JP6916497B1 - Thermophysical property measuring device and method for measuring thermal conductivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method for measuring thermal conductivity which can be applied to a general heat exchange well or a well in shallow ground where there is no water in a hole, and a thermophysical property measuring device which can be used for this measuring method. SOLUTION: A packer having an expansion / contraction portion, a means for pouring fluid into the expansion / contraction portion, a cylindrical heat source wound around the expansion / contraction portion, a temperature sensor arranged on the outer peripheral side of the cylindrical heat source, the cylindrical shape. The cylindrical heat source comprises a power source for supplying power to the heat source and a recording means for recording the temperature measured by the temperature sensor, or the cylindrical heat source is composed of a sheet-shaped heat generating body or an elastic member and the sheet-shaped heat generating body. The packer can move in the hole together with the cylindrical heat source and the temperature sensor when the expansion / contraction portion contracts, and the expansion / contraction portion brings the sheet-shaped heating element and the temperature sensor into close contact with the hole wall during expansion. A thermophysical property measuring device for measuring the thermal physical properties of the ground at the in-situ in the hole, and a method for measuring the thermal conductivity using the device. [Selection diagram] Fig. 1

Description

The present invention relates to a thermophysical property measuring device and a method for measuring thermal conductivity. More specifically, the present invention relates to a thermophysical property measuring device for measuring the thermophysical properties of the ground at the in-situ in the well, and a method for measuring the thermal conductivity of the ground at the in-situ.

The thermal conductivity of soil and ground is an important physical quantity in the fields of earth science, resources, environment, agriculture, civil engineering and construction. In particular, in geothermal heat utilization systems that use geothermal energy, which is one of the renewable energies that have become widespread in Japan and overseas in recent years, the heat conduction of the ground is used to estimate the amount of heat collected during its design and construction. It is necessary to know the rate.

There is a hot water circulation method as a thermal response test for determining the thermal conductivity, which is often used when installing a geothermal heat utilization system. In this method, a U-shaped pipe (U-shaped pipe) to which a temperature sensor is attached is inserted into a well, and after insertion, silica sand or the like is filled between the hole wall and the U-shaped pipe, and then the U-shaped pipe is formed. Hot water is flowed inside, and the thermal conductivity of the depth is obtained from the time change of the temperature sensor attached to the U-shaped tube, and the average thermal conductivity in the depth direction is obtained from the time change of the temperature at the entrance and exit of the U-shaped tube ( Patent Document 1, Patent Document 2, Non-Patent Document 1)

Further, a method using an electric heater has been proposed as a method for easily measuring the thermal conductivity. As one of these methods, a linear electric heating heater (heating wire) is used to heat the inside of the hole, and a temperature sensor is placed along it to monitor the change in temperature over time while heating the heating wire to improve the thermal conductivity. A measuring method has been developed and put into practical use (Non-Patent Document 2).

Furthermore, as an attempt to apply the method using an electric heater in a well with a large hole diameter such as a heat exchange well of a geothermal heat utilization system, a wound heating wire was inserted inside a steel container. A method of heating the inside of a hole and measuring the thermal conductivity has been developed (Patent Document 3).

Japanese Unexamined Patent Publication No. 2003-4680 Japanese Unexamined Patent Publication No. 2018-173293 Japanese Unexamined Patent Publication No. 2007-263957

Geothermal Utilization Promotion Association, Constant Heating / Hot Water Circulation Method Thermal Response Test (TRT) Technical Book August 2018, http://www.geohpaj.org/wp/wp-content/uploads/trt_draft_20180830.pdf Geosystem homepage, http://www.geo-system.jp/image/TCP_HCpunf190131.pdf

The method described in Patent Document 1 and the like has a problem that a U-shaped pipe needs to be buried in the ground and a device on the ground becomes large-scale. Further, since it is actually difficult to pull out the U-shaped pipe from the ground after the heat response test is carried out, it is common to use this U-shaped pipe as it is as a heat exchange pipe of the geothermal heat utilization system. Therefore, even if it becomes clear that the amount of heat collected is insufficient by conducting a heat response test, it is difficult to take measures such as digging deeper into the heat exchange well. If the amount of heat collected is insufficient, it is necessary to re-drill a new heat exchange well to secure the amount of heat collected.

The method described in Non-Patent Document 2 requires a lot of time and heat because the heat source is linear and it is necessary to heat the entire water in the hole in the section, and a sensor is inserted in the center of the hole. There is a problem that it is difficult. Therefore, the pits to which this method can be applied are said to be pits with a small pore diameter (generally up to a pore diameter of about 100 mm). However, since the hole diameter of the heat exchange well installed in the geothermal heat utilization system is generally as large as about 150 mm, it is difficult to apply this method to the heat exchange well of the geothermal heat utilization system.

In the method described in Patent Document 3, the inside of the hole is heated in a place closer to the hole wall, but in reality, the water in the hole is sandwiched between the hole wall and the steel container, and convection or the like is caused. The thermal effect cannot be ignored. If the steel container is designed with an outer diameter that is approximately the same as the hole diameter of the hole in order to reduce such thermal effects, the hole will be bent (the one that was bent in the middle of the excavation process). It cannot even be physically inserted into the hole. Furthermore, the steel container to be inserted into the hole and its contents are heavy for the measurement work, and the work of hanging and lowering is not easy.

Further, all of the above-mentioned conventional methods are indirect methods in which the hole wall is not directly heated, but the water in the hole in the vicinity of the heating element is heated, and the water in the hole heats the wall surface. Therefore, there is a problem that it cannot be applied to shallow soil or ground where there is no in-pore water.

An object of the present invention is to provide a thermal property measuring device for ground and a method for measuring thermal conductivity, which solves the above-mentioned problems of the conventional method. Specifically, it can be applied to general heat exchange wells, and it can be easily applied to wells in shallow ground where there is no water in the holes, which is difficult to measure by conventional methods. To provide a method for measuring the above-mentioned material and a thermophysical property measuring device that can be used for the measuring method.

The present inventors have diligently studied to solve the above problems, and have found that the thermal physical properties of the ground can be measured by utilizing a construction method for ground improvement and a packer conventionally used for ground investigation. Then, based on this finding, further studies were carried out to complete the present invention.
Specifically, the present invention is as follows.

<1> A thermophysical property measuring device for measuring the thermophysical properties of the ground at the in-situ position in the hole.
A packer having a stretchable portion that contracts and expands when the fluid is poured in and out, a means for pouring and pouring the fluid into the stretchable portion, a cylindrical heat source that winds around the stretchable portion, and an outer peripheral side of the cylindrical heat source. It includes a temperature sensor, a power source that powers the cylindrical heat source, and a recording means that records the temperature measured by the temperature sensor.
The cylindrical heat source is composed of a sheet-shaped heating element, or is composed of an elastic member and the sheet-shaped heating element.
The packer can move in the borehole together with the cylindrical heat source and the temperature sensor when the expansion / contraction portion contracts.
The expansion / contraction portion is a thermophysical characteristic measuring device in which the sheet-shaped heating element and the temperature sensor are brought into close contact with the hole wall of the well when expanded.
<2> The thermophysical property measuring device according to <1>, wherein the sheet-shaped heating element is a silicon rubber heater.
<3> The thermophysical characteristic measuring device according to <1> or <2>, which has a heat insulating member between the stretchable portion and the sheet-shaped heating element.
<4> The thermophysical characteristic measuring device according to any one of <1> to <3>, wherein the fluid is air.
<5> The packer includes a pipe and a tubular elastic member, the elastic member is wound around a part of the pipe, and the elastic portion is formed by the outer circumference of the partial portion and the elastic member. The thermophysical property measuring device according to any one of <1> to <4>.
<6> The thermophysical characteristic measuring device according to any one of <1> to <5>, wherein the recording means records time-series data of the temperature measured by the temperature sensor.

<7> A thermal conductivity measuring method for measuring the thermal conductivity of the ground at the in-situ position in the well, and the thermal conductivity using the thermophysical property measuring device according to any one of <1> to <6>. Measuring method.
<8> Placing the packer, the cylindrical heat source, and the temperature sensor in the well.
Inflating the stretchable portion to bring the sheet-shaped heating element and the temperature sensor into close contact with the hole wall of the hole.
Heating the hole wall with the sheet-shaped heating element Recording the time-series data of the change in the temperature measured by the temperature sensor due to the heating by the recording means, and theoretically solving the time-series data or The method for measuring thermal conductivity according to <7>, which comprises obtaining the thermal conductivity by comparing with a reference curve created by using numerical analysis.

The present invention provides a thermophysical property measuring device that can be used in a general heat exchange well. Using the thermophysical property measuring device of the present invention, it is possible to measure the thermal conductivity of shallow soil or ground without perforated water, which was difficult to measure by the conventional in-situ thermal conductivity measuring method. In addition, the thermophysical characteristic measuring device of the present invention can be easily operated because the portion suspended in the well can be reduced in weight.

It is a conceptual diagram of the example of the thermophysical characteristic measuring apparatus of this invention. It is a figure which shows the usage form of the thermophysical characteristic measuring apparatus of this invention. It is a conceptual diagram of the theoretical model of the surface temperature by an infinite length cylindrical heat source. It is a figure which shows the example of the reference curve of thermal conductivity using a theoretical solution. It is a figure which shows the example which verified the influence on the temperature change by a heat capacity. It is a figure which shows the example which evaluated the change of the calorific value and the hole wall temperature in the thermophysical property measuring apparatus of this invention by the model of the cylindrical heat source of infinite length. This is an example of a calculation grid when the temperature data obtained by the thermophysical characteristic measuring apparatus of the present invention is analyzed by a method by numerical analysis. It is a figure which shows the example of the reference curve of the thermal conductivity obtained by the method by the numerical analysis in order to compare the temperature data obtained by the thermophysical characteristic measuring apparatus of this invention. It is a figure which compared the temperature data obtained in the test performed as the Example which concerns on this invention, and the reference curve of the thermal conductivity obtained by the method by a numerical analysis.

Hereinafter, the present invention will be described in detail.
In the present specification, the ground is the crust and is composed of soil. In the present specification, the term "ground" mainly means the ground in which a hole is provided (in the ground).
In the present specification, a well is a drilling hole. The hole is particularly preferably a cylindrical hole provided by excavating the ground. Examples of the wells include holes excavated as heat exchange wells of geothermal heat utilization systems, geological boring survey holes, and the like. In the boring excavation of heat exchange wells, a method of excavating while inserting a casing is common. In addition, if the ground is composed of unconsolidated mud or sand, the ground in the hole is likely to collapse, so it may be protected by a casing. In the present specification, the hole may be provided with a casing. Therefore, in the present specification, the term "hole wall" means the inner wall of the ground in the hole or the inner wall of the casing depending on the presence or absence of the casing in the hole.

In general, the methods for measuring the thermal properties and thermal conductivity of the ground are roughly classified into two types. One is to collect soil, geological samples, and rock samples, and then use the values measured by penetrating or stationary needle-shaped sensors (needle probes) or stationary sensors in the laboratory on the ground (indoors). Measurement method). The other is a method (in-situ measurement method) in which a sensor or the like is inserted into a hole or the like and the value measured at the in-situ position at the depth of the measurement target is used.

As a problem of the indoor measurement method, the state of the sample changes due to physical deformation when collecting the ground sample from the ground or deformation caused by the pressure inside the sample being released on the ground. Sometimes. As a result, there may be a difference between the indoor measurement value and the in-situ measurement value. Therefore, the in-situ measurement method is suitable for knowing the thermal conductivity of the state existing in the underground environment.

In general, there is groundwater in the ground at a depth of several meters, which exists as pore water in the cracks of soil particles and rocks. The thermal conductivity considering the effect of such pore water is particularly called "effective thermal conductivity", and when groundwater is flowing, the thermal conductivity considering the effect including the advection effect is called "apparent effective heat". It is called "conductivity". For example, this "apparent effective thermal conductivity" is indispensable for the preliminary evaluation of the design and construction of heat exchange wells in geothermal heat utilization systems. In order to measure these "effective thermal conductivity" and "apparent effective thermal conductivity", an in-situ measurement method that can measure while maintaining the underground state is indispensable.
The present invention relates to a method for measuring thermal conductivity by an in-situ measuring method and a thermophysical property measuring device that can be used in the method.

Thermophysical property measuring device The thermophysical property measuring device of the present invention is a packer having a stretchable portion that contracts and expands when a fluid is poured in and out, a means for pouring and pouring the fluid into the stretchable portion, and a cylindrical shape that winds around the stretchable portion. It includes a heat source, a temperature sensor arranged on the outer peripheral side of the cylindrical heat source, a power source for supplying power to the cylindrical heat source, and a recording means for recording the temperature measured by the temperature sensor. The thermophysical property measuring device of the present invention can measure the thermophysical properties of the ground at the in-situ position in the well.

<Packer>
The packer includes a stretch site that contracts and expands as the fluid is poured in and out. The packer may include a stretchable portion as well as a portion that does not contract or expand due to the inflow and outflow of fluid. For example, the packer is configured to include a stretchable member that constitutes the stretchable portion and a linear pipe that holds the stretchable member. Typically, there is a structure in which the telescopic member is wound around a part of the pipe (for example, a part near one end). For example, the packer has a substantially columnar structure, and the stretchable portion contracts and expands in the circumferential direction. The shape and size of the stretchable part in the direction in which the stretchable part contracts and expands shall be adjusted to the pit to be measured, and the packer can move in the pit during contraction, and the stretchable part is cylindrical during expansion. The sheet-shaped heating element and temperature sensor in the heat source are designed so that the sheet-shaped heating element and temperature sensor can be brought into close contact with the hole wall of the well. That is, the expansion / contraction portion of the substantially columnar packer has a size that is substantially the same diameter as the hole diameter of the well. The height of the cylindrical expansion / contraction portion wound around the pipe is preferably equal to or higher than the height of the sheet-shaped heating element so that the entire surface of the sheet-shaped heating element in the cylindrical heat source can be pressed.

For the stretchable portion of the packer, for example, a resin such as natural rubber or nylon, or a stretchable member such as cloth is used. The expansion / contraction portion of the packer may be composed of only the expansion / contraction member, but may be composed of the expansion / contraction member and other members. For example, a tubular stretchable member (rubber tube, etc.) is wound around a part of the outer circumference of the pipe in the length direction, and fluid is injected into the space formed between the part of the outer circumference and the stretchable member, and from the space. The fluid can be poured out. That is, the expansion / contraction portion may be formed by the above-mentioned partial outer circumference and the expansion / contraction member. A fluid inlet / outlet can be provided between the inside of the pipe and the space. Further, a tube for connecting the injection port and the means for injecting and injecting the fluid can be provided in the pipe. Alternatively, one end of the tube may be inserted into the space outside the pipe, and the other end may be connected to a means for injecting and discharging the fluid.

When the packer includes the above-mentioned pipe, the pipe can also function as a means for moving the expansion / contraction portion of the packer, the cylindrical heat source, and the temperature sensor in the borehole. For example, the above function can be obtained by using a pipe that is sufficiently long with respect to the length of the expansion / contraction portion (height when placed in the well). Further, by using a screw-in type pipe as a pipe, it is possible to lower (hang) the inside of the hole while extending it on the ground. By this method, the measurement can be easily performed even when the measurement is performed in a well having a depth of 2 meters or more. When the pipe is extended on the ground, the fluid injection / discharge tube may be extended from the inside of the pipe to the outside of the pipe directly above the expansion / contraction part of the packer and fixed along the pipe.

As the pipe, for example, a metal pipe, a vinyl chloride pipe (a pipe made of polyvinyl chloride), an acrylic pipe or the like can be used. It is also preferable to use a screw-in type pipe as described above.

As a packer, for example, a simple packer for groundwater level measurement developed by Miyashita (Yuji Miyashita (2009): Development of a portable packer system for self-injection height measurement, Onchiken Report Vol. 41, 69-72), etc. Can be used. As the packer, a commercially available packer (see, for example, Toyo Shoji Co., Ltd. WEB catalog, https://toyoshoji.com/t-38-t-46-t-58/) may be used.

As the fluid to be poured into and from the stretchable portion of the packer, a gas, a liquid, a mixture of gases and liquids, and the like can be used. Examples of fluids include air, nitrogen, water and the like.

When the packer expands and contracts, the sheet-shaped heating element and the temperature sensor can be brought into close contact with the hole wall. At the time of such close contact, the hole wall can be heated by the sheet-shaped heating element, and the temperature change due to the heating can be measured by the temperature sensor. The above adhesion may be achieved by expanding the expansion / contraction portion and pressing the sheet-shaped heating element and the temperature sensor in the direction of the hole wall. Further, the above-mentioned adhesion means contact to such an extent that the hole wall can be heated by the sheet-shaped heating element and the temperature change due to the heating can be measured by the temperature sensor. The cylindrical heat source and temperature sensor can move in the well together with the packer when the stretchable part of the packer contracts. Therefore, the thermophysical property measuring device of the present invention can measure the thermophysical characteristics at an arbitrary position in the well in the original position by repeating the contraction and expansion of the expansion / contraction portion of the packer.

<Means for pouring in and out of fluid>
A pump may be used as a means for injecting and injecting the fluid into the expansion / contraction portion of the packer. The pump may be, for example, one that can inject and inject the fluid to the inflow / outflow port of the fluid at the expansion / contraction portion of the packer via a tube. If the fluid is air, an air compression pump can be used. The means for pouring and pouring the fluid into the stretchable portion of the packer may further include a tank for storing the fluid, a flow meter for measuring the amount of the fluid, a device for controlling the pouring and pouring of the fluid, a power source, and the like.

<Cylindrical heat source>
The thermophysical characteristic measuring device of the present invention includes a cylindrical heat source. The cylindrical heat source consists of a sheet-shaped heating element or a sheet-shaped heating element and an elastic member. The sheet heating element can be a heating site in a cylindrical heat source.

As the sheet-shaped heating element, a heating element having flexibility enough to follow or move to follow the contraction and expansion of the expansion / contraction portion of the packer and to be in close contact with the hole wall is used. The sheet heating element is preferably water resistant. By using a water-resistant sheet-shaped heating element, it becomes easy to measure at a position below the water table using the thermophysical property measuring device of the present invention. Further, the sheet-shaped heating element preferably has heat resistance and electrical insulation. A preferable example of the sheet-shaped heating element is a silicon rubber heater. The silicon rubber heater has a structure in which a heating element is sandwiched between silicone resin sheets from both sides. As the silicon rubber heater, it is preferable to use a water resistant silicon rubber heater.

The cylindrical heat source is wound around the expansion and contraction part of the packer, and the sheet heating element in the cylindrical heat source is configured to follow or move according to the contraction and expansion of the expansion and contraction part of the packer. Just do it. Therefore, the sheet heating element may be adhered to the surface of the stretchable portion of the packer, but is close to the surface of the stretchable portion so that it can move in the direction of the contraction and expansion as the stretchable portion contracts and expands. It may only be placed in position. It is easier for the expansion and contraction mechanism to work smoothly if the sheet-shaped heating element and the expansion / contraction part are not fixed on the entire surface but on a part of the surface.

The cylindrical heat source is composed of a sheet-shaped heating element and an elastic member, and it is preferable that the sheet-shaped heating element is adjusted by the elastic member so as to follow the contraction and expansion of the expansion / contraction portion of the packer. A rubber sheet can be used as the elastic member. The sheet-shaped heating element and the elastic member may be combined in a cylindrical shape by using an adhesive, a fixture such as a stapler, or a method such as suturing to form a cylindrical heat source.

The cylindrical heat source may cover the entire surface or a part of the stretchable portion of the packer. The expansion and contraction part of the packer may be covered by the entire inner circumference of the cylindrical heat source, and the expansion and contraction part of the packer may be covered by a part of the inner circumference of the cylindrical heat source. It is preferable to cover the.

The sheet-shaped heating element may cover the entire surface or a part of the expansion / contraction portion of the packer. The sheet-shaped heating element is, for example, twice to 20 times as high as the hole diameter (diameter) of the hole (preferably 5 to 20 times as high) and 60 ° to 360 ° around the circumference of the hole. (Preferably 120 ° to 360 °) may be heated. The sheet-shaped heating element may have an area capable of heating this area. Measurement of the thermal conductivity of the ground by using a thermophysical property measuring device that allows the sheet-shaped heating element to be 10 times or more the height of the hole diameter (diameter) of the hole and heat 360 ° around the circumference of the hole. When applied to, a method using a theoretical solution can be used.

<Power supply>
The thermophysical characteristic measuring device of the present invention includes a power source that supplies electric power to a cylindrical heat source. The power source may be a power source for a sheet-shaped heating element. The sheet-shaped heating element can be connected to the power supply by a power supply line. It is preferable that the power supply line has a length such that a cylindrical heat source is inserted into the well and the power supply can be operated on the ground. The power supply line may be arranged, for example, inside (inner circumference side) or outside (outer circumference side) of the pipes constituting the packer.

<Temperature sensor>
The temperature sensor is a member for measuring the hole wall temperature in time series in the thermophysical property measuring device of the present invention. It is preferable that the temperature sensor can measure a difference of 0.01 ° C. For example, a thermistor, a platinum resistance temperature detector, or the like can be selected and used depending on the temperature of the measurement target, the required accuracy, and the like. In the thermophysical characteristic measuring device of the present invention, the temperature sensor is provided on the outer peripheral side of the cylindrical heat source. At this time, it is assumed that the expansion / contraction portion of the packer, the sheet-shaped heating element, and the temperature sensor are arranged in this order.

The temperature sensor is preferably arranged at a portion close to the center of the region formed by the heat generating portion in the sheet-shaped heating element. The temperature sensor may or may not be adhered to the surface of the sheet heating element.

In the thermophysical characteristic measuring device of the present invention, the number of temperature sensors may be one or two or more. For example, in consideration of the soil and the stratum at the position of the ground in the pit to be measured, two or more temperature sensors may be provided and the data of the optimum position may be adopted, or the data of the average value may be adopted. It is also possible to obtain thermophysical property data on the north and south sides of the pit, for example, by using the analysis of the data at different points.

<Recording means>
The thermophysical characteristic measuring device of the present invention includes a recording means for recording the temperature measured by the temperature sensor. The temperature sensor and the recording means can be connected by a signal line. The signal line of the temperature sensor is preferably of a length capable of inserting the temperature sensor into the well and arranging the recording means on the ground. The signal line may be arranged, for example, inside (inner circumference side) or outside (outer circumference side) of the pipes constituting the packer. As the recording means, a recording means capable of recording time-series data of the temperature measured by the temperature sensor is preferable.

<Insulation member>
In the thermophysical characteristic measuring device of the present invention, in order to prevent heat from flowing from the sheet-shaped heating element to the packer, it is preferable to provide a heat insulating member between the stretchable portion of the packer and the sheet-shaped heating element. It is more preferable to provide a heat insulating member between the stretchable portion of the packer and the cylindrical heat source.

<Example of thermophysical property measuring device>
FIG. 1 shows an example of the thermophysical characteristic measuring device of the present invention.
The thermophysical characteristic measuring device of FIG. 1 has a cylindrical heat source to be inserted into a well, a temperature sensor, and a packer, and further has an equipment portion to be installed on the ground. The cylindrical heat source is composed of a water-resistant silicon rubber heater 1, a heat insulating sheet 2, and an elastic rubber sheet 4, and further has a temperature sensor 3 in a portion in contact with the outer periphery thereof. The cylindrical heat source has a cylindrical shape that is wound around the rubber tube 5. As the packer, a simple packer for groundwater level measurement developed by Miyashita is used, and it is composed of a rubber tube 5, a compressed air tube 6, a pipe 7, and a rubber tube fixing wire 8. The pipe 7 is provided with a compressed air inlet / outlet 9 for supplying and discharging compressed air into the tube. A thermistor sensor is used as the temperature sensor 3.

A heat insulating sheet 2 is attached to the surface (inner circumference of the cylindrical heat source) on the packer side with respect to the water resistant silicon rubber heater 1. A non-heat-generating elastic rubber sheet 4 is attached to the end of the water-resistant silicon rubber heater 1 in combination to form a cylindrical heat source in order to follow the expansion and contraction of the expansion and contraction portion of the packer. The temperature sensor 3 is provided at a position near the center of the water-resistant silicon rubber heater 1 in the height direction and at a position farther from the elastic rubber sheet 4. In FIG. 1, the thermophysical characteristic measuring device of the present invention has a temperature sensor signal line 10 and a heater power supply line 11, which are wired to the ground along the inside of the pipe or the outside of the pipe.

The equipment part includes an air compression pump 12, a temperature recorder 13, and a DC power supply 14. As for the water resistant silicon rubber heater 1, the heat insulating sheet 2, the temperature sensor 3, the elastic rubber sheet 4, and the like, commercially available members can be used.

FIG. 2 shows a usage pattern of the thermophysical characteristic measuring device of the present invention. This is an example of using the example shown in FIG. 1 as a thermophysical characteristic measuring device.
A packer is hung from a well in the ground to be measured to a depth to be measured by using a pipe 7 in a state where the stretchable portion is contracted. At this time, the heater power supply line 10 and the temperature sensor signal line 11 are fixed outside the pipe while the pipe is inserted into the hole.

After that, compressed air is injected from the ground through the compressed air tube 6 to expand the expansion / contraction portion of the packer, and the water-resistant silicon rubber heater 1 and the temperature sensor 3 are brought into close contact with the hole wall. Next, a constant electric power is supplied by the DC power supply 14 on the ground to heat the water-resistant silicon rubber heater 1 to heat the hole wall to perform measurement. Then, at the end of measurement, the power is turned off and heating is stopped.

After the heating is stopped, the compressed air at the expansion / contraction portion of the packer is discharged to the ground through the compressed air tube 6, and the expansion / contraction portion of the packer and the cylindrical heat source attached thereto are contracted. Then, the packer can be collected on the ground to complete the measurement, or the packer can be moved to the next measurement target depth in the well (preferably descending), and the measurement can be performed in the same procedure. The measurement is preferably carried out from a shallow depth to a deep depth. This is because there is no disturbance of the water in the hole and the thermal effect is small.

Method for Measuring Thermal Conductivity The thermophysical property measuring device of the present invention can be used for measuring the thermal conductivity of the ground. For example, it can be preferably used for measuring the thermal conductivity (effective thermal conductivity or apparent effective thermal conductivity at a certain depth of groundwater) at the time of excavation of a heat exchange well for installing a geothermal heat utilization system.

The thermal conductivity of the ground can be determined by using time-series data of changes resulting from heating of the sheet-shaped heating element at the temperature measured by the temperature sensor of the thermophysical property measuring device of the present invention. Specifically, the thermal conductivity can be obtained by comparing the reference curve created by using the theoretical solution or the numerical analysis with the above time series data according to the method of analyzing the thermal conductivity described later.

The measurement interval for recording the time-series data of the temperature measured by the temperature sensor can be appropriately set according to the thermophysical properties of the soil and layer position of the ground to be measured, the required measurement accuracy, and the total measurement time. However, it is preferably as short as possible, for example, at intervals of about 1 minute.
After the sheet-shaped heating element and the temperature sensor are brought into close contact with the hole wall, it is preferable to measure the temperature in the natural state before heating for 60 minutes or more.

The amount of electric energy (or voltage and current) for heating in the sheet-shaped heating element when measuring the thermal conductivity of the ground can be set to an appropriate value according to the required amount of heating. Since the appropriate amount of heating depends on the soil of the ground to be measured and the thermophysical properties of the stratum position, the appropriate heating should be examined in advance using the ground information at the time of drilling a hole, the theoretical model of the cylindrical heat source, and the numerical analysis method. It is preferable to set the amount. The heating time varies depending on the pore size of the well and the thermal conductivity of the surrounding soil and ground, but is preferably several hours to several days.

The change in the temperature measured by the temperature sensor due to the heating of the sheet-shaped heating element may be a change in the heating process by the sheet-shaped heating element or a change in the temperature recovery process after heating. That is, the thermal conductivity may be calculated from the temperature-time change (temperature rise) of the hole wall in the heating process (heating method), or the temperature change in the temperature recovery process after heating is also measured to calculate the thermal conductivity (the heat conductivity is calculated). (Recovery method) may be used. When measuring the temperature in the recovery process, it is preferable to continue the temperature recording for several hours to several days after the completion of heating.

As described above, the hole may be provided with a casing. As the casing, a pipe material such as a steel pipe is usually used. Further, as the pipe material, a material having a diameter of about 150 mm is used. For example, since steel pipes have low thermal resistance, it is possible to investigate the thermal conductivity of the surrounding ground (stratum) from the inner wall of the casing by taking an appropriate measurement time. In the method by numerical analysis described later, it is possible to perform an analysis in consideration of the wall thickness and thermal characteristics of this casing, and it is possible to obtain the thermal conductivity of the surrounding soil and ground even with a thick casing or the like. The thermophysical characteristic measuring device of the present invention can be used for measurement in holes of various sizes by appropriately adjusting the size, heating amount, etc. of the sheet-shaped heating element. Of course, if the surrounding strata are rocks or consolidated strata and the inner wall of the ground in the well is in a state where it does not easily collapse, it is possible to measure in a bare hole state without using a casing.

<Analysis method>
As an analysis method for obtaining the thermal conductivity, there are a method using a theoretical solution and a method using a numerical analysis. Kelvin's radiation source function and cylindrical heat source function (both Ingersoll, LR, Zobel, OJ and Ingersoll, AC. (1954) Heat conduction with engineering, geological, and other applications. An analysis method based on McGraw-Hill, New York, 325p.) Is known. As a method using numerical analysis, an analysis method using a numerical model using a finite difference method or a finite element method is known.

The method using the theoretical solution can be used when the actual measurement situation (the shape of the measuring device, the state of the hole, etc.) matches the model assumed by the theoretical solution. In that case, the analysis can be performed accurately and with low calculation cost.

An example of a method using a theoretical solution will be described below. The theoretical solution used in this example is based on a constant heating model when the sheet heating element can be regarded as a cylindrical heat source. In order to analyze using this theoretical solution, it is necessary to satisfy the following multiple conformance conditions.
(1) Outer diameter of the cylindrical heat source (In the present specification, when the term "outer diameter of the cylindrical heat source" is used, the expansion and contraction portion of the packer inside the cylindrical heat source is expanded so that the cylindrical heat source is brought into close contact with the hole wall. When the length is sufficiently long and can be regarded as infinite length (the length is about 5 to 10 times or more of the outer diameter) compared to the outer diameter of the cylindrical heat source at the time.
(2) When the thermal resistance of the casing is small and its thermal effect can be ignored (specifically, when the casing is thin and the material has high thermal conductivity).
(3) When it can be considered that the cylindrical heat source can generate heat over the entire circumference of the outer diameter (specifically, the area of the non-heating portion due to the elastic member in the cylindrical heat source is small, and the influence of the non-heating portion is larger than that of the heat generating portion. (If can be ignored),
(4) When the inside of the cylindrical heat source can be regarded as a heat insulating state (in the thermophysical property measuring device of the present invention, a heat insulating member is provided inside the sheet-shaped heating element, or the fluid poured into the stretchable part of the packer is heat-conducted. It can be regarded as a heat insulating state by using air with a small rate). A theoretical solution based on an infinitely long cylindrical heat source model can be used when the above compatibility conditions are satisfied.

When an infinitely long cylindrical heat source is constantly heated (calorific value Q _l per unit length), the temperature T (r, t) at time t at a distance r from the cylindrical heat source is based on the following theoretical solution. It is known that it is required.

T_i: 初期温度 (K)
Q_l: 円筒状熱源の単位長さあたりの発熱量 (W/m)
k: 地層の熱伝導率 (W/m)
r: 円筒状熱源の中心からの距離 (m)
r_b : 円筒状熱源の外径 (m)
L : 円筒状熱源の長さ (m)
C_p: 地層の熱容量 (J /K・m³)
J₀: 第1種0次ベッセル関数
J₁: 第1種1次ベッセル関数
Y₀ : 第2種0次ベッセル関数
Y₁ : 第2種1次ベッセル関数
x :積分変数

T _i : Initial temperature (K)
Q _l : Calorific value per unit length of cylindrical heat source (W / m)
k: Thermal conductivity of the formation (W / m)
r: Distance from the center of the cylindrical heat source (m)
r _b : Outer diameter of cylindrical heat source (m)
L: Length of cylindrical heat source (m)
C _p : Heat capacity of the formation (J / K ・ m ³ )
J ₀ : Type 1 0th-order Bessel function
J ₁ : Type 1 linear Bessel function
Y ₀ : Type 2 0th-order Bessel function
Y ₁ : Type 2 linear Bessel function
x: Integral variable

The temperature of the hole wall (inner wall of the steel pipe when measuring inside the steel pipe) when the cylindrical heat source is brought into close contact with the boring hole wall (inner wall of the steel pipe when measuring inside the steel pipe) and constantly heated is in the above equation. , R = r _b , which can be calculated (Fig. 3).

The thermal conductivity varies greatly depending on the geology, and generally takes a value in the range of 0.5 to 4.0 W / (m · K). If the advection effect due to the flow of groundwater is included, it is necessary to consider the effect. When there is an advection effect of groundwater, the apparent effective thermal conductivity takes a large value of about 1.5 W / (m · K) or more.

As an example of analysis, FIG. 4 shows the results of calculating each temperature change on the surface of the cylindrical heat source when some values of thermal conductivity are assumed. This calculation assumes the case of using an infinite length cylindrical heat source with an outer diameter r _{0 = 150 mm and heating at a calorific value Q l} = 50 W / m (constant) per unit length. Under this condition, the temperature at the hole wall when the thermal conductivity is changed by 0.1 W / (K ・ m) at 1.0 to 2.5 W / (K ・ m) using the theoretical solution. The predicted value of the series change was calculated. Generally, when excavating, it is possible to obtain advance information about the geology in the depth direction from the shavings when excavating the target depth and the information on the surrounding geological column. In this case, it is assumed that the medium is sand, and the heat capacity is 3.03 MJ / (Km ³ ), which is a typical value of sand.

As is clear from FIG. 4, the time change of the temperature T of the surface of the cylindrical heat source differs depending on the difference in the thermal conductivity of the measurement target (ground). For example, the temperature rise is small. Since the temperature rise range changes depending on the heating amount, the measurement accuracy can be improved by appropriately increasing or decreasing the heating amount according to the thermal conductivity of the measurement target, the measurement time, and the outer diameter of the cylindrical heat source. In the case of a typical stratum, the calorific value Q _l = 50 W / m (constant) shown in this example is suitable. The measurement time is calculated here when heated for 100 hours, but the thermal conductivity is generally calculated with an accuracy of about one digit after the decimal point when used in the design and construction of geothermal heat utilization systems. In that case, a measurement time of about 20 hours is sufficient. Since the heating method in the conventional hot water circulation method requires a heating time of about 60 hours (Non-Patent Document 1), the method of the present invention can reduce the measurement time to less than half.

By the above evaluation, it is possible to heat with a cylindrical heat source, measure the temperature on the surface of the cylindrical heat source, and obtain the thermal conductivity from the time change. Specifically, according to the method shown here, the width of the thermal conductivity expected in advance is calculated at intervals of 0.1 W / (m · K), and a reference curve for each thermal conductivity is created. Then, the time-series data of the time change of the temperature obtained by the actual measurement is compared with the reference curve, the reference curve having a similar tendency is selected, and the thermal conductivity of the selected reference curve is the thermal conductivity of the measured object. It is to decide. As another analysis method, the time-series data of the obtained temperature change over time can be inversely analyzed using the above-mentioned theoretical solution of infinite length cylindrical heat source heating to obtain an unknown thermal conductivity. can.

In the above analysis, the measurement target (medium) is assumed to be sand, and the heat capacity is set to a typical value of 3.03 MJ / (Km ³ ) for sand. It is possible to use a typical value of the heat capacity Cp according to the geology of the target depth from the shavings at the time of excavation and the information of the surrounding geological column chart. In general, the heat capacity of strata has a small difference between geological features. For example, according to the 5th edition of the revised heat transfer engineering data (Japan Society of Mechanical Engineers), the heat capacity (MJ / K ・ m ³ ) for each region is as follows: sand (3.03), gravel (3). .18), clay (3.13), volcanic ash (3.05), peat (3.20), loam layer (3.44), granite (2.92).

For example, assuming sand, in many cases, it falls within the range of heat capacity of ^{± 0.1 MJ / (Km 3), which is a typical value.} An example of verifying the influence of this width on the temperature data measured is shown in FIG. According to the results, the difference due to heat capacity is small compared to the effect of thermal conductivity described above, and in order to analyze the thermal conductivity with an accuracy of 0.1 W / (Km), the stratum at the target depth It can be seen that there is no problem by using a typical heat capacity value.

Further, although the calorific value is illustrated here as 50 W / m, an example in which the calorific value is 30 to 70 W / m and the temperature change corresponding to each calorific value is calculated is shown in FIG. According to the result, it can be seen that the larger the calorific value, the larger the temperature rise range. When selecting an appropriate amount of heat, consider the thermal characteristics (thermal conductivity and heat capacity) of the sample to be measured, the measurement time, and the accuracy of the required thermal conductivity so that a reference curve that can be easily compared with the measured data can be obtained. , It is necessary to examine in advance using theoretical solutions and numerical analysis methods.

When the application of the theoretical model of the infinite length cylindrical heat source does not satisfy the conditions and it is difficult to use the theoretical solution, the method using numerical analysis can be adopted. This method can also be applied to measurement environments and measurement conditions to which theoretical solutions cannot be applied. This method is preferable because the temperature data can be analyzed by reflecting the measurement environment and measurement conditions in the numerical analysis. In the method using numerical analysis, for example, it is possible to perform analysis considering the shape of the sheet-shaped heating element, the thermal effect of the steel pipe (casing), and the non-heating portion of the elastic rubber sheet. In the method using numerical analysis, analysis that reflects the three-dimensional shape of an object and individual physical properties is performed (Fig. 7). The method using numerical analysis needs to use a calculation grid of an appropriate size in order to obtain the required accuracy, and the calculation time is generally longer than the method using an analytical solution.

As an example, an example of a method of creating a reference curve of thermal conductivity considering the above effects by using the finite element method is shown below. For the analysis of the finite element method, highly versatile finite element method software widely used in industry and research fields can be used.

The cylindrical heat source (a combination of a water-resistant silicone rubber heater and elastic rubber) when the expansion and contraction part of the packer is expanded and brought into close contact with the hole wall has an outer diameter of 150 mm (outside the sensor assumed in the theoretical model of the cylindrical heat source). Same as the diameter). The length is 400 mm, and the wall thickness of the steel pipe (casing) is 5 mm. In the cylindrical heat source, the non-heating portion is set to 8.3% of the area of the entire surface of the cylinder in consideration of elastic rubber. The temperature sensor is mounted at the center of the length of the water resistant silicone rubber heater, opposite the non-heating part. As a measurement environment, the surrounding geological formations have thermophysical characteristics (thermal conductivity and heat capacity) assuming a saturated sand layer containing water, and the heating amount Q = 45W / m (the calorific value per area is the entire surface of the cylinder as the heat source. (Equivalent to the calorific value of 50 W / m in the case of). Under this condition, the holes when the thermal conductivity is changed at intervals of 0.1 W / (K ・ m) at 1.0 to 2.5 W / (K ・ m) using the method by the finite element method. Calculate the predicted value of the time series change of the temperature on the wall. FIG. 8 is summarized as a reference curve for each thermal conductivity. Similar to the method for determining the thermal conductivity when the theoretical solution is used, the reference curve and the time series data of the measured temperature are compared, and the one having the closest tendency is taken as the thermal conductivity.

Confirmation that the thermal conductivity can be measured using the thermophysical property measuring device of the present invention using the model device, and that the thermophysical characteristic measuring device of the present invention can operate in the borehole by expansion and contraction of the expansion and contraction part of the packer. Was confirmed.

Thermal conductivity measurement A test device was prepared by winding a heat insulating member around an acrylic pipe and then winding a water-resistant silicone rubber heater on the outside to use it as a cylindrical heat source. The size of this test equipment was an outer diameter of 32 mm, which corresponds to a scale of about one-fifth (20%) of the hole diameter of a general geothermal heat exchange well, and a height of 100 mm. This test device is a model device that does not have a configuration corresponding to the expansion / contraction part of the packer. The water resistant silicone rubber heater was entirely heated. The water resistant silicone rubber heater was connected to a DC power supply. A temperature sensor (thermistor sensor) was attached to the outside of the center of the water-resistant silicone rubber heater with a water-resistant film, and the temperature sensor was connected to the temperature recorder. As the water resistant film, a film having a low thermal resistance and not affecting the temperature measurement was used because it was very thin. Place the measurement part (the part including the cylindrical heat source and the temperature sensor) of the above test device in the central part of the transparent acrylic container (300 mm × 300 mm × 300 mm), and dilute the agar until the cylindrical heat source is hidden in the acrylic container. I poured the water melted in. By leaving it in a natural state, the water was fixed by agar while keeping the water and the cylindrical heat source in close contact with each other. A solid water sample obtained by solidifying pure water with agar having a low concentration has known thermophysical properties and is generally used as a standard sample of thermal conductivity.

Under the natural temperature stability of 15.51 ° C. of the water sample, electric power was supplied from a DC power source to heat the water-resistant silicon rubber heater. The electric energy and heating time settings are appropriate for measuring the thermal conductivity with a resolution of 0.1 W / (mK) using the theoretical model (theoretical solution and numerical analysis result) of the cylindrical heat source described above. As the values, it was calculated in advance that the calorific value per unit length was 45 W / m and the heating time was 1200 seconds, and this was adopted.

FIG. 9 shows the time change actually measured in this heating process. In this embodiment, an analysis method based on numerical analysis is adopted, and the thermal conductivity is set at 0.1 W / (m · K) intervals from 0.4 to 0.7 W / (m · K), respectively. The temperature change (reference curve) corresponding to the rate was calculated. Focusing on the data after 800 seconds in which heat is sufficiently propagated to the surrounding samples in this figure, it can be evaluated that the thermal conductivity of this solid water sample is 0.55 W / (m · K). A typical thermal conductivity (16 ° C.) value for a solid water sample is 0.59 W / (m · K). From this result, it was shown that the thermal conductivity can be sufficiently measured within the range of 0.1 W / (m · K) by performing the analysis using the measurement result by the measuring device of the present invention.

Operation check As a model of the well, we prepared a pipe that imitated the casing of the heat exchange well. As this pipe, a transparent acrylic pipe whose inside can be confirmed from the outside was adopted, and the size was set to an outer diameter of 65 mm, which is about half the outer diameter of the actual casing.
As a model of the thermophysical property measuring device of the present invention, a small device including a packer, a cylindrical heat source, and a temperature sensor was manufactured. A rubber tube having a height of 250 mm was used as the expansion / contraction member constituting the expansion / contraction portion of the packer, and a HIVP tube (impact-resistant hard polyvinyl chloride tube) having an outer diameter of 34 mm was used as the core rod of the packer. When the expansion / contraction portion of the packer was inflated without the cylindrical heat source attached, it was possible to inflate it to a maximum outer diameter of about 90 mm. A cylindrical heat source having a height of 120 mm, an outer diameter of 55 mm, and a thickness of 1.5 mm was attached to the stretchable portion of the packer. The water-resistant silicone rubber heater, which is the heat-generating portion of the cylindrical heat source, occupies 320 ° of the entire circumference of 360 ° of the cylindrical heat source, and the elastic rubber of the non-heating portion is 40 °. This cylindrical heat source was able to follow the expansion of the stretchable part of the packer by the stretchable rubber. When inflated with the cylindrical heat source attached, the stretchable part of the packer could be inflated to a diameter of 75 mm. This is a size that can be sufficiently adhered to the above-mentioned acrylic pipe simulating a casing from the inside. A temperature sensor (thermistor) was attached to the outside of the center of the water-resistant silicone rubber heater with a water-resistant film.

The produced small device was inserted into the above-mentioned acrylic pipe and its operation was tested. As a result, the cylindrical heat source and the temperature sensor can be brought into close contact with the inner wall of the acrylic pipe simulating a well in the ground when the expansion and contraction part of the packer expands, and the small device moves up and down when the expansion and contraction part of the packer contracts. It was confirmed that it can be moved to.

With the thermophysical property measuring device of the present invention, it is possible to measure even in a relatively thick hole with an outer diameter of 150 mm or more, which has been difficult to apply by the method using a linear electric heater. Further, by directly heating the hole wall, the measurement time can be shortened as compared with the hot water circulation method or the method using a conventional electric heater (method using a heating wire or a steel container). For example, in the heating method of the hot water circulation method, a measurement time of about 60 hours is standardly required (Non-Patent Document 1), but in the present invention, the measurement can be performed in about 20 hours, which is less than half of the measurement time. Further, since the thermophysical property measuring device of the present invention can freely change the depth of suspension in the well, the thermal conductivity (including effective thermal conductivity and apparent effective thermal conductivity) of the target formation can be specified. It can be used for pinpoint measurements at depth.

In the conventional method of in-situ measurement, since there is a gap between the heating element and the hole wall, the groundwater between the device and the hole wall is first heated by heating, and then the hole wall is indirectly warmed. board. Therefore, there is a problem that it is difficult to measure shallow soil and ground where there is no in-pore water. However, since the thermophysical property measuring device of the present invention directly heats the hole wall, it is possible to measure the shallow ground regardless of the presence or absence of water in the hole, and the thermal conductivity of the shallow ground is measured at the in-situ. Can be used to

On the measurement work surface, since the part arranged in the well is lightweight, measurement can be performed manually or by a simple hanging mechanism. As an industrial effect, by using the thermophysical characteristic measuring device of the present invention for the thermal response test at the time of installing the geothermal heat utilization system, it is possible to measure more easily than before and the measurement time. Can be shortened. In addition, when hanging and lifting, the outer shape of the cylindrical heat source can be reduced by pouring out the fluid in the expansion and contraction part of the packer, so the hole is bent in the middle of the excavation process. It can also be applied to the measurement in.

1 Water resistant silicone rubber heater 2 Insulation sheet 3 Temperature sensor 4 Elastic rubber sheet 5 Rubber tube 6 Compressed air tube 7 Pipe 8 Rubber tube fixing wire 9 Compressed air inlet / outlet 10 Temperature sensor signal line 11 Heater power supply line 12 Air compression pump 13 Temperature recorder 14 DC power supply 101 Packer 102 Cylindrical heat source

Claims (8)

It is a thermophysical property measuring device for measuring the thermophysical properties of the ground at the in-situ in the hole.
A packer having a stretchable portion that contracts and expands when the fluid is poured in and out, a means for pouring and pouring the fluid into the stretchable portion, a cylindrical heat source that winds around the stretchable portion, and an outer peripheral side of the cylindrical heat source. It includes a temperature sensor, a power source that powers the cylindrical heat source, and a recording means that records the temperature measured by the temperature sensor.
The cylindrical heat source is composed of a sheet-shaped heating element or an elastic member and the sheet-shaped heating element.
The packer can move in the well together with the cylindrical heat source and the temperature sensor when the expansion / contraction portion contracts.
The expansion / contraction portion is a thermophysical characteristic measuring device in which the sheet-shaped heating element and the temperature sensor are brought into close contact with the hole wall of the hole when expanded. The thermophysical property measuring device according to claim 1, wherein the sheet-shaped heating element is a silicon rubber heater. The thermophysical characteristic measuring device according to claim 1 or 2, further comprising a heat insulating member between the telescopic portion and the sheet-shaped heating element. The thermophysical characteristic measuring device according to any one of claims 1 to 3, wherein the fluid is air. Claim 1 in which the packer includes a pipe and a tubular elastic member, the elastic member is wound around a part of the pipe, and the elastic portion is formed by the outer periphery of the part and the elastic member. The thermophysical property measuring device according to any one of the items to 4. The thermophysical characteristic measuring device according to any one of claims 1 to 5, wherein the recording means records time-series data of the temperature measured by the temperature sensor. A method for measuring thermal conductivity for measuring the thermal conductivity of the ground at the in-situ position in a well, and a method for measuring thermal conductivity using the thermophysical property measuring device according to any one of claims 1 to 6. Placing the packer, the cylindrical heat source and the temperature sensor in the well.
Inflating the telescopic portion to bring the sheet-shaped heating element and the temperature sensor into close contact with the hole wall of the hole.
Heating the hole wall with the sheet-shaped heating element Recording the time-series data of the change in the temperature measured by the temperature sensor due to the heating by the recording means, and theoretically solving the time-series data or The method for measuring thermal conductivity according to claim 7, wherein the thermal conductivity is obtained by comparing with a reference curve created by using numerical analysis.

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