JP6471973B2 - Method and apparatus for measuring free gas from groundwater - Google Patents

Description

  The present invention relates to a measurement method and apparatus for free gas from groundwater, and in particular, a measurement method suitable for measuring the amount of free gas generated from groundwater sampled in situ and the volume ratio of free gas and water, and It relates to the device.

  Conventionally, in groundwater surveys, it is common to drill a borehole in the ground and pump groundwater from a target section using an apparatus as shown in FIG. 8 (see, for example, Patent Document 1). The apparatus shown in FIG. 8 includes a packer 2a, a strainer 2b, a pressure gauge 2c, a valve 2d, a JFT rod 2e, a soccer rod 2f, a 3.5 inch tube 2g, a center riser 2h, and a grounder 2 arranged in the borehole 1. A PC pump hydraulic motor 3a, a flow meter 3b, a separator 3c, a gas flow meter 3d, and a ground water quality sensor 3e are disposed.

  On the other hand, a groundwater monitoring system (MP system) is known that collects groundwater in a deep underground state without contacting the atmosphere while maintaining the pressure at the original position (for example, Patent Document 2 and Non-Patent Document 1). reference). In this method, a casing with a packer called an MP casing is installed in a borehole, and groundwater in a section determined thereby is taken into a sampling bottle by opening and closing a sampling port.

  FIG. 9 shows a configuration diagram of the MP system. As shown in this figure, this MP system is composed of casing pipes 5b for each section divided into multiple stages by a plurality of packers 5a installed at predetermined intervals in the depth direction in a borehole 4 provided in the ground. A measurement port 5c for water pressure measurement and a pumping port 5d for water sampling, a location collar 5e for position identification, and an end plug 5f for closing the lower end are provided. The connecting portion of the casing pipe 5b is prevented from leaking water by an O-ring or the like, and the pumping port 5d has a water sampling port (not shown) used for water sampling work or replacement of water in the measurement section.

  A water sampling method using the MP system will be described with reference to FIG. As shown in FIG. 10 (1), a water sampling port 7 a of a sampler bottle 7 for sampling groundwater is connected to the external connection port 6 g at the lower end of the sampler probe 6. By adopting such a configuration, it becomes possible to collect groundwater and measure pore water pressure.

  As a water sampling operation procedure by the sampler probe 6, first, the sampler probe 6 and the sampler bottle 7 connected to the cable 8 are measured from the measurement pipe in the casing pipe 5b (arbitrary measurement) via the winch under the control from the ground. Lower to the position of port 5c). Then, the location arm 6a of the sampler probe 6 is installed in the groove on the inner wall of the measurement port 5c.

  Subsequently, as shown in FIG. 10 (2), with the backing shoe 6b, the introduction port 6d of the pressure sensor 6c of the sampler probe 6 is pressed against the measurement port 5c1 of the measurement port 5c to connect the introduction port 6d to the measurement port 5c1. At the same time, the valve 6f is opened to bring the inlet 6d of the sampler probe 6 and the water sampling port 7a of the sampler bottle 7 into communication. Then, ground water is sampled into the sampler bottle 7 through the inlet 6d of the sampler probe 6, the external connection port 6g, and the water sampling port 7a. In addition, it is also possible to collect water while measuring the pore water pressure in the water collection target section with the pressure sensor 6c.

  Here, the sampler bottle 7 used for water sampling has a hollow structure made of stainless steel, and underground water in a deep underground portion (for example, up to a depth of about 1400 m) can be collected on the ground while maintaining the pressure (sealing pressure). Sampling).

  The sampler bottle 7 collected on the ground is opened after being depressurized, and the enclosed groundwater is transferred to a predetermined sampling bottle on site and then sent to an analysis laboratory for water quality analysis and the like.

JP-A-3-69793 Japanese Patent Laying-Open No. 2015-017905

"HDB-3, installation of long-term groundwater pressure and water quality monitoring equipment in the 4th hole (Nuclear Fuel Cycle Development Organization Business Report)", JNC TJ5410 2004-006, March 2004, Shimizu Corporation

  By the way, when the depth increases, free gas is generated from the pumped-up groundwater, so that the gas phase and the liquid phase are separated using a separator. Each flow rate is measured with an electromagnetic flow meter or the like, but since the measured values are unstable, the reliability of the flow rate and gas / water ratio of both is not high. In addition, in the collection of free gas, air is inevitable and the reliability of the gas composition data is low at present. In the safety assessment of radioactive waste disposal sites constructed deep underground, high-quality gas composition data and gas / water ratio data are required, but the above-mentioned conventional methods cannot obtain good-quality data. difficult.

  For this reason, it has been required to more accurately measure the amount of free gas from the groundwater at the in-situ sampled water.

  The present invention has been made in view of the above, and an object of the present invention is to provide a method and apparatus for measuring free gas from groundwater, which can more accurately measure the amount of free gas from groundwater in the original position. And

In order to solve the above-mentioned problems and achieve the object, the method for measuring free gas from groundwater according to the present invention is a method of collecting the groundwater in a sampler bottle installed at the original position and then collecting the groundwater on the ground. The sampler bottle is depressurized and the amount of free gas from the groundwater is measured by a water displacement method. Water used in the water displacement method is water with increased CO ₂ saturation, and CO The pH value of water is measured while increasing the degree of saturation of ₂ , and when the measured pH value reaches an equilibrium state, the amount of free gas is measured.

Further, the apparatus for measuring free gas from groundwater according to the present invention is configured to release the pressure from the groundwater by releasing the pressure of the sampler bottle collected on the ground after sealing the groundwater to the sampler bottle installed at the original position. An apparatus for measuring the amount of gas by a water displacement method, wherein water having increased CO ₂ saturation used in the water displacement method, saturation increasing means for increasing the CO ₂ saturation of water, and pH value of water And pH value measuring means for measuring the amount of free gas when the measured pH value reaches an equilibrium state.

According to the method for measuring free gas from groundwater according to the present invention, after collecting groundwater in a sampler bottle installed at an in-situ pressure, the sampler bottle collected on the ground is depressurized and released from the groundwater. A method for measuring the amount of gas by a water displacement method, wherein water having increased CO ₂ saturation is used as water used in the water displacement method, and the pH value of water is increased while increasing the CO ₂ saturation. When the measured pH value reaches the equilibrium state, the amount of free gas is measured, so that the CO ₂ in the free gas is prevented from dissolving in the water used in the water replacement method, and from the groundwater in situ. The amount of the free gas can be measured more accurately than the conventional method.

Further, according to the apparatus for measuring free gas from groundwater according to the present invention, after collecting groundwater in a sampler bottle installed in-situ, the pressure of the sampler bottle collected on the ground is released from the groundwater. Is a device for measuring the amount of free gas of water by a water displacement method, wherein the water has a higher degree of CO ₂ saturation used in the water displacement method, a saturation increasing means for increasing the CO ₂ saturation of water, Since there is provided a pH value measuring means for measuring the pH value and a free gas amount measuring means for measuring the amount of free gas when the measured pH value reaches an equilibrium state, It is prevented that the CO ₂ is dissolved, and the amount of free gas from the ground water in the original position can be measured more accurately than the conventional method.

FIG. 1 is a diagram showing an example of a groundwater monitoring system (MP system) to which the method and apparatus for measuring free gas from groundwater according to the present invention is applied. FIG. 2 is a diagram for explaining a groundwater sampling method using a groundwater monitoring system (MP system). FIG. 3 is a side sectional view showing an example of the sampler bottle. FIG. 4 is a flow chart of water collection by the groundwater monitoring system (MP system). FIG. 5 is a schematic flow chart showing an embodiment of a method and apparatus for measuring free gas from groundwater according to the present invention. FIG. 6 is a diagram of a water replacement method showing an embodiment of a method and apparatus for measuring free gas from groundwater according to the present invention. FIG. 7 is a diagram comparing the measured gas composition ratio in the example of the present invention and the comparative example. FIG. 8 is a schematic view of a conventional pumping test apparatus. FIG. 9 is a diagram showing an example of a conventional groundwater monitoring system (MP system), where (1) is an overall cross-sectional view, (2) is a packer, (3) is a measurement port, (4) is a location color, (5) is a casing pipe, (6) is a pumping port, and (7) is a perspective view of an end plug. FIG. 10 is a flow chart of water sampling by a conventional groundwater monitoring system (MP system), (1) before water sampling and (2) during water sampling.

  Embodiments of a method and apparatus for measuring free gas from groundwater according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  First, a groundwater monitoring system (MP system) to which a method and apparatus for measuring free gas from groundwater according to the present invention is applied will be described with reference to FIGS. 1 and 2.

(MP system)
As shown in FIG. 1, this MP system includes a hollow cylindrical casing pipe 14 (casing) in each section divided into a plurality of stages by a plurality of packers 12 installed at predetermined intervals in the depth direction in the borehole 10. ), A measurement port 16 for water pressure measurement, a pumping port 18 for water sampling, a location collar 20 for specifying the position, and an end plug 22 for closing the lower end. The connecting portion of the casing pipe 14 is prevented from leaking water by an O-ring or the like, and the pumping port 18 has a water sampling port used for water sampling work or replacement of water in the measurement section. Moreover, as a dimension of the casing pipe 14 of each step | paragraph, it can be set, for example as about 50-60 mm in internal diameter, and about 1-3 m in length per one.

  As shown in FIG. 2, the MP system includes a sampler probe 24 having a pressure sensor inserted into the casing pipe 14 and connected to the measurement port 16 to measure the pore water pressure outside the casing pipe 14. A sampler bottle 26 for collecting groundwater through the probe 24 is further provided, and groundwater can be collected and the pore water pressure can be measured in multiple sections in the depth direction. Since the sampler probe 24 has the same structure as the conventional one, detailed description thereof is omitted. The sampler bottle 26 is made of stainless steel, and can collect groundwater in a deep underground portion (for example, up to a depth of about 1400 m) on the ground while maintaining its pressure (sealed pressure sampling).

(Sampler bottle)
Next, the configuration and operation of the sampler bottle 26 will be described.
As shown in FIG. 3, the sampler bottle 26 includes a container that is hermetically sealed with a hollow cylindrical portion 30 that extends vertically and a top portion 32 and a bottom portion 34 that block both ends of the sample. The inner surface sides of the top portion 32 and the bottom portion 34 are formed to be flush with each other. The top portion 32 is provided with a small-diameter water sampling port 36 and is connected to an external dedicated valve 38.

  A fixing member 42a is provided in the concave portion 34a formed in the outer portion of the bottom portion 34, and a capacity changing means 28 is provided below the fixing member 42a. The capacity changing means 28 is composed of a piston rod 42 extending in the vertical direction and a horizontal bar-shaped gripping portion 40 provided at the lower end thereof. By pushing and pulling the piston rod 42 via the gripping portion 40, the bottom 34 is moved in the cylindrical axis direction (cylinder extending direction) within the hollow cylindrical portion 30 while maintaining the airtight state of the sampler bottle 26. It can be done.

  When the piston rod 42 is pushed up so that the inner surfaces of the bottom portion 34 and the top portion 32 are brought into close contact with each other without any gaps, gas such as air accumulated in the sampler bottle 26 is discharged to the outside through the water sampling port 36 and groundwater is put. The capacity of the previous sampler bottle 26 can be easily reduced to zero. This operation needs to be performed at the latest before just before sampling, but is preferably performed before the sampler bottle 26 is connected to the sampler probe 24 on the ground. Further, the pushing and pulling operation of the piston rod 42 is performed by a human hand.

  As a capacity changing means 28 in the sampler bottle 26, a configuration in which the bottom 34 can be moved in the cylindrical axis direction in the hollow cylindrical portion 30 by pushing and pulling a piston rod 42 provided outside the bottom 34 will be described. However, it is not limited to this. For example, by changing the distance between the bottom 34 and the top 32 by moving at least one of the bottom 34 and the top 32 along the cylinder axis direction in the hollow cylindrical portion 30 while maintaining the airtight state of the sampler bottle 26, The capacity of the sampler bottle 26 may be changed. Of course, other structures may be adopted as long as the capacity of the sampler bottle 26 is made to be zero immediately before sampling and the gas inside the bottle can be removed.

Next, a specific procedure of groundwater sampling work by the MP system using the sampler bottle 26 will be described.
As shown in FIG. 2, a sampler bottle 26 is connected to the lower side of the sampler probe 24 via a valve (not shown). Here, the sampler probe 24 also functions as a sampler probe. Under the control from the ground, the sampler probe 24 and the sampler bottle 26 are lowered to the water sampling target location in the casing pipe 14 via the cable 11a, the winch 11b, and the like.

  Here, in order to prevent gas such as air existing in the sampler bottle 26 from being mixed into the groundwater, as shown in FIG. The inner surface sides are kept in close contact with each other without any gap, and the gas volume in the sampler bottle 26 before sampling is set to zero.

  Next, as shown in FIG. 4 (1), the sampler probe 24 and the sampler bottle 26 lowered from the ground are installed in the measurement port 16 of the water sampling target location. Here, the location arm 24a of the sampler probe 24 is urged in a protruding direction so as to be able to appear and retract. The sampler probe 24 is fixed to the measurement port 16 by hooking the location arm 24 a in a spiral groove provided on the inner wall of the measurement port 16.

  Subsequently, as shown in FIG. 4 (2), reaction force is taken from the inner wall of the measurement port 16 with the backing shoe 24 b, and the introduction port 24 d of the pressure sensor 24 c of the sampler probe 24 is pushed into the measurement port 16 a of the measurement port 16. The introduction port 24d is connected to the measurement port 16a. Then, the valve 24f is opened to bring the introduction port 24d and the external connection port 24g of the sampler probe 24 into communication with the water sampling port 36 of the sampler bottle 26. Groundwater is sampled into the sampler bottle 26 through the inlet 24d of the sampler probe 24 while measuring the pore water pressure in the sampling target section with the pressure sensor 24c.

  Here, when sampling water, the water level in the hole in the casing pipe 14 is lowered from the head of the groundwater pressure in the target section. In this state, when the sampler probe 24 is installed in the measurement port 16 in the target section and the valve 24f is opened, the groundwater in the target section flows into the sampler bottle 26 due to the pressure difference. When this operating pressure is set to about 20 kPa, for example, the water level in the hole may be adjusted to 20 kPa or less than the water pressure in the target section. The bottom 34 in the bottle is pushed downward by the pressure of the groundwater flowing into the sampler bottle 26, and finally reaches the bottom of the sampler bottle 26, whereby a predetermined volume of groundwater can be collected.

  The amount of free gas can be measured by collecting the sampler bottle 26 on the ground and releasing the pressure. Here, when the groundwater is taken out from the sampler bottle 26, the valve 38 is opened, and the piston rod 42 is pushed up to reduce the capacity of the sampler bottle 26, whereby the groundwater in the sampler bottle 26 can be recovered.

(Measurement method and apparatus for free gas from groundwater)
Next, a method and an apparatus for measuring free gas from groundwater according to the present invention will be described.

As shown in FIG. 5, in the method for measuring free gas from groundwater according to the present invention, after collecting groundwater in a sampler bottle installed in situ (step S1), pressure is applied to the sampler bottle collected on the ground. It is a method for measuring the amount of free gas from the groundwater by opening the surface by water displacement method (step S2), and using water with increased saturation of CO ₂ (carbon dioxide) as water used in the water displacement method, The pH value of water is measured while increasing the degree of saturation of CO ₂ in water (Step S3), and when the measured pH value reaches an equilibrium state (Yes in Step S4), the amount of free gas is measured. (Step S5). The process of step S1 corresponds to a process of sealing water collection of groundwater into the sampler bottle 26 by the MP system.

  In the process of step S2, the sampler bottle 26 collected on the ground is released in pressure, and the amount of free gas from the groundwater is measured by the surface replacement method.

  FIG. 6 is a diagram showing an outline of the water replacement method according to the present invention, and corresponds to a diagram showing an embodiment of a measuring apparatus for free gas from groundwater according to the present invention. As shown in this figure, a graduated cylinder 46 is arranged upside down on the water surface of a container 44 filled with water W. The sampler bottle 26 communicates with a tube 48 via a valve 38, and the end of the tube 48 is disposed inside the graduated cylinder 46. As a result, free gas generated from the ground water inside the sampler bottle 26 can be collected in the measuring cylinder 46. By measuring the amount of collected free gas, the amount of free gas can be grasped.

Also, this is out of the container 44, CO ₂ is disposed a CO ₂ gas generation means 50 for generating a gas, and can supply the generated CO ₂ gas in the container 44 inside the water W. Further, a pH measuring means 52 for measuring the pH value of the water W is arranged inside the container 44 so that the pH value of the water W can be grasped at any time.

By the way, most of deep underground water contains a certain amount of CO ₂ , and its solubility is several tens of times higher than that of other free gases. Therefore, CO ₂ derived from ground water dissolves in water W in the water displacement method. However, the amount of free gas is measured low, and the free gas composition may not be measured correctly. Therefore, the water W used in the water displacement method instead of distilled water, using what as close as possible to the composition of the target ground water, and bubbled with CO ₂ gas by the CO ₂ gas generating unit 50, increasing the saturation of the CO ₂ (Step S3 above). This confirmation is performed by observing the pH value of the water W in the water replacement method with the pH measuring means 52. When CO ₂ is bubbled, the pH value of the water W decreases and reaches an equilibrium at a certain value (Yes in step S4 above). At this time, the amount of free gas is measured (step S5 above). Further, by collecting this gas from the graduated cylinder 46 in water, it is possible to prevent air from entering.

As described above, according to the present invention, it is prevented that the CO ₂ in the free gas dissolves in the water W used in the water replacement method, and the amount of free gas from the ground water at the original position is more accurately determined than the conventional method. Can be measured.

  In addition, the groundwater can be collected by pushing up the movable bottom 34 by the piston rod 42 provided in the sampler bottle 26 (see FIG. 3). The gas / water ratio can be measured by measuring the amount, and the groundwater composition can be obtained by analyzing this water.

(Verification of the effect of the present invention)
Next, verification of the effect of the present invention will be described.
Table 1 compares the gas / water ratio measured about the groundwater samples 1 and 2 sampled in the water sampling section from which a borehole differs in the Example of this invention, and a comparative example. FIG. 7 compares the obtained free gas compositions.

In this exemplary embodiment of the present invention, the measurement results when the pH value was collected free air on the water displacement method using a hole water with increased saturation of CO ₂ until equilibrium (groundwater) is there. Moreover, a comparative example (pumping test) is a measurement result by said conventional pumping test. In the comparative example (pumping test), air is inevitable in collecting free gas. Moreover, a comparative example (distilled water) is a measurement result at the time of collecting free gas by the water displacement method using distilled water.

As shown in Table 1, the gas / water ratio according to the embodiment of the present invention is higher than the values according to the comparative example (pumping test) and the comparative example (distilled water), but this escapes liberated gas. It is thought that it was able to measure without being. Further, as shown in FIG. 7, it can be seen that the present invention can prevent the dissolution of CO ₂ in the free gas in the water used in the water replacement method, and can measure a more accurate gas composition.

  In the environmental impact assessment of radioactive waste disposal, it is very important to understand the deep groundwater quality including the amount and composition of free gas. According to the present invention, it becomes possible to accurately measure the amount and composition of free gas in the groundwater monitoring hole, and to provide basic data for estimating deep groundwater quality.

As described above, according to the method for measuring free gas from groundwater according to the present invention, after collecting groundwater in a sampler bottle installed at an in-situ pressure, the sampler bottle collected on the ground is released by pressure. A method for measuring the amount of free gas from groundwater by a water displacement method, wherein water having increased CO ₂ saturation is used as water for the water displacement method, while increasing the CO ₂ saturation level of water. When the measured pH value reaches an equilibrium state, the amount of free gas is measured, which prevents the CO ₂ in the free gas from being dissolved in the water used in the water replacement method. The amount of free gas from groundwater at the location can be measured more accurately than conventional methods.

Further, according to the apparatus for measuring free gas from groundwater according to the present invention, after collecting groundwater in a sampler bottle installed in-situ, the pressure of the sampler bottle collected on the ground is released from the groundwater. Is a device for measuring the amount of free gas of water by a water displacement method, wherein the water has a higher degree of CO ₂ saturation used in the water displacement method, a saturation increasing means for increasing the CO ₂ saturation of water, Since there is provided a pH value measuring means for measuring the pH value and a free gas amount measuring means for measuring the amount of free gas when the measured pH value reaches an equilibrium state, that is prevented that CO ₂ is dissolved, can be measured more accurately than conventional methods the amount of free gas from groundwater in situ.

  As described above, the method and apparatus for measuring free gas from groundwater according to the present invention includes a sampler collected on the ground after the sampler bottle is installed in its original position and groundwater at this position is sealed in the sampler bottle. It is useful for investigating the quality of groundwater by opening the bottle after decompression, and is particularly suitable for more accurately measuring the amount of free gas from the groundwater.

DESCRIPTION OF SYMBOLS 10 Boring hole 12 Packer 14 Casing pipe 16 Measurement port 16a Measurement port 18 Pumping port 20 Location collar 22 End plug 24 Sampler probe 24a Location arm 24b Backing shoe 24c Pressure sensor 24d Inlet 24e Plunger 24f Valve 24g External connection port 26 Sampler bottle 28 capacity changing means 30 hollow cylindrical portion 32 top 34 bottom 34a concave portion 36 adopted Mizuguchi 38 valve 40 grip portion 42 the piston rod 42a fixed member 44 container 46 graduated cylinder 48 tube 50 CO ₂ gas generating unit 52 pH measurement means W water

Claims (2)

A method of measuring the amount of free gas from the groundwater by water-replacement method after releasing the pressure of the sampler bottle collected on the ground after sealing the groundwater to the sampler bottle installed at the original position,
As water used in the water replacement method, water with increased CO ₂ saturation is used.
A method for measuring free gas from ground water, wherein the pH value of water is measured while increasing the CO ₂ saturation of water, and the amount of free gas is measured when the measured pH value reaches an equilibrium state. . After sealing and collecting groundwater in a sampler bottle installed in the original position, the sampler bottle collected on the ground is pressure-released and the amount of free gas from the groundwater is measured by a water displacement method,
Water with increased CO ₂ saturation used in the water displacement method;
A saturation increasing means for increasing the CO ₂ saturation of water;
PH value measuring means for measuring the pH value of water;
An apparatus for measuring free gas from groundwater, comprising: a free gas amount measuring means for measuring a free gas amount when a measured pH value reaches an equilibrium state.