ENHANCED OIL RECOVERY OF HEAVY OIL BY USING THERMAL AND NON-THERMAL METHODS
World’s conventional oil reservoirs are depleting on an alarming rate and we must find alternate sources to keep the supply undisturbed. Currently the best alternative is the heavy oil which can be extracted by applying different techniques which are different from the conventional methods. Alberta holds the world’s largest reserves of bitumen. This paper deals with the techniques for enhance oil recovery which include thermal and non-thermal methods, along with the projects going on in different parts of the world especially in Canada. Potential of new technologies is assessed and their comparison with already existing technologies is also the focus of this paper. Better understanding of methods may help in the method selection. Facts and figures obtained from different oil fields of the world are also discussed in this report. A few other methods which were tried in past and did not work as desired are also discussed because there is always a potential for further development. Every method is unique and has its limitations; an effort has been made to address those problems and their rectification.
TABLE OF CONTENTS
LIST OF TABLES vii
LIST OF FIGURES viii
LIST OF ABBREVIATIONS USED xi
CHAPTER 1 INTRODUCTION 1
HEAVY OIL RESERVOIRS3
HEAVY HYDROCARBONS AS AN ALTERNATE SOURCE OF PETROLEUM5
CHAPTER 2 NON-THERMAL PRIMARY RECOVERY METHODS 9
GAS CAP DRIVE11
SOLUTION GAS DRIVE OR DISSOLVED GAS DRIVE12
Comparision of solution gas drive with all natural drives14
CHAPTER 3 NON-THERMAL SECONDARY RECOVERY METHODS 15
Conclusion on Cold Production20
PRESSURE PULSE TECHNOLOGY22
Conclusion on Pressure Pulse Technology22
CHAPTER 4 NON-THERMAL TERTIARY RECOVERY METHODS 25
CARBON DIOXIDE FLOODING28
CYCLIC CARBON DIOXIDE STIMULATION30
Miscible Carbon Dioxide-Enhanced oil recovery process31
Immiscible Carbon Dioxide-Enhanced oil recovery process31
CHAPTER 5 THERMAL METHODS 32
HOT FLUID INJECTION33
HOT WATER DRIVE34
STEAM BASED METHODS35
STEAM DRIVE INJECTION36
CYCLIC STEAM INJECTION37
Comparision between Hot Water Drives and steam Drives41
Comparision between Cyclic Steam Injection and steam Drives41
STEAM-ASSISTED GRAVITY DRAINAGE (SAGD)42
FORWARD DRY IN-SITU COMBUSTION47
WET COMBUSTION METHOD49
Conclusions on Forward Dry vs Wet Combustion50
THE THAI PROCESS52
THAI CAPRI PROCESS57
ECONOMICS OF POWER GENERATION REQUIRED FOR THE EOR OPERATIONS
CHAPTER 6 CONCLUSION 58
LIST OF TABLES
Table 1 Screening criteria for selection of recovery methods. 59
LIST OF FIGURES
Figure 1 General relationship of viscosity to API gravity 2
Figure 2 Oil-sand grain structure 3
Figure 3 Distribution of conventional crude oil and heavy hydro carbons 4
Figure 4 Major oil Sand Deposits of Canada 6
Figure 5 Major oil sands project locations in Canada 7
Figure 6 Canadian Crude Oil Production forecast (moderate estimate) 8
Figure 7 Three basic natural drives 10
Figure 8 Water drive 11
Figure 9 Gas-cap drive 12
Figure 10 Solution gas drive 13
Figure 11 Water Flooding Displacing oil 16
Figure 12 Concept of Water Flooding 17
Figure 13 Schematic of Sand Production with Wormholing 18
Figure 14 Heavy oil deposits in Alberta and Saskatchewan, with an indication of
the cold production belt surrounding Lloydminster 20
Figure 15 Schematic for Miscible Enhanced Recovery Processes 21
Figure 16 Schematic for Chemical Enhanced Recovery Process 26
Figure 17 Carbon Dioxide Flooding 30
Figure 18 Oil Recovery by Thermal Methods 32
Figure 19 Hot Fluid Injection 34
Figure 20 Stages of cyclic steam injection 39
Figure 21 Existing EOR methods with cogeneration of steam and electricity 40
Figure 22 SAGD Process (fluid movement in horizontal wells) 40
Figure 23 SAGDProcess. 43
Figure 24 Multi-Level cracking using the asphaltene constituent as an example 46
Figure 25 Schematic diagram of in situ combustion oil recovery 48
Figure 26 THAI – ‘Toe-to-Heel Air Injection’ Process. 54
Figure 27 3D view of THAI Process. 55
Figure 28 Long distance and short distance displacement processes. 56
LIST OF ABBREVIATIONS USED
API. American Petroleum Institute. CHOPS. Cold Heavy Oil Production with Sand. PPT. Pressure Pulse Technology.
VAPEX. Vapor-Assisted Petroleum Extraction. TEOR. Thermally Enhanced Oil Recovery Methods. SAGD. Steam-Assisted Gravity Drainage.
LTO. Low Temperature Oxidation.
CO2. Carbon Dioxide.
H2S. Hydrogen sulfide.
pH. Power of Hydrogen.
COFCAW. Combination Of Forward Combustion And Water Flooding. Bbl. Barrel.
THAI. Toe-to-Heel Air Injection. MWD. Measurement While Drilling. PV. Pore Volume.
OIP. Oil in Place.
OOIP. Original oil in place.
All praises are for The Almighty, the most Beneficial and the most Merciful.
I would like to extend my gratitude to Dr. Michael. J. Pegg who supervised my worked and guided me throughout my degree program. I am also thankful to Dr. Dominic Groulx who added his comments and corrected me where required.
CHAPTER 1 INTRODUCTION
Compared with conventional oil, heavy oil has reduced mobility; it is termed as heavy oil because it has higher specific gravity and density along with viscosity when compared with the conventional oil. The viscosity is between 100 cP or greater and API gravity less than 20°. API gravity is a Specific gravity scale developed by the American petroleum institute to measure the relative density of various petroleum liquids, expressed in degrees. The lower the API number, the heavier the oil and the higher its specific gravity.
Goodarzi et al., (2009) define heavy oil in terms of viscosity as the class of oils ranging from 50 cP to 5000 cP. The high viscosity restricts the easy flow of oil at the reservoir temperature and pressure. Figure-1 is a graph relating viscosity and API ratings and it can be observed that the heavy oil region lies in the high viscosity range.
Ancheyta and Speight (2007) define heavy oil as a viscous type of petroleum that contains a higher level of sulfur as compared to conventional petroleum that occurs in similar locations.
Meyer et al., (2007) explained that the oil becomes heavy as a result of eradication of light fractions through natural processes after evolution from the natural source materials. A high proportion of asphaltic molecules and with substitution in the carbon network of heteroatoms such as nitrogen, sulfur, and oxygen also play an important role in making the oil heavy. Therefore, heavy oil, regardless of source, always contains the heavy fractions of asphaltenes, heavy metal, sulphur, and nitrogen.
The importance of resins and asphaltenes in accumulation, recovery, processing, and utilization of petroleum was highlighted by Raicar and Proctor (1984). They found that most asphaltenes are generated from the kerogen evolution due to the increase in temperature and pressure with the increase in depth. Their opinion is in the light of the fact that asphaltenes are recognized as a
soluble chemically altered fragments of kerogen that migrated out of the source rock during oil catagenesis.
Figure1 General relationship of viscosity to API gravity. [Thomas, 2008]
Origin of heavy oil according to many authors is the result of biodegradation. Larter et al., (2006) believes that first the oil was expelled from its source rock as light or medium oil , and subsequently migrated to a trap, then it is converted into heavy oil through different processes such as water washing, bacterial degradation (aerobic), and evaporation, provided that the trap is elevated into oxidizing zone. This biodegradation can occur at the depth in a subsurface reservoir. Head et.al, (2003) mentioned the depths of the biodegradation oil up to about 4 Km with most biodegraded reservoirs up to 2.5 Km below the sediment surface.
From the above we can conclude that the heavy oil migrated from the deep source rock or deep reservoirs originally as conventional oil. At these depths, water caused weathering and bacteria fed on the oil causing biological degradation by removing hydrogen and thus increasing its density.
HEAVY OIL RESERVOIRS
Heavy oil is reasonably mobile in the reservoirs which have sufficiently high temperature due to which heavy oil can be produced by using conventional methods. Figure-2 shows the typical oil sand grain. The figure explains how each grain is surrounded by a layer of water and bounded by bitumen.
Figure-2 Oil-sand grain structure [Canadian centre for energy information]
The reservoirs of heavy oil are shallow and have less effective seals (up to 1000 meters below the surface line), which is the reason for the low reservoir temperature (40-60 °C). Low sedimentary overburden tends to ease the biodegradation, and the presence of the bottom aquifers further facilitates the process. As mentioned earlier the less effective seal is due to the low seal pressure, which may cause the dissolved gases to leave the oil, increasing its viscosity. The reservoir lithology is usually sandstones deposited as turbidity with high porosity and permeability; the elevated viscosity is compensated by high permeability.
Hydrocarbon resources of heavy oil and oil sands are nearly three times the conventional oil in place in the world. According to Farouq Ali and Meldau (1999) over two trillion barrels of oil is present in the oils sands of Alberta and in Canada the contribution of heavy oil and oil sands resources is 20% of the total oil production.
Figure-3 Distribution of conventional crude oil and heavy hydro carbons [Herron, 2000]
Herron in his article “Heavy Oil: A Solution to Dwindling Domestic Oil Supplies” wrote that the total estimate of worldwide deposits of heavy hydrocarbons is around 5½ trillion barrels and western hemisphere contains four-fifths of these deposits. From the crude distribution showed in figure-3 we can conclude that the outlook for domestic oil supplies can be much improved if the heavy oil hydrocarbon resources (both heavy crude oil and natural bitumen) are included in petroleum sources.
CANADA’S HEAVY OIL INDUSTRY
Canada along with Venezuela holds 90% of the world’s heavy oil and bitumen (oil sands). The largest reserves of bitumen are located in Alberta. The resources of the conventional crude oil in Canada are declining which opens the window for further development of technologies to recover heavy oil. These technologies are discussed in this report. Canada’s present and future energy requirements heavily rely upon the breakthrough in these technologies.
Figure-4 shows Canada’s heavy oil resources which are in northeastern Alberta and western Saskatchewan. In past ten years Canada’s heavy oil industry has experienced a remarkable resurgence, much of which is due the technological advancements.
A number of different projects are in progress in the areas shown in figure-5. In those fields sands are un-cemented with high porosity and permeability. The viscosities of oil range are from few hundred to more than a million cP with 20° to 8° API gravity. The reservoirs are shallow, the solution gas content is low and pressure and temperature are towards the lower side as well. Recoveries were usually limited to 3-5% of the oil in place when early attempts were made to produce from these oils. The reasons for the low recovery were:
1. Low flow rates resulting from the high viscosity.
2. Problems with sand construction.
3. Water breakthrough.
Figure-4 Major oil Sand Deposits of Canada [Nasr and Ayodele, 2005]
But technological wonders such as Horizontal wells, progressive cavity pumps, foamy oil/sand production, and other methods, along with horizontal drilling has solved the above mentioned problems. As significant improvements were seen in both primary and enhanced recoveries which result in better producibility and improved the level of heavy oil recovery considerably.
Figure-5 Major oil sands project locations in Canada
Figure-6 shows the oil production forecast for Canadian crude oil by Nasr and Ayodele (2005). This prediction was made by keeping in mind the current production and the projects carried out in western Canada and as shown in Figure-6 the heavy oil industry will be the biggest contributor of the Canadian crude oil in future.
Figure-6 Canadian Crude Oil Production forecast (moderate estimate) [Nasr and Ayodele, 2005]
CHAPTER 2 NON-THERMAL PRIMARY RECOVERY METHODS
As discussed earlier, many heavy oil reservoirs contains oil that does not flow easily under reservoir conditions which means successful recovery of this resource is based upon developing a mechanism that displaces the heavy oil in the reservoir. All reservoirs have different lithology and some of them are thin or small and overlying gas or underlying water may cause contraction in them which makes them poor candidate for the thermal methods of oil recovery. That means after the application of primary recovery any additional method should be non-thermal.
Primary recovery techniques rely entirely on natural forces within the reservoir that’s why it is not the usual approach of recovery. For example the pressure of natural gas dissolved in oil or present above the oil or the natural pressures surrounding the reservoir rocks can help in the flow of oil. Figure-7 shows different methods and the basic techniques of primary recovery.
These techniques are mostly used to recover conventional oil as compared to heavy oil which depends upon the fluidity of oil in the reservoir. The amount of oil that is recoverable depends upon the reservoir temperature and the permeability of the rocks. A high temperature in the reservoir increases the fluidity. Permeability of rocks can be understood by considering the example of reservoir rocks which are “tight”, such as in shale in which the flow of oil is restricted, but oil flows more freely in the case of permeable rocks such as sandstones.
Meyer and Attanasi (2003) mentioned several very large projects which produce more than 100,000 barrels per day for heavy oil of approximately 12° API. In the Heavy Oil Belt (FAJA) in Venezuela the recovery yield from primary methods is 8 to 15%. It is expected that the heavy oil production from this belt will last for 35 years at a production rate of 600,000 barrels per day. Firozabadi (2001) stated that the recovery from primary production in heavy oil reservoirs may be as high as 20 %; the factors that make it possible will be discussed later..