WO2016114665A2

WO2016114665A2 - Apparatus and method for compensation of extraction of natural gas from a natural gas field

Info

Publication number: WO2016114665A2
Application number: PCT/NL2016/050034
Authority: WO
Inventors: Bernardus Ludgerus Lubertus Hijlkema; Bastiaan KNOORS
Original assignee: Nippelinventions; Liandon B.V.
Priority date: 2015-01-15
Filing date: 2016-01-14
Publication date: 2016-07-21
Also published as: WO2016114665A3; WO2016114665A9

Abstract

Apparatus for compensation of extraction of natural gas (g) from a natural gas field (G), in particular for preventing subsidence of strata located above the natural gas field and/or earthquakes, comprising: - one or more supply channels (1) configured to supply compensation gas to the natural gas field; and - at least a first gas source (11), couplable to the supply channels (1), which contains a non-inert gas (F). The invention further relates to a method for compensating extraction of natural gas (g) from a natural gas field (G), in particular for preventing subsidence of strata located above the natural gas field, comprising: - supplying a non-inert compensation gas to the natural gas field.

Description

Title: Apparatus and method for compensation of extraction of natural gas from a natural gas field The invention relates to an apparatus for compensating extraction of natural gas from a natural gas field, comprising one or more supply channels configured to supply a compensation gas to the natural gas field.

Natural gas is an important resource for energy supply. Natural gas is generally extracted from natural gas fields. A natural gas field (also referred to as gas deposit) usually sits relatively deeply into the ground, for instance at a depth of 1 km or more. The natural gas field sits in particular in one or more underground layers (of sandstone), usually trapped under a gastight underground layer.

The main constituent of such a natural gas field or gas deposit is methane (for example, at least about 80%). Further, the natural gas field can contain other hydrocarbons, and inert gases such as nitrogen, argon and carbon dioxide. To extract the natural gas, usually a number of wells are sunk. The natural gas, which usually has a superatmospheric pressure, can then be extracted from the field.

It has been found that natural gas extraction can lead to problems, in particular to local tremors or earthquakes and associated damage to the surroundings. Indicated as a possible cause of such tremors or earthquakes is a decrease of pressure in the gas deposit that accompanies gas extraction, which can produce sudden relative shifts of the faults. It has been proposed to solve this problem by pumping nitrogen into the gas field to compensate for the natural gas to be discharged from the field, in particular to keep the pressure in the gas field at a specific initial level. An important drawback of this solution is its relatively high cost price.

The present invention contemplates eliminating, or at least reducing, the problems mentioned. In particular, the invention contemplates an improvement of the natural gas extraction whereby damage to the surroundings can be prevented efficiently and in an economically favorable manner. The invention further contemplates an improvement of energy supply.

According to an aspect of the invention, to this end, an apparatus is provided that is characterized by the features of claim 1.

Advantageously, an apparatus for compensating extraction of natural gas from a natural gas field, in particular for preventing subsidence of strata located above the natural gas field and/or earthquakes, comprises:

- one or more supply channels configured to supply one or more compensation gases to the natural gas field; and

- at least a first gas source, couplable to the one or more supply channels, which contains a non-inert gas.

In this manner, a particularly efficient compensation of gas extraction can be achieved (in particular to prevent a pressure decrease in the gas field caused by gas extraction), simply by supplying a non-inert gas. According to an additionally advantageous elaboration of the invention, the non-inert gas consists of air. The air can be, for example, ambient or atmospheric air.

According to a further elaboration, the apparatus is configured for introducing into the gas field per unit time an amount of non-inert gas that is the same as or greater than an amount of natural gas to be extracted from the gas field during that unit time.

In this manner, a complete compensation can be achieved. By supplying a greater amount of compensation gas to the natural gas field, furthermore, pressure in the gas field can be increased. An additional advantage is that the gas field can thus be used as an energy storage. Here, gas present in the gas field can function in particular as a voluminous energy storage medium to store (potential) energy in it, the stored energy being equivalent to a pressure increase in the gas field. The energy can then be simply withdrawn from the energy storage medium by discharging gas (i.e., conversion of potential energy into kinetic energy).

According to an additionally advantageous elaboration of the invention, the apparatus is configured for adding an inert gas as a

separating layer between natural gas present in the gas field and the non-inert gas.

In this manner, an unwanted chemical reaction between non-inert gas and the natural gas can be prevented.

Preferably, the apparatus further comprises at least a second gas source, couplable to the supply channels, which contains an inert gas. The inert gas can be, for example, nitrogen, or flue gas, or an oxygen-free gas, or, for example, a combination of such gases.

According to an elaboration, the apparatus can comprise one or more supply channels from ground level up to or/and into the bottom of a natural gas deposit. Further, to the one or more supply channels, on the ground level, compressed atmospheric air compressors and fittings may be coupled for pressing large amounts of compressed atmospheric air through those ducts. Additionally, the apparatus may comprise an intricate duct system coupled to this supply channel or these supply channels and extending preferably over the entire bottom, in which system there are, maximally spread, billions of small outflow openings for allowing the compressed atmospheric air supplied to flow out as gradually as possible, spread over the entire bottom of the natural gas deposit.

According to a preferred mode, the one or more supply channels are configured to supply compensation gas to the field at a vertical level near a bottom of the gas field. In this manner, the compensation gas can displace the natural gas near or from the bottom of the gas deposit.

According to a preferred mode, the one or more supply channels are configured to supply gas to the field at a vertical level above a bottom of the gas field. Preferably, a compensation gas can displace the natural gas over a relatively large vertical distance, for instance viewed sideways from the supply channel. To this end, the channel may for instance be configured (for instance with a series of outflow openings) to introduce gas into the natural gas field at different vertical positions.

Preferably, a supply channel is configured to feed gas to the field dosed from different positions, while, for instance, a specific dose per position is settable or has been set. Thus, the channel may be configured, for instance, to feed from a first (for instance relatively low) position a first amount/flow of gas (m³/s), and to feed at a second position (for instance, a position which is higher than the first position) a second amount/flow of gas (m³/s). The second amount/flow of gas differs from (is, for instance, smaller than) the first amount of gas, to obtain a mutually different dosage.

According to a further elaboration, the gas field is penetrated by the one or more supply channels, whereby, during operation, compensation gas is introduced into the gas field via the one or more supply channels, such that the compensation gas reaches both a substratum (gas field bottom) and a superstratum (gas field top), and in particular such that the compensation gas forms a barrier between an outer side (extending in the gas field) of each of the one or more supply channels and natural gas present in the gas field.

The term "gas source" is to be taken broadly. Thus, the first gas source mentioned can for instance comprise one or more compressors, for instance air compressors, in particular configured for pressing the non-inert gas through the one or more supply channels.

Likewise, the second gas source can for instance comprise one or more compressors, in particular configured for pressing the inert gas through the one or more supply channels. Furthermore, the second gas source can comprise one or more reservoirs for storing this inert gas, production means for producing such inert gas, and the like. The one or more compressors can generate a considerable amount of heat during operation. Preferably, the apparatus comprises at least a heat reservoir for storing heat that is released in the use of the one or more compressors.

In an extra advantageous aspect, the apparatus comprises means for storing energy in the gas field in the form of rising pressure, for example, rising compressed air pressure. In order to use energy stored in the field, the apparatus can further comprise at least an electricity generator which is drivable by energy stored in the gas field. Here, it is possible that the drive is accompanied by decompression of gas discharged from the gas field. Such decompression usually leads to loss of heat, more specifically, cooling. In that case, it is particularly advantageous if the apparatus is configured to at least partly compensate a cooling entailed in the decompression using heat from the heat reservoir. Thus, a particularly environment -friendly and efficient heat storage can be achieved.

The invention further provides a method for compensating extraction of natural gas from a natural gas field, in particular to prevent subsidence of strata located above the natural gas field, comprising:

- supplying a non-inert compensation gas (for example, air) to the natural gas field.

Thus, the above-mentioned advantages can be achieved.

Preferably, an inert compensation gas is supplied to the gas field before the non-inert compensation gas is supplied to the gas field, in particular such that the inert compensation gas forms a separation between the natural gas and the non-inert gas. It has further been found advantageous, in particular with gas deposits that are relatively thin (e.g., having a vertical dimension of about 100 m) with respect to horizontal dimensions (e.g., more than 1 km), when the compensation gas fills a part of that field that extends between a gas field bottom and a gas field top completely. Thus, pressure decrease in the gas field can be efficiently prevented, and, in particular, different compensation gases can be used (for instance, first an inert gas as a concentric outer buffer and then a non-inert gas in a concentric inner layer). The compensation gases can here form one or more vertical columns in the natural gas field, at least, (concentrically) surround respective supply channels 1. A height of such a column can for instance be more than 10 m, in particular more than 50 m, depending, for instance, on the local height of the gas field (i.e., a distance between a gas field bottom and a gas field top, at or near a location where the compensation gas is introduced into the gas field).

An application that can make use of the innovative method comprises a method for storing energy, whereby gas is supplied to an underground gas field, for example, natural gas field. Thus a, usually voluminous, underground gas field can be deployed as energy buffer.

A volume of such a gas field can be, for example, at least 0.1 km x 1 km x 1 km. The gas to be used with this method can for instance comprise air, or nitrogen, flue gas, waste gas, or a combination of these or other gases.

According to a further elaboration, the method comprises

compressing the gas, wherein upon compression heat is released (is, for instance, abstracted from the gas), wherein the thus released heat is at least partly stored in a heat reservoir.

One aspect of the invention presents a method for generating electricity, for instance in combination with an above described method, comprising discharge of compressed gas, for instance compressed air, from an underground gas field, for instance natural gas field, to drive a

generator.

According to a mode, the gas can be decompressed, wherein a cooling accompanying this decompression is at least partly compensated using heat from a heat reservoir. As follows from the above, an aspect of the invention comprises a method for atmospheric air introduction into natural gas fields, optionally with addition of nitrogen gas.

Addition of nitrogen gas in the form of a separating layer between the natural gas and the atmospheric air for the purpose of precluding explosion hazard is within the possibilities here.

Fresh water floats on salt water because the specific weight of fresh water is approximately 2.5% lighter than that of salt water. Diesel oil floats on water because the specific weight of diesel oil is approximately 15.8% lighter than that of water. Natural gas floats on atmospheric air because the specific mass of natural gas is approximately 35.4% lighter than that of atmospheric air. Therefore, according to one aspect of the invention, natural gas can be forced upwards from a natural gas deposit by the introduction of atmospheric air with practically the same pressure value as the gas pressure obtaining in the natural gas deposit on and/or in the bottom of a natural gas deposit and, simultaneously, from the highest point or the highest points of the natural gas deposit, a corresponding equal amount of natural gas can be extracted from this natural gas deposit without the natural gas extraction leading to a change of state of either the condition of the natural gas deposit and the natural gas field or that of its surroundings and the body of soil located above the natural gas field. Thus, earth subsidence and earthquakes that presently do result from current natural gas extractions will not occur anymore, or occur to a lesser extent, or do not have to occur anymore.

A condition in which an amount of fresh groundwater floats on salt groundwater is a phenomenon that occurs in the ground worldwide and is generally known. When the flow of the groundwater is not too strong, this condition may be qualified as a fairly stable condition, in which mixing of fresh water and salt water occurs only to a limited extent, if at all. When, for instance, into a glass filled with water for one-third, the same amount of colored diesel oil is poured, the diesel oil will practically immediately start to float on the water and the separation between the water and the oil will be visible very clearly. Moreover, in this condition, the glass with such contents can be shaken fairly firmly without mixing of the oil and water starting to occur. The cause of this convincing result resides in the relatively great difference in specific weight between water and oil. In comparison with the above two examples, the mass difference between atmospheric air and natural gas is much greater still, and it may therefore be expected that upon an extremely gradual inflow of compressed atmospheric air from below from a widely branched duct system provided in and/or on the bottom of the natural gas deposit through countless small holes in the order of magnitude of billions, the influent atmospheric air volume will initially spread over the bottom of the natural gas deposit with a very low flow and will then manifest itself as a kind of blanket under the natural gas volume. Also, due to the above-mentioned great difference in mass, as a result of the action of gravity, the separating surface between the atmospheric air volume and the natural gas volume will manifest itself in the form of a virtually horizontal surface. By replenishing the atmospheric air volume from below, any influencing of the interface between the atmospheric air and the natural gas in the form of vortex will hardly occur, if at all. The temperature of the atmospheric air and the atmospheric air humidity will preferably need to have the same value as those of the natural gas to thereby prevent vortex phenomena also.

As follows from the above, introducing a non-inert gas, for example air, can also be effected in an advantageous alternative manner. One or more vertical columns or vertical shells of one ore more compensation gases may then be formed in the natural gas field, for instance an annular outer barrier of inert gas and, located inside of this barrier, a volume of non-inert gas. By making the contribution of the volume of, for instance, compressed atmospheric air per unit time exactly or practically exactly equal to the discharge of the volume of the natural gas, and making the pressure value of the compressed atmospheric air exactly or practically exactly equal to that of the natural gas located in the natural gas deposit, there will be a maintenance of the state of equilibrium in that ground, so that subsidence of the overlying strata need not or cannot occur, and the presently often occurring earthquakes need not or will not occur, at least, will decrease. In case of a condition where natural gas has already been extracted from a natural gas field for a certain period of time, introducing a proportionally larger volume of atmospheric air (or other non-inert gas) relative to the volume then being simultaneously withdrawn from this natural gas field may have as a result that a certain restoration of the subsided ground volume located above the natural gas field is achieved, so that the subsidence of the earth's surface, the ground level, can be compensated by a rise of the ground and the number of earthquakes will be stabilized or can decrease.

By, according to one of the modes of the invention, starting the injection of the natural gas deposit from the bottom of the natural gas deposit with the supply of nitrogen gas, then, owing to the mass weight of the nitrogen gas being of a magnitude practically similar to that of the atmospheric air, practically all natural gas will be displaced upwards from the substratum and bottom of the natural gas deposit, and a likewise practically horizontal separating surface will be formed between the natural gas and the nitrogen gas. Here too, as a result of the great difference in mass weight, mixing of the two gases will be practically impossible. There is no risk here of an explosive mixture being formed.

When by injection the natural gas deposit is filled with an inert gas (e.g., nitrogen gas) for a certain part, for example for 10%, but preferably for a smaller percentage, a switch can be made to introducing a non-inert gas (e.g., atmospheric air) via the same duct infrastructure.

Atmospheric air has a mass weight of approximately 1.29 kg/m³ and nitrogen gas 1.26kg/m³. The ratio between the mass weight of these two gases is quite comparable to the ratio between the specific weight of salt and fresh water. In the above described condition, the behavior between this gas combination and that liquid combination as regards the formation and maintenance of the contact surface between this gas combination and that liquid combination is virtually identical, and, by the same token, mixing of these two gases will hardly occur, if at all.

With the thus resulting methodology and technology, a storage capacity can result, in which varying volumes of both natural gas and compensation gas (for instance, atmospheric air) can be present. Thus, on the one hand, up to a very great extent, as much natural gas as possible can be displaced, extracted from the natural gas deposit, but this natural gas deposit, by introducing, for instance, imported natural gas at the top of the natural gas deposit, can also serve for volume-varying storage of this natural gas. At the same time, the compensation gas volume can serve for storing energy in the form of rising compensation-gas pressure, for instance a rising compressed air pressure through injection of more compressed air into the volume of atmospheric air (if air is deployed as compensation gas). Owing to the huge volume of a natural gas deposit, a rise of that

compensation-gas pressure of just a few bars will already represent a huge energetic storage.

The invention will now be further elucidated on the basis of exemplary embodiments and the drawing. In the drawing:

Figure 1 schematically shows a vertical cross section of a gas field, with an exemplary embodiment of an apparatus according to the invention, during supply of a first compensation gas; Figure 2 shows a similar drawing to Figure 1, with the apparatus during supply of a second compensation gas; and

Figure 3 shows a diagram of a use of an apparatus according to the invention for storage of energy.

In this application, identical or corresponding features are indicated with identical or corresponding reference signs.

Figures 1-3 schematically show a non-limiting example of an apparatus for compensation of extraction of natural gas g from a natural gas field G (of which a part is represented), in particular for preventing subsidence of strata S2 located above the natural gas field.

In this example, the underground natural gas field G known per se is defined by a natural gas containing layer (for example, of sandstone) between one or more superstrata S2 and a substratum Si. A top of the natural gas containing layer G is indicated with T, a bottom of the natural gas containing layer G is indicated with B. It will be clear that such a layer can be formed in various manners and can extend in different directions and orientations. Such a layer can be situated at a relatively great depth XI below the ground level H, for instance a depth XI of 1 km or more. The layer shown is relatively thin, having a thickness that is considerably smaller than the depth X2 (for instance a thickness of less than 200 m, in particular a thickness of approximately 100 m or less).

For the purpose of exploitation, one or more discharge channels 3 known per se are provided, having one or more discharge openings 4, for discharging natural gas g from the natural gas field G. As is known, such channels 3 are constructed by means of drilling wells. Measuring means 8, for example a steam meter, can be provided for measuring a gas flow (flow rate) of discharged natural gas g.

As follows from Figure 1, the apparatus comprises one or more supply channels 1 (in this case only one) configured to supply compensation gas to the natural gas field G, in particular for compensation of pressure decrease in the field. In this example, such supply channels 1 are located, in particular, at a distance from the one or more discharge channels 3. In an alternative embodiment, one or more of the discharge channels 3 can be used, or reversed, for supplying compensation gas to the natural gas field G instead of discharging gas (in this case, a channel can have a double function).

The apparatus further comprises a first gas source 11 couplable to the supply channel 1, which contains a non-inert gas F, and a second gas source 12 couplable to the supply channel 11, which contains an inert gas N.

As mentioned in the above, various compensation gases can be chosen.

The first compensation gas N suppliable by a first gas source 11 can comprise, or consist completely of, for example, nitrogen, carbon dioxide, flue gas or the like.

In an extra advantageous, economically particularly favorable mode of the invention, the second (non-inert) gas comprises air. This gas F may for instance consist completely of ambient air (atmospheric air).

Alternatively, this gas may comprise, for example, flue gas, or a mixture of air with an inert gas (for example, flue gas) and/or with other (inert or non- inert) gas, waste gas, or gases.

The present apparatus is configured for introducing into the gas field G per unit time an amount of non-inert gas F that is the same as or greater than the amount of natural gas to be extracted from the gas field G during this unit time. In this manner, subsidence can be well prevented. Preferably, the apparatus is provided with regulating means 5 for

regulating compensation gas to be supplied via the one or more supply channels 1 into the natural gas field G, preferably regulating means which depend on an amount of natural gas g to be extracted and/or extracted from the natural gas field. Such regulating means may for instance comprise one or more valve means and the like, which are preferably automatically operable, for instance under the influence of a control or controller.

Alternatively or additionally, a manual operation of such regulating means can be applied. The regulating means are preferably configured for setting the gas flow (flow rate, m³/s) of compensation gas N, F to be pumped into the gas field on the basis of, or making use of, a gas flow determined by the measuring means 8, of natural gas g discharged (for instance

instantaneously) from the gas field G.

Preferably, the one or more supply channels 1 reach from the ground level H up to or/and into the bottom B of the gas field G. In the present example, the supply channel 1 penetrates the gas field and the bottom B to reach the substratum Si.

For supply of the compensation gases N, F, various pumping means, one or more compressors and the like can be deployed, which will be clear to the skilled person. The first gas source 11 and the second gas source 12 can comprise one or more compressors (for instance at least a joint compressor, or one or more separate compressors per gas source), in particular configured for pressing the compensation gases N, F through the one or more supply channels 1. According to a further elaboration, to the one or more supply channels 1, on the ground level H, compressed atmospheric air compressors and fittings may be coupled for pressing large amounts of compressed atmospheric air F (if air is used as second compensation gas) through those ducts 1.

As follows from Figures 1-2, the present invention is configured for adding the inert gas N as a separating layer between natural gas g present in the gas field G and the non-inert gas F.

According to a mode, the apparatus can comprise an intricate duct system (not shown), coupled to that supply channel or those supply channels, which preferably extends over or in the entire bottom B and in which there are, maximally spread, billions of small outflow openings for allowing the supplied compressed atmospheric air to flow out as gradually as possible over the whole bottom of the natural gas deposit.

According to the mode shown, the one or more supply channels 1 are configured to supply gas to the gas field G at a vertical level above the bottom B of the field. Preferably, the one or more supply channels 11 are (each) provided with a series of outflow openings 2, to feed gas to the gas field G at different vertical levels (optionally dosed in height). In this manner, a particularly efficient feed of compensation gases can be achieved. During use, for instance, compensation gas can be passed into the gas field via the one or more supply channels 1 such that the compensation gas N, F reaches both the substratum Si (i.e., the gas field bottom B) and the superstratum S2 (i.e., the gas field top T), and in particular such that the compensation gas N, F forms a barrier between an outer side of each of the one or more supply channels 1 and natural gas g present in the gas field. For this, see Figures 1 and 2.

Use of the apparatus comprises, in particular, a method for compensating extraction of natural gas g from the natural gas field G, in particular to prevent subsidence of strata S2 located above the natural gas field. Supply of compensation gas F, N can be carried out simultaneously with the extraction (i.e., instantaneous discharge) of natural gas g, but this is not essential. It is also possible for compensation gas to be pumped in at a time when natural gas extraction is (temporarily) at a standstill.

In the present, additionally advantageous embodiment, first the inert compensation gas N is supplied to the gas field G, as is shown in Figure 1. The inert compensation gas N can be pressed into the gas field G via a supply channel 1 to prevent pressure decrease. In the drawing, the inert compensation gas N reaches both the bottom B and the top T of the gas field, and can fully enclose an outer side of the supply channel 1 situated in the gas field). The inert compensation gas N forms a column, as it were, at least, a substantially annular or tubular barrier around the supply channel 1. However, this is not essential. The inert compensation gas N may also be introduced into the gas field in such a manner that it initially does not reach the bottom B and/or the top T of the gas field G. Such substantially annular or tubular barrier around the supply channel 1 may, for instance, not be formed until a subsequent (non-inert) compensation gas F is introduced.

After a defined amount of the inert compensation gas N has been pumped into the gas field G, the apparatus switches to introducing the non-inert compensation gas F, which is represented in Figure 2. Here, the inert compensation gas N forms a separation between the natural gas g and the non-inert gas F. Switching from feeding one compensation gas to feeding the other compensation gas can proceed abruptly, or via a gradual switch (for instance, with a mixture of the gases N, F being pumped in during a defined transition period).

Preferably, a separation/barrier (between natural gas g and non-inert gas F) formed by the inert gas has a thickness of a few meters, for instance about 10 meters or more, and for instance a barrier thickness of at least 50 m or at least 100 m. The thickness of the barrier, or at least an associated amount of inert gas to be introduced, depends, for instance, on an amount of non-inert gas to be introduced.

After a defined amount of the inert gas N has been introduced, the non-inert gas F is introduced, preferably via the one or more same supply channels 1 (and respective outflow openings 2). The compensation gases F, N will then fill a local part of the field G extending between a gas field bottom B and gas field top T completely (see Figure 2). The risk of unwanted reaction between natural gas g still present in the natural gas field and the non-inert gas F is obviated by the barrier formed by the inert gas N.

A further effect thus accomplished is that relatively little inert gas N is needed to compensate for the pressure decrease resulting from natural gas extraction. The apparatus shown in Figures 1-2 can further be deployed as an apparatus for storing energy in the gas field G in the form of rising pressure, for instance rising compressed air pressure. Figure 3 shows a further elaboration of this. In particular, the compressed gas volume formed by the compensation gases F, N can serve as energy storage. During use, the apparatus can pump such an amount of non-inert gas F (for example, air) via the one or more supply channels 1 into the gas field G (by one or more compressors 30) that the pressure rises by a few bars relative to an initial pressure (and provides a certain overpressure in the gas field G relative to the initial pressure). This initial pressure can for instance be higher than 50 bar, for instance higher than 80 bar, and be, for instance, approximately 85 bar. The energy required to effect the pressure increase can comprise, for instance, excess energy (for example, residual current) from one or more energy generators, power stations, solar panels, windmills and the like, which excess energy can be used for driving one or more compressors of a first gas source 11.

The energy stored in the gas field G can be exploited in a simple manner by allowing an overpressure in the gas field G to decrease, in particular through discharge of the non-inert gas F (which can proceed, for instance, via one or more supply channels by uncoupling from the gas source and coupling to a gas discharge), or via one or more other channels 1'. Then, with the discharged gas F, an energy generator 31, for example a turbine or the like, can be driven. Exploitation of the energy can for instance comprise a fluctuation / change of the pressure of compensation gas F, N stored in the gas field G, within a defined pressure range, for instance within a

bandwidth of plus or minus one or a few bars calculated from a basic pressure. By allowing relatively low pressure fluctuations during energy storage and energy withdrawal, unwanted soil instability or movement is avoided. It is noted that the one or more compressors 30 can generate heat during use. As shown in Figure 3, it is then advantageous when the apparatus is provided with at least a heat reservoir 35 to store heat that is released in the use of the one or more compressors. Such a heat reservoir can be implemented in different manners, for instance as an underground water reservoir or aquifer to which the compressor heat can be supplied by means of suitable heat exchanging means and heat supply duct(s) 32, which will be clear to the skilled person. In addition, compressor heat can for instance be used for heating homes and or buildings (combined or not combined with tap water heating) by supplying the compressor heat to them via a suitable heat drain 38.

Figure 3 further shows that the apparatus may be provided with at least an electricity generator 31 which is drivable by energy stored in the gas field. This drive may be combined with decompression of gas F discharged from the gas field G. In that case, a particularly energetically favorable implementation is for the apparatus to be configured for at least partly compensating a cooling accompanying this decompression using heat from the heat reservoir. To this end, heat can be removed from the heat buffer 35, via suitable heat exchanger means and one or more drains 33.

Use of the system schematically shown in Figure 3 comprises a method for storing energy, comprising the supply of gas, for example air or nitrogen, or a mixture thereof, to the underground gas field, for instance the natural gas field G. The supplied gas is compressed, an amount of heat thereby released is stored in the heat reservoir 35.

If energy (in particular electricity) is to be generated, the generator

31 is driven. To this end, compressed gas is discharged from the

underground gas field and drives the generator 31. Here, decompression of the gas occurs. Cooling associated with this decompression can at least partly be compensated using heat from the heat reservoir 35. According to a further elaboration of the invention, the

decompressed gas is stored for reuse, for instance for reintroduction into the gas field (after compression). To this end, the apparatus is preferably provided with an additional gas storage (not represented), which can be located above ground or, near the ground level, underground (at least, at a vertical level above the natural gas field G). This is especially advantageous if the gas is not air but, for example, nitrogen, a flue gas and/or the like. If only air is utilized as gas to be decompressed, the air may for instance, after decompression, be released to the surroundings.

To one skilled in the art, it will be clear that the invention is not limited to the examples described. Various modifications are possible within the framework of the invention as set forth in the following claims.

Thus, it follows that the term "gas" in this application is to be understood broadly, and can comprise a gas mixture or gaseous fluid.

Further, supplying gas to the gas field (or the gas deposit) can be achieved in different manners, for instance through supply to a bottom of the field and/or elsewhere, which will be clear to the skilled person.

Preferably, the supply is such that the supplied gas forms a vertical separation in the gas field.

The non-inert gas can for instance be an oxygen containing gas, for example, air.

The inert gas may for instance contain no oxygen, and can for instance consist of a noble gas, nitrogen, carbon dioxide or flue gas, or of a combination of these or other inert gases.

In the context of the present application, "inert gas" may be understood to mean that the gas under normal atmospheric conditions

(20 °C and a pressure of 1 atmosphere) will not undergo a chemical reaction with the natural gas (i.e., risk of explosion is precluded).

In the context of the present application, "non-inert gas" may be understood to mean that the gas under normal atmospheric conditions (20 °C and a pressure of 1 atmosphere) can undergo a chemical reaction with the natural gas (i.e., there is a chance of explosion hazard when this non-inert gas mixes with natural gas).

Claims

1. Apparatus for compensating extraction of natural gas (g) from a natural gas field (G), in particular for preventing subsidence of strata located above the natural gas field and/or earthquakes, comprising:

- one or more supply channels (1) configured to supply compensation gas to the natural gas field; and

- at least a first gas source (11), couplable to the one or more supply channels (1), which contains a non-inert gas (F).

2. The apparatus according to claim 1, wherein the non-inert gas (F) consists of air.

3. The apparatus according to claim 2, wherein the air is ambient or atmospheric air.

4. The apparatus according to any one of the preceding claims, wherein the apparatus is configured for introducing into the gas field (G) per unit time an amount of non-inert gas (F) that is the same as or greater than an amount of natural gas to be extracted from the gas field (G) during that unit time.

5. The apparatus according to any one of the preceding claims, wherein the apparatus is configured for adding an inert gas (N) as a separating layer between natural gas present in the gas field (G) and the non-inert gas (F).

6. The apparatus according to any one of the preceding claims, further comprising at least a second gas source (12), couplable to the supply channels (1), which contains an inert gas (N).

7. The apparatus according to claim 6, wherein the inert gas (N) is nitrogen.

8. The apparatus according to claim 6 or 7, wherein the inert gas (N) comprises flue gas.

9. The apparatus according to any one of the preceding claims, comprising regulating means (5) for regulating compensation gas to be introduced via the one or more supply channels (1) into the natural gas field (G), preferably regulating means which depend on an amount of natural gas (g) to be extracted and/or extracted from the natural gas field.

10. The apparatus according to any one of the preceding claims, comprising one or more supply channels (1) from the ground level (H) up to or/and into the bottom of a natural gas deposit.

11. The apparatus according to claim 10, wherein to the one or more supply channels (1) on the ground level (H) compressed atmospheric air compressors and fittings are coupled for pressing large amounts of compressed atmospheric air (F) through these ducts (1).

12. The apparatus according to claim 10 or 11, comprising an intricate duct system coupled to this supply channel or these supply channels and preferably extending over or in the entire bottom, in which system are, maximally spread, billions of small outflow openings for allowing the supplied compressed atmospheric air to flow out as gradually as possible over the entire bottom of the natural gas deposit.

13. The apparatus according to any one of claims 1- 11, wherein the one or more supply channels (1) are configured to supply gas to the field at a vertical level above a bottom (B) of the gas field (G).

14. The apparatus according to any one of claims 1- 11, wherein the one or more supply channels (1) are provided with a series of outflow openings (2), to supply gas to the gas field (G) at different vertical levels.

15. The apparatus according to any one of the preceding claims, wherein the gas field (G) extends between an underground substratum (Si) and an underground superstratum (S2), and is penetrated by one or more supply channels (1), wherein, during use, compensation gas is introduced into the gas field via the one or more supply channels (1), such that the compensation gas reaches both the substratum and the superstratum, and in particular such that the compensation gas forms a barrier between an outer side of each of the one or more supply channels (1) and natural gas (g) present in the gas field.

16. The apparatus according to any one of the preceding claims, wherein said first gas source (11) comprises one or more compressors, for example air compressors, in particular configured for pressing the non-inert gas (F) through the one or more supply channels (1).

17. The apparatus according to claim 16, wherein said one or more compressors generate heat during operation, the apparatus comprising at least a heat reservoir to store heat that is released in use of the one or more compressors.

18. The apparatus according to any one of the preceding claims, comprising means for storing energy in the gas field (G) in the form of rising pressure, for example, rising compressed air pressure.

19. The apparatus according to claim 18, comprising at least an electricity generator which is drivable by energy stored in the gas field.

20. The apparatus according to claims 17 and 19, wherein said drive is accompanied by decompression of gas discharged from the gas field (G), wherein the apparatus is configured to at least partly compensate cooling accompanying this decompression using heat from the heat reservoir.

21. A method for compensating extraction of natural gas (g) from a natural gas field (G), in particular for preventing subsidence of strata located above the natural gas field, comprising:

- supplying a non-inert compensation gas to the natural gas field.

22. A method according to claim 21, wherein the compensation gas consists of air.

23. A method according to claim 21 or 22, wherein an inert

compensation gas (N) is supplied to the gas field (G) before the non-inert compensation gas (F) is supplied to the gas field (G), in particular such that the inert compensation gas (N) forms a separation between the natural gas (g) and the non-inert gas (F).

24. A method according to any one of claims 21-23, wherein the compensation gas fills a part of this field (G) extending between a gas field bottom (B) and gas field top (T) completely.

25. A method for storing energy, for instance in combination with a method according to any one of claims 21-24, comprising supply of gas, for example air or nitrogen, to an underground gas field, for example natural gas field.

26. A method according to claim 25, comprising compressing the gas, wherein upon compression heat is released, wherein at least a part of the heat released is stored in a heat reservoir.

27. A method for generating electricity, for instance in combination with a method according to any one of claims 21-26, comprising discharge of compressed gas, for example compressed air, from an underground gas field, for example natural gas field, to drive a generator.

28. A method according to claims 26 and 27, wherein the gas is decompressed, wherein a cooling accompanying this decompression is at least partly compensated using heat from the heat reservoir.

29. A method according to claim 28, wherein the decompressed gas is stored.