AIR INJECTION STUDIES FOR ENHANCED OIL RECOVERY
Abstract
Conventionally, air injection has been used for recovery of heavy crude oil in the production field, but studies have shown that depletion of light crude oil in the reservoir leads to abandonment of such wells. Hence, this work studied the kinetics and combustion of light crude oil in-situ the reservoir to understand their potentials for high-pressure air injection (HPAI) enhanced oil recovery (EOR). Advanced thermo-kinetic simulation and Pressure-Volume-Temperature tools (AKTS and PVTsim) were coupled with non-isothermal Differential Scanning Calorimetry (DSC) measurements and Accelerating Rate Calorimeter (ARC) for the studies. The combustion and kinetics of three (3) light crude oils obtained from Offshore of Newfoundland, Canada were precisely described by the methods. It was observed that the crude with the lowest API of 30.214 had the lowest enthalpy change of 10.9 J/g and the highest onset oxidation temperature of 220 oC, while the crude with the highest API gravity of 46.963 had the highest enthalpy of 24.6 J/g and the lowest onset oxidation temperature of 140 oC. Effect of 10% water saturation of one of the crude samples (Sample A) was studied and it was observed that there was increase in the onset oxidation temperature by 40 oC and lowering of the enthalpy change by 9 J/g. These findings provided evidence that the versatile Differential Scanning Calorimetry thermograms when coupled with kinetic simulation technique can yield reliable results with respect to oil recovery with high correlation coefficient (r > 0.9). This reliable information such as onset, peak and endset temperatures with their respective heat flow patterns, could then be used to provide precise thermo-kinetic parameters. Kinetic triplets such as activation energy, pre-exponential and the reaction model necessary for reservoir screening in an air injection EOR process can also be accurately determined. Mine tailings containing high pyrrhotite content were then used as catalyst to study its effect on the onset oxidation temperature of the crude oils using ARC. An amount of 20% tailings in crude oil lowered the average onset oxidation temperature from 148 oC to 116 oC. It also had the widest oxidation temperature range of 63 oC between the onset and endset temperature, as well as the highest pressure drop of 2.4 bar, which signifies high conversion in the crude oil oxidation reaction as well as production of miscible flue gas which favoured enhanced oil recovery process. Products of air combustion products in-situ was studied as an injectant in a light oil Nigerian reservoir using a simulated slim tube experiment and was observed than flue gas products from air oxidation at high temperature and pressure favoured enhanced oil recovery.
TABLE OF CONTENT
1.0 INTRODUCTION
1.1 Preamble
1.2 Problem statement…………
1.3 Justification of research…………………
1.4 Aims and Objectives of Research……
1.5 Scope of Research ……………
2.0 LITERATURE RVIEW
2.1 Oil Recovery Processes
2.1.1 Water drive reservoir
2.1.2 Gas cap drive reservoir
2.1.3 Solution gas reservoir
2.2 Enhanced Oil Recovery (EOR) concept
2.3 Enhanced Oil recovery (EOR) Methods
2.3.1 Hot water injection
2.3.2 Steam injection (Huff and Puff)
2.4 Air Injection for Enhanced Oil recovery (EOR)
2.4.1 In-situ combustion
2.4.2 Light oil air injection
2.5 Kinetics of Thermal EOR
2.5.1 Combustion reaction of crude oil
2.5.2 Oxidation of sulphur containing crude oils
2.5.3 Oxidation of mercaptans
2.5.4 Oxidation of aliphatic/cyclic suphides
2.5.5Air injection for reservoir oxidation
2.5.6 Amount of Air Required for EOR
2.6 Arrhenius Studies of EOR Kinetics
2.6.1Arrheniu sstudies of EOR kinetics using O2 consumption bases
2.7 Kinetics of Iso-Conversional Methods
2.7.1 Differential (Friedmans’s)
2.7.2 Ozawa-Flynn-Wall analysis
2.7.3 ASTM E698
2.8 Non Thermal Methods
2.8.1 Vaporising gas drive
2.8.2 Condensing gas drive
2.8.3 Immiscible gas drive
2.9 Reservoir Fluid Studies and Experiment
2.9.1 Primary Tests
2.9.1.1 Specific gravity tests
2.9.1.2 Gas-oil ratio tests
2.9.2 Routine hydrocarbon oil routine tests
2.9.2.1 Compositional analysis od reservoir fluids
2.9.2.2 Constant composition expansion
2.9.2.3 Differential Liberation tests
2.9.2.4 Separator tests
2.9.2.5 Constant volume depletion tests (CVD)
2.9.3 Special Laboratory PVT tests
2.9.3.1 Slim tube experiment
2.9.3.2 Swelling tests
3.0 MATERIALS AND METHODS
3.1 Material and Equipment
3.1.1 Materials and utilities
3.1.2 Equipment
3.1.3 Experimental Procedure
3.1.4 Viscosity determination
3.1.5 Specific heat capacity determination
3.1.6 Differential Scanning Calorimetry (DSC) tests
3.1.7 Accelerating rate Calorimeter (ARC) tests
3.1.8 Mine tailings preparation
3.1.9 Mineral liberation analyser (MLA) for mine tailings studies
3.1.10 PVTSim19 and Design Expert software simulation for oil recovery analysis
4.0 RESULTS AND DISCUSSION
4.1 Properties of crude oil
4.2 Thermal behaviours of Crude Oils using DSC
4.3 Thermal Kinetics of DSC Thermograms of Crude Oils
4.4 The use of Mine Tailings as catalysts in crude oil oxidation reaction
4.5 Effect of Reservoir Conditions on Oil Recovery on Nigerian Oils
5.0 CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
5.2 Recommendations
REFERENCES
APPENDICES
List of Figures
CHAPTER 2
Figure 2.1 Reservoir classification based on drive mechanism
Figure 2.2 Classification of Enhanced Oil Recovery (EOR
Figure 2.3 Steam or Hot water injection
Figure 2.4 Air Injection Route in thermal EOR Process
Figure 2.5 An air injection process diagram
Figure 2.6 Relationship of the reaction progress α vs time for reaction models
Figure 2.7 Schematic representation of miscible displacement
Figure 2.8 Ternary diagram illustrating miscible drives
Figure 2.9 Vaporising gas drives
Figure 2.10 Condensing gas drive
Figure 2.11 Immiscible gas drive
Figure 2.12 Schematic diagram illustrating method for determining Gas to Oil ration
Figure 2.13 Schematic diagram of a constant composition expansion experiment
Figure 2.14 Schematic diagram of a Differential liberation experiment
Figure 2.15 Schematic diagram of a three-stage separator experiment
Figure 2.16 Schematic representation of a constant volume depletion test
Figure 2.17 Schematic diagram of a slim tube apparatus
Figure 2.18 Schematic representation of swelling test
CHAPTER 3
Figure 3.1 The Algorithm Logic of Heat-Wait-Seek Operation in ARC
CHAPTER 4
Figure 4.1 DSC thermograms of crude oil samples at 10K/min
Figure 4.2 Reaction Progress as a function of Temperature for Sample A
Figure 4.3 Reaction Progress as a Function of Temperature for Sample B
Figure 4.4 Reaction Progress as a Function of Temperature for Sample C
Figure 4.5 Reaction Progress as a Function of Temperature for Sample A
Figure 4.6 Reaction rate for Sample A at different ramp rates.
Figure 4.7 Reaction rate for Sample B at different ramp rates.
Figure 4.8 Reaction rate for Sample C at different ramp rates.
Figure 4.9 Reaction rate for Sample A* at different ramp rates.
Figure 4.10 Apparent Activation Energy of Sample A based on ASTM-E698
Figure 4.11 Apparent Activation Energy of Sample B based on ASTM-E698
Figure 4.12 Apparent Activation Energy of Sample C based on ASTM-E698
Figure 4.13 Apparent Activation Energy of Sample A* based on ASTM-E698
Figure 4.14 Activation energy and pre-exponential factor as a function of reaction progress for Sample A
Figure 4.15 Activation energy and pre-exponential factor as a function of reaction progress for
Abbreviations, Definitions, Glossary and Symbols
Abbreviations
ARC – Accelerating rate calorimeter
DSC – Differential scanning calorimetry
PVT – Pressure- Volume- Temperature
DOE – Design of experiment
EOR – Enhanced oil recovery
LTO – Low temperature oxidation
HTO – High temperature oxidation
SRK - Soave - Redlich – Kwong
EOS - Equation of state
s.g – Specific Gravity
Symbols
= Pre-exponential factor c = Critical point
Cp = Specific heat capacity
E = Activation Energy
f (α) = Reaction model
f = Final
i = Initial
n = Reaction order
R = Molar gas constant
Sat = Saturation
T = Temperature
t = Time
v = Darcy velocity
V = Volume
= Reaction progress or conversion
= Heating rate
CHAPTER ONE
1.0 INTRODUCTION
1.1 Preamble
Enhanced Oil Recovery (EOR) is a tertiary recovery process which is normally applied after primary and secondary recovery, to mobilize oil trapped in pores by vicious capillary forces. Thermal, chemical, solvent and gases are the most common form of various EOR process (Isco, 2007). Due to the decline of oil reserves caused by the rising oil production, and clamours for environmentally friendly practice in EOR techniques, petroleum engineers are currently driving EOR projects towards more efficient techniques. One of such efficient technique is the Air/Flue gas injection which is motivated by inexpensive source of air as well as environmentally friendly carbon-dioxide sequestration. The motivation for the use of air as an injectant in the EOR project is because of its abundance, availability and low cost. It can simply be supplied by the use of a compressor, with overall project having low initial and operating cost in comparison to other EOR methods (JOGMEC, 2011).
Air for increasing oil recovery from reservoirs dates back to the 1940’s and early 1950’s (Hvizdos et al., 1983) and by the 1960s and 1970, about forty (40) in-situ full field or pilot projects had been undertaken throughout the world with North America topping such projects (Pwaga et al., 2010). This technique, apart from laboratory studies has been implemented in fields such as West Hackberry in Louisiana, Horse Creek North and South Dakota, Zhongyuan and Liaoche oil fields in China, H field in Indonesia, South Bridge in California and other countries such as Romania, United Kingdom, Japan, Canada, India, Argentina, Venezuela have maintained laboratory and field studies too (Sakthikumar et al., 1996; Ren et al., 1999; Mendoza et al., 2011; Niu et al., 2011; Iwata et al., 2001; Xia et al., 2004; Zhu et al., 2001). Air
has also been used in heavy oil recovery and enhancement of this technique can lead to significant light oil production (Surguchev et al., 1998).
An alternative to air injection is the flue gas (which contains nitrogen and carbon-dioxide) produced from the combustion of oxygen contained in the air to sweep oil. This EOR technique, when applied to light oil is known as light oil air injection while in heavy oil reservoir, it is called in-situ combustion. (Kuhlman, 2004; Teramoto et al., 2006; Turta et al., 2007; Li et al., 2009).
Some studies carried out to describe criteria as well as performance of air injection projects gave positive results even though experimental condition could not mimic the adiabacity of the reservoir (Sakthikumar et al., 1996). Temperature regimes, heat energy content, pressure and temperature dependence during oil combustion were also studied using simple Arhennius type model which assumes constant kinetic parameters throughout the reaction (Hvizdos et al., 1983; Elgibaly, 1998; Niu et al., 2011; Li, et al., 2009). There have been few researches which reports on the complexities of combustion reaction of crude oils where kinetic parameters fluctuate or the alteration of the oxidations zones.
1.2 Problem Statements
The following are the problems, research gaps in literature and previous studies on enhanced oil recovery with reference to light oil air injection projects.
Despite the several thermal and kinetic studies carried out on Enhanced oil recovery, there has been no research that addresses how the kinetic parameters fluctuate during the combustion process for the benefit of oil recovery.
Arrhenius type of equation and simple nth order model have been used to study oxidation of oil and these do not adequately capture the complexity of the reaction (such as the trend of activation energy as reaction progresses), therefore, the need to study other models and techniques.Very few and scanty literatures exist that captures the various oxidation reaction zones of crude oil.
Interaction parameters of temperature, pressure, extent of air oxidation and sulphur content on crude oil recovery have received low discussions in literatures, hence the need to focus attention on them for the benefit of enhanced oil recovery especially in countries like Nigeria where EOR is yet to be fully practiced.
1.3 Justifications of Research
This sections highlights the benefits of this research.
This study will provide insight into improved oil recovery from low producing/ abandoned wells.
The iso-conversional approach will help capture the complexity of crude oil oxidation reaction.
The findings will benefit upstream companies operating in Nigeria currently at the secondary production stage and at verge of abandoning the wells.
This will also help the federal Government of Nigeria during negotiations of oil well sales.
It will open up researches and studies on catalytic potential of Nigeria’s mine tailings.
1.4 Aim and Objectives of Research
The aim of this research work was to investigate the kinetics, combustion of air and combustion air products for enhanced oil recovery.
This aim was achieved by the following objectives:
Using differential iso-conversional method to describe oxidation of crude oils in-situ reservoir.
Studying oxidation behaviours of crude oil in an adiabatic environment to verify non-isothermal differential scanning calorimetry (DSC) results.
Using tailing as catalyst to alter oxidation characteristics of crude oils.
Studying the combined effect of parameters of reservoir conditions such as temperature, pressure, gas content on oil recovery.
1.5 Scope of Research
The scope of this research are focussed on:
Combustion behaviours and kinetics of the oxidation reaction of low pressure reservoir of light crude oils.
The use of mine tailings to improve the reactions for the benefit of improved oil recovery.
Modelling of air injection process with respect to the progress of oxidation kinetics with temperature.
The use of crude oil databank and PVT tests to analyse the enhanced oil recovery process for Nigerian crude oils.
