Abstract:
An enhanced oil recovery method is provided. This method includes; introducing a first essentially pure oxygen stream into a subterranean hydrocarbon-bearing formation traversed by at least one injection well and at least one production well, and initiating and sustaining in-situ combustion in the vicinity of the injection well. This method also includes introducing a second essentially pure oxygen stream and a hydrocarbon-containing fuel gas stream into the combustion device of a power generation system, wherein the combustion device produces an exhaust gas stream comprising water and carbon dioxide. This method also includes separating the exhaust gas stream into a stream of essentially pure water, and a stream of essentially pure carbon dioxide, and introducing at least a portion of the essentially pure carbon dioxide stream into the subterranean hydrocarbon-bearing formation prior to initiating the in-situ combustion.

Description:
[0001]    The present application is a divisional application of U.S. application Ser. No. 12/429,250 filed Apr. 24, 2009 and claims the benefit of U.S. Provisional Application No. 61/048,673, filed Apr. 29, 2008, herein incorporated by reference in its entirety for all purposes. 
     
    
     BACKGROUND 
       [0002]    Since 2002, there has been a general trend of increasing oil prices. This trend is generally expected to continue as a result of a number of factors: increasing oil demand from emerging economies; geopolitical instability in important production areas; and reduced exploration and technological development within the last two decades due to low oil prices. 
         [0003]    Current oil prices, along with international regulations on CO2 emissions (such as the Kyoto Protocol and beyond, Alberta “carbon tax”, California regulation on GHG footprint of fossil fuels, etc.) increases the industries interest in providing innovative solutions that will allow: the increase of oil recovery from a given existing reservoir at a reduced additional cost; reliable performance within a large range of oil/reservoir characteristics; and the reduction of carbon footprint of technologies for enhanced oil recovery. 
         [0004]    The techniques to be employed for oil recovery depend on the particular geological conditions (thin reservoirs . . . , porous reservoirs . . . ) and are typically performed at different stages of the oil production. 
         [0005]    The term Primary Recovery Technologies includes recovery strategies using the natural energy of reservoirs. These technologies are based on the immiscible fluids displacement, and different mechanisms are possible, such as: Gas Cap drive (expansion of the gas phase); Solution Gas Drive (ex-solution of solved Gas); Bottom Water Drive (aquifer displacement). For conventional oil typical performance for primary recovery techniques are around 19% of OOIP (Original Oil in Place): less for heavy oils, more for light oils. 
         [0006]    In the Secondary Recovery, also known as water-flooding, the enhancement of oil production is performed by adding energy to the natural system. Water is typically injected in a well (or a pattern of wells) in order to maintain pressure in the reservoir and to displace oil towards a producer. Initially oil alone is produced. Then as water component progresses, both oil and water are produced. As time advances, the percentage of water (the watercut) increases progressively. For conventional oil, average recovery by Water Flooding is around 32% OIP (Oil In Place) after primary recovery. 
         [0007]    Enhanced Oil Recovery (EOR) techniques are used to further increase the amount of recovered oil, in particular when water-flooding is not effective (or efficient). Some of the various EOR techniques that may be employed include: thermal-based oil recovery: steam flooding , cyclic thermal injection, in-situ combustion; electric heating, microwaves heating; chemical flooding: polymer flooding, micellar flooding; Immiscible Flooding: Nitrogen injection, CO2 injection; Miscible Flooding: lean gas injection, CO2 injection; and microbial injection. 
         [0008]    For conventional oil, primary recovery is usually followed by water-flooding, but most of the enhanced oil technologies are not yet commercially proven. For unconventional oil reserves such as extra heavy oil in Venezuela and Albertan oil sands (characterized by high densities and high viscosities (20&gt;API&gt;7, 10000cPo&lt;m&lt;100cPo or 12&gt;API&lt;7, m&gt;10000cPo) primary and secondary recovery are not sufficient to guarantee oil production and the economic exploitation of these resources is strictly related to the successful development of EOR technologies. The growing relevance of heavy oils in the world oil reserves and in particular of such unconventional oils results in the development of new EOR methods. 
         [0009]    The SAGD (Steam Assisted Gravity Drainage) is a steam flooding technique improved by the use of two horizontal wells: one for steam injection and one for bitumen extraction. The steam heats the formation increasing the viscosity of bitumen which can flow trough the producer. The main drawback of SAGD concerns high SOR (steam on oil ratio), ranging from 2 to 4. The performance of SAGD are strictly dependent upon reservoir properties. Characteristics such gas caps, aquifers, and shale in the reservoir can result in uneconomical operations. 
         [0010]    Steam flooding and SAGD are typically only efficient for shallow reservoirs (&lt;1000 m) thus not being a viable solution for heavy oil resources in area such as the Arabic gulf and Russia. 
         [0011]    The VAPEX (Vapor Extraction) process involves injecting a gaseous hydrocarbon solvent into the reservoir where it dissolves into the bitumen. The bitumen then becomes less viscous and can drain into a lower horizontal well and be extracted. The solvent is typically propane, butane, or CO2 along with a carrier gas. Main drawbacks of this technique are the following. In the case of bitumen or extra heavy oil, blending oil with the solvent without heating the formation produces only small improvements in oil recovery. Solvent is also expensive, can be scarce, and therefore the losses in the reservoir can be important. 
         [0012]    A number of process such as ES-SAGD, LASER or SAVEX are under development in order to provide an hybrid in-situ extraction technology coupling the advantages of steam injection (thermal reduction of oil viscosity) and solvent injection. Lights hydrocarbons are used and solutions to drawbacks such as reservoir depressurization and solvent losses have to be developed. None of these combine the advantages of thermal extraction and miscible and immiscible flooding. 
         [0013]    The In-Situ Combustion(ISC) process is defined as “the propagation of a high temperature front for which the fuel is a coke-like substance, laid down by thermal cracking reactions”. In recent years, that has been a worldwide interest of ISC for conventional oil. 
         [0014]    Compared to mining, SAGD and VAPEX, in-situ combustion based bitumen extraction has the potential to be applied in a wider range of reservoir characteristics and to provide partially upgraded bitumen with better thermal efficiency and reduced environmental impact: Benefits of ISC include: reduced GHG footprint—50% less than SAGD; almost no water consumption; no need for land remediation. Within the ISC, bitumen is partially upgraded in the underground, and the production is performed by thermal flooding (viscosity reduction) and gas flooding (flue gas drive). 
         [0015]    The use of oxygen injection represents one of the main areas of development for this technology. Advantages of oxygen injection for In-Situ combustion operations include: lower compression cost; simple ignition; better thermal efficiency: produced heat is not dispersed trough an inert gas; and easier downstream operations: emulsions are easy to break. Additionally, as in the case of surface oxy-combustion, the use of oxygen will result in the possibility of recovering a CO2-rich stream at the production well, to be used for additional EOR and storage. However, low oil prices and lack of GHG emissions regulations have not justified the use of oxygen in the last twenty years. 
         [0016]    There is a need in society for an in-situ combustion oil recovery process that will improve the economics, improve the oil recovery, reduce the environmental impact, and improve safety. 
       SUMMARY 
       [0017]    The present invention is an enhanced oil recovery method that includes; introducing a first essentially pure oxygen stream into a subterranean hydrocarbon-bearing formation traversed by at least one injection well and at least one production well, and initiating and sustaining in-situ combustion in the vicinity of said injection well. The present invention also includes introducing a second essentially pure oxygen stream and a hydrocarbon-containing fuel gas stream into the combustion device of a power generation system, wherein said combustion device produces an exhaust gas stream comprising water and carbon dioxide. The present invention also includes separating said exhaust gas stream into a stream of essentially pure water, and a stream of essentially pure carbon dioxide, and introducing at least a portion of said essentially pure carbon dioxide stream into said subterranean hydrocarbon-bearing formation prior to initiating said in-situ combustion. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]    The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, and in which: 
           [0019]      FIG. 1  is a schematic representation of one embodiment of the present invention, with a steam turbine for energy production. 
           [0020]      FIG. 2  is a schematic representation of another embodiment of the present invention with a combustion turbine for energy production. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    The present invention is the design of an improved process for enhanced oil recovery based on in-situ combustion. The present invention provides improved economics due to reduced compression costs, the virtual elimination of N2 in the combustion exhaust, and the reduction of O2 requirements. The present invention also provides improved ultimate oil recovery from oil reservoirs, by combining in-situ combustion and CO2 flooding. The present invention provides the dramatic reduction of the environmental footprint of oil recovery technologies, with virtually zero CO2 emissions, and virtually no water being used. The present invention provides improved safety, with CO2 being injected for O2 dilution. 
         [0022]    The present invention accomplishes this by integrating Oxygen-based in situ combustion for oil recovery, oxycombustion for power-energy production, and CO2-flooding. 
         [0023]    In one aspect of the present invention, oil production is performed by O2-based in-situ combustion. In-situ combustion off-gas separation is performed in order to recover a CO2 stream and a fuel gas stream (comprising primarily light hydrocarbons, CO, and H2). The CO2 is compressed and can be either; partially recycled to the injection well (to improve sweep efficiency and High temperature front displacement); or partially sent to a pipe and used for EOR, ECBM, or storage. The oxycombustion water is used for additional injection, wet in-situ combustion. The fuel gas is blended with an additional fuel such as Natural Gas and oxy-burned in order to provide power for the compression of CO2 (for example re-injection, pipeline, etc.). 
         [0024]    The present invention of the integration of oxy-combustion within O2-based in-situ combustion provides improved performance of the in-situ combustion process. This is accomplished by the recovery of a high LHV fuel gas, essentially nitrogen free, in order to reduce NG needs. This is also accomplished by the production of a concentrated CO2 stream as the only gaseous by-product of the process. This results in: the dramatic reduction of the environmental impact of oil upstream operations (zero GHG emissions, reduced water needs); the enhancement of oil recovery performance; and the availability on the oilfield for additional oil recovery. 
         [0025]    Turning now to  FIG. 1 , enhanced oil recovery system  100  is provided. Essentially pure liquid oxygen stream  101  is introduced and at least part of the oxygen is directed into stream  102  is vaporized in vaporizer  103  then into oxy-combustion boiler  110 . At least part of the oxygen is directed into stream  104 , is increased in pressure in pump  105 , and vaporized in vaporizer  106 . The pressurized and vaporized oxygen  107  is then injected into the oil reservoir through an injection well  108   a / 108   b  in order to support in-situ combustion. The pressure at which the vaporized oxygen is introduced into the reservoir may be between about 50% and about 80% of the breakdown pressure. A blended stream  111 , containing at least oil, gas and water, is recovered from production well  112   
         [0026]    In another embodiment, the pressurized and vaporized oxygen  107  is injected into a structure containing a carbonaceous substance such as coal, petroleum coke (petcoke), or biomass, through at least one inlet line  108   a / 108   b.  A blended stream  111 , containing at least oil, gas and water, is recovered from at least one outlet line  112 . 
         [0027]    This blended stream is separated in separator  113 , thereby producing recovered oil stream  114 , and separated water stream  115 . Separated water stream  115  may be used as water injection into injection well  108   a / 108   b.  Recovered gas  116 , which may include CO2, CO, H2O, CH4, light hydrocarbons, H2, and H2S, is introduced to separator  117 . The exact composition of the recovered gas will depend on the nature of the produced oil and the recovery process itself. The recovered gas will be substantially free of nitrogen, due to the oxygen injection. Separator  117  may include, but is not limited to, the following processes: adsorption, absorption, cryogenic systems and membrane systems. The adsorption systems may include, but are not limited to, Rectisol, Selexol, or Amine wash systems. In one embodiment, the membrane system or the combination of cryogenics and membrane system is preferred. A high LHV fuel gas  118 , and a stream that is predominantly composed of CO2  119  are recovered from separator  117 . The high LHV fuel gas  118  may optionally be further purified in gas purification unit  120 . The purified high LHV gas  121  may be combined with natural gas stream  109 , prior to admission to combustion device  110 . 
         [0028]    After combusting the oxygen stream  102  with the fuel gas streams ( 109 ,  121 ), combustion device  110  outputs power  122  to the process (compression) facility, and also outputs an exhaust stream  123  that is predominantly H2O and CO2. Impurities may include predominantly SOx, NOx and Oxygen. Exhaust stream  123  enters separator  124 , which outputs H2O stream  125  and CO2 stream  127 . The H2O stream  125  is then combined with water stream  115 , thereby producing combined stream  126 . Additives can be used in order to control PH Stream Streams  125  and  126 .  126  is then admitted into injection well  108   a / 108   b.  CO2 stream  127  is then combined with CO2 stream  119 , thereby producing combined stream  128  which is partially purified, and introduced into compressor  129 . At least part of the compressed CO2  130  is admitted into injection well  108   a / 108   b.  If any CO2 remains, it may be further purified in purifier  131 , then sent to storage, to a local pipeline, or used for EOR  132 . 
         [0029]    In one embodiment, a Rankine cycle may be employed as follows. Combustion device  110  may be thermally linked to a steam generation device  138 . Steam generation device  138  may produce steam stream  133 , which is introduced into steam turbine  134 . Steam turbine  134  produces power  122  and outputs lower pressure steam. This low pressure steam may be condensed, thereby producing condensate stream  135 . Condensate stream  135  may be introduced to pump  136 , thereby producing higher pressure condensate stream  137  which is returned to the steam generation device  138 . 
         [0030]    Turning now to  FIG. 2 , enhanced oil recovery system  200  is provided. Essentially pure liquid oxygen stream  201  is introduced and increased in pressure in pump  202 . The pressurized oxygen is vaporized in vaporizer  203 . At least part of the oxygen is directed into stream  205  and introduced into combustion turbine combustor  208 . The remaining pressurized and vaporized oxygen  204  is then injected into the oil reservoir through an injection well  206   a / 206   b  in order to support in-situ combustion. The pressure at which the vaporized oxygen is introduced into the reservoir may be between about 50% and about 80% of the breakdown pressure. Natural gas stream  207  is blended with high LHV fuel gas stream  218  (discussed below) and introduced into combustor  208 . 
         [0031]    A blended stream  209 , containing at least oil, gas and water, is recovered from production well  210  This blended stream is separated in separator  211  thereby producing recovered oil stream  212 , and separated water stream  213 . Separated water stream  213  may be used as water injection into injection well  206   a / 206   b.  Recovered gas  214 , which may include CO2, CO, H2O, CH4, light hydrocarbons, H2, and H2S, is introduced to separator  215 . The exact composition of the recovered gas will depend on the nature of the produced oil and the recovery process itself. The recovered gas will be substantially free of nitrogen, due to the oxygen injection. Separator  215  may include, but is not limited to, the following processes: adsorption, absorption, cryogenic systems and membrane systems. The adsorption systems may include, but are not limited to, Rectisol, Selexol, or Amine wash systems. In one embodiment, the membrane system or the combination of cryogenics and membrane system is preferred. A high LHV fuel gas  216 , and a stream that is predominantly composed of CO2  217  are recovered from separator  215 . The high LHV fuel gas  216  may optionally be further purified in gas purification unit  218 . The purified high LHV gas  219  may be combined with natural gas stream  207 , prior to admission to combustor  208 . 
         [0032]    After combusting the oxygen stream  205  with the fuel gas streams ( 207 ,  219 ), combustion turbine (Brayton cycle) ( 223 ,  208 ,  224 ) outputs power  230  to the process (compression) facility. The exhaust stream  225  that is predominantly H2O and CO2, impurities being SOx, NOx and Oxygen, exits expander  223 . Exhaust stream  225  then enters separator  220 , which outputs H2O stream  226  and CO2 stream  231  The H2O stream  226  is then combined with water stream  213  prior to admission into injection well  206   a / 206   b.  Additives can be used in order to control PH Stream  226  CO2 stream  231  is then combined with stream  217 , partially purified, and introduced into compressor  224 . At least part of the compressed CO2 is admitted into injection well  206   a / 206   b.  If any CO2 remains,  228 , it may be further purified in purifier  221 , then sent to storage, to a local pipeline, or used for EOR  222 . 
         [0033]    The skilled artisan will recognize that the reinjected CO2 will improve in-situ combustion process by improving sweep efficiency. The present invention will also improve ultimate oil recovery (miscible/immiscible flooding will act in addition to in-situ combustion). The synergetic CO2 co-injection will reduce O2 needs and improve process economics. The CO2 will improve process safety by diluting O2 at the production well 
         [0034]    In one embodiment, at least a part of the CO2  228  is further purified  221  (to meet pipeline/use specification) and compressed to be exported for storage or can constitute a economically valuable gas supply to additional EOR-EGR-ECBM sites. The present invention also applies to feedstock such as heavy oil, bitumen, petcoke, kerogene, and coal. This process can also be applied to biomass or coal and petcoke used as feedstock of a liquid fuel production process.