Well drilling and completion method for carbonate cementation ultra-low permeability sandstone type uranium resource exploitation

Abstract

The invention relates to the technical field of uranium mining and well drilling construction, in particular to a drilling and well completion method for carbonate cementation ultra-low permeability sandstone type uranium resource mining. The method comprises the steps that firstly, a drill bit A is adopted for drilling a rock stratum, an open hole A is formed, and a small-size drill bit B is replaced for drilling to the designed hole depth; 2, new slurry is adopted to replace old slurry in a drill bit drilling well, comprehensive geophysical prospecting logging is carried out, and the position of a target ore bed is determined; thirdly, the roller bit is used for chambering to the lowering depth to obtain an open hole B, and the open hole B is circularly washed with new slurry after chambering is completed; fourthly, a well pipe is installed in the open hole B; fifthly, a grouting pipe is put into the well pipe, and cement paste is reversely injected into the annular space outside the pipe through a reserved round hole in the pipe wall of the well pipe; sixthly, the ore bed section is cut, and an ore bed cutting section is formed; and seventhly, drilling cleaning is conducted on the ore bed cutting section. Through the'windowing open hole 'drilling construction process research, no filter is arranged, and the problem that the submersible pump cannot be lowered to the filter section due to the fact that the inner diameter of a built-in filter is smaller than the outer diameter of the submersible pump in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of uranium drilling construction technology, and in particular to a well completion method for mining uranium resources in carbonate-cemented ultra-low permeability sandstone. Background Technology

[0002] This uranium deposit is a typical sandstone uranium deposit with complex geological characteristics, characterized by high carbonate cementation and ultra-low permeability. Since 2000, in terms of in-situ leaching uranium mining technology, acid leaching, weak acid and mixed acid / alkali leaching, and CO2+O2 neutral leaching tests have been carried out successively. An environmentally friendly and low-cost CO2+O2 neutral leaching process route suitable for stable production of this complex sandstone uranium deposit has been successfully developed. In terms of borehole structure, various drilling construction techniques such as tray type, projectile type, gravel-filled type, and open-window type with built-in filter have been adopted. However, due to the high mineralization, high chloride, high calcium, high clay content, high sulfate, low permeability, and low grade of the deposit, the geological conditions remain challenging.

[0003] In existing technologies, the inner diameter of the built-in filter in processes such as gravel-filled and window-type built-in filters is smaller than the outer diameter of the submersible pump. Therefore, the submersible pump can only be installed at the upper edge of the filter, resulting in limited dynamic water level drawdown and poor hydraulic linkage during operation. This restricts the efficient development of the deposit, leading to a long mining cycle and high production costs. Summary of the Invention

[0004] This invention provides a drilling and well completion method for mining uranium resources in carbonate-cemented ultra-low permeability sandstone, which solves the problem of insufficient submersible pump depth for positioning in existing technologies.

[0005] The technical solution of the present invention is as follows:

[0006] This invention proposes a drilling and well completion method for mining uranium resources in carbonate-cemented ultra-low permeability sandstone, the method comprising:

[0007] Step 1: Open a well in the rock formation. Use drill bit A to drill a hole in the rock formation and form a bare hole A. When the bare hole A is drilled to the top of the mineralized aquifer, switch to a smaller drill bit B and drill to the designed depth.

[0008] Step 2: Replace the old drilling mud in the well with new drilling mud and conduct comprehensive geophysical exploration to determine the location of the target ore layer;

[0009] Step 3: Determine the depth of the well casing based on the location of the target ore layer, and use a roller cone drill bit to enlarge the hole to the depth to obtain the bare hole B. After enlargement, flush the bare hole B with fresh drilling mud.

[0010] Step 4: Install the well casing inside the bare borehole B, and pre-drill a round hole on the bottom wall of the well casing;

[0011] Step 5: Insert the grouting pipe into the well casing, seal the wellhead device and the grouting pipe under high pressure, and inject cement slurry into the annular space outside the pipe through the reserved round hole in the well casing wall in reverse.

[0012] Step Six: After cement grouting has been completed and the cement has set for several hours, the ore layer is cut to form ore layer cutting section 4;

[0013] Step 7: Drill and clean the cut sections of the ore layer.

[0014] In some embodiments, drill bit A has a diameter of 244 mm and drill bit B has a diameter of 215 mm.

[0015] In some embodiments, the new mud is required to have a viscosity of 20-27s, a sand content of <5%, a density of 1.05-1.1g / mL, and a water loss rate of 25mL / 30min.

[0016] In some embodiments, the diameter of the roller cone drill bit is 244 mm.

[0017] In some embodiments, the well casing is a casing with a diameter of 148 mm and a thickness of 10 mm, and is made of unplasticized polyvinyl chloride.

[0018] In some embodiments, step four specifically includes:

[0019] Step 4.1: Install well pipes with a length of 0.5m below the ground surface. At the bottom of the well pipe, there are three evenly distributed circular holes with a diameter of 25mm on the pipe wall at a distance of 30mm from the bottom. The circular holes serve as outlet holes for injecting cement slurry.

[0020] Step 4.2: Install a set of center locators every 48 meters of well casing. The center locators are processed into lantern shapes. The number of steel bars on the lantern-shaped side of the center locator is 3-4. The maximum diameter of the center locator is not less than 90% of the diameter of the borehole. The diameter of the steel bars on the lantern-shaped side of the center locator is not less than 10mm.

[0021] Step 4.3: Connect the well pipes using pipe clamps. Machine male threads at both ends of the well pipes and female threads at both ends of the pipe clamps. The male thread is a square thread with a nominal diameter of 146mm and a pitch of 6mm, and a thread length of 81.5mm. The female thread is a square thread with a nominal diameter of 146mm and a pitch of 6mm, and a thread length of 80mm. The pipe clamps have a diameter of 160mm, a thickness of 15mm, and a length of 180mm. The outer edges of both ends of the pipe clamps and the inner interfaces of the pipes are chamfered at 45°.

[0022] Step 4.4: Seal the well pipe threads with PTFE tape and 704 adhesive. Wrap the PTFE tape in 2-3 layers or more, and apply the 704 adhesive evenly to the well pipe connection port.

[0023] In some embodiments, in step five, the diameter of the grouting pipe is φ42mm, the lower end of the grouting pipe is located 0.5m above the bottom of the bare hole B, the grouting pipe is fixed in the center hole of the wellhead device by a clamping tool, the wellhead device and the grouting pipe are sealed under high pressure, and a pressure gauge is installed on the wellhead device; the water-cement ratio of the cement is 1:1, sulfur-resistant cement is used for mineral-bearing aquifers, and silicate cement is used above mineral-bearing aquifers.

[0024] In some embodiments, 72 hours after the cement grouting cementing in step six is ​​completed and the ore layer is cut, a rotary cutting drill or a screw cutting drill is used for cutting; during the cutting process, a solid-free flushing fluid is used for flushing; the main agent of the solid-free flushing fluid can be selected according to the requirements, such as sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, hydrolyzed sodium polyacrylonitrile, hydroxypropyl guar gum, plant gum, etc., and the auxiliary agents can be selected such as borax, potassium humate, salt, etc.

[0025] In some embodiments, the viscosity of the solid-free flushing fluid in step six is ​​5-10 mp.s, the funnel viscosity is 18-20 s, and the density is 1-1.05 g / cm3; the cutting drill bit's rotation speed is 80 r / min, the feed rate is 0.6-1 m / h, and the PVC chips generated by the cutting drill bit when cutting the well casing have a thickness of 0.13-0.2 mm, ensuring that the cutting slag discharge rate is ≥70%; after the ore layer is cut in step six, a slag removal process is carried out, and after the slag removal process is completed, the solid-free flushing fluid in the well is replaced with clean water.

[0026] In some embodiments, step seven, drilling and cleaning the ore layer cutting section, specifically includes:

[0027] Step 5.1: Lower the ventilation pipe at the cutting section of the ore deposit and use an air compressor for intermittent well washing. After each time the water turns from turbid to clear, turn off the air compressor and turn it on again after an interval of 0.5-1 hours. Repeat the washing until there is no turbid water.

[0028] Step 5.2: Use a submersible pump to flush the well. After flushing until clear water is completely discharged each time, continue pumping for 2-3 hours and then stop. After an interval of 3-8 hours, flush the well again and repeat until there is no turbid water left.

[0029] The implementation of this invention has the following beneficial effects:

[0030] This invention proposes a drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone. Through research on the "open-hole" drilling construction process, this invention eliminates the need for filters, overcoming the shortcomings of existing technologies such as small drawdown, poor hydraulic linkage, long construction cycles, and high construction costs caused by the internal diameter of the built-in filter being smaller than the outer diameter of the submersible pump, preventing the submersible pump from being lowered to the filter section. This method improves the quality, efficiency, and reduces costs in drilling and production operations. Within one year, 75 boreholes were drilled using the "open-hole" process, resulting in a cumulative cost saving of RMB 1.0086 million. The average water volume per borehole increased by 50.00–66.67%, the leaching agent migration rate between pumping and injection increased by approximately 3.7 times, and the leaching efficiency increased by approximately 2.3 times when achieving the same uranium concentration as in conditional tests. Attached Figure Description

[0031] Figure 1 This is a technical schematic diagram of a drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone, as proposed in an embodiment of the present invention.

[0032] Figure 2 This is a process flow diagram of a drilling and well completion method for mining uranium resources in carbonate-cemented ultra-low permeability sandstone, as proposed in an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of the borehole structure for a drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone, as proposed in an embodiment of the present invention.

[0034] Explanation of reference numerals in the attached drawings: 1. Casing; 2. Open hole B; 3. Cement sheath; 4. Deposit cutting section; 5. Ore layer section; 6. Sand settling pipe. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] like Figures 1 to 3 As shown, this invention proposes a drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone, which includes the following steps:

[0037] Step 1: Open a well in the rock formation. Use a φ244mm drill bit to open a well in the rock formation to form a bare hole A. When the bare hole A is drilled to the top plate of the mineralized aquifer, change to a Ф215mm drill bit and drill to the designed hole depth.

[0038] Step 2: Replace the old drilling mud in the well with new drilling mud and conduct comprehensive geophysical exploration to determine the location of the target mineralization section 5. The new drilling mud should have a viscosity of 20-27s, a sand content of <5%, a density of 1.05-1.1g / mL, and a water loss rate of 25mL / 30min.

[0039] Step 3: Determine the wellbore lowering depth based on the location of the target ore layer 5. Use a Φ244mm roller cone bit to enlarge the hole to the lowering depth to obtain the bare hole B2. After enlargement, flush the bare hole B2 with fresh drilling mud. The fresh drilling mud should have a viscosity of 20-27s, a sand content of <5%, a density of 1.05-1.1g / mL, and a water loss rate of 25mL / 30min.

[0040] Step 4: Install the well casing in the open borehole B2. The well casing is a φ148×10mm unplasticized polyvinyl chloride (UPVC) casing 1. The prepared casing 1 is sequentially lowered into the open borehole B2.

[0041] Step 4.1: Install well pipes with a length of 0.5m below the ground surface. At the bottom of the well pipe, there are three evenly distributed circular holes with a diameter of 25mm on the pipe wall at a distance of 30mm from the bottom. The circular holes serve as outlet holes for injecting cement slurry.

[0042] Step 4.2: Install a set of center locators every 48 meters of well casing. The center locators are processed into lantern shapes. There are 3-4 steel bars on the lantern-shaped side of the center locator. The maximum diameter of the center locator is not less than 90% of the diameter of the borehole. The diameter of the lantern-shaped side steel bars used for processing the center locator is not less than φ10mm.

[0043] Step 4.3: Connect the well pipe with φ160×15mm pipe clamps. Machin male threads at both ends of the well pipe. The male threads are 146×6mm square threads with a thread length of 81.5mm. Machin female threads at both ends of the pipe clamps. The female threads are 146×6mm square threads with a thread length of 80mm. The pipe clamp length is 180mm. Chamfer the outer edges of both ends of the pipe clamps and the inner interface of the pipe at 45°.

[0044] Step 4.4: Seal the well pipe threads with PTFE tape and 704 adhesive. The PTFE tape must be wrapped in 2-3 layers or more, and the 704 adhesive must be evenly applied to the well pipe connection port.

[0045] Step 5: Lower a φ42mm grouting pipe into the well casing, with the lower end of the grouting pipe positioned 0.5m above the bottom of the bare borehole B2. At this point, the well casing is filled with mud. The grouting pipe is fixed in the center hole of the wellhead device using clamping tools. A high-pressure seal is established between the wellhead device and the grouting pipe, and a pressure gauge is installed on the wellhead device. The wellhead device then seals the well casing opening. Cement with a water-cement ratio of 1:1 is injected in reverse through a pre-drilled circular hole at the bottom of the well casing into the annular space outside the casing, sealing the opening. For the mineralized aquifer, 42.5-strength sulfur-resistant cement is used, totaling 3 tons. Above the mineralized aquifer, ordinary 32.5-strength silicate cement is used. This completes the grouting and cementing operation.

[0046] Step 6: After cement grouting and cementing has been completed and the well has been allowed to set for 72 hours, the ore layer section 5 is cut to form the ore layer cutting section 4. Below the ore layer cutting section 4 are the ore layer section 5 and the sand settling pipe 6. When cutting the ore section 5, rotary cutting tools or screw cutting tools are used. During the cutting process, a solids-free flushing fluid is used. The main component of the solids-free flushing fluid can be selected according to requirements, such as sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, hydrolyzed sodium polyacrylonitrile, hydroxypropyl guar gum, or plant gum. Auxiliary agents can be selected, such as borax, potassium hydroxide, or salt. The required viscosity of the solids-free flushing fluid is 5-10 mp.s, the funnel viscosity is 18-20 s, and the density is 1-1.05 g / cm³. The rotary speed of the cutting tool is 80 r / min, and the feed rate is 0.6-1 m / h. The polyvinyl chloride (PVC) chips generated when the cutting tool cuts the well casing have a thickness of 0.13-0.2 mm. The cutting slag discharge rate is calculated based on the collected cutting slag amount and the theoretical cutting slag amount to judge the cutting effect. The required cutting slag discharge rate is ≥70%. After the ore layer section 5 is cut, a slag removal process is carried out. After the slag removal process is completed, the solid-free flushing fluid in the well is replaced with clean water.

[0047] Step 7: After cutting, clean the drill holes.

[0048] Step 5.1: First, lower the ventilation pipes at 4 points in the cutting section of the ore deposit and use an air compressor to perform intermittent well washing. After each time the water turns from turbid to clear, turn off the air compressor and turn it on again after an interval of 0.5-1 hours. Repeat this process until there is no turbid water left.

[0049] Step 5.2: Use a submersible pump to flush the well. After flushing until clear water comes out completely each time, continue pumping for 2-3 hours and then stop. After an interval of 3-8 hours, flush the well again. Repeat this process until there is no turbid water left.

[0050] The above-mentioned drilling method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone adopts open-hole drilling without the installation of filters. This method can solve the shortcomings of existing technologies, such as small drawdown, poor hydraulic linkage, long construction period, and high construction cost, caused by the inner diameter of the built-in filter being smaller than the outer diameter of the submersible pump, which prevents the submersible pump from being lowered to the filter section. This method achieves "quality improvement, efficiency enhancement, and cost reduction" in drilling construction and production operation.

[0051] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A drilling and well completion method for mining uranium resources in carbonate-cemented ultra-low permeability sandstone, characterized in that, The method includes: Step 1: Open a well in the rock formation. Use drill bit A to drill a hole in the rock formation and form a bare hole A. When the bare hole A is drilled to the top of the mineralized aquifer, switch to a smaller drill bit B and drill to the designed depth. Step 2: Replace the old drilling mud in the well with new drilling mud and conduct comprehensive geophysical exploration to determine the location of the target ore layer; Step 3: Determine the depth of the well casing based on the location of the target ore layer, and use a roller cone drill bit to enlarge the hole to the depth to obtain the bare hole B(2). After enlarging the hole, flush the bare hole B(2) with fresh mud circulation. Step 4: Install the well casing inside the bare hole B(2) and pre-drill a round hole on the bottom well casing wall; Step 5: Insert the grouting pipe into the well casing, seal the wellhead device and the grouting pipe under high pressure, and inject cement slurry into the annular space outside the pipe through the reserved round hole in the well casing wall in reverse. Step 6: After cement grouting has been completed and the cement has set for several hours, the ore layer section (5) is cut to form the ore layer cutting section; Step 7: Drill and clean the cut sections of the ore layer.

2. The drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 1, characterized in that, The diameter of drill bit A is 244 mm, and the diameter of drill bit B is 215 mm.

3. The drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 2, characterized in that, The new mud should have a viscosity of 20-27s, a sand content of <5%, a density of 1.05-1.1g / mL, and a water loss rate of 25mL / 30min.

4. The drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 3, characterized in that, The diameter of the roller cone drill bit is 244 mm.

5. The drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 4, characterized in that, The well casing is a casing (1) with a diameter of 148 mm and a thickness of 10 mm. The material is unplasticized polyvinyl chloride.

6. The drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 5, characterized in that, Step four specifically includes: Step 4.1: Install well pipes with a length of 0.5m in sequence below the ground surface. The bottom well pipe has three evenly distributed circular holes with a diameter of 25mm on the pipe wall at a distance of 30mm from the bottom end. These circular holes serve as outlet holes for injecting cement slurry. Step 4.2: Install a set of center locators every 48 meters of well casing. The center locator is processed into a lantern shape. The number of lantern-shaped side steel bars of the center locator is 3-4. The maximum diameter of the center locator is not less than 90% of the diameter of the borehole. The diameter of the lantern-shaped side steel bars of the center locator is not less than 10mm. Step 4.3: Connect the well casing with pipe clamps, machine male threads at both ends of the well casing, and machine female threads at both ends of the pipe clamps; the male thread is a square thread with a nominal diameter of 146mm and a pitch of 6mm, and the thread length of the male thread is 81.5mm; the female thread is a square thread with a nominal diameter of 146mm and a pitch of 6mm, and the thread length of the female thread is 80mm; the pipe clamp has a diameter of 160mm, a thickness of 15mm, and a length of 180mm, and the outer edges of both ends of the pipe clamp and the inner interface of the pipe are chamfered at 45°. Step 4.4: Seal the well pipe threads with PTFE tape and 704 adhesive. Wrap the PTFE tape in 2-3 layers or more, and apply the 704 adhesive evenly to the well pipe connection port.

7. A drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 6, characterized in that, In step five, the diameter of the grouting pipe is φ42mm. The lower end of the grouting pipe is located 0.5m above the bottom of the bare hole B(2). The grouting pipe is fixed in the center hole of the wellhead device by a clamping tool. The wellhead device and the grouting pipe are sealed under high pressure. A pressure gauge is installed on the wellhead device. The water-cement ratio of the cement is 1:

1. The mineral-bearing aquifer uses sulfur-resistant cement, and the mineral-bearing aquifer above uses silicate cement.

8. A drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 7, characterized in that, When the cement grouting cementing in step six is ​​completed and the well is allowed to set for 72 hours, the cutting of the ore layer (5) is carried out. The cutting drill is a rotary cutting drill or a screw cutting drill. During the cutting process, a solid-free flushing fluid is used for flushing. The main agent of the solid-free flushing fluid can be selected according to the requirements, such as sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, hydrolyzed sodium polyacrylonitrile, hydroxypropyl guar gum, plant gum, etc., and the auxiliary agents can be borax, potassium humate, salt, etc.

9. A drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 8, characterized in that, In step six, the viscosity of the solid-free rinsing solution is 5-10 mp.s, the viscosity at the funnel is 18-20 s, and the density is 1-1.05 g / cm³. 3 The cutting drill bit has a rotation speed of 80 r / min and a feed rate of 0.6-1 m / h. The polyvinyl chloride chips generated by the cutting drill bit when cutting the well casing have a thickness of 0.13-0.2 mm, ensuring that the slag discharge rate is ≥70%. After the cutting of the six mineral layers (5) in step six, a slag cleaning process is carried out. After the slag cleaning process is completed, the solid-free flushing fluid in the well is replaced with clean water.

10. A drilling and well completion method for uranium resource mining in carbonate-cemented ultra-low permeability sandstone as described in claim 8, characterized in that, Step seven, specifically the drilling and cleaning of the ore layer cutting section, includes: Step 5.1: Lower the ventilation pipe at the cutting section (4) of the ore deposit and use an air compressor for intermittent well washing. After each water discharge changes from turbid to clear, turn off the air compressor and turn it on again after an interval of 0.5-1 hours. Repeat the washing until there is no turbid water. Step 5.2: Use a submersible pump to flush the well. After flushing until clear water is completely discharged each time, continue pumping for 2-3 hours and then stop. After an interval of 3-8 hours, flush the well again and repeat until there is no turbid water left.

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