Patent Publication Number: US-2023134985-A1

Title: Method of underground storage of injection gas containing co2 gas and enhanced oil recovery

Description:
TECHNICAL FIELD 
     The present invention relates to underground storage of injection gas containing CO 2  gas and enhanced recovery of oil contained in a permeable formation such as an oil reservoir using a fine bubble-generating device utilizing the Venturi effect. 
     Priority is claimed on Japanese Patent Application No. 2021-022419, filed Feb. 16, 2021. the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In recent years, due to the use of large amounts of fossil fuels due to the increase in energy demand accompanying rapid economic growth, the concentration of carbon dioxide (hereinafter, abbreviated as CO 2  gas in this specification) in the atmosphere has increased to a critical level. 
     In addition, at the Conference of the Parties to the United Nations Framework Convention on Climate Change (collectively called COP) held in Paris in 2015, the “Paris Agreement”, which is an international framework for climate change issues after 2020, was agreed and entered into effect on November 2016. The key items of the Paris Agreement include “holding the increase in the global average temperature to well below 2.0° C. above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5° C. above pre-industrial levels”, “to undertake rapid reductions thereafter in accordance with the best available science, so as to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of the century”. 
     As a result, as one of the measures against global warming, the immediate introduction of a global carbon dioxide capture and storage technology (hereinafter, abbreviated as CCS in this specification), and carbon dioxide capture, utilization, and storage technology (hereinafter, abbreviated as CCUS in this specification) is required. 
     CCS is used to collect CO 2  gas emitted from power plants and chemical factories separately from other gases, and inject and store the CO 2  gas into a stable formation deep underground. CCS is a technology that can significantly suppress CO 2  gas emissions, and is expected to contribute to measures against global warming along with energy saving, renewable energy. On the other hand, the worldwide spread of CCS has not progressed as expected. There are several reasons for this, such as technological uncertainty, concerns about storage safety, and laws and regulations that have not been improved. In particular, due to an increase in CO 2  gas separation and recovery costs, which account for majority of the costs, business feasibility may be difficult to predict. 
     Therefore, CCUS, which aims to produce value-added products by directly or indirectly using CO 2  gas instead of simply storing the recovered CO 2  gas, and to compensate for the cost of recovery, has attracted attention. For this reason, a technology for injecting gas containing CO 2  gas into an oil reservoir using an enhanced oil recovery technology (hereinafter, abbreviated as FOR in this specification), which is one of the CCUS technologies, is a technically reliable method. Such technology can store CO 2  gas underground as a measure against global warming, and can also improve the economic effect while increasing the oil recovery rate of oil, so that the utilization of FOR technology is indispensable. 
     There are primary to tertiary recovery methods for recovering oil from oil reservoirs. The primary recovery method is oil production by flowing oil production and artificial lift, and the secondary recovery method is to increase the amount of oil produced by injecting water or produced gas into an oil reservoir to recover the oil reservoir pressure. It is said that the primary and secondary recovery methods can increase the oil recovery rate from 30% to 40%. The tertiary recovery method is also called EOR, and is a recovery method applied after the application of the secondary recovery method, and known methods include a chemical injection method, a thermal injection method, a gas injection method including CO 2  gas, and a microbial enhanced oil recovery method. These methods allow improvement in the oil recovery rate by increasing the fluidity of oil or decreasing the surface tension between water and oil through injection of chemicals, steam, and hot water into an oil reservoir, or creating a mixed state (miscible state) in a supercritical region between an injection gas containing CO 2  gas and oil. It is said that the recovery rate can be increased up to about 50% to 60% by applying these recovery methods. 
     As a method of storing a large amount of CO 2  gas underground, there is a method of injecting CO 2  gas into an underground aquifer. Japanese Patent No. 5315346 proposes a storage method in which CO 2  gas stored in a CO 2  gas tank is boosted by a pumping device and injected from an injection well drilled vertically to the formation, CO 2  gas is formed into microbubbles by a porous filter provided at the lower end of the injection well, and the microbubbles are dispersed into the formation water to store CO 2  gas underground. Japanese Patent No. 5399436 proposes a storage apparatus and a storage method in which CO 2  gas is injected by a pumping device from an injection well drilled horizontally to the formation, CO 2  gas is formed into microbubbles by a porous filter provided at the lower end of the injection well, and the microbubbles are dispersed into the formation water to store CO 2  gas underground. 
     In the technique described in Japanese Unexamined Patent Application, First Publication No. 2008-6367, the formation water in the aquifer is once pumped up, CO 2  gas separated and recovered from exhaust gas of a plant facility is formed into microbubbles by an injector method in which CO 2  gas is released into water as bubbles in the well, and is then mixed with injection water to enter a gas-liquid, mixed state, and the mixture is injected into the aquifer again. This method requires a water well for pumping formation water and a pump for pumping up water from water well, which causes an increase in the scale of the entire system, and there is a problem in that the power for storage also increases. Furthermore, the injection pressure into the aquifer needs to be balanced with the pumping pressure at the pumping well, and the pumping amount and the injection amount need to be matched, so that there is a problem in that CO 2  gas cannot be stored efficiently. 
     Japanese Unexamined Patent Application, First Publication No. 2008-01.9644 proposes an enhanced recovery method and an enhanced recovery system for oil, or natural gas in which an injection gas is rotated at a high speed in a tubing pipe and a microbubble-generating device that have been moved downward in a well while being injected from the surface, injection water is injected between a casing pipe and the tubing pipe from the surface to allow the injection gas to generate microbubbles and be mixed in the injection water so as to create a gas-liquid mixed fluid in the well, and this is injected into an oil layer or a gas layer from an injection well to penetrate into fine gaps in the layer, whereby enhanced recovery of oil or gas is achieved by the microbubbles in the injection water. 
     CITATION LIST 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent No. 5315346 
         Patent Document 2: Japanese Patent No. 5399436 
         Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2008-6367 
         Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2008-019644 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a system for underground storage of an injection gas containing CO 2  gas and enhanced oil recovery, by efficiently generating fine bubbles from an injection gas using a fine bubble-generating device utilizing the Venturi effect, mixing the fine bubbles with injection water to generate a gas-liquid mixed fluid containing the fine bubbles, and allowing the gas-liquid mixed fluid to penetrate into gaps of a permeable formation such as an oil reservoir, through an injection well. 
     Solution to Problem 
     In the present invention, a method of underground storage of an injection gas containing CO 2  gas and enhanced oil recovery includes: a step of boosting injection water by a high-pressure pump so as to be injected into a fine bubble-generating device; a step of increasing the velocity of the boosted injection water by narrowing the flow of a fluid through a high-pressure nozzle so as to be jetted as high-pressure water jet, thereby suctioning an injection gas into the fine bubble-generating device by a negative pressure generated by the Venturi effect downstream of the high-pressure nozzle; a step of generating a gas-liquid mixed fluid containing fine bubbles by mixing the suctioned injection gas formed into fine bubbles by the shear force of the high-pressure water jet, with the injection water, while reducing the velocity of this at a throat part in the fine bubble-generating device, converting the velocity energy into a pressure energy, and finally boosting the gas-liquid mixed fluid containing fine bubbles to the same pressure; and a step of allowing the boosted gas-liquid mixed fluid containing fine bubbles to penetrate into the permeable formation such as an oil reservoir, by moving the gas-liquid mixed fluid in a wellhead and the inside of a well. 
     The present invention may have a configuration in which, in a case where the fine bubble-generating device is placed in an injection pipe forming two flow paths using two pipes, a water flow path is a water injection pipe, and a gas flow path is a gas injection pipe. 
     In addition, the present invention may have a configuration in which the two flow paths have a double pipe structure of an outer pipe and an inner pipe, the water flow path is provided between the inner side of the outer pipe and the outer side of the inner pipe, the gas flow path is provided on the inner side of the inner pipe, and the fine bubble-generating device is placed at the lower end of the inner pipe. 
     In addition, the present invention may have a configuration in which the two flow paths also have a double pipe structure of an outer pipe and an inner pipe, the gas flow path is provided between the inner side of the outer pipe and the outer side of the inner pipe, the water flow path is provided on the inner side of the inner pipe, and the fine bubble-generating device is placed at the lower end of the outer pipe. 
     The injection gas means a hydrocarbon gas, an oil field flare gas, nitrogen gas, CO 2  gas, a combustion exhaust gas, and a gas in which these are mixed. Therefore, in a case where CO 2  gas, an oil field flare gas, a combustion exhaust gas, or a gas in which these are mixed is used as the injection gas, the injection gas containing CO 2  gas can be stored underground in the permeable formation such as an oil reservoir, which is effective in measures against global warming. 
     While river water or seawater is used as the injection water, formation water produced from a production well may be reused by being mixed with the injection water such as river water or seawater. In either case, the injection water containing water other than that derived from the formation is injected. Therefore, the injection water is treated with chemicals or the like added before the injection so as not to cause the obstruction of fine gaps due to the swelling of the formation or the like by the injection water. 
     The fine bubbles mean bubbles having a diameter of 100 μm or less, and include microbubbles (bubbles having a diameter of 1 μm to 100 μm) and nanobubbles (bubbles having a diameter of several ten to several hundred nanometers). 
     In addition, oil, natural gas, and formation water recovered from fine gaps by the fine bubbles in the oil reservoir are produced as a production fluid from the production well together with the injection water and the injection gas that have been injected from the injection well and moved to the production well through the oil reservoir. This production fluid is separated into oil, natural gas and injection gas, and formation water and injection water by a three-phase separator that separates production fluids with different specific gravities on the surface. The oil is transferred to a crude oil tank and sold, the natural gas and the injection gas are transferred to an injection gas tank and reused as an injection gas, and the formation water and the injection water further separated are also transferred to an injection water tank and reused as injection water. 
     Advantageous Effects of Invention 
     By adopting the mechanism of the present invention, the high-pressure injection water is injected into the high-pressure nozzle in the fine bubble-generating device from one high-pressure pump, and is increased in velocity by narrowing the flow of the fluid by the high-pressure nozzle to be jetted as the high-pressure water jet, thereby generating a negative pressure by the Venturi effect downstream of the high-pressure nozzle. As a result, the injection gas is suctioned into the fine bubble-generating device, forms fine bubbles by the shear force of the high-pressure water jet, and is mixed with the injection water, whereby the gas-liquid mixed fluid containing fine bubbles can be generated. 
     In addition, by allowing the gas-liquid mixed fluid containing fine bubbles to be injected and penetrate into the gaps of the permeable formation such as the oil reservoir, oil, natural gas, and formation water can be recovered from the fine gaps in the permeable formation such as the oil reservoir, which is effective in enhancing the recovery of oil and natural gas from the production well drilled at a point other than the injection well. In addition, the gas-liquid mixed fluid containing fine bubbles generates a downward flow due to the density difference from the formation water and the formation inclination, and the density of the fine bubbles is increased by the additional pressure in the bubbles (Laplace pressure) due to their extremely small particle sizes and the formation pressure, so that the gas-liquid mixed fluid has an extremely small relative upward flow velocity (Stokes velocity) with respect to the formation water. Therefore, the injection gas containing CO 2  gas can be stored underground. 
     In addition, due to the negative pressure generated by the Venturi effect downstream of the high-pressure nozzle, the injection gas is naturally suctioned into the fine bubble-generating device, so that there is no need to use a complicated pumping and storage system such as a gas pump or a gas tank for supplying the injection gas, and an effect of reducing the facility cost is expected. 
     Next, the production fluid is produced from the production well, and is separated into oil, natural gas and injection gas, and formation water and injection water by a three-phase separator that separates production fluids with different specific gravities on the surface. Oil is transferred to a crude oil tank and sold. The natural gas and the injection gas, which have a gas phase, are transferred to an injection gas tank and reused as an injection gas. In addition, the separated formation water and the injection water are also transferred to an injection water tank and reused as injection water. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing a method of underground storage of injection gas containing CO 2  gas and enhanced oil recovery, in which a fine bubble-generating device is placed in an injection pipe forming two flow paths using two pipes. 
         FIG.  2    is a diagram showing a method of underground storage of injection gas containing CO 2  gas and enhanced oil recovery, in which a fine bubble-generating device is placed in a wellhead. 
         FIG.  3    is a diagram showing a method of underground storage of injection gas containing CO 2  gas and enhanced oil recovery, in which a fine bubble-generating device is placed on the surface. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. An object of the present invention is to achieve enhanced oil recovery by recovering oil and natural gas present at fine gaps of a permeable formation such as an oil reservoir, by using a gas-liquid mixed fluid containing fine bubbles, and to store an injection gas containing CO 2  gas underground. 
     First Embodiment 
     A method of underground storage of injection gas  103  containing CO 2  gas and enhanced oil recovery includes: in an injection well.  101  in which an injection pipe  202   a  forming two flow paths using two pipes shown in  FIG.  1    is placed, a step of boosting injection water  102  by a high-pressure pump so as to be injected through a water injection pipe  104 ; a step of jetting a high-pressure water jet  206  which is increased in velocity by narrowing the flow of a fluid through a high-pressure nozzle  204  of a fine bubble-generating device  207  placed at the lower end of the water injection pipe  104 , and suctioning the injection gas  103  through a gas injection pipe  105  by a negative pressure generated by the Venturi effect downstream of the high-pressure nozzle  204 ; a step of generating a gas-liquid mixed fluid containing fine bubbles by allowing the suctioned injection gas  103  to form fine bubbles by the shear force of the high-pressure water jet  206  and be mixed with the injection water  102 ; and a step of allowing the gas-liquid mixed fluid containing the fine bubbles to directly penetrate into a permeable formation  208  such as an oil reservoir. 
     Second Embodiment 
     A method of underground storage of injection gas  103  containing CO 2  gas and enhanced oil recovery includes: in a state where a fine bubble-generating device  207  shown in  FIG.  2    is placed in a wellhead  106 , a step of, as in the first embodiment, boosting injection water  102  by a high-pressure pump so as to inject the injection water  102  through a water injection pipe  104 ; a step of jetting a high-pressure water jet  206  which is increased in velocity by narrowing the flow of a fluid through a high-pressure nozzle  204  of the fine bubble-generating device  207  placed in the wellhead  106 , and suctioning the injection gas  103  through a gas injection pipe  105  by a negative pressure generated by the Venturi effect downstream of the high-pressure nozzle  204 : a step of generating a gas-liquid mixed fluid containing fine bubbles by allowing the suctioned injection gas  103  to form fine bubbles by the shear force of the high-pressure water jet  206  and be mixed with the injection water  102 ; and a step of allowing the gas-liquid mixed fluid to penetrate into a permeable formation  208  such as an oil reservoir, through an injection pipe  202   b.    
     Third Embodiment 
     A method of underground storage of injection gas  103  containing CO 2  gas and enhanced oil recovery includes: in a state where a fine bubble-generating device  207  shown in  FIG.  3    is placed on a surface, a step of, as in the first embodiment, boosting injection water  102  by a high-pressure pump so as to inject the injection water  102  through a water injection pipe  104 ; a step of jetting a high-pressure water jet  206  which is increased in velocity by narrowing the flow of a fluid through a high-pressure nozzle  204  of the fine bubble-generating device  207  placed on the surface, and suctioning the injection gas  103  through a gas injection pipe  105  by a negative pressure generated by the Venturi effect downstream of the high-pressure nozzle  204 ; a step of generating a gas-liquid mixed fluid containing fine bubbles by allowing the suctioned injection gas  103  to form fine bubbles by the shear force of the high-pressure water jet  206  and be mixed with the injection water  102 ; and a step of allowing the gas-liquid mixed fluid to penetrate into a permeable formation  208  such as an oil reservoir, through a wellhead  106  and an injection pipe  202   b.    
     The fine bubble-generating device  207  is composed of the gas injection pipe  105 , the water injection pipe  104 , the high-pressure nozzle  204 , and a throat  205  forming an outer cylinder, and a hard metal is used. Cases where the fine bubble-generating device  207  is placed in the inner pipe of two pipes or a double pipe in the well, is placed in the wellhead  106 , and is placed on the surface are considered. In any case, the fine bubble-generating device  207  has a hollow coaxial cylindrical shape. Since the particle size of the fine bubbles depends on the degree of the shear force of the high-pressure water jet  206 , a risk of plugging the high-pressure nozzle  204  and the throat  205  with floating solid in the injection water  102  is greatly reduced compared to a porous filter formed of ceramic material. In addition, since the injection gas  103  is suctioned into the fine bubble-generating device  207  by the negative pressure generated by the Venturi effect downstream of the high-pressure jet  206 , the pumping device for increasing the flow rate of the injection gas  103  does not need to be large. Furthermore, increasing the inside diameter of the high-pressure nozzle  204  reduces the pressure loss of the fluid, and it is easy to accelerate the amount of the injection gas  103 , but requires attention to maintaining the bubble diameter of the fine bubbles. 
     REFERENCE SIGNS LIST 
     
         
         
           
               101 : Injection well 
               102 : Injection water 
               103 : Injection gas 
               104 : Water injection pipe 
               105 : Gas injection pipe 
               106 : Wellhead 
               201 : Surface 
               202   a : Injection pipe forming two flow paths using two pipes 
               202   b : Injection pipe 
               203 : Packer 
               204 : High-pressure nozzle 
               205 : Throat 
               206 : High-pressure water jet 
               207 : Fine bubble-generating device 
               208 : Permeable formation