JP3416728B2 - Long-distance geothermal property measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground thermophysical property measuring device for grasping a sensor longitudinal profile of a ground thermophysical property.

[0002]

2. Description of the Related Art Conventionally, a needle probe method has been used to measure the thermal conductivity of the seabed or geothermal area. This is a method that can measure the thermal conductivity at that point without disturbance, and has been used in the geological survey of the ocean and the geothermal field.

[0003]

The needle probe method is based on the measurement of the thermal conductivity of a semi-infinite cylinder, and does not consider the distribution of thermal conductivity in the longitudinal direction. Further, no consideration is given to thermophysical properties other than thermal conductivity, and no consideration is given to heat transport other than heat conduction.

[0004]

In order to solve the above-mentioned problems, the present invention provides a geothermophysical property which is arranged over a long distance on the ground or rock in the ground and comprises an optical fiber for temperature measurement and an outer metal coating of the optical fiber. Has a quantity measuring sensor,
Provide a geothermophysical property measuring device characterized in that the optical fiber is caused to generate heat by supplying electricity to the geothermal property measuring sensor to supply heat to the ground / rock, and the temperature response can be measured by the optical fiber. To do.

The above-mentioned thermophysical quantity measuring sensor has a difference in thermophysical quantity including thermal conductivity, thermal inertia, convective heat transport quantity and thermal diffusion coefficient of the ground / rock along the longitudinal direction of the thermophysical quantity measuring sensor. In addition, it is possible to detect and monitor the infiltration of groundwater by measuring the above-mentioned changes in the thermophysical properties.

The thermophysical quantity measuring sensor may be arranged in a plane or a line.

Heat is generated by applying a constant voltage input to the thermophysical quantity measuring sensor, and the temperature change of the ground and rock along the longitudinal direction of the thermophysical quantity measuring sensor due to the heat generation is measured by the optical fiber, It is possible to measure the thermophysical properties of the ground and rock along the longitudinal direction of the thermophysical property measurement sensor.

A sine wave modulated voltage input is applied to the ground thermophysical quantity measuring sensor to supply a heat quantity to the ground / rock, and the ground / rock shape along the longitudinal direction of the thermophysical quantity measuring sensor accompanying the heat quantity supply By measuring the phase difference between the temperature amplitude and the supplied heat quantity with the optical fiber, the thermophysical quantity along the longitudinal direction of the thermophysical quantity measuring sensor can be measured.

Further, in order to solve the above-mentioned problems, the present invention installs a temperature measuring optical fiber inside a coaxial cylindrical pipeline for hot / cold water circulation, which is installed over a long distance on the ground or rock. Having a ground thermophysical quantity measuring sensor consisting of, by injecting hot water / cold water into the pipeline, the heat quantity is supplied from the pipeline to the ground / rock, and the temperature response is obtained by the optical fiber. Provided is a ground thermophysical property measuring device characterized by being capable of measuring.

The thermophysical quantity measurement sensor using the pipeline has a thermophysical property including thermal conductivity, thermal inertia quantity, convective heat transport quantity and thermal diffusion coefficient of the ground / rock along the longitudinal direction of the thermophysical quantity measurement sensor. The configuration is such that it is possible to measure the difference in the amount of water and detect and monitor the infiltration of groundwater by the change in the amount of thermophysical properties.

The thermophysical quantity measurement sensor using the pipeline is arranged in a plane or a line.

[0012] By adding hot water or cold water at a constant temperature to the thermophysical quantity measuring sensor by the pipeline, the calorie is supplied from the pipeline to the ground / rock, and the thermophysical quantity measuring sensor is provided in the longitudinal direction by the supplied calorie. It is possible to measure the temperature change along the longitudinal direction of the thermophysical property measurement sensor by measuring the temperature change of the ground / rock along the temperature measurement fiber.

A heat quantity is supplied to the ground by adding hot water or cold water whose temperature changes in a constant cycle to the ground thermophysical quantity measuring sensor by the pipeline, and the length of the thermophysical quantity measuring sensor accompanying the heat quantity supply is increased. By measuring the temperature amplitude of the ground / rock along the direction and the phase difference with the supplied heat quantity with the temperature measuring fiber, the thermophysical quantity of the ground / rock along the longitudinal direction of the thermophysical quantity measuring sensor can be measured.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of ground physical property measurement according to the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a diagram showing the overall concept of a ground thermophysical property measuring apparatus and a method of performing measurement by the apparatus according to the present invention.

The ground thermophysical property measuring device according to the present invention has an electrically heated ground thermophysical property sensor 1 that electrically generates heat in the ground. The structure of the ground thermophysical quantity sensor 1 is shown in FIG. 2 (a) and FIG. 2 (b) which is an enlarged view of a main part thereof. Here, the thermophysical properties of the present invention are thermal conductivity, thermal inertia, convective heat transport, and thermal diffusion coefficient.

As another form of the ground thermophysical property measuring device according to the present invention, there is provided a coaxial cylindrical ground thermophysical property sensor 2 for injecting hot water or cold water into the ground. The structure of this sensor is shown in FIG. 3 (a) and an enlarged view of the main part of FIG.
Shown in.

Electric heating type ground thermophysical property measuring sensor 1
Is composed of an optical fiber for temperature measurement and an outer metal coating of the optical fiber. Specifically, in the center of the ground thermophysical property measurement sensor 1, the calorific value per unit length is uniform,
An optical fiber 3 for temperature measurement having a heat source outer coating 8 covered with an insulating coating 4 is installed. By supplying a constant current to the heat source outer coating 8 from the heat supply device 6 on the ground surface, the heat source outer coating 8 is caused to generate heat. The heat-source external coating 8 that has generated heat heats the electrically-heated ground thermophysical quantity measuring sensor 1 and the surrounding ground / rock 5, and the heat is transmitted to the ground.

Coaxial cylindrical type ground thermophysical property measuring sensor 2
Similarly, in the case of, hot water or cold water is poured into the coaxial cylindrical pipeline to supply heat to the ground. However, in the case of the coaxial cylindrical ground thermophysical property measurement sensor 2, the amount of heat supplied to the ground per unit length is the same as in the case of the electrically heated ground thermophysical property measurement sensor 1 over the longitudinal direction of the sensor. All are not constant, and are expressed by the product of the temperature drop (increase) of hot / cold water per unit length and the heat capacity of hot / cold water per unit length in the pipeline.

Here, when the ground thermal conductivity around the electrically heated ground thermophysical property measuring sensor 1 is high, heat is easily transferred to the ground, and the ground thermophysical property measuring sensor 1 of the electrically heating type is Although the temperature does not rise very much, if the thermal conductivity of the ground / bedrock 5 around the electric heating type ground thermophysical property measurement sensor 1 is low, it is difficult to transfer heat to the ground, and the electric heating type ground thermophysical properties The temperature of the measurement sensor 1 rises.

Here, the temperature distribution in the sensor longitudinal direction and its change over time are measured by the temperature measuring optical fiber 3 installed inside the electrically heated ground thermophysical property measuring sensor 1, and the temperature in the sensor longitudinal direction is measured from the temperature distribution. The physical properties can be measured. In the case of the coaxial cylindrical type ground thermophysical quantity measuring sensor 2, when the thermal conductivity of the ground is high, the temperature drop on the sensor surface becomes large, and the heat quantity supply to that portion increases.

(Embodiment) An embodiment of the ground thermophysical property measuring apparatus according to the present invention will be described below. As an example of the present invention,
About the thermophysical property measuring device, a small test device was manufactured and the experiment of the ground thermophysical property measuring method was concretely conducted. An experimental ground thermophysical property measuring sensor 13 according to this embodiment is shown in FIG. 4, and has a diameter of 89 mm and a length of about 2 m, and has a metal pipe 8 covered with an outer film PVC 11 on a PVC pipe 9 for temperature measurement. The optical fiber-3 is wound around.

The outer metal film 8 is a stainless pipe having a thickness of 0.4 mm, and is used as a heat source by energizing the stainless pipe. As the optical fiber 13 for temperature measurement, GI-200 / 250 optical fiber manufactured by Hitachi Cable, Ltd. was used.

As the optical fiber thermometer, FTR070 manufactured by Hitachi Cable, Ltd. was used. The temperature resolution of this optical fiber thermometer is 1 m. The optical fiber is wound around a vinyl chloride pipe 9 having a length of 2 m for 127 m, and the resolution in the depth direction of the electrically heated thermophysical property sensor is 1.57 cm. The temperature resolution of this optical fiber thermometer is 0.1 degree.

The experimental ground thermophysical quantity measuring sensor 13 according to this embodiment was inserted into the ground and heated to measure the temperature in the depth direction of the ground. The temperature rise profile in the ground obtained by this experiment is shown in FIG. However, the temperature at time 0 is the initial temperature. As is clear from FIG. 5, the difference in temperature change in the vertical direction appears. These are due to the difference in the thermal conductivity of the surrounding soil, and in fact, different types of soil are also collected in soil sampling.

As can be seen from the difference in the temperature rise distribution in the ground shown in FIG. 5, in the present invention, the stratum can be discriminated from the difference in the thermophysical quantity in the vertical direction. Further, the thermal conductivity can be calculated by using the relationship between the electric power supplied to the external metal film 8 and the temperature of the temperature measuring optical fiber 3.

The following equation (1) for calculating the thermal conductivity using the relational expression of the amount of heat supplied and the temperature rise temperature in unsteady heat conduction is shown below.

[0027]

[Equation 1]

In the equation (1), under the condition that a ² / κt is sufficiently small (after a sufficient time has elapsed), the following equation (2) can be approximated.

[0029]

[Equation 2]

Whether or not the approximation of the equation (2) is sufficiently satisfied is determined by plotting the relationship between log (t) and temperature on a semi-logarithmic graph and judging by the slope of the temperature gradient. Here, in the region where the relation of the expression (2) is established, the gradient between log (t) and temperature indicates Q / (4πK).

The thermal conductivity was calculated using the above equation.
FIG. 6 shows an example showing the gradient between log (t) and temperature. As shown in FIG. 6, in a region where it has been determined that a linear relationship holds in the relationship between log (t) and temperature after sufficient time has passed,
Least-squares approximation is performed to calculate the gradient between log (t) and temperature.

FIG. 7 shows the thermal conductivity distribution calculated by performing the above analysis at each point in the depth direction. As shown in FIG. 7, the heat conduction profile for each depth is shown. As described above, according to the present invention, it is possible to measure the temperature in the ground or the thermophysical quantity in the depth direction of the underground with a simple device and method.

An example of application of a method utilizing the response of the optical fiber surface temperature when a sinusoidal heat flow is used will be given. In the method using the sinusoidal heat flow, a physical quantity that is closely related to the heat capacity of the ground, which is the thermal inertia of the ground, is used. The thermal inertia of the ground indicates the degree of resistance to the temperature change of the material surface, and is represented by (λρc) ^1/2 . Here, λ: thermal conductivity, ρ: density, c: specific heat, the unit is
It is J m ^-2 K ^-1 s- ^(1/2) .

Now, the diameter of the ground thermophysical quantity measuring sensor is set to D
, The heat flow per unit length is A sin (ωt + φ)
The temperature response T of the sensor surface when given by / πD is expressed by the following equation (3).

[0035]

[Equation 3]

Where ω is an arbitrary angular frequency and t
Is time, φ is arbitrary phase, and A is amplitude of heat flow per unit length.

As can be seen from the equation (3), in the heat conduction of the steady cycle, the phase is delayed by π / 4 according to the applied heat flow.

Further, when the heat flow moves only when the ground follows the heat conduction, the thermal inertia amount can be obtained from the response of the amplitude of the heat flow given to the sensor and the sensor surface temperature according to the equation (3). is there.

As shown in the equation (3), when the heat transport of the ground follows only heat conduction, the phase of the heat flow and the surface temperature is π / 4.
It shifts. However, heat transfer in the ground is not controlled only by heat conduction, and in order to solve this problem,
R-RC as shown in FIG. 8 in which heat resistance is added to the RC parallel circuit having two components of heat capacity and heat resistance of ground, with heat flow as current, temperature as voltage, and heat capacity as capacitor Introduce a series / parallel equivalent thermal circuit model.

In the parallel circuit part of this model, the phase delay component due to the capacitor component is π / 2. Therefore, in the case of the heat conduction type, in order to deviate the phase between the heat flow and the surface temperature by π / 4,
In the ground, a thermal resistance having the same impedance as the capacitor component may be added to the parallel circuit. Here, the temperature of the probe surface is T, and the underground temperature at a position sufficiently distant from the probe is a constant temperature T ₀ .

In FIG. 8, R1 is the thermal resistance from the probe to the ground, and R2 is the decrement of the thermal resistance associated with non-conducting heat transfer due to convective heat transfer or the like, which is 0 in the conducting ground. In addition, the thermal resistance (R1) from the probe to the ground is 0
If it can be regarded as, the above model can be considered as an RC parallel circuit.

Laboratory experiments were conducted to verify the above model. In the experiment, as shown in FIG. 9, sand was packed in an acrylic water tank having a length of 70 cm, a width of 40 cm, and a height of 25 cm, a rod heater having a diameter of 15 mm was inserted, and the heater was heated by applying rectangular wave voltage control. . The voltage applied to the heater is a rectangular wave with a maximum value of 10V.

Here, the difference in phase difference caused by convective heat transfer between dry sand and wet sand saturated with water will be shown. Figure 1
0 (a) is the case where a rectangular wave with a 90-minute cycle is added to the dry sand, and FIG. 10 (b) is the case where water is added to the dry sand to saturate it. In the analysis, the DC component was removed, and the Fourier series first-order component was used to detect the phase difference.

From FIG. 10 (a), the phase delay in the case of dry sand is 669 seconds, and from FIG. 10 (b) it is 4 in the case of saturated wet sand.
It turns out that it is 24 seconds. In the experiment, heating with a 90-minute cycle was added, but in the case where heat transfer in the ground is governed only by heat conduction, theoretically, the phase difference is π / 4 (675).
Seconds) should be delayed.

In the case of dry sand, the value is almost equal to the theoretical value, and in the case of saturated wet sand, the value is considerably smaller than the theoretical value. This is because in the case of saturated wet sand, convective heat transfer due to water occurs, so that the reduction of the thermal resistance component indicated by R2 is effective.

As described above, by adding the sinusoidal heat flow to the ground thermophysical quantity measuring sensor and measuring the temperature response of the ground thermophysical quantity measuring sensor, the contribution of the ground thermophysical quantity and the convective heat transfer component Can be estimated. The convective heat transfer component in this case indicates the heat transfer component of water in the ground,
From this, it is considered possible to determine the existence of water in the ground and the flow velocity of the water flow.

Although the embodiments of the present invention have been described with reference to the drawings based on the embodiments, the present invention is not limited to the embodiments and the technical matters of the above claims are not limited. It goes without saying that there are various embodiments within the range.

[0048]

According to the present invention, it is possible to easily determine the thermophysical property amount of the stratum in the longitudinal direction of the sensor, and it is possible to discriminate the stratum type by the difference in the thermophysical property amount. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to grasp the thermal physical properties of the underground, and therefore it can be used for designing and evaluating an underground heat storage / waste heat system. In addition, it is possible to easily perform geological surveys by utilizing the difference in thermophysical properties of the stratum.

Further, the present invention can be arranged in a linear shape, a plane shape, or a space shape. Therefore, it is possible to monitor the state of groundwater infiltration in nuclear waste treatment facilities, industrial waste treatment facilities, tunnels, etc. by using changes in the water content through changes in the thermophysical properties of the surrounding ground. .

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the present invention. The present invention comprises a ground thermophysical property measuring sensor, an optical fiber thermometer above the ground, and a power supply unit for supplying a heat source external coating, and is installed over a long distance in the underground ground and rock.

FIG. 2 is a sketch of an electrically heating type ground thermophysical property measuring sensor used in the present invention. The sensor consists of a heat source external coating covered with an insulating coating and an optical fiber for temperature measurement.

FIG. 3 is a sketch of a coaxial cylindrical type ground thermophysical property measuring sensor used in the present invention. The sensor consists of a coaxial / cylindrical pipeline that circulates hot water and supply water, and an optical fiber for temperature measurement is placed inside the pipeline.

FIG. 4 is a sensor prototyped as an application example of the present invention. The sensor is a PVC pipe having a diameter of 89 mm and a length of 2 m wound with an optical fiber having a metal coating.

FIG. 5 is a temperature rise profile in the ground when the ground is heated. It can be seen that there is a difference in the temperature rise profile due to the difference in underground thermal conductivity.

FIG. 6 is a logarithmic temperature-temperature profile used for calculation of thermal conductivity. The thermal conductivity is calculated from the temperature gradient of this profile.

FIG. 7 is a vertical thermal conductivity profile. The difference in thermal conductivity can be measured in the depth direction.

FIG. 8 is a conceptual diagram of an R-RC thermal AC circuit. here,
R1 is the thermal resistance from the sensor to the ground, and R2 is the thermal resistance of the ground. The temperature outside the target ground is the constant temperature T _0.
I am trying.

FIG. 9 is an experimental soil tank used for the experiment. A sand sample was packed inside the soil tank, and a bar heater was installed at the center of the soil tank to supply heat from the outside. The surface temperature of the rod heater was measured with a thermocouple.

FIG. 10 is a graph showing a phase difference between dry sand and saturated wet condition. The phase lag for dry sand is 669 seconds and for saturated wet sand is 424 seconds.

[Explanation of symbols]

1 Electric heating type thermophysical property measurement sensor 2 Coaxial cylindrical ground thermophysical property measurement sensor 3 Temperature measurement optical fiber 4 insulating film 5 ground, bedrock 6 Heat supply device 7 Optical fiber thermometer 8 Heat source external coating 9 PVC pipe 10 External metal coating 11 External coating PVC 12 Optical fiber for temperature measurement 13 Experimental thermophysical property measurement sensor

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Claims (3)

(57) [Claims] 1. A geothermophysical property having a geothermophysical property measuring sensor which is arranged over a long distance on the ground or rock in the ground, and which comprises an optical fiber for temperature measurement and an external metal coating of the optical fiber which generates heat when supplied with electricity. A quantity measuring device for supplying heat quantity to the ground / rock by applying a sinusoidal modulation voltage input to the ground thermophysical quantity measuring sensor, and along the longitudinal direction of the thermophysical quantity measuring sensor accompanying the heat quantity supply. From the temperature distribution of the ground / rock and its time change, the temperature amplitude and the phase difference with the supplied heat quantity can be measured by the optical fiber, and the thermophysical quantity of the ground / rock along the longitudinal direction of the thermophysical quantity measurement sensor can be measured. Geothermal physical property measurement device characterized by. 2. The thermophysical quantity measuring sensor includes a thermophysical quantity including thermal conductivity, thermal inertia, convective heat transport quantity, and thermal diffusion coefficient of the ground / rock along the longitudinal direction of the thermophysical quantity measuring sensor. The ground thermophysical property measuring device according to claim 1, wherein the ground thermophysical property measuring device is configured to detect and monitor the infiltration of groundwater based on the change in the thermophysical property. 3. The ground thermophysical property measuring device according to claim 1, wherein the thermophysical property measuring sensor is arranged in a plane or a line.