A device and method for normal water injection and backwashing of casing-lost water wells

Abstract

The present invention relates to the field of oilfield injection and production, and discloses a device and method for normal water injection and backwashing of a casing-lost water well. The device comprises a water injection oil pipe, an inner pipe, a first large-diameter packer, a second large-diameter packer, a first well-washing valve, a second well-washing valve, a first screen pipe, and a second screen pipe. The inner pipe is installed inside the water injection oil pipe, and the axis of the water injection oil pipe, the inner pipe, and the casing are the same. The first large-diameter packer is located above the casing loss point, and the second large-diameter packer is located below the casing loss point. The first well-washing valve, the first screen pipe, the second screen pipe, and the second well-washing valve are installed in sequence from top to bottom between the inner pipe and the water injection oil pipe. The present invention is based on the common casing loss situation of water wells. Through a reasonable structural layout, the leakage point is sealed, and the conversion of the water injection channel is realized. It can perform normal water injection and backwashing of the well; replenish formation energy and improve crude oil recovery rate; it is easy to operate, low-cost, and extends the maintenance-free period of the water well.

Description

Technical Field

[0001] The invention relates to the field of oilfield injection and production, and in particular to a device and method for performing normal water injection and backwashing on a casing-lost water well. Background Art

[0002] During the waterflooding process of oilfield development, normal water injection into wells is crucial. Accurate and economical water injection effectively replenishes formation energy, expands the swept volume, displaces crude oil, and improves oilfield recovery. However, during water injection, poor water quality can cause scaling in the tubing, and temporary well shutdowns can cause sand production in the formation. This can easily lead to increased oil pressure, stuck tubing, shortened maintenance-free periods, and compromised normal water well injection. Water wells require regular backwashing to remove soft scale on the tubing walls and sand from the formations within the wellbore. During oilfield development, especially in the later stages of development, water well casing can leak from the upper portion due to various factors, including cementing quality, formation stress, and surface water corrosion. The expandable packers commonly used in water wells retract during backwashing, causing low pressure at the casing leak point, allowing flushing water to enter the leaking point and preventing reverse circulation flushing. If the leak is above 600 meters and the oil layer casing cement return is higher than that, it can be restored through overhaul and replacement of casing. For Φ177.8mm casing, normal water injection can also be carried out using pump sealing and casing patching methods. However, for Φ139.7mm casing, which is commonly used for oil production in water wells, due to the small internal diameter of the casing, once the casing is lost, normal water injection cannot be carried out using these conventional methods. It can only be sealed and closed by inserting an expandable packer for water injection, and the well cannot be backwashed like normal production wells. Therefore, how to perform normal water injection and backwashing in wells with casing leakage is a technical problem that needs to be solved urgently. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a device and method for normal water injection and backwashing of casing-lost water wells. The technical solution is as follows:

[0004] The cam is connected with the water supply pipe of the water injection device, and the cam is connected with the water supply pipe of the water injection device, and the cam is connected with the water supply pipe of the water injection device.

[0005] Furthermore, the first well flushing valve includes a first oil pipe coupling, a pressure cap, a pressure ring and a sealing collar connected in sequence from top to bottom. The first oil pipe coupling is installed on the inner side of the water injection oil pipe, and the external thread of the pressure cap is engaged with the internal thread of the first oil pipe coupling.

[0006] Furthermore, the second well flushing valve includes a baffle surrounding the inner tube and a second oil pipe coupling. The outer side of the baffle is connected to the oil pipe short-circuit. The oil pipe short-circuit includes a body section and a coupling section at its upper end and a male buckle section at its lower end. The upper end of the second oil pipe coupling is connected to the inner side of the baffle.

[0007] Furthermore, the inner diameter of the casing is 139.7 mm, the outer diameter of the water injection oil pipe is 88.9 mm, the inner diameter is 75.9 mm, and the outer diameter of the inner pipe is 48 mm.

[0008] Furthermore, the first large-diameter packer adopts a Y111 packer.

[0009] Furthermore, the second largest diameter packer adopts a Y211 packer.

[0010] A method for normal water injection and backwashing based on a casing leakage well, which relies on the above-mentioned device for normal water injection and backwashing based on a casing leakage well, includes the following process:

[0011] (1) Normal water injection process: water is injected from the wellhead through the first flushing valve, inner pipe, second flushing valve and bell mouth in sequence, and enters the injection layer;

[0012] (2) Backwashing process: The backwashing water flows from the annular space between the water injection oil pipe and the casing through the first screen pipe, the annular space between the water injection oil pipe and the inner pipe, the second screen pipe, the annular space between the water injection oil pipe and the casing, the bell mouth, the second backwashing valve, the inner pipe, the first backwashing valve and the water injection oil pipe, and enters the wellhead, completing a cycle.

[0013] Furthermore, when the injected water flows through the inner tube, it passes through the first large-diameter packer, the casing leakage point and the corresponding position of the second large-diameter packer.

[0014] Furthermore, the well-washing water passes through the first large-diameter packer, the casing leakage point and the corresponding position of the second large-diameter packer when flowing through the water injection oil pipe and the annular space of the inner pipe.

[0015] Furthermore, the backwashing of the well is carried out for 2 to 3 weeks until the effluent water quality is clean.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects:

[0017] 1. The present invention is based on the common casing leakage situation of water wells. Through reasonable structural layout, the conversion of water injection channels is realized, and normal water injection and backwashing of wells can be achieved.

[0018] 2. The present invention can effectively increase the number of water injection wells, increase the service life of the water wells, strengthen the injection-production correspondence, and improve the recovery rate of the water drive unit.

[0019] 3. The present invention is applicable to the development of oil field water injection. By using the packer to seal the leakage point, the casing leakage well can be effectively controlled, effective water injection can be achieved, the reserve utilization of the corresponding oil well potential layer can be improved, the contradiction between the oil well layers and the plane can be effectively resolved, the formation energy can be replenished, the crude oil production can be increased, and the crude oil recovery rate of the block can be improved.

[0020] 4. The present invention is simple to operate, has low investment cost, and extends the maintenance-free period of the water well. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structural layout of the present invention;

[0022] Figure 2 This is a schematic structural diagram of the first well flushing valve of the present invention;

[0023] Figure 3 This is a schematic structural diagram of the second well flushing valve of the present invention;

[0024] In the figure: 1-casing, 2-first large-diameter packer, 3-inner pipe, 4-water injection tubing, 4.1-outer diameter, 4.2-inner diameter, 5-first well flushing valve, 6-first screen pipe, 7-second large-diameter packer, 8-second screen pipe, 9-second well flushing valve, 10-bell mouth, 11-artificial bottom hole, 12-pressure cap, 13-pressure ring, 14-sealing collar, 15-first tubing coupling, 16-tubing short circuit, 16.1-body section, 16.2-coupling section, 16.3-male buckle section, 17-baffle, 18-second tubing coupling. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to specific embodiments and accompanying drawings. Example 1

[0026] See also Figure 1 、 Figure 2 and Figure 3A device for normal water injection and backwashing of casing-lost water wells, comprising a water injection oil pipe 4, an inner pipe 3, a first large-diameter packer 2, a second large-diameter packer 7, a first well-washing valve 5, a second well-washing valve 9, a first screen pipe 6, and a second screen pipe 8; the water injection oil pipe 4 is installed inside the casing 1, and the inner pipe 3 is installed inside the water injection oil pipe 4. The axis of the water injection oil pipe 4, the inner pipe 3 and the casing 1 are the same. The lower end of the water injection oil pipe 4 is provided with a bell mouth 10, which is located below the water injection layer. ; The first large diameter packer 2 and the second large diameter packer 7 are installed between the casing 1 and the water injection oil pipe 4, the first large diameter packer 2 is located above the leakage point of the casing 1, and the second large diameter packer 7 is located below the leakage point of the casing 1; the first well flushing valve 5, the first screen pipe 6, the second screen pipe 8 and the second well flushing valve 9 are installed in sequence from top to bottom between the inner tube 3 and the water injection oil pipe 4, the first screen pipe 6 is located above the first large diameter packer 2, and the second screen pipe 8 is located below the second large diameter packer 7. Example 2

[0027] See also Figure 1 、 Figure 2 and Figure 3 A device for normal water injection and backwashing in a casing-lost water well, based on the technical solution described in Example 1, comprises a first well-washing valve 5 comprising a first tubing coupling 15, a pressure cap 12, a pressure ring 13, and a sealing collar 14 connected in sequence from top to bottom. The first tubing coupling 15 is mounted on the inner side of the injection tubing 4, and the external threads of the pressure cap 12 engage with the internal threads of the first tubing coupling 15. A second well-washing valve 9 comprises a baffle 17 surrounding the inner tube 3 and a second tubing coupling 18. The outer side of the baffle 17 is connected to an tubing short-circuit 16. The tubing short-circuit 16 comprises a body section 16.1, a coupling section 16.2 at its upper end, and a pin section 16.3 at its lower end. The upper end of the second tubing coupling 18 is connected to the inner side of the baffle 17. Example 3

[0028] See also Figure 1 、 Figure 2 and Figure 3 A device for normal water injection and backwashing in a cased water loss well, based on the technical solution described in Example 1, features a casing 1 with an inner diameter of 139.7 mm, an injection oil pipe 4 with an outer diameter of 88.9 mm and an inner diameter of 75.9 mm, and an inner pipe 3 with an outer diameter of 48 mm. This design, coupled with the other components, facilitates both installation and smooth water injection and backwashing processes. Example 4

[0029] See also Figure 1 、 Figure 2 and Figure 3. A device for normal water injection and backwashing of casing-lost water wells. On the basis of the technical solution described in Example 1, the first large-diameter packer 2 adopts a Y111 packer; the second large-diameter packer 7 adopts a Y211 packer. The Y111 packer is a compression packer that relies on a compression rubber cylinder to achieve a stratification effect. The packer has no slip design and can be sealed by lowering the tubing string, and can be easily unsealed by lifting the tubing string. Its unique structural design mainly includes a compression component and a sealing component. The compression component is responsible for applying pressure, while the sealing component ensures that it can maintain excellent sealing performance under high-pressure environments. This packer has a simple and efficient structure, which enables it to play a key role in processes such as stratified oil production, testing, water finding, water plugging, and acidizing. The Y211 packer is equipped with a slip support mechanism to ensure its stability. During the setting process, the tubing is lifted up and then lowered. The spring tension of the centralizer is used to move the centralizing block along the track, thereby blocking the casing and compressing the rubber sleeve to seal the annular space of the oil casing. The unsealing process is relatively simple. Only the tubing is lifted up. After the cone is withdrawn, the slips and rubber sleeve are automatically retracted to achieve unsealing. This type of packer is widely used in downhole operations such as stratified oil testing, stratified oil production, casing leak detection, water blocking, water detection and water injection. Example 5

[0030] See also Figure 1 、 Figure 2 and Figure 3 A method for normal water injection and backwashing of a casing leakage well includes the following steps:

[0031] (1) Normal water injection process: The injected water passes through the first flushing valve 5, the inner pipe 3, the second flushing valve 9 and the bell mouth 10 from the wellhead in sequence and enters the injection layer; when the injected water flows through the inner pipe 3, it passes through the first large-diameter packer 2, the casing leakage point and the corresponding position of the second large-diameter packer 7.

[0032] (2) Backwashing process: The well-washing water flows from the annular space between the water injection oil pipe 4 and the casing 1 through the first screen pipe 6, the annular space between the water injection oil pipe 4 and the inner pipe 3, the second screen pipe 8, the annular space between the water injection oil pipe 4 and the casing 1, the bell mouth 10, the second well-washing valve 9, the inner pipe 3, the first well-washing valve 5 and the water injection oil pipe 4, and enters the wellhead, completing a cycle. When the well-washing water flows through the annular space between the water injection oil pipe 4 and the inner pipe 3, it passes through the first large-diameter packer 2, the casing leakage point and the corresponding position of the second large-diameter packer 7. Backwashing is carried out for 2 to 3 weeks until the water quality is clean.

[0033] Water injection well application example

[0034] Well GO8-21-9 in Gudong, Shengli Oilfield: This is a water injection reservoir with multi-layer development. It was put into production on August 14, 1986. The outer diameter of the casing is 139.7 mm, the cement return height is 390.2 meters, the artificial well bottom is 1460 meters, and the cementing quality is unqualified.2 (perforation section 1235.1-1237.6 meters), Ngs4 2 (perforation section 1271.6-1276.6 meters), Ngs5 3+4 (perforation section 1432.0-1435.0 m), Ngs5 3 (perforation section 1338.5-1344.8 meters), Ngs6 2 (The well section is 1364.0-1368.0 meters). On May 14, 2013, Ngs3 2 、 Ngs4 2 The injection layer involved five oil wells. On February 10, 2022, a significant drop in casing and oil pressure was observed, from 13.55 MPa to 8.2 MPa. A casing pressure test revealed leakage between 770.2 and 771.5 meters. The leak was sealed with an expandable packer and then water was injected. After 103 days of production, the pump pressure reached equilibrium on May 24, when no water could be injected and production was halted. The backwash well pressure was 3.5 MPa, indicating no flow. This indicated that the injection layer was buried in sand. Due to a lack of energy replenishment in the corresponding water wells, the fluid level dropped, and the fluid supply gradually deteriorated. In October 2024, the decision was made to repair well GO8-21-9. Dissection revealed formation sand production and severe tubing scaling. To achieve longevity and extend the water injection cycle while maintaining tight costs, a production string was designed for casing leak-off wells. Matching upper and lower wellwash valves were developed to enable regular backwashing of the well, minimizing the damage caused by injection scaling and formation sand production. Following completion on October 15, 2024, the well was backwashed regularly every three months, with two backwashes completed to date. Production at the corresponding five wells has gradually improved. A comparison of before-and-after data shows a cumulative increase of 261.5 tons of oil production, demonstrating excellent results. Following the successful trial, a survey of wells with casing leak-off was conducted, with plans to expand the use of six more.

[0035] In order to enable those skilled in the art to better understand the present invention, its basic working principle is briefly introduced as follows:

[0036] 1. Development of well flushing valve

[0037] When the leak is sealed, an inner pipe 3 is lowered into the common water injection oil pipe 4 between the sealing pipe strings to set up a system that can circulate and connect them. Wherein, the development of the well flushing valve is a key.

[0038] 1. Development of the first well flushing valve 5: See Figure 2. Take a 60.3mm outer diameter oil pipe short link (with a coupling at the upper end and a length greater than 40cm) and insert it into an 88.9mm outer diameter ordinary oil pipe short link (less than 40cm in length, with a coupling at the upper end and a male buckle at the lower end), and weld it firmly at the lower end of the 88.9mm oil pipe short link to seal it. When making the pressure cap 12, the inner diameter is 50.3mm (which can smoothly pass through the inner tube 3 with an outer diameter of 48cm), and the outside is equipped with a male buckle, which can be buckled onto the first oil pipe coupling 15 with an outer diameter of 60.3mm, which is used to compress the special sealing collar 14. Make an annular pressure ring 13 with an inner diameter of 50.0mm and an outer diameter of 58mm.

[0039] 2. Development of the second well flushing valve 9: see Figure 3 The second oil pipe coupling 18 with an outer diameter of 48 mm is welded to the lower end of the ordinary oil pipe short link 16 with an outer diameter of 88.9 mm (with a coupling at the upper end and a male buckle at the lower end).

[0040] 2. Water injection and backwash well matching methods

[0041] Step 1: Preparation: Transport the operation and related auxiliary equipment to the well site, complete the preparatory work before the operation and conduct the start-up acceptance.

[0042] Step 2: Start the operation. Remove the wellhead device, install the wellhead blowout preventer, pull out all the tubing in the well, and remove all tools in the well according to the construction design.

[0043] Step 3: Flush sand and scrape the wall of casing 1. Use a pump truck to flush sand to the designed position and circulate it for cleaning. Scrape the inner wall of casing 1 to 20 meters below the oil layer through the inner diameter of casing 1.

[0044] Step 4: Pressure test casing 1. Pressure test the upper and lower sections of casing 1, excluding the recorded leak point. Maintain the pressure at 15 MPa for 30 minutes. A pressure drop of no more than 0.5 MPa is considered acceptable. Pressure test the leak point to understand the leak situation. Obtain complete and accurate data to prevent the occurrence of new dew points. Pull out the entire string.

[0045] Step 5: Run the completion string. Using the water injection tubing 4, connect the bellmouth 10, water injection tubing 4, second flushing valve 9, second screen 8, second large-diameter packer 7 (using a Y211 and located below the leak), first large-diameter packer 2 (using a Y111 and located above the leak), first screen 6, first flushing valve 5, and inner pipe 3, among other tools, to the required depth. The requirements include: the inner tube 3 has a diameter of 40mm, the outer diameter of the coupling is D55mm, and the outer diameter of the body is D48mm. The static sealing pressure of the sealing collar 14 of the first well flushing valve 5 is 10MPa, and the buckle verification load of the inner tube 3 is 10KN. During operation, when lowering the last inner tube 3, the pressure cap 12 and the pressure ring 13 are inserted in advance. Because the first oil pipe coupling 15 cannot pass through the pressure ring 13, the pressure ring 13 and the pressure cap 12 are supported by hand during the lowering process of the last inner tube 3 to prevent them from falling into the outer shell. After the inner tube 3 is in place, it is connected with the female buckle in the lower joint by buckle, and the inner tube 3 is lifted (10KN) to verify whether it is firmly connected.

[0046] Step 6: The second largest diameter packer 7, i.e., the Y211 packer, is raised and lowered into the tubing string to seal it. The operation method is as follows: (1) Lift the tubing string to adjust the sealing pressure height. The lifting height of the tubing string is determined according to the well depth; (2) Slowly lower it and observe the weight gauge. If the weight gauge falls back, it indicates that the Y211 packer has started to seal; (3) Apply pressure of 60 to 80 kN to make it fully sealed.

[0047] Step 7: Install the wellhead and inject water. Backwash the well for two cycles to remove debris and then inject water. Water is injected from the wellhead → first flushing valve 5 → inner pipe 3 (through the packer and leakage point) → second flushing valve 9 → bell mouth 10, and then enters the injection zone.

[0048] Step 8: Monitoring: Use oxygen-activated water flow logging to monitor leak points, sealing conditions of the sealing layers, and suction conditions of each layer.

[0049] Step 9: Observe the changes in oil casing pressure and record various data.

[0050] Step 10: Backwashing. When the casing pressure changes and the well needs backwashing, the flushing water flows from the casing annular space → first screen 6 → the annular space between the water injection tubing 4 and the inner pipe 3 (through the packer and the leak point) → second screen 8 → casing annular space → bellmouth 10 → second flushing valve 9 → inner pipe 3 → first flushing valve 5 → water injection tubing 4 → wellhead, completing a complete cycle. Backwash the well for 2-3 cycles until the water quality is clean.

[0051] 3. Relevant technical requirements

[0052] 1. The packer must be sealed tightly and intact.

[0053] 2. The sealing collar 14 must be sealed intact. To ensure success, a pressure test of 10 MPa can be performed on the first well flushing valve 5 when it is lowered.

[0054] 3. Analysis method of pressure changes in oilfield water injection wells:

[0055] (1) Wellhead oil-casing pressure differential analysis method: Determine the reasonable value of the oil-casing pressure differential based on the amount of water injection and the condition of the downhole tools, and compare it with the actual measured oil-casing pressure differential to judge the working condition of the downhole tubing. First, for wells with an oil-casing pressure differential greater than 1MPa and a significant change in water volume after back injection, analyze whether the tubing is scaled or sand is blocking the tail pipe. It is necessary to verify whether the tubing is scaled or sand is blocking the tail pipe by flushing the well in time. Second, when the oil-casing pressure differential is less than the reasonable value, it is preliminarily judged that the upper part of the tubing is leaking or the packer has failed, which can be verified by flushing the well.

[0056] (2) Wellhead casing pressure analysis method: The casing pressure directly reflects the water absorption pressure of the water injection formation. The change of casing pressure indicates the change of the water absorption capacity of the formation. When the casing pressure rises, the formation blockage condition is analyzed in time. When the casing pressure drops, the dynamic liquid level of the surrounding oil wells is analyzed to see if there is a change. First, when the water injection volume does not change much and the dynamic liquid level of the surrounding corresponding oil wells does not change much, the formation is analyzed to be blocked based on the increase of casing pressure, and well washing measures are formulated and implemented in time (if well washing is ineffective, operations are carried out according to dynamic needs); second, when the water injection volume does not change much and the dynamic liquid level of the surrounding corresponding oil wells does not change much, for water injection wells with blocked stop injection layers or leak points, when the casing pressure drops, the blocking failure of the stop injection layer or leak point is analyzed, resulting in the failure of the blocking layer and the increase of the water absorption capacity of the formation. Test and leakage detection measures should be formulated in time.

Claims

1. A device for normal water injection and backwashing of casing leakage wells, characterized in that: It includes a water injection oil pipe, an inner pipe, a first large-diameter packer, a second large-diameter packer, a first well flushing valve, a second well flushing valve, a first screen pipe and a second screen pipe; the water injection oil pipe is installed inside the casing, and the inner pipe is installed inside the water injection oil pipe. The axial center lines of the water injection oil pipe, the inner pipe and the casing are the same, and the lower end of the water injection oil pipe is provided with a bell mouth, which is located below the water injection layer; the first large-diameter packer and the second large-diameter packer are installed between the casing and the water injection oil pipe, the first large-diameter packer is located above the casing leakage point, and the second large-diameter packer is located below the casing leakage point; the first well flushing valve, the first screen pipe, the second screen pipe and the second well flushing valve are installed in sequence from top to bottom between the inner pipe and the water injection oil pipe, the first screen pipe is located above the first large-diameter packer, and the second screen pipe is located below the second large-diameter packer.

2. The device for normal water injection and backwashing of a casing-lost water well according to claim 1, characterized in that: The first well flushing valve includes a first oil pipe coupling, a pressure cap, a pressure ring and a sealing collar connected in sequence from top to bottom. The first oil pipe coupling is installed on the inner side of the water injection oil pipe, and the external thread of the pressure cap is engaged with the internal thread of the first oil pipe coupling.

3. The device for normal water injection and backwashing of a casing-lost water well according to claim 1, characterized in that: The second well flushing valve includes a baffle surrounding the inner tube and a second oil pipe coupling. The outer side of the baffle is connected to the oil pipe short connection. The oil pipe short connection includes a body section and a coupling section at its upper end and a male buckle section at its lower end. The upper end of the second oil pipe coupling is connected to the inner side of the baffle.

4. The device for normal water injection and backwashing of a casing-lost water well according to claim 1, characterized in that: The inner diameter of the casing is 139.7 mm, the outer diameter of the water injection oil pipe is 88.9 mm, the inner diameter is 75.9 mm, and the outer diameter of the inner pipe is 48 mm.

5. The device for normal water injection and backwashing of a casing-lost water well according to claim 1, characterized in that: The first large diameter packer is a Y111 packer.

6. The device for normal water injection and backwashing of a casing-lost water well according to claim 1, characterized in that: The second largest diameter packer is a Y211 packer.

7. A method for normal water injection and backwashing of a casing leakage well, characterized in that: The method is based on a device for normal water injection and backwashing of a casing-lost water well according to any one of claims 1 to 6, and includes the following process: (1) Normal water injection process: water is injected from the wellhead through the first flushing valve, inner pipe, second flushing valve and bell mouth in sequence, and enters the injection layer; (2) Backwashing process: The backwashing water flows from the annular space between the water injection oil pipe and the casing through the first screen pipe, the annular space between the water injection oil pipe and the inner pipe, the second screen pipe, the annular space between the water injection oil pipe and the casing, the bell mouth, the second backwashing valve, the inner pipe, the first backwashing valve and the water injection oil pipe, and enters the wellhead, completing a cycle.

8. The method for normal water injection and backwashing of a casing-lost water well according to claim 7, characterized in that: When the injected water flows through the inner pipe, it passes through the first large-diameter packer, the casing leakage point and the corresponding position of the second large-diameter packer.

9. The method for normal water injection and backwashing of a casing-lost water well according to claim 7, characterized in that: When the well-washing water flows through the annular space between the water injection oil pipe and the inner pipe, it passes through the first large-diameter packer, the casing leakage point and the corresponding position of the second large-diameter packer.

10. The method for normal water injection and backwashing of a casing-lost water well according to claim 7, characterized in that: The backwashing is carried out for 2 to 3 weeks until the effluent water is clean.

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