A method and system for nitrogen foam fluid sand-carrying flowback stimulation

Abstract

The application discloses a nitrogen foam fluid sand-carrying flowback stimulation method and system, and belongs to the technical field of oil and gas development. The method comprises the following steps: obtaining target well basic data and determining construction parameters; generating nitrogen foam fluid on the ground; pumping the nitrogen foam fluid into a wellbore through a coiled tubing connected with a bidirectional flushing tool; adjusting foam density according to formation pressure during sand washing; and using the nitrogen foam fluid to flow back solid particles to the ground. For a target well with a vertical depth difference between point A and point B greater than 50 m and an upwarping structure, an asymmetric forward and backward sand washing strategy is adopted. The application adopts the above-mentioned nitrogen foam fluid sand-carrying flowback stimulation method and system, and through the synergistic effect of ground controllable foaming, a bidirectional flushing tool, asymmetric forward and backward sand washing and a sewage adaptive formula, the problems of unstable foam quality, continuous oil pipe self-locking, low sand washing efficiency and high sewage reuse frictional resistance in the complex well conditions of long horizontal sections and high pressure leakage coexisting are solved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas development technology, and in particular to a method and system for enhancing production through nitrogen foam fluid carrying sand back to the source. Background Technology

[0002] Nitrogen foam fluid flushing technology is an important means to solve the problems of wellbore blockage in low-pressure oil and gas wells, lost circulation wells, and horizontal wells. This technology utilizes the characteristics of low density and low fluid column pressure of foam fluid, which makes it easy to establish circulation; at the same time, foam fluid has high apparent viscosity and strong sand-carrying capacity; in addition, foam has a selective temporary plugging effect on high-permeability layers, which can "plug large areas but not small ones", making it particularly suitable for complex well conditions with strong heterogeneity and lost circulation layers.

[0003] Currently, the commonly used nitrogen foam sand flushing method in existing technologies typically involves directly injecting nitrogen and a foaming agent into the well through a tee, allowing it to naturally generate foam fluid in the wellbore and formation. This method has the following technical drawbacks: Foam forms naturally downhole and is greatly affected by wellbore temperature, pressure, and fluid mixing conditions. This makes it difficult to guarantee continuous, uniform, and high-quality foam fluid, resulting in poor sand-carrying stability and affecting sand flushing effectiveness. For long horizontal wells, especially complex trajectory wells with upward-curving structures (significant vertical depth difference between points A and B), self-locking is prone to occur during coiled tubing installation. Conventional flushing tools are insufficient to effectively assist in lowering the tubing string, and sand jamming accidents are likely to occur during sand flushing.

[0004] Existing sand flushing processes mostly employ a simple, equidistant advance-retreat operation mode. For complex well conditions where lost circulation zones and high-pressure zones coexist, there is a lack of targeted dynamic control methods, making it difficult to achieve effective synergy between temporarily plugging lost circulation zones and balancing high-pressure zones. As oilfield development enters the mid-to-late stages, a large amount of produced wastewater needs treatment and reuse. However, the wastewater has high salinity and suspended solids content, and directly using it to formulate foaming solutions will lead to decreased foaming performance and increased tubing friction. Currently, there is a lack of foam formulations and drag-reducing measures specifically for high-salinity base fluids.

[0005] Therefore, there is an urgent need in this field for a nitrogen foam fluid sand-carrying and return method and system that can achieve high-quality foam generation and safe and efficient sand flushing for complex well conditions with long horizontal sections, leakage and high pressure. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for increasing production by using nitrogen foam fluid to carry sand back to the reactor, in order to solve the above-mentioned problems.

[0007] This invention provides a method for increasing production through nitrogen foam fluid carrying sand backflow, comprising the following steps: S1: Obtain basic data of the target well, including horizontal section length, vertical depth at point A, vertical depth at point B, location of lost flow zone, location of high pressure zone, and dogleg data; S2: Based on the aforementioned basic data, construction parameters are determined through software simulation. These construction parameters include foam density, construction discharge rate, nitrogen discharge rate, and construction pressure. S3: On the ground, the foaming agent is mixed with the base liquid to form a foaming aqueous solution, and the foaming aqueous solution and nitrogen are simultaneously injected into the foam generating device to generate nitrogen foam fluid on the ground through the foam generating device. S4: The generated nitrogen foam fluid is pumped into the wellbore of the target well through a coiled tubing, the end of which is connected to a bidirectional flushing tool; S5: During sand flushing, adjust the foam density based on formation pressure monitoring data, increasing the foam mass to 0.7-0.9 g / cm³ when crossing lost circulation zones. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3 ; S6: Use the nitrogen foam fluid to return the carried solid particles and insoluble substances to the ground.

[0008] Preferably, the base liquid in step S3 is reclaimed water from oilfield produced wastewater or backflow fluid after sedimentation treatment, and the mineralization of the base liquid does not exceed 50,000 mg / L, and the suspended solids content does not exceed 200 mg / L; the mixing ratio of the foaming agent to the base liquid is 0.3-0.8 wt% of the foaming agent. The nitrogen foam fluid has a foaming volume of not less than 500 mL and a half-life of not less than 15 min under the condition of mineralization of 30000-50000 mg / L.

[0009] Preferably, in step S4, when the nitrogen foam fluid is pumped into the wellbore of the target well through a coiled tubing, a drag-reducing agent is added to the nitrogen foam fluid, or the base fluid is replaced with slickwater with a viscosity of less than 10 mPa·s.

[0010] Preferably, step S4 further includes: After the sand surface is detected, the coiled tubing is raised to a preset distance above the sand surface, the pump is started, and after the circulation is normal, the coiled tubing is lowered at a speed of no more than 5m / min to flush the sand. Every 30-50m of advance, the load is checked and the load variation is controlled within 10kN-20kN. At the same time, the well is raised to the maximum dogleg position for well flushing until there is no sand at the outlet before continuing to lower it.

[0011] Preferably, for target wells where the vertical depth difference between points A and B is greater than 50m and the horizontal section has an upward-curving structure, an asymmetric advance-retreat sand flushing strategy is adopted. The asymmetric advance-retreat sand flushing strategy includes: after each advance of the coiled tubing by a first distance, the tubing is raised by a second distance. The first distance is greater than the second distance. The ratio of the first distance to the second distance is dynamically adjusted according to the rate of change of the inclination angle of the horizontal section of the well. The range of the ratio is 1.5:1 to 3:1. For well sections with a dogleg degree greater than 15° / 30m, the ratio is adjusted to 2:1 and the sand flushing rate is reduced to below 3m / min.

[0012] Preferably, the basic data of the target well obtained in step S1 also includes obtaining the pressure data of the adjacent well and the sand flushing construction data; the construction parameters determined by software simulation in step S2 include: predicting the formation pressure of the target well based on the pressure data of the adjacent well, simulating and calculating the friction and construction pressure when the coiled tubing is run into the target depth, and calculating the minimum settling velocity of sand particles in nitrogen foam fluid, so that the minimum flow velocity of nitrogen foam fluid in the wellbore is greater than the minimum settling velocity.

[0013] Preferably, a verification step is also included after sand flushing: Step S7: After flushing the sand to the target depth, raise the coiled tubing to 10-20m above the sand surface, and circulate the well at a flow rate of 300-400L / min for more than 20 minutes until the sand content at the inlet and outlet is consistent. Step S8: Pull the coiled tubing to the wellhead and shut the well in for 2-6 hours; Step S9: After the settling period, the coiled tubing is lowered again to re-probe the sand surface. If the sand surface rises above the preset threshold, steps S3 to S6 are repeated to perform additional sand flushing. If the sand surface rises within the preset threshold, the sand flushing is deemed successful.

[0014] A nitrogen foam fluid-carrying sand return enhancement system includes: The data acquisition and simulation module acquires the basic data of the target well and determines the construction parameters through software simulation. The basic data includes the horizontal section length, vertical depth at point A, vertical depth at point B, location of the lost flow zone, location of the high pressure zone, and dogleg data. The ground foam generating unit includes a foaming agent injection subsystem, a nitrogen supply subsystem, and a foam generator, which mixes foaming agent, base liquid, and nitrogen on the ground to generate nitrogen foam fluid; wherein, the outlet of the foaming agent injection subsystem is connected to the first inlet of the foam generator through a first pipeline, and the outlet of the nitrogen supply subsystem is connected to the second inlet of the foam generator through a second pipeline. The pumping unit has its inlet connected to the outlet of the foam generator via a third pipeline, and its outlet connected to the inlet of the coiled tubing via a fourth pipeline, injecting the generated nitrogen foam fluid into the well at a set discharge rate. The coiled tubing is connected to a bidirectional flushing tool at its end to deliver nitrogen foam fluid to the target formation at the bottom of the well; the coiled tubing is connected to the pumping unit via a fourth pipeline; The monitoring and control unit is electrically connected to the data acquisition and simulation module, the foaming agent injection subsystem, the nitrogen supply subsystem, the foam generator, the pumping unit, and sensors installed at the wellhead and tubing. It monitors formation pressure, flow rate, and flowback fluid parameters in real time during construction. Based on the formation pressure monitoring data, it sends control commands to the foaming agent injection subsystem and the nitrogen supply subsystem to adjust the foam density, increasing the foam mass to 0.7-0.9 g / cm³ when crossing lost circulation zones. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3 ; The monitoring and control unit is also used to implement an asymmetric advance and retreat sand flushing strategy for target wells with a vertical depth difference of more than 50m between points A and B and an upward structure in the horizontal section. After each advance of the coiled tubing by a first distance, it is controlled to be raised by a second distance, where the first distance is greater than the second distance.

[0015] Preferably, the two-way flushing tool includes: The tool body has a reversing mechanism inside; An axial injection nozzle is located at the front end of the tool body; At least one radial injection port is disposed on the side wall of the tool body; The reversing mechanism switches to axial injection mode when the coiled tubing is obstructed during descent and to radial injection mode when the coiled tubing is lifted.

[0016] The monitoring and control unit also includes a construction connection control module, which monitors the volume of the external discharge tank and the unloading distance. The input end of the construction connection control module is electrically connected to the liquid level sensor installed on the external discharge tank and the positioning module installed on the transport vehicle, and the output end is electrically connected to the pumping unit. It is used to issue an early warning signal and adjust the pumping discharge rate of the pumping unit when the volume of the external discharge tank is lower than the first threshold or the unloading distance exceeds the second threshold.

[0017] Therefore, the above-mentioned method and system for increasing production by using nitrogen foam fluid to carry sand back to its source has the following beneficial effects: (1) A uniform, controllable and stable nitrogen foam fluid is generated by a surface foam generator, which overcomes the defect of unstable quality of natural foaming downhole. In conjunction with step S5, the foam density is adjusted in real time according to the formation pressure. When crossing the lost circulation zone, the foam quality is increased to enhance the temporary plugging effect, and when crossing the high pressure zone, the foam density is decreased to balance the formation pressure, thus realizing the fine control of complex well conditions.

[0018] (2) A bidirectional flushing tool is connected to the end of the coiled tubing. When the coiled tubing is lowered and encounters resistance, the tool switches to the axial spray mode to flush away sand plugs. When it is pulled up, it switches to the radial spray mode to clean the well wall, which effectively solves the technical problem of coiled tubing self-locking in long horizontal sections and upturned structure wells.

[0019] (3) For target wells with a vertical depth difference of more than 50m between points A and B and an upward structure in the horizontal section, an asymmetric advance-retreat sand flushing strategy is adopted. After each advance of the first distance of the coiled tubing, the second distance is raised. For well sections with a dogleg degree of more than 15° / 30m, the ratio is adjusted to 2:1 and the sand flushing speed is reduced, which overcomes the defects of low efficiency and easy stuck drill in conventional equidistant advance-retreat.

[0020] (4) For the base liquid of oilfield produced wastewater, the mineralization is limited to no more than 50,000 mg / L, the foaming agent is 0.3-0.8 wt%, the foaming volume of nitrogen foam fluid is not less than 500 mL, the half-life is not less than 15 min, and drag-reducing agents are added or replaced with slickwater with a viscosity of less than 10 mPa·s, which effectively reduces the friction of the tubing generated by the high mineralization base liquid and realizes the recycling of water resources.

[0021] (5) The volume of the external discharge tank and the unloading distance are monitored in real time through the construction connection control module. When the volume is lower than the threshold, an early warning is issued and the pump discharge rate is adjusted to avoid construction interruption. The reliability of the sand flushing quality is ensured through the re-exploration and verification steps after the sand flushing is completed.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a nitrogen foam fluid sand-carrying and return system for increased production according to the present invention; Figure 2 This is a schematic diagram of the bidirectional flushing tool in a nitrogen foam fluid sand-carrying return system for production enhancement according to the present invention.

[0024] Reference numerals: 1. Data acquisition and simulation module; 2. Foaming agent injection subsystem; 3. Nitrogen supply subsystem; 4. Foam generator; 5. First pipeline; 6. Second pipeline; 7. Pumping unit; 8. Third pipeline; 9. Fourth pipeline; 10. Coiled tubing; 11. Two-way flushing tool; 12. Monitoring and control unit; 111. Tool body; 112. Reversing mechanism; 113. Axial injection port; 114. Radial injection port. Detailed Implementation

[0025] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. 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.

[0026] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0027] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0028] This invention provides a method for increasing production through nitrogen foam fluid carrying sand backflow, comprising the following steps: Step S1: Obtain the basic data of the target well, including the horizontal section length, vertical depth at point A, vertical depth at point B, location of the lost flow zone, location of the high-pressure zone, and dogleg data.

[0029] Specifically, step S1 also includes acquiring pressure data from adjacent wells and sand flushing operation data to provide a reference for the simulation calculation of subsequent construction parameters.

[0030] Step S2: Based on the aforementioned basic data, the construction parameters are determined through software simulation. These parameters include foam density, construction discharge rate, nitrogen discharge rate, and construction pressure.

[0031] Specifically, determining construction parameters through software simulation includes: predicting the formation pressure of the target well based on pressure data from adjacent wells; simulating and calculating the frictional resistance and construction pressure when the coiled tubing is run to the target depth; and calculating the minimum settling velocity of sand particles in nitrogen foam fluid, ensuring that the minimum flow velocity of the nitrogen foam fluid in the wellbore is greater than the minimum settling velocity. These simulation calculations ensure the rationality and feasibility of the construction parameters.

[0032] Step S3: On the ground, the foaming agent is mixed with the base liquid to form a foaming aqueous solution, and the foaming aqueous solution and nitrogen are injected into the foam generating device at the same time to generate nitrogen foam fluid on the ground through the foam generating device.

[0033] The base fluid is reclaimed water from oilfield produced wastewater or backflow fluid after sedimentation treatment. The salinity of the base fluid does not exceed 50,000 mg / L, and the suspended solids content does not exceed 200 mg / L. The mixing ratio of the foaming agent to the base fluid is 0.3-0.8 wt% of the foaming agent. Using the above ratio and parameters, the nitrogen foam fluid has a foaming volume of not less than 500 mL and a half-life of not less than 15 min under salinity conditions of 30,000-50,000 mg / L, ensuring that the foam fluid has good stability and sand-carrying capacity.

[0034] Step S4: The generated nitrogen foam fluid is pumped into the wellbore of the target well through a coiled tubing, the end of which is connected to a bidirectional flushing tool.

[0035] Specifically, step S4 further includes: after the sand surface is detected, the coiled tubing is raised to a preset distance above the sand surface, the pump is started, and after the circulation is normal, the coiled tubing is lowered at a speed of no more than 5m / min to flush the sand; every 30-50m of advance, the load is checked and the load change is controlled within 10kN-20kN, while the tubing is raised to the maximum dogleg position to flush the well until there is no sand at the outlet before continuing to lower it.

[0036] In step S4, when the nitrogen foam fluid is pumped into the wellbore of the target well through the coiled tubing, a drag-reducing agent is added to the nitrogen foam fluid, or the base fluid is replaced with slickwater with a viscosity of less than 10 mPa·s, in order to reduce the tubing friction generated by the high-salinity base fluid.

[0037] Step S5: During the sand flushing process, adjust the foam density based on formation pressure monitoring data, increasing the foam mass to 0.7-0.9 g / cm³ when crossing the lost circulation zone. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3 .

[0038] Through the above dynamic adjustments, on the one hand, high foam quality is used in the lost circulation zone to enhance the temporary plugging effect on the high permeability zone and prevent working fluid leakage; on the other hand, low foam quality is used in the high pressure zone to reduce the fluid column pressure, balance the formation pressure, and prevent well kick or blowout, thus achieving refined control of complex well conditions.

[0039] Step S6: Use the nitrogen foam fluid to return the carried solid particles and insoluble matter to the ground.

[0040] For target wells with a vertical depth difference greater than 50m between points A and B and an upward-curving structure in the horizontal section, an asymmetric advance-retreat sand flushing strategy is adopted. This strategy involves advancing the coiled tubing a first distance, then raising it a second distance. The first distance is greater than the second distance, and the ratio of the first to second distances is dynamically adjusted based on the rate of change of the well inclination angle in the horizontal section. The ratio ranges from 1.5:1 to 3:1. For well sections with a dogleg greater than 15° / 30m, the ratio is adjusted to 2:1, and the sand flushing speed is reduced to below 3m / min.

[0041] This asymmetric advance-back sand flushing strategy can effectively prevent sand particles from falling back and burying the pipe, improve sand flushing efficiency, and avoid self-locking or stuck pipe accidents in complex trajectory well sections.

[0042] The method of the present invention also includes a verification step after sand washing is completed: Step S7: After flushing the sand to the target depth, raise the coiled tubing to 10-20m above the sand surface, and circulate the well at a flow rate of 300-400L / min for more than 20 minutes until the sand content at the inlet and outlet is consistent. Step S8: Pull the coiled tubing to the wellhead and shut the well in for 2-6 hours; Step S9: After the settling period, the coiled tubing is lowered again to re-probe the sand surface. If the sand surface rises above the preset threshold, steps S3 to S6 are repeated to perform additional sand flushing. If the sand surface rises within the preset threshold, the sand flushing is deemed successful.

[0043] The above verification steps can ensure the quality and reliability of sand flushing operations and avoid repeated operations caused by sand surface rebound.

[0044] This invention also provides a nitrogen foam fluid-carrying sand return system for production enhancement, comprising: The data acquisition and simulation module 1 is used to acquire the basic data of the target well and determine the construction parameters through software simulation. The basic data includes the horizontal section length, vertical depth at point A, vertical depth at point B, location of the lost layer, location of the high-pressure layer, and dogleg data. The data acquisition and simulation module 1 is electrically connected to the monitoring and control unit and is used to transmit the determined construction parameters to the monitoring and control unit.

[0045] The ground foam generating unit includes a foaming agent injection subsystem 2, a nitrogen supply subsystem 3, and a foam generator 4, used to mix foaming agent, base liquid, and nitrogen on the ground to generate nitrogen foam fluid. The outlet of the foaming agent injection subsystem 1 is connected to the first inlet of the foam generator 4 via a first pipeline 5, and the outlet of the nitrogen supply subsystem 3 is connected to the second inlet of the foam generator 4 via a second pipeline 6. The foaming agent injection subsystem 2 is used to meter and inject the foaming agent, the nitrogen supply subsystem 3 is used to provide high-pressure nitrogen, and the foam generator 4 is used to forcibly mix and shear the foaming aqueous solution with nitrogen.

[0046] The pumping unit 7, with its inlet connected to the outlet of the foam generator 4 via a third pipeline 8 and its outlet connected to the inlet of the coiled tubing 10 via a fourth pipeline 9, is used to inject the generated nitrogen foam fluid into the well at a set discharge rate. The pumping unit 7 is electrically connected to the monitoring and control unit to receive discharge control commands sent by the monitoring and control unit.

[0047] The coiled tubing 10 is connected at its end to a bidirectional flushing tool 11 for delivering nitrogen foam fluid to the target formation at the bottom of the well. The coiled tubing 10 is connected to the pumping unit 7 via a fourth pipe 9.

[0048] The bidirectional flushing tool 11 includes: a tool body 111, which has a reversing mechanism 112 inside; an axial injection port 113 located at the front end of the tool body 111; and at least one radial injection port 114 located on the side wall of the tool body 111. The upper end of the tool body 111 is fixedly connected to the end of the coiled tubing 10 by threads or a flange. The reversing mechanism 111 is connected to the axial injection port 113 and the radial injection port 114 respectively through flow channels inside the tool body. When the coiled tubing 10 is lowered and encounters obstruction, the reversing mechanism switches to axial injection mode, causing nitrogen foam fluid to be injected forward from the axial injection port; when the coiled tubing 10 is raised, it switches to radial injection mode, causing nitrogen foam fluid to be injected into the annulus from the radial injection port.

[0049] The monitoring and control unit 12 is electrically connected to the data acquisition and simulation module 1, the foaming agent injection subsystem 2, the nitrogen supply subsystem 3, the foam generator 4, the pumping unit 7, and sensors installed at the wellhead and tubing string. It is used to monitor formation pressure, flow rate, and flowback fluid parameters in real time during construction. Based on the formation pressure monitoring data, it sends control commands to the foaming agent injection subsystem 2 and the nitrogen supply subsystem 4 to adjust the foam density, increasing the foam mass to 0.7-0.9 g / cm³ when crossing lost circulation zones. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3The monitoring and control unit is also used to implement an asymmetric advance-retreat sand flushing strategy for target wells where the vertical depth difference between points A and B is greater than 50m and the horizontal section has an upward-curving structure. After each advance of the coiled tubing a first distance, it is controlled to be raised a second distance, where the first distance is greater than the second distance.

[0050] The monitoring and control unit also includes a construction connection control module for monitoring the volume of the external discharge tank and the unloading distance. The input of the construction connection control module is electrically connected to the liquid level sensor installed on the external discharge tank and the positioning module installed on the transport vehicle, and the output is electrically connected to the pumping unit. When the volume of the external discharge tank is lower than a first threshold or the unloading distance exceeds a second threshold, it issues an early warning signal and adjusts the pumping rate of the pumping unit to maintain construction continuity and avoid construction interruptions and downhole risks caused by poor connection.

[0051] To more clearly and in detail introduce the nitrogen foam fluid sand-carrying return method and system for increased production provided by the embodiments of the present invention, specific embodiments will be described below, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the raw materials and equipment used in the following embodiments are all commercially available products.

[0052] Example 1 This embodiment provides a nitrogen foam fluid sand-carrying and backflow enhancement method, applied to sand flushing operations in oilfield wells. The basic characteristics of the well are as follows: build-up point 2100m, point A 2612m (vertical depth 2426.01m), point B 4130.05m (vertical depth 2358.91m), horizontal section length 1520m, vertical depth difference between points A and B 67.1m, and an upward-curving structure in the horizontal section. This well exhibits both lost circulation and high-pressure zones, resulting in a complex well trajectory with a maximum dogleg angle of 18° / 30m.

[0053] Step S1: Obtain basic data for the target well: Basic data for the oilfield well was obtained, including the horizontal section length of 1520m, vertical depth at point A of 2426.01m, vertical depth at point B of 2358.91m, location of the lost circulation zones (located at 2800-2950m and 3200-3350m), location of the high-pressure zones (located at 3500-3650m), and dogleg data. Pressure data from adjacent wells was also obtained, and the formation pressure of this well was predicted to be 23MPa.

[0054] Step S2: Determine construction parameters through software simulation: Based on the above data, simulation calculations were performed using specialized software. The simulation calculated the frictional resistance at a depth of 4000m for a 6000m coiled tubing to be 32MPa, with an operating pressure of 45MPa. The nitrogen discharge rate was set at 1200Nm. 3The foam-based fluid discharge rate is 300-400 L / min. The minimum settling velocity of sand particles in the nitrogen foam fluid is calculated to be 0.001 m / s. The minimum flow velocity of the nitrogen foam fluid at the bottom of the well is 0.9 m / s, which is greater than the settling velocity of the sand particles, ensuring safe sand carrying.

[0055] Step S3: Generate nitrogen foam fluid on the ground: The base liquid is reclaimed water from oilfield wastewater after sedimentation treatment, with a mineralization of 42,000 mg / L and a suspended solids content of 180 mg / L. A foaming agent is mixed with the base liquid at a ratio of 0.5 wt% to form a foaming aqueous solution. The foaming aqueous solution and nitrogen gas are simultaneously injected at a pressure resistance of 70 MPa and a maximum flow rate of 5 m³ / h. 3 In a foam generator with a speed of [value] / min, forced mixing and shearing are performed on the ground to generate foam with a density of 0.1-0.9 g / cm³. 3 Adjustable nitrogen foam fluid. Testing showed that the generated nitrogen foam fluid had a foaming volume of 580 mL and a half-life of 22 min under a salinity of 42000 mg / L, meeting construction requirements. Simultaneously, 0.1 wt% of a drag-reducing agent was added to the nitrogen foam fluid to reduce tubing friction.

[0056] Step S4: Pump the nitrogen foam fluid into the wellbore through the coiled tubing. The coiled tubing used was 50.8mm in diameter and 6000m in length, with a bidirectional flushing tool connected to the end. The running speed was controlled as follows: 3m / min for the first 50m, 20m / min after 50m past the wellhead, reduced to 8m / min 50m above the build-up point, and further reduced to 4m / min 50m above point A to probe the sand surface. The sand surface was found at 2786m, and this was confirmed by repeated probing three times. The coiled tubing was then raised to 5m above the sand surface, the pump was started, and after circulation was normal, the coiled tubing was lowered at 4m / min for sand flushing. The load was checked every 40m of advance, with load variation controlled within 15kN, while simultaneously raising the tubing to the maximum dogleg position for well flushing until no sand was visible at the outlet before continuing to lower the tubing.

[0057] Step S5: Adjust the foam density according to the formation pressure: During sand flushing, formation pressure is monitored in real time. When crossing lost circulation zones (2800-2950m and 3200-3350m), the foam quality is increased to 0.8g / cm³. 3 High-quality foam is used to temporarily seal the high-permeability layer and prevent leakage of the working fluid. When traversing the high-pressure layer (3500-3650m), the foam quality is reduced to 0.4g / cm³. 3To reduce fluid column pressure and balance formation pressure, an asymmetric advance-retreat sand flushing strategy was adopted due to the greater than 50m vertical depth difference between points A and B and the presence of an upward tilt in the horizontal section: every 12m of coiled tubing advance was followed by a 6m retraction, with the advance distance to retraction distance ratio being 2:1. For well sections with a dogleg greater than 15° / 30m (3200-3350m), the ratio was adjusted to 2:1 and the sand flushing rate was reduced to 2.5m / min.

[0058] Step S6, Return: By utilizing the low density, high viscoelasticity, and temporary plugging properties of nitrogen foam fluid, solid particles and insoluble substances carried by the fluid are returned to the ground.

[0059] Steps S7 to S9, verification after sand flushing: After flushing the sand to the target depth of 4008m, the coiled tubing is pulled up to 15m above the sand surface. The well is then circulated at a flow rate of 350L / min for 25 minutes until the sand content at the inlet and outlet is consistent. The coiled tubing is then pulled back to the wellhead, and the well is shut in and allowed to stand for 4 hours. After the standing period, the coiled tubing is run back in to re-examine the sand surface. The sand surface is located at 4008.5m, with a rise of 0.5m, which is 1m below the preset threshold, indicating that the sand flushing is successful.

[0060] Construction results: In this embodiment, the total sand flushing footage was 1222m (2786-4008m), and the liquid usage was 480m³. 3 7m of mud and sand (including fracturing sand) were flushed out. 3 Wastewater recycling: approximately 700m³ 3 During the operation, the coiled tubing experienced three instances of self-locking, but each time it was successfully released using the axial jet mode of the bidirectional flushing tool, preventing any stuck drill bit incidents. The operating pressure remained stable between 43-47 MPa, within the design limit.

[0061] Example 2 This embodiment is basically the same as Embodiment 1, except that: this embodiment uses a method of replacing the base liquid to reduce friction for a base liquid with high mineralization, rather than adding a drag-reducing agent.

[0062] The base fluid is reclaimed water from oilfield wastewater after sedimentation treatment, with a salinity of 48,000 mg / L and a suspended solids content of 150 mg / L. Considering that high salinity may lead to significant tubing friction, this embodiment replaces the base fluid with slickwater with a viscosity of 5 mPa·s, which is mixed with a foaming agent at a ratio of 0.6 wt% to form a foaming aqueous solution. The foaming aqueous solution and nitrogen gas are simultaneously injected into the foam generating device to generate nitrogen foam fluid on the ground.

[0063] Testing showed that the generated nitrogen foam fluid had a foaming volume of 550 mL and a half-life of 18 min under a salinity of 48000 mg / L. During construction, the simulated friction was 28 MPa, which was about 4 MPa lower than that of the original base fluid. The actual construction pressure was 41 MPa, which was lower than the construction pressure in Example 1, proving that replacing it with slickwater can effectively reduce the tubing friction caused by the high salinity base fluid.

[0064] Example 3 This embodiment is basically the same as Embodiment 1, except that: in this embodiment, the ratio of the asymmetric advance and retreat sand flushing strategy is dynamically adjusted for different horizontal well inclination angle change rates.

[0065] In this embodiment, the target well exhibits a relatively large change rate in inclination angle in the horizontal section, reaching 12° / 30m in the 3000-3200m section and 10° / 30m in the 3400-3600m section. The ratio of the forward distance to the upward distance is dynamically adjusted based on this change rate: in sections with an inclination angle change rate greater than 10° / 30m, the ratio is adjusted to 1.8:1 (9m forward, 5m upward); in sections with an inclination angle change rate less than 5° / 30m, the ratio is adjusted to 2.5:1 (15m forward, 6m upward). Through this dynamic adjustment, the sand flushing efficiency in this embodiment is approximately 15% higher than in Embodiment 1, and the total sand flushing time is shortened to 4 days.

[0066] Comparative Example 1 This comparative example uses a conventional nitrogen foam rinsing method to contrast with Example 1.

[0067] Comparative Example 1 was also applied to the oilfield well in Example 1, but adopted the "downhole natural foaming" method commonly used in the prior art: nitrogen and foaming agent were injected into the well through a tee, causing it to naturally generate foam fluid in the wellbore and formation. During the sand flushing process, an equidistant advance and retreat strategy was adopted, advancing 10m and pulling up 10m, without adjusting the foam density according to the lost circulation zone and high pressure zone, and the end of the coiled tubing was not connected to a bidirectional flushing tool.

[0068] Construction results: Due to the natural formation of foam downhole, the foam quality was unstable, resulting in significant working fluid loss when crossing the lost circulation zone, with a loss volume of 120m³. 3 During the crossing of a high-pressure zone, a well kick occurred due to the failure to adjust the foam density in time, causing the wellhead pressure to surge to 12 MPa, forcing the well to be shut in to reduce pressure. In the 3200-3350m section with a significant dogleg, the coiled tubing became self-locked. Without bidirectional flushing tools to assist in unblocking, the coiled tubing became stuck, ultimately requiring 12 hours of reverse circulation well control operations to free it. The total sand flushing footage reached was only 800m, with 620m of fluid used. 3 3.5m of mud and sand were flushed out. 3The construction period lasted as long as 8 days, and the formation was contaminated due to leakage and well surge.

[0069] Comparative Example 2 This comparative example is basically the same as Example 1, except that: instead of using an asymmetric advance and retreat sand-rushing strategy, a conventional equidistant advance and retreat strategy is used, advancing 10m and rising 10m.

[0070] Construction Results: In the horizontal section with an upward-curving structure (3000-3500m), the equidistant advance / retreat strategy resulted in severe sand fallback, leading to low sand flushing efficiency. On average, three flushing operations were required for every 10m of drilling footage. In the section with a dogleg greater than 15° / 30m (3200-3350m), the measured load change due to sand fallback reached 45kN, exceeding the safety range, resulting in two minor stuck drill incidents. Although these were resolved by moving the tubing string, they severely impacted the construction progress. The total sand flushing footage was 1222m, and the fluid used was 560m³. 3 5.2m of mud and sand were flushed out. 3 The construction period is 6.5 days, which is 1.5 days longer than that of Example 1.

[0071] Comparative Example 3 This comparative example is basically the same as Example 1, except that: the base liquid is untreated oilfield wastewater with a mineralization of 62000 mg / L and a suspended solids content of 350 mg / L. No drag-reducing agent was added, and it was not replaced with slickwater.

[0072] Construction Results: After the foaming agent was mixed with the base liquid, the foaming performance decreased significantly, with a measured foaming volume of only 280 mL and a half-life of 5 min, indicating poor foam stability. During construction, the friction of the tubing increased, with a simulated friction of 38 MPa and an actual construction pressure reaching 52 MPa, close to the equipment's upper limit. When crossing the leakage layer, the unstable foam quality resulted in poor temporary plugging, leading to a leakage of 85 m³. 3 Total sand flushing footage: 1222m; liquid usage: 520m. 3 4.8m of mud and sand were flushed out. 3 The construction period was 6 days, and the high mineralization of the base liquid exacerbated equipment corrosion.

[0073] Comparative Example 4 This comparative example is basically the same as Example 1, except that: no construction connection control module was set up, and the volume of the external discharge tank and the unloading distance were not monitored.

[0074] Construction Results: During the sand flushing process, construction was forced to be interrupted twice due to insufficient capacity of the external discharge tank and a long unloading distance, with each interruption lasting approximately 1.5 hours. During the period when the coiled tubing was stationary in the well, a stuck drill bit occurred once due to sand settling; it was successfully released within one hour using a movable tubing string. The construction period was extended to 6 days, one day longer than in Example 1, and downhole risks were increased.

[0075] The construction effects of Examples 1-3 and Comparative Examples 1-4 are compared in Table 1 below.

[0076] Table 1. Comparison of construction effects between Examples 1-3 and Comparative Examples 1-4

[0077] Comparing Example 1 with Comparative Example 1, it can be seen that the present invention generates high-quality foam through a surface foam generator. Combined with dynamic adjustment of foam density based on formation pressure and the application of a two-way flushing tool, it effectively solves the technical problems of unstable quality of naturally generated foam, coexistence of leakage and well kick, shortening the construction cycle by 37.5%, increasing the amount of mud and sand flushed out by 100%, and eliminating stuck drill accidents. Comparing Example 1 with Comparative Example 2, it can be seen that the present invention adopts an asymmetric advance-retreat flushing strategy for horizontal wells with an upturned structure, effectively preventing sand particles from falling back, improving flushing efficiency, shortening the construction cycle by 23.1%, stabilizing load changes, and avoiding the risk of stuck drill. Comparing Example 1 with Comparative Example 3, it can be seen that the present invention limits performance parameters for high-mineralization base fluids and adds drag-reducing agents, effectively ensuring stable foam quality and construction pressure, avoiding problems of decreased foaming performance and increased tubing friction. Comparing Example 1 with Comparative Example 4, it can be seen that the present invention monitors the volume of the external discharge tank and the unloading distance through a construction connection control module, effectively avoiding construction interruptions, reducing downhole risks, and shortening the construction cycle by 16.7%. Examples 2 and 3 further verify the technical effects of replacing the slick water to reduce friction and dynamically adjusting the asymmetric advance-retreat ratio to improve efficiency, demonstrating the flexibility and adaptability of the technical solution of the present invention.

[0078] Therefore, this invention employs the aforementioned nitrogen foam fluid sand-carrying and return method and system for enhanced production. It generates uniform, controllable, and stable nitrogen foam fluid through a surface foam generator, overcoming the instability of naturally generated downhole foam. In step S5, the foam density is adjusted in real-time according to formation pressure. This increases foam quality to enhance temporary plugging when crossing lost circulation zones and decreases it to balance formation pressure when crossing high-pressure zones, achieving precise control over complex well conditions. A bidirectional flushing tool is connected to the end of the coiled tubing. This tool switches to axial jet mode to flush away sand plugs when the coiled tubing is lowered and to radial jet mode to clean the wellbore when it is pulled up, effectively solving the technical problem of coiled tubing self-locking in long horizontal sections and upturned wells. For target wells with a vertical depth difference of more than 50m between points A and B and an upward-curving structure in the horizontal section, an asymmetric advance-retreat sand flushing strategy is adopted. After each advance of the first distance, the coiled tubing is raised by a second distance. For well sections with a dogleg degree greater than 15° / 30m, the ratio is adjusted to 2:1 and the sand flushing speed is reduced, which overcomes the shortcomings of conventional equidistant advance-retreat, such as low efficiency and easy stuck drill.

[0079] For the base fluid of oilfield produced wastewater, the salinity is limited to no more than 50,000 mg / L, the foaming agent to 0.3-0.8 wt%, the nitrogen foam fluid to have a foaming volume of no less than 500 mL and a half-life of no less than 15 min, and drag-reducing agents are added or slickwater with a viscosity of less than 10 mPa·s is used to effectively reduce the tubing friction caused by high-salinity base fluids and achieve water resource recycling. The construction connection control module monitors the volume of the discharge tank and the unloading distance in real time, and issues an early warning and adjusts the pump discharge rate when it falls below the threshold to avoid construction interruption; the reliability of sand flushing quality is ensured through a re-exploration and verification step after sand flushing.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for increasing production by using nitrogen foam fluid to carry sand back to the reactor, characterized in that, Includes the following steps: S1: Obtain basic data of the target well, including horizontal section length, vertical depth at point A, vertical depth at point B, location of lost flow zone, location of high pressure zone, and dogleg data; S2: Based on the aforementioned basic data, construction parameters are determined through software simulation. These construction parameters include foam density, construction discharge rate, nitrogen discharge rate, and construction pressure. S3: On the ground, the foaming agent is mixed with the base liquid to form a foaming aqueous solution, and the foaming aqueous solution and nitrogen are simultaneously injected into the foam generating device to generate nitrogen foam fluid on the ground through the foam generating device. S4: The generated nitrogen foam fluid is pumped into the wellbore of the target well through a coiled tubing, the end of which is connected to a bidirectional flushing tool; S5: During sand flushing, adjust the foam density based on formation pressure monitoring data, increasing the foam mass to 0.7-0.9 g / cm³ when crossing lost circulation zones. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3 ; S6: Use the nitrogen foam fluid to return the carried solid particles and insoluble substances to the ground.

2. The method for increasing production by using nitrogen foam fluid to carry sand back to its source according to claim 1, characterized in that, The base liquid mentioned in step S3 is reclaimed water from oilfield produced wastewater or backflow fluid after sedimentation treatment. The mineralization of the base liquid does not exceed 50,000 mg / L, and the suspended solids content does not exceed 200 mg / L. The mixing ratio of the foaming agent to the base liquid is 0.3-0.8 wt% of the foaming agent. The nitrogen foam fluid has a foaming volume of not less than 500 mL and a half-life of not less than 15 min under the condition of mineralization of 30000-50000 mg / L.

3. The method for increasing production by using nitrogen foam fluid to carry sand back to its source according to claim 1, characterized in that, In step S4, when the nitrogen foam fluid is pumped into the wellbore of the target well through coiled tubing, a drag-reducing agent is added to the nitrogen foam fluid, or the base fluid is replaced with slickwater with a viscosity of less than 10 mPa·s.

4. The method for increasing production by using nitrogen foam fluid to carry sand back to its source according to claim 1, characterized in that, Step S4 further includes: After the sand surface is detected, the coiled tubing is raised to a preset distance above the sand surface, the pump is started, and after the circulation is normal, the coiled tubing is lowered at a speed of no more than 5m / min to flush the sand. Every 30-50m of advance, the load is checked and the load variation is controlled within 10kN-20kN. At the same time, the well is raised to the maximum dogleg position for well flushing until there is no sand at the outlet before continuing to lower it.

5. The method for increasing production by using nitrogen foam fluid to carry sand back to its source according to claim 4, characterized in that, For target wells with a vertical depth difference of more than 50m between points A and B and an upward-curving structure in the horizontal section, an asymmetric advance-retreat sand flushing strategy is adopted. The asymmetric advance-retreat sand flushing strategy includes: after each advance of the coiled tubing by a first distance, the tubing is raised by a second distance. The first distance is greater than the second distance. The ratio of the first distance to the second distance is dynamically adjusted according to the rate of change of the inclination angle of the horizontal section of the well. The range of the ratio is 1.5:1 to 3:

1. For well sections with a dogleg degree greater than 15° / 30m, the ratio is adjusted to 2:1 and the sand flushing rate is reduced to below 3m / min.

6. The method for increasing production through nitrogen foam fluid carrying sand back discharge according to claim 1, characterized in that, The basic data of the target well obtained in step S1 also includes obtaining the pressure data of the adjacent well and the sand flushing construction data; the construction parameters determined by software simulation in step S2 include: predicting the formation pressure of the target well based on the pressure data of the adjacent well, simulating and calculating the friction and construction pressure when the coiled tubing is run into the target depth, and calculating the minimum settling velocity of sand particles in nitrogen foam fluid, so that the minimum flow velocity of nitrogen foam fluid in the wellbore is greater than the minimum settling velocity.

7. The method for increasing production through nitrogen foam fluid carrying sand back discharge according to claim 1, characterized in that, It also includes verification steps after sand flushing: Step S7: After flushing the sand to the target depth, raise the coiled tubing to 10-20m above the sand surface, and circulate the well at a flow rate of 300-400L / min for more than 20 minutes until the sand content at the inlet and outlet is consistent. Step S8: Pull the coiled tubing to the wellhead and shut the well in for 2-6 hours; Step S9: After the settling period, the coiled tubing is lowered again to re-probe the sand surface. If the sand surface rises above the preset threshold, steps S3 to S6 are repeated to perform additional sand flushing. If the sand surface rises within the preset threshold, the sand flushing is deemed successful.

8. A production enhancement system for nitrogen foam fluid carrying sand back discharge, characterized in that, include: The data acquisition and simulation module acquires the basic data of the target well and determines the construction parameters through software simulation. The basic data includes the horizontal section length, vertical depth at point A, vertical depth at point B, location of the lost flow zone, location of the high pressure zone, and dogleg data. The ground foam generating unit includes a foaming agent injection subsystem, a nitrogen supply subsystem, and a foam generator, which mixes foaming agent, base liquid, and nitrogen on the ground to generate nitrogen foam fluid; wherein, the outlet of the foaming agent injection subsystem is connected to the first inlet of the foam generator through a first pipeline, and the outlet of the nitrogen supply subsystem is connected to the second inlet of the foam generator through a second pipeline. The pumping unit has its inlet connected to the outlet of the foam generator via a third pipeline, and its outlet connected to the inlet of the coiled tubing via a fourth pipeline, injecting the generated nitrogen foam fluid into the well at a set discharge rate. The coiled tubing is connected to a bidirectional flushing tool at its end to deliver nitrogen foam fluid to the target formation at the bottom of the well; the coiled tubing is connected to the pumping unit via a fourth pipeline; The monitoring and control unit is electrically connected to the data acquisition and simulation module, the foaming agent injection subsystem, the nitrogen supply subsystem, the foam generator, the pumping unit, and sensors installed at the wellhead and tubing. It monitors formation pressure, flow rate, and flowback fluid parameters in real time during construction. Based on the formation pressure monitoring data, it sends control commands to the foaming agent injection subsystem and the nitrogen supply subsystem to adjust the foam density, increasing the foam mass to 0.7-0.9 g / cm³ when crossing lost circulation zones. 3 When passing through a high-pressure layer, the foam mass is reduced to 0.3-0.5 g / cm³. 3 ; The monitoring and control unit is also used to implement an asymmetric advance and retreat sand flushing strategy for target wells with a vertical depth difference of more than 50m between points A and B and an upward structure in the horizontal section. After each advance of the coiled tubing by a first distance, it is controlled to be raised by a second distance, where the first distance is greater than the second distance.

9. A nitrogen foam fluid sand-carrying return system for production enhancement according to claim 8, characterized in that, Two-way flushing tools include: The tool body has a reversing mechanism inside; An axial injection nozzle is located at the front end of the tool body; At least one radial injection port is disposed on the side wall of the tool body; The reversing mechanism switches to axial injection mode when the coiled tubing is obstructed during descent and to radial injection mode when the coiled tubing is lifted.

10. A nitrogen foam fluid-based sand-carrying and return system for increased production according to claim 8, characterized in that, The monitoring and control unit also includes a construction connection control module, which monitors the volume of the external discharge tank and the unloading distance. The input end of the construction connection control module is electrically connected to the liquid level sensor installed on the external discharge tank and the positioning module installed on the transport vehicle. The output end is electrically connected to the pumping unit. When the volume of the external discharge tank is lower than the first threshold or the unloading distance exceeds the second threshold, an early warning signal is issued and the pumping rate of the pumping unit is adjusted.

Images