Horizontal well flowback gravel migration simulation experiment system and method

Abstract

The application discloses a horizontal well flowback gravel migration simulation experiment system and method, and belongs to the technical field of petroleum engineering and oil and gas field development, and comprises a visual sand retention unit, a conveying pump, a flowback liquid collecting tank, an automatic sand adding mechanism and a data acquisition system; the data acquisition system comprises an electromagnetic flowmeter, a first pressure gauge, a second pressure gauge, a microwave solid flow sensor and a high-definition camera arranged on one side of the visual sand retention unit; and a scale ruler capable of measuring the internal gravel deposition height is arranged on the visual sand retention unit. The visual sand retention unit can be used for observing the migration and plugging conditions of the gravel, so that the sand carrying effect under different working conditions can be intuitively observed by experimenters. The application establishes a comprehensive dimensionless factor for evaluating the flowback effect based on the gravel flowback efficiency, the wellbore pressure loss and the gravel bed stability, comprehensively judges the flowback effect, and performs grade division on the flowback effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petroleum engineering and oil and gas field development, and particularly relates to a horizontal well flowback gravel migration simulation experiment system and method. BACKGROUND

[0002] In the development of sandstone and conglomerate reservoirs, horizontal wells have become the mainstream development method due to the advantages of expanding the reservoir contact area and improving the recovery rate. However, the sandstone and conglomerate reservoirs generally have the characteristics of loose cementation, strong lithological heterogeneity, and easy sand production of formation sand, so an artificial sand blocking barrier must be constructed through the gravel packing sand control process to ensure long-term stable production of oil wells. The gravel migration and gravel bed accumulation at the bottom of the wellbore frequently occur during the flowback stage, which is a key link connecting well completion and formal production, not only weakening the sand control effect, but also possibly leading to a series of engineering problems such as wellbore blockage and production decline.

[0003] The core task of the flowback stage is to flow back the formation gravel and drilling fluid retained during the well completion process to the wellbore to create conditions for production. However, the sudden drop of the wellbore pressure in this process causes the redistribution of the formation stress, which, combined with the flow characteristics of the horizontal well, directly leads to the gravel accumulation and the formation of the gravel bed. The phenomenon of gravel migration frequently occurs during the flowback stage, and if the gravel accumulation process cannot be improved, the sand control barrier is prone to failure, the gravel bed occupies the space at the bottom of the wellbore, and the fluid flow channel is narrowed, resulting in a significant increase in the along-the-way resistance of the wellbore. Field cases show that when the height of the gravel bed reaches 1 / 3 of the diameter of the wellbore, the pressure loss of the wellbore can increase by more than 50%, and even the pressure balance in the wellbore is destroyed due to the gravel accumulation, thereby causing blowout accidents and directly causing the oil well production to decrease by 20%-30%. The migrated gravel particles move with the fluid and can cause erosion and wear of the downhole pump, valve and other production tools, shorten the service life of the tools, and increase the frequency of workover. According to the statistical data of sandstone and conglomerate oilfields, the average workover period of the wells with gravel migration is shortened by 40% compared with normal wells, and the oil and gas flow resistance increases and the oil well production decreases.

[0004] Therefore, in-depth research on the gravel migration mechanism during the flowback stage, the revelation of the synergy law of stress change and fluid scouring, and the optimization of flowback process parameters have important theoretical value and engineering significance for reducing the risk of gravel bed formation and ensuring the long-term development of sandstone and conglomerate horizontal wells. At present, the industry has alleviated the problem through the development of bypass pipe filling systems and the optimization of sand-carrying fluid formulations, but individualized solutions for complex sandstone and conglomerate reservoirs still need to be further explored. Based on this, the horizontal well flowback gravel migration simulation experiment system and method are used to study the migration characteristics of gravel particles (gravel and formation sand) in the wellbore during the flowback stage, and the system can provide direct basis for the optimization of field mining schemes. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art, and provide a horizontal well flowback gravel migration simulation experiment system.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] The horizontal well flowback gravel migration simulation experiment system comprises a visual sand retention unit for simulating a horizontal wellbore, a delivery pump, a flowback liquid collecting tank, an automatic sand adding mechanism and a data acquisition system.

[0008] The inlet end of the visual sand retention unit is connected to the outlet end of the delivery pump through a liquid inlet pipe, the outlet end of the visual sand retention unit is connected to the flowback liquid collecting tank through a liquid outlet pipe, the liquid outlet pipe is connected to a filtering mechanism in the flowback liquid collecting tank, and the inlet end of the delivery pump is connected to the flowback liquid collecting tank through a liquid inlet branch pipe.

[0009] The discharge outlet of the automatic sand adding mechanism is connected to the inlet end of the visual sand retention unit.

[0010] The data acquisition system comprises an electromagnetic flowmeter arranged on the liquid inlet pipe, a first pressure gauge arranged at the joint of the liquid inlet pipe and the visual sand retention unit, a second pressure gauge arranged at the joint of the liquid outlet pipe and the visual sand retention unit, a microwave solid flow sensor arranged at the discharge outlet of the automatic sand adding mechanism, and a high-definition camera arranged on one side of the visual sand retention unit.

[0011] A scale ruler capable of measuring the internal gravel deposition height is arranged on the visual sand retention unit.

[0012] Preferably, the visual sand retention unit comprises a PMMA (polymethyl methacrylate) tube, and the visual sand retention unit is flange-connected with the liquid inlet pipe and the liquid outlet pipe.

[0013] Preferably, the outlet end of the delivery pump is connected to the flowback liquid collecting tank through a liquid return branch pipe.

[0014] Valves are arranged on the liquid inlet pipe and the liquid return branch pipe.

[0015] Preferably, the automatic sand adding mechanism comprises a horizontal material silo, a feeding port is arranged on the upper side of the horizontal material silo, and a discharge outlet is arranged on the lower side of the horizontal material silo.

[0016] A conveying shaft is coaxially arranged in the horizontal material silo, helical conveying blades are arranged on the conveying shaft, and the axial ends of the conveying shaft are sealingly and rotatably connected to the horizontal material silo.

[0017] One axial end of the conveying shaft is connected to a conveying motor.

[0018] Preferably, the shaft of the conveying shaft and the output shaft of the conveying motor are coaxially fixedly connected through a shaft coupling.

[0019] Preferably, the horizontal material silo comprises a main cylinder in a cylindrical structure, bearing housings are coaxially fixedly arranged at the axial two ends of the main cylinder, and the two ends of the conveying shaft pass through the corresponding bearing housings.

[0020] The bearing housings and the conveying shaft are coaxially arranged in sequence along the axial direction and are provided with a sealing ring, a spring, a positioning sleeve, a bearing and a bearing end cover.

[0021] The conveying shaft is rotationally matched with the bearing housing through the bearing.

[0022] The bearing end cover is fixedly arranged at one end of the bearing housing away from the main cylinder and is pressed against the outer ring of the corresponding bearing at the inner end, one end of the positioning sleeve is pressed against the outer ring of the corresponding bearing, the other end of the spring is abutted with one end of the sealing ring, and the other end of the sealing ring is abutted with the stepped end face of the inner hole of the bearing housing.

[0023] The application also provides a horizontal well flowback gravel migration simulation experiment method.

[0024] The horizontal well flowback gravel migration simulation experiment method is implemented based on a horizontal well flowback gravel migration simulation experiment system and comprises the following steps.

[0025] Step 1: determining core experiment parameters.

[0026] The core experiment parameters include flowback fluid flow rate , flowback fluid viscosity , flowback fluid density , gravel particle size, gravel reference volume fraction , and sand adding rate .

[0027] The gravel reference volume fraction is the ratio of the volume of the gravel added into the visual sand retention unit to the total volume of the flow passage inside the visual sand retention unit during the experiment process.

[0028] Step 2: forming variable combinations of the core experiment parameters, determining the specific values of each variable in each experiment variable combination as experiment input data, and numbering each set of experiment input data, wherein the total number of experiment input data is N.

[0029] Step 3: let i=1, i represents the serial number of the experiment input data.

[0030] Step 4, preparing experimental flowback fluid consistent with the viscosity and density of the flowback fluid in the i-th set of experimental input data; preparing quartz sand as experimental gravel consistent with the grain size and reference volume fraction of the gravel in the i-th set of experimental input data;

[0031] Step 5, preparing quartz sand consistent with the grain size of the experimental gravel, and obtaining the critical start-up flow rate of the gravel through experiments ;

[0032] Step 6, obtaining the volume of the experimental gravel according to the reference volume fraction of the experimental gravel and the total volume of the flow channel inside the visual sand retention unit, and pouring the corresponding volume of the experimental gravel into the automatic sand adding mechanism;

[0033] injecting the experimental flowback fluid into the flowback fluid collection tank;

[0034] starting the delivery pump to continuously introduce the experimental flowback fluid into the visual sand retention unit, and adjusting the displacement of the delivery pump so that the measurement data of the electromagnetic flowmeter reaches the flow rate value of the flowback fluid in the i-th set of experimental input data;

[0035] When there is no gas bubble in the visual sand retention unit, starting the automatic sand adding mechanism to inject the experimental gravel into the visual sand retention unit, and the measurement data of the microwave solid flow sensor reaches the sanding rate value in the i-th set of experimental input data;

[0036] starting timing from the start of the automatic sand adding mechanism, and ending timing when the gravel deposition in the visual sand retention unit is stable, and recording the time when the gravel bed reaches a stable state ;

[0037] recording the measurement values of the first pressure gauge and the second pressure gauge at the timing end;

[0038] Step 7, comprehensively judging the flowback effect corresponding to the i-th set of experimental input data based on the gravel flowback efficiency, the wellbore pressure loss, and the gravel bed stability;

[0039] Step 8, cleaning the experimental flowback fluid and the experimental gravel in the experimental system;

[0040] Step 9, if i

[0041] Preferably, the step 5 comprises the following sub-steps:

[0042] Step 51, weighing 50g of quartz sand consistent with the grain size of the experimental gravel, pouring the quartz sand into the visual sand retention unit from the inlet end of the visual sand retention unit, and knocking the pipe wall of the visual sand retention unit to make the quartz sand deposit at the bottom of the pipe to form a flat sand layer;

[0043] Step 52, inject experimental flowback fluid into the flowback fluid collection tank, start the delivery pump to flow experimental flowback fluid into the visual sand retention unit at the minimum displacement;

[0044] Then gradually increase the delivery pump displacement by 0.5 L / min, and after each increase, stabilize for 5 min, and observe the gravel state in the visual sand retention unit. When the sand layer edge begins to show particle rolling or the whole sand layer appears to be cracked, record the measurement data of the electromagnetic flowmeter , the critical start-up flow rate of gravel , wherein is the inner diameter of the visual sand retention unit;

[0045] Step 53, clean up the experimental flowback fluid and experimental gravel in the experimental system.

[0046] Preferably, the step 7 comprises the following sub-steps:

[0047] Step 71, determine the gravel flowback efficiency dimensionless factor :

[0048] ;

[0049] wherein, wherein is the experimental gravel volume flow rate recovered in the post-experiment flowback fluid collection tank, , is the volume of the experimental gravel after drying recovered in the post-experiment flowback fluid collection tank; is the experimental gravel volume flow rate injected by the automatic sand injection mechanism, ; is the flowback fluid density, is the gravel density; is the flowback fluid actual velocity, = , is the flowback fluid flow rate;

[0050] Determine the wellbore pressure loss dimensionless factor :

[0051] ;

[0052] wherein, is the actual pressure loss along the visual sand retention unit, and is the difference between the measurement value of the first pressure gauge and the measurement value of the second pressure gauge at the end of each experiment; is the theoretical value of the pure liquid phase pressure loss, which is calculated by the formula , is the experimental flowback fluid viscosity, is the horizontal length of the visual sand retention unit; is the viscosity of water; is the gravel volume fraction, ;

[0053] Non-dimensional factor of gravel bed stability :

[0054] ;

[0055] wherein, is the maximum height of the gravel bed when the gravel deposition is stable, is the experimental calibration time;

[0056] Step 72, establishing a comprehensive non-dimensional factor for evaluating the flowback effect :

[0057] ;

[0058] ; ; ;

[0059] wherein, the non-dimensional factor of the gravel flowback efficiency is a positive factor, and is in the range of [0.3, 0.8], ; the non-dimensional factor of the wellbore pressure loss is a negative factor, and is in the range of [1, 3], ; the non-dimensional factor of the gravel bed stability is a negative factor, and is in the range of [0.3, 1], ;

[0060] Step 73, comprehensively judging the flowback effect according to the numerical range of the non-dimensional factor .

[0061] Preferably, the step 73 is specifically:

[0062] when , the level of the flowback effect is excellent;

[0063] when , the level of the flowback effect is good;

[0064] when , the level of the flowback effect is medium;

[0065] when , the level of the flowback effect is qualified;

[0066] when , the level of the flowback effect is unqualified.

[0067] The beneficial effects of the present application are:

[0068] The present application provides a horizontal well flowback gravel migration simulation experiment system and method for studying the migration characteristics of gravel particles (gravel, formation sand) in the wellbore during the flowback stage. The visual sand retention unit can observe the migration and plugging of the gravel, and the gravel flowback law can be studied more truly and effectively. The automatic sand adding mechanism in the present application can simulate the characteristics of continuous and pulse sand discharge, and provides a systematic experimental research means for the optimization of flowback technology under complex sand discharge conditions of oil and gas wells. Based on the gravel flowback efficiency, wellbore pressure loss and gravel bed stability, a comprehensive dimensionless factor for evaluating the flowback effect is established. Based on the numerical range of the dimensionless factor , the flowback effect is comprehensively judged, and the flowback effect is graded, which can provide a direct basis for the optimization of field production schemes. BRIEF DESCRIPTION OF DRAWINGS

[0069] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation on the present application.

[0070] Figure 1 is a connection schematic diagram of the horizontal well flowback gravel migration simulation experiment system of the present application;

[0071] Figure 2 is a structural schematic diagram of the automatic sand adding mechanism in the present application;

[0072] Figure 3 is a schematic diagram of the internal structure of the horizontal material silo in the present application;

[0073] Figure 4 is a partial enlarged view of A in Figure 3 ;

[0074] Among them:

[0075] 1, visual sand retention unit; 11, liquid inlet pipe; 12, liquid outlet pipe; 13, liquid inlet branch pipe; 14, liquid return branch pipe; 2, conveying pump; 3, flowback liquid collection tank; 4, automatic sand adding mechanism; 41, horizontal material silo; 411, bearing seat; 412, sealing ring; 413, spring; 414, positioning sleeve; 415, bearing; 416, bearing end cover; 42, feeding port; 43, discharging port; 44, conveying shaft; 45, spiral conveying blade; 46, conveying motor; 47, shaft coupling; 5, electromagnetic flowmeter; 6, first pressure gauge; 7, second pressure gauge; 8, high-definition camera. DETAILED DESCRIPTION

[0076] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0077] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0078] In this invention, terms such as "upper," "lower," "bottom," and "top" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0079] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0080] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0081] Example 1:

[0082] like Figures 1-4 As shown, the horizontal well runoff gravel transport simulation experimental system includes a visualization sand retention unit 1 for simulating a horizontal wellbore, a delivery pump 2, a runoff liquid collection tank 3, an automatic sand adding mechanism 4, and a data acquisition system.

[0083] The inlet end of the visual sand retention unit 1 is connected to the outlet end of the conveying pump 2 through the liquid inlet pipe 11. The outlet end of the visual sand retention unit 1 is connected to the return liquid collection tank 3 through the liquid outlet pipe 12. The liquid outlet pipe 12 is connected to the filter mechanism in the return liquid collection tank 3 to filter and intercept the sand particles in the liquid outlet pipe 12. The filter mechanism is existing technology, and its specific implementation structure will not be described in detail here. The inlet end of the conveying pump 2 is connected to the return liquid collection tank 3 through the liquid inlet branch pipe 13.

[0084] The discharge port 43 of the automatic sand feeding mechanism 4 is connected to the inlet end of the visual sand retention unit 1;

[0085] The data acquisition system includes an electromagnetic flow meter 5 installed on the inlet pipe 11, a first pressure gauge 6 installed at the junction of the inlet pipe 11 and the visual sand retention unit 1, a second pressure gauge 7 installed at the junction of the outlet pipe 12 and the visual sand retention unit 1, a microwave solid flow sensor installed at the outlet 43 of the automatic sand adding mechanism 4, and a high-definition camera 8 installed on one side of the visual sand retention unit 1.

[0086] The visualization sand retention unit 1 is equipped with a scale that can measure the height of internal gravel deposition.

[0087] Preferably, the visualization sand retention unit 1 includes an acrylic plexiglass tube, and the visualization sand retention unit 1 is connected to the inlet pipe 11 and the outlet pipe 12 by flanges.

[0088] Specifically, a support assembly is built at the bottom of the acrylic tube to ensure that the acrylic tube is in a horizontal and stable state.

[0089] Preferably, the outlet end of the delivery pump 2 is connected to the return liquid collection tank 3 via a return branch pipe 14;

[0090] Valves are installed on both the inlet pipe 11 and the return branch pipe 14.

[0091] Preferably, the automatic sand feeding mechanism 4 includes a horizontal silo 41, with a feed inlet 42 on the upper part of one side of the horizontal silo 41 and a discharge outlet 43 on the lower part of one side of the horizontal silo 41.

[0092] The horizontal silo 41 has a conveying shaft 44 coaxially arranged inside, and the conveying shaft 44 is provided with spiral conveying blades 45. The two ends of the conveying shaft 44 are sealed and rotated with the horizontal silo 41.

[0093] One axial end of the conveying shaft 44 is adapted to be connected to the conveying motor 46.

[0094] Preferably, one axial end of the conveying shaft 44 is coaxially fixedly connected to the output shaft of the conveying motor 46 via a coupling 47.

[0095] Preferably, the horizontal silo 41 includes a main cylinder with a cylindrical structure, and bearing seats 411 are coaxially fixed at both ends of the main cylinder, and the two ends of the conveying shaft 44 pass through the corresponding bearing seats 411.

[0096] A sealing ring 412, a spring 413, a positioning sleeve 414, a bearing 415, and a bearing end cover 416 are coaxially arranged between the bearing housing 411 and the conveying shaft 44 along the axial direction.

[0097] The conveying shaft 44 is rotatably coupled to the bearing seat 411 via the bearing 415;

[0098] The bearing end cap 416 is fixedly installed in the bearing seat 411 at one end away from the main cylinder, and its inner end presses against the outer ring of the corresponding bearing 415. One axial end of the positioning sleeve 414 presses against the outer ring of the corresponding bearing 415, and the other axial end abuts against one end of the spring 413. The other end of the spring 413 abuts against one end of the sealing ring 412, and the other end of the sealing ring 412 abuts against the stepped end face of the inner hole of the bearing seat 411.

[0099] During installation, first, the sealing ring 412 is installed to the innermost side of the bearing housing 411, and a preload is applied by the spring 413. Second, a positioning sleeve 414 is installed between the bearing 415 and the spring 413. One end of the positioning sleeve 414 abuts against the spring 413, and the other end presses against the outer ring of the bearing 415. Finally, the bearing end cover 416 is installed so that it fits against the outer ring of the bearing 415 and is fastened to the bearing housing 411 with screws to complete the positioning.

[0100] Example 2:

[0101] The horizontal well flowback gravel migration simulation experiment method, based on the horizontal well flowback gravel migration simulation experiment system in Example 1, includes the following steps:

[0102] Step 1: Determine the core experimental parameters;

[0103] The core experimental parameters include the flow rate of the drain fluid. , backflow fluid viscosity , backflow liquid density Gravel particle size, gravel reference volume fraction Sand addition rate ;

[0104] Among them, gravel baseline volume fraction The ratio of the volume of gravel added to the visual sand retention unit 1 during the experiment to the total flow volume inside the visual sand retention unit 1;

[0105] Step 2: The core parameters of each experiment are combined into variables. The specific values ​​of each variable in each experimental variable combination are determined as experimental input data, and each group of experimental input data is numbered. The total number of experimental input data is N.

[0106] Step 3, let i=1, where i represents the sequence number of the experimental input data;

[0107] Step 4: Prepare experimental backflow solution with the same viscosity and density values ​​as those in the i-th experimental input data. Specifically, use water, hydroxypropyl guar gum, and potassium chloride to prepare the experimental backflow solution; prepare quartz sand with the same gravel size and gravel reference volume fraction values ​​as those in the i-th experimental input data as experimental gravel.

[0108] Step 5: Prepare quartz sand with the same particle size as the experimental gravel, and obtain the critical starting flow velocity of the gravel through experiments. ;

[0109] Step 6: Based on the gravel baseline volume fraction value and the total flow volume inside the visualized sand retention unit 1, obtain the volume of the experimental gravel, measure the corresponding volume of experimental gravel and pour it into the automatic sand adding mechanism 4.

[0110] Inject the experimental backflow liquid into the backflow liquid collection tank 3;

[0111] Start the transfer pump 2 and continuously pump the experimental backflow liquid into the visualization sand retention unit 1. Adjust the discharge rate of the transfer pump 2 so that the measurement data of the electromagnetic flowmeter 5 reaches the backflow liquid flow rate value in the i-th set of experimental input data.

[0112] Once there are no more air bubbles in the visual sand retention unit 1, the automatic sand adding mechanism 4 is activated to inject experimental gravel into the visual sand retention unit 1. The measurement data of the microwave solid flow sensor reaches the sand adding rate value in the i-th set of experimental input data.

[0113] Timing begins when the automatic sand-adding mechanism 4 is activated and ends when the gravel deposition in the visualized sand-retention unit 1 stabilizes, recording the time it takes for the gravel bed to reach a stable state. Gravel depositional stability refers to a gravel bed height change of ≤1mm within 5 minutes.

[0114] Record the measured values ​​of the first pressure gauge 6 and the second pressure gauge 7 at the end of the timing.

[0115] Step 7: Based on gravel runoff efficiency, wellbore pressure loss, and gravel bed stability, comprehensively judge the runoff effect of the corresponding i-th set of experimental input data;

[0116] Step 8: Clean the experimental backflow solution and experimental gravel from the experimental system;

[0117] Step 9: If i < N, let i = i + 1 and proceed to step 4; otherwise, the experiment ends.

[0118] Preferably, step 5 includes the following sub-steps:

[0119] Step 51: Weigh 50g of quartz sand with the same particle size as the experimental gravel, pour it into the visual sand retention unit 1 from the inlet end of the visual sand retention unit 1, and tap the tube wall of the visual sand retention unit 1 to make the quartz sand deposit at the bottom of the tube to form a flat sand layer.

[0120] Step 52: Inject experimental backflow liquid into backflow liquid collection tank 3, start transfer pump 2, and introduce experimental backflow liquid into visual sand retention unit 1 at minimum discharge rate;

[0121] Then, gradually increase the discharge rate of the delivery pump 2 in increments of 0.5 L / min. After each increase, run the pump stably for 5 minutes and observe the gravel condition within the visual sand retention unit 1. When particle rolling begins to appear at the edge of the sand layer or cracks appear throughout the sand layer, record the measurement data from the electromagnetic flowmeter 5. Gravel critical start-up velocity ,in To visualize the inner diameter of sand-trapping unit 1;

[0122] Step 53: Clean the experimental backflow solution and experimental gravel from the experimental system.

[0123] Preferably, step 7 includes the following sub-steps:

[0124] Step 71: Determine the dimensionless factor of gravel return efficiency. :

[0125] ;

[0126] Among them, This refers to the volumetric flow rate of the experimental gravel recovered in the return liquid collection tank 3 after the experiment. , The volume of the experimental gravel recovered in the post-experiment return liquid collection tank 3 after drying is shown. The volumetric flow rate of experimental gravel injected by the automatic sand-adding mechanism 4. ; For the density of the backflow liquid, Density of gravel; The actual velocity of the backflow liquid. = , This refers to the flow rate of the backflow fluid.

[0127] Determine the dimensionless factor of wellbore pressure loss :

[0128] ;

[0129] in, To visualize the actual pressure loss along the sand retention unit 1, the difference between the measured value of the first pressure gauge 6 and the measured value of the second pressure gauge 7 at the end of each experimental timing is used. The theoretical value of pressure loss in the pure liquid phase is given by the formula. Calculations show that To test the viscosity of the reflux liquid, To visualize the horizontal length of sand-retaining unit 1; The viscosity of water; This represents the volume fraction of gravel. In this invention, all viscosities are those at 20°C.

[0130] Determine the dimensionless factor for gravel bed stability :

[0131] ;

[0132] in, This represents the maximum height of the gravel bed when gravel deposition is stable. For experimental calibration time;

[0133] Step 72: Establish a comprehensive dimensionless factor for evaluating the effect of return flow. :

[0134] ;

[0135] ; ; ;

[0136] Among them, the gravel backflow efficiency is a dimensionless factor. It is a positive factor, and Between [0.3, 0.8], ; Dimensionless factor of wellbore pressure loss It is a negative factor, and Within the range [1, 3], ; Dimensionless factor for gravel bed stability It is a negative factor, and Between [0.3, 1], ;in , , The numerical range is determined by the field data;

[0137] Step 73, based on the dimensionless factor The numerical range is used to comprehensively judge the effect of the back-row.

[0138] Preferably, step 73 specifically comprises:

[0139] when The backflow effect is rated as excellent, indicating that when using the input data of this set of experiments for backflow experiments, the sand carrying efficiency is high, the pressure loss is small, and there is no risk of siltation.

[0140] when The backflow effect was rated as good, indicating that when using the experimental input data of this set for backflow experiments, the sand carrying efficiency was high, the pressure loss was controllable, and the risk of siltation was low.

[0141] when The backflow effect is rated as medium, indicating that when using this set of experimental input data for backflow experiments, the sand carrying efficiency meets the standard, the pressure loss is medium, and the risk of siltation is medium.

[0142] when The backflow effect is rated as qualified, indicating that when using the experimental input data of this set for the backflow experiment, the sand carrying efficiency is low, the pressure loss is high, and the risk of siltation is high.

[0143] when The backflow effect was deemed unqualified, indicating that the sand carrying efficiency was very low, the pressure loss exceeded the safe range, and the siltation risk exceeded the safe range when using the experimental input data for the backflow experiment, and the design values ​​of each parameter were unreasonable.

[0144] To verify the comprehensive dimensionless factor used in this application to evaluate the effect of return discharge... The reasonableness of the calculation will be determined by the method used in this application. The experimental parameters were compared with the actual flowback effects of wells A and B in the field. Based on the similarity criterion between the inner diameter and length of the visualized sand-holding unit 1 in the experimental system and the inner diameter and length of the horizontal well in the field, the flowback fluid flow rate was determined by the flowback fluid flow rate in the field, and the sand-addition rate was determined by the sand-addition rate in the field. All other parameters were consistent with those in the field. The experimental parameter values ​​and the field parameter values ​​for well A are shown in Table 1, and the experimental parameter values ​​and the field parameter values ​​for well B are shown in Table 2.

[0145] Table 1. Experimental parameter values ​​and field parameter values ​​for Well A

[0146]

[0147] After conducting experiments based on the experimental parameters in Table 1, the critical starting velocity for gravel was determined. It is 0.72 m / s; It is 0.275 MPa; It is 0.018 m; It is 1680s. Calculations show that... The value was 0.95, and the flowback effect was rated as excellent. When well A flowed back based on the field parameters in Table 1, the field monitoring showed a gravel flowback efficiency of 86%, a wellbore pressure loss of 0.14 MPa, and no gravel bed accumulation, consistent with the experimental results. The evaluation result of 0.95 is highly consistent, demonstrating the comprehensive dimensionless factor used in this application to evaluate the effect of return rejection. The rationality of it.

[0148] Table 2. Experimental parameter values ​​and field parameter values ​​for Well B

[0149]

[0150] After conducting experiments based on the experimental parameters in Table 2, the critical starting velocity for gravel was determined. It is 1.15 m / s; It is 0.285 MPa; It is 0.068 m; It is 2700. Calculations show that... The value was 0.35, indicating that the gravel return efficiency was unqualified. However, when well B performed gravel return based on the field parameters in Table 2, the field monitoring showed a gravel return efficiency of 39%, a wellbore pressure loss of 1.1 MPa, and a risk of sedimentation, which is consistent with the experimental results. The evaluation result of 0.35 is highly consistent, demonstrating the comprehensive dimensionless factor used in this application to evaluate the effect of rejection. The rationality of it.

[0151] This invention provides a simulation experimental system and method for gravel migration during horizontal well flowback, used to study the migration characteristics of gravel particles (gravel and formation sand) within the wellbore during the flowback stage. The visualized sand-holding unit 1 allows observation of gravel migration and blockage, enabling more realistic and effective research on gravel flowback patterns and facilitating intuitive observation of sand-carrying effects under different operating conditions. The automatic sand-adding mechanism 4 in this invention can simulate continuous and pulsed sand production characteristics, providing a systematic experimental research method for optimizing flowback processes under complex sand production conditions in oil and gas wells. Based on gravel flowback efficiency, wellbore pressure loss, and gravel bed stability, this invention establishes a comprehensive dimensionless factor for evaluating flowback effectiveness. Based on dimensionless factors The numerical range of the data, combined with a comprehensive assessment of the backflow effect and the classification of the backflow effect levels, can provide a direct basis for optimizing on-site mining plans.

[0152] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they are not intended to limit the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A simulation experiment method for gravel migration during horizontal well flowback, implemented based on a simulation experiment system for gravel migration during horizontal well flowback, characterized in that... The horizontal well flowback gravel transport simulation experimental system includes a visualization sand retention unit to simulate the horizontal wellbore, a delivery pump, a flowback fluid collection tank, an automatic sand addition mechanism, and a data acquisition system; The inlet end of the visual sand retention unit is connected to the outlet end of the delivery pump through an inlet pipe. The outlet end of the visual sand retention unit is connected to the return liquid collection box through an outlet pipe. The outlet pipe is connected to the filter mechanism inside the return liquid collection box. The inlet end of the delivery pump is connected to the return liquid collection box through an inlet branch pipe. The discharge port of the automatic sand feeding mechanism is connected to the inlet end of the visual sand retention unit; The data acquisition system includes an electromagnetic flow meter installed on the inlet pipe, a first pressure gauge installed at the junction of the inlet pipe and the visual sand retention unit, a second pressure gauge installed at the junction of the outlet pipe and the visual sand retention unit, a microwave solid flow sensor installed at the outlet of the automatic sand adding mechanism, and a high-definition camera installed on one side of the visual sand retention unit. The visualization sand-retention unit is equipped with a scale that can measure the height of internal gravel deposition. The experimental method includes the following steps: Step 1: Determine the core experimental parameters; The core experimental parameters include the flow rate of the drain fluid. , backflow fluid viscosity , backflow liquid density Gravel particle size, gravel reference volume fraction Sand addition rate ; Among them, gravel baseline volume fraction This is the ratio of the volume of gravel added to the visualized sand-retention unit during the experiment to the total flow volume inside the visualized sand-retention unit; Step 2: The core parameters of each experiment are combined into variables. The specific values ​​of each variable in each experimental variable combination are determined as experimental input data, and each group of experimental input data is numbered. The total number of experimental input data is N. Step 3, let i=1, where i represents the sequence number of the experimental input data; Step 4: Prepare experimental backflow solution with the same viscosity and density values ​​as those in the i-th experimental input data; prepare quartz sand with the same gravel size and gravel reference volume fraction values ​​as those in the i-th experimental input data as experimental gravel. Step 5: Prepare quartz sand with the same particle size as the experimental gravel, and obtain the critical starting flow velocity of the gravel through experiments. ; Step 6: Based on the gravel baseline volume fraction value and the total flow volume inside the visualized sand retention unit, obtain the volume of the experimental gravel, measure the corresponding volume of experimental gravel and pour it into the automatic sand feeding mechanism. Inject the experimental drain fluid into the drain fluid collection tank; Start the delivery pump and continuously flow the experimental backflow liquid into the visualized sand retention unit. Adjust the flow rate of the delivery pump so that the measurement data of the electromagnetic flowmeter reaches the backflow liquid flow rate value in the i-th set of experimental input data. Once there are no more air bubbles in the visualized sand retention unit, the automatic sand adding mechanism is activated to inject experimental gravel into the visualized sand retention unit. The measurement data from the microwave solid flow sensor reaches the sand adding rate value in the i-th set of experimental input data. Timing begins when the automatic sand-addition mechanism starts and ends when the gravel deposition within the visualized sand-retention unit stabilizes, recording the time it takes for the gravel bed to reach a stable state. ; Record the measured values ​​of the first pressure gauge and the second pressure gauge at the end of the timing. Step 7: Based on gravel runoff efficiency, wellbore pressure loss, and gravel bed stability, comprehensively judge the runoff effect of the corresponding i-th set of experimental input data; Step 8: Clean the experimental backflow solution and experimental gravel from the experimental system; Step 9: If i < N, let i = i + 1 and proceed to step 4; otherwise, the experiment ends. Step 7 includes the following sub-steps: Step 71: Determine the dimensionless factor of gravel return efficiency. : ； Among them, This refers to the volumetric flow rate of the experimental gravel recovered in the return liquid collection tank after the experiment. , This refers to the volume of the experimental gravel recovered from the post-experiment return liquid collection tank after drying. The volumetric flow rate of experimental gravel injected into the automatic sand-feeding mechanism. ; For the density of the backflow liquid, Density of gravel; The actual velocity of the backflow liquid. = , For the backflow fluid flow rate, To visualize the inner diameter of the sand-trapping unit; Determine the dimensionless factor of wellbore pressure loss : ； in, To visualize the actual pressure loss along the sand-holding unit, the difference between the measured values ​​of the first pressure gauge and the second pressure gauge at the end of each experimental timing is used. The theoretical value of pressure loss in the pure liquid phase is given by the formula. Calculations show that To test the viscosity of the reflux liquid, To visualize the horizontal length of the sand-retention unit, To visualize the inner diameter of the sand-trapping unit; The viscosity of water; This represents the volume fraction of gravel. ; Determine the dimensionless factor for gravel bed stability : ； in, This represents the maximum height of the gravel bed when gravel deposition is stable. To visualize the inner diameter of the sand-trapping unit, For experimental calibration time; Step 72: Establish a comprehensive dimensionless factor for evaluating the effect of return flow. : ； ； ； ； Among them, the gravel backflow efficiency is a dimensionless factor. It is a positive factor, and Between [0.3, 0.8], ; Dimensionless factor of wellbore pressure loss It is a negative factor, and Within the range [1, 3], ; Dimensionless factor for gravel bed stability It is a negative factor, and Between [0.3, 1], ; Step 73, based on the dimensionless factor The numerical range is used to comprehensively judge the effect of the back-row.

2. The horizontal well gravel migration simulation experimental method as described in claim 1, characterized in that, The visualization sand retention unit includes an acrylic glass tube, and the visualization sand retention unit is connected to the inlet pipe and the outlet pipe by flanges.

3. The horizontal well gravel migration simulation experimental method as described in claim 1, characterized in that, The outlet end of the delivery pump is connected to the return liquid collection tank via a return branch pipe. Valves are installed on both the inlet pipe and the return branch pipe.

4. The horizontal well gravel migration simulation experimental method as described in claim 1, characterized in that, The automatic sand feeding mechanism includes a horizontal silo, with a feed inlet on the upper part of one side of the horizontal silo and a discharge outlet on the lower part of one side of the horizontal silo. The horizontal silo has a conveying shaft coaxially arranged inside, and the conveying shaft is equipped with spiral conveying blades. The two ends of the conveying shaft are sealed and rotated with the horizontal silo. One axial end of the conveyor shaft is adapted to be connected to the conveyor motor.

5. The horizontal well gravel migration simulation experimental method as described in claim 4, characterized in that, One axial end of the conveying shaft is coaxially and fixedly connected to the output shaft of the conveying motor via a coupling.

6. The horizontal well gravel migration simulation experimental method as described in claim 4, characterized in that, The horizontal silo includes a main cylinder with a cylindrical structure. Bearing seats are coaxially fixed at both ends of the main cylinder, and the two ends of the conveying shaft pass through the corresponding bearing seats. A sealing ring, a spring, a positioning sleeve, a bearing, and a bearing end cap are coaxially arranged between the bearing housing and the conveying shaft in sequence along the axial direction. The conveyor shaft is rotatably coupled to the bearing housing via a bearing; The bearing end cap is fixedly installed in the bearing housing at one end away from the main cylinder, and its inner end presses against the outer ring of the corresponding bearing. One axial end of the positioning sleeve presses against the outer ring of the corresponding bearing, and the other axial end abuts against one end of the spring. The other end of the spring abuts against one end of the sealing ring, and the other end of the sealing ring abuts against the stepped end face of the inner hole of the bearing housing.

7. The horizontal well gravel migration simulation experimental method as described in claim 1, characterized in that, Step 5 includes the following sub-steps: Step 51: Weigh 50g of quartz sand with the same particle size as the experimental gravel, pour it into the visual sand retention unit from the inlet end, and tap the tube wall of the visual sand retention unit to make the quartz sand deposit at the bottom of the tube to form a flat sand layer. Step 52: Inject the experimental backflow liquid into the backflow liquid collection tank, start the delivery pump, and introduce the experimental backflow liquid into the visual sand retention unit at the minimum discharge rate; Then, gradually increase the pump flow rate in increments of 0.5 L / min, and run the pump stably for 5 minutes after each increase. Observe the gravel condition within the visualized sand retention unit. When particle rolling begins to appear at the edge of the sand layer or cracks appear throughout the sand layer, record the measurement data from the electromagnetic flowmeter. Gravel critical starting velocity ,in To visualize the inner diameter of the sand-trapping unit; Step 53: Clean the experimental backflow solution and experimental gravel from the experimental system.

8. The horizontal well gravel migration simulation experimental method as described in claim 1, characterized in that, Step 73 specifically involves: when The return-to-work effect is rated as excellent; when The return-to-work effect is rated as good; when The level of the backflow effect is medium; when The return-to-work effect is rated as qualified; when The return process was deemed unsatisfactory.

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