Photovoltaic direct-drive paraffin removal and control method and device

Abstract

The invention relates to the technical field of borehole cleaning methods, in particular to a photovoltaic direct-drive paraffin removal and control method and device, and the photovoltaic direct-drive paraffin removal and control device comprises a photovoltaic array, an electric coupling control system for underground electric heating paraffin removal and an underground heating device. The underground electric heating device is directly driven through power generation of the photovoltaic array, liquid flow in a shaft is heated for paraffin removal and prevention operation, the thermal washing paraffin removal cost of a single oil well can be greatly reduced, and carbon emission is reduced through green electricity; according to the electric coupling control system for underground electric heating paraffin removal, the generating capacity of the photovoltaic array can be dynamically matched with the electric power of each underground electric heating device in a starting state, and the generating capacity of the photovoltaic array is reasonably configured, so that the occupied area can be reduced while the generating power of the photovoltaic array meets the underground heating power; the construction cost is saved, the light discarding rate is reduced, it is ensured that all oil wells can conduct paraffin removal and control operation in time, energy consumption can be reduced, the paraffin removal period can be shortened, and the oil well thermal washing paraffin removal cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wellbore cleaning methods, and is a photovoltaic direct-drive wax cleaning and preventing method and device. BACKGROUND

[0002] Petroleum is mainly a mixture of various components of hydrocarbons, and the phase state of various components of hydrocarbons changes with the change of mining conditions. The solid material in it is mainly alkane containing carbon atoms numbered from 16 to 64, which is called paraffin. Pure paraffin is a white slightly transparent crystalline body.

[0003] During the production process of an oil well, when the temperature and pressure decrease and gas is precipitated, the paraffin dissolved in crude oil crystallizes and precipitates when certain conditions are reached. With further changes in conditions, paraffin continues to precipitate, and its crystals accumulate and deposit on equipment and tools such as oil pipes, casings, sucker rods, and oil pumps. This phenomenon is called waxing. However, the waxing of an oil well is not a white crystal, but a mixture of black semi-solid and solid paraffin, asphalt, gum, and other impurities.

[0004] After the oil well is waxed, the inner diameter of the oil outlet channel in the wellbore gradually narrows, the back pressure of the formation gradually increases, the resistance to oil flow increases, and the overall production of the oil well is significantly reduced. When waxing occurs in the oil pipe or the sucker rod, the resistance to oil flow in the oil pipe increases, the working load of the oil pumping machine is increased, the wax sticking of the oil pump is caused, and the pump efficiency of the oil pump is seriously affected, which greatly reduces the production of crude oil and even damages the oil pumping equipment, leading to production safety accidents.

[0005] Currently, oil fields usually use hot washing trucks to clean the wax of each oil well in the group of submersible screw pump oil wells, but this method has the problems of high wax cleaning cost, long hot washing period, and high wax cleaning energy consumption. In addition, due to the different well conditions of each screw pump oil well, the waxing rate and waxing point of these oil wells are different, making it difficult to ensure timely wax cleaning for each oil well during the wax cleaning operation using the hot washing truck, resulting in reduced production and increased power consumption of these oil wells. SUMMARY

[0006] The present application provides a photovoltaic direct-drive wax cleaning and preventing method and device, which overcomes the shortcomings of the prior art and effectively solves the problems of high wax cleaning cost, long hot washing period, and high wax cleaning energy consumption in the existing wax cleaning operation of submersible screw pump oil wells, and cannot timely clean the wax according to the well conditions of each oil well.

[0007] One of the technical solutions of the present application is achieved by the following measures: a photovoltaic direct-drive wax cleaning and preventing method, comprising the following steps:

[0008] (1) Selecting a suitable screw pump oil well group in a selected area, determining the wax deposition law and wax removal period of each oil well according to the well condition parameters of each oil well;

[0009] (2) Setting downhole electric heating devices in each oil well of the screw pump oil well group, and determining the total power of the downhole electric heating of the screw pump oil well group;

[0010] (3) Simulating the daily power generation curves of different photovoltaic installed power conditions in combination with the light resource conditions of the well site of the screw pump oil well group, selecting the photovoltaic installed capacity matched with the total power of the downhole electric heating, and setting the photovoltaic array at a suitable position of the well site;

[0011] (4) Connecting the photovoltaic array with each downhole electric heating device through the downhole electric heating and wax removal power coupling control system, which can establish a multi-well rotation heating system with the lowest light abandonment rate as the objective function according to the power generation of the photovoltaic array and the screw pump power, liquid production, wax deposition law and wax removal period of each oil well, dynamically configure the heating sequence, time length and heating frequency of each oil well, automatically control the start and stop of the downhole electric heating device of each oil well, and timely complete the wax removal and prevention operation.

[0012] The following is a further optimization or / and improvement of the above technical solutions of the invention:

[0013] The above wax deposition law and wax deposition period of each oil well obtained according to the well condition parameters of each oil well can include:

[0014] The growth rate of the paraffin deposition thickness in each oil well is obtained according to the well condition parameters of each oil well by the following formula:

[0015]

[0016] Wherein, υ h is the growth rate of the wax deposition thickness, m / s; W is the total paraffin deposition rate in each oil well, Kg / (m 2 ·s); ρ s is the density of solid paraffin, Kg / m 3 ; H s is the content of wax in the non-flowing layer, %; ρ o is the density of crude oil in the trapping layer, Kg / m 3 ;

[0017] The wax deposition law and wax deposition period of each oil well can be obtained by combining the growth rate of the paraffin deposition thickness in each oil well with the liquid production.

[0018] The total paraffin deposition rate in each oil well can include: the molecular diffusion deposition rate of paraffin on the inner wall of the oil pipe is obtained by the following formula in combination with the wax deposition mechanism of the screw pump well and the wax deposition mechanism of the oil well:

[0019]

[0020] wherein, W ml is the mass transfer rate of dissolved paraffin molecules to the pipe wall, Kg / (m 2 ·s);C d is the deposition constant, generally taken as 1.5 Kg·m / s 2 ; C h is the unit conversion factor, taken as 0.8267578;C p is the constant-pressure specific heat of the wellbore fluid, KJ / (Kg·℃);ρ s is the density of the solid paraffin, Kg / m 3 ; ρ l is the density of the wellbore fluid, Kg / m 3 ; μ is the viscosity of the fluid, Pa·s;V is the volumetric flow rate of the wellbore, m 3 / s;k is the thermal conductivity of the wellbore fluid, KJ / (m·s·℃);d t is the tubing diameter, m;dT / dL is the wellbore axial temperature gradient, ℃ / m;T t is the temperature of the inner wall of the tubing, ℃;

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

[0022]

[0023] wherein, W dl is the mass of crystalline wax deposited per unit time and per unit area by shear dispersion, Kg / (m 2 ·s);C d is the deposition constant, generally taken as 1500;C h is the unit conversion factor, 0.8267578;γ is the shear rate, 1 / s;T t is the temperature of the inner wall of the tubing, ℃;T C is the temperature at the center of the tubing, ℃;

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

[0025] W = W ml + W dl

[0026] The above downhole electric heating paraffin removal electric coupling control system can also be connected with network electricity, and when the power generation of the photovoltaic array is insufficient, the network electricity is used to realize supplementary power supply.

[0027] In the above wax removal and prevention process, the single well heating time can be not less than 5 hours, if the wellhead produced liquid temperature can be greater than 80 DEG C, then stop heating, if the wellhead produced liquid temperature is always less than 80 DEG C, continue heating for at least 5 hours.

[0028] The second technical solution of the present application is realized by the following measures: a photovoltaic direct-drive wax removal and prevention device, comprising: a photovoltaic array, an electrically coupled control system for downhole electric heating wax removal, and a downhole heating device, the photovoltaic array can provide stable power supply for the electrically coupled control system for downhole electric heating wax removal and the downhole heating system; the electrically coupled control system for downhole electric heating wax removal can monitor the real-time power generation of the photovoltaic array, determine the heating power and heating time of the downhole electric heating system at a certain time, and dynamically match the power generation of the photovoltaic array with the start and stop of the downhole electric heating system; each screw pump well is provided with a downhole heating device.

[0029] The following is a further optimization or / and improvement of the above technical solution of the application:

[0030] The above electrically coupled control system for downhole electric heating wax removal can include an MPPT controller, a voltage stabilizer, a follow-up matching control system and a detection system, the photovoltaic array is connected in series with the MPPT controller, the voltage stabilizer and the follow-up matching control system in turn, and the detection system is connected with the follow-up matching control system; wherein the MPPT controller can make the photovoltaic array always operate at the maximum power point; the detection system can detect the direct current input voltage, current and heating power of each downhole electric heating device, the direct current output active power, reactive power, power factor, daily power generation and total power generation of the photovoltaic array, the well condition parameters of each well and the power of the screw pump; after receiving the detection data of 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 result and the wax deposition law of each well, to realize the rotation cutting heating of each well.

[0031] The above follow-up matching control system can include a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply loop, an intelligent electric meter and a detection system, wherein the PLC controller can calculate the photovoltaic output curve of the photovoltaic array according to 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.

[0032] The well condition parameters of each well can include the oil layer temperature, wellhead produced liquid temperature, surface temperature, paraffin density, oil pipe inner diameter, daily liquid production, oil layer depth, crude oil viscosity, crude oil density, heat transfer coefficient, fluid specific heat at constant pressure and wellbore axial temperature gradient in each well.

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

[0034] The application directly drives the downhole electric heating device by the photovoltaic array power generation to heat the liquid flow in the wellbore to perform the wax cleaning and prevention operation, can greatly reduce the hot washing wax cleaning cost of a single oil well, reduces the carbon emission through green electricity; the downhole electric heating wax cleaning electric coupling control system can dynamically configure the heating sequence, time length and heating frequency of each oil well with the lowest light abandonment rate as the objective function according to the power generation of the photovoltaic array, the power of the screw pump of each oil well, the liquid production, the wax deposition law and the wax cleaning period, establishes the rotation heating system of each oil well, dynamically matches the power generation of the photovoltaic array and the power consumption of each downhole electric heating device in the starting state, reasonably configures the power generation of the photovoltaic array, makes the power generation of the photovoltaic array meet the downhole heating power, reduces the occupied area, saves the construction cost and reduces the light abandonment rate, ensures that each oil well can timely perform the wax cleaning and prevention operation, reduces the energy consumption, shortens the wax cleaning period and greatly reduces the hot washing wax cleaning cost of the oil well. BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a control flow chart of the downhole electric heating wax cleaning electric coupling control system in the embodiment 1 of the application. Figure 1

[0036] FIG. 3 is a wax deposition thickness determination wax cleaning period flow chart of the embodiment 1-5 of the application. Figure 2

[0037] FIG. 5 is a principle diagram of the embodiment 6-7 of the application. Figure 3 DETAILED DESCRIPTION

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

[0039] The application will be further described in combination with the embodiments as follows:

[0040] Embodiment 1: as shown in the accompanying drawings, the photovoltaic direct drive wax cleaning and prevention method comprises the following steps: Figure 1

[0041] (1) selecting a suitable screw pump oil well group in a selected area, determining the wax deposition law and the wax cleaning period of each oil well according to the well condition parameters of each oil well;

[0042] (2) setting the downhole electric heating device in each oil well of the screw pump oil well group, and determining the total power consumption of the downhole electric heating of the screw pump oil well group;

[0043] (3) combining the light resource conditions of the well site of the screw pump oil well group, simulating the daily power generation power curve under different photovoltaic installed power conditions, selecting the photovoltaic installed capacity matched with the total power consumption of the downhole electric heating, and setting the photovoltaic array at a suitable position of the well site;

[0044] ​​​​(4) the photovoltaic array is connected with each downhole electric heating device through the electric coupling control system for downhole electric heating paraffin removal, and the electric coupling control system for downhole electric heating paraffin removal can establish a multi-well round cutting heating system with the lowest light abandonment rate as an objective function according to the power generation of the photovoltaic array, the screw pump power of each oil well, the liquid production, the paraffin deposition law and the paraffin removal period, dynamically configure the heating sequence, the heating duration and the heating frequency of each oil well, automatically control the start and stop of the downhole electric heating device of each oil well, and timely complete the paraffin removal and prevention operation.

[0045] During use, the well condition parameters of each oil well can be obtained through existing detection devices of each oil well, or through special detection devices; the paraffin deposition law and the paraffin deposition period of each oil well can be determined through a mature mathematical model in the prior art, or obtained through the existing paraffin removal operation frequency and period, and in the 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 operation area are different, multiple screw pump well groups can be set, the distribution area position and distance of each oil well can be determined, or the number and construction cost of the photovoltaic array can be calculated to reasonably divide, and when the distribution of each oil well in the same oil production area is relatively concentrated, only one well group can be set; the downhole electric heating device is selected from the downhole electric heating devices commonly known by those skilled in the art in the prior art; the heating duration can be set according to the paraffin deposition law and the paraffin deposition rate of each oil well (the paraffin removal period), to ensure that at least one well can be effectively cleaned on the same day.

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

[0047] If the power generation of the photovoltaic array reaches the starting power of the downhole electric heating device, the multi-well round cutting heating system is started, and the start and stop system is consistent with the illumination condition.

[0048] When the power generation of the photovoltaic array can normally start the downhole heating device, but is insufficient to heat the produced liquid to the preset paraffin removal temperature threshold, the downhole heating device can be operated in a low-power state, and the heating duration and the heating frequency can be determined in combination with the illumination time and the paraffin deposition law, and usually the heating is continued for a certain time to effectively prevent paraffin deposition in the wellbore by increasing the temperature of the liquid flow in the well.

[0049] When the power generation of the photovoltaic array is sufficient to normally start all downhole heating devices in the paraffin removal cycle, the downhole heating devices can directly heat the produced liquid to the paraffin removal temperature threshold and then stop heating, so that the oil wells in the paraffin removal cycle can complete the paraffin removal operation on schedule; at this time, although the remaining power of the photovoltaic array is insufficient to heat the produced liquid of the remaining downhole heating devices to the paraffin removal temperature threshold, it can enable the remaining downhole heating devices to operate in a low-power state and heat to prevent paraffin at a low temperature (relative to the paraffin removal heating temperature); if all oil wells in the paraffin removal cycle complete the paraffin removal operation, and the photovoltaic array still generates power normally, the other downhole heating devices can be operated in a low-power state, and paraffin can be prevented through continuous low-temperature heating.

[0050] When the power generation of the photovoltaic array is insufficient to normally start all downhole heating devices in the paraffin removal cycle, the heating sequence and heating duration of the oil wells in the paraffin removal cycle can be determined comprehensively in combination with the screw pump power, the liquid production, the paraffin deposition law, the paraffin removal cycle of the oil wells in the paraffin removal cycle, and the real-time power generation of the photovoltaic array, and then the heating can be switched to complete the paraffin removal operation; at this time, if there is still remaining power, it can also be used for heating paraffin prevention of the oil wells in the waiting state or the remaining oil wells.

[0051] The above technical solution directly drives the downhole electric heating device through the power generation of the photovoltaic array to heat the liquid flow in the wellbore for paraffin removal and paraffin prevention, which can greatly reduce the hot washing paraffin removal cost of a single oil well and reduce carbon emissions through green electricity.

[0052] The above technical solution is based on the power generation capacity of the photovoltaic array, the formation liquid supply capacity, and the screw pump lifting capacity, takes ensuring constant production and constant screw pump output power as constraint conditions, and takes the lowest light abandonment rate as the target. The downhole electric heating paraffin removal power coupling control system enables the power generation of the photovoltaic array and the power consumption of the downhole electric heating devices in the starting state to be dynamically matched through multi-well round heating system, reasonably allocates the power generation of the photovoltaic array, optimizes the heating duration of the downhole heating devices, effectively reduces energy consumption and the light abandonment rate of the photovoltaic array, and at the same time ensures that the oil wells can be timely paraffin removal and paraffin prevention, shortens the paraffin removal cycle, and greatly reduces the hot washing paraffin removal cost of the oil well.

[0053] Embodiment 2: as shown in the accompanying Figure 2 The above technical solution directly drives the downhole electric heating device through the power generation of the photovoltaic array to heat the liquid flow in the wellbore for paraffin removal and paraffin prevention, which can greatly reduce the hot washing paraffin removal cost of a single oil well and reduce carbon emissions through green electricity.

[0054] According to the well condition parameters of each oil well, the growth rate of the paraffin deposition thickness in each oil well is obtained by the following formula:

[0055]

[0056] wherein, υ h is the growth rate of the wax deposition thickness, m / s; W is the total paraffin deposition rate in each oil well, Kg / (m2 s) ; p s is the density of solid paraffin, Kg / m 3 ; H s is the content of wax in the non-flowing layer, %; p o is the density of crude oil in the trapping layer, Kg / m 3 ;

[0057] The growth rate of the paraffin deposition thickness in each oil well is combined with the production fluid condition, and the paraffin deposition law and the paraffin deposition period of each oil well can be obtained.

[0058] During use, the paraffin removal period of each oil well can be accurately determined by the above formula. When the paraffin deposition rate of the oil well is fast, it indicates that the paraffin removal period interval of the oil well is short, and the heating period of the round cutting needs to be shortened. When the paraffin deposition rate of the oil well is slow, it indicates that the paraffin removal period interval of the oil well is long, and the heating period can be appropriately prolonged. Therefore, the round cutting frequency and the heating period of each oil well can be accurately determined according to the paraffin deposition law and the paraffin deposition period of each oil well, so that the solar energy resources of each oil well can be reasonably and fully utilized, the energy consumption is reduced, and the round cutting paraffin removal operation of as many oil wells as possible can be completed while meeting the normal production of the oil wells. According to the needs, the growth rate of the paraffin deposition thickness can be obtained based on various mathematical models for calculating paraffin deposition in the prior art for treating the paraffin deposition problem of the oil well, which can be a diffusion-shearing-aging model, a diffusion-shearing deposition model, or a diffusion-shearing-erosion experiment model, etc.

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

[0060]

[0061] wherein, W ml is the mass transfer rate of the dissolved paraffin molecules to the pipe wall, Kg / (m 2 ·s) ; C d is the deposition constant, generally taken as 1.5 Kg·m / s 2 ; C h is a unit conversion coefficient, taken as 0.8267578; C p is the constant pressure specific heat of the wellbore fluid, KJ / (Kg·℃) ; p s is the density of solid paraffin, Kg / m 3 ; p l is the density of the wellbore fluid, Kg / m 3 ; μ is the viscosity of the fluid, Pa·s; V is the volumetric flow rate of the wellbore, m 3 / s; k is the thermal conductivity coefficient of the wellbore fluid, KJ / (m·s·℃) ; d t ​is the tubing diameter, m; dT / dL is the wellbore axial temperature gradient, ℃ / m; T t is the tubing inner wall temperature, ℃.

[0062] In the above technical solution, the molecular diffusion deposition rate of paraffin on the inner wall of the tubing can be obtained by Fick equation, that is,

[0063]

[0064] wherein, C d is the deposition constant, generally taken as 1.5 Kg·m / s 2 ; C l is the diffusion coefficient of paraffin molecules; p s is the density of solid paraffin, Kg / m 3 ; μ is the viscosity of fluid, Pa·s; dw / dT is the concentration gradient related to temperature of dissolved paraffin, 1 / ℃; dT / dr is the radial temperature gradient of the tubing wall, ℃ / m;

[0065] The above formula is normalized to obtain the following formula:

[0066]

[0067] The experimental data is regressed to obtain the following formula:

[0068]

[0069] wherein, C h is the unit conversion coefficient, taken as 0.8267578; T t is the tubing inner wall temperature, ℃;

[0070] According to the principle of thermal equilibrium, the radial temperature gradient of the fluid can be obtained as:

[0071]

[0072] wherein, V is the volumetric flow rate of the wellbore, m 3 / s; p l is the density of the wellbore fluid, Kg / m 3 ; C p is the specific heat at constant pressure of the wellbore fluid, KJ / (Kg·℃); k is the thermal conductivity coefficient of the wellbore fluid, KJ / (m·s·℃); d t is the tubing diameter, m; dT / dL is the wellbore axial temperature gradient, ℃ / m;

[0073] The above formula can be obtained by simultaneously solving the molecular diffusion deposition rate W ml of paraffin on the inner wall of the tubing.

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

[0075]

[0076] wherein, W dl is the mass of the crystalline wax deposited by shear dispersion per unit time and per unit area, Kg / (m 2 ·s); C d is the deposition constant, generally taken as 1500; C h is the unit conversion coefficient, 0.8267578; γ is the shear rate, 1 / s; T t is the temperature of the inner wall of the oil pipe, ℃; T C is the temperature at the center of the oil pipe, ℃.

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

[0078] W dl = C d K * C * γ

[0079] wherein, W dl is the mass of the crystalline wax deposited by shear dispersion per unit time and per unit area, Kg / (m 2 ·s); C d is the deposition constant, generally taken as 1500; K * is the shear deposition rate constant, Kg / m 2 ; γ is the shear rate, 1 / s; C * is the volume concentration of the wax crystal at the wall surface, %;

[0080] The above formula is normalized to obtain the following formula:

[0081]

[0082] wherein, the unit conversion coefficient;

[0083] The normalized result of the molecular diffusion deposition rate obtained according to the above formula is:

[0084]

[0085] wherein, C h is the unit conversion coefficient, 0.8267578;

[0086] Analysis of the experimental data shows that:

[0087] W dl * = 1.022 γ

[0088] The above formula can be obtained simultaneously to get the shearing dispersion deposition rate W of paraffin in the oil pipe dl .

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

[0090] W = W ml + W dl

[0091] In the embodiment 4, the electric coupling control system for downhole electric heating paraffin removal can also be connected with the grid electricity, and when the power generation of the photovoltaic array is insufficient, the grid electricity is used to realize the supplementary power supply.

[0092] Through such a setting, the grid electricity can be used as a backup power supply, and when the power generation of the photovoltaic array is insufficient due to the winter, rainy season or other extreme weather, the electric coupling control system for downhole electric heating paraffin removal can automatically switch the grid electricity to continue to rotate the downhole heating devices according to the paraffin removal period of each oil well, so as to ensure that each oil well can complete the paraffin removal operation on schedule.

[0093] In the embodiment 5, during the paraffin removal and prevention process, the heating time of a single well is not less than 5 hours, if the temperature of the wellhead produced liquid can be greater than 80℃, the heating is stopped, and if the temperature of the wellhead produced liquid is always less than 80℃, the heating is continued for at least 5 hours.

[0094] During use, the electric coupling control system for downhole electric heating paraffin removal can reasonably allocate the power generation of the photovoltaic array according to the power generation law of the photovoltaic array and the downhole rotation heating system, that is, when the photovoltaic array generates electricity, the downhole electric heating cable is started to heat and the paraffin removal and prevention operation is performed, and when the photovoltaic array does not generate electricity, the heating is stopped. In combination with the winter light conditions, in order to achieve the expected paraffin removal and prevention effect, the heating time of a single well should be not less than 5 hours, and the heating time can also be determined according to the shortest winter sunshine time in different regions.

[0095] In the embodiment, the paraffin removal temperature threshold can be 80℃, for the oil well in the paraffin removal period, when the temperature of the wellhead produced liquid reaches 80℃ or above, the heating is automatically stopped, and the oil well is implemented for paraffin removal operation, and at the same time, other downhole heating devices can be switched to work, so as to reduce energy waste and reduce the light abandonment rate. When the temperature of the wellhead produced liquid always fails to reach 80℃, it indicates that the downhole heating device is running in a low-power state, and the produced liquid is heated by low-temperature heating to implement paraffin prevention operation.

[0096] In addition, whether the heating of the oil well in the paraffin removal period is started again after the first heating to 80℃ can be determined according to the on-site paraffin removal law of each oil well and the monitored oil pipe pressure, and at this time, the last heating paraffin removal effect needs to be considered comprehensively.

[0097] In the embodiment 6, as shown in FIG. 6, the electric coupling control system for downhole electric heating paraffin removal comprises a downhole electric heating cable, a downhole electric heating cable control device, a photovoltaic array, a grid electricity connection device and a central control device. Figure 3As shown, the photovoltaic direct-drive wax removal device comprises a photovoltaic array, an electrically coupled control system for downhole electric heating wax removal, and a downhole heating device. The photovoltaic array can provide stable power supply for the electrically coupled control system for downhole electric heating wax removal and the downhole heating system. The electrically coupled control system for downhole electric heating wax removal 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 time, and dynamically match the power generation of the photovoltaic array with the start-stop of the downhole electric heating system. Each screw pump well is provided with a downhole heating device.

[0098] By such arrangement, the electrically coupled control system for downhole electric heating wax removal can dynamically configure the heating sequence, duration and frequency of each well according to the real-time power generation of the photovoltaic array, the screw pump power, the liquid production, the wax deposition law and the wax removal period of each well, take the minimum light abandonment rate as the objective function, establish a rotation heating system for each well, dynamically match the power generation of the photovoltaic array with 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, reduce the occupied area, save the construction cost and reduce the light abandonment rate, ensure that each well can timely perform wax removal and paraffin prevention operation, reduce energy consumption and wax removal cost, shorten the wax removal period, ensure the stable oil well production and improve the produced liquid temperature, and replace the original ground gathering and heating device.

[0099] Embodiment 7: as shown in the accompanying Figure 3 As shown, the electrically coupled control system for downhole electric heating wax removal comprises an MPPT controller, a voltage stabilizer, a follow-up matching control system and a detection system. The photovoltaic array is connected in series with the MPPT controller, the voltage stabilizer and the follow-up matching control system in sequence, and the detection system is connected with the follow-up matching control system. The MPPT controller can make the photovoltaic array always operate at the maximum power point. The detection system can detect the direct current input voltage, current and heating power of each downhole electric heating device, the direct current output active power, reactive power, power factor, daily power generation and total power generation of the photovoltaic array, the well condition parameters of each well and the power of the screw pump. After receiving the detection data of the detection system, the follow-up matching control system can intelligently process the detection data, automatically control the start-stop of each downhole electric heating device according to the processing result and the wax deposition law of each well, and realize the rotation heating of each well.

[0100] Embodiment 8: the follow-up matching control system comprises a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply loop, an intelligent electric meter and a detection system. The PLC controller can calculate the photovoltaic output curve of the photovoltaic array according to the detection data of the detection system, and automatically control and adjust the heating power, heating duration and heating frequency of each downhole electric heating device in combination with the screw pump load characteristic curve.

[0101] In the above technical solution, PLC serves as a control unit, which can automatically control the start and stop of the downhole electric heating device of each oil well and control the operation strategy of the screw pump well group according to the calculation results of the mathematical model predicted by the wax deposition law of the oil well.

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

[0103] Example 10: As shown in the 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. Non-essential technical features can be added or removed according to actual needs to meet the requirements of different situations.

Claims

1. A method of photovoltaic direct drive clean and paraffin removal, characterized in that, The following steps are involved: (1) Select a group of screw pump oil wells suitable for the region, 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 oil well of the screw pump oil well group and determine the total power consumed by the downhole electric heating of the screw pump oil well group; (3) Combined with the light resource conditions of the screw pump oil well group, the daily power generation curves of different photovoltaic installed power conditions were simulated, the photovoltaic installed capacity that matched the total power consumption of underground electric heating was selected, and the photovoltaic array was set up at the appropriate location of the well site; (4) The photovoltaic array is connected to each downhole electric heating device through an electric coupling control system for downhole electric heating and wax removal. The electric coupling control system for downhole electric heating and wax removal can establish a multi-well rotation heating system based on the power generation of the photovoltaic array and the screw pump power, liquid production, wax deposition law and wax removal cycle of each oil well, with the lowest light abandonment rate as the objective function, dynamically configure the heating sequence, duration and heating 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 time.

2. The photovoltaic direct drive clean and anti-waxing method according to claim 1, characterized in that, The method of obtaining the wax deposition pattern and wax removal cycle of each oil well includes: According to the well parameters of each oil well, the growth rate of paraffin deposition thickness in each oil well is obtained by the following formula: wherein υ h is the growth rate of the wax deposit thickness, m / s; W is the total wax deposit rate in each oil well, Kg / (m 2 ·s); p s is the density of solid paraffin, Kg / m 3 ; H s is the content of wax in the non-flowing layer, %; p o is the density of crude oil in the trapping layer, Kg / m 3 ; By combining the growth rate of paraffin deposition thickness in each oil well with the liquid production situation, the wax deposition law and wax deposition cycle of each oil well can be obtained.

3. The photovoltaic direct drive clean and anti-waxing method according to claim 2, characterized in that, The total paraffin deposition rate in each oil well includes: combining the wax deposition mechanism of the screw pump well and the wax deposition mechanism of the oil well, and obtaining the molecular diffusion deposition rate of the paraffin on the inner wall of the oil pipe by the following formula; wherein, W ml is the mass transfer rate of dissolved paraffin molecules to the pipe wall, Kg / (m 2 ·s); C d is the deposition constant, generally taken as 1.5 Kg·m / s 2 ; C h is a unit conversion factor, taken as 0.8267578; C p is the constant pressure specific heat of the wellbore fluid, KJ / (Kg·℃); p s is the density of the solid paraffin, Kg / m 3 ; p l is the density of the wellbore fluid, Kg / m 3 ; m is the viscosity of the fluid, Pa·s; V is the volumetric flow rate of the wellbore, m 3 / s; k is the thermal conductivity of the wellbore fluid, KJ / (m·s·℃); d t is the tubing diameter, m; dT / dL is the wellbore axial temperature gradient, ℃ / m; T t is the tubing inner wall temperature, ℃; The shear diffusion deposition rate of paraffin in the oil pipe is obtained by the following formula: wherein W dl is the mass of crystalline wax deposited by shear dispersion per unit time and per unit area, Kg / (m 2 ·s); C d is the deposition constant, generally taken as 1500; C h is the unit conversion factor, 0.8267578; γ is the shear rate, 1 / s; T t is the temperature of the inner wall of the tubing, °C; T C is the temperature at the center of the tubing, °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 clean and anti-waxing method according to claim 1 or 2 or 3, characterized in that, The electric coupling control system for underground electric heating and wax removal can also be connected to the grid. When the power generation of the photovoltaic array is insufficient, the grid can be used for supplementary power supply.

5. The photovoltaic direct drive clean and anti-waxing method according to claim 1 or 2 or 3, characterized in that, During the paraffin 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 be continued for at least 5 hours.

6. The photovoltaic direct drive clean and anti-waxing method according to claim 4, characterized in that, During the paraffin 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 be continued for at least 5 hours.

7. A device for implementing the method of claim 1-6, characterized in that, include: Photovoltaic array, electric coupling control system for underground electric heating and paraffin removal, and underground heating device. The photovoltaic array can provide stable power for the electric coupling control system for underground electric heating and paraffin removal and the underground heating system. The electric coupling control system for downhole electric heating and wax removal 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 dynamically match the power generation of the photovoltaic array 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 of claim 7, wherein, The electric coupling control system for the downhole electric heating wax removal comprises an MPPT controller, a voltage stabilizer, a follow-up matching control system and a detection system, the photovoltaic array is connected in series with the MPPT controller, the voltage stabilizer and the follow-up matching control system in sequence, and the detection system is connected with the follow-up matching control system; wherein the MPPT controller can enable the photovoltaic array to operate at the maximum power point all the time; the detection system can detect the direct current input voltage, current and heating power of each downhole electric heating device, the direct current 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 of 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 result and the wax deposition law of each oil well, so as to realize the rotation cutting heating of each oil well.

9. The apparatus of claim 8, wherein, The follow-up matching control system comprises a PLC controller, a DC input circuit, a control circuit, a protection circuit, an auxiliary power supply loop, an intelligent electric meter and a detection system, wherein the PLC controller can calculate the photovoltaic output curve of the photovoltaic array according to 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; or / and, the well condition parameters of each oil well comprise the oil layer temperature, wellhead liquid temperature, surface temperature, paraffin density, oil pipe inner diameter, daily liquid production, oil layer depth, crude oil viscosity, crude oil density, heat transfer coefficient, fluid constant-pressure specific heat and wellbore axial temperature gradient in each oil well.

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

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