JP7115692B2 - Method for combined stimulation of geothermal reservoir and method for descaling in well - Google Patents

Description

The present invention relates to a method for combined stimulation of a geothermal reservoir and a method for descaling in a wellbore.

In geothermal power generation, power is generated by extracting high-temperature, high-pressure geothermal fluid (steam, hot water) from a geothermal reservoir. A geothermal reservoir is a layer in which water derived from rainwater heated near a magma chamber is stored in the form of a high-temperature, high-pressure geothermal fluid in a low-permeability stratum (cap rock).
In geothermal power generation, geothermal fluid extracted from a production well that reaches a geothermal reservoir is used for power generation, and then returned to the ground through a reinjection well. The geothermal reservoir where such production wells or return wells are located requires permeability to facilitate extraction of the geothermal fluid. It's not easy to guess.

Formation permeability is also required in conventional oil wells, where a method of stimulating the formation with an acidic solution is employed to improve the permeability of the formation.
For example, in Patent Document 2, GLDA, which is a chelating agent, and hydrochloric acid, hydrobromic acid, hydrofluoric acid, hydroiodic acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, citric acid, lactic acid, malic acid, tartaric acid, maleic acid , boric acid, and one or more acids selected from hydrogen sulfide, using an acidic aqueous solution having a pH of less than 3 as a solubilizer for a carbonate formation in which an oil well is provided, thereby improving the permeability of the formation. disclosed.
Chelating agents used in oil wells include EDTA, NTA, HEDTA, and GLDA, as shown in Non-Patent Document 1.

In addition, geothermal fluid contains various components in the ground, and scale such as calcium is likely to adhere to the inner wall of the well forming the production well from which the geothermal fluid is extracted. Therefore, a method of removing scale from the inner wall of a well with a chelating agent has been investigated (Patent Document 1).
In a reinjection well whose reduction capacity has decreased due to scale deposition, it is being studied to improve the water injection index by introducing low-temperature hot water (60° C.) (Non-Patent Document 2).

Japanese Patent No. 5228452 Japanese Patent No. 5462804

Thermal Stability of Oilfield Aminopolycarboxylic Acids/Salts (K. Sokhanvarian, et al, Society of Petroleum Engineers, 2016) Effect of temperature of reducing hot water on reduction capacity (Journal of the Geothermal Society of Japan, Vol. 19, No. 4 (1997), pp. 197-208)

In geothermal reservoirs where wells used for geothermal power generation are built, the geothermal fluid extracted from production wells is used for power generation and then returned to the ground using reinjection wells for circulation. be. That is, acidic aqueous solutions such as those used in oil wells cannot be used to stimulate geothermal reservoirs.

In addition, as shown in Non-Patent Document 1, the concentrations of chelating agents such as EDTA, NTA, HEDTA, and GLDA decrease at high temperatures. Specifically, it is shown that the 100% concentration of the chelating agent becomes 40% to 60% in 4 hours under conditions of 400 degrees Fahrenheit (approximately 200 degrees Celsius). In the chelating agent shown in Non-Patent Document 1, even under the condition of 350 degrees Fahrenheit (about 180 degrees Celsius), the chelating agent with a concentration of 100% becomes 60% in 8 hours (see Non-Patent Document, FIG. 3). ).
The temperature of the geothermal reservoir for geothermal power generation is higher than the temperature of the oil well formation, and it has been difficult to stimulate the formation using these chelating agents alone.

Patent Document 1 discloses a chelating agent selected from nitrilotriacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid, but these are used only for removing scale attached to the inner wall of the well, and geothermal storage Improving the permeability of the layer is not considered.
In addition, Non-Patent Document 2 suggests that introducing low-temperature hot water (60°C) into the well temporarily improves the water injection index, but at the same time, introducing high-temperature hot water (159°C) It also disclosed that the water injection index was lowered, and the effect was temporary.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a combined stimulation method for a geothermal reservoir that stimulates the geothermal reservoir to improve the permeability of the geothermal reservoir, and a method for removing scale in a well provided in the geothermal reservoir. and

The present invention is characterized by having any of the following aspects.
[1]
a first step of injecting normal temperature water from a well into a geothermal reservoir to cool a cracked rock formation or formation of the geothermal reservoir ;
a second step of injecting a chelating agent from the well into the geothermal reservoir following the first step .
[2]
The method for combined stimulation of a geothermal reservoir according to [1], wherein the chelating agent contains one or more selected from the group consisting of GLDA, salts of GLDA, HEDTA, and salts of HEDTA.
[3]
The combined stimulation method for a geothermal reservoir according to [2], wherein in the step of injecting a chelating agent from the well into the geothermal reservoir, scale adhering to the inner wall of the well is removed.

According to the present invention, the stimulation of said geothermal reservoir with said water by injecting water from a well into said geothermal reservoir followed by said stimulation of said geothermal reservoir by injecting a chelating agent from said well into said geothermal reservoir. and stimulating the geothermal reservoir with a chelating agent to improve the permeability of the geothermal reservoir and remove scale adhering to the inner wall of the well. it becomes possible to

1 is a schematic diagram illustrating one embodiment of a geothermal reservoir combined stimulation method; FIG. (a) shows a schematic diagram of a well provided in the geothermal reservoir, (b) shows a schematic diagram of the process of injecting water from the well provided in the geothermal reservoir into the geothermal reservoir, and (c) ) shows a schematic diagram of the process of injecting a chelating agent into a geothermal reservoir from a well provided in the geothermal reservoir. 1 is a schematic cross-sectional view of a test apparatus for conducting laboratory tests on complex stimulation of a geothermal reservoir; FIG. 4 is a graph showing changes over time in differential pressure of the chelating agent obtained in Example 1. FIG. 4 is a graph showing changes over time in the concentration of elements in the waste liquid obtained in Example 1. FIG. 2 is an X-ray CT image comparing the pre-test and post-test conditions of the granite sample used in Example 1. FIG. (a) is an X-ray CT image before the test, and (b) is an X-ray CT image after the test. 4 is a graph showing changes over time in differential pressure of the chelating agent obtained in Example 2. FIG. 5 is a graph showing changes over time in the concentration of elements in the waste liquid obtained in Example 2. FIG. 4 is an X-ray CT image comparing the pre-test and post-test conditions of the granite sample used in Example 2. FIG. (a) is an X-ray CT image before the test, and (b) is an X-ray CT image after the test. 5 is a graph showing changes over time in differential pressure of the aqueous nitric acid solution obtained in Comparative Example 1. FIG. 5 is a graph showing changes over time in the concentration of elements in the waste liquid obtained in Comparative Example 1. FIG. 4 is an X-ray CT image comparing the state of the granite sample used in Comparative Example 1 before and after the test. (a) is an X-ray CT image before the test, and (b) is an X-ray CT image after the test.

An embodiment of the combined stimulation method for a geothermal reservoir according to the present invention will be described below with reference to the drawings.
It should be noted that each embodiment shown below is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make it easier to understand the features of the present embodiment, there are cases where the essential parts are shown in an enlarged manner, and the dimensional ratio of each component is the same as the actual one. Not necessarily.

The combined stimulation method for a geothermal reservoir according to the present embodiment includes a step of injecting water W from a well 10 into a geothermal reservoir 100 and a step of injecting a chelating agent C from the well 10 into the geothermal reservoir 100. have.

[well]
FIG. 1(a) shows a well 10 used in the geothermal power generation facility of this embodiment. Well 10 may be a production well or a reinjection well of a geothermal power plant.
Wellbore 10 has steel pipe 11 embedded in a hole drilled to reach geothermal reservoir 100 .
The geothermal reservoir 100 is a layer in which water derived from rainwater or the like heated near the magma chamber 200 is stored in the form of a high-temperature, high-pressure geothermal fluid.
The steel pipe 11 is provided with an outlet 12 in contact with the geothermal reservoir 100 in the pipe wall on the lower tip side. Valves 16 and 17 having valves capable of opening and closing the flow path are provided at the wellhead 13 on the ground side of the steel pipe 11. The pipe connected from the valve 16 is connected to a geothermal power generation facility (not shown), and the valve 17 is A tank 23 for supplying the chelating agent C and a tank 22 for supplying the water W are connected.

[Method for complex stimulation of geothermal reservoir]
Next, the geothermal reservoir complex stimulation method of this embodiment will be described.
(1) Stimulation of Geothermal Reservoir with Water In the combined stimulation method of the geothermal reservoir of the present embodiment, first, the valves 16 and 17 of the wellhead 13 are closed so that the wellhead 13 is sealed.
Next, as shown in FIG. 1(b), the valve 17 is opened, and the well 10 is filled with the water W from the tank 22 using the pump 21. and
After the inside of the well 10 is filled with the water W, the pump 21 further pressurizes the well 10 to supply the water W into the well 10, and the water W is injected into the geothermal reservoir 100 through the outlet 12 of the well 10. .

At this time, the water pressure by the pump 21 varies greatly depending on the permeability of the reservoir and the amount of injection, and may exceed 100 MPa from the gravity flow state (atmospheric pressure). Prepare a pump with a horsepower corresponding to the required water pressure and injection amount.
As the water W, water at room temperature may be used.

The geothermal reservoir 100 is a rock layer or stratum having cracks with a temperature of about 150 to 350. When room temperature water is injected into this, the rock layer or stratum cools and shrinks, opening cracks 101 and increasing gaps.
The injection of water W into the geothermal reservoir 100 is assumed to be several tens kl to several tens of thousands kl until a sufficient temperature drop is obtained and depending on the region to be stimulated. A specific amount of injection is determined by a simulation that numerically reflects the reservoir conditions.

(2) Stimulation of Geothermal Reservoir by Chelating Agent Next, the well 10 is filled with the chelating agent C by supplying the chelating agent C from the tank 23 using the pump 21 . At this time, by supplying the chelating agent C into the well 10 , the water W in the well 10 is forced into the geothermal reservoir 100 through the outlet 12 to replace the inside of the well 10 with the chelating agent C.
After the well 10 is filled with the chelating agent C, the chelating agent C is supplied into the well 10 by applying pressure with the pump 21 , and the chelating agent C is injected into the geothermal reservoir 100 through the outlet 12 .

The water pressure by the pump 21 when injecting the chelating agent C varies greatly depending on the permeability of the reservoir and the injection amount, and may exceed 100 MPa from the gravity flow state (atmospheric pressure). Prepare a pump with a horsepower corresponding to the required water pressure and injection amount.
Chelating agent C selected from glutamic acid N,N-diacetic acid (GLDA), salts of GLDA, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), and salts of HEDTA can be used.
As the chelating agent C, one selected from GLDA or its salts and HEDTA or its salts may be added to water, and the concentration thereof is preferably 10 to 30 wt%, more preferably about 20 wt. %.
Although the temperature of the chelating agent C is not particularly limited, it is preferable to use the chelating agent C at room temperature like water.
An acid such as nitric acid may be added to the chelating agent, but the pH is preferably in the range of 4.0 to 6.0 in consideration of environmental impact.
The injection of the chelating agent C into the geothermal reservoir 100 depends on the amount of minerals and the region to be stimulated, and injection of several kl to several thousand kl is assumed. A specific amount of injection is determined by a simulation that numerically reflects the reservoir conditions.

When a chelating agent C is injected into a geothermal reservoir 100 in which cracks 101 in rock layers or strata are open due to stimulation by water, carbonate mineral veins in the rock layers or strata are dissolved to form voids 102 such as wormholes. In addition, it is possible to dissolve colored minerals (biotite, amphibole), etc. in rock layers or strata to form voids 102 .
Even if the crack 101 in the rock layer or stratum opens temporarily with only water stimulation, the rock layer or stratum will expand and the crack 101 will close when the temperature returns to normal, so the permeability of the geothermal reservoir 100 will be constantly increased. difficult to improve.
However, when the chelating agent C is injected continuously after the stimulation with water and the geothermal reservoir 100 is stimulated with the chelating agent C, the carbonate mineral veins and colored minerals in the crack 101 are dissolved. , the permeability of the geothermal reservoir 100 can be maintained.
GLDA, GLDA salts, HEDTA, and HEDTA salts used as chelating agent C tend to decrease in reactivity at high temperatures and are expensive. First, it is important to stimulate the geothermal reservoir 100 with water.

(3) Recovery of chelating agent The chelating agent C is preferably recovered quickly via the valve 17 after the geothermal reservoir 100 is stimulated by the chelating agent C.
GLDA or a salt thereof, which is a chelating agent C used in the combined stimulation method for a geothermal reservoir of the present embodiment, is a kind of glutamic acid and is a biodegradable chelating agent used as a cleaning agent or cleaning additive. Salts are used as bactericidal and antiseptic agents in cosmetics and the like, and are chelating agents with low environmental load.
By recovering these chelating agents C promptly after stimulation, the load on the environment can be reduced as much as possible.

(4) Geothermal power generation After the chelating agent C is recovered, the valve 17 is closed and the valve 16 connected to the geothermal power generation facility (not shown) is appropriately opened to perform geothermal power generation using the geothermal fluid from the geothermal reservoir 100. can do
In the geothermal reservoir 100 stimulated by the geothermal reservoir complex stimulation method of the present invention, voids 102 such as wormholes are formed, so that the geothermal fluid has good permeability and geothermal power can be efficiently generated. I can.

Geothermal fluid contains various mineral components in the ground, and if geothermal power generation is continuously performed, these minerals may precipitate and adhere to the geothermal reservoir 100 and the permeability of the reservoir may decrease. be.
However, the combined geothermal reservoir stimulation method of the present invention can also be applied to geothermal reservoirs 100 with such reduced reservoir permeability to improve reservoir permeability in geothermal reservoirs 100. can do

(5) Removal of Scale in Wells As described above, geothermal fluid contains various underground mineral components, and scale such as calcium tends to adhere to the inner wall of the well 10 from which the geothermal fluid is extracted.
However, according to the geothermal reservoir complex stimulation method of the present invention, in the step of stimulating the geothermal reservoir with the chelating agent, when filling the well 10 with the chelating agent C, the inner wall of the well 10 of scale can be removed.
The scale on the inner wall of the well 10 may be removed by allowing the chelating agent C to stay in the well 10 for a certain period of time to allow the chelating agent and the scale to react. It may be performed while being forced into the geothermal reservoir 100 .

In the following, it is schematically demonstrated by laboratory tests that the method of the present invention can improve the permeability of a geothermal reservoir by stimulating the geothermal reservoir in multiple ways.

(Example 1)
A test was conducted using the test apparatus 300 shown in FIG.
As a test apparatus, a test apparatus 300 having a pressure vessel 310 , a mantle heater 311 covering the pressure vessel 310 , and a pressure maintaining pump 318 for adjusting the pressure inside the pressure vessel 310 was prepared.
Next, a granite sample 320 (25 mm in diameter and 25 mm in length) was placed in the center of the pressure vessel 310 and covered with a fluororubber sleeve 321 around it. Further, the inside of the pressure vessel 310 is filled with silicone oil 313 for sealing pressure.
The granite sample 320 was preheated in an electric furnace (570° C., 120 min) to form cracks in the sample 320 before use.
Next, the temperature inside the pressure vessel 310 is set to 200° C. and the sealing pressure is set to 15 MPa. After circulating until the pressure difference between the upstream side and the downstream side, measured by , back pressure: 5 MPa). The flow rate was adjusted by injection pump 314 and the back pressure was adjusted by pressure regulator 312 . The temperature inside pressure vessel 310 was measured using thermometer 317 .
By circulating room temperature water in the pressure vessel, cracks formed in the granite sample 320 are opened, and then by circulating the room temperature GLDA aqueous solution, the GLDA aqueous solution penetrates into the cracks and the granite sample 320 is formed. It was confirmed that the internal permeability was improved.
As the GLDA aqueous solution, a GLDA-Na ₄ aqueous solution (concentration: 40 wt %), water, and a 20 wt % GLDA-Na ₄ aqueous solution of pH 4.0 prepared by mixing nitric acid were used.

FIG. 3 shows the change in the difference between the fluid pressure measured by the pressure gauge 315 on the upstream side of the granite sample 320 in the test of Example 1 and the pressure of the fluid measured by the pressure gauge 316 on the downstream side.
According to FIG. 3, water is first circulated in the pressure vessel 310 to saturate the rock with water and bring it to the initial state. At this time, cracks formed in the granite sample 320 open.
Next, after the inside of the pressure vessel 310 is replaced with the GLDA aqueous solution, when the GLDA aqueous solution is circulated, the difference in fluid pressure between the upstream side and the downstream side of the granite sample 320 becomes small, and the inside of the granite sample 320 An approximately 1.7-fold improvement in permeability was shown.

FIG. 4 shows the results of analyzing the components of the waste liquid recovered from the pressure vessel 310 in the test of Example 1 using ICP-OES (manufactured by Agilent Technologies).
FIG. 4 shows that the concentration of Fe, Ca, Al, and Mg in the waste liquid increases at the initial stage when the GLDA aqueous solution is circulated in the pressure vessel 310, and then becomes a constant value. FIG. 4 also shows that the concentrations of K and Si gradually increase and then remain constant. The concentration changes of these six elements are: potassium feldspar (KAlSi ₃ O ₈ ), plagioclase (NaAlSi ₃ O ₈ —CaAl ₂ Si ₂ O ₈ ), biotite (K(Mg, Fe) ₃ AlSi ₃ O ₁₀ (OH , F) ₂ ), and amphibole (Ca ₂ (Mg, Fe) ₄ Al(AlSi ₇ O ₂₂ )(OH) ₂ ), but most notably The changed Fe concentration change reflects the dissolution behavior of biotite and hornblende (mainly biotite since the content of hornblende is small).
FIG. 4 also shows that the concentrations of K and Si in the effluent increase gradually and then become constant, which indicates the dissolution behavior of feldspars.
Thus, in the granite sample 320 of Example 1, it was shown that mainly biotite was dissolved.

In FIG. 5, an X-ray CT image of the cross section of the granite sample 320 before the test in Example 1 (taken using a microfocus X-ray CT device (manufactured by Comscan Techno Co., Ltd.)) (FIG. 5(a)) and , with the cross-sectional X-ray CT image of the granite sample 320 after the test (Fig. 5(b)).
According to FIG. 5, it was confirmed by the test of Example 1 that the amphibole 410 and the biotite 411 in the granite sample 320 were dissolved to form voids (black portions).

(Example 2)
The same test as in Example 1 was performed by replacing the GLDA aqueous solution with the HEDTA aqueous solution. As the HEDTA aqueous solution, a 20 wt % HEDTA- _Na3 aqueous solution with a pH of 4.0 prepared by mixing HEDTA- _Na3 dihydrate, water, and nitric acid was used.

FIG. 6 shows the change in the difference between the fluid pressure measured by the pressure gauge 315 on the upstream side of the granite sample 320 in the test of Example 2 and the pressure of the fluid measured by the pressure gauge 316 on the downstream side.
According to FIG. 6, first, water is passed through the pressure vessel 310 to saturate the rock with water and bring it to the initial state. At this time, cracks formed in the granite sample 320 open.
Next, after the inside of the pressure vessel 310 is replaced with the HEDTA aqueous solution, when the HEDTA aqueous solution is circulated, the difference in fluid pressure between the upstream side and the downstream side of the granite sample 320 becomes small, and the inside of the granite sample 320 An approximately 1.5-fold improvement in permeability was shown.

FIG. 7 shows the results of ICP-OES analysis of the components of the waste liquid recovered from the pressure vessel 310 in the test of Example 2. As shown in FIG.
FIG. 7 shows that the concentration of Fe, Ca, Al, and Mg in the waste liquid increases at the initial stage when the HEDTA aqueous solution is circulated in the pressure vessel 310, and then becomes a constant value. FIG. 4 also shows that the concentrations of K and Si gradually increase and then remain constant. The concentration changes of these six elements are: potassium feldspar (KAlSi ₃ O ₈ ), plagioclase (NaAlSi ₃ O ₈ —CaAl ₂ Si ₂ O ₈ ), biotite (K(Mg, Fe) ₃ AlSi ₃ O ₁₀ (OH , F) ₂ ), and amphibole (Ca ₂ (Mg, Fe) ₄ Al(AlSi ₇ O ₂₂ )(OH) ₂ ), but most notably The changed Fe concentration change reflects the dissolution behavior of biotite and hornblende (mainly biotite since the content of hornblende is small).

8 shows a cross-sectional X-ray CT image (taken using a microfocus X-ray CT device) of the granite sample 320 before the test in Example 2 (FIG. 8(a)) and the granite sample 320 after the test. was compared with the cross-sectional X-ray CT image (FIG. 8(b)).
According to FIG. 8, it was confirmed by the test of Example 1 that the biotite 411 in the granite sample 320 was dissolved to form voids (black portions).

(Comparative example 1)
The same test as in Example 1 was performed by replacing the aqueous GLDA solution with an aqueous nitric acid solution. As the nitric acid aqueous solution, an aqueous solution adjusted to pH 4.0 using nitric acid was used.

FIG. 9 shows the change in the difference between the fluid pressure measured by the upstream pressure gauge 315 and the downstream pressure gauge 316 of the granite sample 320 in the Comparative Example 1 test.
According to FIG. 9, first, water is passed through the pressure vessel 310 to saturate the rock with water and bring it to the initial state. At this time, cracks formed in the granite sample 320 open.
Next, after the inside of the pressure vessel 310 was replaced with the nitric acid aqueous solution, the nitric acid aqueous solution was circulated. As a result, although the difference in fluid pressure between the upstream side and the downstream side of the granite sample 320 decreased once, it eventually returned to the initial value, indicating that the permeability remained almost unchanged.
This is probably because the voids caused by the dissolution of the nitric acid aqueous solution are so small that they cannot be maintained under confining pressure.

FIG. 10 shows the results of ICP-OES analysis of the components of the waste liquid recovered from the pressure vessel 310 in the test of Comparative Example 1. As shown in FIG.
In FIG. 10, when the nitric acid aqueous solution is circulated in the pressure vessel 310, no significant increase in the element concentration in the waste liquid, which indicates the dissolution behavior of minerals, occurs. was shown not to be significantly enhanced.

FIG. 11 shows an X-ray CT image of the upper end surface of the granite sample 320 before the test in Comparative Example 1 (taken using a microfocus X-ray CT device) (FIG. 11(a)) and the granite sample after the test. 320 was compared with the X-ray CT image of the upper end surface (FIG. 11(b)).
According to FIG. 11, it was confirmed that no significant dissolution of minerals occurred in the test of Comparative Example 1.

As described above, according to Examples 1 and 2, even if the inside of the pressure vessel 310 is set to a high temperature of 200° C., by injecting water into the pressure vessel 310 and then injecting the chelating agent, the inside of the granite sample 320 It was shown that colored minerals such as biotite can be selectively dissolved to form voids.
Therefore, the method of the present invention can improve the permeability of geothermal reservoirs.

100: geothermal reservoir 101: crack 102: void 200: magma chamber 10: well 11: steel pipe 12: outlet 13: wellhead 16, 17: valve 21: pump 22, 23: tank 300: test device 310: pressure Container 311: Mantle heater 312: Pressure regulator 313: Silicone oil 314: Injection pump 315, 316: Pressure gauge 317: Thermometer 318: Pressure maintenance pump 319: Plug 320: Sample 321: Sleeve 410: Hornblende 411: Black mica

According to the geothermal reservoir composite stimulation method of the present invention, the permeability of the geothermal reservoir used for geothermal power generation can be improved in both production wells and return wells while minimizing the load on the environment. can. In addition, in the process of performing the combined stimulation of the geothermal reservoir according to the present invention, it is possible to remove scale adhering to the inner wall of the well used for geothermal power generation.

Claims (3)

a first step of injecting normal temperature water from a well into a geothermal reservoir to cool a cracked rock formation or formation of the geothermal reservoir ;
a second step of injecting a chelating agent from the well into the geothermal reservoir following the first step . 2. The method for combined stimulation of a geothermal reservoir according to claim 1, wherein the chelating agent contains one or more selected from the group consisting of GLDA, salts of GLDA, HEDTA, and salts of HEDTA. 3. The combined stimulation method for a geothermal reservoir according to claim 2, wherein in the step of injecting the chelating agent from the well into the geothermal reservoir, scale adhering to the inner wall of the well is removed.

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