Table 1.1: Distribution of heavy oil and bitumen resources Meyer and Attanasi (2003).

23 Chapter 2 Experimental apparatus For this study, two types of experiments were conducted. Kinetic experiments, referenced 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 Comment 1 H kin Combustion only 2 H kin pentane 3 H kin kerosene 4 H kin 100 ml kerosene 5 H kin 25 ml kerosene Failed/Plug 6 H kin 100 ml C5 Failed/Plug 7 H kin 50 ml C5 8 H kin 100 ml C10 9 H kin 100 ml C5 10 H kin Combustion only 11 H tub 500 ml of C5 Table 2.1: Experiments with Hamaca oil. The column Experiment describes the type of experiment conducted. Combustion 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

24 CHAPTER 2. EXPERIMENTAL APPARATUS 14 Test Oil Type Experiment Comment 20 W1 kin Combustion only 21 W1 kin 100 ml C5 22 W1 kin 25 ml kerosene 23 W1 kin Combustion only Failed/Leak 24 W1 kin Combustion only 25 W1 kin 25 ml kerosene 26 W1 tub Combustion only Failed/Leak 27 W1 tub Combustion only 28 W1 tub 500 ml C5 29 W11 kin Combustion only 30 W11 kin 25 ml C5 31 W11 kin Combustion only Pb in gas measurements 32 W2 tub Combustion only 33 W2 kin Combustion only 34 W2 kin 25 ml C5 35 W2 tub 500 ml C5 Failed/Short circuit 36 W2 kin Combustion with metallic additives Failed/Plug 37 W2 kin Combustion with metallic additives Failed/Plug 38 W2 tub 500 ml C5 39 W2 kin Combustion with metallic additives 40 W2 tub Combustion with metallic additives 41 W2 kin Coke combustion 42 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 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.

25 CHAPTER 2. EXPERIMENTAL APPARATUS 15 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 experiments. 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 models: 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.

26 CHAPTER 2. EXPERIMENTAL APPARATUS General equipment 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 O 2 analyzer was calibrated to 20.7%. Finally, a mixture of 10% of CO 2 and 10% of CH 4 was flowed to calibrate the CO 2 and CH 4 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 Properties of the oils Hamaca Oil The reservoir properties are excellent, with porosity values of up to 36% and permeability 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.

27 CHAPTER 2. EXPERIMENTAL APPARATUS 17 API Gravity 10.5 Viscosity 8,394 cp Asphaltenes 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 cp Asphaltenes 3% Table 2.4: Properties of the West Sak Oil 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(NO 3 ) 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

28 CHAPTER 2. EXPERIMENTAL APPARATUS 18 Component Sand Kaolin Clay Water Oil Weight 8500 g 450 g 400 g 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 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.

29 CHAPTER 2. EXPERIMENTAL APPARATUS Procedure Figure 2.1: Schematic of a kinetic cell (Sarathi, 1999). 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

30 CHAPTER 2. EXPERIMENTAL APPARATUS 20 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 O 2,CO,CO 2, and CH 4 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 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 in. thick to avoid heat conduction along the tube and tube diameter is approximately 3 inches. The

31 CHAPTER 2. EXPERIMENTAL APPARATUS 21 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.

32 CHAPTER 2. EXPERIMENTAL APPARATUS 22 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 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

33 CHAPTER 2. EXPERIMENTAL APPARATUS 23 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 CO 2 and CO concentrations in the effluent gas were used to confirm whether the high temperature combustion reactions were active or not.

34 Chapter 3 Results 3.1 Kinetic experiments Hamaca Oil In-situ combustion Figure 3.1(a) represents effluent gas compositions profiles for a pure in-situ combustion with the Hamaca oil, without any previous solvent injection. Figure 3.1(b) presents O 2 and temperature profiles. In agreement with the literature, LTO reactions 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, CO 2,and CH 4 that appeared in the effluent gas. These reactions are very exothermic and create the heat necessary to sustain the combustion. CO, CO 2, and CH 4 did not react during both LTO and HTO reactions and are less easy to interpret than O 2. Thus, our further interpretations will be based on O 2 and temperature profiles. 24

35 CHAPTER 3. RESULTS 25 (a) Concentration profiles during in-situ combustion. (b) O 2 concentration and temperature profiles during in-situ combustion. Figure 3.1: Concentration and temperature profiles during in-situ combustion.

36 CHAPTER 3. RESULTS 26 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; solvent has already been injected previously for test 9, 8, and 4. During HTO reactions, the fuel is burned and CO, CO 2, and CH 4 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 exothermic of heavy ends of fuel HTO reactions in 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

37 CHAPTER 3. RESULTS 27 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

38 CHAPTER 3. RESULTS 28 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 Increase in solvent in temperature Test 10 No solvent Test 9 Pentane C Test 8 Decane C Test 4 Kerosene C9-C Table 3.1: Increase in temperature during HTO reactions for Hamaca oil. Two different amounts of C 5 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

39 CHAPTER 3. RESULTS 29 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 precipitated 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

40 CHAPTER 3. RESULTS 30 Figure 3.4: Temperature profiles after injecting pentane at different pressures. presented in Figure 3.5, very little O 2 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.

41 CHAPTER 3. RESULTS 31 Figure 3.5: O 2 profiles after kerosene injections.

42 CHAPTER 3. RESULTS 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 CORNING R 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.

43 CHAPTER 3. RESULTS 33 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 O 2,CO,CO 2 and CH 4 during test 33, a combustion without any previous solvent injection. Compared to Hamaca oil, the concentration in O 2 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 O 2 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 CO 2 was produced relative to the case without solvent injection. Pentane dissolved a large part of the oil and there was enough remaining

44 CHAPTER 3. RESULTS 34 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 combustion 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

45 CHAPTER 3. RESULTS 35 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.

46 CHAPTER 3. RESULTS 36 (a) O 2 profiles. (b) CO 2 profiles. Figure 3.9: Concentration profiles after pentane injection. Experiment Comment Increase in 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.

47 CHAPTER 3. RESULTS 37 Figure 3.10: Temperature profiles during combustion with metallic additives.

48 CHAPTER 3. RESULTS 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 experiments by modeling them as first order reactions (Abu-Khamsin, 1984). The calculation 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 constant, 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 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 measurements 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

49 CHAPTER 3. RESULTS 39 HTO reactions Test Experiment Ea Ea/R Temperature kj/mol K K 10 Combustion only 83 10, ml of C5 + Combustion , mlofC10+Combustion , ml of kerosene + Combustion , 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 reactions Experiment Ea Ea/R Temperature kj/mol K K Combustion only 62 7, ml of C5 + Combustion 60 7, Combustion with metallic additives 58 7, 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

50 CHAPTER 3. RESULTS 40 heavy ends. The fuel deposited is then heavier than without solvent injection.

51 CHAPTER 3. RESULTS Tube experiments Hamaca Oil Figure 3.11 presents O 2,CO,CO 2 and CH 4 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 O 2 appeared very late and CO and CO 2 were produced throughout the experiment. These observations are consistent with effective combustion. The high content of CH 4 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 pentane. From Figure 3.12, temperature profiles during the combustion show very well the

52 CHAPTER 3. RESULTS 42 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 pentane. 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 combustion was stopped before it reached the end the tube.

53 CHAPTER 3. RESULTS 43 Figure 3.13: Sand after the tube experiment with Hamaca oil. Figure 3.14: Burned sand from the tube experiment with Hamaca oil.

54 CHAPTER 3. RESULTS 44 Figure 3.15: Coke from the tube experiment with Hamaca oil. Figure 3.16: Unburned sand from the tube experiment with Hamaca oil.

55 CHAPTER 3. RESULTS 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

56 CHAPTER 3. RESULTS 46 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, O 2 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 CO 2 concentration decreased steadily whereas O 2 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 CO 2 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.

57 CHAPTER 3. RESULTS 47 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 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.

58 CHAPTER 3. RESULTS 48 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 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