Double-barrier petroleum-polluted underground water remediation method

Abstract

The invention provides a double-barrier petroleum-polluted groundwater remediation method which comprises the following steps: drilling barrier liquid injection wells at the boundary of a polluted site, drilling a monitoring well between two adjacent barrier liquid injection wells, and drilling liquid nitrogen injection wells at the peripheries of the barrier liquid injection wells. The double isolation walls adopted by the device can be rapidly formed, after polluted underground water is extracted, liquid nitrogen is gasified, guar gum is naturally degraded, secondary pollution is avoided, the polluted underground water can be conveniently and rapidly extracted, the working efficiency is improved, after a viscous guar gum solution makes full contact with the soil, pores between the soil can be closed, and the soil can be effectively protected. And after liquid nitrogen freezing, double barrier of external frozen soil and internal frozen guar gum and soil cementing is formed, and the barrier performance is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of groundwater remediation in environmental protection, and in particular relates to a double-barrier method for remediating petroleum-contaminated groundwater. Background Art

[0002] During the exploration, extraction, and transportation of oil, crude oil leaks and migration into shallow groundwater often occur, which can harm the groundwater environment. When groundwater is polluted, protecting water sources and restoring the groundwater environment have become one of the most important tasks.

[0003] Currently, a common method for remediating oil-contaminated groundwater is to pump the contaminated groundwater to the surface. However, this process extracts a large amount of uncontaminated groundwater, resulting in a waste of groundwater resources. Localized over-extraction of groundwater can also trigger geological disasters such as ground subsidence and even collapse. Therefore, before extracting contaminated groundwater, a ground-level water barrier is constructed to block the flow between contaminated and uncontaminated groundwater. This allows only the groundwater within the barrier to be extracted, preventing over-extraction.

[0004] This method is widely used in practical applications, but there are also some problems. The water-blocking wall is usually formed by drilling holes in the ground and injecting cement. This cement water-blocking wall will remain permanently in the underground soil, causing secondary impacts on the environment. For example, Patent No. CN111424696B proposes a barrier wall construction device and method for soil and groundwater remediation, which adopts the method of injecting cement slurry to construct a group of water-blocking walls. In order to solve this problem, liquid nitrogen can be used to freeze the ground to form a frozen water-blocking wall. This method freezes the underground soil to form a water barrier. Due to the extremely low temperature of liquid nitrogen, the moisture in the soil will form ice crystals during the freezing process, thereby forming a stable frozen soil layer. This method has less impact on the environment because the frozen water barrier is temporary, and the soil will return to its natural state after the freezing process. For example, Patent No. CN106216381B proposes an integrated system and treatment method for frozen isolation and in-situ thermal desorption of contaminated soil. Frozen isolation uses frozen wells to form an icy isolation barrier around a repair area to prevent the migration and flow (inflow or outflow) of pollutants in the repair area. It can also inhibit the flow of groundwater into the repair area, which can reduce the amount of groundwater that needs to be treated. However, there are also some problems with frozen water barriers. The strength or thickness of the frozen soil is limited. During the suction process, there are problems of local leakage and poor barrier effect. Therefore, it is particularly important to further improve the barrier performance of the water barrier while avoiding secondary pollution of the environment. Summary of the Invention

[0005] The purpose of the present invention is to provide a double-barrier petroleum-contaminated groundwater remediation method, which addresses the problem of secondary pollution caused by cement water barriers during the contaminated groundwater remediation process and the problem of limited wastewater performance of liquid nitrogen freezing water barriers.

[0006] To this end, the technical solutions provided by the present invention are as follows:

[0007] A double-barrier oil-contaminated groundwater remediation method involves drilling barrier liquid injection wells at the boundary of the contaminated site, drilling monitoring wells between two adjacent barrier liquid injection wells, and drilling liquid nitrogen injection wells outside the barrier liquid injection wells.

[0008] Inject barrier liquid into the barrier liquid injection well. During the injection process, continuously observe the groundwater sample in the monitoring well. When barrier liquid is detected in the groundwater of the monitoring well, stop the injection.

[0009] Liquid nitrogen is injected into the liquid nitrogen injection well. During the injection process, the soil temperature is detected by the temperature sensor in the monitoring well. When the soil temperature drops to the set value, the injection is stopped;

[0010] Drill a pumping well in the center of the contaminated site to extract groundwater from the contaminated area. Continuously monitor the groundwater quality and stop extracting when the petroleum hydrocarbon content in the groundwater drops to the set value.

[0011] Before drilling barrier liquid injection wells at the boundary of the contaminated site, the contaminated groundwater remediation area is set as a circle, and the barrier liquid injection wells are evenly distributed around the circle.

[0012] The distance between the bottom end of the barrier liquid injection well and the bottom of the contaminated groundwater is greater than 2m, and a barrier liquid injection string is lowered into the well.

[0013] The liquid nitrogen injection well is arranged on a circle 1-1.5 m away from the circle where the barrier liquid injection well is located.

[0014] The distance from the bottom end of the liquid nitrogen injection well to the bottom of the contaminated groundwater is greater than 2m. A liquid nitrogen injection string is inserted into the liquid nitrogen injection well. Multiple liquid nitrogen injection holes are evenly distributed around the string. The left and right spacing and the top and bottom spacing of the liquid nitrogen injection holes are both 1-1.2m.

[0015] The depth of the monitoring well is the same as that of the liquid nitrogen injection well. The monitoring well is a steel pipe column with monitoring holes opened every 1-1.2m in the vertical direction. A soil temperature sensor is placed in each monitoring hole.

[0016] The barrier liquid is a guar gum solution with a mass concentration of 1-1.5%.

[0017] During the process of extracting contaminated groundwater from the pumping well, the temperature sensor data of the monitoring well is tracked in real time. When the temperature is higher than 0°C, the extraction is stopped and liquid nitrogen is injected again through the liquid nitrogen injection well until the temperature is lower than -4°C. Then the injection of liquid nitrogen is stopped and the pumping operation is resumed.

[0018] The distance from the bottom of the pumping well to the bottom of the contaminated groundwater is greater than 5m, and a pumping pipe is inserted into the well.

[0019] The beneficial effects of the present invention are:

[0020] The double isolation wall adopted by the present invention can be formed quickly, and after the contaminated groundwater is extracted, the liquid nitrogen is gasified and the guar gum is naturally degraded, without secondary pollution. The contaminated groundwater can be extracted conveniently and quickly, thereby improving work efficiency. After the viscous guar gum solution is fully in contact with the soil, the pores between the soil can be sealed, reducing the flow performance of the groundwater. After being frozen by liquid nitrogen, a double barrier of external frozen soil and internal frozen guar gum cemented with soil is formed, further improving the barrier performance.

[0021] The dual barrier system of this invention is stronger than frozen soil alone. Because the soil contains oil and high-viscosity guar gum liquid, leakage is prevented. This viscous liquid can also provide short-term isolation, especially when the frozen body is cold enough to melt the liquid. Furthermore, guar gum is a biodegradable natural polysaccharide polymer that hydrolyzes naturally over time. The hydrolysis product is pollution-free and has a low viscosity similar to water, which does not affect the groundwater environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a plan view of an embodiment of the present invention;

[0023] Figure 2 This is a schematic cross-sectional view of a liquid nitrogen injection well;

[0024] Figure 3 It is a schematic diagram of the monitoring well cross section.

[0025] In the figure: 1. Barrier liquid injection well; 2. Monitoring well; 3. Liquid nitrogen injection well; 4. Pumping well; 5. Contaminated site boundary; 6. Liquid nitrogen freezing boundary; 7. Liquid nitrogen injection hole; 8. Monitoring well. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0027] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided so as to provide a thorough and complete disclosure of the present invention and fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention.

[0028] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0029] Example 1

[0030] This embodiment provides a double-barrier method for remediating petroleum-contaminated groundwater. A barrier liquid injection well 1 is drilled at the boundary 5 of the contaminated site. A monitoring well 2 is drilled between two adjacent barrier liquid injection wells 1. A liquid nitrogen injection well 3 is drilled outside the barrier liquid injection well 1.

[0031] Inject barrier liquid into barrier liquid injection well 1. During the injection process, continuously observe the groundwater sample in monitoring well 2. When barrier liquid is detected in the groundwater of monitoring well 2, stop the injection.

[0032] Liquid nitrogen is injected into the liquid nitrogen injection well 3. During the injection process, the soil temperature is detected by the temperature sensor in the monitoring well 2. When the soil temperature drops to the set value, the injection is stopped;

[0033] A pumping well 4 is drilled in the center of the contaminated site to extract groundwater from the contaminated area. The groundwater quality is continuously monitored and the extraction is stopped when the petroleum hydrocarbon content in the groundwater drops to a set value.

[0034] This invention uses a barrier fluid that is in full contact with the soil to seal soil pores and reduce groundwater flow. Liquid nitrogen freezing then creates a double barrier: externally frozen soil and internally bonded barrier fluid and soil. This improves the barrier performance of the watertight wall, allowing for quick construction of the wall and groundwater remediation. This avoids the permanent effects of traditional cement walls and the poor barrier performance of liquid nitrogen-frozen walls.

[0035] Example 2

[0036] Based on Example 1, this example provides a double-barrier method for remediating petroleum-contaminated groundwater. Figure 1 As shown, before drilling the barrier liquid injection well 1 at the boundary 5 of the contaminated site, the contaminated groundwater remediation area is set to a circle, and the barrier liquid injection wells 1 are evenly distributed around the circle.

[0037] The contaminated site boundary 5 is set as a circle with the pumping well 4 as the center of the circle to isolate and extract the contaminated groundwater.

[0038] Example 3

[0039] Based on Example 1, this example provides a double-barrier method for remediating petroleum-contaminated groundwater. The distance from the bottom end of the barrier liquid injection well 1 to the bottom of the contaminated groundwater is greater than 2 m, and a barrier liquid injection string is lowered.

[0040] The barrier liquid is a guar gum solution with a mass concentration of 1-1.5%.

[0041] Guar gum solution is viscous. After full contact with the soil, it can seal the pores between the soil and reduce the flow performance of groundwater. After being frozen by liquid nitrogen, it forms a double barrier of external frozen soil and internal frozen guar gum and soil, further improving the barrier performance.

[0042] Example 4

[0043] On the basis of Example 1, this example provides a double-barrier method for remediating petroleum-contaminated groundwater, wherein the liquid nitrogen injection well 3 is located on a circle 1-1.5 m away from the circle where the barrier liquid injection well 1 is located.

[0044] The distance between the bottom of the liquid nitrogen injection well 3 and the bottom of the contaminated groundwater is greater than 2m. A liquid nitrogen injection string is lowered into the liquid nitrogen injection well 3. Multiple liquid nitrogen injection holes 7 are evenly distributed around the string. The left and right spacing and the upper and lower spacing of the liquid nitrogen injection holes 7 are both 1-1.2m. Figure 2 The circle where the liquid nitrogen injection well 3 is located is the liquid nitrogen freezing boundary 6.

[0045] Example 5

[0046] Based on Example 1, this example provides a double-barrier method for remediating petroleum-contaminated groundwater. The depth of the monitoring well 2 is the same as that of the liquid nitrogen injection well 3. The monitoring well 2 is a steel pipe string with monitoring holes 8 opened every 1-1.2 m in the vertical direction. A soil temperature sensor is placed in each monitoring hole 8. Figure 3 shown.

[0047] The soil temperature is detected by the soil temperature sensor to determine whether to stop injecting liquid nitrogen.

[0048] Example 6

[0049] This embodiment provides a double-barrier method for remediating petroleum-contaminated groundwater, comprising the following steps:

[0050] Step 1: The contaminated groundwater remediation area is set as a circle. A barrier liquid injection well 1 is drilled at the boundary 5 of the contaminated site. The distance between the bottom of the well and the bottom of the contaminated groundwater is greater than 2m. The barrier liquid injection string is lowered.

[0051] Step 2: Drill a liquid nitrogen injection well 3 1 meter outside the barrier liquid injection well 1 facing the contaminated groundwater, with the bottom end of the well at a distance of more than 2 meters from the bottom of the contaminated groundwater. Insert a liquid nitrogen injection string, and lay liquid nitrogen injection holes 7 around the string at intervals of 1 meter.

[0052] Step 3: Drill a monitoring well 2 between two adjacent barrier liquid injection wells 1. The depth of the monitoring well 2 is the same as that of the liquid nitrogen injection well 3. The steel pipe is made of a steel pipe with small holes opened every 1m. A soil temperature sensor is placed in each hole to monitor the soil temperature.

[0053] Step 4: Inject barrier liquid into barrier liquid injection well 1. The barrier liquid is a guar gum solution with a concentration of 1-1.5%. During the injection of the barrier liquid, continuously observe the groundwater sample in monitoring well 2. When the barrier liquid is detected in the groundwater of monitoring well 2, stop the injection.

[0054] Step 5: Inject liquid nitrogen into liquid nitrogen injection well 3, and continuously track the data of the temperature sensors in monitoring well 2. When each temperature sensor detects that the soil temperature has dropped below -4°C, stop injecting;

[0055] Step 6: Drill a pumping well 4 at the center of the groundwater contamination area. The distance between the bottom of the well and the bottom of the contaminated groundwater is greater than 5 meters. Insert the pumping pipe.

[0056] Step 7: Extract groundwater from the contaminated area and continuously monitor the groundwater quality. Stop extraction when the petroleum hydrocarbon content in the groundwater drops to 10 mg / L.

[0057] The dual barrier system of this invention is stronger than simply freezing soil. Because the soil contains oil and high-viscosity guar gum liquid, leakage is prevented. This viscous liquid can also provide short-term isolation, especially when the frozen body is cold enough to melt the liquid. Furthermore, guar gum is a biodegradable natural polysaccharide polymer that hydrolyzes naturally over time. The hydrolysis product is pollution-free and has a low viscosity similar to water, which does not affect the groundwater environment.

[0058] Example 7

[0059] In order to further introduce the present invention, this embodiment takes a certain groundwater contaminated area as an example to specifically describe the remediation method.

[0060] A certain groundwater pollution area is a polluted groundwater area with a vertical well of 100m and a pollution depth of 20m.

[0061] Construction preparation

[0062] Tidy up the construction site and equip it with water and electricity;

[0063] Planning the locations of different wells;

[0064] Prepare barrier liquid, the concentration of guar gum solution is 1.5%, and the liquid preparation volume is about 480 cubic meters.

[0065] Prepare a soil temperature sensor with a measuring range of -40°C to 120°C and an operating voltage of 12V to 24V.

[0066] Repair process

[0067] Step 1: Drill barrier liquid injection well 1 at the contaminated site boundary 5, with a depth of 22m, and lower the barrier liquid injection string;

[0068] Step 2: Drill a liquid nitrogen injection well 3 at a depth of 22m, 1 meter outside the barrier liquid injection well 1 facing the contaminated groundwater, and lower the liquid nitrogen injection string;

[0069] Step 3: Drill a monitoring well 2 at a depth of 22 m between two adjacent barrier liquid injection wells 1 and place a soil temperature sensor there to monitor soil temperature.

[0070] Step 4: Inject barrier liquid into barrier liquid injection well 1. The barrier liquid is a 1.5% guar gum solution. During the injection of the barrier liquid, the groundwater sample in monitoring well 2 should be continuously observed. When the barrier liquid is detected in the groundwater of monitoring well 2, the injection is stopped.

[0071] Step 5: Inject liquid nitrogen into liquid nitrogen injection well 3, and continuously track the data of the temperature sensors in monitoring well 2. When each temperature sensor detects that the soil temperature has dropped below -4°C, stop injecting;

[0072] Step 6: Drill a pumping well 4 at the center of the groundwater contaminated area with a depth of 25m and lower the pumping pipe into the well.

[0073] Step 7: Extract groundwater from the contaminated area and continuously monitor the groundwater quality. Stop extraction when the petroleum hydrocarbon content in the groundwater drops to 10 mg / L.

[0074] Step 8: During the extraction of contaminated groundwater from pumping well 4, the temperature sensor data of monitoring well 2 is tracked in real time. When the temperature is higher than 0°C, extraction is stopped and liquid nitrogen is injected again. When the temperature is lower than -4°C, the injection of liquid nitrogen is stopped and the pumping operation is resumed.

[0075] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention falls within the scope of protection of the present invention.

Claims

1. A double-barrier method for remediating petroleum-contaminated groundwater, characterized in that: Drill barrier liquid injection wells at the boundary of the contaminated site, drill monitoring wells between two adjacent barrier liquid injection wells, and drill liquid nitrogen injection wells outside the barrier liquid injection wells; Inject barrier liquid into the barrier liquid injection well. During the injection process, continuously observe the groundwater sample in the monitoring well. When barrier liquid is detected in the groundwater of the monitoring well, stop the injection. Liquid nitrogen is injected into the liquid nitrogen injection well. During the injection process, the soil temperature is detected by a temperature sensor in the monitoring well. When the soil temperature drops to a set value, the injection is stopped. Drill a pumping well in the center of the contaminated site to extract groundwater from the contaminated area. Continuously monitor the groundwater quality and stop extracting when the petroleum hydrocarbons in the groundwater drop to the set value.

2. A double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: Before drilling barrier liquid injection wells at the boundary of the contaminated site, the contaminated groundwater remediation area is set as a circle, and the barrier liquid injection wells are evenly distributed around the circle.

3. A double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: The distance from the bottom end of the barrier liquid injection well to the bottom of the contaminated groundwater is greater than 2m, and a barrier liquid injection pipe column is lowered into the well.

4. A double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: The liquid nitrogen injection well is arranged on a circle 1-1.5 m away from the circle where the barrier liquid injection well is located.

5. The double-barrier petroleum-contaminated groundwater remediation method according to claim 1 is characterized by: The distance from the bottom end of the liquid nitrogen injection well to the bottom of the contaminated groundwater is greater than 2m. A liquid nitrogen injection pipe column is lowered into the liquid nitrogen injection well. A plurality of liquid nitrogen injection holes are evenly distributed around the pipe column. The left-right spacing and the top-bottom spacing of the liquid nitrogen injection holes are both 1-1.2m.

6. A double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: The depth of the monitoring well is the same as that of the liquid nitrogen injection well. The monitoring well is a steel pipe column, and monitoring holes are opened every 1-1.2m in the vertical direction. A soil temperature sensor is placed in each monitoring hole.

7. The double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: The barrier liquid is a guar gum solution with a mass concentration of 1-1.5%.

8. The double-barrier petroleum-contaminated groundwater remediation method according to claim 1 is characterized by: During the process of extracting contaminated groundwater from the pumping well, the temperature sensor data of the monitoring well is tracked in real time. When the temperature is higher than 0°C, the extraction is stopped and liquid nitrogen is injected again through the liquid nitrogen injection well. After the temperature drops below -4°C, the injection of liquid nitrogen is stopped and the pumping operation is resumed.

9. The double-barrier petroleum-contaminated groundwater remediation method according to claim 1, characterized in that: The distance from the bottom of the pumping well to the bottom of the contaminated groundwater is greater than 5m, and a pumping pipe column is inserted.

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