Ground property adjustment method and hydrocarbon recovery method using the same

Abstract

A ground property adjustment method characterized by: solidifying the ground by proliferating microorganisms, in the ground, that are capable of producing a biological membrane (biofilm), have urease activity, and can cause calcium ions to precipitate as calcium carbonate through decomposition of urea by the urease activity. Microorganisms may precipitate calcium carbonate on the surface of a biological membrane by incorporating carbon dioxide in the environment.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation application of International Application number PCT / JP2023 / 39289, filed on Oct. 31, 2023, which claims priority under 35 U.S.C § 119(a) to Japanese Patent Application No. 2022-195172, filed on Dec. 6, 2022, contents of which are incorporated herein by reference in their entirety.BACKGROUND OF THE INVENTION

[0002] The present disclosure relates to a ground property adjustment method for adjusting properties of the ground, and a hydrocarbon recovery method for recovering hydrocarbons using the ground property adjustment method.

[0003] A method of improving properties such as permeability of the seabed by utilizing carbon dioxide produced by a hydrolytic enzyme reaction of urea is known.

[0004] For example, Japanese Patent No. 6842765 describes a hydrocarbon recovery method for recovering a production fluid containing hydrocarbons from a production well provided in the seabed in which microorganisms that produce carbon dioxide for promoting the deposition of calcium carbonate exist. The hydrocarbon recovery method includes injecting, into the production well, a composition used for producing carbon dioxide by microorganisms, decompressing an inside of the production well after injecting the composition, and recovering the hydrocarbons after lowering internal pressure of the production well.

[0005] Further, WO2021-181881A describes a hydrocarbon recovery method for recovering a production fluid containing hydrocarbons from a production well provided in ground in which Type 1 microorganisms that produce a biological membrane (biofilm) and Type 2 microorganisms that produce carbon dioxide for promoting deposition of calcium carbonate exist. It is described that the hydrocarbon recovery method includes injecting, into the production well, a culture medium for increasing the Type 1 microorganisms, injecting, into the production well, a composition used for producing carbon dioxide by the Type 2 microorganisms, decompressing an inside of the production well after the culture medium and the composition are injected, and recovering the hydrocarbon after lowering internal pressure of the production well.

[0006] In the method described in Japanese Patent No. 6842765, for example, it may be necessary for microorganisms to continue to inject, into the production well, the composition used for carbon dioxide production until the ground solidifies. In addition, in the method described in WO2021-181881A, microorganisms for producing the biological membrane and microorganisms for producing carbon dioxide are utilized to improve the ground property. Therefore, if one of the two types of microorganisms is not present in the seabed, it may be necessary to introduce microorganisms from an external source.

[0007] As a result of intensive studies, the present inventors have found that there are microorganisms capable of producing a biological membrane and having urease activity. The present inventors have found that the microorganisms capable of producing the biological membrane and having urease activity can cause calcium ions to precipitate as calcium carbonate through the decomposition of urea by the urease activity, thereby enabling the solidification of the ground.BRIEF SUMMARY OF THE INVENTION

[0008] Furthermore, the present inventors have also found that the abovementioned microorganisms can precipitate calcium carbonate on the surface of a biological membrane by incorporating carbon dioxide in the environment.

[0009] A ground property adjustment method according to a first aspect of the present disclosure is characterized by: solidifying the ground by proliferating microorganisms, in the ground, that are capable of producing a biological membrane, have urease activity, and can cause calcium ions to precipitate as calcium carbonate through decomposition of urea by the urease activity.

[0010] A hydrocarbon recovery method according to a second aspect of the present disclosure is the hydrocarbon recovery method using a ground property adjustment method which solidifies the ground by proliferating microorganisms, in the ground, that are capable of producing a biological membrane, have urease activity, and can cause calcium ions to precipitate as calcium carbonate through decomposition of urea by the urease activity, the hydrocarbon recovery method including: a first injecting of injecting a culture medium for proliferating the microorganisms into a production well; a second injecting of injecting the urea into the production well; proliferating the microorganisms; decompressing the production well after the first injecting, the second injecting, and the proliferating; and recovering hydrocarbons from the production well.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 illustrates an overview of a hydrocarbon recovery method according to an embodiment.

[0012] FIG. 2 illustrates the overview of the hydrocarbon recovery method of the embodiment.

[0013] FIG. 3 shows the relationship between solution pH and calcium carbonate solubility.

[0014] FIG. 4 shows a configuration of an injection apparatus.

[0015] FIG. 5 is a flowchart showing a process of the ground property adjustment method.

[0016] FIG. 6 shows a configuration of a carbon dioxide storage system according to a second embodiment.

[0017] FIG. 7 shows a plurality of bacterial species for which the ground consolidation effect was confirmed.

[0018] FIG. 8A shows the results of the confirming the growth rate and urease activity of strain Sporosarcina newyorkensis AT1-C 2012, strain Sporosarcina newyorkensis AT1-CW2 2018, and Sporosarcina pasteurii.

[0019] FIG. 8B shows the results of confirming the growth rate and urease activity of strain Sporosarcina newyorkensis AT1-C 2012, strain Sporosarcina newyorkensis AT1-CW2 2018, and Sporosarcina pasteurii.

[0020] FIG. 9 shows the crystallization of calcium carbonate by the growth of Sporosarcina newyorkensis species in a B4 medium.

[0021] FIG. 10 shows examples of colony shapes of the strains Sporosarcina newyorkensis AT1-C 2012 and Sporosarcina newyorkensis AT1-CW2 2018.

[0022] FIG. 11 shows the colony shapes formed by the strains Sporosarcina newyorkensis AT1-C 2012 and Sporosarcina newyorkensis AT1-CW2 2018.DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present disclosure will be described through exemplary embodiments, but the following exemplary embodiments do not limit the disclosure according to the claims, and not all of the combinations of features described in the exemplary embodiments are necessarily essential to the solution means of the disclosure.

[0024] The present disclosure is characterized by proliferating microorganisms, in the ground, that are capable of producing a biological membrane (biofilm), have urease activity, and can cause calcium ions to precipitate as calcium carbonate through the decomposition of urea by their urease activity, thereby solidifying the ground. Hereinafter, as a first embodiment, a hydrocarbon recovery method and a hydrocarbon recovery system using the present ground property adjustment method will be described. Furthermore, as a second embodiment, a case in which the present ground property adjustment method is applied to the carbon dioxide recovery and storage technology will be described.First Embodiment[Overview of the Ground Property Adjustment Method]

[0025] FIGS. 1 and 2 are each a diagram illustrating an overview of the present ground property adjustment method. In FIGS. 1 and 2, a hydrocarbon recovery system 1 and a production well 2 are shown.

[0026] The hydrocarbon recovery system 1 is a system for recovering a production fluid containing hydrocarbons. The hydrocarbon recovery system 1 is an apparatus for recovering, for example, methane hydrate, natural gas, or petroleum as hydrocarbons contained in the seabed. The hydrocarbon recovery system 1 is mounted on a ship for recovering methane hydrate, for example. Hereinafter, a case where hydrocarbon is methane hydrate will be mainly described as an example.

[0027] The hydrocarbon recovery system 1 includes an injection apparatus 11, a recovery apparatus 12, a pressure regulating apparatus 13, and a control apparatus 14. The control apparatus 14 is a computer that controls the injection apparatus 11, the recovery apparatus 12, and the pressure regulating apparatus 13. The control apparatus 14 executes a process for recovering hydrocarbons by executing programs stored in a storage medium or based on an operator's operation.

[0028] The production well 2 is a well for recovering the methane hydrate buried in a methane hydrate layer in the seabed. The production well 2 includes (i) an injection pipe 21 for injecting various substances used to prevent the soil and sand contained in the seabed from flowing into the production well 2, (ii) a recovery pipe 22 for recovering the methane hydrate, and (iii) an opening part 23.

[0029] The present ground property adjustment method is characterized in that the biological membrane (biofilm) is produced on microorganisms that exist in the seabed in order to prevent the soil and sand contained in the seabed from flowing into the production well 2. The biological membrane contains microbial DNA, protein, and metals such as calcium, and has viscous properties. The biological membrane suppresses the movement of seawater within the pores of the seabed.

[0030] The microorganisms used for producing a biological membrane in the present ground property adjustment method have urease activity in addition to being capable of producing the biological membrane. The reaction catalyzed by the urease activity of the microorganisms is represented by the following equations:CO(NH2)2+2H2O→2NH4++CO32−  Equation (1)CO32−+Ca2+→CaCO3 (under high pH conditions)  Equation (2)CO(NH2)2 in Equation (1) is urea. As shown in Equation (1), carbonate ions are produced through the decomposition of urea by the urease activity of the microorganisms. As shown in Equation (2), the carbonate ions react with calcium ions in the environment and precipitate as calcium carbonate.

[0032] Microorganisms precipitate calcium carbonate by incorporating carbon dioxide present in the pore water or pore air of the seabed via the biological membrane they produce. In the present ground property adjustment method, such microorganisms are proliferated in the seabed to solidify it.

[0033] In the present ground property adjustment method, for example, at least one species of microorganism among Sporosarcina newyorkensis (hereinafter, also referred to as S. newyorkensis), Staphylococcus hominis, Lysinibacillus fusiformis, Sporosarcina pasteurii (hereinafter, also referred to as S. pasteurii), or Sporosarcina aquimarina (hereinafter, also referred to as S. aquimarina) is proliferated in the ground. In a preferred example, the S. newyorkensis species is the strain S. newyorkensis AT1-C 2012 or the strain S. newyorkensis AT1-CW2 2018. The strain S. newyorkensis AT1-C 2012 refers to S. newyorkensis collected from the trial well (AT1-C) during the 2012 methane hydrate demonstration project in the Nankai Trough. Also, the strain S. newyorkensis AT1-CW2 2018 refers to S. newyorkensis collected in the trial well (AT1-CW2) during the 2018 methane hydrate demonstration project in the Nankai Trough.

[0034] In the present ground property adjustment method, the above-described microorganisms produce organic acids. The produced organic acids promote the uptake of calcium ions by the microorganisms. The organic acids are, for example, lactic acid or formic acid.

[0035] FIG. 3 shows the relationship between solution pH and calcium ion solubility. The vertical axis of FIG. 3 represents the solubility of calcium ions as a percentage. The horizontal axis of FIG. 3 represents the pH of the solution. The decalcification pH shown in FIG. 3 indicates the pH value at which calcium salts contained in the ground start to dissolve.

[0036] As shown in the graph of FIG. 3, the lower the solution pH, the higher the solubility of calcium ions. When microorganisms metabolize organic substances to produce organic acids, these organic acids lower the pH of the surrounding environment of the microorganisms, making calcium salts (mainly calcium carbonate) contained in the soil more likely to dissolve. Some of the calcium ions released by the dissolution of calcium salts are incorporated by microorganisms and used to precipitate calcium carbonate.

[0037] The present ground property adjustment method promotes production of a biological membrane and calcium carbonate by performing (i) a first injecting step of injecting a culture medium for proliferating microorganisms into the production well 2, (ii) a second injecting step of injecting a composition such as urea, which is decomposed by the microorganisms, into the production well 2, and (iii) a proliferating step of proliferating the microorganisms. The microorganisms precipitate calcium carbonate on the surface of biological membrane by incorporating carbon dioxide from the environment. As a result, the soil and sand in a region “a” near the opening part 23 in the methane hydrate layer, shown in FIGS. 1 and 2, can be solidified.

[0038] According to the present ground property adjustment method, by solidifying the soil and sand in the region “a” using not only calcium carbonate but also a biological membrane, it is possible to prevent the soil and sand from flowing into the hydrocarbon production well while keeping the amount of precipitated calcium carbonate within a predetermined range. When the soil and sand is solidified by the biological membrane, it is easy for the ground to return to its original state after the recovery of the methane hydrate is completed. Therefore, in the present ground property adjustment method, it is possible to reduce damage to the environment as compared to the case of increasing the amount of calcium carbonate to be produced. Furthermore, in the present ground property adjustment method, by solidifying the soil and sand in the region “a” by using not only calcium carbonate but also the biological membrane, it is possible to shorten the time until the soil and sand solidifies.

[0039] In addition, according to the present ground property adjustment method, microorganisms capable of producing a biological membrane and having urease activity are proliferated in the ground to solidify the ground. Since the present ground property adjustment method does not require the use of two or more types of microorganisms, it is possible to reduce the amount or variety of culture media or nutrient salts injected into the ground for proliferation of microorganisms, compared to a case where two or more types of microorganisms are used. Furthermore, in the present ground property adjustment method, if no microorganisms are present in the seabed, it is sufficient to introduce only one type of microorganism into the ground. As a result, the cost required for culturing the microorganisms to be introduced can be reduced compared to a case where two or more types of microorganisms are introduced into the ground. Hereinafter, the configuration and operation of the hydrocarbon recovery system 1 used to implement the ground property adjustment method will be described in detail.[Configuration of the Hydrocarbon Recovery System 1]

[0040] FIG. 4 shows a configuration of the injection apparatus 11. Hereinafter, a method of recovering hydrocarbons by the hydrocarbon recovery system 1 will be described with reference to FIGS. 1, 2 and 4.

[0041] The injection apparatus 11, as shown in FIG. 1, is an apparatus that, before recovering the methane hydrate, injects a composition, which is necessary for preventing soil and sand from flowing into the production well 2, into the production well 2 through the injection pipe 21. The injection apparatus 11 functions as (i) a first injection part that injects the culture medium for increasing the microorganisms into the production well 2 and (ii) a second injection part that injects the composition used for producing carbon dioxide by the microorganisms into the production well 2.

[0042] As shown in FIG. 4, the injection apparatus 11 includes a culture medium tank 111, a urea tank 112, a calcium salt tank 113, a nutrient salt tank 114, a valve 115, a valve 116, a valve 117, a valve 118, and a pump 119. The culture medium tank 111 is a tank for storing a culture medium to be injected into the production well 2. The urea tank 112 is a tank for storing the urea to be injected into the production well 2. The calcium salt tank 113 is a tank for storing the calcium salt to be injected into the production well 2. The nutrient salt tank 114 is a tank for storing the nutrient salts to be injected into the production well 2.

[0043] The valve 115 is a valve for adjusting an amount of the culture medium stored in the culture medium tank 111 to be injected into the production well 2 under the control of the control apparatus 14. The valve 116 is a valve for adjusting an amount of the urea stored in the urea tank 112 to be injected into the production well 2 under the control of the control apparatus 14. The valve 117 is a valve for adjusting an amount of the calcium salt stored in the calcium salt tank 113 to be injected into the production well 2 under the control of the control apparatus 14. The valve 118 is a valve for adjusting an amount of the nutrient salt stored in the nutrient salt tank 114 to be injected into the production well 2 under the control of the control apparatus 14. The pump 119 is a pump for forcing the culture medium, urea, calcium salt, and nutrient salt into the production well 2.

[0044] The injection apparatus 11 increases the activity level at which microorganisms form a biological membrane by adding a culture medium suitable for microorganisms derived from an MH-bearing layer to the ground, by injecting the culture medium into the production well 2. The culture medium to be injected into the production well 2 by the injection apparatus 11 includes, for example, a B4 medium, a T.S.B (Trypticase Soy Broth) medium, an LB medium, or an NH4-YE medium. The B4 medium contains 4.0 g / L yeast extract, 5.0 g / L glucose, and 15.0 g / L agar. When urea is added, the culture medium is prepared by sterilizing the B4 medium and then adding calcium acetate (filter sterilized) to 0.25 wt % and urea (filter sterilized) to 2 wt %.

[0045] The T.S.B medium is prepared by using Difco (registered trademark) Tryptic Soy Agar of a premix type. The LB medium contains 10.0 g / L tryptone, 5.0 g / L yeast extract, 5.0 g / L sodium chloride, and 16.0 g / L agar. The NH4-YE medium contains 20.0 g / L yeast extract, 10.0 g / L (NH4)2SO4, 15.7 g / L 2-amino-2-hydroxymethyl-1,3-propanediol, and 20.0 g / L agar.

[0046] The composition to be injected into the production well 2 by the injection apparatus 11 is a composition used for producing carbon dioxide by microorganisms having urease activity, which hydrolyze urea, and is, for example, urea. Urea is decomposed by microorganisms having urease activity and is used to produce carbon dioxide. The formation of carbon dioxide promotes the deposition of calcium carbonate.

[0047] The injection apparatus 11 may further include a step of injecting a nutrient salt containing a calcium source or the like for the microorganisms into the seabed before or during the proliferating step of proliferating the microorganisms. For example, the nutrient salt is calcium chloride, calcium acetate, or calcium nitrate. As described above, by the injection apparatus 11 injecting nutrient salt, deposition of calcium carbonate by microorganisms can be promoted even in a nutrient-deficient seabed for microorganisms.

[0048] The injection apparatus 11 may inject casein dissolved under alkaline conditions derived from ammonia produced by the hydrolysis reaction of urea into the ground. Casein is difficult to dissolve in a seawater environment alone, but it can be more easily dissolved by utilizing ammonia produced during the hydrolysis of urea. By adding casein dissolved under such alkaline conditions, the viscosity of the soil and sand in the region “a” near the opening part 23 increases, it is possible to prevent the soil and sand from flowing into the hydrocarbon production well due to the flow of seawater or the like.

[0049] The recovery apparatus 12 functions as a recovery part for recovering methane hydrate from the production well 2, and has a pump (not shown) for sucking methane hydrate. Under the control of the control apparatus 14, the recovery apparatus 12 injects (i) the culture medium for the injection apparatus 11 to active the microorganisms and (ii) urea for promoting deposition of calcium carbonate by carbon dioxide produced by the microorganisms. The recovery apparatus 12 starts the recovery of methane hydrate after a predetermined time has passed since the injection of the culture medium and urea. The predetermined time is, for example, a period of time required for the deposition of calcium carbonate due to a reaction between (i) the calcium salt present in the seabed and (ii) the carbon dioxide produced by hydrolysis of urea by the microorganisms having urease activity.

[0050] In this way, the recovery apparatus 12 can recover the methane hydrate in a state in which the soil and sand in the region “a” near the production well 2 in the methane hydrate layer are solidified. As a result, since the soil and sand does not flow into the production well 2 while the recovery apparatus 12 recovers the methane hydrate, the recovery efficiency of the methane hydrate can be improved.

[0051] The pressure regulating apparatus 13 is an apparatus for regulating pressure inside the production well 2 under the control of the control apparatus 14. The pressure regulating apparatus 13 functions as a decompression part that decompresses the inside of the production well 2 to move microorganisms present in the seabed toward the side of the production well 2, or after the first injecting step, the second injecting step, and the proliferating step described above, decompresses the inside of the production well 2 to recover the methane hydrate, for example.

[0052] The opening part 23 is a mesh-like area provided at a position near a tip of the injection pipe 21 on a wall surface of the production well 2. The urea injected through the injection pipe 21 is injected into the seabed from the recovery pipe 22, and the urea is absorbed by the microorganisms in the seabed. It is preferable that the opening part 23 is provided in a part of the seabed around the production well 2 that has high permeability. In this way, the urea can be preferentially injected into the ground where the probability of the soil and sand flowing into the production well 2 is high, and therefore the ground where the probability of the soil and sand flowing into the production well 2 is high can be solidified efficiently.[Method for Promoting Solidification of Seabed]

[0053] In the ground property adjustment method, the following steps may be executed in order to promote solidification of the seabed.(1) Injecting Nutrient Salts

[0054] The ground property adjustment method may further include a step of injecting the nutrient salts serving as the nutrients for the microorganisms to activate hydrolysis of urea by the microorganisms. The nutrient salts are, for example, calcium chloride, calcium acetate, or calcium nitrate. The nutritional salts may include urea. The injection apparatus 11 injects nutrient salts suitable for microorganisms, thereby enhancing their ability to produce a biological membrane. Additionally, the injection apparatus 11 injects nutrient salts suitable for microorganisms, thereby enhancing their ability to hydrolyze urea.(2) Injecting Microorganisms

[0055] In order to increase the amount of carbon dioxide used for the deposition of calcium carbonate, the ground property adjustment method may further include a microorganism injecting step of injecting microorganisms capable of producing a biological membrane and having urease activity. The ground property adjustment method may further include, in order to prepare microorganisms to be injected, a step of culturing the microorganisms to be injected into the production well 2 in an anaerobic environment where water recovered from the production well 2 exists. The step of culturing the microorganisms is performed prior to the microorganism injecting step. In the step of culturing the microorganisms, for example, at least one species of microorganism among S. newyorkensis, Staphylococcus hominis, Lysinibacillus fusiformis, S. pasteurii, or S. aquimarina is cultured. In a preferred example, the S. newyorkensis species includes the strain S. newyorkensis AT1-C 2012 or the strain S. newyorkensis AT1-CW2 2018.

[0056] In the step of culturing microorganisms, microorganisms having the same genetic information as that of microorganisms having a high activity in the seabed may be cultured. By injecting the microorganisms cultured in this manner into the production well 2, the production amount of the biological membrane by the cultured microorganisms and the deposition amount of calcium carbonate increase.[Process of the Ground Property Adjustment Method]

[0057] FIG. 5 is a flowchart showing a process of the ground property adjustment method. First, in order to move the microorganisms present in the seabed toward the side of the production well 2, the control apparatus 14 regulates the internal pressure of the production well 2 to be a first pressure P1 by controlling the pressure regulating apparatus 13 (S11). As the amount of microorganisms existing in the region “a” near the production well 2 increases, the production amount of the biological membrane and the deposition amount of calcium carbonate in the region “a” increase. Therefore, the control apparatus 14 can more effectively prevent the soil and sand from flowing into the production well 2 by lowering the internal pressure of the production well 2 to the first pressure P1.

[0058] Next, by controlling the injection apparatus 11, the control apparatus 14 executes the first injecting step of injecting the culture medium for activating the microorganisms into the production well 2 (S12). Thereafter, the control apparatus 14 waits until the first period of time required for the microorganisms to produce a sufficient amount of biological membrane passes (S13).

[0059] When the first period of time has passed (YES in S13), the control apparatus 14 executes the second injecting step of injecting urea into the production well 2 by controlling the injection apparatus 11 (S14). When the urea is injected by the injection apparatus 11, the microorganisms hydrolyze the urea to produce carbon dioxide. The calcium carbonate is deposited due to a reaction between (i) the injected calcium salt and (ii) carbonate ions based on the carbon dioxide. The control apparatus 14 waits until the second period of time necessary for depositing the calcium carbonate that corresponds to the amount of urea injected by the injection apparatus 11 passes (step S15).

[0060] When the second period of time has passed (YES in S15), the control apparatus 14 regulates the internal pressure of the production well 2 to be the second pressure P2 by controlling the pressure regulating apparatus 13 (S16). The second pressure P2 is a pressure lower than the first pressure P1, for example. If the second pressure P2 is sufficiently low, the methane hydrate present in the high-pressure environment in the seabed moves toward the side of the production well 2. The control apparatus 14 causes the recovery apparatus 12 to recover the methane hydrate that has moved toward the side of the production well 2 (step S17).

[0061] After lowering the internal pressure of the production well 2 to the second pressure P2 and starting the recovery of the methane hydrate, the control apparatus 14 determines whether or not to the recovery of the methane hydrate (S18). When the operator performs an operation to end the recovery of the methane hydrate (YES in S18), the control apparatus 14 ends the recovery of the methane hydrate.

[0062] When it is determined that the operation for completing the recovery of the methane hydrate has not been performed (NO in S18), the control apparatus 14 determines whether or not the amount of the methane hydrate to be recovered within a unit time is equal to or larger than a threshold value (S19). If the amount of the methane hydrate to be recovered within the unit time is equal to or larger than the threshold value (YES in S19), the control apparatus 14 returns to step S17 and continues the recovery of the methane hydrate.

[0063] On the other hand, if the amount of the methane hydrate to be recovered within the unit time is less than the threshold value (NO in S19), the control apparatus 14 returns processing to step S11 and repeats processing from step S11 to step S17. That is, the control apparatus 14 further recovers the methane hydrate after the culture medium and urea are injected into the production well 2. In this way, it is possible to promote the solidification of the seabed at the time when a cavity occurs in the seabed due to the methane hydrate being recovered from the seabed. As a result, the soil and sand can be prevented from flowing into the production well 2 even after the recovery of the methane hydrate has progressed.

[0064] It should be noted that when the amount of methane hydrate to be recovered within the unit time is less than the threshold value in step S19, the control apparatus 14 may return to step S14 instead of step S11 and inject the urea.

[0065] In addition, the control apparatus 14 may wait in a state in which water flow inside the production well 2 is restricted until a predetermined period passes since an execution of the first injecting step. The predetermined period is a period determined on the basis of an amount of the biological membrane required to be produced, and is, for example, two weeks. The control apparatus 14 reduces water flow inside the production well 2 by regulating pressure inside the production well 2 with the pressure regulating apparatus 13, for example. Since the control apparatus 14 reduces the water flow inside the production well 2, it becomes easier for the microorganisms to produce the biological membrane.Second Embodiment

[0066] In the second embodiment, a method for suppressing leakage of carbon dioxide stored in the ground using CCS (Carbon dioxide Capture and Storage) technology, in which carbon dioxide emitted from industrial activities is captured and stored in the ground, will be described. FIG. 6 shows a configuration of a carbon dioxide storage system 200 according to the second embodiment.

[0067] The carbon dioxide storage system 200 differs from the hydrocarbon recovery system 1 of FIG. 1 in that it does not include the recovery apparatus 12 but includes a storage apparatus 201. The storage apparatus 201 injects carbon dioxide, which has been produced and recovered from industrial activities or the like, into a reservoir layer in the ground. The reservoir layer is a geological formation having pores capable of storing carbon dioxide. The ground is not limited to the seabed and may also be on land.

[0068] The injection apparatus 11 injects the same culture medium, such as urea, calcium salt, and nutrient salt, as in the first embodiment into a shielding layer. The shielding layer is a layer that does not allow carbon dioxide to pass through. The injection apparatus 11 injects microorganisms into the shielding layer. Microorganisms are capable of producing biological membranes and have urease activity. The microorganisms are, for example, at least one species among S. newyorkensis, Staphylococcus hominis, Lysinibacillus fusiformis, S. pasteurii, or S. aquimarina.

[0069] The injection apparatus 11 injects microorganisms into a location in the ground where the microorganisms can easily penetrate under pressurized conditions. A place with many pores in the shielding layer is one example of such a location, but it may also be a geological formation other than the shielding layer. By injecting the microorganisms into the location in the ground where the microorganisms easily penetrate under pressurized conditions, the injection apparatus 11 can preferentially inject urea into the ground where the stored carbon dioxide in the reservoir layer has a high likelihood of leaking. Therefore, the injection apparatus 11 can efficiently solidify the ground where there is a high likelihood of stored carbon dioxide leaking.

[0070] In the example of FIG. 6, the injection apparatus 11 injects, in addition to the microorganisms, a culture medium suitable for the microorganisms to be injected into the shielding layer, thereby increasing the activity level at which the microorganisms form a biological membrane. The culture medium is, for example, B4 medium, T.S.B (Trypticase Soy Broth) medium, LB medium or NH4—YE medium. The injection apparatus 11 injects a composition such as urea and a nutrient salt containing a calcium source or the like for the microorganisms into the shielding layer.

[0071] If it is expected that microorganisms will dissipate upon injection of microorganisms, a thickener is added to the infusion fluid used to inject the microorganisms. The thickener is, for example, casein or gellan gum. Since microorganisms are retained together with nutrient salts and the like in the pores of the ground through the effect of the thickener, the microorganisms proliferate in the pores and precipitate calcium carbonate, thereby forming a structure similar to a skeletal structure.

[0072] The microorganisms form this skeleton structure to an extent that prevents the biological membrane from being washed away by water flow or the like. Then, the microorganisms incorporate carbon dioxide through the formed biological membrane, and further precipitate calcium carbonate using the incorporated carbon dioxide. By forming the biological membrane in the pores, the microorganisms clog the pores in the shielding layer of the ground (bioclogging). In this way, the ground property adjustment method of the second embodiment can suppress the leakage of carbon dioxide stored in the ground through the pores of the shielding layer without using conventional water-blocking methods such as water glass.EmbodimentsVerification Experiment 1

[0073] FIG. 7 shows examples of a plurality of microorganisms for which the effect of ground consolidation has been confirmed. FIG. 7 illustrates the changes in adhesion and internal friction angle when S. newyorkensis, Staphylococcus hominis, Lysinibacillus fusiformis, S. pasteurii and S. aquimarina are introduced into the soil. The term “No treatment” in FIG. 7 refers to a control sample in which no microorganisms were added into the soil. The internal friction angle in FIG. 7 represents the resistance of the soil to shear force due to friction between soil particles, expressed in degrees. As shown in the first and second rows from the top of FIG. 7, for each of the microorganisms S. newyorkensis, Staphylococcus hominis, Lysinibacillus fusiformis, S. pasteurii and S. aquimarina, an increase in both adhesion force and internal friction force of the ground was confirmed compared to the case where no microorganisms were added.

[0074] As shown in the third row from the top of FIG. 7, it was found that the sedimentation rate of calcium carbonate increased when the respective microorganisms, S. newyorkensis, Staphylococcus hominis, Lysinibacillus fusiformis, S. pasteurii and S. aquimarina, proliferated in the soil. This suggests that the ability of S. newyorkensis to precipitate calcium carbonate contributes to the increase in adhesion force and internal friction forces in the soil.Verification Experiment 2

[0075] Two strains of S. newyorkensis isolated as urease-producing bacteria were investigated for properties associated with the MICP (Microbially-induced carbonate precipitation) method, in which calcium carbonate was precipitated into the pores of the ground to solidify the ground using the hydrolytic action of urea.

[0076] FIGS. 8A and 8B each show the results of confirming the growth rate and urease activity of strain Sporosarcina newyorkensis AT1-C 2012, (hereinafter also referred to as microorganism A), strain Sporosarcina newyorkensis AT1-CW2 2018, (hereinafter also referred to as microorganism B), and Sporosarcina pasteurii (hereinafter also referred to as microorganism C). First, each of the microorganisms A, B, and C was cultured overnight at 30° C. in 2 mL of LB+2% urea medium. After washing the bacterial cells with a culture medium that did not contain urea, the bacterial cells were added to 1 mL of an LB medium, and the medium was resuspended. The concentration of the bacterial cells was adjusted so that the suspension reached an absorbance of 0.05 under irradiation with light at a wavelength of 600 nanometers in 10 mL of an LB medium (pH of 7.0) or LB+2% urea medium, and then the cultivation of the bacterial cells was started. During this period, change over time in the turbidity (absorbance at a wavelength of 600 nanometers) of the culture medium was measured.

[0077] The microorganisms A, B, and C were cultured in the LB medium under conditions with urea addition (indicated by white markers and dashed lines) or without urea addition (indicated by black markers and solid lines). As shown in FIG. 8A, microorganisms A and B, which are considered usable in the MICP method, were found not to require urea for proliferation (FIG. 8A). However, the growth of microorganisms A and B slowed under conditions without urea addition.

[0078] It was confirmed that the addition of urea was necessary for the proliferation of microorganism C, a closely related species that has often been used in the MICP method. Therefore, although it is preferable to add urea for the formation of a biological membrane by microorganisms A and B, the addition of urea is suggested to not be essential. In contrast, the addition of urea is suggested to be essential for the formation of biological membrane by microorganism C.

[0079] FIG. 8B shows the change over time in pH when microorganisms A, B, and C were cultured under conditions with urea addition (indicated by white markers and broken lines) and without urea addition (indicated by black markers and solid lines). The same cultivation method as in FIG. 8A was performed, and pH was measured using LAQUAact, (Horiba, Japan). Regarding the urease activity, which is considered important for MICP, it was confirmed that, as with microorganism C, the pH of the culture medium was increased by adding urea to the culture medium in microorganisms A and B. Therefore, it was strongly suggested that microorganisms A and B produce ammonia as a by-product by decomposing added urea through the catalytic action of urease, as shown in the above Equation (1) (FIG. 8B).Verification Experiment 3

[0080] To observe important calcium carbonate deposition and biomineralization for MICP, S. newyorkensis species were cultured using B4 medium to observe whether calcium carbonate precipitated.

[0081] FIG. 9 shows the crystallization of calcium carbonate by proliferation of S. newyorkensis species in B4 medium. After microorganism A (upper side in FIG. 9) and microorganism B (lower side in FIG. 9) were cultured overnight in the LB medium, the absorbance at a wavelength of 600 nanometers was measured, diluted so that the absorbance at a wavelength of 600 nanometers was 1.0, and further diluted to ⅕. The diluted culture solution was dropped onto 5 μl of B4 medium under the condition of adding CaCl2 (right side of FIG. 9) or not adding CaCl2 (left side of FIG. 9). The cells were cultured under aerobic conditions at 30° C. for 4 days and then observed.

[0082] In the sample on the right side of FIG. 9, the point-like material distributed throughout the culture medium indicates crystals. Biological membranes are shown in the lower left corner of each sample in FIG. 9. As shown in FIG. 9, crystals were formed only in the B4 medium containing CaCl2. Crystals formed widely throughout the medium as well as in the S. newyorkensis colonies. As a result of culturing in the B4 medium, both microorganism A and microorganism B produced crystals in the culture medium. The formation of this crystal did not occur when CaCl2 was removed from the B4 medium (FIG. 9, left). This result strongly suggests that the crystal contains Ca.

[0083] Crystals were widely distributed throughout the culture medium as well as in the colonies. This result may suggest that not only does the strain incorporate calcium into the colony, but that chemical CaCO3 crystallization occurs throughout the culture medium due to the increased pH of the medium. Therefore, it is possible that carbon dioxide can be fixed in the culture medium. With respect to this phenomenon, there was no significant difference between microorganism A and microorganism B.

[0084] As described above, it was confirmed that microorganisms A and B precipitate CaCO3 in the B4 medium under conditions in which CaCl2 was added to the B4 medium. At this time, crystals are formed not only in the colonies but also around the colonies. Therefore, it can be seen that the crystals are formed due to a change in the environment of the culture medium (strong alkali) rather than being produced by the microorganisms.

[0085] FIG. 10 shows examples of colony shapes of microorganism A and microorganism B. Microorganism A and microorganism B were each cultured in LB medium to form colonies. The left side of FIG. 10 shows a colony of microorganism A, and the right side of FIG. 10 shows a colony of microorganism B. It was confirmed that a biological membrane was formed in each of the colonies.

[0086] FIG. 11 shows the colony shapes formed by microorganisms A and B. The left side of FIG. 11 shows the colony of microorganism A, and the right side of FIG. 11 shows the colony of microorganism B. Microorganisms A and B were cultured under microaerobic conditions, where the carbon dioxide concentration was higher than that of the atmosphere, with calcium chloride added to T.S.B medium. In both the colonies on the left and right sides of FIG. 11, a biological membrane was formed, and it was confirmed that calcium carbonate crystals had precipitated on the surface of the formed biological membrane.[Effects of the Present Ground Property Adjustment Method]

[0087] According to the present ground property adjustment method, microorganisms capable of producing a biological membrane and having urease activity are proliferated in the ground to solidify the ground. Since the present ground property adjustment method does not require the use of two or more types of microorganisms, it is possible to reduce the amount or variety of culture media or nutrient salts injected into the ground for proliferation of microorganisms, compared to a case where two or more types of microorganisms are used. Furthermore, if no microorganisms are present in the seabed, it is sufficient to introduce only one type of microorganism into the ground. As a result, the cost required for culturing the microorganisms to be introduced can be reduced compared to a case where two or more types of microorganisms are introduced into the ground.

[0088] The present disclosure is explained on the basis of the exemplary embodiments. The technical scope of the present disclosure is not limited to the scope explained in the above embodiments and it is possible to make various changes and modifications within the scope of the disclosure. For example, all or part of the apparatus can be configured with any unit which is functionally or physically dispersed or integrated. Further, new exemplary embodiments generated by arbitrary combinations of them are included in the exemplary embodiments of the present disclosure. Further, effects of the new exemplary embodiments brought by the combinations also have the effects of the original exemplary embodiments.

Claims

1. Aground property adjustment method comprising:solidifying the ground by proliferating microorganisms, in the ground, that are capable of producing a biological membrane, have urease activity, and can cause calcium ions to precipitate as calcium carbonate through decomposition of urea by the urease activity.

2. The ground property adjustment method according to claim 1, wherein the microorganisms precipitate calcium carbonate on a surface of the biological membrane by incorporating carbon dioxide in the environment.

3. The ground property adjustment method according to claim 1, wherein, as the microorganisms, at least one of Sporosarcina newyorkensis species, Staphylococcus hominis species, Lysinibacillus fusiformis species, Sporosarcina pasteurii species, or Sporosarcina aquimarina species is proliferated in the ground.

4. The ground property adjustment method according to claim 1, wherein, as the microorganisms, Staphylococcus hominis species or Lysinibacillus fusiformis species is proliferated in the ground.

5. The ground property adjustment method according to claim 1, further comprising:injecting a nutrient salt containing a calcium source into the ground before or during proliferating the microorganisms.

6. The ground property adjustment method according to claim 1, further comprising:injecting casein dissolved under alkaline conditions derived from ammonia produced by hydrolysis reaction of urea into the ground.

7. The ground property adjustment method according to claim 1, wherein the microorganisms produce organic acids, and the organic acids promote uptake of calcium ions by the microorganisms.

8. A hydrocarbon recovery method using a ground property adjustment method which solidifies the ground by proliferating microorganisms, in the ground, that are capable of producing a biological membrane, have urease activity, and can cause calcium ions to precipitate as calcium carbonate through decomposition of urea by the urease activity, the hydrocarbon recovery method comprising:a first injecting of injecting a culture medium for proliferating the microorganisms into a production well;a second injecting of injecting the urea into the production well;proliferating the microorganisms;decompressing the production well after the first injecting, the second injecting, and the proliferating; andrecovering hydrocarbons from the production well.

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