CN109810687B - Environment-friendly acidizing working fluid suitable for increasing yield of low-permeability coal bed gas reservoir - Google Patents
Environment-friendly acidizing working fluid suitable for increasing yield of low-permeability coal bed gas reservoir Download PDFInfo
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Abstract
The invention provides an environment-friendly acidizing working fluid suitable for increasing the yield of a low-permeability coal bed gas reservoir, and belongs to the technical field of coal bed gas development. The environment-friendly acidification working solution disclosed by the invention comprises organic acid, a chelating agent, an anti-swelling agent, a corrosion inhibitor and the like, wherein each 100 parts of water comprises the following components in parts by mass: 7-9 parts of organic acid, 4-5 parts of chelating agent, 4 parts of anti-swelling agent and 0.5-1 part of corrosion inhibitor; the organic acid is composed of formic acid and citric acid, the chelating agent is composed of glutamic acid N, N-diacetic acid (GLDA) and N-beta-hydroxyethyl ethylenediamine triacetic acid (HEDTA), and the anti-swelling agent is composed of potassium chloride and ammonium chloride. The environment-friendly acidizing working solution has a good corrosion effect on crystalline minerals in the coal rock, and can increase the crack width and porosity of the coal rock so as to increase the gas logging permeability; meanwhile, the additive has low corrosivity on the pipe, cannot pollute underground water of a coal mine, cannot influence the quality of coal products produced in the later period, and has a good application prospect in increasing the yield of a low-permeability coal bed gas reservoir.
Description
Technical Field
The invention relates to the technical field of coal bed gas development, in particular to an environment-friendly acidizing working solution suitable for increasing the yield of a low-permeability coal bed gas reservoir.
Background
Coal bed gas is an important unconventional natural gas, is adsorbed on the surface of coal matrix particles or exists in the pore cracks of coal rocks in a free state, and is an associated mineral resource of coal. Although China has abundant coalbed methane resources, because of the low permeability (generally 0.001-0.1mD), the development and utilization of coalbed methane are restricted.
Although the hydraulic fracturing technology widely used in the low-permeability coal bed gas production increase at present can effectively communicate the cleavage and structural fractures in coal rocks, the fractures can be closed under high pressure due to the strong stress sensitivity of the coal rocks, so that the coal bed gas desorption and the final gas production effect of a coal bed gas well are influenced, and the high pressure is easy to communicate the coal bed with the aquifer of the top and bottom plates.
On the other hand, the acidizing technology is one of the important means for high oil and gas yield in oil and gas field development, and is to inject one or more kinds of acid liquor into a stratum through a well hole, and after the acid liquor erodes coal-rock cement or plugs in pores and cracks of the stratum, the permeability of the stratum can be recovered or improved. The conventional acid liquid such as hydrochloric acid or earth acid in the traditional acidification technology has the problems of strong corrosivity to well pipes and easy generation of precipitates such as calcium fluoride and silica gel, thereby causing secondary damage. Therefore, a novel acidification technology which can adapt to the physical properties of the reservoir is urgently needed in the yield increasing operation of the low-permeability coal-bed gas well.
The Chinese invention patent 'chemical formula of acidizing solution for improving coal bed permeability' (publication number: 106497540A) provides a chemical formula of acidizing solution for improving coal bed permeability, which comprises the following components in percentage by weight: 12-15% of hydrochloric acid, 2-2.5% of hydrofluoric acid, 2.5-3% of acidification retarder, 1.5-1.8% of acidification corrosion inhibitor, 0.3-0.5% of iron ion stabilizer, 2-2.2% of anti-swelling agent and the balance of water. The invention mainly aims at the mineral components such as calcite, dolomite, silicate and the like contained in the coal bed, and the mineral components flow out of the coal bed along with the acidizing solution after being dissolved by the acidizing solution, so that the cracks and the connectivity of the cracks in the coal bed are increased, the permeability of the coal bed is increased, and the extraction effect of coal bed gas is improved. However, as the main components of the formula are hydrochloric acid and hydrofluoric acid, hydrochloric acid is easy to generate to cause the migration of illite minerals in the acidification process, hydrofluoric acid is easy to produce calcium fluoride precipitate, and the two acid solutions are strong in corrosion to a bottom hole drilling tool.
The invention patent of China 'an acidification blocking remover for removing pollution blocking of a coal bed gas well' (publication number: 104073230A) provides the acidification blocking remover for removing the pollution blocking of the coal bed gas well, which comprises 3.0-5.0% of sulfamic acid, 3.0-5.0% of ammonium bifluoride, 0-2.0% of acetic acid, 1.0-2.0% of formaldehyde, 0.5-1.0% of acetylene glycol, 0.5-1.0% of ammonium chloride and the balance of water in percentage by weight. The method has the characteristics of strong corrosion capacity and low corrosion rate, and silicate minerals, carbonate minerals and the like in a hydrofluoric acid corrosion coal layer are slowly generated by using acetic acid, sulfamic acid and ammonium bifluoride. But the blocking remover contains fluoride, has high harm to residual acid and pollutes the environment.
The Chinese invention patent 'a blocking remover suitable for complex lithologic reservoir acidification and an acidification blocking removal method' (publication number: 103484088B) discloses a blocking remover suitable for complex lithologic reservoir acidification, which is prepared by mixing the following raw materials in percentage by weight: 10-25% of hydrazine hydrochloride, 2-6% of fluorine-containing compound, 0.3-3% of acidification corrosion inhibitor, 0.3-3% of demulsification cleanup additive, 0.3-3% of iron ion stabilizer for acidification, 0.3-3% of clay stabilizer and the balance of water. The blocking remover adopts powdery hydrazine hydrochloride and fluorine-containing compounds to be mixed and then slowly generates hydrofluoric acid in a reservoir for blocking removal, and has the characteristics of convenient raw material transportation, safe use and environmental protection: hydrofluoric acid is generated in the stratum by hydrazine hydrochloride and fluorine-containing compounds, so that the aim of retarding is fulfilled, and the permeability and the penetration depth of the reservoir stratum are obviously superior to those of the conventional earth acid. The plugging removal cost is low, the penetration depth is large, the reaction speed of acid rock can be well controlled, the acidification plugging removal efficiency is improved, meanwhile, the corrosion of acid liquor to metal pipelines and equipment is reduced, and stratum pollution is prevented. The method has the disadvantages that a large amount of hydrazine hydrochloride and fluorine-containing compounds are added in the formula, and potential threats exist to coal mine underground water.
Hydrochloric acid, hydrofluoric acid or earth acid and the like are directly used for increasing the yield of a low-permeability coal bed gas reservoir, so that the problem of serious well pipe corrosion is caused, and the water quality of underground water of a coal mine is also adversely affected to a certain extent.
Disclosure of Invention
In view of the above, the invention provides an environment-friendly acidizing working solution which is suitable for increasing the yield of a low-permeability coal bed gas reservoir, has a good corrosion effect on minerals in a coal bed, has a good effect of increasing the permeability and porosity of coal rocks, is low in corrosivity on underground pipes, and has good environmental protection.
The invention provides an acidification working solution suitable for increasing the yield of a low-permeability coal bed gas reservoir, which consists of organic acid, a chelating agent, an anti-swelling agent, a corrosion inhibitor and water, wherein each 100 parts of water contains the following components in parts by mass: 7-9 parts of organic acid, 4-5 parts of chelating agent, 4 parts of anti-swelling agent and 0.5-1 part of corrosion inhibitor.
Further, the organic acid consists of 3-5 parts of formic acid and 3-5 parts of citric acid, the chelating agent consists of 3-5 parts of glutamic acid N, N-diacetic acid (GLDA) and 1-2 parts of N-beta-hydroxyethyl ethylenediamine triacetic acid (HEDTA), the anti-swelling agent consists of 1-3 parts of potassium chloride and 1-3 parts of ammonium chloride, and the corrosion inhibitor is water-soluble imidazoline.
Compared with the prior art, the technical scheme provided by the invention has the beneficial effects that:
(1) the formula of the environment-friendly acidizing working solution does not contain hydrofluoric acid or hydrochloric acid, cannot pollute underground water of a coal mine, cannot influence the quality of coal products produced in the later period, and has low corrosivity on underground pipes;
(2) the organic acid in the formula of the environment-friendly acidizing working fluid consists of formic acid and citric acid, and the organic acid and the citric acid have good retarding effect and are not easy to cause particle migration in coal rocks;
(3) according to the formula of the environment-friendly acidizing working fluid, chelating agents HEDTA and GLDA can form stable and soluble chelates with metal cations such as calcium, iron and magnesium, and meanwhile, the chelating agents HEDTA and GLDA and organic acids are cooperated to enhance the corrosion capacity of crystalline minerals in coal rocks and the like, and the corrosion of acid liquor to downhole drilling tools and the like is reduced.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.
FIG. 1 is a scanning electron microscope image of No. 3 coal rock in Shanxi Chengzhuang area without being soaked in the chelating acid of the present invention;
FIG. 2 is a scanning electron microscope image of the coal rock 3# in Shanxi Chengzhuang area soaked in the chelating acid according to the present invention;
FIG. 3 is a graph showing the pressure drop during the hydrochloric acid displacement in Shanxi Chengzhuang No. 3 coal in accordance with an embodiment of the present invention;
FIG. 4 is a graph showing the pressure drop during displacement of the environmentally friendly acidizing fluid of example 1 in Shanxi Chengzhuang No. 3 coal rock according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
The formic acid in the embodiment of the invention is produced by chemical reagent of national medicine group, and the mass concentration is 88%; citric acid is produced by national drug group chemical reagent limited, glutamic acid N, N-diacetic acid (GLDA) is produced by Shanghai Mianning chemical company limited, N-beta-hydroxyethyl ethylenediamine triacetic acid (HEDTA) is produced by Shanghai Vanning chemical company limited, potassium chloride is produced by national drug group chemical reagent limited, ammonium chloride is produced by national drug group chemical reagent limited, and water-soluble imidazoline is produced by Shandong Yousio chemical technology company limited.
Example 1
The preparation method of the environment-friendly acidizing working fluid disclosed by the embodiment 1 of the invention comprises the following steps:
taking a proper amount of 88 mass percent formic acid, adding water to a constant volume of 100mL, diluting the formic acid concentration to 3 percent, and then adding 4g of citric acid, wherein 4g of citric acid and formic acid form organic acid; then adding 3g of potassium chloride and 1g of ammonium chloride, and forming an anti-swelling agent by 3g of potassium chloride and 1g of ammonium chloride; then adding 3g of GLDA and 2g of HEDTA, and forming a chelating agent by 3g of GLDA and 2g of HEDTA; and finally, adding 0.5g of water-soluble imidazoline serving as a corrosion inhibitor to prepare the environment-friendly acidizing working solution.
In addition, 100mL of water was added with only 2g of potassium chloride and 2g of ammonium chloride to prepare a pre-solution/post-solution.
Example 2
The preparation method of the environment-friendly acidizing working fluid in the embodiment 2 of the invention comprises the following steps:
taking a proper amount of 88 mass percent formic acid, adding water to a constant volume of 100mL, diluting the formic acid concentration to 5 percent, and then adding 3g of citric acid, wherein 3g of citric acid and formic acid form organic acid; then adding 2g of potassium chloride and 2g of ammonium chloride, and forming an anti-swelling agent by using 2g of potassium chloride and 2g of ammonium chloride; then adding 4g of GLDA and 1g of HEDTA, and forming a chelating agent by 4g of GLDA and 1g of HEDTA; and finally, adding 0.8g of water-soluble imidazoline serving as a corrosion inhibitor to prepare the environment-friendly acidizing working solution.
Example 3
The preparation method of the environment-friendly acidizing working fluid in the embodiment 3 of the invention comprises the following steps:
taking a proper amount of 88 mass percent formic acid, adding water to a constant volume of 100mL, diluting the formic acid concentration to 4 percent, and then adding 5g of citric acid, wherein 5g of citric acid and formic acid form organic acid; then adding 1g of potassium chloride and 3g of ammonium chloride, and forming an anti-swelling agent by 1g of potassium chloride and 3g of ammonium chloride; then adding 3g of GLDA and 1g of HEDTA, and forming a chelating agent by 3g of GLDA and 1g of HEDTA; and finally, adding 1g of water-soluble imidazoline serving as a corrosion inhibitor to prepare the environment-friendly acidizing working solution.
The mineral composition and mineral occurrence state of the 3# coal rock sample in Shanxi Henzhuang area are analyzed:
an experimental instrument: an X' Pert PRO ray powder crystal diffractometer, a Quanta 200 environment scanning electron microscope (FEI Co., Ltd.), and a Zhongxing 101 electrothermal blowing drying oven.
Experimental analysis steps:
(1) the selected coal samples are the coal core and the large coal sample at the bottom of the well, and the small coal sample knocked off from the coal sample is ground by a grinding cymbal and passes through a 100-mesh screen.
(2) Spreading the coal powder which is sieved by a 100-mesh sieve on a smooth and clean sample conveying plate, placing the sample conveying plate in an electric heating air blowing drying box, drying at the temperature of 60 ℃ for 24 hours, and taking out the sample conveying plate.
(3) The results of measuring the mineral content and the amorphous content in the coal sample by the K value quantitative analysis method are shown in table 1.
TABLE 1 mineral composition of 3# coal rock in Shanxi Chengzhuang area
| Mineral component | Chlorite (chlorite) | Kaolinite | Illite stone | Iron dolomite | Amorphous content |
| Content/% | 7 | 18 | 10 | 2 | 63 |
(4) A small coal rock sample is taken and a Quanta 200 environment scanning electron microscope is used for observing the surface morphology of the coal rock before and after the environment-friendly acidizing working solution of the embodiment 1 is soaked, the results are respectively shown in fig. 1 and fig. 2, and the fracture width of the coal rock after the coal rock is soaked in the environment-friendly acidizing working solution of the embodiment 1 is increased by comparing the fig. 1 and the fig. 2.
The invention is suitable for evaluating the static erosion effect of the environment-friendly acidizing working fluid for increasing the yield of the coal bed gas on the coal rock:
an experimental instrument: beaker, electronic balance (accurate to 0.01g), glass funnel, etc.
Preparing coal dust: selecting a No. 3 coal core of Shanxi Chengzhuang, crushing, sieving with a 100-mesh sieve, repeatedly sieving to ensure uniform granularity of coal dust, drying the sieved coal dust at 80 ℃ for 4h, drying, and sealing in a drying bottle for later use.
The corrosion rate measuring method comprises the following steps: the dried coal dust was taken out at room temperature and weighed, and the mass of each portion was 4.00 g. Mixing coal dust and different acid solutions according to a weight ratio of 1: 10, shaking to make the acid liquor fully contact with the coal dust, standing for 16h, filtering with filter paper after reaction, drying and heating at 100 ℃ for 40 min, and weighing the filter paper and the coal dust. Calculating the erosion rate of the coal dust according to the mass of the coal dust before and after the reaction, as shown in a formula (1); the calculation results are shown in table 2 below. All the waste acid liquid in the experiment is poured into the waste liquid recycling bin for unified treatment.
TABLE 2 erosion Rate of different acidizing fluids to coal petrography
| Type of acidifying liquid | Coal dust erosion Rate/%) |
| 15% hydrochloric acid | 2.5 |
| Example 1 | 3.99 |
| Example 2 | 5.20 |
| Example 3 | 3.75 |
As can be seen from table 2, compared with the common hydrochloric acid, the acidizing working fluid applicable to the coal bed gas yield increase provided by the embodiment of the present invention has a stronger erosion capacity for coal dust, which is 2.08 times as high as 15% hydrochloric acid at most.
Thirdly, simulating the actual working condition of the environment-friendly acidizing working fluid suitable for increasing the yield of the coal bed gas by using a rock core displacement experiment:
an experimental instrument: the test device comprises a special core drilling machine, an LCMP-1A metallographic specimen grinding and polishing machine and a TC-50 core acidizing flow tester.
The experimental method comprises the following steps:
(1) and (4) drilling a coal core. Opening a switch of the special core drilling machine to ensure that the drill bit can normally rotate and the water circulation can cool the drill bit; closing the switch, aligning the coal block with the thickness of more than 20mm to the drill bit, and fixing the coal block on the workbench to ensure that the coal block does not shake violently in the drilling process; and opening the switch, and rotating the rocker to drill the coal core.
(2) And (5) manufacturing a polished coal sample. The purpose of polishing the drilled coal sample is to obtain a smoother, cleaner, ideal surface for accurate and reliable data. Selecting broken coal blocks with smooth surfaces and uniform sizes as much as possible, grinding and polishing the surfaces of the coal samples by using a metallographic specimen grinding and polishing machine, selecting a fixed speed of 800r/min, selecting 1000 meshes of abrasive paper, carrying out one-time abrasive paper replacement for every two coal samples, putting the ground coal samples into an electrothermal blowing drying box, setting the temperature to be 120 ℃, and taking out the coal samples after 0.5h to obtain the polished coal samples.
(3) Ensuring that the liquid in a liquid storage container and various pumps in the TC-50 type core acidizing flow experimental instrument is sufficient; opening power supplies of all parts of the instrument, putting the prepared rock sample into a rubber sleeve of the rock core holder, installing a holder plug, and slightly jacking the rock sample; opening a valve of the ring-opening pressure pump, and closing the valve of the ring-opening pressure pump when the pressure is increased to about 4.0 MPa; and opening computer software, carrying out equipment on-line, selecting a constant current mode, and setting the constant current speed to be 0.5 mL/min. After the software is normally connected with the instrument, opening a container valve filled with the pad fluid, and starting to observe the change of the upstream pressure; after the upstream pressure is kept stable, acid liquor is injected for measurement, a container valve filled with the pre-solution is closed, the solution is changed until the upstream pressure is observed to have obvious pressure drop, and at the moment, the acid liquor is completely permeated, and the connectivity of coal pores is enhanced; closing the valve of the container filled with acid liquor, opening the valve of the container filled with postposition liquor, injecting postposition liquor, and observing the changes of upstream pressure and liquid permeability.
Fig. 3 and 4 record the pressure drop and the measured permeability change of the coal core in the displacement acidification process of 5% hydrochloric acid and the environment-friendly acidification working fluid in example 1, respectively. The results show that the 5% hydrochloric acid displacement can cause secondary damage to the reservoir, the coal rock liquid permeability is reduced from 0.052mD to 0.042mD, and the acidizing working fluid formula provided in example 1 can improve the liquid permeability of the coal rock core from 0.039mD to 0.048 mD.
Fourthly, the influence of the environment-friendly acidizing working fluid suitable for increasing the yield of the coal bed gas on the porosity of the coal rock is as follows:
an experimental instrument: JHCI-core evacuation saturation experimental device; a core drilling machine; electronic balance, etc.
The experimental method comprises the following steps:
(1) preparing NH with the mass fraction of 5%4And (4) Cl solution.
(2) The coal rock core before and after being displaced by the acidizing working fluid provided by the embodiment 1-3 of the invention is placed into a screen mesh, is placed into an electric heating air blowing drying oven, is set to be 120 ℃, is taken out after 1 hour and is placed into a vacuum instrument, is taken out after being sealed and extracted for 4 hours, is weighed, and retains 2 decimal places. The vacuum instrument is used for completely pumping out gas in the coal core pore space.
(3) Placing each weighed small coal briquette in a beaker separately, carefully and lightly placing the small coal briquettes in the moving process to ensure that the small coal briquettes are not chipped, and if the small coal briquettes are chipped, replacing the coal briquettes; recording the position of the coal briquette and numbering; adding 5% NH in turn4And (4) taking out the Cl solution after soaking for 24 hours, carefully absorbing the liquid on the surface of the coal briquette by using filter paper, weighing and recording data. The porosity can be obtained according to the following water absorption formula (2):
the porosity change of the coal sample before and after the acidizing working fluid suitable for increasing the yield of the coal bed gas is used for displacement is shown in the following table 3, and it can be seen from the table 3 that the porosity of the coal core can be increased by 37.17% to the maximum extent after the acidizing working fluid provided by the invention is used for displacement.
TABLE 3 porosity change before and after coal core Displacement
| Displacement media | Pre-displacement porosity/%) | Post-displacement porosity/%) | Increase factor/%) |
| Example 1 | 3.74 | 5.13 | 37.17 |
| Example 2 | 2.87 | 3.57 | 24.39 |
| Example 3 | 2.31 | 2.79 | 20.78 |
Fifthly, the acidizing working fluid applicable to the yield increase of the coal bed gas has the following influence on the permeability of the coal rock gas:
an experimental instrument: JHGP gas permeability measuring instrument and the like.
The experimental method comprises the following steps: coal cores before and after displacement by using the acidizing working fluid provided by the embodiment 1-3 of the invention are loaded into the core holder, and the left side and the right side of the core holder are fixed; opening a nitrogen cylinder switch, and adjusting the ring pressure to be 1.2 MPa; the upstream pressure was adjusted, values for upstream pressure and flow were recorded, and data was read three times for each sample and averaged. After the experiment is finished, the upstream pressure regulating valve is closed firstly, the air release valve is opened, the gas in the pipeline is released, the nitrogen cylinder valve is closed, the left air release valve is opened, the gas remained at the opening of the nitrogen cylinder is released, the experiment result is shown in table 4, the gas permeability of the coal rock core after the displacement experiment is obviously improved, and the highest gas permeability can reach 5.48 times.
TABLE 4 Change in permeability of coal core before and after Displacement
| Displacement media | Permeability before Displacement/mD | Permeability after Displacement/mD | Increase by multiple |
| Example 1 | 0.26 | 0.99 | 2.81 |
| Example 2 | 0.71 | 0.77 | 0.08 |
| Example 3 | 0.21 | 1.36 | 5.48 |
Sixthly, evaluating the corrosivity of the acidizing working fluid applicable to the coal bed gas yield increase on a P110 test piece:
an experimental instrument: electronic balance (accurate to 0.01g), etc.
The experimental method comprises the following steps: the experimental procedure is carried out according to the oil and gas industry standard SY/T5405-1996 of the people's republic of China.
(1) Taking out the P110 standard corrosion test piece, measuring its size with vernier caliper, tying the plastic thin line on the test piece hole and the other end on the glass rod, keeping the hanging state, using the knotted number as the serial number of the same group of test pieces, and recording the serial number of the test piece itself and the initial quality in the table.
(2) Experiment at normal temperature: hanging the tied test piece, placing into a beaker at certain intervals, and using 20cm of acid solution according to the surface area of each square centimeter of the test piece3And pouring the prepared acid liquor into the beaker in sequence to ensure that the acid liquor completely soaks the test piece, and covering the surface of the beaker with a preservative film.
(4) Recording the reaction starting time, taking out the test piece when the reaction reaches the preset time, immediately washing the test piece with clear water, then brushing the test piece with a soft brush, shearing off a thin plastic line, wiping the surface of the test piece with filter paper, and photographing and comparing the test piece with the initial test piece after recording the quality.
(5) The corrosion rate is calculated according to equation (3):
in the formula: v. ofiMonolithic corrosion rate, g/(m)2H); Δ t-reaction time, h; delta miTest piece corrosion loss, g; a-surface area of test piece, mm2。
The standard corrosion test piece of this experiment is 2800mm2(ii) a The corrosion rates of the P110 standard corrosion coupon in different acidified working fluids are shown in table 5 below.
TABLE 5 Corrosion Rate of P110 Standard test coupons in different acidified working fluids
| Test medium | Corrosion rate g/(m)2·h) |
| Example 1 | 0.39 |
| Example 2 | 0.54 |
| Example 3 | 0.58 |
| 15% hydrochloric acid | 4.91 |
As can be seen from table 5, the corrosion rate of the environment-friendly acidizing working fluid provided by embodiments 1 to 3 of the present invention to the P110 test piece is low, and the corrosion rate is only 11.88% of 15% hydrochloric acid at most, which indicates that the environment-friendly acidizing working fluid of the present invention has little damage to the downhole tubular product.
In conclusion, the invention provides the environment-friendly acidizing working solution suitable for increasing the yield of the low-permeability coal bed gas reservoir, wherein the acid solution is organic acid (formic acid and citric acid), the retarding effect is good, and the quality of coal produced in the later period is not affected; meanwhile, chelating agents GLDA and HEDTA are added, so that metal ions such as calcium, iron and magnesium can be effectively chelated, a stable and soluble chelate is further generated, precipitates such as ferric hydroxide are prevented from being generated, and the acidification effect is enhanced; meanwhile, the corrosion to the underground drilling tool is reduced, and the method is environment-friendly.
The features of the embodiments and embodiments described herein above may be combined with each other without conflict.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (4)
1. The environment-friendly acidizing working solution suitable for increasing the yield of a low-permeability coal bed gas reservoir is characterized by being prepared by mixing organic acid, a chelating agent, an anti-swelling agent, a corrosion inhibitor and water, wherein each 100 parts of water comprises the following components in parts by mass: 7-9 parts of organic acid, 4-5 parts of chelating agent, 4 parts of anti-swelling agent and 0.5-1 part of corrosion inhibitor, wherein the organic acid consists of formic acid and citric acid, the chelating agent consists of glutamic acid N, N-diacetic acid and N-beta-hydroxyethyl ethylenediamine triacetic acid, the anti-swelling agent consists of potassium chloride and ammonium chloride, and the corrosion inhibitor is imidazoline.
2. The environment-friendly acidizing working fluid suitable for increasing the yield of a hypotonic coalbed methane reservoir as claimed in claim 1, wherein the mass parts of the formic acid are 3-5 parts, and the mass parts of the citric acid are 3-5 parts.
3. The environment-friendly acidizing working fluid suitable for stimulation of a hypotonic coalbed methane reservoir as claimed in claim 1, wherein the mass part of glutamic acid N, N-diacetic acid is 3-4 parts, and the mass part of N-beta-hydroxyethylethylenediamine triacetic acid is 1-2 parts.
4. The environment-friendly acidizing working fluid suitable for increasing the yield of a low-permeability coal bed gas reservoir as claimed in claim 1, wherein the mass part of potassium chloride is 1-3 parts, and the mass part of ammonium chloride is 1-3 parts.
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