A visualization apparatus and method for simulating deposition of solid phase in a waxy crude oil wellbore flow

Abstract

This invention belongs to the technical field of experimental equipment for oil and gas field development engineering, specifically relating to a visualization device and method for simulating solid phase deposition in the flow of waxy crude oil in a wellbore. This invention connects two or more wellbore simulation units in series to form a wellbore flow simulation system. A coiled section and a sapphire glass visible section are connected in series and placed within a visible temperature control device, enabling the simulation of temperatures at different locations in the wellbore. Furthermore, the sapphire glass visible section can be removed entirely. This invention is simple to operate and can realistically simulate the solid phase deposition behavior of crude oil on the metal wellbore wall. It solves the problems of existing visualization devices being unable to handle high-pressure conditions and accurately reproduce the actual flow environment in the wellbore, and also better addresses the issue of existing devices being unable to achieve in-situ sampling while maintaining the integrity of the wax crystal microstructure.

Description

Technical Field

[0001] This invention belongs to the technical field of experimental equipment for oil and gas field development engineering, and specifically relates to a visualization device and method for simulating solid phase deposition in the wellbore flow of waxy crude oil. Background Technology

[0002] As my country's oil and gas exploration and development continues to advance into deeper and ultra-deep reservoirs, the types of resources encountered are becoming increasingly complex. Deep and ultra-deep reservoirs contain a high proportion of oil and gas resources with high wax and asphaltene content, presenting unique challenges to their extraction. In the original high-temperature and high-pressure reservoir conditions, these oil and gas typically exist in a dissolved state, containing heavy components such as wax and asphaltene. However, during the process of being lifted to the surface, as temperature and pressure continuously decrease, these components gradually reach a supersaturated state, precipitating from the crude oil and forming solid particles. Under the influence of flow shear forces and intermolecular forces, the initial precipitates collide and aggregate, eventually adhering and depositing on the inner wall of the tubing. This deposition process continuously reduces the effective cross-sectional area of ​​the oil and gas flow channel, leading to a sharp, nonlinear increase in wellbore flow resistance. This, in turn, causes increased production pressure differentials, a significant decrease in production, or drastic fluctuations, making it difficult to achieve the goal of efficient and stable extraction. More seriously, if the deposition process is not effectively controlled, the solid deposition layer will continue to thicken, potentially causing partial or even complete wellbore blockage, forcing the shutdown of individual wells. Subsequent unblocking and well cleaning operations are often lengthy, costly, and involve significant downhole risks, leading to substantial economic losses and safety challenges for oilfield production. According to incomplete statistics, wax-bearing wells in Northwest China's oilfields undergo an average of 12-15 hot-washing and wax removal operations per year. Each operation incurs direct costs exceeding 100,000 yuan (including equipment, chemicals, energy, and labor), and the operations also cause complete production interruptions, resulting in cumulative annual production losses of 5%-10%. Furthermore, the wax removal operation itself, especially when using coiled tubing or scrapers, carries the risk of downhole accidents such as tool jamming and damage to the production tubing. Therefore, deeply understanding the dynamic mechanisms of solid phase deposition in wellbores under complex deep-earth conditions and developing precise prediction and control technologies have become critical technical challenges that urgently need to be addressed for the safe and efficient development of deep oil and gas resources.

[0003] Currently, Chinese scholars have designed various specialized experimental instruments and conducted extensive indoor research on solid-phase deposition during oil and gas flow. For example, Chinese patent CN211477945U discloses a wax deposition experimental device with visualization capabilities. This device consists of a closed-loop system comprising an oil storage tank, a variable frequency oil pump, a test section, and a flow meter. The test section is composed of multiple transparent acrylic tubes connected in series, with detachable connections between each section. While this design can simulate the flow of crude oil under different pipe diameters, the significant difference between the surface properties of acrylic glass and metal wellbore makes it difficult to accurately reflect the adhesion behavior of crude oil on the metal pipe wall. Furthermore, the limited pressure-bearing capacity of acrylic glass makes it unsuitable for simulating the high-pressure flow environment downhole. Another Chinese patent, CN119958811A, proposes an integrated experimental device for multiphase flow drag reduction and wax deposition simulation. This device can better simulate the deposition process of crude oil on the pipe wall, but its structure is complex and lacks visualization capabilities, making it difficult to meet the cutting-edge needs for process visualization and dynamic monitoring in current deposition mechanism research.

[0004] Based on a survey and analysis of existing publicly available patents, current solid-phase deposition experimental devices mainly suffer from the following technical limitations: ① Existing devices cannot accurately reproduce the solid-phase deposition dynamics of crude oil on the walls of real metal wellbores; ② Most devices lack visualization capabilities, and some visualization devices cannot accommodate high-pressure conditions due to material strength limitations, thus making it difficult to accurately reproduce the actual flow environment of the wellbore; ③ Existing devices cannot achieve in-situ sampling while maintaining the integrity of the wax crystal microstructure, making it difficult to obtain undisturbed sediment samples for further microscopic analysis. Summary of the Invention

[0005] To address the problems of existing technologies, this invention discloses a visualization device and method for testing the solid-phase deposition behavior during the flow of waxy crude oil in a wellbore. This invention connects two or more wellbore simulation units in series to form a wellbore flow simulation system. A coiled section and a sapphire glass viewing section are connected in series and placed within a visible temperature control device, enabling the simulation of temperatures at different locations in the wellbore. Furthermore, the sapphire glass viewing section can be removed entirely. This invention is simple to operate and can realistically simulate the solid-phase deposition behavior of crude oil on the metal wellbore wall. It solves the problems of existing visualization devices being unable to handle high-pressure conditions and accurately reproduce the actual flow environment of the wellbore, and also better addresses the issue of existing devices being unable to achieve in-situ sampling while maintaining the integrity of the wax crystal microstructure.

[0006] The technical problem to be solved by the present invention is achieved by the following technical solution: a visualization device for simulating solid phase deposition in the flow of waxy crude oil in a wellbore, comprising a fluid injection system, a wellbore flow simulation system, a gas purging sampling system and a flow differential pressure monitoring module; The wellbore flow simulation system includes a wellbore simulation unit and a back pressure valve. Two or more wellbore simulation units are connected in series. The outlet of the last wellbore simulation unit is connected to the back pressure valve. Each wellbore simulation unit outlet is equipped with an injection control valve and an outflow control valve. The wellbore simulation unit includes a coil section, a sapphire glass viewing section, and a viewing temperature control device. The coil section and the sapphire glass viewing section are connected in series and are installed inside the viewing temperature control device. The gas purging and sampling system includes a purging gas supply unit and a sampling pipeline. The wellbore simulation unit is equipped with a purging gas supply unit and a sampling pipeline at both ends. A purging gas injection valve is installed at the outlet of the purging gas supply unit, and a sampling valve is installed on the sampling pipeline. The flow differential pressure monitoring module includes a flow differential pressure and temperature monitoring system and temperature and pressure monitoring units installed at the inlet and outlet of the coil section. The temperature and pressure monitoring units are respectively connected to the flow differential pressure and temperature monitoring system. The fluid injection system includes an oil-gas injection unit, a gas injection unit, and an oil-gas control valve. The oil-gas injection unit and the gas injection unit are connected to the inlet of the gas purging and sampling system through the oil-gas control valve. The coiled section is a one-piece molded metal tube. The number of wellbore simulation units can be adjusted, and each coiled section is housed within a visible temperature control device to simulate temperature changes from the bottom of the well to the wellhead. Therefore, the more coiled sections are used, the more accurate the simulation of wellbore temperature changes will be. The coiled sections in this invention are mainly used to simulate the flow in the wellbore (from the bottom to the wellhead), thereby simulating the temperature changes in the wellbore, with a focus on studying the solid phase deposition morphology and sedimentary layer evolution under temperature gradients.

[0007] The purpose of this sweeping and blowing invention is threefold: first, to test the weight; second, to allow the collected sediment to be used for other purposes; and third, to ensure that the device is cleaned by sweeping and blowing after each experiment to avoid affecting the next experiment.

[0008] Preferably, the oil and gas injection unit of the present invention includes a first ISCO plunger pump, a first plunger pump control valve, and an oil sample tank; The first ISCO plunger pump is connected to the oil sample tank, and a first plunger pump control valve is provided between the first ISCO plunger pump and the oil sample tank. The gas injection unit includes a second ISCO plunger pump, a second plunger pump control valve, and a gas sample container; The second ISCO plunger pump is connected to the gas sample tank, and a second plunger pump control valve is provided between the second ISCO plunger pump and the gas sample tank; The outlets of the oil sample container and the gas sample container are respectively connected to the oil and gas control valve.

[0009] Preferably, the first ISCO plunger pump and the second ISCO plunger pump can achieve constant flow / constant pressure dual-mode injection. The constant flow mode is used to simulate the constant production process of an oil well; the constant pressure mode is used to simulate the constant pressure production process of an oil well.

[0010] Preferably, in this invention, the inner diameter of the coil section within each wellbore simulation unit may be the same or different; The inner diameter of the coiled section and the sapphire glass visible section within each wellbore simulation unit is the same. This identical diameter ensures consistent flow conditions (same Reynolds number), facilitating subsequent calculations of sediment thickness. Furthermore, simulating the wellbore together with the coiled section, and given that the wellbore inner diameter is generally constant, the identical inner diameter of the sapphire glass visible section and the coiled section aligns with the actual requirements of wellbore simulation.

[0011] Preferably, the sapphire glass viewing section of this invention includes a viewing reinforcement sleeve and a sapphire tube. The sapphire tube is embedded within the viewing reinforcement sleeve, and the viewing reinforcement sleeve has a viewing window. Sealing gaskets are provided between the inlet and outlet ends of the sapphire tube and the inner wall of the viewing reinforcement sleeve. The viewing reinforcement sleeve enhances the pressure-bearing capacity of the sapphire tube, the sealing gaskets ensure a tight seal at both ends of the sapphire tube, and the viewing window allows observation of the state inside the sapphire tube.

[0012] Preferably, the present invention further includes a sample collection bucket disposed at the outlet of the sampling pipeline. The sample collection bucket is used to collect solid deposits present in the coil section, and the collected solid deposits are used for component analysis testing.

[0013] Preferably, a waste liquid collection tank is provided at the outlet of the back pressure valve of the present invention.

[0014] This invention also discloses a method for simulating solid phase deposition in the wellbore flow of waxy crude oil, utilizing the aforementioned visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil, comprising the following steps: S1. Set the visual temperature control device to the target temperature and maintain it for a predetermined time; S2. Inject waxy oil samples using the oil and gas injection unit at a preset flow rate, and inject gas samples using the gas injection unit at a preset flow rate. After the absolute pressure in the wellbore flow simulation system reaches the target value set in the experiment, shut down the oil and gas injection unit and the gas injection unit. S4. After all the test oil samples have been displaced, adjust the set pressure of the back pressure valve until the back pressure valve is completely unobstructed, thereby releasing all the pressure in the wellbore flow simulation system. S5. Use the oil and gas injection unit to inject air to completely displace the oil sample present in the wellbore flow simulation system; S6. Close the oil and gas control valve, open all valves in the wellbore flow simulation system and gas purging sampling system, adjust the back pressure valve to the maximum back pressure, turn on the purging gas supply unit to purge solid sediments, and use the collected sediments after purging for composition testing. S7. Repeat steps S1-S5, disassemble the visible section of the sapphire glass, and take non-destructive in-situ samples of the sediment in the visible section. The samples are used for solid phase sediment micromorphology characterization tests. S8. Replace the oil sample or reset the temperature of the visual temperature control device, and repeat steps S1-S7 to test the solid phase deposition law of oil samples with different temperature environments or different components. S9. The flow differential pressure data of the oil sample throughout the entire deposition process, stored in the flow differential pressure and temperature monitoring system, is used to reveal the wax deposition patterns in each coil section. After all the deposited wax in the system is swept out in step S6, the experiment needs to be repeated in step S7 for non-destructive in-situ sampling. Then, the sapphire glass viewing section is disassembled to remove the sample that has not undergone sweep-out shearing, achieving the purpose of non-destructive sampling. The swept-out sample undergoes irreversible changes in its microstructure due to the high-speed shearing of high-pressure gas; therefore, the sample swept out by high-pressure gas can only be used for compositional analysis. Only the sample removed from the sapphire glass viewing section can be used for microscopic observation and testing.

[0015] Preferably, in this invention, the temperature within the visible temperature control device of each wellbore simulation unit decreases sequentially along the fluid flow direction.

[0016] In a preferred embodiment of the present invention, the specific method for determining the wax deposition pattern in step S9 is as follows: Crude oil flow regime determination: Combining the simulated wellbore parameters and crude oil flow parameters, the flow regime determination of crude oil in each coil section of crude oil is carried out according to the flow regime determination formula (1). When Re < 2100, the crude oil flow is laminar; when Re > 2100, the crude oil flow is turbulent. (1) In the formula, Re is the Reynolds number, which is dimensionless; ρ Fluid density, kg / m³ 3 ; v The average flow velocity of the fluid inside the coil, in m / s; D Let m be the initial inner diameter of the coil. μThe dynamic viscosity of the fluid is Pa·s; the density of crude oil is tested according to the national standard GB / T1884-2000 "Laboratory Determination of Density of Crude Oil and Liquid Petroleum Products (Density Meter Method)". The viscosity-temperature curve of crude oil is tested according to the industry standard SY / T 7549-2000 "Determination of Viscosity-Temperature Curve of Crude Oil (Rotation Viscometer Method)". The density of crude oil can also be obtained by other reasonable methods, mainly depending on the experimenter. The average flow rate depends on the flow rate set by the experiment using the device, not calculated. If a pump is used for fluid injection, the average flow rate can be calculated by the flow rate / coil cross-sectional area. The initial inner diameter of the coil is the inner diameter of the coil section itself. The purpose of testing the viscosity-temperature curve is to obtain the viscosity of crude oil over a large temperature range, mainly used for determining the flow state of crude oil in formula (1). The purpose of testing density is the same as that of testing viscosity-temperature curve.

[0017] Calculate the bending correction factor for coil flow: If the crude oil is in a laminar flow state, calculate according to formula (2); if the crude oil is in a turbulent flow state, calculate according to formula (3); (2) (3) In the formula, F curv This is the bending correction factor for coil flow, dimensionless; D eff Where is the effective diameter of the coil, in meters (m). R c Where is the coil bending radius, in meters; coil bending radius R c It refers to the distance from the centerline of the bend in the coil section to the center of curvature of the bend. The effective pipe diameter of the coil is calculated as follows: Based on the determined crude oil flow state, if it is a laminar flow state, then select formula (4) to calculate the effective pipe diameter of the coil after the crude oil produces solid phase deposition in the coil; if it is a turbulent flow state, then select formula (5) to calculate the effective pipe diameter. (4) (5) In the formula, Q denoted as the volumetric flow rate of crude oil in the experiment, in m³ / s; L The total length of the coil is in meters (m). ΔP calc To calculate the pressure difference, Pa; The specific value of the effective pipe diameter obtained from formulas (4) and (5) requires iterative calculation. First, let D... eff (0) = D0, substitute it into the flow regime determination formula (1) to determine the flow regime, and then, depending on the flow regime, substitute D0 into formula (2) or formula (3) to calculate F.curv (0), the calculated F is determined according to different flow regimes. curv (0) Substitute D0 into formula (4) or formula (5) to calculate ΔP. calc (0), compare with the calculated ΔP calc (0) Whether the error between the measured ΔP and the actual ΔP is within the preset threshold range. If it is within the preset threshold range, then set D. eff The initial value D0 is the correct effective pipe diameter value; if the error is not within the preset threshold range, then a new D is assumed. eff D eff (1) = D1, and the above calculation is performed using the binary search method in a loop; when the error is within the preset threshold range, the effective pipe diameter assumption is considered correct, the calculation is stopped, and the effective pipe diameter D is output. eff =The value of Dn; D0 has no specific requirements, but it must be less than the initial coil inner diameter (because the inner diameter at its maximum is the inner diameter before solid phase deposition, i.e., the initial coil inner diameter). Estimate a reasonable initial value and substitute it into the calculation. If the calculated ΔP calc If the value of ΔP is larger than the measured value, then a smaller ΔP needs to be assumed when using the bisection method for iterative calculations next time. eff Similarly, if the calculated ΔP calc If the value of ΔP is smaller than the measured value, then a larger ΔP needs to be assumed when using the bisection method for iterative calculations next time. eff .

[0018] The error determination formula is shown in formula (6): (6) In the formula, ΔP calc To calculate the pressure difference, Pa; ΔP The experimental pressure difference is expressed in Pa. Calculate the thickness of the sedimentary layer: Calculate the thickness of the sedimentary layer according to formula (7); (7) In the formula, δ denoted as the thickness of the sedimentary layer, in meters (m).

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention solves the problem that existing devices cannot accurately reproduce the solid-phase deposition dynamics of crude oil on the real metal wellbore wall. It accurately reproduces the deposition pattern of crude oil in the actual wellbore by using a coil section with replaceable material.

[0020] 2. This invention has a visualization function, and the overall connection strength of the wellbore flow simulation system is high. The key pressure-bearing component, the coil section, is integrally cast. The visible section is made of sapphire glass, which has high pressure resistance and can accurately reproduce the pressure environment inside the wellbore.

[0021] 3. The present invention can achieve in-situ non-destructive sampling of sediments while maintaining the integrity of the microstructure of wax crystals. The undisturbed sediment samples obtained can be used for further micromorphological characterization tests.

[0022] 4. The solid-phase deposition law monitoring method proposed in this invention is simple and easy to implement. It only requires monitoring the flow pressure difference throughout the entire process to calculate the evolution law of the deposition layer. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to the present invention; Figure 2 A schematic diagram of the visible section of sapphire glass; Figure 3 This is a top view of the coil section. Figure 4 This is a schematic diagram of the wax crystal deposition morphology of waxy crude oil. Figure 5 This is a graph showing the variation of the flow pressure difference in waxy crude oil. Figure 6 This is a diagram showing the variation in the thickness of the wax deposit layer during the flow of waxy crude oil. In the diagram, 1 represents a wellbore simulation unit, 2 represents a back pressure valve, 100 represents an injection control valve, and 200 represents an outflow control valve. 101 Coil section, 102 Sapphire glass viewing section, 103 Visual temperature control device; 3. Purge gas supply unit, 4. Sampling pipeline, 300 purge gas injection valve, 400 sampling valve, 5. Flow differential pressure and temperature monitoring system, 6. Temperature and pressure monitoring unit, 500 oil and gas control valve; 7 First ISCO plunger pump, 8 First plunger pump control valve, 9 Oil sample tank, 10 Second ISCO plunger pump, 11 Second plunger pump control valve, 12 Gas sample tank; 1021 Visible reinforcement sleeve, 1022 Sapphire tube body, 1023 Visible window, 1024 Sealing gasket; 13 Sample collection container, 14 Waste liquid collection container. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0025] like Figure 1 As shown, a visualization device for simulating solid phase deposition in the flow of waxy crude oil in a wellbore includes a fluid injection system, a wellbore flow simulation system, a gas sweeping sampling system, and a flow differential pressure monitoring module.

[0026] The wellbore flow simulation system includes a wellbore simulation unit 1 and a back pressure valve 2. Two or more wellbore simulation units are connected in series. The outlet of the last wellbore simulation unit is connected to the back pressure valve 2. Each wellbore simulation unit 1 is equipped with an injection control valve 100 and an outflow control valve 200 at its inlet and outlet, respectively.

[0027] The wellbore simulation unit 1 includes a coil section 101, a sapphire glass viewing section 102, and a viewing temperature control device 103. The coil section 101 and the sapphire glass viewing section 102 are connected in series and disposed within the viewing temperature control device 103, which has a viewing window or opening. In this embodiment, the viewing temperature control device 103 is a water bath used to simulate the temperature environment of the wellbore or wellhead. Visualization during the experiment is mainly achieved by observing the sapphire glass viewing section with the naked eye or a microscope. The temperature control system uses water bath temperature control and does not affect visual observation. The sapphire glass viewing section can not only be used for macroscopic visualization experiments but can also be removed intact and without damage after the experiment, thereby completing in-situ sampling of the wax deposition layer for subsequent microscopic morphological characterization testing of the wax crystal morphology.

[0028] The gas purging and sampling system includes a purging gas supply unit 3 and a sampling pipeline 4. In this embodiment, the purging gas supply unit 3 is a high-pressure nitrogen cylinder. The wellbore simulation unit 1 is equipped with a purging gas supply unit 3 and a sampling pipeline 4 at both ends. A purging gas injection valve 300 is installed at the outlet of the purging gas supply unit 3, and a sampling valve 400 is installed on the sampling pipeline 4. The number of sampling pipelines 4 is the same as the number of coil sections 101, and the main function of the sampling pipelines 4 is to collect sediments from different coils (because different coils are set at different temperatures, the composition and morphology of solid sediments produced by crude oil in different coils may also be different, therefore they need to be collected separately).

[0029] The flow differential pressure monitoring module includes a flow differential pressure and temperature monitoring system 5 and temperature and pressure monitoring units 6 installed at the inlet and outlet of the coil section 101. The temperature and pressure monitoring units 6 are connected to the flow differential pressure and temperature monitoring system 5. The temperature and pressure monitoring units 6 are used to monitor the temperature and pressure at the inlet and outlet of the coil section and input the temperature and pressure differential into the flow differential pressure and temperature monitoring system 5.

[0030] In this embodiment, two wellbore simulation units 1 are provided, and a purge gas supply unit 3 is located between the two wellbore simulation units 1. Two sampling pipelines 4 are provided, connected to the injection control valve 100 at the inlet side of the first wellbore simulation unit 1 and the outflow control valve 200 at the outlet side of the second wellbore simulation unit 1, respectively. The first sampling pipeline 4 is positioned 5-10 cm before the temperature and pressure monitoring unit 6, and the second sampling pipeline 4 is positioned 5-10 cm after the sapphire glass viewing section. In this embodiment, the purging of both wellbore simulation units 1 can be achieved simultaneously using only one purge gas supply unit 3.

[0031] The fluid injection system includes an oil-gas injection unit, a gas injection unit, and an oil-gas control valve 500. The oil-gas injection unit and the gas injection unit are connected to the inlet of the gas purging sampling system through the oil-gas control valve 500.

[0032] The coil section 101 is a one-piece molded metal tube. The coil section is integrally cast and its structural design can withstand the high pressure conditions in deep or ultra-deep well environments, with a maximum pressure of 70 MPa.

[0033] The oil and gas injection unit includes a first ISCO plunger pump 7, a first plunger pump control valve 8, and an oil sample tank 9.

[0034] The first ISCO plunger pump 7 is connected to the oil sample tank 9, and a first plunger pump control valve 8 is provided between the first ISCO plunger pump 7 and the oil sample tank 9.

[0035] The gas injection unit includes a second ISCO plunger pump 10, a second plunger pump control valve 11, and a gas sample container 12.

[0036] The second ISCO plunger pump 10 is connected to the gas sample tank 12, and a second plunger pump control valve 11 is provided between the second ISCO plunger pump 10 and the gas sample tank 12.

[0037] The outlets of the oil sample tank 9 and the gas sample tank 12 are respectively connected to the oil and gas control valve 500. The first ISCO plunger pump 7 and the second ISCO plunger pump 10 can achieve constant flow / constant pressure dual-mode injection. The first ISCO plunger pump 7 is used to control the flow rate of crude oil in the system, and the second ISCO plunger pump 10 is used to control the gas sample injection volume. The oil sample tank 9 is used to store the original oil sample. The gas sample tank 12 is used to mix the original gas sample.

[0038] The visualization device for simulating solid phase deposition in the flow of waxy crude oil in a wellbore also includes a sample collection bucket 13 located at the outlet of the sampling pipeline 4.

[0039] A waste liquid collection tank 14 is provided at the outlet of the back pressure valve 2. In this embodiment, two wellbore simulation units 1 are provided. Oil and gas samples are pumped in through the first ISCO plunger pump and the second ISCO plunger pump, flow through the oil and gas control valve, and undergo solid phase deposition in the first coil section, the first sapphire glass visible section, the second coil section, and the second sapphire glass visible section. Then, they flow into the waste liquid collection tank 14 through the back pressure valve 2.

[0040] The inner diameter of the coil section 101 in each wellbore simulation unit 1 may be the same or different.

[0041] The inner diameters of the coil section 101 and the sapphire glass visible section 102 within each wellbore simulation unit 1 are the same.

[0042] like Figure 2 As shown, the sapphire glass viewing section 102 includes a viewing reinforcement sleeve 1021 and a sapphire tube 1022. The sapphire tube 1022 is embedded in the viewing reinforcement sleeve 1021. A viewing window 1023 is provided on the viewing reinforcement sleeve 1021. Sealing gaskets 1024 are provided between the inlet and outlet ends of the sapphire tube 1022 and the inner wall of the viewing reinforcement sleeve 1021.

[0043] A method for simulating solid phase deposition in the wellbore flow of waxy crude oil, utilizing the visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to this embodiment, includes the following steps: S1. Adjust the visible temperature control device 103 to the target temperature and maintain it for 30 minutes to ensure that the coil section 101 and the sapphire glass visible section 102 reach the target temperature.

[0044] S2. Preheat the test oil sample at 80℃ for 30 minutes to ensure complete dissolution of the wax crystals. Then, place the preheated oil sample into the oil sample container. Simultaneously, inject the prepared pressurized gas into the gas sample container. Natural gas can be used as the pressurized gas.

[0045] Waxy oil samples were injected using the oil and gas injection unit at a preset flow rate, and gas samples were injected using the gas injection unit at a preset flow rate. Once the absolute pressure in the wellbore flow simulation system reached the target value set in the experiment, the oil and gas injection unit and the gas injection unit were shut down.

[0046] Specifically, adjust the flow rate of the first ISCO plunger pump (1.2-10 ml / min) to inject the oil sample, and adjust the flow rate of the second ISCO plunger pump (5-20 ml / min) to inject the gas sample. Once the absolute pressure in the wellbore flow simulation system reaches the experimentally set target value (≤70 MPa), close the second ISCO plunger pump and its control valve. Injecting at the above flow rates makes it easier to ensure that the crude oil flows in a single phase, avoiding increased flow resistance caused by two-phase oil-gas flow.

[0047] S4. After all the oil sample has been displaced, adjust the set pressure of the back pressure valve 2 until it is fully unobstructed, thereby releasing all the pressure in the wellbore flow simulation system. Displacement here means using a pump to squeeze the crude oil in the sample tank, causing it to flow into the device and then into the waste liquid tank. Since this device is mainly used to simulate wellbore flow, the temperature in the wellbore is simulated by a temperature control system (water bath or oil bath), while the pressure in the wellbore is simulated by the back pressure valve. The principle of the back pressure valve is to adjust its opening to set the back pressure. Once all the crude oil has flowed from the sample tank to the waste liquid collection tank, the experiment ends. Then, the opening of the back pressure valve needs to be slowly increased to depressurize the entire device. When the back pressure valve is fully unobstructed, the internal pressure of the entire device is equal to atmospheric pressure, and then the next step can be performed.

[0048] S5. Use the oil and gas injection unit to inject air to displace all the oil samples present in the wellbore flow simulation system. Because after all the crude oil in the oil sample tank flows through the device into the waste liquid tank, there will still be residual oil in the device's coils that cannot flow out naturally. At this time, it is necessary to inject air at a low speed to push out the remaining crude oil in the coils, thus leaving only the sediment.

[0049] S6. Close the oil and gas control valve 500, open all valves in the wellbore flow simulation system and the gas purging sampling system, adjust the back pressure valve 2 to the maximum back pressure, and turn on the purging gas supply unit 3 to purge solid sediments. The sediments collected after purging are used for composition testing.

[0050] S7. Repeat steps S1-S5 to disassemble the sapphire glass visible section 102 and perform non-destructive in-situ sampling of the sediments in the visible section. The samples are used for solid phase sediment micromorphology characterization tests.

[0051] S8. Replace the oil sample or reset the temperature of the visual temperature control device 103, and repeat steps S1-S7 to test the solid phase deposition law of oil samples with different temperature environments or different components.

[0052] The oil sample flow differential data stored in the S9 flow differential pressure and temperature monitoring system 5 during the entire deposition process are used to reveal the wax deposition patterns in each coil section 101.

[0053] Along the direction of fluid flow, the temperature inside the visible temperature control device 103 of each wellbore simulation unit 1 decreases sequentially.

[0054] In step S9, the specific method for determining the wax deposition pattern is as follows: Crude oil flow regime determination: Combining the simulated wellbore parameters and crude oil flow parameters, the flow regime determination of crude oil in the simulated wellbore is carried out according to the flow regime determination formula (1) in each crude oil coil section 101.

[0055] When Re < 2100, the crude oil flow is laminar; when Re > 2100, the crude oil flow is turbulent.

[0056] (1) In the formula, Re is the Reynolds number, which is dimensionless; ρ Fluid density, kg / m³ 3 ; v The average flow velocity of the fluid inside the coil, in m / s; D Let m be the initial inner diameter of the coil. μ Let be the dynamic viscosity of the fluid, Pa·s.

[0057] Calculate the bending correction factor for coil flow: If the crude oil is in a laminar flow state, calculate according to formula (2); if the crude oil is in a turbulent flow state, calculate according to formula (3).

[0058] (2) (3) In the formula, F curv This is the bending correction factor for coil flow, dimensionless; D eff Where is the effective diameter of the coil, in meters (m). R c Where is the bending radius of the coil, in meters. For example... Figure 3 As shown, the coil bending radius R c It refers to the distance from the centerline of the bend in section 101 of the coil to the center of curvature of the bend.

[0059] The effective pipe diameter of the coil is calculated as follows: Based on the determined crude oil flow state, if it is a laminar flow state, then select formula (4) to calculate the effective pipe diameter after the crude oil produces solid phase deposition in the coil. If it is a turbulent flow state, then select formula (5) to calculate the effective pipe diameter.

[0060] (4) (5) In the formula, Q is the volumetric flow rate of crude oil in the experiment, m³ / s; L The total length of the coil is in meters (m). ΔP calc To calculate the pressure difference, Pa.

[0061] Obtaining the specific value of the effective pipe diameter through formulas (4) and (5) requires iterative calculation, and the general method includes the following steps: Step 1: First, assume an effective diameter D. eff The initial value, i.e., D eff(0) = D0. Depending on the flow regime, substitute D0 into formula (2) or formula (3) to obtain the bending correction coefficient F. curv (0); Step 2: Based on the different flow regimes, the obtained bending correction coefficient F curv (0) Substitute the initial effective diameter value D0 into formula (4) or formula (5) to obtain the pressure difference ΔP. calc (0); Step 3: Calculate the pressure difference ΔP based on the error judgment formula. calc (0) Whether the error between the measured pressure difference ΔP and the actual pressure difference is within an acceptable range (≤0.5%). If it is within the acceptable range, then the D assumed in step 1... eff The initial value D0 is the correct effective pipe diameter value.

[0062] Step 4: If the error is unacceptable, then re-assume an effective diameter D. eff The value of D eff (1) = D1, and the calculation of steps 1-3 is performed cyclically using the bisection method until the calculated pressure difference ΔP is obtained. calc (n) When the error between the measured pressure difference ΔP and (n) is within an acceptable range, the cycle stops and the effective pipe diameter D is output. eff The value is Dn.

[0063] It should be noted that the effective diameter D is assumed here. eff The value must always be less than or equal to the initial inner diameter D of the coil, and greater than or equal to 0.

[0064] The error determination formula is shown in formula (6): (6) In the formula, ΔP calc To calculate the pressure difference, Pa; ΔP The experimental pressure difference, in Pa, can be measured using a temperature and pressure monitoring unit.

[0065] Calculate the thickness of the sedimentary layer: Calculate the thickness of the sedimentary layer according to formula (7); (7) In the formula, δ denoted as the thickness of the sedimentary layer, in meters (m).

[0066] Figure 4 The images show the microscopic morphology of sediment samples obtained through in-situ non-destructive sampling. It can be observed that most of the sediments are needle-shaped and have a layered structure, while a small portion of the sediments are spherical.

[0067] Figure 5This demonstrates the flow pressure differential of waxy crude oil tested by this device. Before 25 minutes, the flow pressure differential mainly showed an upward trend, indicating that the thickness of the deposit layer inside the coil was continuously increasing. After 25 minutes, the flow pressure differential decreased, indicating that the reduction in pipe diameter was suppressed at this point, thus reducing the flow pressure differential.

[0068] Figure 6 The variation of solid deposit thickness over time, calculated using the above method, is shown. It can be observed that the deposit thickness in the coil initially increases rapidly, then decreases slightly. This indicates that the wax deposit thickness in the wellbore does not exhibit a simple increasing trend, but rather is slightly stripped and carried away with increasing deposition time, eventually being discharged from the wellhead along with the oil flow.

Claims

1. A visualization device for simulating solid phase deposition during the flow of waxy crude oil in a wellbore, characterized in that: Includes a fluid injection system, a wellbore flow simulation system, a gas purging and sampling system, and a flow differential pressure monitoring module; The wellbore flow simulation system includes a wellbore simulation unit (1) and a back pressure valve (2). Two or more wellbore simulation units are connected in series. The outlet of the last wellbore simulation unit is connected to the back pressure valve (2). Each wellbore simulation unit (1) is equipped with an injection control valve (100) and an outflow control valve (200) at its inlet and outlet. The wellbore simulation unit (1) includes a coil section (101), a sapphire glass visible section (102), and a visible temperature control device (103). The coil section (101) and the sapphire glass visible section (102) are connected in series and are installed inside the visible temperature control device (103). The gas purging and sampling system includes a purging gas supply unit (3) and a sampling pipeline (4). The wellbore simulation unit (1) is provided with a purging gas supply unit (3) and a sampling pipeline (4) at both ends. A purging gas injection valve (300) is provided at the outlet of the purging gas supply unit (3), and a sampling valve (400) is provided on the sampling pipeline (4). The flow differential pressure monitoring module includes a flow differential pressure and temperature monitoring system (5) and a temperature and pressure monitoring unit (6) installed at the inlet and outlet of the coil section (101). The temperature and pressure monitoring unit (6) is connected to the flow differential pressure and temperature monitoring system (5). The fluid injection system includes an oil-gas injection unit, a gas injection unit, and an oil-gas control valve (500). The oil-gas injection unit and the gas injection unit are connected to the inlet of the gas purging sampling system through the oil-gas control valve (500). The coil section (101) is a one-piece molded metal tube.

2. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 1, characterized in that: The oil and gas injection unit includes a first ISCO plunger pump (7), a first plunger pump control valve (8), and an oil sample tank (9); The first ISCO plunger pump (7) is connected to the oil sample tank (9), and a first plunger pump control valve (8) is provided between the first ISCO plunger pump (7) and the oil sample tank (9). The gas injection unit includes a second ISCO plunger pump (10), a second plunger pump control valve (11), and a gas sample container (12). The second ISCO plunger pump (10) is connected to the gas sample tank (12), and a second plunger pump control valve (11) is provided between the second ISCO plunger pump (10) and the gas sample tank (12). The outlet ends of the oil sample tank (9) and the gas sample tank (12) are respectively connected to the oil and gas control valve (500).

3. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 2, characterized in that: The first ISCO plunger pump (7) and the second ISCO plunger pump (10) can achieve constant flow / constant pressure dual-mode injection.

4. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 1, characterized in that: The inner diameter of the coil section (101) in each wellbore simulation unit (1) may be the same or different; The inner diameters of the coil section (101) and the sapphire glass visible section (102) within each wellbore simulation unit (1) are the same.

5. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 1, characterized in that: The sapphire glass viewing section (102) includes a viewing reinforcement sleeve (1021) and a sapphire tube (1022). The sapphire tube (1022) is embedded in the viewing reinforcement sleeve (1021). The viewing reinforcement sleeve (1021) is provided with a viewing window (1023). Sealing gaskets (1024) are provided between the inlet and outlet ends of the sapphire tube (1022) and the inner wall of the viewing reinforcement sleeve (1021).

6. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 1, characterized in that: It also includes a sample collection bucket (13) located at the outlet of the sampling pipeline (4).

7. The visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 1, characterized in that: A waste liquid collection tank (14) is provided at the outlet of the back pressure valve (2).

8. A method for simulating solid phase deposition in the wellbore flow of waxy crude oil, utilizing the visualization device for simulating solid phase deposition in the wellbore flow of waxy crude oil as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Adjust the visual temperature control device (103) to the target temperature and maintain it for a predetermined time; S2. Inject waxy oil samples using the oil and gas injection unit at a preset flow rate, and inject gas samples using the gas injection unit at a preset flow rate. After the absolute pressure in the wellbore flow simulation system reaches the target value set in the experiment, shut down the oil and gas injection unit and the gas injection unit. S4. After all the test oil samples have been displaced, adjust the set pressure of the back pressure valve (2) until the back pressure valve (2) is completely unobstructed, thereby releasing all the pressure in the wellbore flow simulation system. S5. Use the oil and gas injection unit to inject air to completely displace the oil sample present in the wellbore flow simulation system; S6. Close the oil and gas control valve (500), open all valves in the wellbore flow simulation system and the gas purging sampling system, adjust the back pressure valve (2) to the maximum back pressure, turn on the purging gas supply unit (3) to purge solid sediments, and use the collected sediments after purging for composition testing. S7. Repeat steps S1-S5, disassemble the visible section of sapphire glass (102), and take non-destructive in-situ samples of the sediment in the visible section. The samples are used for solid phase sediment micromorphology characterization tests. S8. Replace the oil sample or reset the temperature of the visual temperature control device (103), repeat steps S1-S7, and conduct solid phase deposition law tests for oil samples with different temperature environments or different components. The flow differential pressure data of the oil sample stored in the S9 flow differential pressure and temperature monitoring system (5) during the entire deposition process are used to reveal the wax deposition pattern in each coil section (101).

9. The method for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 8, characterized in that: Along the direction of fluid flow, the temperature in the visible temperature control device (103) of each wellbore simulation unit (1) decreases sequentially.

10. The method for simulating solid phase deposition in the wellbore flow of waxy crude oil according to claim 8, characterized in that, In step S9, the specific method for determining the wax deposition pattern is as follows: Crude oil flow regime determination: Combining the simulated wellbore parameters and crude oil flow parameters, the flow regime determination of crude oil in the simulated wellbore is carried out according to the flow regime determination formula (1) in each crude oil coil section (101). When Re < 2100, the crude oil flow is laminar; when Re > 2100, the crude oil flow is turbulent. （1） In the formula, Re is the Reynolds number, which is dimensionless; ρ Fluid density, kg / m³ 3 ; v The average flow velocity of the fluid inside the coil, in m / s; D Let m be the initial inner diameter of the coil. μ Let be the dynamic viscosity of the fluid, Pa·s; Calculate the bending correction factor for coil flow: If the crude oil is in a laminar flow state, calculate according to formula (2); if the crude oil is in a turbulent flow state, calculate according to formula (3); （2） （3） In the formula, F curv This is the bending correction factor for coil flow, dimensionless; D eff Where is the effective diameter of the coil, in meters (m). R c Where is the bending radius of the coil, in meters; The effective pipe diameter of the coil is calculated as follows: Based on the determined crude oil flow state, if it is a laminar flow state, then select formula (4) to calculate the effective pipe diameter of the coil after the crude oil produces solid phase deposition in the coil; if it is a turbulent flow state, then select formula (5) to calculate the effective pipe diameter. （4） （5） In the formula, Q denoted as the volumetric flow rate of crude oil in the experiment, in m³ / s; L The total length of the coil is in meters (m). ΔP calc To calculate the pressure difference, Pa; The specific value of the effective pipe diameter obtained by formula (4) and formula (5) needs to be calculated iteratively. First, let D eff (0)=D0, bring it into the flow state determination formula (1) to determine the flow state, then according to the different flow states, bring D0 into formula (2) or formula (3) to calculate F curv (0), according to the different flow states, bring the calculated F curv (0) and D0 into formula (4) or formula (5) to calculate ΔP calc (0), compare the calculated ΔP calc (0) with the measured ΔP to determine whether the error is within the preset threshold range. If it is within the preset threshold range, the set D eff initial value D0 is the correct effective pipe diameter value; if the error is not within the preset threshold range, assume another D eff , that is, D eff (1)=D1, and use the bisection method to perform the above calculation; when the error is within the preset threshold range, it is considered that the effective pipe diameter assumption is correct, the calculation is stopped, and the effective pipe diameter D eff =Dn is output. The error determination formula is shown in formula (6): （6） In the formula, ΔP calc To calculate the pressure difference, Pa; ΔP The experimental pressure difference is expressed in Pa. Calculate the thickness of the sedimentary layer: Calculate the thickness of the sedimentary layer according to formula (7); （7） In the formula, δ denoted as the thickness of the sedimentary layer, in meters (m).

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