JP2019157481A - Gas production system - Google Patents

Abstract

To control the decomposition of gas hydrate for each production tube by separately providing a production tube that takes in a gas-liquid mixture containing gas and water and a separation tube that separates the gas-liquid mixture to produce gas when producing gas by decomposing gas hydrate.SOLUTION: A gas production system comprises a production tube provided with a hole provided at a tip and opened to an outside so that a gas-liquid mixture containing bubbles obtained by decomposition of gas hydrate is taken into the internal liquid, a separation tube with a gas-liquid separation device that separates gas from the liquid that has taken in the gas-liquid mixture introduced from the production tube and a pump that sucks the liquid after separation to the outside, a gas production line for conveying the separated gas to the outside, a liquid discharge line for discharging the liquid to the outside, a resupply line that branches off from the liquid discharge line and returns a portion of the liquid to the production tube, a first valve for adjusting the flow rate of the resupply line, and a control device for controlling the opening of the first valve.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas production system that produces gas by decomposing underground gas hydrate.

In recent years, natural gas hydrate has attracted attention as a natural gas resource. Natural gas emits less carbon dioxide when combusted than oil and coal, and natural gas hydrate consisting of natural gas and water is a promising resource in terms of suppressing global warming.
Natural gas hydrate is an inclusion compound having a crystal structure in which methane molecules are surrounded by water molecules in a cage shape. Natural gas hydrate exists in a solid state in a low-temperature and high-pressure environment, and stably exists in the surface layer of the deep sea bottom and the subsurface of the sea bottom satisfying such an environment.

Conventionally, as a method for extracting natural gas from natural gas hydrate present in the seabed, a decompression method for decomposing natural gas hydrate by applying a reduced pressure to the high water pressure applied to the natural gas hydrate is known. (For example, Patent Document 1).
In the depressurization method, concretely, using a pipe (riser pipe) that carries natural gas from the seabed to the sea, the seawater level in the pipe is lowered by discharging the seawater in the pipe, and the seawater pressure in the riser pipe is low. Is decomposed by acting on a formation (hydrate layer) in the seabed containing natural gas hydrate. Natural gas produced by decomposition of natural gas hydrate is taken into seawater in the riser pipe as a gas-liquid mixture mixed with liquid. Seawater that has taken in the multiphase flow is gas-liquid separated into natural gas and seawater in the riser pipe and discharged to the sea respectively.

  In order to stably increase the production volume of natural gas using the decompression method, it is important to maintain the pressure acting on the natural gas hydrate within the range of the pressure at which the natural gas hydrate decomposes (decomposition pressure). . For this reason, in the depressurization method, liquid such as water and seawater that has entered the riser pipe is discharged so that the liquid level in the riser pipe is adjusted to a height position corresponding to the decomposition pressure. In other words, the pressure reduction method measures the pressure (bottom pressure) at the tip of the riser pipe with the intake port that takes in the multiphase flow, and constantly monitors the measured pressure, while the liquid level in the riser pipe changes according to the fluctuations in the measured pressure. The height position is adjusted. Such adjustment of the liquid level is performed by controlling the number of revolutions of the pump to control the discharge amount of seawater.

JP 2010-261252 A

By the way, in order to produce natural gas practically and efficiently using the decompression method, the gas-liquid mixture containing natural gas and seawater taken in multiple pipes is collected in a separate pipe and provided in this pipe. A system is assumed in which gas-liquid separation is performed by the gas-liquid separation apparatus and the liquid after the gas-liquid separation is sucked up to the ground using a pump provided in a pipe.
In this case, however, the inflow of the gas-liquid mixture taken into each production pipe and the content of natural gas vary, so natural gas hydrate is decomposed under the conditions common to each pipe to accurately control natural gas production. Difficult to do.

  Therefore, the present invention produces a gas by decomposing a gas hydrate such as natural gas hydrate and producing a gas by separating the gas-liquid mixture from a production pipe that takes in the gas-liquid mixture containing gas and water. An object of the present invention is to provide a gas production system in which a separation pipe is provided separately, and the decomposition of the gas hydrate can be controlled for each production pipe.

One embodiment of the present invention is a gas production system that decomposes gas hydrate in the ground to produce gas. The system
A tube having a tip portion configured to be buried in the ground, by reducing the pressure acting on the gas hydrate outside the tube using the pressure of the liquid in the tube, A production pipe having a hole provided at the tip and opened to the outside of the pipe so as to take in a gas-liquid mixture containing bubbles generated by decomposition from gas hydrate into the liquid in the pipe;
A gas-liquid separation device configured to be embedded in the ground and introduced from the production pipe into the gas from the liquid that has taken in the gas-liquid mixture; A pump for sucking liquid to the outside, and a separation pipe provided separately from the production pipe,
A liquid supply line connecting the production pipe and the separation pipe;
A liquid discharge line extending from the separation tube and discharging the sucked liquid to the outside;
A gas production line extending from the separation pipe and transported to the outside as the gas for producing the separated gas;
A resupply line that branches off from the liquid discharge line and returns a portion of the sucked up liquid to the production pipe;
A first valve provided in the resupply line for adjusting the flow rate of the resupply line;
A control device for controlling the opening of the first valve;
Is provided.

Inside the production pipe, the liquid supplied from the resupply line is used as a driving fluid, and the discharge amount of the liquid in the production pipe is sucked and discharged upward according to the flow rate of the driving fluid. An ejector pump is provided,
It is preferable that the pressure at the tip portion is controlled by adjusting the discharge amount.

  It is preferable that the control device controls the opening degree of the first valve based on a measured value of the pressure of the liquid in the production pipe.

  The control device performs control to increase the opening of the first valve when the measured pressure value is higher than a target bottom hole pressure, and when the measured pressure value is lower than the target bottom hole pressure, It is preferable to control so as to reduce the opening of one valve.

The liquid supply line is provided with a shutoff valve that shuts off the supply of the liquid from the production pipe to the separation pipe,
It is preferable that the control device controls the shutoff valve based on a differential pressure between measured pressures at two different positions in the depth direction of the production pipe in the liquid.

  The control device controls to close the shut-off valve when the differential pressure is greater than or equal to a predetermined threshold, and controls to open the shut-off valve when the differential pressure is less than a predetermined threshold; Is preferred.

A circulation line is provided that branches off from the liquid discharge line and returns a part of the sucked-up liquid to the separation pipe;
The circulation line is provided with a second valve for adjusting the flow rate of the circulation line,
It is preferable that the control device controls the opening degree of the second valve based on a difference between the measured pressure in the gas phase in the separation pipe and the measured pressure in the liquid phase.

  It is preferable that the circulation line includes a heating device that heats a part of the liquid flowing through the circulation line.

  Each of a plurality of distributed production pipes dispersedly arranged at a plurality of locations is connected to the separation pipe via the liquid supply line as the production pipe, and the control device includes the first of the distributed production pipes. It is preferable to control the opening of the valve.

The production pipe and the separation pipe are buried in the seabed;
It is preferable that the pump is provided so as to be positioned below the sea bottom in the separation pipe.

  It is preferable that the connection position of the liquid supply line with the separation pipe is above the pump.

  The above-described gas production system is a system in which a production pipe that takes in a gas-liquid mixture containing gas and water and a separation pipe that separates the gas-liquid mixture and produces gas are provided separately. Hydrate decomposition can be controlled.

It is a figure showing roughly the gas production system of one embodiment. It is a figure explaining an example of the control which the control apparatus of the gas production system shown in FIG. 1 performs.

Hereinafter, the gas production system of the present invention will be described. In the following description, natural gas hydrate is taken as an example of gas hydrate, but the gas hydrate is not limited to natural gas hydrate.
In addition, the gas production system referred to in the present specification generates gas by decompressing and decomposing underground gas hydrate, and is different from a system that generates gas from gas hydrate present on the seafloor surface. .

(Overview of gas production system)
FIG. 1 is a diagram schematically illustrating a gas production system (hereinafter simply referred to as a system) 10 according to an embodiment. Hereinafter, a system 10 that decomposes natural gas hydrate in the seabed to produce natural gas will be described as an example.

The system 10 is a system in which natural gas obtained by decomposing from natural gas hydrate in the ground is separated from liquid and taken out to the ground in a pipe extending into the ground.
The system 10 mainly includes production pipes 12a and 12b, a separation pipe 14, liquid supply lines 20a and 20b, a liquid discharge line 22, a gas production line 24, resupply lines 26a and 26b, and a control device 30. And mainly.
The production pipes 12a and 12b are an example of a plurality of production pipes distributed and arranged at different locations in the hydrate layer. According to another embodiment, there is a configuration in which at least three production pipes are provided and three or more production pipes and one separation pipe are connected by a line.

The production pipes 12a and 12b are long pipes configured to be buried in the ground. The production pipes 12a and 12b are embedded in a well in the seabed. A well is a hole provided by excavation. Holes 16a and 16b opened in the underground gas hydrate layer (outside) are provided at the front ends of the production pipes 12a and 12b. That is, the holes 16a and 16b provided at the front ends of the production pipes 12a and 12b are provided so as to be located in the hydrate layer in the seabed. The production pipes 12a and 12b are generated by decomposing from the gas hydrate by reducing the pressure acting on the gas hydrate outside the production pipes 12a and 12b using the pressure of the liquid in the production pipes 12a and 12b. The gas-liquid mixture containing bubbles is taken into the liquid in the production pipes 12a and 12b through the holes 16a and 16b. The pressure of the liquid in the production pipes 12a and 12b is configured to be lower than the pressure in the gas hydrate layer.
Screens (not shown) are provided in the holes 16a and 16b. The screen is a member that takes in bubbles and water generated by the decomposition of natural gas hydrate, as well as seawater, and separates and removes sand and mud. The screen is, for example, a sheet-like or plate-like structure having a large number of holes, and is composed of a plurality of structures having different hole sizes and shapes.

The production pipes 12a and 12b penetrate the upper layer including the sea bottom X, and are closed in the hydrate layer 5 located in the lower layer. The upper layer includes, for example, a muddy layer containing a lot of mud. The hydrate layer includes, for example, a lot of mud and sand, and has a sandy layer that spreads in the lateral direction, in which the gas hydrate is taken into the sand and mud. The boundary between the upper layer and the hydrate layer is, for example, at a position several hundred meters below the sea bottom, and the sea bottom X is at a position several thousand hundred meters from the sea surface Y, for example.
The rear ends of the production pipes 12a and 12b (the end opposite to the front end) are above the sea bottom X, while the front ends of the production pipes 12a and 12b are several hundred meters (for example, 300 m) from the sea bottom X. The production pipes 12a and 12b extend from the sea bottom X downward into the ground by several hundred meters in order to be located in the hydrate layer located deep in the ground.

  The separation tube 14 is a long tube configured to be buried in the ground. The separation tube 14 extends vertically downward, and a tip portion is embedded in a well in the seabed. It is a hole provided by excavation. Most of the separation tube 14, for example, 80% or more of the length of the tube is embedded in the sea bottom. The length of the separation tube 14 is, for example, several tens of meters (for example, about 50 m).

The liquid supply lines 20a and 20b are constituted by pipes connecting the production pipes 12a and 12b and the separation pipe 14.
The liquid discharge line 22 is a pipe that extends from the separation pipe 14 and discharges the liquid sucked up by the pump 18 to the outside (for example, the ground).
The gas production line 24 includes a pipe that extends from the separation pipe and conveys the separated gas to the outside (for example, the ground) as a gas for producing the separated gas.
The resupply lines 26a and 26b branch from the liquid discharge line 22, and are configured by pipes so that a part of the liquid in the liquid discharge line 22 is returned to the production pipes 16a and 16b.

  Ejector pumps 46a and 46b are provided inside the production pipes 12a and 12b. The ejector pumps 46a and 46b cause the liquid at the bottom in the production pipes 16a and 16b to be discharged upward, and the pressure at the bottom (bottom pressure) ). The ejector pumps 46a and 46b use the liquid supplied from the resupply lines 26a and 26b as the driving fluid, and the discharge amount of the liquid in the production pipes 12a and 12b is sucked and discharged upward according to the flow rate of the driving fluid. It is configured to change. By adjusting the discharge amount of the liquid by the ejector pumps 46a and 46b, the pressure at the bottom of the production pipes 12a and 12b, that is, the front end (bottom pressure) is controlled, and the decomposition of the gas hydrate is controlled. The driving fluid supplied to the ejector pumps 46a and 46b is a high-pressure liquid pressurized by the pump 18 described later and supplied into the production pipes 12a and 12b via the resupply lines 26a and 26b. The liquid discharged from the ejector pumps 46a and 46b and flowing upward is supplied to the separation tube 14 via the liquid supply lines 20a and 20b. For this reason, as shown in FIG. 1, it is preferable that the opening positions of the resupply lines 26a and 26b are inside the production pipes 12a and 12b and at the driving fluid intake ports of the ejector pumps 26a and 26b.

  The separation tube 14 collects the liquid supplied from the production tubes 12a and 12b. The cross-sectional area inside the pipe of the separation pipe 14 is larger than the cross-sectional area inside the pipes of the production pipes 12a and 12b, for example, two times or more, more than four times larger than the cross-sectional area inside the pipes of the production pipes 12a and 12b. Is preferred.

Inside the separation tube 14, a gas-liquid separation device 45 that separates the gas in the bubbles from the liquid that has taken in the gas-liquid mixture introduced from the production tubes 12 a and 12 b, and a pump that sucks up the separated liquid 18 are provided.
In the gas-liquid separator 45, the liquid level is formed so that the gas phase and the liquid phase are separated. The gas production line 24 is provided above the separation pipe 14b, preferably on the ceiling surface, and conveys gas to the ground.
The pump 18 is a rotary pump that is provided in the vicinity of the bottom in the separation pipe 14 and is configured to suck and pressurize the liquid at the bottom with the pump and convey it to the ground. The pump 18 is provided with a drive motor (not shown).
The pump 18 is connected to the liquid discharge line 22, and the liquid pressurized by the pump 18 ascends the liquid discharge line 22 toward the ground.

A part of the separation pipe 14 protrudes above the sea floor X, and most of it is provided in the ground deeper than the sea bottom. The pump 18 is provided in the vicinity of the bottom of the separation pipe 14 and is located several tens of meters (for example, about 30 m) below the internal liquid level. The gas-liquid separation device 45 provided in the separation tube 14 includes a descending path for flowing the liquid downward in order to exclude a part of the bubbles from the liquid. Such a gas-liquid separation method is a gravity separation method in which separation is performed using gravity (specific gravity) applied to a gas and a liquid. Therefore, the longer the distance of the descending path, the better the gas-liquid separation.
Since the pump 18 has a large cross-sectional area inside the separation pipe 14, the flow rate of the downward flow of the liquid flowing in the separation pipe 14 is low, and the pump 18 is provided near the bottom in the separation pipe 14, and therefore the distance of the liquid downward path Is long. For this reason, bubbles are hardly dragged by the liquid flow and move to the pump 18, and gas-liquid separation can be performed satisfactorily. In addition, since the pump 18 is provided near the bottom of the separation tube 14, even if bubbles enter the pump 18, since the pressure is high and the size of the bubbles is small by the head pressure, the bubbles are pumped. The effect on the pressure performance of 18 is small.
According to one embodiment, it is preferable that the pump 18 is provided below the sea bottom surface X and is provided at the distal end portion (lowermost end portion) of the separation pipe 14 in order to perform gas-liquid separation satisfactorily.

  A centrifuge (not shown) may be provided inside the separation tube 14 in order to separate liquid and bubbles before being sucked into the pump 18. When the liquid containing the bubbles approaches the rotating body of the centrifuge, the liquid flows along a swirl flow created by the rotation of the rotating body. At this time, centrifugal force acts on the bubbles and the liquid, and the liquid has a greater specific gravity than the bubbles. Therefore, the liquid moves away from the rotation center line, and the bubbles are collected closer to the rotation center line than the liquid. At this time, the bubbles that are collected and enlarged are configured to float on the liquid surface Z.

  Near the end of the liquid discharge line 22 on the ground side, a flow meter 42 is provided. Information on the measured flow rate F2 measured by the flow meter 42 is sent to the control device 30 provided on the ground portion of the system 10. The control device 30 generates a signal for adjusting the rotational speed of the pump 18 according to the measured flow rate F2 of the flow meter 42, and transmits this signal to the pump 18.

  Near the end of the gas production line 24 on the ground side, a valve 44 and a flow meter 46 are provided. Information on the measured flow rate F <b> 1 measured by the flow meter 46 is sent to the control device 30. Further, information on the gas phase measurement pressure P <b> 1 measured by the pressure gauge 40 provided in the separation tube 14 is sent to the control device 30. The gas in the gas production line 24 is sent to the outside (ground) by the pressure of the gas phase in the separation tube 14. Therefore, the control device 30 generates a signal for adjusting the opening degree of the valve 44 in accordance with the measured flow rate F1 and the measured pressure P1, and transmits this signal to the valve 44.

A resupply line 48 is provided so as to branch from the middle of the liquid discharge line 22. The resupply line 48 is configured such that the pressurized liquid is supplied again into the separation tube 14. The resupply line 48 opens to a ceiling portion in the separation pipe 14, that is, a gas phase portion. The resupply line 48 is provided with a valve (second valve) 50 and a heater 52. The heater 52 can adjust the temperature of the liquid to be supplied again. For example, when the system 10 is started up, a heated liquid can be supplied to the liquid surface in order to prevent hydrate from regenerating in the separation tube 14 under high pressure conditions in the separation tube 14. Moreover, foaming can be suppressed by spraying a liquid with respect to foaming on the liquid level Z as needed.
The valve 50 adjusts the flow rate of the liquid flowing in the resupply line 48 so that the liquid level in the separation tube 14 is in an appropriate range. Specifically, information on the measured pressures P5 and P1 measured by the pressure gauges 38 and 40 provided in the separation pipe 14 is sent to the control device 30, and the control device 30 controls the valve according to the measured pressures P5 and P1. A signal for controlling the opening degree of 50 is generated, and this signal is sent to the valve 50. Thereby, the position of the liquid level Z in the separation tube 14 can be maintained in an appropriate range.

The resupply lines 26a and 26b are provided with heaters 54a and 54b and valves (first valves) 28a and 28b. The heaters 54a and 54b can adjust the temperature of the liquid resupplied to the production pipes 12a and 12b. At the branch position of the resupply lines 26a, 26b of the liquid discharge line 22 of the resupply lines 26a, 26b, the pressure of the liquid is increased by the pressurization of the pump 18 (for example, several tens of MPa), and the production pipe It is higher than the pressure (for example, several MPa) of the liquid in 12a, 12b. For this reason, the liquid flows from the liquid discharge line 22 toward the production pipes 12a and 12b through the resupply lines 26a and 26b. The valves 28a and 28b are configured to adjust the opening degree of the valves 28a and 28b in accordance with information on the pressure P4 measured by the pressure gauges 32a and 32b provided at the bottoms of the production pipes 16a and 16b. Specifically, information on the measured pressure P4 is transmitted from the pressure gauges 32a and 32b to the control device 30. The control device 30 generates a signal for adjusting the opening degree of the valves 28a and 28b according to the measured pressure P4, and transmits this signal to the valves 28a and 28b.
When the measurement pressure P4 is low, the decomposition of the gas hydrate is promoted, and when the measurement pressure P4 is high, the decomposition of the gas hydrate is suppressed. Therefore, the opening degree of the valves 28a and 28b is adjusted in order to adjust the level of the measurement pressure P4 so that the decomposition rate of the gas hydrate is constant. When the measured pressure P4 is low, the control device 30 reduces the opening amount of the valves 28a and 28b to suppress the upward discharge amount of the liquid in the production pipes 12a and 12b by the ejector pumps 46a and 46b. Thereby, the flow volume of the liquid supplied in the separation pipe 14 via the liquid supply lines 20a and 20b is suppressed. Thereby, the pressure (bottom pressure) at the bottom of the production pipes 12a and 12b can be increased. When the measured pressure P4 is high, the opening amounts of the valves 28a and 28b are increased, and the discharge amount of the liquid in the production pipes 12a and 12b by the ejector pumps 46a and 46b is increased. Thereby, the flow rate of the liquid supplied into the separation pipe 14 via the liquid supply lines 20a and 20b is increased. Thereby, the pressure (bottom pressure) at the bottom of the production pipes 12a and 12b can be lowered. Thereby, the pressure (measurement pressure P4) at the bottom of the production pipes 16a and 16b is set to the target bottom pressure (target BOP) so that the decomposition rate of the gas hydrate in the vicinity of each of the production pipes 16a and 16b becomes constant. You can get closer.

  The liquid supply lines 20a and 20b are provided with shutoff valves 39a and 39b. The shutoff valves 39 a and 39 b are opened and closed by a signal from the control device 30. Specifically, information on the measured pressure P2 by the pressure gauges 34a and 34b and information on the measured pressure P3 by the pressure gauges 36a and 36b at different positions in the depth direction of the production pipes 16a and 16b are sent to the control device 30. . The control device 30 generates a signal for opening and closing the shutoff valves 39a and 39b according to the difference between the measured pressure P2 and the measured pressure P3, and transmits this signal to the shutoff valves 39a and 39b. If the ratio of the gas contained in the liquid is different, the difference between the measured pressure P2 and the measured pressure P3 is different. For this reason, the ratio of the gas contained in the liquid can be estimated from this difference. When the difference between the measured pressure P2 and the measured pressure P3 is small, it is estimated that the gas ratio is large, so the shutoff valves 39a and 39b are opened. When the difference between the measurement pressure P2 and the measurement pressure P3 is large, it is estimated that the gas ratio is small. Therefore, the shutoff valves 39a and 39b are closed so that no liquid is supplied to the separation pipe 14.

  FIG. 2 is a diagram for explaining an example of control performed by the control device 30.

When the measured pressure P4 at the tip (bottom) of the production pipes 12a and 12b is lower than the target bottom pressure (target BOP), the control device 30 generates a signal for reducing the opening degree of the valves 28a and 28b. To 28a and 28b. Since the opening degree of the valves 28a and 28b becomes small, the flow rate of the high-pressure liquid supplied to the production pipes 12a and 12b decreases, the amount of liquid discharged from the ejector pumps 46a and 46b decreases, and the liquid supply line 20 Since the amount flowing through the separation pipe 14 is reduced, the pressure at the tip (bottom) of the production pipes 12a and 12b increases and approaches the target bottom pressure.
When the measured pressure P4 at the tip (bottom) of the production pipes 12a and 12b is higher than the target well bottom pressure, a signal for increasing the opening degree of the valves 28a and 28b is generated and sent to the valves 28a and 28b. Since the opening degree of the valves 28a and 28b is increased, the flow rate of the high-pressure liquid supplied to the production pipes 12a and 12b is increased, and the amount of liquid discharged from the ejector pumps 46a and 46b is increased. Since the amount flowing through the separation pipe 14 increases, the pressure at the tip (bottom) of the production pipes 12a and 12b decreases and approaches the target bottom pressure.
When the measured pressure P4 at the tip (bottom) of the production pipes 12a and 12b is the same as the target well bottom pressure, a signal for maintaining the opening degree of the valves 28a and 28b is generated and sent to the valves 28a and 28b.

  The signal for increasing the opening degree or the signal for reducing the opening degree may be a signal having a different degree of changing the opening degree according to the difference between the measured pressure P4 and the target bottom hole pressure, or the opening degree may be completely changed. It may be a signal to open or completely close. Moreover, the range which has an upper limit and adjustment may be sufficient as the target well bottom pressure for maintaining the opening degree of valve | bulb 28a, 28b.

When the measured flow rate F1 measured by the flow meter 30 provided on the ground (outside) of the gas production line 24 is smaller than the preset set value SV, the control device 30 measures the measured pressure P1 that is the determination condition of the valve 44. When the set value SV _P1 is decreased and the measured flow rate F1 is larger than the preset set value SV, the control device 30 increases the set value SV _P1 for the measured pressure P1, which is a condition for determining the opening degree of the valve 44. When the measured flow rate F1 is the same as the preset set value SV, the set value SV _P1 is maintained. Further, when the measured pressure P1 of the pressure gauge 40 provided in the separation pipe 14 is smaller than the set value SV _P1 , the control device 30 generates a signal for reducing the opening of the valve 44, and the measured pressure P1 is set to the set value SV. If it is larger than _P1 , a signal for increasing the opening of the valve 44 is generated. If the measured pressure P1 is the same as the set value SV _P1 , a signal for maintaining the opening of the valve 44 is generated, and this signal is sent to the valve 44. . Thereby, the amount of gas production is controlled in accordance with the measured pressure P1 of the gas phase in the separation pipe 14. Even if the flow rate of the gas is small and an attempt is made to increase the flow rate, the gas needs to be accumulated in the separation pipe 14 to some extent. For this reason, when controlling to increase the gas flow rate, the control device 30 performs control so that the increase in the flow rate is determined according to the amount of gas accumulated in the separation pipe 14, that is, the measured pressure P1.

  In addition, when the measured flow rate F2 measured by the flow meter 42 provided in the liquid discharge line 22 is less than the preset set value SV, the control device 30 generates a signal for increasing the rotational speed of the pump 18 and measures the measured flow rate F2. When the flow rate F2 is larger than the set value SV, a signal for decreasing the rotation speed of the pump 18 is generated. When the measured flow rate F2 is the same as the set value SV, a signal for maintaining the rotation speed of the pump 18 is generated. It is sent to a drive motor (not shown) connected to the pump 18. Thereby, the discharge amount of the liquid can be controlled.

Further, the control device 30 calculates a differential pressure DP2 between the measured pressure P2 measured by the pressure gauges 34a and 34b provided in the production pipes 12a and 12b and the measured pressure P4 measured by the pressure gauges 36a and 36b. When the differential pressure DP2 is lower than the preset set value SV, a signal for opening the shutoff valves 39a and 39b provided in the liquid supply lines 20a and 20b is generated, and the differential pressure DP2 is equal to or higher than the set value SV. A signal for closing the shutoff valves 39a and 39b is generated, and this signal is sent to the shutoff valves 39a and 39b. Accordingly, the shutoff valves 39a and 39b open and close the valves.
When the differential pressure DP2 is smaller than the set value SV, it can be determined that the gas in the production pipes 12a and 12b is mixed in a sufficient ratio. The gas can be produced by supplying it to the separation tube 14 and performing gas-liquid separation. When the differential pressure DP2 is equal to or higher than the set value SV, it is determined that the gas in the production pipes 12a and 12b is not mixed in a sufficient ratio and is not supplied to the separation pipe. The production pipe whose differential pressure DP2 is equal to or higher than the set value SV is removed from the production system 10 as a production pipe that is not sufficiently obtained from the liquid and does not contribute to gas production, for example. In some cases, the target bottom bottom pressure BOP may be reset to a different value, and the decomposition of the gas hydrate may be promoted so that the liquid contains a large amount of gas.

Further, the control device 30 calculates a differential pressure DP3 between the measured pressure P1 measured by the pressure gauge 40 provided in the separation pipe 14 and the measured pressure P5 measured by the pressure gauge 38, and the differential pressure DP3 is When the preset value SV is smaller than the preset value SV, a signal for increasing the opening degree of the valve 50 provided in the resupply line 48 is generated. When the differential pressure DP3 is larger than the set value SV, the opening degree of the valve 50 is set. If the differential pressure DP3 is the same as the set value SV, a signal for maintaining the opening degree of the valve 50 is generated, and this signal is sent to the valve 50.
When the differential pressure DP3 is smaller than the set value SV, it can be determined that the position of the liquid level Z in the separation pipe 14 is low, and the liquid is supplied from the resupply line 48, so that the position of the liquid level Z is within the target range. Can be maintained.

Note that the set value SV to be compared with the above-described measurement value or the like may be a certain value, or a range having an upper limit and addition / subtraction.
Further, the degree to which the opening degree of the valve is increased or decreased may be varied depending on the difference between the set value SV and the measured value to be compared.

Using such a gas production system 10, gas hydrate decomposition and gas production are performed.
As described above, when the system 10 re-feeds the liquid from the separation pipe 14 to the production pipes 12a and 12b via the re-feed lines 26a and 26b, the controller 30 uses the valves 28a and 28b to re-feed the line 26a. 26b is adjusted, the pressure at the bottom of each of the production pipes 12a and 12b can be controlled efficiently, and the decomposition of the gas hydrate can be controlled for each of the production pipes 12a and 12b.
At this time, since the opening degree of the valves 28a and 28b is adjusted according to the measured pressure P4 of the pressure at the tip end in the production pipes 12a and 12b, the pressure (bottom bottom pressure) at the tip end in the production pipes 12a and 12b is adjusted. The target pressure can be maintained. Since the opening degree of the valves 28a and 28b is adjusted according to the respective measured pressures P4 of the resupply lines 26a and 26b, the pressure (bottom pressure) at the front end in the production pipes 12a and 12b is set between the production pipes 12a and 12b. Can be arranged.

  Since the production pipes 12a and 12b are provided with ejector pumps 46a and 4b, even if the positions in the depth direction of the holes 32a and 32b of the production pipes 12a and 12b vary greatly, it is possible to adjust the liquid discharge amount. Therefore, the pressure (bottom pressure) at the bottom of the production pipes 12a and 12b can be made uniform, and the decomposition of gas hydrate and the amount of gas generated can be individually controlled between the production pipes 12a and 12b.

  The liquid supply lines 20a and 20b are provided with shutoff valves 39a and 39b, and the control device 30 controls the opening of the shutoff valves 39a and 39b based on the differential pressure between the measured pressure P2 and the measured pressure P3. Therefore, the ratio of the gas contained in the liquid can be easily determined, and the supply of the liquid containing the gas to the separation pipe 14 of the production pipes 12a and 12b having a small gas ratio can be stopped.

  Most of the separation pipes 14 provided separately from the production pipes 12a and 12b, for example, 80% or more of the length of the pipes are buried in the sea bottom (underground). It can be simplified. Further, since the pump 18 is provided in the vicinity of the distal end portion of the separation pipe 14 having a cross-sectional area wider than that of the production pipes 12a and 12b, the distance of the liquid descending path becomes long and the liquid descending speed is low. The amount of bubbles entrained in the descending flow is small, and gas-liquid separation can be performed satisfactorily.

  The production pipes 12a and 12b and the separation pipe 14 are buried in the seabed, and the pump 18 is provided so as to be positioned below the sea bottom X in the separation pipe 14 to perform gas-liquid separation with high accuracy. To preferred. At this time, it is preferable that the connection position of the liquid supply lines 20a and 20b with the separation pipe 14 is above the pump 18 from the viewpoint that gas-liquid separation can be efficiently performed by the gravity separation method.

  In the gas production system 10 of the present embodiment, a plurality of production pipes dispersedly arranged at a plurality of locations are connected to the separation pipe 14 via the liquid supply lines 20a and 20b as production pipes 12a and 12b, respectively. No. 30 can practically and stably produce gas by controlling the opening degree of the valves 28a and 28b provided in the production pipes arranged in a distributed manner.

  The gas production system of the present invention has been described in detail above. However, the present invention is not limited to the above embodiment, and various improvements and modifications may be made without departing from the spirit of the present invention. is there.

DESCRIPTION OF SYMBOLS 10 Gas production system 12a, 12b Production pipe 14 Separation pipe 16a, 16b Hole 18 Pump 20a, 20b Liquid supply line 22 Liquid discharge line 24 Gas production line 26a, 26b, 48 Resupply line 28a, 28b Valve 30 Controller 32a, 32b , 34a, 34b, 36a, 36b, 38, 40 Pressure gauge 39a, 39b Shutoff valve 42, 46 Flow meter 44 Valve 45 Gas-liquid separator 46a, 46b Ejector pump 50 Valve 52, 54a, 54b Heater

Claims (11)

A system for producing gas by decomposing gas hydrate in the ground,
A tube having a tip portion configured to be buried in the ground, by reducing the pressure acting on the gas hydrate outside the tube using the pressure of the liquid in the tube, A production pipe having a hole provided at the tip and opened to the outside of the pipe so as to take in a gas-liquid mixture containing bubbles generated by decomposition from gas hydrate into the liquid in the pipe;
A gas-liquid separation device configured to be embedded in the ground and introduced from the production pipe into the gas from the liquid that has taken in the gas-liquid mixture; A pump for sucking liquid to the outside, and a separation pipe provided separately from the production pipe,
A liquid supply line connecting the production pipe and the separation pipe;
A liquid discharge line extending from the separation tube and discharging the sucked liquid to the outside;
A gas production line extending from the separation pipe and transported to the outside as the gas for producing the separated gas;
A resupply line that branches off from the liquid discharge line and returns a portion of the sucked up liquid to the production pipe;
A first valve provided in the resupply line for adjusting the flow rate of the resupply line;
A control device for controlling the opening of the first valve;
A gas production system comprising: Inside the production pipe, the liquid supplied from the resupply line is used as a driving fluid, and the discharge amount of the liquid in the production pipe is sucked and discharged upward according to the flow rate of the driving fluid. An ejector pump is provided,
The gas production system according to claim 1, wherein the gas production system is configured to control the pressure at the tip by adjusting the discharge amount.   The gas production system according to claim 1 or 2, wherein the control device controls the opening degree of the first valve based on a measurement value of the pressure of the liquid in the production pipe.   The control device performs control to increase the opening of the first valve when the measured pressure value is higher than a target bottom hole pressure, and when the measured pressure value is lower than the target bottom hole pressure, The gas production system according to claim 3, wherein control is performed so as to reduce the opening of one valve. The liquid supply line is provided with a shutoff valve that shuts off the supply of the liquid from the production pipe to the separation pipe,
The said control apparatus controls the said cutoff valve based on the differential pressure | voltage of the measured pressure of two positions where the depth direction in the said liquid of the said production pipe differs in the opening degree of the said cutoff valve. The gas production system according to any one of the above.   The control device controls to close the shut-off valve when the differential pressure is greater than or equal to a predetermined threshold, and controls to open the shut-off valve when the differential pressure is less than a predetermined threshold. Item 6. The gas production system according to Item 5. A circulation line is provided that branches off from the liquid discharge line and returns a part of the sucked-up liquid to the separation pipe;
The circulation line is provided with a second valve for adjusting the flow rate of the circulation line,
The said control apparatus controls the opening degree of a said 2nd valve | bulb based on the difference of the measurement pressure in the gaseous phase in the said separation pipe, and the measurement pressure in a liquid phase. Gas production system as described in.   The gas production system according to claim 7, wherein the circulation line includes a heating device that heats a part of the liquid flowing through the circulation line.   Each of a plurality of distributed production pipes dispersedly arranged at a plurality of locations is connected to the separation pipe via the liquid supply line as the production pipe, and the control device includes the first of the distributed production pipes. The gas production system of any one of Claims 1-8 which controls the opening degree of a valve. The production pipe and the separation pipe are buried in the seabed;
The gas production system according to any one of claims 1 to 9, wherein the pump is provided so as to be positioned below the sea bottom in the separation pipe. The gas production system according to claim 10, wherein a connection position of the liquid supply line with the separation pipe is above the pump.

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