Non-moving tubular column under-pressure efficient well repair operation method

Abstract

The invention relates to the technical field of operation construction processes in an immovable string oil casing, and particularly discloses an immovable string pressurized efficient workover operation method, which comprises the following steps: preparation at the early stage of construction: checking a construction site and equipment, and confirming well conditions and parameters of a construction well; equipment butt joint and wellhead sealing deployment, wherein continuous oil pipe injection head installation, linkage debugging of a blowout prevention box and a blowout preventer, circulation and power system connection and connection of a continuous oil pipe and a well entering tool are included; under-pressure well entering and operation implementation, wherein well mouth channel opening, coiled tubing tripping-in and tool feeding-in, circulating system starting and pressure balance adjusting and target operation implementation are included; the operation process dynamic control comprises pressure real-time monitoring and adjustment, continuous oil pipe dynamic protection and emergency disposal; controlling bottom hole pressure; after the operation is finished, the tool is pulled out; according to the method, the environmental pollution risk is reduced, and well control safety risks such as formation reverse sand discharge blockage, overflow, well kick and blowout caused by bottom hole pressure unbalance in the operation process are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fixed string oil casing operation construction process, in particular to a fixed string high-efficiency workover operation method. BACKGROUND

[0002] With the progress of oilfield development mode, efficient and safe operation mode has become the development direction of oilfield construction. The fixed string workover operation has been widely recognized in oilfield construction because of its low construction cost, short operation cycle and the ability to complete the operation under pressure. However, the current workover operation has many operation links, long construction time and serious environmental and safety hazards. The most important problem is that the lifting and lowering of the original well string operation is easy to cause a series of problems: first, the mechanical disassembly of the string is easy to cause damage, affecting the durability and service life of the string after production, and causing quality problems; second, oil dirt and well fluid are easy to be carried to the ground during the lifting and lowering process, causing environmental pollution; third, the formation pressure cannot be effectively balanced, and suction overflow is easy to occur, causing well control safety problems, and the suction effect also causes formation sand blockage, further damaging the formation quality.

[0003] The existing workover operation construction process is based on the design of disassembling the wellhead and lifting and lowering the original well string. The process steps in the deployment stage only include: parking the equipment and vehicles in place, disassembling the wellhead, placing the supporting circulation pool, installing the hydraulic blowout preventer and control pipeline operation console, arranging the oil pipe row, stand, hoisting the cabin to connect the power, driving the anchor, and pulling the rope. After the completion of the construction preparation, the core processes such as lifting the original well string, lowering the construction string, and checking the operation of the original well string after the completion of the construction and lowering into the well are still needed, and the overall construction time needs at least 4-7 days.

[0004] In addition, during the deployment and construction process of the minor repair operation, high-risk links such as hoisting operation and power connection operation are involved. The overall process of disassembling the wellhead, lifting and lowering the original well string and the construction string has high construction risk and low timeliness. At the same time, during the lifting and lowering of the original well string and the construction string, the bottom hole formation pressure cannot be continuously controlled and balanced, which not only produces suction overflow, increases environmental and well control risks, but also easily returns sand to cause irreversible damage to the formation, increasing the maintenance cost and time cost of subsequent recovery of production and injection allocation. Therefore, a process method is needed to more safely and efficiently solve the problems of formation sand blockage, string dirt blockage and thick oil wax blockage without lifting the original well string. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide a fixed string high-efficiency workover operation method to achieve the goals of pipe diameter inspection, sand flushing, dirt flushing, string cleaning and injection allocation improvement in workover construction.

[0006] The technical solution adopted by the present application to solve its technical problems is: a fixed string high-efficiency workover operation method, comprising the following steps:

[0007] S1. Pre-construction preparation: Inspection of construction site and equipment, confirmation of well condition and parameters of construction well;

[0008] S2. Equipment docking and wellhead sealing deployment: including installation of coiled tubing injection head, linkage debugging of blowout preventer box and blowout preventer, connection of circulation and power system, and connection of coiled tubing and well entry tool;

[0009] S3. Pressurized well entry and operation implementation: including wellhead access opening, coiled tubing running and tool delivery, circulation system startup and pressure balance adjustment, and target operation implementation;

[0010] S4. Dynamic control of the operation process: including real-time pressure monitoring and adjustment, dynamic protection of coiled tubing, and emergency response;

[0011] S5. Bottom hole pressure control: Bottom hole pressure P bh Stable at formation pressure P f ~formation fracturing pressure P frac Inside the window, the bottom pressure P bh =P mh +P fric +P sc +P throttle -P swab ;

[0012] S6. Operation completed. Tools retrieved. Start the injection head and retrieve the coiled tubing and well tools at a constant speed, controlling the retrieval speed at 5-12 m / min.

[0013] Specifically, the steps for equipment docking and wellhead sealing deployment in step S2 are as follows:

[0014] S21. Installation of coiled tubing injection head: Position the coiled tubing injection head directly above the wellhead using hoisting equipment, connect it to the wellhead test valve group using a docking flange, and secure it with clamps. Ensure the connection surface is well sealed and leak-free. After the injection head is installed, check its verticality. The deviation should not exceed 0.5°.

[0015] S22. Blowout Preventer (BOP) Box and BOP Linkage Testing: Start the BOP hydraulic control system and apply initial clamping force to the sealing elements. The initial pressure should be set to 1.2 times the well tubing pressure. Check the sealing performance. Operate the BOP assembly switch to confirm the linkage between the BOP, injection head, and wellhead. If it is a multi-stage BOP box, test the sealing effect of each stage of the sealing components.

[0016] S23. Connection of Circulation and Power System: ① The outlet of the wellhead side valve is connected to the inlet of the high-pressure throttle valve via a rigid high-pressure pipeline, and the outlet of the high-pressure throttle valve is connected to the circulation pump tank. The joint is sealed with a high-pressure sealing gasket; ② A plug valve is installed at the tail of the coiled tubing and connected to the outlet of the construction vehicle via a high-pressure hose. The pipeline is checked for aging and damage, and the pressure rating is matched; ③ The control pipelines connecting the construction vehicle's operating platform to the injection head, blowout preventer, and high-pressure throttle valve are used for centralized control;

[0017] S24. Connection of coiled tubing and well entry tools: According to the construction requirements, connect the special well entry tools of flushing tools and sand flushing tools to the head of coiled tubing through threads and tighten with a torque wrench. After all equipment tubing is connected, perform a pressure test. The test pressure is 1.5 times the construction pressure, and there should be no leakage after stabilizing the pressure for 10 minutes.

[0018] Specifically, the specific steps for pressurized well entry and operation implementation in step S3 are as follows:

[0019] S31. Wellhead Access Opening: After confirming that all equipment connections are properly sealed and the control system is functioning normally, open the wellhead test valve and production valve to establish an access passage to the well. During the process, monitor wellhead pressure changes. If the pressure rises abnormally, immediately close the valves to investigate the problem.

[0020] S32. Coiled tubing running and tool delivery: Start the injection head and run the coiled tubing connected to the well tool into the well. The running speed is controlled at 5-15 m / min. During the operation, the blowout preventer hydraulic control system monitors the well pressure in real time and automatically adjusts the sealing element clamping force to counteract the high pressure in the well.

[0021] S33. Circulation System Start-up and Pressure Balance Adjustment: After the wellhead tool reaches the target working depth, start the pump on the work vehicle to pump the working fluid into the coiled tubing and establish a circulation loop; manually adjust the opening of the high-pressure throttle valve through the control panel, and fine-tune the flow rate according to the circulation pressure monitoring data: ① If the circulation pressure is lower than the preset value, reduce the opening of the throttle valve to increase the flow resistance and increase the circulation pressure; ② If there are signs of overflow, immediately reduce the opening of the throttle valve to increase the circulation pressure and suppress the overflow; ③ Maintain the bottom hole pressure stable within the formation pressure-formation fracture pressure window throughout the process;

[0022] S34. Target Operation Implementation: Complete the corresponding operations according to construction requirements: ① Sand flushing operation: Maintain the preset displacement, use the high-pressure jet of the sand flushing tool to impact the formation sand plugs, carry the sand particles through the annulus of the original well tubing and coiled tubing, the wellhead gate valve, and the high-pressure throttle valve into the circulation tank to achieve sand particle separation; ② Diametering operation: Control the injection head to advance the coiled tubing at a uniform speed, so that the diametering tool moves along the inner wall of the original well tubing to remove scale and wax plugs in the tubing and ensure that the tubing diameter meets the requirements; ③ Unblocking or scale removal operation: Use the high-pressure jet tool to spray unblocking agent / scale removal agent, in conjunction with the circulation operation, to carry the blockages and scale in the tubing to the surface.

[0023] Specifically, the steps for dynamic control of the work process in step S4 are as follows:

[0024] S41. Real-time pressure monitoring and adjustment: The well pressure, blowout preventer clamping force, circulating pressure, and pressure before and after the high-pressure throttle valve are monitored in real time via the control panel, and the data is recorded every 5 minutes. If the well pressure fluctuates more than ±0.5MPa, the opening of the high-pressure throttle valve and the blowout preventer clamping force are adjusted immediately to control the pressure balance.

[0025] S42. Dynamic protection of coiled tubing: During the operation of the injection head, the stress state of the coiled tubing is monitored in real time; if jamming occurs, the lowering or lowering is stopped immediately, and the circulation pressure is adjusted by the construction vehicle pump to release the jamming. It is forbidden to forcibly lower the tubing string.

[0026] S43. Emergency Response: ① If a single-stage sealing component of the blowout preventer box is damaged, immediately activate the backup sealing component of the multi-stage blowout preventer box, while reducing the operating speed, adjusting the clamping force, and suspending the operation to replace the sealing element if necessary; ② If a serious overflow or well kick occurs, immediately shut down the blowout preventer assembly, cut off the fluid passage in the well, start the emergency well kill procedure, and inject well kill fluid through the construction vehicle pump to balance the formation pressure.

[0027] Specifically, P in step S5 mh The fluid column pressure inside the coiled tubing is the base pressure.

[0028] P fric : The frictional pressure of the working fluid in the coiled tubing and the annulus of the original well string;

[0029] P sc : The sealing compensation pressure of the blowout preventer;

[0030] P throttle The throttling back pressure of the high-pressure throttling valve is the pressure generated by flow regulation;

[0031] P swab The suction or excitation pressure during the raising or lowering of the coiled tubing; raising the tubing string is for suction, and lowering the tubing string is for excitation.

[0032] Specifically, the pressure control logic in step S5 is as follows: the flow rate is adjusted by the high-pressure throttle valve, changing P. throttle Combined with the P of the pop filter box sc Compensation, maintenance :

[0033] If P bh <P f There is a risk of overflow: reduce the opening area of ​​the high-pressure throttle valve → P throttle Increase → P bh Increase;

[0034] If P bh >P frac There is a risk of well leakage: increasing the opening area of ​​the high-pressure throttle valve → P throttle Decrease → P bh reduce.

[0035] The present invention has the following beneficial effects:

[0036] The present invention designs a high-efficiency well workover operation method with pressure without moving the original well string. It adopts a combination of pressure operation with coiled tubing and dual-core pressure control components, abandoning the traditional operation logic of disassembling and assembling the wellhead and running the original well string. Using coiled tubing as the operation carrier, the injection head is connected to the wellhead to directly send special well-entry tools such as flushing, sand flushing, and gauging into the original well tubing for operation. The entire process does not involve disassembling or running the original well string, thus avoiding traditional problems such as string damage, environmental pollution, and formation suction from the source.

[0037] The present invention presents a method for efficient well workover under pressure with a stationary tubing string. It incorporates a dual-core pressure control component design: a coiled tubing blowout preventer (CT BOP) and a high-pressure choke valve. Existing technologies lack a linkage mechanism between dynamic sealing and precise flow control. The present invention achieves dynamic sealing and pressure compensation between the coiled tubing and the wellhead annulus through the BOP, and achieves fine-tuning of the outlet flow rate through the high-pressure choke valve. The two work together to maintain formation pressure balance and are suitable for high-risk conditions such as high pressure and gas-bearing environments.

[0038] This invention presents a highly efficient well workover operation method with pressurized tubing, improving the construction deployment method. Through an integrated deployment of a continuous tubing injection head, specialized well entry tools, blowout preventer sealing, high-pressure choke valve flow control, and construction vehicle pump circulation, it eliminates the cumbersome preparation steps required by traditional methods, such as erecting frames, installing ground anchors, and setting up circulation tanks and tubing. While achieving well workover objectives such as sand flushing, borehole clearing, unblocking, and scale removal, it significantly shortens the construction cycle to 1-2 days (avoiding the traditional 4-7 day period), avoids high-risk operations such as hoisting and power connection, eliminates mechanical damage from tripping the original tubing string, reduces environmental pollution risks, and avoids well control safety risks such as formation backflow, sand blockage, overflow, well kick, and blowout caused by bottomhole pressure imbalance during the operation. Attached Figure Description

[0039] Figure 1 A schematic diagram of the equipment used for efficient well workover operations with pressure and without moving the tubing string.

[0040] Figure 2 This is a structural diagram of a blowout preventer box and blowout preventer.

[0041] Figure 3 This is a schematic diagram of the wellhead structure.

[0042] Figure 4 This is a schematic diagram of the internal structure of a high-pressure throttle valve.

[0043] Figure 5 This is a schematic diagram of the well casing.

[0044] In the diagram: 1-Blowout Preventer (BOP) box; 2-Working vehicle; 3-Continuous tubing reel; 4-Circulating pump tank; 5-Blowout Preventer assembly; 6-Adjusting bracket; 7-Valve assembly; 8-Wellhead; 9-Well tubing string; 10-Flange; 701-Valve body; 702-Valve core; 703-Top cover; 704-Guide sleeve; 705-Throttle port; 706-Handwheel. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0046] like Figures 1-5 As shown, a highly efficient well workover operation method with pressure applied without moving the original tubing string is proposed. This method utilizes a collaborative technical solution of moving the original well tubing string, applying pressure with coiled tubing, and using dual-core pressure control components to achieve efficient and safe well workover operations. It is applicable to well workover scenarios such as sand flushing, borehole cleaning, unblocking, and scale removal within the casing and tubing without moving the original tubing string.

[0047] 1. Pre-construction preparation

[0048] 1.1 Inspection of construction site and equipment

[0049] (1) Site planning: Based on the terrain of the construction well site, determine the parking positions of equipment such as coiled tubing construction vehicle 2, construction vehicle pump, circulating pump tank 4, and control panel, and ensure that the equipment spacing meets safety standards, the work area is free of obstacles, and emergency passages are reserved.

[0050] (2) Equipment inspection: ① Continuous tubing injection head: Check whether its lifting and clamping functions are normal, and ensure that the blowout preventer 1 device at the bottom of the injection head is in place. Figure 2 ① The sealing elements (rubber core / packing) are undamaged, and the hydraulic control system pressure is stable; ② Blowout preventer assembly 5 ( Figure 2): Check the sealing performance of each gate valve and the reliability of the hydraulic control pipeline connections to ensure the blowout preventer switches flexibly; ③ High-pressure throttle valve ( Figure 4 1) Check that the valve body 701 and valve core 702 are free from wear and erosion, that the handwheel 706 and valve stem are adjusted smoothly, and that the seals of the top cover 703, guide sleeve 704, and throttle port 705 are intact. Confirm that their pressure resistance rating meets the well control requirements of the construction well (not lower than the estimated pressure in the well); 2) Enter the well: Select the corresponding special tools according to the construction target (such as sand flushing, diameter adjustment), check the tool connection threads and the integrity of the working parts, and ensure that the tool size matches the original well tubing; 3) Auxiliary equipment: Check that the construction vehicle pump power system, circulating pump tank 4 liquid level monitoring device, plug valve, and other equipment are functioning normally.

[0051] 1.2 Well Condition and Parameter Confirmation

[0052] (1) Collect basic data of the construction well: including well depth, original well tubing specifications (diameter, wall thickness), formation pressure, formation fracture pressure, fluid properties in the well (oil / gas / water content, viscosity), etc., determine the well control level, and select single-stage or multi-stage blowout preventer 1 (multi-stage blowout preventer 1 is selected for high pressure and gas-bearing wells).

[0053] (2) Calculate the core construction parameters: calculate the required circulating pressure and blowout box 1 clamping force based on the formation pressure; determine the output displacement range of the construction vehicle pump based on the construction target (such as sand flushing displacement requirements) and preset the initial adjustment opening of the high pressure throttle valve.

[0054] 2. Construction steps

[0055] 2.1 Equipment docking and wellhead sealing deployment

[0056] (1) Installation of coiled tubing injection head: Position the coiled tubing injection head directly above the wellhead using hoisting equipment, connect it to the wellhead test valve group 7 using the docking flange 6, and tighten it with clamps. Ensure the connection surface is well sealed and leak-free. After the injection head is installed, check its verticality. The deviation should not exceed 0.5° to avoid wear of the coiled tubing during operation.

[0057] (2) Debugging of the linkage between the blowout preventer box 1 and the blowout preventer: Start the hydraulic control system of the blowout preventer box 1, apply the initial clamping force to the sealing element, and set the initial pressure according to 1.2 times the pressure of the tubing string in the well. Check the sealing performance; operate the switch of the blowout preventer group 5 to confirm the linkage between the blowout preventer and the injection head and the wellhead; if it is a multi-stage blowout preventer box 1, test the sealing effect of each stage of the sealing components respectively.

[0058] (3) Connection of circulation and power system: ① The outlet of the valve on the side of the wellhead 8 is connected to the inlet of the high-pressure throttle valve through a rigid high-pressure pipeline, and the outlet of the high-pressure throttle valve is connected to the circulation pump tank. The joint is sealed with a high-pressure sealing gasket; ② A plug valve is installed at the end of the coiled tubing and connected to the outlet of the construction vehicle 2 through a high-pressure hose. The pipeline is checked for aging and damage, and the pressure level is matched; ③ The control pipelines of the operating platform of the construction vehicle 2 are connected to the injection head, blowout preventer, and high-pressure throttle valve to achieve centralized control.

[0059] (4) Connection of coiled tubing to well entry tools: According to the construction requirements, the special well entry tools of flushing tools and sand flushing tools are connected to the head of coiled tubing through threads and tightened with a torque wrench (the tightening torque meets the requirements of the tool manual). After all equipment tubing is connected, a pressure test is performed. The test pressure is 1.5 times the construction pressure, and there is no leakage after stabilizing the pressure for 10 minutes.

[0060] 2.2 Pressurized well entry and operation implementation

[0061] (1) Wellhead access opening: After confirming that all equipment connections are sealed well and the control system is normal, open the wellhead test valve and production valve to establish the well access channel; during the process, monitor the pressure change at the wellhead 8. If the pressure rises abnormally, immediately close the valve to investigate the problem.

[0062] (2) Coiled tubing running and tool delivery: Start the injection head and run the coiled tubing connected to the well tool into the well. The running speed is controlled at 5-15 m / min (adjusted according to the well pressure, and the speed is appropriately reduced for high-pressure wells). During the operation, the blowout preventer hydraulic control system monitors the well pressure in real time and automatically adjusts the sealing element clamping force to counteract the high pressure in the well and ensure that there is no leakage in the annulus seal. Figure 1 (This refers to the overall working status of the equipment during coiled tubing construction).

[0063] (3) Circulation system startup and pressure balance adjustment: When the well tool is lowered to the target working depth (according to the well string diagram ( Figure 5 After confirming the location, start the pump on the work vehicle and pump the working fluid (clean water, workover fluid, etc.) into the coiled tubing to establish a circulation loop. Manually adjust the opening of the high-pressure throttle valve through the control panel and fine-tune the flow rate according to the circulation pressure monitoring data: ① If the circulation pressure is lower than the preset value, reduce the opening of the throttle valve to increase the flow resistance and increase the circulation pressure; ② If there are signs of overflow (abnormal rise in the liquid level of the circulation tank), immediately reduce the opening of the throttle valve to increase the circulation pressure and suppress the overflow; ③ Keep the bottom hole pressure stable within the formation pressure-formation fracture pressure window throughout the process to avoid excessive pressure differential that could damage the formation.

[0064] (4) Implementation of target operations: Complete the corresponding operations according to construction requirements: ① Sand flushing operation: Maintain the preset discharge rate, use the high-pressure jet of the sand flushing tool to impact the formation sand blockage, carry the sand particles through the annulus of the original well tubing and coiled tubing, the wellhead gate valve, and the high-pressure throttle valve into the circulation tank to achieve sand separation; ② Diametering operation: Control the injection head to advance the coiled tubing at a uniform speed, so that the diametering tool moves along the inner wall of the original well tubing to remove the scale and wax blockage in the tubing and ensure that the tubing diameter meets the requirements; ③ Unblocking or scale removal operation: Spray unblocking agent / scale removal agent through the high-pressure jet tool, and cooperate with the circulation operation to carry the blockage and scale in the tubing to the surface.

[0065] 2.3 Dynamic control of the work process

[0066] (1) Real-time pressure monitoring and adjustment: The well pressure, blowout preventer clamping force, circulating pressure, and pressure before and after the high-pressure throttle valve are monitored in real time through the control panel, and the data is recorded every 5 minutes. If the well pressure fluctuation exceeds ±0.5MPa, the opening of the high-pressure throttle valve and the blowout preventer clamping force are adjusted immediately to control the pressure balance.

[0067] (2) Dynamic protection of coiled tubing: During the operation of the injection head, the stress state of the coiled tubing is monitored in real time; if it gets stuck, the insertion or removal is stopped immediately, and the circulation pressure is adjusted by the construction vehicle pump to release the stuck. It is forbidden to forcibly remove the tubing string.

[0068] (3) Emergency response: ① If the single-stage sealing component of the blowout preventer box is damaged (minor leakage is detected), immediately activate the backup sealing component of the multi-stage blowout preventer box, reduce the operating speed, adjust the clamping force, and suspend the operation to replace the sealing element if necessary; ② If a serious overflow or well kick occurs, immediately shut down the blowout preventer assembly, cut off the fluid passage in the well, start the emergency well kill process, and inject well kill fluid through the construction vehicle pump to balance the formation pressure.

[0069] 2.4 Bottomhole Pressure Control Formula

[0070] During coiled tubing operations, the bottom hole pressure P bh Stable at formation pressure P f ~formation fracturing pressure P frac Inside the window, the bottom pressure P bh =P mh +P fric +P sc +P throttle -P swab .

[0071] In the formula: P mh The fluid column pressure inside the coiled tubing is the base pressure.

[0072] P fric : The frictional pressure of the working fluid in the coiled tubing and the annulus of the original well string;

[0073] P sc : The sealing compensation pressure of the blowout preventer;

[0074] P throttle The throttling back pressure of the high-pressure throttling valve is the pressure generated by flow regulation;

[0075] P swab The suction or excitation pressure during the raising or lowering of the coiled tubing; raising the tubing string is for suction, and lowering the tubing string is for excitation.

[0076] 2.4.1 Calculation of pressure for each component

[0077] 1. Liquid column pressure (P) mh )

[0078] The vertical fluid column pressure of the working fluid in the coiled tubing, formula:

[0079] P mh =0.00981×ρ×H.

[0080] ρ: Density of the working fluid (g / cm³) 3 );

[0081] H: Operating depth (vertical well depth, m);

[0082] 0.00981: Unit conversion factor (to convert g / cm³) 3 (m converted to MPa).

[0083] 2. Flow friction pressure (P) fric )

[0084] Frictional resistance (P) of the working fluid flowing in the coiled tubing fric，CT ) + Friction of the original well casing annulus (P) fric，ann Formula: P fric =P fric，CT +P fric，ann ;

[0085] Among them, internal friction (applicable to turbulent flow):

[0086] ;

[0087] Annular friction (suitable for turbulent flow):

[0088] .

[0089] Parameter description:

[0090] f: Friction coefficient (0.02~0.04 for turbulent flow, needs to be corrected according to the fluid flow pattern);

[0091] Q: Working fluid discharge rate (m³)3 / d);

[0092] L: Flow length (operation depth, m);

[0093] d: Inner diameter of coiled tubing (cm);

[0094] D: Inner diameter of the original well tubing (cm).

[0095] 3. Blowout preventer seal compensation pressure (P) sc )

[0096] To maintain the annular seal, the blowout preventer requires a clamping force (to counteract the well pressure), as shown in the formula:

[0097] P sc =k×P bh ;

[0098] k: Compensation coefficient (usually taken as 1.1~1.3, 1.3 for high-pressure wells to ensure reliable sealing).

[0099] P bh Real-time bottom hole pressure (requires adjustment via pressure sensor feedback).

[0100] 4. Throttling back pressure (P) of high-pressure throttle valve throttle )

[0101] The back pressure generated by the flow regulation of the throttle valve is used to derive the following formula based on the flow rate at the throttle orifice:

[0102] ;

[0103] Parameter description:

[0104] Q: Flow rate through the throttle valve (m³) 3 / s);

[0105] Cd: Flow coefficient (0.6~0.8, experimentally determined);

[0106] A: Throttling valve opening area (m²) 2 );

[0107] ρ: Density of the working fluid (kg / m³) 3 );

[0108] 10 -6 : Convert the unit to MPa.

[0109] 5. Suction / excitation pressure (P) swab )

[0110] Pressure fluctuations during coiled tubing tripping, formula:

[0111] ;

[0112] K: Empirical coefficient (0.012 for starting the tubing string, 0.018 for lowering the tubing string);

[0113] v: Coiled tubing tripping speed (m / s);

[0114] u: Viscosity of the working fluid (mPa.s);

[0115] L: Working depth (m);

[0116] d: Outer diameter of coiled tubing (cm).

[0117] 2.4.2 Core Logic of Pressure Control

[0118] Flow rate is adjusted by a high-pressure throttle valve, changing P throttle Combined with the P of the pop filter box sc Compensation, maintenance :

[0119] If P bh <P f There is a risk of overflow: reduce the opening area of ​​the high-pressure throttle valve → P throttle Increase → P bh Increase;

[0120] If P bh >P frac There is a risk of well leakage: increasing the opening area of ​​the high-pressure throttle valve → P throttle Decrease → P bh reduce.

[0121] 3. Construction completion

[0122] 3.1 Completion of Task and Removal of Tools

[0123] (1) When the operation target is achieved (such as sand blockage removal and qualified tubing diameter), keep the circulation system running for a sufficient time according to the depth volume to ensure that there are no residual blockages or sand particles in the well; slowly adjust the opening of the high pressure throttle valve to keep the circulation pressure within the balance range.

[0124] (2) Start the injection head and pull out the coiled tubing and well tools at a constant speed. The pulling speed is controlled at 5-12 m / min. During the pulling process, the blowout preventer box is kept dynamically sealed and the high-pressure throttle valve is kept at an appropriate opening to avoid formation pressure imbalance due to suction. Observe the liquid level in the circulation tank in real time to confirm that there is no backflow of formation fluid.

[0125] 3.2 Equipment dismantling and site cleanup

[0126] (1) After the tool is retrieved, close the wellhead test valve and production valve, and shut down the construction vehicle pump, injection head and other equipment; disassemble the connecting hose between the coiled tubing and the construction vehicle pump, the connecting pipeline between the high pressure throttle valve and the circulating pump tank 4, and the connecting flange 10 between the injection head and the wellhead in sequence. During the disassembly process, ensure the pipeline ports are sealed to prevent residual fluid leakage.

[0127] (2) Recover coiled tubing, well tools, blowout preventer box 1, blowout preventer and other equipment, check the equipment status, replace and maintain worn parts; clean the work site, recover waste work fluid and debris, and ensure that the site meets environmental protection requirements. There is no need to remove traditional work anchors, ropes and other facilities, which greatly shortens the finishing time.

[0128] 3.3 Construction Quality Acceptance

[0129] (1) Check the original well tubing condition: Confirm that there is no leakage or deformation of the tubing through the wellhead 8 monitoring device, and that the inner diameter of the tubing meets the requirements; (2) Formation condition assessment: Monitor whether the formation pressure is stable and whether there are any signs of sand production or overflow; (3) Construction data compilation: Summarize the pressure, discharge, operation time and other data during the construction process to form a construction report.

[0130] 1. The bottom of the coiled tubing injection head is equipped with a blowout preventer (BOP) box 1 device, which has the ability to seal and pressurize during construction and is connected to the BOP. During construction, the end of the tubing is always inside the injection head. The head of the coiled tubing is connected to the well tool (such as flushing tool, caliper, sand flushing tool, high-pressure jet tool) according to the operation requirements.

[0131] 2. Connect the injection head to the wellhead, tighten the clamps, open the test and production gates to open the well access channel, connect the valve outlet on the side of the wellhead to the rigid pipeline into the circulation pump tank, and connect the coiled tubing with a plug valve at the end to the pump of the construction vehicle to provide circulation power. The tools are then lowered into the well for operation and construction.

[0132] 3. Core Pressure Control Component 1: Coiled Tubing Blowout Preventer Box 1 (CT Blowout Preventer Box). Its main function is to seal the annulus between the coiled tubing and the wellhead during coiled tubing runs, trips, or circulation operations, preventing high-pressure fluids (oil, gas, water) from being ejected from the well. The core working principle is to apply pressure to the outer wall of the coiled tubing through sealing elements to achieve a dynamic seal, accommodating the vertical movement and rotation of the coiled tubing.

[0133] Sealing mechanism: The blowout preventer 1 has built-in elastic sealing elements (such as rubber cores or packing). By hydraulic or mechanical means, the sealing elements are squeezed to make them radially contract and tightly wrap around the outer wall of the coiled tubing, thereby preventing the fluid in the well from overflowing from the annular channel between the tubing and the blowout preventer.

[0134] Pressure balancing and compensation: During operation, the high pressure inside the well will act on the sealing element. The hydraulic control system of the blowout preventer 1 will provide the corresponding clamping force to counteract the pressure inside the well and ensure the sealing effect. During the operation, the tension pressure of the blowout preventer can be manually adjusted according to the pressure inside the well to achieve sealing under pressure, ensure formation pressure balance, and minimize the impact of pressure.

[0135] Adaptable to dynamic operations: The material and structure of the sealing element are specially designed to withstand high pressure and reduce friction damage while maintaining sealing performance when the coiled tubing moves up and down, meeting the dynamic operation requirements of coiled tubing such as raising and lowering, pumping, and sand flushing.

[0136] Depending on the well control level and well pressure, a single-stage or multi-stage blowout preventer can be used: it contains two or more sets of sealing components, which can achieve graded sealing. If one set of seals is damaged, the other set can still maintain the seal. It is suitable for high-risk well conditions such as high pressure and gas-containing wells.

[0137] 4. Core Pressure Control Component Two: The circulation outlet adopts a high-pressure throttle valve. Its core requirements are high pressure resistance (usually ≥10MPa-100MPa), reliable flow regulation accuracy, excellent sealing performance, and erosion / cavitation resistance. A dedicated structure and working principle have been designed for high-pressure operating conditions.

[0138] The core function of the valve is to manually and precisely adjust the flow rate of high-pressure liquid by changing the flow cross-sectional area inside the valve, and it also has a certain function of shutting off flow (but it mainly focuses on "flow regulation" rather than "shutdown").

[0139] Valve working principle: The valve stem drives the valve core 702 to move up and down, changing the gap between the valve core 702 and the valve seat—the smaller the gap, the greater the flow resistance and the smaller the flow rate; conversely, the larger the gap, the greater the flow rate. Under high-pressure conditions, the flow rate is controlled through the throttling effect of the valve core 702, while simultaneously withstanding the high pressure differential and erosion caused by the throttling.

[0140] Valve structural features:

[0141] Valve body 701: Made of forged steel (WCB), stainless steel (304 / 316) or alloy structural steel, integrally forged (avoiding casting defects and ensuring high pressure bearing capacity).

[0142] Valve core 702: Commonly used wear-resistant and erosion-resistant materials. Valve core 702 is mostly streamlined (to reduce fluid impact and reduce cavitation).

[0143] Sealing: Hard seals (metal-to-metal seals) or high-pressure-specific soft seals (reinforced PTFE, V-rings) are used to ensure no leakage under high-pressure environments;

[0144] Valve stem: Thickened design + guide sleeve to prevent bending and deformation under high pressure and improve regulation stability.

[0145] The role of high-pressure throttle valves in operational scenarios: to manually and precisely control the outlet flow rate, and to coordinate with the pump circulation pressure of the construction vehicle to balance the pressure inside the construction well, thereby reducing the impact of pressure differential on the formation; by reducing the outlet flow rate to increase the construction circulation pressure, it can effectively suppress construction quality problems caused by pressure imbalance, such as overflow and sand backflow from the formation.

[0146] 5. Dual pressure control components working together:

[0147] ①. Coiled tubing blowout preventer box 1 – Core of annular seal and pressure compensation

[0148] Core function: Dynamically seals the coiled tubing and wellhead annulus to prevent high-pressure fluid from gushing out, adapting to dynamic operation scenarios where the coiled tubing moves up and down.

[0149] Key mechanism: Radial shrinkage sealing is achieved by hydraulically / mechanically compressing elastic sealing elements (rubber core, packing), combined with a pressure compensation design (manual / automatic adjustment of clamping force) to counteract high pressure inside the well and maintain formation pressure balance;

[0150] Adaptability: Single-stage / multi-stage seals can be selected according to the well control level to meet the needs of high-pressure, gas-containing and other high-risk working conditions.

[0151] ②. High-pressure throttle valve – the core of flow regulation and pressure balance

[0152] Core functions: Manually and precisely adjust the operating circulation outlet flow rate, and coordinate with the construction vehicle pump circulation pressure to control the well pressure;

[0153] Key mechanism: The flow resistance is controlled by adjusting the gap between the needle / streamlined valve core and the valve seat, so as to achieve fine flow regulation. Hard seals or high-pressure soft seals are used to ensure no leakage under high pressure.

[0154] Operational Value: By controlling the outlet flow rate through the throttle valve and regulating the circulating pressure in conjunction with the blowout preventer, overflow and formation sand production are suppressed, excessive pressure differentials can be avoided to prevent formation damage, ensuring safe and precise live-line operations and achieving efficient and low-risk live-line operations.

[0155] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0156] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for efficient well workover operations under pressure without moving the tubing string, characterized in that, Includes the following steps: S1. Pre-construction preparation: Inspection of construction site and equipment, confirmation of well condition and parameters of construction well; S2. Equipment docking and wellhead sealing deployment: including installation of coiled tubing injection head, linkage debugging of blowout preventer box and blowout preventer, connection of circulation and power system, and connection of coiled tubing and well entry tool; S3. Pressurized well entry and operation implementation: including wellhead access opening, coiled tubing running and tool delivery, circulation system startup and pressure balance adjustment, and target operation implementation; S4. Dynamic control of the operation process: including real-time pressure monitoring and adjustment, dynamic protection of coiled tubing, and emergency response; S5. Bottom hole pressure control: Bottom hole pressure P bh Stable at formation pressure P f ~formation fracturing pressure P frac Inside the window, the bottom pressure P bh =P mh +P fric +P sc +P throttle -P swab ; S6. Operation completed. Tools retrieved. Start the injection head and retrieve the coiled tubing and well tools at a constant speed, with the retrieval speed controlled at 5-12 m / min.

2. The method for efficient well workover under pressure using a stationary tubing string according to claim 1, characterized in that, The specific steps for equipment docking and wellhead sealing deployment in step S2 are as follows: S21. Installation of coiled tubing injection head: Position the coiled tubing injection head directly above the wellhead using hoisting equipment, connect it to the wellhead test valve group using a docking flange, and secure it with clamps. Ensure the connection surface is well sealed and leak-free. After the injection head is installed, check its verticality. The deviation should not exceed 0.5°. S22. Blowout Preventer (BOP) Box and BOP Linkage Testing: Start the BOP hydraulic control system and apply initial clamping force to the sealing elements. The initial pressure should be set to 1.2 times the well tubing pressure. Check the sealing performance. Operate the BOP assembly switch to confirm the linkage between the BOP, injection head, and wellhead. If it is a multi-stage BOP box, test the sealing effect of each stage of the sealing components. S23. Connection of Circulation and Power System: ① The outlet of the wellhead side valve is connected to the inlet of the high-pressure throttle valve via a rigid high-pressure pipeline, and the outlet of the high-pressure throttle valve is connected to the circulation pump tank. The joint is sealed with a high-pressure sealing gasket; ② A plug valve is installed at the tail of the coiled tubing and connected to the outlet of the construction vehicle via a high-pressure hose. The pipeline is checked for aging and damage, and the pressure rating is matched; ③ The control pipelines connecting the construction vehicle's operating platform to the injection head, blowout preventer, and high-pressure throttle valve are used for centralized control; S24. Connection of coiled tubing and well entry tools: According to the construction requirements, connect the special well entry tools of flushing tools and sand flushing tools to the head of coiled tubing through threads and tighten with a torque wrench. After all equipment tubing is connected, perform a pressure test. The test pressure is 1.5 times the construction pressure, and there should be no leakage after stabilizing the pressure for 10 minutes.

3. The method for efficient well workover under pressure using a stationary tubing string according to claim 1, characterized in that, The specific steps for pressurized well entry and operation implementation in step S3 are as follows: S31. Wellhead Access Opening: After confirming that all equipment connections are properly sealed and the control system is functioning normally, open the wellhead test valve and production valve to establish an access passage to the well. During the process, monitor wellhead pressure changes. If the pressure rises abnormally, immediately close the valves to investigate the problem. S32. Coiled tubing running and tool delivery: Start the injection head and run the coiled tubing connected to the well tool into the well. The running speed is controlled at 5-15 m / min. During operation, the blowout preventer's hydraulic control system monitors the well pressure in real time and automatically adjusts the sealing element clamping force to counteract the high pressure inside the well; S33. Circulation System Start-up and Pressure Balance Adjustment: After the wellhead tool reaches the target working depth, start the pump on the work vehicle to pump the working fluid into the coiled tubing and establish a circulation loop; manually adjust the opening of the high-pressure throttle valve through the control panel, and fine-tune the flow rate according to the circulation pressure monitoring data: ① If the circulation pressure is lower than the preset value, reduce the opening of the throttle valve to increase the flow resistance and increase the circulation pressure; ② If there are signs of overflow, immediately reduce the opening of the throttle valve to increase the circulation pressure and suppress the overflow; ③ Maintain the bottom hole pressure stable within the formation pressure-formation fracture pressure window throughout the process; S34. Target Operation Implementation: Complete the corresponding operations according to construction requirements: ① Sand flushing operation: Maintain the preset displacement, use the high-pressure jet of the sand flushing tool to impact the formation sand plugs, carry the sand particles through the annulus of the original well tubing and coiled tubing, the wellhead gate valve, and the high-pressure throttle valve into the circulation tank to achieve sand particle separation; ② Diametering operation: Control the injection head to advance the coiled tubing at a uniform speed, so that the diametering tool moves along the inner wall of the original well tubing to remove scale and wax plugs in the tubing and ensure that the tubing diameter meets the requirements; ③ Unblocking or scale removal operation: Use the high-pressure jet tool to spray unblocking agent / scale removal agent, in conjunction with the circulation operation, to carry the blockages and scale in the tubing to the surface.

4. The method for efficient well workover under pressure using a stationary tubing string according to claim 1, characterized in that, The specific steps of dynamic control of the work process in step S4 are as follows: S41. Real-time pressure monitoring and adjustment: The well pressure, blowout preventer clamping force, circulating pressure, and pressure before and after the high-pressure throttle valve are monitored in real time via the control panel, and the data is recorded every 5 minutes. If the well pressure fluctuates more than ±0.5MPa, the opening of the high-pressure throttle valve and the blowout preventer clamping force are adjusted immediately to control the pressure balance. S42. Dynamic protection of coiled tubing: During the operation of the injection head, the stress state of the coiled tubing is monitored in real time; if jamming occurs, the lowering or lowering is stopped immediately, and the circulation pressure is adjusted by the construction vehicle pump to release the jamming. It is forbidden to forcibly lower the tubing string. S43. Emergency Response: ① If a single-stage sealing component of the blowout preventer box is damaged, immediately activate the backup sealing component of the multi-stage blowout preventer box, while reducing the operating speed, adjusting the clamping force, and suspending the operation to replace the sealing element if necessary; ② If a serious overflow or well kick occurs, immediately shut down the blowout preventer assembly, cut off the fluid passage in the well, start the emergency well kill procedure, and inject well kill fluid through the construction vehicle pump to balance the formation pressure.

5. The method for efficient well workover under pressure using a stationary tubing string according to claim 1, characterized in that, P in step S5 mh The fluid column pressure inside the coiled tubing is the base pressure. P fric : The frictional pressure of the working fluid in the coiled tubing and the annulus of the original well string; P sc : The sealing compensation pressure of the blowout preventer; P throttle The throttling back pressure of the high-pressure throttling valve is the pressure generated by flow regulation; P swab The suction or excitation pressure during the raising or lowering of the coiled tubing; raising the tubing string is for suction, and lowering the tubing string is for excitation.

6. The method for efficient well workover under pressure using a stationary tubing string according to claim 5, characterized in that, The logic for pressure control in step S5 is as follows: The flow rate is adjusted by using a high-pressure throttle valve to change P. throttle Combined with the P of the pop filter box sc Compensation, maintenance : If P bh <P f There is a risk of overflow: reduce the opening area of ​​the high-pressure throttle valve → P throttle Increase → P bh Increase; If P bh >P frac There is a risk of well leakage: increasing the opening area of ​​the high-pressure throttle valve → P throttle Decrease → P bh reduce.

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