Photovoltaic direct drive paraffin removal method and device

Abstract

The present application relates to the technical field of wellbore cleaning method, and is a photovoltaic direct drive wax cleaning and preventing method and device. The photovoltaic direct drive wax cleaning and preventing device comprises a photovoltaic array, an electric coupling control system for downhole electric heating wax cleaning, and a downhole heating device. The present application directly drives the downhole electric heating device by generating electricity through the photovoltaic array to heat the liquid flow in the wellbore for wax cleaning and preventing operation, which can greatly reduce the hot washing wax cleaning cost of a single oil well and reduce carbon emissions through green electricity. The electric coupling control system for downhole electric heating wax cleaning can dynamically match the power generation of the photovoltaic array and the power consumption of each downhole electric heating device in the starting state, reasonably configure the power generation of the photovoltaic array, make the power generation of the photovoltaic array meet the downhole heating power, and at the same time, reduce the occupied area, save the construction cost, reduce the light abandonment rate, ensure that each oil well can timely perform the wax cleaning and preventing operation, reduce the energy consumption, shorten the wax cleaning period, and greatly reduce the hot washing wax cleaning cost of the oil well.

Description

Technical Field

[0001] This invention relates to the field of wellbore cleaning methods, specifically a photovoltaic direct-drive method and apparatus for removing and preventing waxing. Background Technology

[0002] Petroleum is primarily a mixture of hydrocarbons of various components. The phases of these hydrocarbons vary depending on the extraction conditions. The solid components are mainly alkanes containing 16 to 64 carbon atoms, a substance known as paraffin. Pure paraffin is a white, slightly transparent crystalline solid.

[0003] During oil well production, as temperature and pressure decrease and gases are released, paraffin dissolved in the crude oil crystallizes and precipitates under certain conditions. With further changes in conditions, paraffin continues to precipitate, and its crystals accumulate and deposit on equipment and tools such as tubing, casing, sucker rods, and pumps. This phenomenon is called wax deposition. However, oil well wax deposition is not white crystals, but rather a mixture of black semi-solid and solid paraffin, asphalt, gum, silt, and other impurities.

[0004] When wax forms on an oil well, the inner diameter of the wellbore's oil outlet gradually decreases, increasing back pressure on the formation and adding resistance to oil flow, significantly reducing the well's overall production. When wax forms on the tubing or sucker rod, it increases resistance to oil flow within the tubing, thereby increasing the workload of the pumping unit and causing wax jamming in the pump. This severely impacts pump efficiency, significantly reducing crude oil production and, in severe cases, damaging the pumping equipment and leading to production safety accidents.

[0005] Currently, oilfields typically use hot washing trucks to remove wax from individual wells in submersible screw pump well groups. However, this method suffers from high wax removal costs, long hot washing cycles, and high energy consumption. Furthermore, due to the varying well conditions of each screw pump well, the wax deposition rate and point differ, making it difficult to ensure timely wax removal for every well during hot washing truck operations. This results in reduced production and increased power consumption in these wells. Summary of the Invention

[0006] This invention provides a photovoltaic direct-drive wax removal and prevention method and device, which overcomes the shortcomings of the prior art. It can effectively solve the problems of high wax removal cost, long hot washing cycle and high wax removal energy consumption in existing submersible screw pump oil well wax removal operations, and the inability to remove wax in a timely manner according to the well conditions of each oil well.

[0007] One of the technical solutions of this invention is achieved through the following measures: a photovoltaic direct-drive wax removal method, comprising the following steps:

[0008] (1) Select a suitable screw pump oil well group in the area, and determine the wax deposition pattern and wax removal cycle of each oil well based on the well condition parameters of each oil well;

[0009] (2) Install downhole electric heating devices in each well of the screw pump well group and determine the total power consumption of downhole electric heating for the screw pump well group;

[0010] (3) Based on the light resource conditions of the well site of the screw pump oil well group, simulate the daily power generation curve under different photovoltaic installation power conditions, select the photovoltaic installation capacity that matches the total power consumption of downhole electric heating, and set up a photovoltaic array at a suitable location in the well site;

[0011] (4) Connect the photovoltaic array to each downhole electric heating device through the downhole electric heating and wax removal electric coupling control system. The downhole electric heating and wax removal electric coupling control system can establish a multi-well rotation heating system based on the power generation of the photovoltaic array and the screw pump power, production volume, wax deposition pattern and wax removal cycle of each oil well, with the lowest light rejection rate as the objective function. It can dynamically configure the heating sequence, duration and frequency of each oil well, automatically control the start and stop of the downhole electric heating device of each oil well, and complete the wax removal and prevention operation in a timely manner.

[0012] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0013] The above-mentioned wax deposition patterns and cycles for each oil well, obtained based on well condition parameters, may include:

[0014] Based on the well condition parameters of each oil well, the growth rate of paraffin deposition thickness in each oil well is obtained by the following formula;

[0015]

[0016] Among them, υ h W represents the growth rate of paraffin deposition thickness, in m / s; W represents the total paraffin deposition rate in each well, in kg / (m³). 2 ·s); ρ s The density of solid paraffin, in kg / m³ 3 H s The content of wax in the non-flowing layer, %; ρ o The density of crude oil in the trap layer is expressed in kg / m³. 3 ;

[0017] By combining the growth rate of paraffin deposition thickness in each oil well with the fluid production situation, the wax deposition pattern and wax deposition cycle of each oil well can be obtained.

[0018] The total paraffin deposition rate in each of the above-mentioned oil wells can include: combining the paraffin deposition mechanism of screw pump wells and the paraffin deposition mechanism of oil wells, the molecular diffusion deposition rate of paraffin on the inner wall of the tubing can be obtained by the following formula;

[0019]

[0020] Among them, W ml The mass transfer rate of dissolved paraffin molecules to the tube wall, Kg / (m 2 ·s); C d This is the sedimentation constant, typically taken as 1.5 kg·m / s. 2 C h The unit conversion factor is 0.8267578; C p ρ is the isobaric specific heat of the fluid in the wellbore, in kJ / (kg·℃); s The density of solid paraffin, in kg / m³ 3 ;ρ l The density of the fluid in the wellbore is expressed in kg / m³. 3 μ is the viscosity of the fluid, Pa·s; V is the volumetric flow rate of the wellbore, m³ / s. 3 / s; k is the thermal conductivity coefficient of the fluid in the wellbore, KJ / (m·s·℃); d t dT / dL is the tubing diameter, in meters; dT / dL is the axial temperature gradient of the wellbore, in degrees Celsius per meter; T t Temperature of the inner wall of the oil pipe, in °C;

[0021] The shear dispersion deposition rate of paraffin in the tubing is obtained by the following formula;

[0022]

[0023] Among them, W dl The mass of crystalline wax deposited per unit time and per unit area by shear dispersion, in kg / (m²). 2 ·s); C d C is the sedimentation constant, typically taken as 1500; h The unit conversion factor is 0.8267578; γ is the shear rate, 1 / s; T t T represents the temperature of the inner wall of the oil pipe, in °C. C Temperature at the center of the oil pipe, in °C;

[0024] The total paraffin deposition rate W in each oil well is obtained by the following formula;

[0025] W = W ml +W dl

[0026] The aforementioned downhole electric heating dewaxing control system can also be connected to the grid power supply. When the power generation of the photovoltaic array is insufficient, it can be supplemented by the grid power supply.

[0027] During the above-mentioned wax removal and prevention process, the heating time for a single well should not be less than 5 hours. If the temperature of the produced fluid at the wellhead is greater than 80°C, the heating should be stopped. If the temperature of the produced fluid at the wellhead is always less than 80°C, the heating should continue for at least 5 hours.

[0028] The second technical solution of the present invention is achieved through the following measures: a photovoltaic direct-drive wax removal device, comprising: a photovoltaic array, a downhole electric heating wax removal electrocoupling control system, and a downhole heating device. The photovoltaic array can provide a stable power supply to the downhole electric heating wax removal electrocoupling control system and the downhole heating system. The downhole electric heating wax removal electrocoupling control system can monitor the real-time power generation of the photovoltaic array, determine the heating power and heating duration of the downhole electric heating system at a certain moment, so that the power generation of the photovoltaic array can be dynamically matched with the start and stop of the downhole electric heating system. Each screw pump oil well is equipped with a downhole heating device.

[0029] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0030] The aforementioned downhole electric heating dewaxing electrical coupling control system may include an MPPT controller, a voltage regulator, a follow-up matching control system, and a detection system. The photovoltaic array is connected in series with the MPPT controller, voltage regulator, and follow-up matching control system in sequence, and the detection system is connected to the follow-up matching control system. Among them, the MPPT controller enables the photovoltaic array to always operate at its maximum power point; the detection system can detect the DC input voltage, current, and heating power of each downhole electric heating device, the DC output active power, reactive power, power factor, daily power generation, and total power generation of the photovoltaic array, the well condition parameters of each oil well, and the power of the screw pump; after receiving the detection data from the detection system, the follow-up matching control system can intelligently process the detection data and automatically control the start and stop of each downhole electric heating device according to the processing results and the wax deposition pattern of each oil well, realizing the rotational heating of each oil well.

[0031] The aforementioned follow-up matching control system may include a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply circuit, a smart electricity meter, and a detection system. The PLC controller can calculate the photovoltaic output curve of the photovoltaic array based on the detection data from the detection system, and automatically control and adjust the heating power, heating duration, and heating frequency of each downhole electric heating device in conjunction with the load characteristic curves of each screw pump.

[0032] The well condition parameters of each of the above-mentioned oil wells may include the oil layer temperature, wellhead fluid temperature, surface temperature, paraffin density, tubing inner diameter, daily fluid production, oil layer depth, crude oil viscosity, crude oil density, thermal conductivity, fluid specific heat at constant pressure, and wellbore axial temperature gradient.

[0033] The aforementioned downhole electric heating device can be a downhole heating cable.

[0034] This invention directly drives a downhole electric heating device through photovoltaic array power generation, heating the fluid flow inside the wellbore for wax removal and prevention operations. This significantly reduces the cost of hot washing and wax removal for a single oil well and reduces carbon emissions through green electricity. The downhole electric heating and wax removal electrical coupling control system can dynamically configure the heating sequence, duration, and frequency of each oil well based on the power generation of the photovoltaic array, the screw pump power, fluid production, wax deposition pattern, and wax removal cycle of each oil well, with the minimum curtailment rate as the objective function. This establishes a rotating heating system for each oil well, dynamically matching the power generation of the photovoltaic array with the power consumption of each downhole electric heating device in the start-up state. The rational configuration of the photovoltaic array's power generation ensures that the power generation of the photovoltaic array meets the downhole heating power while reducing the footprint, saving construction costs, and reducing curtailment rate. This ensures that each oil well can carry out wax removal and prevention operations in a timely manner, while reducing energy consumption, shortening the wax removal cycle, and significantly reducing the cost of hot washing and wax removal for oil wells. Attached Figure Description

[0035] Appendix Figure 1 This is a control flowchart of the downhole electric heating wax removal electrocoupling control system in Embodiments 1-2 of the present invention.

[0036] Appendix Figure 2 The flowchart shows the wax removal cycle for determining the wax thickness in Examples 1-5 of the present invention.

[0037] Appendix Figure 3 This is a schematic diagram of embodiments 6-7 of the present invention. Detailed Implementation

[0038] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0039] The present invention will be further described below with reference to embodiments:

[0040] Example 1: As shown in the attached document Figure 1 As shown, the photovoltaic direct-drive wax removal method includes the following steps:

[0041] (1) Select a suitable screw pump oil well group in the area, and determine the wax deposition pattern and wax removal cycle of each oil well based on the well condition parameters of each oil well;

[0042] (2) Install downhole electric heating devices in each well of the screw pump well group and determine the total power consumption of downhole electric heating for the screw pump well group;

[0043] (3) Based on the light resource conditions of the well site of the screw pump oil well group, simulate the daily power generation curve under different photovoltaic installation power conditions, select the photovoltaic installation capacity that matches the total power consumption of downhole electric heating, and set up a photovoltaic array at a suitable location in the well site;

[0044] (4) Connect the photovoltaic array to each downhole electric heating device through the downhole electric heating and wax removal electric coupling control system. The downhole electric heating and wax removal electric coupling control system can establish a multi-well rotation heating system based on the power generation of the photovoltaic array and the screw pump power, production volume, wax deposition pattern and wax removal cycle of each oil well, with the lowest light rejection rate as the objective function. It can dynamically configure the heating sequence, duration and frequency of each oil well, automatically control the start and stop of the downhole electric heating device of each oil well, and complete the wax removal and prevention operation in a timely manner.

[0045] During use, the well condition parameters of each oil well can be obtained through existing oil well detection devices or through dedicated detection devices; the wax deposition pattern and wax deposition cycle of each oil well can be determined through mature mathematical models in existing technologies or through existing wax removal operation frequency and cycle. In this embodiment, each oil well in the screw pump oil well group can be an electric submersible screw pump oil well; since the distribution areas of each oil well in the same oil production area are different, multiple screw pump well groups can be set up. Each screw pump well group can be determined according to the distribution area location and distance of each oil well, or it can be reasonably divided by calculating the number of photovoltaic arrays and construction costs. When the distribution of each oil well in the same oil production area is relatively concentrated, only one well group can be set up; the downhole electric heating device is selected from the downhole electric heating devices known and commonly used by those skilled in the art in the prior art; the heating time can be set according to the wax deposition pattern and wax deposition rate of each oil well (wax removal cycle) to ensure that at least one well can be effectively wax removed on the same day.

[0046] The multi-well rotation heating system and dynamic configuration of the heating sequence, duration, and frequency of each oil well in the above technical solution may include:

[0047] If the power generation of the photovoltaic array reaches the starting power of the downhole electric heating device, the multi-well rotation heating system will be activated, and the start-stop system will be consistent with the illumination conditions.

[0048] When the power generation of the photovoltaic array is sufficient to start the downhole heating device normally, but insufficient to heat the produced fluid temperature to the preset dewaxing temperature threshold, the downhole heating device can be operated in a low-power state. The heating duration and heating frequency can be determined in combination with the illumination time and the wax deposition pattern. Usually, it is continuously heated for a certain period of time to effectively prevent wax deposition in the wellbore by increasing the temperature of the fluid flow in the well.

[0049] When the photovoltaic array generates enough power to start all downhole heating devices in the dewaxing cycle, the downhole heating devices can directly heat the produced fluid to the dewaxing temperature threshold and then stop heating, so that the oil wells in the dewaxing cycle can complete the dewaxing operation on schedule. At this time, although the remaining power of the photovoltaic array is not enough to heat the produced fluid to the dewaxing temperature threshold of the other downhole heating devices, it can enable the other downhole heating devices to operate at low power and heat at low temperature (relative to the dewaxing heating temperature) to prevent waxing. If all oil wells in the dewaxing cycle have completed the dewaxing operation, the photovoltaic array can still generate power normally, which can enable the other downhole heating devices to operate at low power and achieve dewaxing through continuous low temperature heating.

[0050] When the power generation of the photovoltaic array is insufficient to start all downhole heating devices in the wax removal cycle, the heating sequence and heating duration of each well in the wax removal cycle can be determined by combining the screw pump power, fluid production, wax deposition pattern, wax removal cycle, and real-time power generation of the photovoltaic array. The heating can then be switched in turn to complete the wax removal operation. If there is any remaining power, it can also be used for heating and wax prevention operations of the waiting wells or other wells.

[0051] The above-mentioned technical solution uses photovoltaic array power generation to directly drive the downhole electric heating device, which heats the fluid flow in the wellbore for wax removal and anti-waxing operations. This can greatly reduce the cost of hot washing and wax removal for a single oil well and reduce carbon emissions through green electricity.

[0052] The above technical solution is based on the photovoltaic array's power generation capacity, formation fluid supply capacity, and screw pump lifting capacity. It is constrained by ensuring constant production and constant screw pump output power, and aims to minimize the curtailment rate. The downhole electric heating dewaxing and electrical coupling control system uses a multi-well rotation heating system to dynamically match the power generation of the photovoltaic array with the power consumption of each downhole electric heating device in the start-up state. This rationally allocates the power generation of the photovoltaic array, optimizes the heating time of each downhole heating device, effectively reduces energy consumption and lowers the curtailment rate of the photovoltaic array, while ensuring that each oil well can carry out dewaxing and anti-waxing operations in a timely manner, shortening the dewaxing cycle and significantly reducing the cost of hot washing dewaxing in oil wells.

[0053] Example 2: As shown in the attached document Figure 2 As shown, obtaining the wax deposition patterns and wax removal cycles of each oil well includes:

[0054] Based on the well condition parameters of each oil well, the growth rate of paraffin deposition thickness in each oil well is obtained by the following formula;

[0055]

[0056] Among them, υ h W represents the growth rate of paraffin deposition thickness, in m / s; W represents the total paraffin deposition rate in each well, in kg / (m³).2 ·s); ρ s The density of solid paraffin, in kg / m³ 3 H s The content of wax in the non-flowing layer, %; ρ o The density of crude oil in the trap layer is expressed in kg / m³. 3 ;

[0057] By combining the growth rate of paraffin deposition thickness in each oil well with the fluid production situation, the wax deposition pattern and wax deposition cycle of each oil well can be obtained.

[0058] During use, the above formula can accurately determine the wax removal cycle of each oil well. When the wax deposition rate of an oil well is fast, it indicates that the wax removal cycle interval is short, and the rotation heating cycle needs to be shortened. When the wax deposition rate of an oil well is slow, it indicates that the wax removal cycle interval is long, and the heating cycle can be appropriately extended. Thus, based on the wax deposition pattern and cycle of each oil well, the rotation frequency and heating cycle of each oil well can be accurately determined, ensuring that each oil well can rationally and fully utilize solar energy resources, reduce energy consumption, and complete the rotation wax removal operation for multiple oil wells as much as possible while meeting the normal production needs of the oil wells. Depending on the requirements, the growth rate of wax deposition thickness can be obtained based on various mathematical models for calculating wax deposition in existing technologies for dealing with oil well wax deposition problems. These models can be diffusion-shear-aging models, diffusion-shear deposition models, or diffusion-shear-erosion experimental models, etc.

[0059] Example 3: As shown in the attached document Figure 2 As shown, the total paraffin deposition rate in each oil well includes: combining the paraffin deposition mechanism of screw pump wells and the paraffin deposition mechanism of oil wells, the molecular diffusion deposition rate of paraffin on the inner wall of the tubing is obtained by the following formula;

[0060]

[0061] Among them, W ml The mass transfer rate of dissolved paraffin molecules to the tube wall, Kg / (m 2 ·s); C d This is the sedimentation constant, typically taken as 1.5 kg·m / s. 2 C h The unit conversion factor is 0.8267578; C p ρ is the isobaric specific heat of the fluid in the wellbore, in kJ / (kg·℃); s The density of solid paraffin, in kg / m³ 3 ;ρ l The density of the fluid in the wellbore is expressed in kg / m³. 3 μ is the viscosity of the fluid, Pa·s; V is the volumetric flow rate of the wellbore, m³ / s. 3 / s; k is the thermal conductivity coefficient of the fluid in the wellbore, KJ / (m·s·℃); d tdT / dL is the tubing diameter, in meters; dT / dL is the axial temperature gradient of the wellbore, in degrees Celsius per meter; T t The temperature of the inner wall of the oil pipe is ℃.

[0062] In the above technical solution, the molecular diffusion deposition rate of paraffin on the inner wall of the oil pipe can be obtained by the Fick equation, i.e.;

[0063]

[0064] Among them, C d This is the sedimentation constant, typically taken as 1.5 kg·m / s. 2 C l Let ρ be the diffusion coefficient of paraffin molecules; s The density of solid paraffin, in kg / m³ 3 μ is the viscosity of the fluid, Pa·s; dw / dT is the temperature-dependent concentration gradient of dissolved paraffin, 1 / ℃; dT / dr is the radial temperature gradient at the pipe wall, ℃ / m.

[0065] Normalizing the above equation yields the following equation:

[0066]

[0067] Regression analysis of the experimental data yielded the following formula:

[0068]

[0069] Among them, C h The unit conversion factor is 0.8267578; T t Temperature of the inner wall of the oil pipe, in °C;

[0070] Based on the principle of thermal equilibrium, the radial temperature gradient of the fluid can be obtained as follows:

[0071]

[0072] Where V is the volumetric flow rate of the wellbore, m 3 / s;ρ l The density of the fluid in the wellbore is expressed in kg / m³. 3 C p d is the isobaric specific heat of the fluid in the wellbore, kJ / (kg·℃); k is the thermal conductivity coefficient of the fluid in the wellbore, kJ / (m·s·℃); d t dT / dL is the tubing diameter, in meters; dT / dL is the axial temperature gradient of the wellbore, in degrees Celsius / m.

[0073] Combining the above equations, we can obtain the molecular diffusion deposition rate W of paraffin on the inner wall of the tubing. ml .

[0074] The shear dispersion deposition rate of paraffin in the tubing is obtained by the following formula;

[0075]

[0076] Among them, W dl The mass of crystalline wax deposited per unit time and per unit area by shear dispersion, in kg / (m²). 2 ·s); C d C is the sedimentation constant, typically taken as 1500; h The unit conversion factor is 0.8267578; γ is the shear rate, 1 / s; T t T represents the temperature of the inner wall of the oil pipe, in °C. C Temperature at the center of the oil pipe, in °C.

[0077] In the above technical solution, the shear dispersion deposition rate of paraffin inside the tubing can be expressed as:

[0078] W dl =C d K * C * γ

[0079] Among them, W dl The mass of crystalline wax deposited per unit time and per unit area by shear dispersion, in kg / (m²). 2 ·s); C d K is the sedimentation constant, typically taken as 1500. * Let Kg / m be the shear deposition rate constant. 2 γ is the shear rate, 1 / s; C * The volume concentration of wax crystals at the wall surface, in %;

[0080] Normalizing the above equation yields the following equation:

[0081]

[0082] in, Unit conversion factor;

[0083] The normalized result of the molecular diffusion deposition rate obtained from the above formula is as follows:

[0084]

[0085] Among them, C h The unit conversion factor is 0.8267578;

[0086] Analysis of the experimental data yielded the following results:

[0087] W dl * =1.022γ

[0088] Combining the above equations, we can obtain the shear dispersion deposition rate W of paraffin in the tubing. dl .

[0089] The total paraffin deposition rate W in each oil well is obtained by the following formula;

[0090] W = W ml +W dl

[0091] Example 4: The downhole electric heating dewaxing control system can also be connected to the grid power supply. When the power generation of the photovoltaic array is insufficient, the grid power supply can be used to supplement the power supply.

[0092] With this setup, grid power can serve as a backup power source. When the photovoltaic array is affected by winter, rainy season, or other extreme weather and the power generation is insufficient to start the downhole heating device, the downhole electric heating dewaxing power coupling control system can automatically switch to grid power and continue to switch downhole heating devices in rotation according to the dewaxing cycle of each oil well, thereby ensuring that each oil well can complete the dewaxing operation on schedule.

[0093] Example 5: During the wax removal process, the heating time for a single well shall not be less than 5 hours. If the temperature of the produced fluid at the wellhead is greater than 80°C, the heating shall be stopped. If the temperature of the produced fluid at the wellhead is always less than 80°C, the heating shall continue for at least 5 hours.

[0094] During operation, the downhole electric heating dewaxing electrocoupling control system can rationally allocate the power generation of the photovoltaic array by combining the power generation pattern of the photovoltaic array and the downhole rotating heating system. Specifically, when the photovoltaic array is generating power, the downhole electric heating cable is activated to begin heating and dewaxing operations; heating stops when the photovoltaic array is not generating power. Considering winter sunlight conditions, to achieve the desired dewaxing effect, the heating time for a single well should generally not be less than 5 hours. The heating time can also be determined by comprehensively considering the shortest winter sunshine hours in different regions.

[0095] In this embodiment, the dewaxing temperature threshold can be 80°C. For oil wells in the dewaxing cycle, when the temperature of the produced fluid at the wellhead reaches above 80°C, heating is automatically stopped, allowing the oil well to undergo dewaxing operations. At the same time, other downhole heating devices can be switched on to reduce energy waste and lower the curtailment rate. If the temperature of the produced fluid at the wellhead consistently fails to reach 80°C, it indicates that the downhole heating device is operating at low power, using low-temperature heating of the produced fluid to implement dewaxing operations.

[0096] In addition, whether to restart heating after the oil well in the dewaxing cycle has been heated to 80°C for the first time can be determined based on the dewaxing pattern of each oil well and the monitored tubing pressure. At this time, it is necessary to take into account the dewaxing effect of the previous heating.

[0097] Example 6: As attached Figure 3As shown, the photovoltaic direct-drive wax removal device includes: a photovoltaic array, a downhole electric heating wax removal electrical coupling control system, and a downhole heating device. The photovoltaic array can provide a stable power supply to the downhole electric heating wax removal electrical coupling control system and the downhole heating system. The downhole electric heating wax removal electrical coupling control system can monitor the real-time power generation of the photovoltaic array, determine the heating power and heating duration of the downhole electric heating system at a certain moment, and enable the power generation of the photovoltaic array to be dynamically matched with the start and stop of the downhole electric heating system. Each screw pump oil well is equipped with a downhole heating device.

[0098] With this configuration, the downhole electric heating dewaxing control system can dynamically configure the heating sequence, duration, and frequency of each oil well based on the real-time power generation of the photovoltaic array, the screw pump power, fluid production, wax deposition pattern, and dewaxing cycle of each oil well, with the minimum curtailment rate as the objective function. This establishes a rotating heating system for each oil well, dynamically matching the power generation of the photovoltaic array with the power consumption of each downhole electric heating device in operation. This rational configuration of the photovoltaic array's power generation ensures that the power output meets the downhole heating power requirements while reducing the footprint, saving construction costs, and minimizing curtailment. It ensures that each oil well can perform timely dewaxing and anti-waxing operations, while reducing energy consumption and dewaxing costs, shortening the dewaxing cycle, and maintaining stable oil well production while increasing the temperature of the produced fluid. This system can replace the original surface gathering and transportation heater.

[0099] Example 7: As attached Figure 3 As shown, the downhole electric heating dewaxing control system includes an MPPT controller, a voltage regulator, a follow-up matching control system, and a detection system. The photovoltaic array is connected in series with the MPPT controller, voltage regulator, and follow-up matching control system in sequence, and the detection system is connected to the follow-up matching control system. The MPPT controller enables the photovoltaic array to always operate at its maximum power point. The detection system can detect the DC input voltage, current, and heating power of each downhole electric heating device, the DC output active power, reactive power, power factor, daily power generation, and total power generation of the photovoltaic array, the well condition parameters of each oil well, and the power of the screw pump. After receiving the detection data from the detection system, the follow-up matching control system can intelligently process the detection data and automatically control the start and stop of each downhole electric heating device according to the processing results and the wax deposition pattern of each oil well, realizing the rotational heating of each oil well.

[0100] Example 8: The follow-up matching control system includes a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply circuit, a smart electricity meter, and a detection system. The PLC controller can calculate the photovoltaic output curve of the photovoltaic array based on the detection data of the detection system, and automatically control and adjust the heating power, heating time, and heating frequency of each downhole electric heating device in combination with the load characteristic curve of each screw pump.

[0101] In the above technical solution, the PLC, as the control unit, can automatically control the start and stop of the downhole electric heating device of each oil well based on the calculation results of the mathematical model predicting the wax deposition law of the oil well, and control the operation strategy of the screw pump well group.

[0102] Example 9: The well condition parameters of each oil well include the oil layer temperature, wellhead fluid temperature, surface temperature, paraffin density, tubing inner diameter, daily fluid production, oil layer depth, crude oil viscosity, crude oil density, thermal conductivity, fluid specific heat at constant pressure, and wellbore axial temperature gradient.

[0103] Example 10: As attached Figure 1 As shown, the downhole electric heating device can be a downhole heating cable.

[0104] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for removing wax from direct-drive photovoltaic systems, characterized in that, Includes the following steps: (1) Select a suitable screw pump oil well group in the area, and determine the wax deposition pattern and wax removal cycle of each oil well based on the well condition parameters of each oil well; (2) Install downhole electric heating devices in each well of the screw pump well group and determine the total power consumption of downhole electric heating for the screw pump well group; (3) Based on the light resource conditions of the well site of the screw pump oil well group, simulate the daily power generation curve under different photovoltaic installation power conditions, select the photovoltaic installation capacity that matches the total power consumption of downhole electric heating, and set up a photovoltaic array at a suitable location in the well site; (4) Connect the photovoltaic array to each downhole electric heating device through the downhole electric heating and wax removal electric coupling control system. The downhole electric heating and wax removal electric coupling control system can establish a multi-well rotation heating system based on the power generation of the photovoltaic array and the screw pump power, production volume, wax deposition pattern and wax removal cycle of each oil well, with the lowest light rejection rate as the objective function. It can dynamically configure the heating sequence, duration and frequency of each oil well, automatically control the start and stop of the downhole electric heating device of each oil well, and complete the wax removal and prevention operation in a timely manner.

2. The photovoltaic direct-drive wax removal method according to claim 1, characterized in that, The process of obtaining the wax deposition patterns and wax removal cycles for each oil well includes: Based on the well condition parameters of each oil well, the growth rate of paraffin deposition thickness in each oil well is obtained by the following formula; Among them, υ h W represents the growth rate of paraffin deposition thickness, in m / s; W represents the total paraffin deposition rate in each well, in kg / (m³). 2 ·s); ρ s The density of solid paraffin, in kg / m³ 3 H s The content of wax in the non-flowing layer, %; ρ o The density of crude oil in the trap layer is expressed in kg / m³. 3 ; By combining the growth rate of paraffin deposition thickness in each oil well with the fluid production situation, the wax deposition pattern and wax deposition cycle of each oil well can be obtained.

3. The photovoltaic direct-drive wax removal method according to claim 2, characterized in that, The total paraffin deposition rate in each oil well includes: the molecular diffusion deposition rate of paraffin on the inner wall of the tubing, obtained by combining the paraffin deposition mechanism of screw pump wells and the paraffin deposition mechanism of oil wells through the following formula; Among them, W ml The mass transfer rate of dissolved paraffin molecules to the tube wall, Kg / (m 2 ·s); C d This is the sedimentation constant, typically taken as 1.5 kg·m / s. 2 C h The unit conversion factor is 0.8267578; C p ρ is the isobaric specific heat of the fluid in the wellbore, in kJ / (kg·℃); s The density of solid paraffin, in kg / m³ 3 ;ρ l The density of the fluid in the wellbore is expressed in kg / m³. 3 μ is the viscosity of the fluid, Pa·s; V is the volumetric flow rate of the wellbore, m³ / s. 3 / s; k is the thermal conductivity coefficient of the fluid in the wellbore, KJ / (m·s·℃); d t dT / dL is the tubing diameter, in meters; dT / dL is the axial temperature gradient of the wellbore, in degrees Celsius per meter; T t Temperature of the inner wall of the oil pipe, in °C; The shear dispersion deposition rate of paraffin in the tubing is obtained by the following formula; Among them, W dl The mass of crystalline wax deposited per unit time and per unit area by shear dispersion, in kg / (m²). 2 ·s); C d C is the sedimentation constant, typically taken as 1500; h The unit conversion factor is 0.8267578; γ is the shear rate, 1 / s; T t T represents the temperature of the inner wall of the oil pipe, in °C. C Temperature at the center of the oil pipe, in °C; The total paraffin deposition rate W in each oil well is obtained by the following formula; W=W ml +W dl 。 4. The photovoltaic direct-drive wax removal method according to claim 1, 2, or 3, characterized in that, The downhole electric heating dewaxing control system can also be connected to the grid power supply. When the photovoltaic array's power generation is insufficient, it can be supplemented by grid power.

5. The photovoltaic direct-drive wax removal method according to claim 1, 2, or 3, characterized in that, During the wax removal process, the heating time for a single well should not be less than 5 hours. If the temperature of the produced fluid at the wellhead is greater than 80°C, the heating should be stopped. If the temperature of the produced fluid at the wellhead is always less than 80°C, the heating should continue for at least 5 hours.

6. The photovoltaic direct-drive wax removal method according to claim 4, characterized in that, During the wax removal process, the heating time for a single well should not be less than 5 hours. If the temperature of the produced fluid at the wellhead is greater than 80°C, the heating should be stopped. If the temperature of the produced fluid at the wellhead is always less than 80°C, the heating should continue for at least 5 hours.

7. An apparatus for implementing the photovoltaic direct-drive anti-wax removal method according to any one of claims 1-6, characterized in that, include: Photovoltaic array, downhole electric heating dewaxing electro-coupled control system and downhole heating device; The photovoltaic array can provide a stable power supply for the downhole electric heating dewaxing electro-coupled control system and downhole heating system. The downhole electric heating dewaxing electrocoupling control system can monitor the real-time power generation of the photovoltaic array, determine the heating power and heating duration of the downhole electric heating system at a certain moment, and enable the power generation of the photovoltaic array to be dynamically matched with the start and stop of the downhole electric heating system; each screw pump oil well is equipped with a downhole heating device.

8. The apparatus according to claim 7, characterized in that, The downhole electric heating dewaxing electrical coupling control system includes an MPPT controller, a voltage regulator, a follow-up matching control system, and a detection system. The photovoltaic array is connected in series with the MPPT controller, voltage regulator, and follow-up matching control system in sequence, and the detection system is connected to the follow-up matching control system. The MPPT controller enables the photovoltaic array to always operate at its maximum power point. The detection system can detect the DC input voltage, current, and heating power of each downhole electric heating device, the DC output active power, reactive power, power factor, daily power generation, and total power generation of the photovoltaic array, the well condition parameters of each oil well, and the power of the screw pump. After receiving the detection data from the detection system, the follow-up matching control system can intelligently process the detection data and automatically control the start and stop of each downhole electric heating device according to the processing results and the wax deposition pattern of each oil well, realizing the rotational heating of each oil well.

9. The apparatus according to claim 8, characterized in that, The servo-matching control system includes a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply circuit, a smart electricity meter, and a detection system. The PLC controller can calculate the photovoltaic output curve of the photovoltaic array based on the detection data from the detection system, and automatically control and adjust the heating power, heating duration, and heating frequency of each downhole electric heating device in conjunction with the load characteristic curves of each screw pump. Alternatively, the well condition parameters of each oil well include the oil layer temperature, wellhead fluid temperature, surface temperature, paraffin density, tubing inner diameter, daily fluid production, oil layer depth, crude oil viscosity, crude oil density, thermal conductivity coefficient, fluid specific heat at constant pressure, and wellbore axial temperature gradient.

10. The apparatus according to claim 7, 8, or 9, characterized in that, The downhole electric heating device is a downhole heating cable.

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