Patent Description:
The race to enhance and increase the removal of CO<NUM> from the environment is leading to a number of innovations in this area, from rapid removal of CO<NUM> from the atmosphere ranging to the collection of CO<NUM> at the source of emission or from industrial processes. Innovation concerning various means of measurement of the rate and quantity of mineralized and stored CO<NUM> is also a related area. The oceans take up CO<NUM> from the atmosphere and are responsible for absorbing around a third of the CO<NUM> emitted by fossil fuel burning, deforestation, and cement production since the industrial revolution. While this is beneficial in terms of limiting the rise in atmospheric CO<NUM> concentrations and hence global warming, the so-called greenhouse effect, there are direct consequences for ocean chemistry. Ocean acidification describes the lowering of seawater pH and carbonate saturation that results from increasing atmospheric CO<NUM> concentrations. There are also indirect and potentially adverse biological and ecological consequences of the chemical changes currently taking place in the oceans and as projected into the future. Enhanced CO<NUM> mineralization is a recognized way to store and or mineralise CO<NUM> underground or above ground. There is a need for an innovative process for CO<NUM> gas-liquid injection for underground storage and/or mineralisation which may provide for higher mass transfer ratios and buffer capacities when compared to traditional technologies, thereby increasing dissolution rates and concentrations of CO<NUM> within a fluid-mixture.

<CIT> discloses "carbon storage in basalts" (CSB) and the technique for storage of CO<NUM> is to dissolve the CO<NUM> in water and store it in basalts.

<NPL>, describes stabilizing encapsulated droplets of CO<NUM> which are then sufficiently stable to remain in this form and not float to the surface.

There are, however, improvements to be made over the prior art.

The present disclosure provides a method wherein gas nanoparticles or nanobubbles of CO<NUM> gas are injected and dissolved on-surface (e.g., above ground) in a storage tank or injection pipes. Compared to traditional sparging technologies that often result in gas bubble sizes in the micron level, this method proved to be more efficient. Micron-sized bubbles have proved to be challenging to handle during on-surface sparging because of the larger size of these bubbles, and there is a higher potential for coalescence of micron-sized bubbles to take place while injected into a fluid stream. Coalescence would in turn result in the formation of even increasingly larger bubble sizes. These coalesced larger bubble sizes would rise faster and quickly to the surface of the injection fluid. Once at the surface of the fluid, these bubbles would burst due to the buoyancy effect, releasing the CO<NUM> back into the atmosphere resulting in decreased efficiency of CO<NUM> mineralization. This is highly challenging to control when injecting large volumes of CO<NUM> rich fluids at greater depths due to the increasing hydrostatic pressures. However, with the proposed CO<NUM> gas-liquid injection process for underground CO<NUM> storage and/or mineralization, there is a reduced effect of coalescence and buoyancy as the CO<NUM> is injected in the form of nanobubbles and dissolved into a pressurized fluid-mixture stream.

Accordingly, a first aspect of the disclosure relates to a method of carbon dioxide mineralization and storage comprising the steps of:.

In an embodiment of said aspect, the CO<NUM> nanobubbles are generated using a nanobubble membrane generator.

In another embodiment of said aspect, freely combinable with all aspects and embodiments, the injection well and/or injection well casing has a plurality of longitudinal perforations at a depth of <NUM> to <NUM> in said rock formation.

In another embodiment of said aspect, also freely combinable with all aspects and embodiments, the fluid is an aqueous fluid, selected from the group consisting of water, seawater, and brackish water. Preferably the fluid also comprises a conservative tracer. By the term conservative tracer is herein meant a tracer or marker substance / indicator substance which is not lost in the system and can be recovered and/or detected. One example is fluorescein, which is stable at least during shorter periods of time (days) but which then degrades biologically.

In another embodiment of said aspect, said nanobubble generator comprises: a pump, an inlet, a gas pressure gauge, a gas connection, a gas flow meter, a pump pressure gauge, and a discharge flow valve. Preferably the CO<NUM> nanobubble generator operates at a pressure in an interval of <NUM> - <NUM> bar, preferably <NUM> - <NUM> bar, such as <NUM> - <NUM> bar. Most preferably the pressure is about <NUM> bar, such as <NUM> bar ± <NUM>%. Preferably the generated CO<NUM> nanobubbles have an average diameter of about <NUM> - <NUM>, or <NUM> - <NUM>, or preferably <NUM> - <NUM>, more preferably <NUM>-<NUM>.

In another embodiment of said aspect, also freely combinable with all aspects and embodiments, said injection and observation wells have substantially the same depth.

In yet another embodiment of said aspect, also freely combinable with all aspects and embodiments, the method comprises a step of adjusting the fluid flow rate at one or more permeable zones by selecting a length and a distribution of the longitudinal perforations. Preferably the length of the longitudinal perforations is at least <NUM> and the distribution along the injection well casing is adapted to the depth and extent of said one or more permeable zones.

In another embodiment of said aspect, also freely combinable with all aspects and embodiments, a high-pressure zone is created within said injection well below a packed off interval during the injecting and a low-pressure zone is created during the recycling through the observation well.

In another embodiment of said aspect, also freely combinable with all aspects and embodiments, carbon dioxide and fluid mixture flows from a high-pressure zone to a low-pressure zone and a fluid volume of the carbon dioxide and water mixture is recycled back through at least one observation well.

In another embodiment of said aspect, also freely combinable with all aspects and embodiments, the rate of mineralization is enhanced by heating the water before pumping it into the mafic or ultramafic layer.

Another aspect relates to a system for carbon dioxide mineralization and storage comprising a nanobubble generator, a water storage module or buffer tank, pumps, at least two boreholes, wherein said pumps are arranged to inject a mixture of CO<NUM> nanobubbles and water into one borehole, and to recover water from another borehole, recirculating water to said water storage module or buffer tank.

The present aspects and embodiments have several advantages over existing technologies since they provide higher mass transfer rate; thermodynamically metastable bubbles that can remain suspended in fluids for extended periods of time; higher buffer capacities; higher CO<NUM> mineralisation or storage volumes; allow for a reduced depth of CO<NUM> injection; and reduced amounts of fluid to be injected.

One embodiment of the present disclosure involves the drilling of vertical and/or horizontals wells into mafic or ultramafic rock formation and injecting water rich of nanobubbles of CO<NUM> to react with said rocks producing carbonate rocks and thereby permanently entrapping CO<NUM>.

Another embodiment of the present disclosure involves a method to decrease the amount of fluid required to achieve CO<NUM> mineralization. By utilizing nanobubbles, a higher CO<NUM> concentration can be obtained in the same volume of fluid resulting in an enhanced efficiency due to increased mass transfer properties. This also means that injection depths can be shallower making it more feasible to store/mineralize CO<NUM> already at depths of <NUM> - <NUM> mbgl (metres below ground level), such as <NUM> - <NUM> mbgl, or about <NUM> mbgl.

The drawings show embodiments of the disclosed subject matter for the purpose of illustrating the invention and embodiments thereof. However, it should be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:.

Objects, features, and advantages of the present invention will become apparent from the following detailed description.

Herein, the use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of one or more," "at least one," and "one or more than one. " The term "about" means, in general, the stated value plus or minus <NUM> %. The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or".

Referring now to <FIG>, the experimental set-up embodies a process for dispersing CO<NUM> gas into a fluid for the purpose of forming nanobubbles. In the experimental set-up, a reactor vessel <NUM> was filled with crushed rock samples to represent the mafic or ultramafic rock formation. In a field trial and in full-scale operation, the carbon dioxide nanobubbles and fluid mixture is pumped into one or more boreholes extending into a mafic or ultramafic rock layer. In this experimental set-up, as well as in large scale operation in the field, the process is intended to be substantially closed, minimizing the water consumption.

Exemplary laboratory and/or field trial scale processes have utilized a fluid mixture that was originally stored on-surface and was pumped at a pressure of about <NUM> bar, CO<NUM> injection mass flow rate of about <NUM>/s, H<NUM>O injection flow rate of about <NUM>/s and an injection depth of about <NUM> mbgl into the injection well. Other conditions such as a pressure of <NUM>-<NUM> bar preferably <NUM>-<NUM> bar or <NUM>-<NUM> bar, a CO<NUM> injection mass flow rate of <NUM>-<NUM>/s, preferably <NUM>-<NUM>/s or <NUM>-<NUM>/s, an H<NUM>O injection flow rate of <NUM>-<NUM>/s, <NUM>-<NUM>/s or about <NUM>/s, and an injection depth of <NUM>-<NUM> mbgl, <NUM>-<NUM> mbgl or about <NUM> mbgl can also be used.

A flow of pressurized CO<NUM> (at a pressure in an interval of <NUM>-<NUM> bar, such as <NUM>-<NUM> bar, preferably <NUM> - <NUM> bar, and most preferably about <NUM> bar) is regulated through a manifold and a set of mass flow controllers prior to injection into the pressurized fluid mixture stream. Calculated mass flow set points control the overall CO<NUM> injection process in relation to fluid mixture flows. For an example, to inject <NUM> metric tonne of CO<NUM> per day in the <NUM> mbgl zone, a fluid mixture flow rate of <NUM>/min and <NUM> bar pressure are preferably used. These values (e.g., pressure, CO<NUM> injection mass flow rate, H<NUM>O injection flow rate, injection depth, mass flow set points, and fluid mixture flow rate are only exemplary and can be scaled upwards for commercial scale processes by a factor of <NUM>×, <NUM>×, <NUM>,<NUM>×, <NUM>,<NUM>× and/or <NUM>,<NUM>×.

Referring to <FIG>, some embodiments of the disclosed invention include a water looping or recirculation system including pumps (not shown) and a water storage module (<NUM>), a carbon dioxide injection module and injection well (<NUM>), a mafic or ultramafic formation, here schematically illustrated as a horizontal layer (P), and an observation well module (<NUM>) for monitoring and controlling carbonation reactions. The process begins by identifying a suitable location with the rock layer being preferably at least <NUM> thick or at least <NUM> thick. An injection borehole is drilled into this rock layer. Said borehole is preferably at least <NUM>, preferably at least <NUM> deep and up to a maximum of <NUM> in depth with the preferred depth being between <NUM> to <NUM> deep or about <NUM> mbgl. An observation borehole is drilled alongside the injection borehole with hydraulic connection between the two holes. The injection borehole is fitted with an engineered well casing (preferably steel or concrete) which is perforated at the targeted areas for mineralization in the geological formation (see <FIG> and the text further below for more details). In the continuous injection process water is first pumped from the observation borehole or another source to a buffer storage tank on surface. The buffer tank is fitted to receive water from different sources such as underground water resources, seawater, treated water etc. The water, at ambient temperature, is then pumped at pressure through the injection pipeline to the injection borehole well head by using a set of booster pumps. The formation temperature at <NUM> depth is about <NUM> - <NUM>.

Referring to <FIG>, this embodiment shows an example of a nanobubble generator. Here, the generator comprises a pump (<NUM>), an inlet (<NUM>), a gas pressure gauge (<NUM>), a gas connection (<NUM>), a gas flow meter (<NUM>), a pump pressure gauge (<NUM>), a discharge flow valve (<NUM>), and a starter (<NUM>). The nanobubble generator typically operates at flow rate of <NUM>-<NUM><NUM>/hr and a maximum liquid pressure of <NUM> barG (gauge pressure). Typical operating conditions include a temperature of <NUM>-<NUM>, preferably <NUM>-<NUM>, and a CO<NUM> pressure of <NUM>-<NUM> barG, preferably <NUM>-<NUM> barG.

There are various methods and corresponding equipment for generating gas nanoparticles or nano bubbles in a liquid. The main methods are based on decompression, hydrodynamic cavitation, or membrane technology. Hydrodynamic cavitation can be achieved for example by ultrasonication or high-shear methods. The generation of nanobubbles is a complex physicochemical process that depends significantly on several parameters, including temperature, electrolyte concentration, dissolved gas concentration in solution as well as type and concentration of reagents, see e.g. <NPL>.

Another embodiment of the present disclosure is a programmable logic controller that automates the CO<NUM> injection process by controlling the CO<NUM> mass flow controllers, fluid-mixture booster pumps and respective valves to enhance CO<NUM> mass transfer ratios into the fluid mixture stream and achieving maximum buffer capacities per unit volume.

In an embodiment of this disclosure, the proposed gas-liquid injection process involves bubble sizes of <NUM>-<NUM>, <NUM>-<NUM> or <NUM>-<NUM>, preferably <NUM>-<NUM> in average diameter in fluid-mixtures. The bubbles are neutrally buoyant and can remain suspended in fluids for a period of time from <NUM> days up to <NUM> months without rising to the surface. This allows for shallower injection, higher gas transfer ratio, as well as increased CO<NUM> concentration in fluids. Experiments have shown an enhanced mass transfer coefficient of <NUM>-<NUM> which is <NUM>-fold better than what is achieved with regular bubble sizes, e.g., bubbles having an average diameter in the micron range.

In a further preferred embodiment of the present disclosure, CO<NUM> gas-liquid injection relies on nanobubble membrane generators that generate billions of CO<NUM> bubbles. Referring to <FIG>, at <NUM> barG (gauge pressure) the average count was <NUM> × <NUM>^<NUM> bubbles per ml; at <NUM> barG the average count was <NUM> × <NUM>^<NUM> bubbles per ml; and at <NUM> barG the average count was <NUM> × <NUM>^<NUM> bubbles per ml.

A nanoparticle analyser (NanoSight NS300, Malvern Panalytical Ltd. , United Kingdom) operating according to the principle of light scattering was used to measure average number and size of the bubbles through Brownian motion estimations. The analyser incorporated three lasers with different wavelengths and a colour camera to visualize the displacement of bubbles from <NUM> to <NUM> microns. Displacement is interpreted as Brownian motion, or, for larger bubbles, settling or creaming and can therefore be readily converted to particle size for each bubble, allowing highresolution size distribution analysis. Same technique is also used to measure average bubble number and density for a specific volume of fluid. The analyser uses a cuvette that includes a black insert which houses a magnetic stir bar to keep larger bubbles suspended and mix the bubbles between videos. Samples were continuously collected from nanobubble membrane generators and transferred directly into the system cuvette without further preparation to measure average bubble size and density.

The nanobubbles are then injected at high pressure (><NUM> bar) into a fluid-mixture. The generated nanobubbles' buoyancy is insignificant allowing for extended suspension times within a fluid resulting in increased mass transfer within the fluid. The nanobubbles are thermodynamically metastable allowing for high residence time in fluids up to a few months.

Mafic and ultramafic rocks can contain silicate minerals including olivine, serpentine, pyroxene and plagioclase. Olivine rocks often contain magnesium, oxygen, and silicon. Olivine is the most abundant mineral in the earth's mantle until a depth of <NUM>. The composition is usually a combination of SiO<NUM> and Mg<NUM>+ and minor amounts of Ca<NUM>+. Typically, silicon bonds with <NUM> oxygen molecules forming a pyramid structure so that the charges of cations and anions are balanced, and Mg<NUM>+ occupies the empty space between the SiO<NUM> structure. These bonds can be easily triggered to react with carbonic acid. The reaction of olivine with CO<NUM> can be accomplished by the following reaction pathway:.

MgSiO<NUM> + <NUM> CO<NUM> → <NUM> MgCO<NUM> + SiO<NUM>     [<NUM>].

It is also proven that the rate of reaction increases significantly when water is introduced. Water aids the solubilization of CO<NUM> forming carbonic acid and therefore makes the mineralization and ion exchange process far easier and more efficient. Below is the reaction pathway in the presence of water:.

CO<NUM> + H<NUM>O → H<NUM>CO<NUM> → H+ + HCO<NUM>-     [<NUM>].

Mg<NUM>SiO<NUM> + <NUM>+ → Mg<NUM>+ + SiO<NUM> + <NUM><NUM>O     [<NUM>].

Mg<NUM>+ + HCO<NUM>- → MgCO<NUM> + H+     [<NUM>].

Some mafic and ultramafic rocks contain mainly the minerals olivine and pyroxene. In the presence of water and CO<NUM>, the following reaction occurs:.

<NUM><NUM>SiO<NUM> (olivine) + CaMgSi<NUM>O<NUM> (pyroxene) + CO<NUM> + <NUM><NUM>O → <NUM><NUM>Si<NUM>O<NUM>(OH)<NUM> (serpentine) + CaCO<NUM> (calcite)     [<NUM>].

Another aspect concerns a method for carbon dioxide sequestration utilizing pyroxene minerals. Pyroxene is one of the groups in an inosilicate mineral, which is also abundantly found out in mafic and ultramafic rocks. The general chemical formula for pyroxene is XY(Z)<NUM>O<NUM>, in which X is an ion such as Na+, Ca<NUM>+, Mn<NUM>+, Fe<NUM>+, Mg<NUM>+, or Li+, and Y is Mn<NUM>+, Fe<NUM>+, Mg<NUM>+, Fe<NUM>+, Al<NUM>+, Cr<NUM>+, or Ti<NUM>+ and Z is Si<NUM>+ or Al<NUM>+. Most commonly, pyroxene can often be found as Mg<NUM>SiO<NUM> and CaMgSi<NUM>O<NUM>. Naturally, pyroxenes react with CO<NUM> according to the following equations:.

Mg<NUM>SiO<NUM> + <NUM> CO<NUM> → <NUM> MgCO<NUM> + SiO<NUM>     [<NUM>].

CaMgSi<NUM>O<NUM> + 2CO<NUM> → CaMg(CO<NUM>)<NUM> + 2SiO<NUM>     [<NUM>].

However, similar to olivine, water increases the rate of reaction, therefore, in presence of water, below is the reaction pathway for a reaction between CO<NUM> and pyroxene:.

<NUM><NUM>SiO<NUM> + CaMgSi<NUM>O<NUM> + CO<NUM> + <NUM><NUM>O → <NUM><NUM>Si<NUM>O<NUM>(OH)<NUM> + CaCO<NUM>     [<NUM>].

CaAl<NUM>Si<NUM>O<NUM> + CO<NUM> + <NUM><NUM>O → CaCO<NUM> + Al<NUM>Si<NUM>O<NUM>(OH)<NUM>     [<NUM>].

The present disclosure relates to a method that utilizes the above reaction pathways (especially equations <NUM> - <NUM>) to convert and/or store CO<NUM> into mafic and ultramafic rocks, as defined above, as a first aspect of the invention. The proposed method also enhances the above reaction rates leading to complete mineralization of total injected CO<NUM> volumes within two to twelve months from injection. The invention also discloses various operating conditions such as temperature, pressure, flowrate (depends on rock permeability), etc. that affect the process efficiency, and at which improved sequestration is obtained. Some embodiments of the present invention also cover engineering aspects such as utilizing renewable energy, water looping / recycling, and process configuration and design.

In an experimental set-up, nanobubbles were produced by introducing pressurized CO<NUM> into a nanobubble generator operating according to the membrane principle. CO<NUM> gas from a gas cylinder at a pressure of <NUM>, <NUM> and <NUM> barG was mixed with tap water at room temperature. During operation of the nanobubble generator, the temperature increased to about <NUM> - <NUM>. Water pressure was maintained at <NUM> - <NUM> barG.

The size and amount of nanobubbles was determined using a particle analyzer (NanoSight NS300, Malvern Panalytical Ltd. , UK) and found to be in the interval of <NUM> - <NUM>. The concentration of nanobubbles was pressure dependent, as shown in <FIG>, where the chart shows the number of bubbles per ml water at a pressure of <NUM>, <NUM> and <NUM> barG.

Samples of the water-nanobubble mixture were stored in room temperature and inspected at regular intervals. The nanobubbles were found to be stable or metastable, remaining suspended in water for at least <NUM> days.

Claim 1:
A method of carbon dioxide mineralization and storage
characterized in that the method comprises:
- generating CO<NUM> nanobubbles in a fluid forming a carbon dioxide and fluid mixture,
- injecting said mixture into a rock formation comprising mafic or ultramafic rock via an injection well (<NUM>) wherein the carbon dioxide and fluid mixture is flowed through said injection well (<NUM>) or an injection well casing disposed in the rock formation,
- reacting carbon dioxide in said carbon dioxide and fluid mixture with said rock formation to form calcites and magnesites in the rock formation; and
- recycling at least a portion of the fluid from said rock formation via an observation well (<NUM>).