This disclosure relates generally to hydrocarbon extraction.
Pure carbon dioxide (CO2) has many industrial uses. The separation of CO2 from a mixed-gas source may be accomplished by a capture and regeneration process. More specifically, the process generally includes a selective capture of CO2, by, for example, contacting a mixed-gas source with a solid or liquid adsorber/absorber followed by a generation or desorption of CO2 from the adsorber/absorber. One technique describes the use of bipolar membrane electrodialysis for CO2 extraction/removal from potassium carbonate and bicarbonate solutions.
For capture/regeneration systems, a volume of gas that is processed is generally inversely related to a concentration of CO2 in the mixed-gas source, adding significant challenges to the separation of CO2 from dilute sources such as the atmosphere. CO2 in the atmosphere, however, establishes equilibrium with the total dissolved inorganic carbon in the oceans, which is largely in the form of bicarbonate ions (HCO3—) at an ocean pH of 8.1-8.3. Therefore, a method for extracting CO2 from the dissolved inorganic carbon of the oceans would effectively enable the separation of CO2 from atmosphere without the need to process large volumes of air.
Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described.
Embodiments of an apparatus and method for enhanced hydrocarbon extraction are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Throughout the specification and claims, compounds/elements are referred to both by their chemical name (e.g., carbon dioxide) and chemical symbol (e.g., CO2). It is appreciated that both chemical names and symbols may be used interchangeably and have the same meaning.
This disclosure provides for the removal of carbon from water sources containing dissolved inorganic carbon (e.g., bicarbonate ions HCO3—), converting the dissolved carbon into dissolved CO2 gas, stripping the CO2 gas from the water source, and using the CO2 to extract oil or natural gas from hydrocarbon wells. Enhanced oil recovery (EOR) is a method for extracting additional fossil fuel from an existing well by injecting CO2 into the well to displace and eject hydrocarbons. The economic potential for EOR in nearshore and offshore wells is enormous. Using CO2 extracted from the ocean to remove hydrocarbons from existing oil wells may be more environmentally friendly than drilling a new well. CO2 from the ocean is sequestered in the existing well to help offset the hydrocarbons extracted. In addition, the alkalinity of the decarbonized seawater is restored by addition of NaOH prior to returning the water to the ocean, resulting in reabsorption of CO2 from the atmosphere into the parcel of returned water. Further, there is no need to drill a new well, limiting further environmental damage and reducing the chance of drilling accidents.
As shown, input 102 is coupled to a water reservoir containing dissolved inorganic carbon (e.g., bicarbonate ions). The water reservoir may be an ocean, lake, river, manmade reservoir, or brine outflow from a reverse osmosis (“RO”) process. Input 102 may receive the water through a system of channels, pipes, and/or pumps depending on the specific design of the facility. As shown, water received through input 102 is diverted into two separate sections of system 100A. A first (smaller) portion of the water is diverted to treatment unit 104, while a second (larger) portion of the water is diverted to precipitation unit 106. One skilled in the art will appreciate that large aggregate may be removed from the water at any time during the intake process.
In the illustrated embodiment, the first portion of water is diverted into treatment unit 104. Treatment unit 104 outputs a relatively pure stream of aqueous NaCl. In other words, an aqueous solution (possibly including seawater) is input to treatment unit 104, and aqueous NaCl is output from treatment unit 104. Treatment unit 104 may be used to remove organic compounds and other minerals (other than NaCl) not needed in, or harmful to, subsequent processing steps. For example, removal of chemicals in the water may mitigate scale buildup in electrodialysis unit 110. Treatment unit 104 may include filtering systems such as: nanofilters, RO units, ion exchange resins, precipitation units, microfilters, screen filters, disk filters, media filters, sand filters, cloth filters, and biological filters (such as algae scrubbers), or the like. Additionally, treatment unit 104 may include chemical filters to removed dissolved minerals/ions. One skilled in the art will appreciate that any number of screening and/or filtering methods may be used by treatment unit 104 to remove materials, chemicals, aggregate, biologicals, or the like.
Electrodialysis unit 110 is coupled to receive aqueous NaCl and electricity, and output aqueous HCl, aqueous NaOH, and brine (to brine output 132). Aqueous HCl and aqueous NaOH output from electrodialysis unit 110 may be used to drive chemical reactions in system 100A. The specific design and internal geometry of electrodialysis unit 110 is discussed in greater detail in connection with
In the illustrated embodiment, precipitation unit 106 has a first input coupled to receive an aqueous solution including dissolved inorganic carbon (e.g., seawater) from input 102. Precipitation unit 106 also has a second input coupled to electrodialysis unit 110 to receive aqueous NaOH. In response to receiving the aqueous solution and the aqueous NaOH, precipitation unit 106 precipitates calcium salts (for example, but not limited to, CaCO3) and outputs the aqueous solution. However, in other embodiments, other chemical processes may be used to basify the aqueous solution in precipitation unit 106. For example, other bases (not derived from the input aqueous solution) may be added to the aqueous solution to precipitate calcium salts.
In one embodiment, NaOH is added to incoming seawater until the pH is sufficiently high to allow precipitation of calcium salts without significant precipitation of Mg(OH)2. The exact pH when precipitation of CaCO3 occurs (without significant precipitation of Mg(OH)2) will depend on the properties of the incoming seawater (alkalinity, temperature, composition, etc.); however, a pH of 9.3 is typical of seawater at a temperature of 25° C. In a different embodiment, the quantity of NaOH added is sufficient to precipitate CaCO3 and Mg(OH)2, then the pH is lowered (e.g., by adding HCl from electrodialysis unit 110 until the pH is <9.3) so that the Mg(OH)2 (but not CaCO3) redissolves.
In one embodiment, precipitation unit 106 may be a large vat or tank. In other embodiments precipitation unit 106 may include a series of ponds/pools. In this embodiment, precipitation of calcium salts may occur via evaporation driven concentration (for example using solar ponds) rather than, or in combination with, adding basic substances. Precipitation unit 106 may contain internal structures with a high surface area to promote nucleation of CaCO3; these high surface area structures may be removed from the precipitation unit 106 to collect nucleated CaCO3. Precipitation unit 106 may include an interior with CaCO3 to increase nucleation kinetics by supplying seed crystals. The bottom of precipitation unit 106 may be designed to continually collect and extract precipitate to prevent large quantities of scale buildup.
In another or the same embodiment, heat may be used to aid precipitation. For example solar ponds may be used to heat basified water. In continuously flowing systems, low temperature waste heat solution may be flowed through heat exchange tubes with basified seawater on the outside of the tubes. Alternatively, heating the bottom of precipitation unit 106 may be used to speed up precipitation.
After CaCO3 is precipitated from the water, CaCO3 is transferred to acidification unit 108. In the depicted embodiment, acidification unit 108 is coupled to receive CaCO3 from precipitation unit 106 and coupled to receive aqueous HCl from electrodialysis unit 110. In response to receiving CaCO3 and aqueous HCl, acidification unit 108 produces CO2. In the depicted embodiment, acidification unit 108 is used to evolve CaCO3 into CO2 gas and aqueous CaCl2 according to the following reaction: CaCO3 (s)+2HCl (aq)→CaCl2 (aq)+H2O (1) +CO2 (g). Reaction kinetics may be increased by agitating/heating the acidified mixture. By adding HCl to CaCO3, CO2 is spontaneously released due to the high equilibrium partial pressure of CO2 gas. This may eliminate the need for membrane contactors or vacuum systems.
Acidification unit 108 is coupled to transport system 198. In the depicted embodiment transport system 198 may be a system of pipes, pumps, chambers, and/or gas cylinders coupled directly between acidification unit 108 and hydrocarbon well 182. However, in other embodiments, transport system 198 may not be directly coupled. In other words, the CO2 extracted from acidification unit 108 may be contained in compress gas cylinders or the like, which are transported to hydrocarbon well 182 to displace the hydrocarbons (e.g., oil and natural gas) from hydrocarbon well 182. However, for purposes of this disclosure it may be said that transport system 198 is “coupled” to both acidification unit 108 and hydrocarbon well 182 even when the CO2 is contained in chambers and trucked to hydrocarbon well 182 for hydrocarbon extraction. Discontinuity in the transport process is contemplated by the claims in the instant application.
In one embodiment, transport system 198 may alter the temperature or the pressure of the CO2 prior to or after transport, so the CO2 is denser than the gas phase of CO2 when the CO2 enters hydrocarbon well 182. To accomplish this, transport system 198 may include compression and dehydration unit 178 to remove water from the CO2 and to change a phase of the CO2 into at least one of a liquid or a supercritical fluid.
CO2 used in EOR is of a purity >95%, and the temperature and pressure of the CO2 is adjusted to ensure that the CO2 is in a denser phase than the gas phase of CO2 (either liquid or supercritical)—for CO2, a supercritical fluid occurs at temperatures greater than 31.1° C., and pressures greater than 7.38 MPa. One noteworthy advantage of system 100A is that producing CO2 from CaCO3 eliminates the need for N2O2 degassing steps; the CO2 extracted by addition of HCl to CaCO3(s) can be sent directly to compression and dehydration unit 178 to produce the >95% purity liquid or supercritical CO2 appropriate for EOR.
Once all CO2has been extracted from acidification unit 108, wastewater containing CaCl2 is output from system 100A via CaCl2 output 116. In one embodiment, the wastewater is returned to the ocean or other water source after the pH of the wastewater has been adjusted. In other embodiments, the wastewater is sequestered in hydrocarbon well 182 and used as part of the EOR process (water injection).
In the depicted embodiment, the second portion of seawater (that was used as a carbon source in precipitation unit 106) is flowed to a pH and alkalinity adjustment unit 112. The pH and alkalinity adjustment unit 112 is coupled to electrodialysis unit 110 to receive HCl and NaOH, and adjust a pH and alkalinity of the combined second portion of the aqueous solution and basic solution to a pH and alkalinity of seawater (or other environmentally safe pH value). In one embodiment, the pH and alkalinity of wastewater flowed into pH and alkalinity adjustment unit 112 is monitored in real time, and HCl or NaOH is flowed into pH and alkalinity adjustment unit 112 in response to the real time measurements. Adjusting the pH of wastewater flowing from system 100A ensures minimal environmental impact of running system 100A, while adjusting the alkalinity ensures sufficient reabsorption of atmospheric CO2 once the water is returned to the ocean.
In the depicted embodiment, electrodialysis unit 110 is coupled to receive aqueous NaCl, and to output aqueous HCl and aqueous NaOH. Degasification unit 107 has a first input coupled to receive an aqueous solution including dissolved inorganic carbon, and a second input coupled to electrodialysis unit 110 to receive the aqueous HCl. In response to receiving the aqueous solution and the aqueous HCl, degasification unit 107 evolves CO2 from the aqueous solution and outputs the aqueous solution. As shown, the aqueous solution may include seawater, and the aqueous NaCl may also be derived, at least in part, from seawater. Degasification unit 107 may include membrane contactors to remove dissolved N2 and O2 gas from the aqueous solution, prior to evolving the CO2 from the aqueous solution. This results in >95% purity CO2 at the outset of the degasification and dehydration process. It is worth noting that in other embodiments, other gases may be extracted from the aqueous solution. Furthermore, any of the processes described above may be vacuum assisted.
Transport system 198 is coupled to degasification unit 107 to transport the CO2 from degasification unit 107 into hydrocarbon well 182 (to displace the hydrocarbons in hydrocarbon well 182). In one embodiment, the transport system 198 alters at least one of a temperature or a pressure of the CO2 either before or after transport so the CO2 is denser than the gas phase of CO2 when the CO2 enters hydrocarbon well 182. In the depicted embodiment, transport system 198 includes compression and dehydration unit 178 to remove water from the CO2 and to change a phase of the CO2 into at least one of a liquid or a supercritical fluid.
Systems 100A-100B may be coupled to, and run by, electronic control systems. Regulation and monitoring may be accomplished by a number of sensors throughout the system that either send signals to a controller or are queried by controller. For example, with reference to electrodialysis unit 110, monitors may include one or more pH gauges to monitor a pH within the units as well as pressure sensors to monitor a pressure among the compartments in electrodialysis unit 110 (to avoid inadvertent mechanical damage to electrodialysis unit 110). Another monitor may be a pH gauge placed within precipitation unit 106 to monitor a pH within the tank. The signals from such pH monitor or monitors allows a controller to control a flow of brine solution (from input 102) and a basified solution (from electrodialysis unit 110) to maintain a pH value of a combined solution that will result in a precipitation of CaCO3.
Alternatively, systems 100A-100B may be controlled manually. For example, a worker may open and close valves to control the various water, acid, and base flows in systems 100A-100B. Additionally, a worker may remove precipitated calcium salts from precipitation unit 106. However, one skilled in the relevant art will appreciate that systems 100A-100B may be controlled by a combination of manual labor and mechanical automation, in accordance with the teachings of the present disclosure.
In the depicted embodiment, electrodialysis unit 110 representatively consists of several cells in series, with each cell including a basified solution compartment (compartments 210A and 210B illustrated); an acidified solution compartment (compartments 225A and 225B illustrated); and a brine solution compartment (compartments 215A and 215B).
Broadly speaking, under an applied voltage provided to electrodialysis unit 110, water dissociation inside the BPM (and the ion-selective membranes comprising a BPM) will result in the transport of hydrogen ions (H+) from one side of the BPM, and hydroxyl ions (OH−) from the opposite side. AEMs/CEMs, as their names suggest, allow the transport of negatively/positively charged ions through the membrane. The properties of these membranes such as electrical resistance, burst strength, and thickness are provided by the manufacturer (e.g., Neosepta ACS and CMX-S are monovalent-anion and monovalent-cation permselective membranes, respectively). In one embodiment, electrodialysis unit 110 includes electrodes 260A and 260B of, for example, nickel manufactured by De Nora Tech Inc.
Block 301 illustrates receiving an aqueous solution including dissolved inorganic carbon. In one embodiment, the aqueous solution includes seawater containing bicarbonate ions (HCO3—).
Block 303 discloses extracting the dissolved inorganic carbon from the aqueous solution to create CO2by changing a pH of the aqueous solution. In one embodiment this may include increasing the pH of the aqueous solution to precipitate salts containing carbon, and applying acid to the salts to evolve CO2 gas. This process may include adding aqueous NaOH to the aqueous solution (to increase the pH), and applying HCl to the salts (to evolve the CO2). In an alternate embodiment, extracting the dissolved inorganic carbon includes decreasing the pH of the aqueous solution to remove CO2 gas from the aqueous solution. In this embodiment, decreasing the pH includes adding aqueous HCl to the aqueous solution, and the aqueous HCl is produced by an electrodialysis unit. Further, N2 and O2 may be removed from the aqueous solution before decreasing the pH of the aqueous solution.
Block 305 shows pumping the CO2 into the hydrocarbon well. In one embodiment, the density of the CO2 may be altered to be greater than the density of CO2 gas by adjusting the temperature or and/or pressure. Thus, the CO2 pumped into the well may be a liquid or a supercritical fluid of greater than 95% purity.
Block 307 illustrates extracting the hydrocarbons from the hydrocarbon well, in response to pumping CO2 into the well. The CO2 may mix with and/or displace hydrocarbons (e.g., oil or natural gas) in the well, resulting in their migration towards the surface. CO2 injection into a hydrocarbon well is a miscible displacement process. A miscible displacement process may maintain pressure in the well and improve oil displacement due to reduced interfacial tension between oil and water in the well. Carbon dioxide may be best suited for miscible displacement because it reduces oil viscosity, and may be less expensive than other gases.
In the case of CO2 EOR, the first step includes injecting water into the well. In one embodiment this may include wastewater from the CO2 extraction process. Once the reservoir is pressurized with water, CO2 is pumped down into the well. The CO2 gas then comes in contact with the oil. The oil-CO2 contact area creates a miscible zone that is easily moved/extracted. In some instances, oil field workers may alternate between injection of CO2 and water, because water helps sweep oil towards the production area. Method 300 disclosed here may be used for producing CO2 in places where there is ample seawater but no CO2 supply chain. Thus, method 300 may enable the recovery of millions of barrels of otherwise inaccessible oil.
The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.