METHOD FOR STORING AND USING A FIRST GAS AND A SECOND GAS, WHICH IS DENSIER THAN THE FIRST GAS, IN AN AQUIFER OR A DEPLOYED RESERVOIR

Description

Technical Field

[0001] The present invention relates to the storage and use of gas in underground reservoirs, particularly storage in aquifers or depleted reservoirs. The invention is especially applicable to the storage of dihydrogen. Previous technique

[0002] We are familiar with underground gas storage reservoirs, which are aquifers. These reservoirs have a dome shape and are composed of porous rock in which the gas is stored. The gas is held within the reservoir by an impermeable layer that defines this dome shape and the top of the reservoir (this impermeable layer can be called cap rock), and by water that forms the bottom of the storage area. We also know of reservoirs called depleted reservoirs, which have the same structure as aquifers but initially contained hydrocarbons (gas or oil) mixed with some water, rather than water alone.

[0003] These reservoirs are traditionally used to store natural gas. However, there is a need to store other types of gas, particularly hydrogen, in underground reservoirs. Indeed, hydrogen production is expected to increase, and surface hydrogen storage capacity is limited.

[0004] Document FR 2 168 942 describes a process in which a denser gas called secondary gas is stored below another gas in an aquifer reservoir.

[0005] We know from the document "Enabling large-scale hydrogen storage in porous media - the scientific challenges" (Heinemann N. et al., 2021, Energy Environ. Sci., 2021, 14, 853-864.) about the storage of dihydrogen in porous / permeable media, and the use of wells to inject and withdraw gas.

[0006] However, the storage of dihydrogen in porous media presents difficulties due to reaction mechanisms that can occur as a result of interactions between the aquifer water and the rock, these interactions being known in particular from the document "Overview of available test results and regulatory limits for Hydrogen admission into existing natural gas infrastructure and end use" (Marcogaz Technical Association of the European Natural Gas Industry, 2019).

[0007] Two types of reactions are particularly well known: Abiotic reactions occur when interactions with rock arise from geochemical imbalances resulting from the introduction of dihydrogen (and its dissolution in water), as well as from their kinetics (a very slow reaction rate with little ultimate industrial impact). Biotic reactions occur when interactions originate from the growth of anaerobic bacteria present in the environment, which feed, among other things, on dihydrogen dissolved in the water. These reactions can lead to changes in water chemistry (for example, in pH), which can induce secondary abiotic reactions.

[0008] These reactions can impact the quality of the extracted gas (for example, because they lead to the formation of hydrogen sulfide (H2S)). They can also impact storage efficiency since hydrogen may be consumed. Finally, these reactions affect storage performance because they can alter the petrophysical properties of the reservoir if the permeability of certain parts of the reservoir is irreversibly degraded.

[0009] We know of methods to characterize the reaction risks associated with the introduction of dihydrogen into a porous reservoir, but they require the implementation of complex characterization and validation steps which do not allow us to completely eliminate the risks, nor to move forward quickly enough to develop an industrial project.

[0010] We are familiar with the upstream risk assessments, in particular: Statistical studies conducted on bacterial populations sampled in various hydrocarbon deposits and storage facilities (Strobel G., Hagemann B., Huppertz TM, Ganzer L.: "Underground bio-methanation: Concept and potential", Renewable and Sustainable Energy Reviews, 123, 2020; or Thaysen EM et al, 2021, Hydrogen Storage in Porous Media as a Basis for Site Selection, Renewable and Sustainable Energy Reviews, Preprint 5) can be used to assess the risk of upstream biotic reactions given the characteristics of the site studied (in particular its temperature and water composition). Geochemical simulation tools can be used based on known information about the site studied to assess the risk of abiotic reactions, according to methods described in the following documents: Truche, L., Jodin-Caumon M.-C., Lerouge C., Berger G., Mosser-Ruck R., Giffaut E., Michau D., 2013, Sulphide mineral reactions in clay-rich rock induced by high hydrogen pressure. Application to disturbed or natural settings up to 250 °C and 30 bar, Chemical Geology 351 (2013) 217-228, Thüns N., Krooss B.M., Zhang Q., Stanjek H., 2019, The effect of H2 pressure on the reduction kinetics of hematite at low temperatures, International Journal of Hydrogen Energy 44 (2019) 27615-27625, Shi Z. et al, 2020, Impacts of the subsurface storage of natural gas and hydrogen mixtures, International Journal of Hydrogen Energy 45 (2020) 8757-8773, et Ziegler L., 2021, H2_ReacT - Transport of hydrogen in rocks considering abiotic chemical and microbial redox reactions, presentation at the Underground Sun Conversion Stakeholder Workshop, April 14th, 2021. .

[0011] On connait également des méthodes de caractérisation en laboratoire: For example, if the conditions of a site correspond to a risk zone, sampling of reservoir rocks, formation water, and bacterial fauna can be implemented, which requires a dedicated protocol (biological sampling). Reactions can be evaluated in the laboratory via experiments under reservoir conditions with the targeted fluids and rock fragments in autoclaves that have been previously sterilized and then inoculated with bacterial cultures from representative biological samples. These experiments make it possible to identify the predominant reactions and their kinetics (Ranchou-Peyruse M. et al, 2019, Geological gas-storage shapes deep life, Environmental Microbiology (2019) 21(10), 3953-3964). It should be noted that the induced changes in terms of porosity and permeability are still the subject of very early-stage R&D and cannot be directly deduced from this type of experiment (Ott H.(2021, BioPore - Motivation, Project and Findings, presentation at the Underground Sun Conversion Stakeholder Workshop, April 14th, 2021). This constitutes an additional source of uncertainty.

[0012] We also know of characterizations and simulations at the reservoir scale: For example, once this laboratory characterization step is completed, it becomes possible to initiate the development of a compositional and reaction model and to perform initial assessments at the reservoir scale. At this stage, it is also recommended to design and then implement a sufficiently large-scale pilot project on-site to collect the data necessary to validate the reservoir model scaling steps. Validating this step is crucial to finding the right balance between computation time (number of grid cells) and accurate representation of geological heterogeneities in a context where the number of mechanisms to consider is high, all within a 3D geometry.

[0013] While natural gas storage is well-established, storing other gases, such as hydrogen, remains challenging. For example, hydrogen storage presents specific risks.

[0014] Currently, hydrogen storage in salt caverns is known. Hydrogen storage in porous reservoirs remains at the study and validation stage, with no industrial projects currently under development.

[0015] That being said, current studies have confirmed that such storage in porous reservoirs is feasible with controlled risks, but only under particularly favorable conditions which limit the cases in which storage is feasible: low aquifer activity, temperature between 25 and 50°C, water composition without sulfates, mineralogy without pyrites or iron oxides.

[0016] Current solutions for storing gases such as dihydrogen are therefore particularly limited, due to the risk of dihydrogen reaction in the subsoil which can induce a degradation of the quality of the gas at the point of withdrawal, a loss of a significant fraction of the stored dihydrogen, and finally a reduction in the permeability of the reservoir induced by biotic and / or abiotic reactions.

[0017] The invention aims to resolve at least some of the aforementioned drawbacks. Description of the invention

[0018] To this end, the invention proposes a method for storing and utilizing a first gas and a second gas denser than the first gas in an aquifer or depleted reservoir, by means of an installation comprising: a first well (possibly one or more first wells) opening into an upper part of the reservoir and connected to a first gas transportation network, a second well (possibly one or more second wells) opening into a lower part of the reservoir (the upper part being above the lower part) and connected to a second gas transportation network, the process comprising storing the first gas in the upper part of the reservoir, storing the second gas in the lower part of the reservoir, exploiting the first gas from the first well, and exploiting the second gas from the second well, the exploitation of the first being able to be carried out simultaneously and separately from the exploitation of the second gas.

[0019] The invention therefore proposes to exploit, that is, inject or withdraw gas, two distinct gases through two different wells that both open into the same reservoir. This exploitation can be carried out simultaneously and separately, meaning that the first gas can be withdrawn / injected while the second gas is being withdrawn / injected. Furthermore, the first gas can be injected / withdrawn while no withdrawal / injection activity is being carried out on the second gas (typically, it is stored), and the second gas can be injected / withdrawn while no withdrawal / injection activity is being carried out on the first gas (typically, it is stored), although in this latter case, one gas is not actually exploited (it is stored). In other words, the exploitation of the first gas is carried out independently of the exploitation of the second gas.

[0020] As an example, and without limitation, a single underground reservoir can be used for two gases, in a manner equivalent to operating two completely independent underground storage reservoirs, each dedicated to one of the gases and connected to its respective transmission networks and processing facilities. This characteristic is particularly important in a context where the need for storage of new gases is increasing, requiring the use of dedicated transmission networks, while storage for historically used gases remains necessary, and suitable underground storage reservoirs are scarce.

[0021] In fact, and as an example, for each gas, there can be a processing plant between the reservoir and the gas transmission network (therefore, there can be two processing plants for two different gases stored for their two separate networks). A gas processing plant can perform dehydration and desulfurization, for example. These simultaneous and separate operations are implemented, for instance, for a given volume range of the first and second gases. This given range can be a given distribution of volumes, so that a given non-zero volume of the first gas (for example, within a volume range) and a given non-zero volume of the second gas are always maintained in the reservoir (for example, within a volume range).

[0022] Because of the difference in density between the two gases and the targeted injection method, the two gases remain separated inside the reservoir in the vertical direction, and a person skilled in the art will be able to determine the depth at which the wells open to obtain this configuration, depending in particular on the volumes to be stored.

[0023] It should be noted that the concept of volume is used in this application. Of course, these volumes refer to the pressure at which the gases are stored in a tank, that is, a pressure suitable for that tank, which a person skilled in the art will be able to determine. This suitable pressure is the pressure exerted on the gas at the depth of the tank where it is stored.

[0024] It has therefore been observed that it is possible to store and exploit two different gases independently in the subsoil.

[0025] Furthermore, it should be noted that if the first gas is one that can be involved in aqueous-phase reactions that could affect its storage and use (in terms of gas quality, energy loss, and reduced permeability / porosity), the first gas is separated from the mobile, and therefore more reactive, water at the bottom of the storage tank due to the presence of the second gas between the first gas and the water. The invention thus improves the storage of at least the first gas, if this gas participates in aqueous-phase reactions that degrade its storage.

[0026] According to a particular implementation method, the first gas is dihydrogen.

[0027] The invention is particularly well-suited for a first gas that is less dense than the second, which is dihydrogen. This is because the second, denser gas, located in the lower part, is the one that will be in contact with the water in the aquifer (or the depleted reservoir). Reactions that impact dihydrogen storage generally occur in the aqueous phase after some of the dihydrogen has dissolved in the water (it should be noted that pressure and temperature, as well as aquifer movements induced by storage activity, can affect storage). This dissolution is limited by the presence of the second gas between the first gas and the water at the bottom of the reservoir, which thus acts as a buffer to limit undesirable reactions.

[0028] According to a particular implementation method, the second is natural gas.

[0029] Storing natural gas as a second gas is particularly well-suited for use as the gas that will interface with the water at the bottom of the reservoir, given the well-established practices for storing natural gas in aquifers or depleted reservoirs. Furthermore, natural gas is well-suited when hydrogen is the primary gas.

[0030] According to a particular implementation method, the exploitation of the first gas involves the exploitation of a single so-called useful volume of the first gas, the process including a step of defining the useful volume of the first gas, the total volume of the first gas in the reservoir being equal to the sum of the useful volume of the first gas with a so-called cushion gas of the first gas located at the interface with the second gas.

[0031] Thus, in this particular implementation method, the exploitation of the first gas is limited so as to always maintain a volume of the first gas that will not be withdrawn (the cushion volume), and which is located at the interface with the second gas. This allows only a portion of good quality (for example, in terms of composition) of the first gas to be exploited, because the cushion volume may contain some of the second gas that diffuses into the first gas.

[0032] For example, the cushion volume can be fixed. The usable volume can be defined as a range of volumes.

[0033] According to a particular implementation method, the exploitation of the second gas involves the exploitation of a single so-called useful volume of the second gas, the process including a step of defining the useful volume of the second gas, the total volume of the second gas in the reservoir being equal to the sum of the useful volume of the second gas with a so-called upper cushion volume of the second gas located at the interface with the first gas and another so-called lower cushion volume of the second gas located below the useful volume of the second gas (in particular in the interface zone with the water).

[0034] In this particular implementation method, the use of the second gas is limited to ensure that two volumes of the second gas are always not withdrawn (the two cushion volumes), located respectively at the interface with the first gas (or even the cushion volume of the first gas) and with the reservoir water. This allows only a portion of good quality (for example, in terms of composition) of the second gas to be used, as the cushion volumes may contain some of the first gas that diffuses into the second gas, or be affected by contact with the water.

[0035] According to a particular implementation method, the steps of defining the useful volume of the first gas and the useful volume of the second gas are carried out during a preliminary phase in which observational data of the operation of the tank and a modeling of the tank are used.

[0036] This phase can be carried out prior to the independent storage and exploitation of the first and second gas, for example when the reservoir contains only one type of gas (for example the second gas).

[0037] According to a particular implementation method, observation data on the operation of the tank are obtained by tracing tests or by observation data from the successive exploitation of different gases in the tank.

[0038] According to a particular implementation method, the process includes an update of the useful volume of the first gas and the useful volume of the second gas taking into account observational data from the exploitation of the first gas or the exploitation of the second gas.

[0039] This update may involve modifying the cushion volumes used to maintain good quality of the withdrawn gas. For example, if a second gas is detected in the withdrawal of the first gas with a concentration exceeding a target value, the cushion volume of the first gas can be increased.

[0040] According to a particular implementation method, a third gas, denser than the second gas, is stored between the second gas and the water in the reservoir.

[0041] This third gas can be used as a cushioning gas at the interface with the water.

[0042] According to one implementation method, the reservoir initially contains only the second gas, or, if the process involves the storage of the third gas, only the third gas.

[0043] This method of implementation is particularly well suited to the storage of a first gas, for example dihydrogen, in a reservoir initially used to store natural gas (the second gas).

[0044] The invention also proposes an installation for storing and utilizing a first gas and a second gas denser than the first gas in an aquifer or depleted reservoir, comprising: a first well (possibly one or more first wells) opening into an upper part of the reservoir and connected to a first gas transportation network, a second well (possibly one or more first wells) opening into a lower part of the reservoir and connected to a second gas transportation network, the installation being configured to allow storage of the first gas in the upper part of the reservoir, storage of the second gas in the lower part of the reservoir, exploitation of the first gas by the first well, and exploitation of the second gas by the second well, the exploitation of the first gas being able to be implemented simultaneously and separately from the exploitation of the second gas.

[0045] This installation can be configured to implement all the implementation modes of the process as defined above. Brief description of the drawings

[0046] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings, which illustrate an example of an embodiment without being limiting in any way. In the figures: [ Fig. 1 ] There figure 1 is a schematic representation of an installation based on an example. Fig. 2 ] There figure 2 is a schematic representation of an installation based on another example. Fig. 3 ] There figure 3 is a schematic representation of an installation based on another example. Fig. 4 ] There figure 4 is a schematic representation of the distribution of volumes according to an example. Fig. 5 ] There figure 5 illustrates the steps of a process using an example. Fig. 6 ] There figure 6 illustrates a numerical model of the volumetric concentration of natural gas at different storage times, using an example. Fig. 7 ] There figure 7 illustrates the modeled changes in the fraction of dihydrogen produced in the upper and lower parts of the tank, using an example. Fig. 8 ] There figure 8 is a schematic representation of an installation. Description of the implementation methods

[0047] We will now describe the storage and exploitation processes of two distinct gases, and the installations used to implement these storage systems.

[0048] In this description, storage facilities are aquifer reservoirs or depleted reservoirs (aquifers initially containing hydrocarbons (gas or oil), for example, an aquifer with variable activity) in which the reservoir has a roughly dome shape, composed of porous rock in which the gas is stored. The gas is retained in the reservoir by an impermeable layer that defines this dome shape and the top of the reservoir (the impermeable layer can be called cap rock), and by liquid water that defines the bottom of the storage facility.

[0049] The invention finds application in the storage and exploitation of a low-density gas which may possibly react in aqueous phase (for example after dissolution in water), which it facilitates by also storing a second, denser gas between the first gas and the water in the tank.

[0050] In this description, the first gas is dihydrogen and the second gas is natural gas. Other first gases and other second gases can be used; for example, helium (H2) as the first gas with nitrogen (N2) as the second gas can be used.

[0051] Storing and utilizing hydrogen in an aquifer or depleted reservoir is challenging due to abiotic and biotic reactions that impact storage and utilization performance (particularly in terms of gas quality, energy loss, and permeability / porosity reduction). These reactions generally occur in the aqueous phase after some of the hydrogen gas dissolves in the water. As expected, pressure and temperature also influence these reactions, as does transport via aquifer movements induced by storage and utilization activities.

[0052] To limit the impact of these reactions, a second gas, denser than hydrogen, is used to act as a buffer and separate the hydrogen from the aqueous phase. Thus, for any type of aquifer or depleted reservoir, the risks of water quality loss, energy loss, and reduced permeability / porosity can be limited.

[0053] Since natural gas has a marginal reaction potential, it has become apparent that it can be used as a buffer gas in relation to dihydrogen. Furthermore, since a well opens into the lower part of the reservoir where the natural gas will be stored, it can also be exploited independently.

[0054] As one might expect, when a reservoir is already used to store natural gas (initially containing mainly methane), this gas can be used as a second gas and therefore as a cushion gas in relation to the first gas, which is dihydrogen.

[0055] For initial filling (a tank that initially contains water), other gases can be used, such as nitrogen as a second gas. In fact, the second gas can be chosen based on its density compared to the first, taking into account the chemical reactions it participates in within the aqueous phase. Furthermore, the second gas can be selected to avoid introducing risks such as corrosion associated with the introduction of carbon dioxide or oxygen that accompany nitrogen.

[0056] As explained above, we are using two gases with different densities, meaning two gases with different molar masses. For example, dihydrogen and natural gas have a molar mass difference of approximately 14 grams per mole. This difference is even greater if we use a second gas such as nitrogen or carbon dioxide. It has been observed that good separation of the two gases is achieved vertically with molar mass differences of approximately 12 grams per mole.

[0057] In addition to the separation, here we also have independent exploitation and storage of the two gases.

[0058] An example of an INS installation is shown on the figure 1 , where we see a cross-section of an aquifer reservoir 100 (an identical installation is also conceivable for a depleted reservoir). This reservoir is bounded at its upper part by an impermeable dome 101, and at its lower part by water 102. The part between the water and the dome is what will be called here the reservoir, comprising porous rock and which will receive gases.

[0059] Regarding the installation of the figure 1 A plurality of wells are planned. In particular, a first well 103 is planned in a central part of the reservoir, and this well opens into an upper part of the reservoir (its lower end 103A opens into this upper part). The invention is not limited to a single first well, and can be implemented by means of a plurality of first wells opening into the upper part.

[0060] A second well 104 is also provided in a peripheral section to the left of the first well 103 in the figure, and this well opens into a lower section of the reservoir, located between the upper section and the bottom of the reservoir (its lower end 104A opens into this lower section). Optionally, another second well 104' is provided in a peripheral section to the right of the first well 101, and this well opens into the lower section of the reservoir (its lower end 104A' opens into the lower section). In fact, the invention is not limited to one or two second wells and can be implemented using a plurality of second wells opening into the lower section.

[0061] It can be noted that the two second wells 104 and 104' terminate in the reservoir by means of screens 105 and 105' in a manner known in itself, which begin in the lower part and terminate here at the bottom of the reservoir.

[0062] The first well 103 is connected to a transport network 106 for a first gas, which in this case is dihydrogen. The term "network" here refers to a set of buried or above-ground pipelines capable of injecting dihydrogen through the first well 103 and capable of withdrawing dihydrogen through the first well 103.

[0063] The second well 104 is connected to a transport network 107 of a second gas which is in this case natural gas.

[0064] If reservoir 100 initially contains natural gas, hydrogen can be introduced into the upper part of the reservoir using the first well 103, while maintaining natural gas in the lower part. The introduction of hydrogen results in a volume V1 of hydrogen stored in the reservoir and a volume V2 of natural gas stored in the reservoir. In the figure, volume V1 actually refers to the upper part of the reservoir occupied by this volume, and volume V2 refers to the lower part of the reservoir. These two parts are defined by the gases that compose them (as can be understood, diffusion and dispersion are possible at the interface; however, a person skilled in the art will be able to delineate these two parts).

[0065] These two volumes naturally separate due to the difference in density between the two gases. As illustrated in the figure, volume V1 is not in contact with the bottom of the tank or the liquid water, which allows for the storage and use of dihydrogen under optimal conditions.

[0066] Therefore, separate operations for hydrogen and natural gas can be implemented independently of each other. Those skilled in the field might refer to this independent operation as a co-activity.

[0067] To further improve the respective exploitation of the two gases, consideration can be given to the diffusion that can occur at the interface between the two gases, and possibly at the interface with water.

[0068] Thus, on the figure 2 , another installation was represented (but in which the references of the figure 1 are reused to designate the same elements), in which the openings of the second wells 104 and 104', at the level of the screens 105 and 105', differ from those of the figure 1 Since some are sealed to delimit a depth range of 110 meters in which natural gas can flow, natural gas that is not affected by the presence of dihydrogen or water is being extracted, which can impact the quality of the operation.

[0069] On the figure 3 We have shown yet another installation, which differs from that of the figures 1 et 2 in that a third well 120 is planned, opening at the periphery of the reservoir towards the bottom of the reservoir (its end 120A arrives a little before the bottom and well below the ends of the second wells).

[0070] This installation allows a third gas, typically an inert gas such as nitrogen, to be injected into the bottom of the tank, so that the water does not affect the production of natural gas.

[0071] In the modes of embodiment of figures 2 And 3 , so-called cushion volumes are used. This is further detailed with reference to the figure 4 .

[0072] In this figure, the left-hand side shows a schematic representation of the distribution of natural gas in an aquifer containing only natural gas. Thus, the reference VT_GN designates the total volume of natural gas in this reservoir, VU_GN_ini a usable volume of natural gas in this reservoir, and VC_GN_ini a cushion volume of natural gas in this reservoir.

[0073] Here, a usable volume is a volume that can be drawn out / injected, while a cushion volume is a volume that is not intended to be drawn out / injected.

[0074] On the left side of the figure, there is a schematic representation of the gas distribution in a tank such as that of the figure 2 , with two different gases and cushion volumes. Starting from the bottom of the tank, we have: a lower cushion volume VC_GN_2 of natural gas, at the interface with the water, a usable volume VU_GN of natural gas (containing natural gas with a good level of purity), this volume being at the level of the openings of the figure 2 , an upper cushion volume VC_GN_1 of natural gas (mainly composed of methane), a cushion volume VC_H2 of dihydrogen (mainly composed of dihydrogen), a useful volume VU_H2 of dihydrogen (comprising dihydrogen with a good level of purity).

[0075] It can be noted that between the cushion volumes VC_GN_1 and VC_H2, there is a gradient in the concentration of dihydrogen, which increases in the direction of the surface.

[0076] As a guideline, consider an aquifer initially containing natural gas with a usable volume of 690 Mm³ and a cushion volume of 810 Mm³. If this reservoir is to be used for storing and utilizing hydrogen, a usable volume of 200 Mm³ of hydrogen (corresponding to 16,820 tonnes at a given pressure) can be chosen. To prevent mixing between the gases, at least in the areas to be utilized, 25% of the cushion gas (the sum of the cushion volumes) should be hydrogen, representing approximately 200 Mm³ out of the total cushion volume of 810 Mm³. This results in a remaining usable volume of 490 Mm³ of natural gas. The use of the cushion volume containing dihydrogen makes it possible to avoid mixing between the two gases in the part called the useful volume, and to obtain two true useful volumes.Furthermore, the usable volume of natural gas is arranged, as can be seen on the . figure 4 , between two cushion volumes.

[0077] It can be noted that the water clearance (distance between the zone and the point of withdrawal of the second gas) is modified compared to the initial configuration of the tank, this modification being acceptable.

[0078] It should also be noted that the ratio of usable volume to total volume is greater when the reservoir contains only one gas (natural gas) compared to when it contains two gases, assuming the usable volume for both gases remains the same as the initial usable volume for the single gas. If the total volume remains constant under bottom conditions, the usable volume with two gases is reduced compared to the initial configuration with a single gas because the water clearance for natural gas is then reduced by the need to place some of the natural gas cushion gas in the upper part (VC_GN_1). It is worth noting that the concept of water clearance is well known to those in the field and corresponds to the distance (possibly an elevation) to be maintained between the lowest part of the well (here, the natural gas well) and the water table, to avoid drawing in water.

[0079] We will now describe, with reference to the figure 5 , how are volumes defined, for example the volumes of the figure 4 These steps can be implemented on a computer. The first steps are those implemented in an initial phase P1, which precedes the use of the tank for two gases.

[0080] We consider an aquifer reservoir, for example, a new reservoir (for example, one that initially contains water) or a reservoir already in operation for storing natural gas (as a secondary gas). In fact, the reservoir can be a reservoir conforming to French standards NF EN 1918-1 or 2, in their June 2016 versions.

[0081] In a first step, observational data on the operation of the tank can be obtained.

[0082] This achievement can be implemented in two alternative ways, and it applies to both existing and new tanks.

[0083] In step S1, tracer tests are performed, in which an inert element (sometimes called a tracer) is added to the injected gas for a short period of time (typically, this injection is analogous to a Dirac delta function). A withdrawal is then performed to analyze the gas and determine the concentration of the injected element. Several measurements can be taken regularly, and a distorted Gaussian-shaped change in concentration is generally observed, illustrating the mixing of the tracer with a gas present in the reservoir, resulting from diffusion and, above all, dispersion mechanisms.

[0084] Alternatively, step S1' can be implemented, in which observational data on the operation of gases stored and extracted from the reservoir are obtained. For example, if the reservoir has been used to successively store and extract different gases with varying compositions, the associated observational data can be used. In fact, this data can indicate changes in the gas composition over time and is analogous to the data obtained by implementing step S1.

[0085] In fact, in the present description, observational data may be concentration curves of a gas as a function of time.

[0086] Next, step S2 can be implemented, in which a reservoir model is calibrated using data obtained in steps S1 or S1'. More specifically, a reservoir model can be used that simulates the dynamic gas flows, gas transport mechanisms, and physicochemical reaction mechanisms between the gas, water, and rock. This allows for the simulation of the gas composition that will be extracted from a given location / depth within the storage facility. Several solutions exist for modeling a storage facility. Indeed, numerous commercial and academic codes are capable of simulating, at a minimum, the compositional mechanisms of gas mixing. Examples include ECLIPSE 300, marketed by Schlumberger, and STARS, marketed by the Canadian company Computer Modelling Group Ltd.We are also familiar with the HYTEC code developed by the Ecole des Mines de Paris.

[0087] This model can, thanks to its calibration, reflect the heterogeneities of the reservoir in the composition values ​​it delivers.

[0088] We can then implement the S3 tank sizing step, in which we determine using the model the usable volumes and cushions for the tank (for example to have a given level of purity for the usable volumes).

[0089] For example, for the storage and use of natural gas and dihydrogen, this step may include the determination of the volumes VC_GN_2, VU_GN, VC_GN_1, VH_H2, and VU_H2 described above.

[0090] The model also allows us to determine the flow rates to be used for operation, etc. Furthermore, the uncertainties inherent in a subsurface model can be taken into account to achieve good independent operation of the two gases.

[0091] These steps are implemented during phase P1, which precedes the storage and exploitation of the two gases.

[0092] During the P2 phase of reservoir operation, while the two gases are being operated independently, a step S4 can be implemented to obtain observational data on the operation of both gases in a manner analogous to that implemented in phase P1 at step S1'. This allows observation of changes in the composition of the extracted gases as a function of time, the different volumes present in the reservoir, and the different flow rates used.

[0093] In this step S4, we can compare the observed data with those obtained in the initial phase, which allows us to recalibrate (step S5) the model with new parameters, and then to determine new volumes and flow rates for the reservoir.

[0094] There figure 6 This presents three graphical representations of numerical models of the volumetric concentration of natural gas in a reservoir into which dihydrogen will be injected and which initially contained natural gas. The three representations correspond to vertical cross-sections of a portion of the reservoir since the volumetric concentration of natural gas can be seen in a horizontal direction, from the edge of the reservoir to its center, and in a vertical direction, from the bottom of the reservoir (where water is present) to the top of the reservoir.

[0095] In the left-hand graph, the reservoir contains only natural gas above the water. The middle graph represents the introduction of hydrogen into the upper part of the reservoir (specifically, the situation at the end of the hydrogen injection), and we can see that the natural gas concentration decreases in this area. The right-hand graph represents the situation after hydrogen withdrawal; the model clearly shows that even after withdrawal, there is still a low concentration of natural gas in the upper part of the reservoir.

[0096] There figure 7 shows a model of the evolution over time of the fraction of dihydrogen produced (which is obtained during a withdrawal), both in the upper part of a reservoir and in the lower part (by two separate wells), after the introduction of dihydrogen into a reservoir initially containing natural gas.

[0097] As can be seen, after the introduction of dihydrogen, the molar fraction of dihydrogen in the upper part of the tank remains above 80% (the lowest values ​​correspond to the end of the withdrawal phases). In the lower part of the tank, the molar fraction of dihydrogen remains below 10%, which may be acceptable for certain applications.

[0098] There figure 8 shows an installation similar to that of the figure 1 , non-exhaustive and provided as an example, on which the transport networks of the first gas and the second gas have been made more visible.

[0099] More specifically, we have represented here in a more complete way the transport network 106 of the first gas, and the transport network 107 of the second gas.

[0100] Within the first gas transport network, a first gas processing workshop 130 was represented, for example used to implement dehydration and desulfurization of the first gas.

[0101] A second gas treatment plant 140 is also shown in the figure; this plant is located within the second gas transmission network. This treatment plant is used, for example, to carry out dehydration and desulfurization of the second gas.

[0102] The installations and processes described above allow two gases to be stored and used independently, provided that these two gases have different densities.

[0103] Thus, one gas can be withdrawn while the second gas is being injected, withdrawn, or simply stored; the first gas can be injected while the second gas is being injected, withdrawn, or simply stored. It is also possible to withdraw the second gas while the first gas is being injected, withdrawn, or simply stored, or to inject the second gas while the first gas is being injected, withdrawn, or simply stored.

[0104] This is well suited for storing dihydrogen with natural gas, given that natural gas storage cycles are seasonal, and those of dihydrogen can be faster.

Claims

1. A method for storing and mining a first gas and a second gas denser than the first gas in a water bearing or depleted reservoir (100), by means of an installation comprising: - a first well (103) opening into an upper part (V1) of the reservoir and connected to a transport network for the first gas (106), - a second well (104,104') opening into a lower part (V2) of the reservoir and connected to a transport network for the second gas (107), the method comprising storing the first gas in the upper part of the reservoir, storing the second gas in the lower part of the reservoir, mining the first gas by the first well, and mining the second gas by the second well, the mining of the first gas being able to be implemented simultaneously and separately from the mining of the second gas.

2. The method according to claim 1, wherein the first gas is dihydrogen.

3. The method according to claim 1 or 2, wherein the second gas is natural gas.

4. The method according to any one of claims 1 to 3, wherein the mining of the first gas includes mining only a so-called useful volume of the first gas, the method includes a step of defining the useful volume of the first gas, the total volume of the first gas in the reservoir being equal to the sum of the useful volume of the first gas with a so-called cushion volume of the first gas located at the interface with the second gas.

5. The method according to any one of claims 1 to 4, wherein the mining of the second gas includes mining only a so-called useful volume of the second gas, the method includes a step of defining the useful volume of the second gas, the total volume of the second gas in the reservoir being equal to the sum of the useful volume of the second gas with a so-called upper cushion volume of the second gas located at the interface with the first gas and another so-called lower cushion volume of the second gas located below the useful volume of the second gas.

6. The method according to claims 4 and 5, wherein the steps of defining the useful volume of the first gas and the useful volume of the second gas are carried out during a preliminary phase wherein observation data of the reservoir operation and a reservoir model are used.

7. The method according to claim 6, wherein the observation data of the reservoir operation are obtained by tracer tests or by observation data from the successive mining of different gases in the reservoir.

8. The method according to claim 6 or 7, includes an update of the useful volume of the first gas and the useful volume of the second gas taking into account observation data from the mining of the first gas or the mining of the second gas.

9. The method according to any one of claims 1 to 8, wherein a third gas denser than the second gas is stored between the second gas and the water of the reservoir.

10. The method according to any one of claims 1 to 9, wherein the reservoir initially includes only the second gas, or, if the method is that of claim 9, only the third gas.

11. An installation for storing and mining a first gas and a second gas denser than the first gas in a water bearing or depleted reservoir (100), comprising: - a first well (103) opening into an upper part (V1) of the reservoir and connected to a transport network for the first gas (106), - a second well (104,104A) opening into a lower part (V2) of the reservoir and connected to a transport network for the second gas (107), the installation being configured to allow storage of the first gas in the upper part of the reservoir, storage of the second gas in the lower part of the reservoir, mining of the first gas by the first well, and mining of the second gas by the second well, the mining of the first gas being able to be implemented simultaneously and separately from the mining of the second gas.