JP2009236874A - Monitoring method of underground permeation of carbon dioxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitoring method of underground permeation of carbon dioxide capable of secularly and continuously measuring the behavior of carbon dioxide press-filled underground for a long time, predicting the situation of carbon dioxide before carbon dioxide leaks out onto the ground surface, and monitoring the situation of underground penetration of carbon dioxide with a simple work by using a relatively compact device. <P>SOLUTION: In a production system in which a plurality of boreholes communicated with underground coal layers (a main layer 1 and a lower layer 2) are formed, gaseous carbon dioxide is press-filled from a press-in well 3 communicated with the lower layer 2 and fixed to coal or the like in the lower layer 2, and thereafter, hydrocarbon gas mainly consisting of methane gas substituted with carbon dioxide and emitted is collected from a production hole 4, survey meters by γ-ray scintillation are installed on bottoms in observation holes formed at five points (A, B, C, D, E), gaseous carbon dioxide is press-filled in the press-in well 3, and the secular change of the γ ray dosage rate is examined by the survey meters to monitor the situation of underground penetration of carbon dioxide and the production situation of underground gas associated therewith. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  This invention relates to the behavior of the injected carbon dioxide in the ground when carbon dioxide is injected into the underground coal bed and adsorbed on the coal, or when the hydrocarbon-based gas generated by substitution with carbon dioxide is recovered. The present invention relates to a carbon dioxide underground infiltration monitoring method.

  In general, coal has an action of adsorbing gas due to its fine void structure, and a large amount of hydrocarbon-based gas mainly containing methane gas is usually contained in the underground coal layer.

  In particular, coal has the property of adsorbing carbon dioxide several times as much as methane. If carbon dioxide and methane gas contained in coal are replaced, it is one of the greenhouse gases that cause global warming. A certain amount of carbon dioxide can be efficiently fixed in the coal bed, and methane gas, which is clean energy, can be recovered by replacing it with carbon dioxide, which can be used effectively.

  This recovery method will be explained in detail. When carbon dioxide is injected into the underground coal seam from the borehole leading to the coal seam, the carbon dioxide is selectively adsorbed to the coal twice to several times as much as methane. Instead, hydrocarbon-based gas mainly composed of methane gas adsorbed on coal is released.

  As described above, it is known that methane gas contained in a large amount in a coal bed can be recovered and used as a fuel gas from another borehole by using carbon dioxide-methane substitution. (For example, Patent Document 1)

  The above technology can be used in deep coal seams where it is difficult to mine coal or in low-grade, low-economic coal seams, and carbon dioxide is one of the greenhouse gases whose emission regulations have been tightened in recent years. It can be said that this is an excellent resource recycling technology that can stably fix this and can effectively use the recovered combustible natural gas resources.

  In addition, in order to investigate what kind of useful gas is contained at what concentration when carbon dioxide is injected into the ground and flammable gas such as methane gas is recovered from the coal bed, Raman probe And a Raman scattering light analyzer installed in a hollow tube embedded in the ground in advance, and a gas monitoring technique is known. (Patent Document 2)

JP 2004-3326 A JP 2004-309143 A

  However, the conventional gas monitoring technology that evaluates underground gas components obtains information on the type and concentration of the gas that has flowed out, and it can only be detected when the injected carbon dioxide leaks out. It was not possible to grasp in advance the amount of gas expected and the influence over time in the future.

  The information obtained by investigating the geological structure does not correspond to the behavior of the injected carbon dioxide in the ground, and it was not possible to fully know the behavior of carbon dioxide in the ground beforehand.

  In addition, it is not necessary to obtain temporary data as in the case of investigating the geological structure for general ore exploration. Measurements that require extensive equipment every time are impractical.

  Accordingly, an object of the present invention is to solve the above-described problems and continuously measure the behavior of carbon dioxide injected into the ground over time and leak carbon dioxide to the ground surface. It is possible to predict the situation before, and to monitor the penetration of carbon dioxide into the ground by a simple operation using a relatively small device.

  In order to solve the above-mentioned problems, in the present invention, a plurality of wells leading to an underground coal bed are provided, and carbon dioxide is injected from at least one of these boreholes to penetrate the coal bed. When the hydrocarbon-based gas in the coal bed replaced with the permeated carbon dioxide is produced from other wells, the upper part of the coal bed between the carbon dioxide injection well and the hydrocarbon-based gas production well By installing multiple survey meters by γ-ray scintillation at intervals in the ground, and examining the temporal changes in the total amount of spatial γ dose rate of multiple nuclides measured at each position by these survey meters, It was a method for monitoring the penetration of carbon dioxide into the ground consisting of monitoring the state of gas penetration or leakage to the surface.

In the monitoring method of the present invention configured as described above, when carbon dioxide is injected into the underground coal formation at high pressure, carbon dioxide that travels in the coal formation while diffusing transmits the pressure to the formation. The natural radioactive gas uniformly contained therein is pushed up to the ground surface by the transmitted pressure.
That is, normally, the rock formations, uranium 0.4～4Ppm, thorium contains 1～16Ppm, but ²²² Rn and ²²⁰ Rn of its decay element is contained in the formation, rock, it is generally Difficult to move.
However, when these ²²² Rn and ²²⁰ Rn are subjected to the discharge pressure of carbon dioxide gas from the lower part of the fault, they rise.

  Therefore, when the change in radiation dose rate over time is examined with a survey meter at multiple observation holes provided at intervals in the ground, such as near the ground surface above the coal bed, carbon dioxide penetrates into the coal bed. When the survey meter shows a change in the radiation dose rate over time in the observation hole installed above the coal bed at the point where the survey is expected to occur, carbon dioxide will reach the basement of the survey meter installation location. You can see that it has penetrated.

The radon natural radioactive gas ⁽²²² Rn) and thoron ⁽²²⁰ Rn), respectively can be taken in a survey meter according γ ray scintillating as radiation dose rate of γ-rays of ²¹⁴ Bi and ²⁰⁸ Tl is these daughter elements .

Of the multiple nuclides, only certain nuclides change the spatial γ dose rate over time, while the spatial γ dose rates of other nuclides may not change stably over time, for example ⁴⁰ K The air gamma dose rate is always constant.

Therefore, by examining the time course of the total amount of space γ dose rate of a plurality of species including ⁴⁰ K, ⁴⁰ because it is seen changes over time of the total amount of space γ dose rate for nuclides other than K, other nuclides than ⁴⁰ K Thus, it is possible to monitor the penetration state of carbon dioxide gas in the ground or the leakage state to the ground surface.

In particular, when the nuclides are ²¹⁴ Bi, ²⁰⁸ Tl, and ⁴⁰ K, the radon ( ²²² Rn) or the thoron ( ²²⁰ Rn) can be obtained by examining the time course of the total amount of these spatial γ dose rates. Since the time-dependent changes in the total amount of space γ dose of ²¹⁴ Bi and ²⁰⁸ Tl, which are the nuclides that emit the first γ-rays thereafter, can be seen, it is possible to monitor the penetration of carbon dioxide gas in the ground or the leakage to the ground surface You can be sure.

  Further, in order to remove error factors such as atmospheric pressure on the ground surface, the position where the survey meter is installed in the ground is preferably 40 cm or more below the ground surface, and in order to completely remove the influence, the depth is preferably 5 m or less.

  Moreover, it is preferable in order to measure more correctly that the position which installs a survey meter is a position which touches the underground ventilation path which consists of a tomographic plane above a coal bed.

  The carbon dioxide monitoring method according to the present invention utilizes a phenomenon in which pressure is transmitted to the formation when carbon dioxide penetrates into the underground coal formation, and the radioactive gas is pushed up to the ground surface. By investigating changes in natural radiation dose rate over time with a survey meter using line scintillation, the behavior of carbon dioxide injected into the ground can be continuously measured over a long period of time, and can be predicted before carbon dioxide leaks to the ground surface. . In addition, there is an advantage that the method can be easily monitored at a low cost using a relatively small device.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, in the embodiment, a coal bed composed of a main layer 1 and a lower layer 2 existing in the ground is provided with two wells composed of a press-in well 3 and a production well 4 leading to the lower layer 2. A hydrocarbon-based gas containing methane gas as a main component, which is injected into the well 2 from the carbon dioxide injection pipe 8 of the injection well 3 and fixed to the coal in the lower layer 2 and then replaced with carbon dioxide. Is recovered from the production well 4. This is a carbon dioxide underground penetration monitoring method applied in this carbon dioxide fixing and hydrocarbon gas production system.

  In such a production system, observation holes (depths) drilled at five points (A, B, C, D, E) at intervals above the coal bed between the injection well 3 and the production well 4. The detector of the radiation dose rate meter (survey meter) is installed within about 40cm, and the time-dependent change of the γ-ray dose rate is examined (with the radiation dose rate meter at the same time as injecting carbon dioxide gas in the injection well 3). Therefore, the behavior of the injected carbon dioxide in the ground, that is, the state of carbon dioxide penetration into the ground is monitored.

  It should be noted that the observation holes drilled at five points (A, B, C, D, E) are about 270 m between A and B, about 20 m between B and C, about 90 m between C and D, D-E. The distance is about 90m.

  As the carbon dioxide used in the present invention, one obtained by separating and recovering exhaust gas containing carbon dioxide from a large-scale generation source such as a thermal power plant can be used. High-purity carbon dioxide can be obtained relatively easily by the amine method in which it is absorbed and recovered by an amine absorbent such as monoethanolamine.

  When liquefied carbonic acid is used, it is pumped from the liquefied carbonic acid storage tank 5 via the booster pump 6, heated by the evaporator 7, vaporized, and then introduced into the press-fit well 3.

  The injection of carbon dioxide may be performed not only from one injection well 3 as shown, but also from a plurality of injection wells. In addition, at the initial stage of the press-fitting, it is preferable to perform the press-fitting while destroying the coal layer and actively forming a large number of cracks by carrying out at a relatively high pressure. It is also preferable to prevent clogging of the cracks, and in this way, carbon dioxide can be permeated over a wide range over a longer period.

  It is preferable to install the production well 4 at a distance necessary to sufficiently adsorb carbon dioxide that has penetrated into the coal bed from the injection well. Such a distance would be required to be at least tens of meters. Note that the production well 4 only needs to be separated from the press-fit well 3 by the predetermined distance according to the three-dimensional positional relationship, and is not necessarily separated in the planar direction.

  For example, carbon dioxide may be injected into the deep part of the coal layer to collect underground gas containing methane gas from the shallow part of the same region, and in the case of a coal layer that extends flatly from the deep part to the shallow part. May be produced from a shallow portion by injecting carbon dioxide in the deep portion.

  Usually, the underground gas containing water vapor or the like recovered from the production well 4 is separated from the liquid by the gas-liquid separator 10 and the liquid components are recovered in the drain tanks 9a and 9b, and the separated methane gas is the main component. A hydrocarbon-based gas is obtained. If necessary, further refine the gas and deliver it to the facility.

The radiation dose rate meter used in the present invention is preferably one that can measure γ-rays with high penetrating power. For example, a survey meter by γ-ray scintillation can be adopted.
A typical example of a survey meter by γ-ray scintillation is a NaI (Tl) scintillation survey meter, which includes a NaI (Tl) scintillation detector (probe), a survey meter body, and data connected as necessary. Consists of a recorder. The detector is provided with a crystal of sodium iodide (including thallium), and secondary electrons are generated by the interaction between sodium iodide and incident γ rays. The dose rate information of γ-rays is obtained from the intensity of fluorescence generated when the light is excited and returned to the steady state from the excitation. Examples of commercially available γ-ray scintillation survey meters that can be used include NaI (Tl) scintillation survey meter (TCS-161) manufactured by Aloka.

  The interval and number of survey meters installed by γ-ray scintillation are not particularly limited. The size of the underground coal layer used and the nature of the geological formation above it, the injection well and the production well Depending on the distance, it may be installed with a width of about 10 meters to several hundred meters.

  In the geological structure of Minami-Dayubari, Hokkaido, which has the coal bed shown in Fig. 1, an actual measurement test of γ-ray dose rate was conducted. The distance between the injection well 3 and the production well 4 was 194 m away, and the production well 4 was provided at a location higher in the coal bed slope than the injection well 3.

  Then, the injection well 3 is continuously pressed for 25 days (from November 9 to November 24) under the conditions of carbon dioxide injection (injection pressure (MPa) and injection amount (t)) shown in FIG. The data of points B and C of the γ-ray dose rate obtained at this time (NaI (Tl) scintillation spectrometer manufactured by Aloka Co., Ltd. was used for reference) are shown in the charts of FIGS.

As is clear from these figures, immediately after the injection of carbon dioxide, the change in the ²¹⁴ Bi γ dose rate and the change in ²⁰⁸ Tl had the same tendency. This is thought to indicate the movement of radon gas in soil and rocks at shallow depths.

And after the press injection of carbon dioxide gas, an increase in the γ-ray dose rate was observed at points B and C. After that, production of hydrocarbon-based gas mainly composed of methane gas started from production well 4 before and after November 20, and the production volume was 50 m ³ / day before carbon dioxide gas injection. After the injection of carbon dioxide, there was a tendency to increase to around 150 m ³ / day.

In the peak changes in Figs. 3 and 4, the change in ²⁰⁸ Tl is small compared to the change in the ²¹⁴ Bi γ-ray dose rate because the radon gas from the deep part has been pushed up and moved in view of the difference in half-life. it is conceivable that.

  Next, after temporarily stopping the injection of carbon dioxide gas to stabilize the infiltration state of carbon dioxide gas in the ground or the leakage state to the ground surface, NaI (Tl) scintillation survey made by Aloka at point B A meter (TCS-161) was provided side by side with the NaI (Tl) scintillation spectrometer, and the difference between the data was examined.

As is clear from the results of FIG. 5 showing the measurement results at that time and the results of FIG. 3 at the same point, the relationship between the measurement by the spectrometer and the measurement results by the survey meter is shown in FIG. Then, ²¹⁴ Bi (indicated by Bi-214 in the figure), ²⁰⁸ Tl (indicated by Tl-208 in the figure), and ⁴⁰ K (indicated by K-40 in the figure) were separately measured. The meter (FIG. 5) did not perform nuclide fractionation and the total amount of ²¹⁴ Bi, ²⁰⁸ Tl, and ⁴⁰ K was measured.

Looking at FIG. 3 here, the count value of ⁴⁰ K is constant and only ²¹⁴ Bi fluctuates.
Therefore, the fluctuation in the survey meter is considered to coincide with the fluctuation of ²¹⁴ Bi measured by the spectrometer.
It can also be seen from FIG. 5 that the total amount of the spatial γ dose rate of the survey meter is also measured in correspondence with the ²¹⁴ Bi spatial γ dose rate measured by the spectrometer.
Therefore, it is possible to monitor the penetration of carbon dioxide gas in the ground or the leakage to the ground surface by examining the temporal change in the total amount of space γ dose rate of natural radiation gas containing multiple nuclides measured at each position by a survey meter. I understand.

  For reference, Table 1 shows an example of measurement of the γ dose rate measured with a survey meter when fluid (hot spring and steam) moves at the Arima hot spring source in Hyogo Prefecture. By the way, the source of Arima Onsen is pushed out of hot spring water by carbon dioxide. Therefore, when self-injecting, radon gas is pushed up together with carbon dioxide.

As is clear from the results in Table 1, using the γ-ray scintillation survey meter, the same data as the dose rate change of the radon daughter nuclide ( ²¹⁴ Bi) measured with the spectrometer was obtained. It is estimated that the penetration of carbon dioxide gas in the ground or the leakage to the ground surface can be monitored by examining the change over time in the total amount of the space γ dose rate of natural radiation gas using the measurement results.

  The γ-ray scintillation survey meter can easily capture changes in the dose rate of radon gas in the field without bringing the measurement data back to the laboratory. It is thought that the penetration and crushing situation into the coal bed can be grasped in a timely manner.

  Thus, in order to adjust the production rate of hydrocarbon-based gas, the amount and pressure of carbon dioxide injection should be adjusted appropriately, and planned measurement of methane gas etc. using the measurement data obtained as described above. Production can be done in a timely manner.

Schematic illustration of carbon dioxide gas penetration monitoring method Chart showing the relationship between CO2 injection conditions and changes in production gas over time Chart showing changes in radiation dose rate over time at point B Chart showing changes in radiation dose rate over time at point C Chart showing changes in radiation dose rate over time at point B

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main layer 2 Lower layer 3 Injection well 4 Production well 5 Liquefied carbon dioxide storage tank 6 Booster pump 7 Evaporator 8 Carbon dioxide injection pipe 9a, 9b Drain tank 10 Gas-liquid separation apparatus

Claims (4)

  A plurality of boreholes that lead to the underground coal bed are provided, carbon dioxide is injected from at least one of these boreholes and penetrated into the coal bed, and in the coal bed replaced with the penetrated carbon dioxide When producing other hydrocarbon-based gas from other boreholes, a survey meter by γ-ray scintillation is used with a gap in the ground above the coal bed between the carbon dioxide injection well and the hydrocarbon-based gas production well. Monitor the infiltration of carbon dioxide gas in the ground or the leakage to the surface of the earth by investigating changes over time in the total amount of the spatial γ dose rate of multiple nuclides measured at each position using these survey meters. A method for monitoring the penetration of carbon dioxide into the ground. The method for monitoring underground penetration of carbon dioxide according to claim 1, wherein the natural radiation containing a plurality of nuclides is natural radiation containing ²¹⁴ Bi, ²⁰⁸ Tl and ⁴⁰ K.   The method for monitoring carbon dioxide gas penetration into the ground according to claim 1 or 2, wherein the survey meter is installed in the ground at a depth of 40 cm or more below the surface of the coal layer.   The method for monitoring underground penetration of carbon dioxide according to any one of claims 1 to 3, wherein a position where the survey meter is installed is a position in contact with an underground air passage formed of a fault plane above the coal bed.

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