CN117948097A - Combustible ice safe exploitation system and method based on reservoir transformation - Google Patents
Combustible ice safe exploitation system and method based on reservoir transformation Download PDFInfo
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Abstract
The invention discloses a combustible ice safe exploitation system and a method based on reservoir transformation, which relate to the technical field of marine natural gas hydrate exploitation and comprise the steps of arranging a combustible ice safe exploitation system; extracting pore fluid of the overlying sedimentary deposit by using a first branch production well, and injecting liquid carbon dioxide mixed liquid by using a first branch injection well to construct a carbon dioxide hydrate cap layer to carry out geological repair on the overlying sedimentary deposit; extracting the combustible ice in the pores of the combustible ice reservoir by using a second branch production well, and injecting seawater through a second branch injection well to accelerate the decomposition of the combustible ice; when the third preset condition is reached, stopping the combustible ice exploitation operation, and injecting liquid carbon dioxide mixed liquid through a second branch injection well to carry out geological repair on the combustible ice reservoir; finally, the bottom hole cavity of the horizontal injection well and the horizontal production well is filled. According to the invention, double-layer geological repair is carried out on the overlying sedimentary layer and the combustible ice reservoir, so that stratum collapse and large-scale methane leakage are avoided, and safe and efficient development of the combustible ice is realized.
Description
Technical Field
The invention relates to the technical field of marine natural gas hydrate exploitation, in particular to a combustible ice safe exploitation system and method based on reservoir transformation.
Background
Natural gas hydrate, also known as combustible ice, is a unique non-stoichiometric crystalline compound, one of the most abundant natural gas sources on earth. The combustible ice consists of water molecules connected by hydrogen bonds and gas molecules mainly comprising CH4, wherein most of the combustible ice is distributed in the submarine sediment. Combustible ice is considered an important alternative energy source due to the great methane reserves, high energy density, clean combustion, and other advantages.
Depressurization to produce hydrates is considered the most viable method. However, unlike conventional oil and gas resources, combustible ice is buried in the subsea sediment in solid form, having a certain cementing and skeletal support effect on sediment particles; in addition, the upper cover layer of the combustible ice reservoir is usually not formed into rock or trapped, and has the characteristic of high permeability. In the large-scale depressurization exploitation process, besides the danger of massive invasion of overlying seawater, the danger of decomposition phase change of combustible ice can exist to damage the stability of a reservoir and an overlying layer structure, and geological and environmental disasters such as stratum collapse, submarine landslide, methane leakage and the like can be caused. Because of the huge methane reserves, the methane released by the instantaneous decomposition of only one thousandth of combustible ice in the ocean in the world can exceed 4% of the total annual emission of methane in the world, and a large amount of leaked methane can cause ocean acidification to exacerbate climate warming. Therefore, in the development process of the combustible ice, the formation stability is maintained, and the large-scale methane leakage is prevented, so that the key for realizing the safe and efficient development of the combustible ice is realized.
Compared with combustible ice exploitation methods such as a depressurization method and a heat shock method, the CH4-CO 2 hydrate displacement development has unique advantages in maintaining the stability of ocean stratum and guaranteeing the safety development of combustible ice, can realize the collection of CH4, can realize the long-term ocean sealing of greenhouse CO 2 gas, and has win-win effect. However, this method has serious problems of low replacement efficiency, small replacement area, and easy blockage of the replacement process.
Disclosure of Invention
The invention provides a combustible ice safety exploitation system and a method based on reservoir transformation, which are used for overcoming the defect that safety is hidden in the combustible ice exploitation process in the prior art, and can prevent the invasion of overlying seawater, maintain the stratum stability and prevent methane from leaking to the seawater environment in the combustible ice exploitation process, and greatly improve the exploitation efficiency while improving the combustible ice exploitation safety.
In order to solve the technical problems, the technical scheme of the invention is as follows:
The invention provides a combustible ice safe exploitation system based on reservoir reconstruction, which comprises a horizontal injection unit, a horizontal production unit and an environment monitoring unit;
The horizontal injection unit comprises a horizontal injection well, an injection controller, a first branch injection well, a second branch injection well, a first liquid storage tank, a second liquid storage tank, a first injection switch valve and a second injection switch valve;
The input end of the horizontal injection well is respectively connected with the first liquid storage tank and the second liquid storage tank, and the output end of the horizontal injection well is respectively connected with the input end of the first branch injection well and the input end of the second branch injection well; the first injection switch valve is arranged at the input end of the first branch injection well, the second injection switch valve is arranged at the input end of the second branch injection well, and the control ends of the first injection switch valve and the second injection switch valve are connected with the injection controller;
The horizontal production unit comprises a horizontal production well, a production controller, a first branch production well, a second branch production well, a first production switch valve and a second production switch valve;
The input end of the horizontal production well is respectively connected with the output end of the first branch production well and the output end of the second branch production well; the first production switching valve is arranged at the output end of the first branch production well, the second production switching valve is arranged at the output end of the second branch production well, and the control ends of the first production switching valve and the second production switching valve are connected with the production controller;
The environment monitoring unit is arranged on the surface of the overlying deposition layer and is in communication connection with the injection controller and the production controller.
Preferably, the horizontal injection unit further comprises first shaft heaters uniformly distributed on the shaft wall surface of the horizontal injection well; the control end of the first shaft heater is connected with the injection controller;
The horizontal production unit further comprises second shaft heaters which are uniformly distributed on the shaft wall surface of the horizontal production well; the control end of the second shaft heater is connected with a production controller.
The first and second wellbore heaters are used to prevent the formation of solid hydrates in a horizontal injection well or a horizontal production well during carbon dioxide hydrate cap formation or flammable ice production, resulting in wellbore plugging.
Preferably, the horizontal injection unit further comprises a first injection nozzle and a second injection nozzle;
the input end of the first injection nozzle is connected with the output end of the first branch injection well; the input end of the second injection nozzle is connected with the output end of the second branch injection well;
The first injection nozzle and the second injection nozzle are multidirectional injection nozzles.
The multi-directional injection nozzle is used for reducing the occurrence probability of fluid stagnation caused by overlarge resistance due to local large flow when the first branch injection well and the second branch injection well are used for injecting liquid, and is beneficial to transporting and diffusing the injected liquid around.
Preferably, the first liquid storage tank is used for storing liquefied carbon dioxide mixed liquor;
the liquefied carbon dioxide mixed solution comprises liquid carbon dioxide, a carbon dioxide hydrate formation inhibitor and a carbon dioxide hydrate formation promoter;
The carbon dioxide hydrate inhibitor comprises one or more of polyvinylpyrrolidone, polyvinylcaprolactam and hydroxy terminated polycaprolactam;
the carbon dioxide hydrate promoter comprises leucine.
Preferably, the concentration of the carbon dioxide hydrate formation inhibitor is 300 to 10000ppm; the concentration of the carbon dioxide hydrate formation promoter is 50-1000 ppm.
Liquid carbon dioxide has a greater ability to flow and diffuse in the sediment pores relative to gaseous carbon dioxide; although the carbon dioxide hydrate formation inhibitor and the carbon dioxide hydrate formation promoter have opposite effects on the formation rate of the carbon dioxide hydrate, the effect of prolonging the nucleation time of the carbon dioxide hydrate and loosening the formation state of the carbon dioxide hydrate to increase the diffusion range can be achieved through the regulation of the dosage ratio. The carbon dioxide hydrate inhibitor is a kinetic inhibitor, so that the nucleation time for converting liquid carbon dioxide into solid carbon dioxide hydrate can be obviously prolonged, the generation rate of the carbon dioxide hydrate is delayed, and the phenomenon that the liquid carbon dioxide generates a large amount of hydrates too early to transport to a remote place is avoided; although the carbon dioxide hydrate formation promoter can slightly accelerate the nucleation of carbon dioxide hydrate, the formed carbon dioxide hydrate state can be obviously loosened so as to ensure that sediment pores are not seriously blocked even if solid carbon dioxide hydrate is generated in the injection process, so that the liquid carbon dioxide water is promoted to be further conveyed to a far place. Comparing the concentrations of the carbon dioxide hydrate formation inhibitor and the carbon dioxide hydrate formation promoter, it can be seen that the carbon dioxide hydrate formation inhibitor is 1 order of magnitude of the carbon dioxide hydrate formation promoter, so that better nucleation inhibition of the carbon dioxide hydrate is obtained by a higher amount of the inhibitor concentration, while a lower amount of the promoter is only to loosen the generated carbon dioxide hydrate, otherwise, too high a concentration of the promoter may cause the carbon dioxide hydrate to form earlier, thereby resulting in a deterioration in the diffusion capacity of the carbon dioxide.
Preferably, the second tank is used for storing seawater; the temperature of the seawater is 45-65 ℃.
The seawater with the temperature of 45-65 ℃ is used for heat shock, the temperature of the injected seawater is too low to achieve a good heat shock effect, the temperature is too high, and the heat loss is serious; by taking in the on-site seawater and heating to 45-65 ℃, the method can accelerate the decomposition of the combustible ice and has higher heat utilization efficiency.
Preferably, the system further comprises a number of pressure sensors;
the pressure sensors are uniformly arranged on the wall surface of the shaft of the horizontal injection well and the horizontal production well, which are positioned on the part of the upper deposition layer.
The surrounding of the shaft is a methane leakage frequency high-frequency area, and the pressure of each layer of the sediment in the longitudinal direction can be obtained in real time by installing the pressure sensor in the vertical direction of the shaft, so that the shaft damage and methane leakage caused by overlarge layer pressure difference are prevented.
Preferably, the environment monitoring unit comprises a plurality of submarine settlement monitors and a plurality of methane sensors;
The seabed sedimentation monitor and the methane sensor are uniformly arranged on the surface of the overlying sedimentary layer.
The submarine settlement monitor and the methane sensor are respectively used for monitoring submarine landslide geological events and methane leakage events in the combustible ice exploitation process.
The invention also provides a combustible ice safe exploitation method based on reservoir reconstruction, which comprises the following steps of:
S1: selecting a combustible ice mining development target area to set up the combustible ice safety mining system, comprising: the horizontal injection well and the horizontal production well sequentially penetrate through the sea water layer, the overlying sedimentary layer and the flammable ice reservoir; the output end of the first branch injection well is arranged in the overlying sediment layer, and the output end of the second branch injection well is arranged in the flammable ice reservoir; the input end of the first branch production well is arranged in the overlying sediment layer, and the input end of the second branch production well is arranged in the flammable ice reservoir layer; uniformly arranging a plurality of submarine sedimentation monitors and methane sensors on the surface of the overlying sedimentary layer;
S2: the first production switching valve is controlled to be opened by the production controller, and the first branch production well extracts interstitial fluid in sediment to reduce pressure; the first injection switch valve is controlled to be opened by the injection controller, liquefied carbon dioxide mixed liquid in the first liquid storage tank is injected into the upper deposition layer through the horizontal injection well and the first branch injection well, and the liquefied carbon dioxide mixed liquid flows in the upper deposition layer and forms a carbon dioxide hydrate cover layer under the driving of the pressure difference of the first branch injection well and the first branch production well; when a first preset condition is reached, the first production switch valve is controlled to be closed by the production controller, and the first injection switch valve is controlled to be closed by the injection controller;
S3: the second production switch valve is controlled to be opened by the production controller, pore fluid in the combustible ice storage layer is extracted by the second branch production well, and depressurization exploitation is carried out on the combustible ice; when the second preset condition is reached, the second injection switch valve is controlled to be opened by the injection controller, and the seawater in the second liquid storage tank is intermittently injected into the flammable ice storage layer through the horizontal injection well and the second branch injection well;
S4: when the third preset condition is reached, the second production switch valve is controlled to be closed by the production controller, and the exploitation of the combustible ice is finished; the liquefied carbon dioxide mixed liquid in the first liquid storage tank is controlled to be switched through the injection controller, and is injected into the combustible ice storage layer through the horizontal injection well and the second branch injection well;
s5: filling the bottom hole cavity of the horizontal injection well and the horizontal production well.
Preferably, in the step S2, the injection pressure driving force of the first branch injection well is 1 to 4MPa. The injection pressure driving force of the first branch injection well cannot enable the overlying deposit layer to be subjected to stress deformation, and the injection pressure driving force refers to a value that the injection pressure is higher than the initial pressure of the overlying layer, namely, the injected liquefied carbon dioxide mixture is in a high-pressure liquid state. By having the injection pressure higher than the overburden pressure, fluid transport can be driven distally under local pressure differentials.
Preferably, in the step S2, the depressurization amplitude of the first branch production well is 1 to 4MPa. The depressurization pressure of the first branch production well cannot cause stress deformation of the overlying deposit layer and is higher than the equilibrium pressure of combustible ice decomposition in the combustible ice reservoir.
The stress deformation of the upper coating is mainly related to the non-uniform local pressure, and as other coating layers are not arranged above the upper coating deposition layer, once the stress deformation possibly causes the rupture of the reservoir, the leakage of CH 4 free gas in the combustible ice reservoir is induced, so that the occurrence of large deformation is avoided.
Preferably, in the step S2, the pressure difference between the first branch injection well and the first branch production well is 2 to 8MPa.
Preferably, in the step S3, the process of depressurization exploitation of the combustible ice by the second branch production well is constant-speed depressurization; the depressurization rate is 1-2 MPa/day.
The constant-speed depressurization is realized by controlling the reservoir fluid extraction rate, so that the production pressure is basically kept to be reduced at a constant speed, and the depressurization rate is reasonably regulated and controlled, so that formation deformation and massive sand discharge caused by too fast or uneven depressurization can be avoided, and the production efficiency of the combustible ice can be improved.
Preferably, the first preset condition is: the output rate of the liquefied carbon dioxide mixed solution of the first branch production well is 30% of the injection rate of the liquefied carbon dioxide mixed solution of the first branch injection well;
the second preset condition is: the second branch production well extracts pore fluid in the combustible ice storage layer, and the production pressure of the pore fluid in the combustible ice storage layer is reduced to a constant pressure; the constant pressure is 3-5 MPa;
the third preset condition is: the average combustible ice daily collection amount of the second branch production well is continuously lower than a preset collection amount for 3 days, and the preset collection amount is 500m 3/day.
For the first preset condition, due to the existence of the pressure difference between the first branch injection well and the first branch production well region, the liquefied carbon dioxide mixed solution continuously flows from the high-pressure injection region to the low-pressure production region, wherein a part of liquid carbon dioxide stays in the upper deposition layer in the process to form carbon dioxide hydrate, and a part of liquid carbon dioxide flows into the first branch production well and is produced, when the production rate reaches a set value of 30%, the liquid carbon dioxide basically covers a path from the high-pressure region to the low-pressure region, and a relatively complete carbon dioxide hydrate cover layer can be formed.
For the third preset condition, because intermittent blockage may exist in the development process of the combustible ice, daily gas production for 3 consecutive days is taken as a judgment standard to eliminate the influence of intermittent blockage.
In step S4, the injected liquefied carbon dioxide mixed solution is used to form carbon dioxide hydrate in the combustible ice reservoir to perform formation remediation on the combustible ice reservoir, so that methane leakage in the later period of the end of exploitation is avoided. Compared with the injection of liquefied carbon dioxide during the production of the combustible ice, the injection after the production is finished can reduce the inhibiting effect on the decomposition of the combustible ice after the generation of the carbon dioxide hydrate, increase the decomposition yield of the combustible ice and improve the sealing efficiency of the carbon dioxide hydrate.
Preferably, before the step S3, the horizontal injection unit and the horizontal production unit are further closed for several days, so that the carbon dioxide hydrate cap layer is aged and densified.
Preferably, in step S5, cement is injected into the horizontal injection well and the horizontal production well to fill the bottom hole cavity. Because the vicinity of the drilling area is a high-incidence area of methane leakage, cement is injected into the bottom of the well on the basis of repairing the combustible ice reservoir by the carbon dioxide hydrate, and the occurrence of methane leakage can be further avoided.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
Firstly, setting a combustible ice safety exploitation system in a target area of a selected combustible ice mineral exploitation target; then, extracting pore fluid of the overburden deposit by using a first branch production well, and injecting liquid carbon dioxide mixed liquid by using a first branch injection well to construct a carbon dioxide hydrate cap layer to carry out geological repair on the overburden deposit, so that the overburden deposit has strong supporting capability, collapse of the overburden deposit is prevented, invasion of overburden seawater is avoided, formation stability is maintained, and methane leakage to the overburden seawater environment is prevented; then, extracting the combustible ice in the pores of the combustible ice reservoir by using a second branch production well, and injecting seawater through a second branch injection well to accelerate the decomposition of the combustible ice when the second preset condition is reached; when the third preset condition is reached, stopping the combustible ice exploitation operation, injecting liquid carbon dioxide mixed solution through a second branch injection well, carrying out geological restoration on the combustible ice reservoir, avoiding the situation of methane leakage in the later period of the exploitation end, and simultaneously increasing the hydrate replacement efficiency and the carbon dioxide submarine sealing capacity; finally, filling the bottom hole of the horizontal injection well and the horizontal production well, and further avoiding the occurrence of methane leakage. According to the invention, double-layer geological repair is carried out on the overlying sedimentary layer and the combustible ice reservoir, so that stratum collapse and large-scale methane leakage are avoided, and safe and efficient development of the combustible ice is realized.
Drawings
FIG. 1 is a schematic diagram of a reservoir retrofit-based combustible ice safety mining system according to example 1;
FIG. 2 is a schematic diagram of a reservoir retrofit-based combustible ice safety mining system according to example 2;
FIG. 3 is a flow chart of a method for safe exploitation of combustible ice based on reservoir reformation as described in example 3;
In the figure, 1-horizontal injection well, 2-injection controller, 3-first branch injection well, 4-second branch injection well, 5-first liquid storage tank, 6-second liquid storage tank, 7-first injection switch valve, 8-second injection switch valve, 9-horizontal production well, 10-production controller, 11-first branch production well, 12-second branch production well, 13-first production switch valve, 14-second production switch valve, 15-first injection nozzle, 16-second injection nozzle, 17-pressure sensor, 18-seabed sedimentation monitor, 19-methane sensor.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
For the purpose of better illustrating the embodiments, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the actual product dimensions;
It will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical scheme of the invention is further described below with reference to the accompanying drawings and examples.
Example 1
The embodiment provides a combustible ice safe exploitation system based on reservoir reformation, which comprises a horizontal injection unit, a horizontal production unit and an environment monitoring unit, as shown in fig. 1;
The horizontal injection unit comprises a horizontal injection well 1, an injection controller 2, a first branch injection well 3, a second branch injection well 4, a first liquid storage tank 5, a second liquid storage tank 6, a first injection switch valve 7 and a second injection switch valve 8;
The input end of the horizontal injection well 1 is respectively connected with the first liquid storage tank 5 and the second liquid storage tank 6, and the output end of the horizontal injection well 1 is respectively connected with the input end of the first branch injection well 3 and the input end of the second branch injection well 4; the first injection switch valve 7 is arranged at the input end of the first branch injection well 3, the second injection switch valve 8 is arranged at the input end of the second branch injection well 4, and the control ends of the first injection switch valve 7 and the second injection switch valve 8 are connected with the injection controller 2;
The horizontal production unit comprises a horizontal production well 9, a production controller 10, a first branch production well 11, a second branch production well 12, a first production switch valve 13 and a second production switch valve 14;
The input end of the horizontal production well 9 is respectively connected with the output end of the first branch production well 11 and the output end of the second branch production well 12; the first production switch valve 13 is arranged at the output end of the first branch production well 11, the second production switch valve 14 is arranged at the output end of the second branch production well 12, and the control ends of the first production switch valve 13 and the second production switch valve 14 are connected with the production controller 10;
the environmental monitoring unit is disposed on the surface of the overlying deposit and is in communication with the injection controller 2 and the production controller 10.
Example 2
The embodiment provides a combustible ice safe exploitation system based on reservoir reformation, which comprises a horizontal injection unit, a horizontal production unit and an environment monitoring unit as shown in fig. 2;
The horizontal injection unit comprises a horizontal injection well 1, an injection controller 2, a first branch injection well 3, a second branch injection well 4, a first liquid storage tank 5, a second liquid storage tank 6, a first injection switch valve 7, a second injection switch valve 8, a first shaft heater, a first injection nozzle 15 and a second injection nozzle 16;
The input end of the horizontal injection well 1 is respectively connected with the first liquid storage tank 5 and the second liquid storage tank 6, and the output end of the horizontal injection well 1 is respectively connected with the input end of the first branch injection well 3 and the input end of the second branch injection well 4; the output end of the first branch injection well 3 is connected with the input end of the first injection nozzle 15, and the output end of the second branch injection well 4 is connected with the input end of the second injection nozzle 16;
The first injection switch valve 7 is arranged at the input end of the first branch injection well 3, the second injection switch valve 8 is arranged at the input end of the second branch injection well 4, and the control ends of the first injection switch valve 7 and the second injection switch valve 8 are connected with the injection controller 2; the first shaft heaters are uniformly distributed on the shaft wall surface of the horizontal injection well 1; the control end of the first shaft heater is connected with the injection controller 2;
In this embodiment, the first injection nozzle 15 and the second injection nozzle 16 are all multi-directional injection nozzles;
The first liquid storage tank 5 is used for storing liquefied carbon dioxide mixed liquor;
the liquefied carbon dioxide mixed solution comprises liquid carbon dioxide, a carbon dioxide hydrate formation inhibitor and a carbon dioxide hydrate formation promoter;
The carbon dioxide hydrate inhibitor comprises one or more of polyvinylpyrrolidone, polyvinylcaprolactam and hydroxy terminated polycaprolactam;
the carbon dioxide hydrate promoter comprises leucine.
The concentration of the carbon dioxide hydrate formation inhibitor is 300-10000 ppm; the concentration of the carbon dioxide hydrate formation promoter is 50-1000 ppm.
The second liquid storage tank 6 is used for storing seawater; the temperature of the seawater is 45-65 ℃.
The horizontal production unit comprises a horizontal production well 9, a production controller 10, a first branch production well 11, a second branch production well 12, a first production switch valve 13, a second production switch valve 14 and a second shaft heater;
The input end of the horizontal production well 9 is respectively connected with the output end of the first branch production well 11 and the output end of the second branch production well 12; the first production switch valve 13 is arranged at the output end of the first branch production well 11, the second production switch valve 14 is arranged at the output end of the second branch production well 12, and the control ends of the first production switch valve 13 and the second production switch valve 14 are connected with the production controller 10; the second shaft heaters are uniformly distributed on the shaft wall surface of the horizontal production well 9; the control end of the second shaft heater is connected with the production controller 10;
the system further comprises a number of pressure sensors 17;
the pressure sensors 17 are uniformly arranged on the wall surface of the shaft of the horizontal injection well 1 and the horizontal production well 9, which are positioned on the part of the upper deposition layer;
The environmental monitoring unit comprises a plurality of submarine settlement monitors 18 and a plurality of methane sensors 19; the seabed sedimentation monitor 18 and the methane sensor 19 are uniformly arranged on the surface of the overlying sedimentary layer, and are in communication connection with the injection controller 2 and the production controller 10.
In particular implementations, the first wellbore heater and the second wellbore heater are used to prevent the formation of solid hydrates in a horizontal injection well or a horizontal production well during carbon dioxide hydrate cap formation or flammable ice production, resulting in wellbore plugging. The multi-directional injection nozzle is used for reducing the occurrence probability of fluid stagnation caused by overlarge resistance due to local large flow when the first branch injection well and the second branch injection well are used for injecting liquid, and is beneficial to transporting and diffusing the injected liquid around. The surrounding of the shaft is a methane leakage frequency high-frequency area, and the pressure of each layer of the sediment in the longitudinal direction can be obtained in real time by installing the pressure sensor in the vertical direction of the shaft, so that the shaft damage and methane leakage caused by overlarge layer pressure difference are prevented. The submarine settlement monitor and the methane sensor are respectively used for monitoring submarine landslide geological events and methane leakage events in the combustible ice exploitation process.
Example 3
The embodiment provides a method for safely exploiting combustible ice based on reservoir reformation, which is based on the exploitation system of the embodiment 2, as shown in fig. 3, and comprises the following steps:
s1: selecting a combustible ice mining development target area to set up the combustible ice safety mining system, comprising: the horizontal injection well 1 and the horizontal production well 9 sequentially penetrate through the sea water layer, the overlying sedimentary layer and the flammable ice reservoir; the output end of the first branch injection well 3 is arranged in the overlying sediment layer, and the output end of the second branch injection well 4 is arranged in the flammable ice reservoir; the input end of the first branch production well 11 is arranged in the upper deposition layer, and the input end of the second branch production well 12 is arranged in the combustible ice storage layer; a plurality of submarine sedimentation monitors 18 and methane sensors 19 are uniformly arranged on the surface of the overlying sedimentary layer;
S2: the first production switching valve 13 is controlled to be opened by the production controller 10, and the first branch production well 11 extracts the pore fluid in the sediment for depressurization; the first injection switch valve 7 is controlled to be opened by the injection controller 2, liquefied carbon dioxide mixed liquid in the first liquid storage tank 5 is injected into the upper sedimentary deposit through the horizontal injection well 1 and the first branch injection well 3, and the liquefied carbon dioxide mixed liquid flows in the upper sedimentary deposit and forms a carbon dioxide hydrate cover layer under the driving of the pressure difference of the first branch injection well 3 and the first branch production well 11; when the first preset condition is reached, the first production switch valve 13 is controlled to be closed by the production controller 10, and the first injection switch valve 7 is controlled to be closed by the injection controller 2;
The upper coating layer is mainly related to non-uniform local pressure deformation, and as no other coating layer exists above the upper coating deposition layer, once the stress deformation possibly causes the rupture of the reservoir layer, the leakage of CH 4 free gas in the flammable ice reservoir layer is induced, so that the occurrence of large deformation is avoided, and the method comprises the following steps:
The injection pressure pushing force of the first branch injection well is 1-4 MPa; the injection pressure driving force of the first branch injection well cannot enable the overlying deposit layer to be subjected to stress deformation, and the injection pressure driving force refers to a value that the injection pressure is higher than the initial pressure of the overlying layer, namely, the injected liquefied carbon dioxide mixture is in a high-pressure liquid state. By having the injection pressure higher than the overburden pressure, fluid transport can be driven distally at a localized pressure differential;
The depressurization amplitude of the first branch production well is 1-4 MPa; the depressurization pressure of the first branch production well cannot enable the overlying deposit layer to undergo stress deformation and is higher than the combustible ice decomposition equilibrium pressure in the combustible ice reservoir;
the pressure difference between the first branch injection well and the first branch production well is 2-8 MPa;
In this embodiment, the liquefied carbon dioxide mixed liquid includes liquid carbon dioxide, a carbon dioxide hydrate formation inhibitor, and a carbon dioxide hydrate formation promoter;
The carbon dioxide hydrate inhibitor comprises one or more of polyvinylpyrrolidone, polyvinylcaprolactam and hydroxy terminated polycaprolactam;
the carbon dioxide hydrate promoter comprises leucine.
The concentration of the carbon dioxide hydrate formation inhibitor is 300-10000 ppm; the concentration of the carbon dioxide hydrate formation promoter is 50-1000 ppm.
Liquid carbon dioxide has a greater ability to flow and diffuse in the sediment pores relative to gaseous carbon dioxide; although the carbon dioxide hydrate formation inhibitor and the carbon dioxide hydrate formation promoter have opposite effects on the formation rate of the carbon dioxide hydrate, the effect of prolonging the nucleation time of the carbon dioxide hydrate and loosening the formation state of the carbon dioxide hydrate to increase the diffusion range can be achieved through the regulation of the dosage ratio. The carbon dioxide hydrate inhibitor is a kinetic inhibitor, so that the nucleation time for converting liquid carbon dioxide into solid carbon dioxide hydrate can be obviously prolonged, the generation rate of the carbon dioxide hydrate is delayed, and the phenomenon that the liquid carbon dioxide generates a large amount of hydrates too early to transport to a remote place is avoided; although the carbon dioxide hydrate formation promoter can slightly accelerate the nucleation of carbon dioxide hydrate, the formed carbon dioxide hydrate state can be obviously loosened so as to ensure that sediment pores are not seriously blocked even if solid carbon dioxide hydrate is generated in the injection process, so that the liquid carbon dioxide water is promoted to be further conveyed to a far place. Comparing the concentrations of the carbon dioxide hydrate formation inhibitor and the carbon dioxide hydrate formation promoter, it can be seen that the carbon dioxide hydrate formation inhibitor is 1 order of magnitude of the carbon dioxide hydrate formation promoter, so that better nucleation inhibition of the carbon dioxide hydrate is obtained by a higher amount of the inhibitor concentration, while a lower amount of the promoter is only to loosen the generated carbon dioxide hydrate, otherwise, too high a concentration of the promoter may cause the carbon dioxide hydrate to form earlier, thereby resulting in a deterioration in the diffusion capacity of the carbon dioxide.
The first preset condition is as follows: the output rate of the liquefied carbon dioxide mixed solution of the first branch production well is 30% of the injection rate of the liquefied carbon dioxide mixed solution of the first branch injection well; because of the pressure difference between the first branch injection well and the first branch production well, the liquefied carbon dioxide mixed solution continuously flows from the high-pressure injection zone to the low-pressure production zone, wherein a part of liquid carbon dioxide is remained in the overlying deposit layer in the process to form carbon dioxide hydrate, and a part of liquid carbon dioxide flows into the first branch production well and is produced, when the production rate reaches a set value of 30%, the liquid carbon dioxide basically covers a path from the high-pressure zone to the low-pressure zone, and a complete carbon dioxide hydrate cover layer can be formed. After the carbon dioxide hydrate cover layer is formed, the horizontal injection unit and the horizontal production unit are closed for a plurality of days, so that the carbon dioxide hydrate cover layer is aged and compacted;
according to the embodiment, the carbon dioxide hydrate cover layer with wider covering range and stronger strength is built on the upper sedimentary layer, so that the carbon dioxide hydrate cover layer has strong supporting capability, the upper sedimentary layer is prevented from collapsing, the invasion of the upper seawater is effectively avoided, the stratum stability is maintained, the methane is prevented from leaking to the upper seawater environment in the subsequent combustible ice development process, and the exploitation efficiency is greatly improved while the combustible ice development safety is improved.
S3: the second production switch valve 14 is controlled to be opened by the production controller 10, and the second branch production well 12 is used for pumping pore fluid in the combustible ice storage layer and carrying out depressurization exploitation on the combustible ice; when the second preset condition is reached, the second injection switch valve 8 is controlled to be opened by the injection controller 2, and the seawater in the second liquid storage tank 6 is intermittently injected into the flammable ice reservoir through the horizontal injection well 1 and the second branch injection well 4;
the process of depressurization exploitation of the combustible ice by the second branch production well is constant-speed depressurization; the depressurization rate is 1-2 MPa/day;
the second preset condition is: the second branch production well extracts pore fluid in the combustible ice storage layer, and the production pressure of the pore fluid in the combustible ice storage layer is reduced to a constant pressure; the constant pressure is 3-5 MPa;
The constant-speed depressurization is realized by controlling the reservoir fluid extraction rate, so that the production pressure is basically kept to be reduced at a constant speed, and the depressurization rate is reasonably regulated and controlled, so that formation deformation and massive sand discharge caused by too fast or uneven depressurization can be avoided, and the production efficiency of the combustible ice can be improved.
In the embodiment, the temperature of the seawater is 45-65 ℃, the seawater with the temperature of 45-65 ℃ is used for playing a role in heat shock, the temperature of the injected seawater is too low to play a good role in heat shock, the temperature is too high, and the heat loss is serious; by taking in the on-site seawater and heating to 45-65 ℃, the method can accelerate the decomposition of the combustible ice and has higher heat utilization efficiency.
S4: when the third preset condition is reached, the second production switching valve 14 is controlled to be closed by the production controller 10, and the exploitation of the combustible ice is finished; the injection controller 2 controls the liquefied carbon dioxide mixed liquid in the first liquid storage tank 5 to be injected into the combustible ice storage layer through the horizontal injection well 1 and the second branch injection well 4;
In consideration of the fact that intermittent blockage may exist in the combustible ice development process, in order to eliminate the influence of intermittent blockage, a third preset condition is set, namely when the daily average collection amount of the combustible ice of the second branch production well is continuously lower than a preset collection amount for 3 days, the exploitation of the combustible ice is finished, and the preset collection amount is 500m 3/day.
And then the injected carbon dioxide mixed solution is used for repairing the stratum of the combustible ice reservoir by utilizing the carbon dioxide mixed solution to form carbon dioxide hydrate in the combustible ice reservoir, so that methane leakage at the later period of exploitation is avoided. Compared with the injection of liquefied carbon dioxide during the production of the combustible ice, the injection after the production is finished can reduce the inhibiting effect on the decomposition of the combustible ice after the generation of the carbon dioxide hydrate, increase the decomposition yield of the combustible ice and improve the sealing efficiency of the carbon dioxide hydrate.
S5: filling the bottom hole cavities of the horizontal injection well 1 and the horizontal production well 9; specifically, horizontal injection wells and horizontal production wells are filled with cement to fill the bottom hole cavity. Because the vicinity of the drilling area is a high-incidence area of methane leakage, cement is injected into the bottom of the well on the basis of repairing the combustible ice reservoir by the carbon dioxide hydrate, and the occurrence of methane leakage can be further avoided.
In the specific implementation process, the first shaft heater and the second shaft heater are used for preventing solid hydrate from forming in the horizontal injection well or the horizontal production well in the carbon dioxide hydrate overburden construction process or the flammable ice exploitation process, so that the shaft is blocked, and the exploitation efficiency is further improved. The multi-directional injection nozzle is used for reducing the occurrence probability of fluid stagnation caused by overlarge resistance due to local large flow when the first branch injection well and the second branch injection well are used for injecting liquid, so that the injection liquid is beneficial to transporting and diffusing all around, and the dosage ratio of the carbon dioxide hydrate formation inhibitor and the carbon dioxide hydrate formation promoter in the liquefied carbon dioxide mixed liquid is regulated, so that the diffusion capacity of the carbon dioxide mixed liquid is synergistically enhanced, the diffusion distance and the diffusion depth of the carbon dioxide mixed liquid are increased, a carbon dioxide hydrate cover layer with wider coverage range is formed, and then the carbon dioxide hydrate cover layer is more compact through the aging process of the carbon dioxide hydrate cover layer for a plurality of days; compared with a single carbon dioxide hydrate cap layer construction method, the carbon dioxide hydrate of the overburden sediment layer is not only an intermediate target product, but also a second guarantee for the safe and efficient development of the methane hydrate, and is mainly used for safely and stably completing the methane hydrate reservoir repair process service after the exploitation of the methane hydrate reservoir is completed when the carbon dioxide hydrate is taken as the intermediate target product, so that the invasion of overburden seawater can be effectively avoided, the formation stability can be maintained, and the methane leakage to the overburden seawater environment can be prevented. According to the embodiment, on the basis of constructing the carbon dioxide hydrate cover layer, the combustible ice depressurization-heat shock combined exploitation operation is carried out, so that compared with simple depressurization exploitation or heat shock, the water production can be reduced, and the exploitation efficiency and the economic benefit are improved. In addition, the invention solves the problem of low replacement efficiency of CH 4-CO2 hydrate, and remarkably increases the replacement efficiency of the hydrate and the sea bottom sealing capacity of the carbon dioxide by decomposing the combustible ice and then injecting the carbon dioxide into the combustible ice primary reservoir.
The same or similar reference numerals correspond to the same or similar components;
The terms describing the positional relationship in the drawings are merely illustrative, and are not to be construed as limiting the present patent;
It is to be understood that the above examples of the present invention are provided by way of illustration only and not by way of limitation of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (10)
1. The combustible ice safety exploitation system based on reservoir reformation is characterized by comprising a horizontal injection unit, a horizontal production unit and an environment monitoring unit;
the horizontal injection unit comprises a horizontal injection well (1), an injection controller (2), a first branch injection well (3), a second branch injection well (4), a first liquid storage tank (5), a second liquid storage tank (6), a first injection switch valve (7) and a second injection switch valve (8);
the input end of the horizontal injection well (1) is respectively connected with the first liquid storage tank (5) and the second liquid storage tank (6), and the output end of the horizontal injection well (1) is respectively connected with the input end of the first branch injection well (3) and the input end of the second branch injection well (4); the first injection switch valve (7) is arranged at the input end of the first branch injection well (3), the second injection switch valve (8) is arranged at the input end of the second branch injection well (4), and the control ends of the first injection switch valve (7) and the second injection switch valve (8) are connected with the injection controller (2);
The horizontal production unit comprises a horizontal production well (9), a production controller (10), a first branch production well (11), a second branch production well (12), a first production switch valve (13) and a second production switch valve (14);
The input end of the horizontal production well (9) is respectively connected with the output end of the first branch production well (11) and the output end of the second branch production well (12); the first production switch valve (13) is arranged at the output end of the first branch production well (11), the second production switch valve (14) is arranged at the output end of the second branch production well (12), and the control ends of the first production switch valve (13) and the second production switch valve (14) are connected with the production controller (10);
The environment monitoring unit is arranged on the surface of the overlying deposition layer and is in communication connection with the injection controller (2) and the production controller (10).
2. The reservoir retrofit-based combustible ice safety production system of claim 1 wherein the horizontal injection unit further comprises first wellbore heaters uniformly distributed on a wellbore wall of the horizontal injection well (1); the control end of the first shaft heater is connected with an injection controller (2);
The horizontal production unit further comprises second shaft heaters which are uniformly distributed on the shaft wall surface of the horizontal production well (9); the control end of the second shaft heater is connected with a production controller (10).
3. The reservoir retrofit-based combustible ice safety production system of claim 1 wherein the horizontal injection unit further comprises a first injection nozzle (15) and a second injection nozzle (16);
The input end of the first injection nozzle (15) is connected with the output end of the first branch injection well (3); the input end of the second injection nozzle (16) is connected with the output end of the second branch injection well (4);
the first injection nozzle (15) and the second injection nozzle (16) are multi-directional injection nozzles.
4. Reservoir retrofit-based combustible ice safety exploitation system according to claim 1, wherein the first tank (5) is adapted to store a liquefied carbon dioxide mixture;
the liquefied carbon dioxide mixed solution comprises liquid carbon dioxide, a carbon dioxide hydrate formation inhibitor and a carbon dioxide hydrate formation promoter;
The carbon dioxide hydrate inhibitor comprises one or more of polyvinylpyrrolidone, polyvinylcaprolactam and hydroxy terminated polycaprolactam;
the carbon dioxide hydrate promoter comprises leucine.
5. Reservoir retrofit-based combustible ice safety mining system according to claim 1, characterized in that the second tank (6) is used for storing seawater; the temperature of the seawater is 45-65 ℃.
6. Reservoir retrofit-based combustible ice safety production system according to claim 1, characterized in that the system further comprises several pressure sensors (17);
The pressure sensors (17) are uniformly arranged on the wall surface of the shaft of the horizontal injection well (1) and the horizontal production well (9) which are positioned on the part of the upper deposition layer.
7. The reservoir retrofit-based combustible ice safety mining system according to claim 1, wherein the environmental monitoring unit includes a number of subsea settlement monitors (18) and a number of methane sensors (19);
The seabed sedimentation monitor (18) and the methane sensor (19) are uniformly arranged on the surface of the overlying sedimentary layer.
8. A method of safe exploitation of combustible ice based on reservoir modification, characterized in that it is based on the exploitation system according to claims 1-7, the method comprising:
S1: selecting a combustible ice mining development target area to set up the combustible ice safety mining system, comprising: the horizontal injection well (1) and the horizontal production well (9) sequentially penetrate through the sea water layer, the overlying sedimentary layer and the flammable ice reservoir; the output end of the first branch injection well (3) is arranged in the overlying sediment layer, and the output end of the second branch injection well (4) is arranged in the flammable ice reservoir; the input end of the first branch production well (11) is arranged in the overlying sediment layer, and the input end of the second branch production well (12) is arranged in the flammable ice reservoir layer; a plurality of submarine sedimentation monitors (18) and methane sensors (19) are uniformly arranged on the surface of the overlying sedimentary layer;
S2: the first production switching valve (13) is controlled to be opened by the production controller (10), and the first branch production well (11) extracts the pore fluid in the sediment to reduce the pressure; the first injection switch valve (7) is controlled to be opened through the injection controller (2), liquefied carbon dioxide mixed liquid in the first liquid storage tank (5) is injected into the upper deposition layer through the horizontal injection well (1) and the first branch injection well (3), and the liquefied carbon dioxide mixed liquid flows in the upper deposition layer and forms a carbon dioxide hydrate cover layer under the driving of the pressure difference of the first branch injection well (3) and the first branch production well (11); when the first preset condition is reached, the first production switch valve (13) is controlled to be closed by the production controller (10), and the first injection switch valve (7) is controlled to be closed by the injection controller (2);
S3: the second production switch valve (14) is controlled to be opened by the production controller (10), and the second branch production well (12) is used for extracting pore fluid in the flammable ice storage layer and carrying out depressurization exploitation on the flammable ice; when the second preset condition is reached, the second injection switch valve (8) is controlled to be opened by the injection controller (2), and the seawater in the second liquid storage tank (6) is intermittently injected into the flammable ice storage layer through the horizontal injection well (1) and the second branch injection well (4);
s4: when the third preset condition is reached, the second production switch valve (14) is controlled to be closed by the production controller (10), and the exploitation of the combustible ice is finished; the injection controller (2) is used for controlling and switching the liquefied carbon dioxide mixed liquid in the first liquid storage tank (5) to be injected into the combustible ice storage layer through the horizontal injection well (1) and the second branch injection well (4);
s5: filling the bottom hole cavity of the horizontal injection well (1) and the horizontal production well (9).
9. The reservoir retrofit-based combustible ice safety mining method of claim 8, wherein the first preset condition is: the output rate of the liquefied carbon dioxide mixed liquor of the first branch production well (11) is 30% of the injection rate of the liquefied carbon dioxide mixed liquor of the first branch injection well (3);
The second preset condition is: -the production pressure of the pore fluid in the combustible ice reservoir pumped by the second branch production well (12) is reduced to a constant pressure; the constant pressure is 3-5 MPa;
the third preset condition is: the average collection amount of combustible ice of the second branch production well (12) is continuously lower than a preset collection amount for 3 days, and the preset collection amount is 500m 3/day.
10. The method of reservoir retrofit-based combustible ice safe recovery of claim 8, wherein prior to step S3, the horizontal injection unit and the horizontal production unit are further adapted to be well-closed for several days to age and densify the carbon dioxide hydrate cap layer.
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