Method for predicting wax deposition amount in conveying process of oil-water mixed conveying pipeline

Abstract

The invention relates to a method for predicting the wax deposition amount in the conveying process of an oil-water mixed conveying pipeline. The method comprises the following steps: measuring the temperature of soil near a buried oil-water mixed conveying pipeline; measuring the temperature of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions and the speed of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions; an oil-water mixture sample is obtained at an on-site wellhead sampling point, and the water content of the oil-water mixture in the conveying process of the oil-water mixed conveying pipeline is calculated; scraping off wax deposits from the oil-water mixed transportation pipeline, and calculating the wax deposition thickness; the wax deposition amount of the oil-water mixed transportation pipeline is comprehensively influenced by the water content, the inlet speed, the inlet temperature and the soil temperature in the oil-water mixed transportation pipeline, and the multi-physical-quantity operation parameters are combined to form a multi-parameter combination form orthogonal table; and establishing a multi-parameter combination mathematical model in the operation process of the oil-water mixed transportation pipeline, and predicting wax deposition in the transportation process of the oil-water mixed transportation pipeline. The method realizes accurate and convenient prediction of the wax deposition amount in the conveying process of the oil-water mixed conveying pipeline.

Description

Technical field:

[0001] The invention relates to the technical field of oil and gas storage and transportation, and in particular to a method for predicting wax deposition in a transportation process of an oil-water mixed pipeline. Background technology:

[0002] As most oil fields enter the middle and late stages of production, water content, input costs and energy consumption continue to increase, and higher requirements are put forward for normal temperature gathering and transportation. Influenced by many factors such as transportation technology, topography, and oil properties, heating or heat tracing is often used in the gathering and transportation process, resulting in an increase in electricity and fuel oil consumption from the wellhead to the metering room, which generally accounts for 30% to 40% of the total energy consumption of crude oil production, and the resulting increase in carbon dioxide emissions. At the same time, the occurrence of wax deposition during transportation will cause the effective flow area of ​​the pipeline to decrease, the energy loss to increase significantly, and even pipeline or equipment blockage accidents in severe cases. Against the background of the continuous increase in water content and the increasingly severe situation of energy conservation and consumption reduction, it is necessary to study the relationship between the wax deposition amount of easy-to-condense and high-viscosity crude oil gathering and transportation pipelines and the water content and oil-water mixture operating parameters with the goal of energy conservation and consumption reduction and safe operation of pipelines, so as to provide technical support for normal temperature gathering and transportation production and operation.

[0003] For the oil-water mixed pipeline transportation process, a loop test device is usually used to study the wax deposition law of the oil-water two-phase. However, the wax deposition amount of the oil-water mixed pipeline is affected by the dynamic changes of the actual working conditions on site. The internal corrosion of the pipeline during long-term operation leads to complex changes in roughness. In addition, the loop test device is an indoor pipeline, and the research object is part of the horizontal pipeline. The comprehensive influence of the local elbows, vertical pipes and long-distance horizontal pipelines from the wellhead to the metering room on the flow and wax deposition of crude oil is ignored. Therefore, the use of the loop test device to study the wax deposition law of the oil-water two-phase will cause certain errors. At the same time, in actual production, there is a close relationship between water content and wax deposition process. The presence of water phase will distort and reduce the wax diffusion path. The higher the water content, the smaller the internal temperature gradient, the lower the concentration gradient of wax molecules, and the driving force of wax molecule diffusion. Therefore, it is necessary to establish a new wax deposition amount prediction method in the oil-water mixed pipeline transportation process, and consider the influence of water content changes on wax deposition thickness, so as to achieve accurate and convenient prediction of wax deposition amount in the oil-water mixed pipeline transportation process.

[0004] In summary, the current prediction methods for wax deposition in oil-water mixed pipelines have certain limitations and cannot continuously, accurately and conveniently calculate the wax deposition in the oil-water mixed pipeline transportation process. Summary of the invention:

[0005] The object of the present invention is to provide a method for predicting the wax deposition amount during the transportation process of an oil-water mixed transportation pipeline. This method for predicting the wax deposition amount during the transportation process of an oil-water mixed transportation pipeline is used to solve the problem that when studying the wax deposition law of oil-water two-phase in the current oil-water mixed transportation pipeline using a loop test device, it cannot truthfully reflect the fluid flow and heat transfer characteristics in the actual mixed transportation pipeline, resulting in certain errors.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: This method for predicting the wax deposition amount during the transportation process of an oil-water mixed transportation pipeline includes the following steps:

[0007] Step 1: Arrange thermocouple thermometers in the soil near the buried depth position of the on-site oil-water mixed transportation pipeline to measure the soil temperature near the buried pipeline; measure the temperature of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions through the thermocouple thermometer at the pipeline temperature measurement interface in the metering room; measure the velocity of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions through the volumetric flowmeter in the straight section of the pipeline in the metering room.

[0008] Step 2: Obtain an oil-water mixture sample at the on-site wellhead sampling point, and calculate the water content of the oil-water mixture during the transportation process of the oil-water mixed transportation pipeline.

[0009] Step 3: Scrape the wax deposits from the pipeline wall during the operation of the oil-water mixed transportation pipeline, weigh the scraped wax deposits, and calculate the wax deposition thickness according to the size of the wax deposits and the pipeline size.

[0010] Step 4: The wax deposition amount in the oil-water mixed transportation pipeline is comprehensively affected by multiple physical quantity operation parameters. The multiple physical quantity operation parameters include the water content, inlet velocity, inlet temperature, and soil temperature in the oil-water mixed transportation pipeline. Combine the multiple physical quantity operation parameters to form an orthogonal table in the form of multiple parameter combinations.

[0011] Step 5: Establish a multiple parameter combination mathematical model for the operation process of the oil-water mixed transportation pipeline to predict the wax deposition during the transportation process of the oil-water mixed transportation pipeline:

[0012]

[0013] In the formula: h s is the calculated value of the wax deposition thickness, mm; represents the regression coefficient of the established model; z1, z2,... z w are the power coefficients of the parameters in the regression model; d represents the degree of the polynomial.

[0014] In the above solution, step two is specifically as follows: By changing the opening and closing size of the water injection valve in the oil-water mixed transportation pipeline, the water content of the oil-water mixture in the pipeline is controlled; Prepare a clean, dry and well-sealed sampler, and take samples near the wellhead of the oil-water mixed transportation pipeline. When sampling, slowly open the sampling valve on the pipeline, let the fluid flush the sampling port for a period of time to remove the impurities remaining at the sampling port, and then align the sampler with the sampling port to allow the oil-water mixture to flow into the container;

[0015] Bring the obtained oil-water mixture back to the laboratory, and adopt the static separation method. Place the oil-water mixture in a transparent graduated cylinder and let it stand for a period of time to completely separate the oil and water. Calculate the water content by measuring the volumes of the oil layer and the water layer.

[0016] In the above solution, step three is specifically as follows: During the operation of the oil-water mixed transportation pipeline, place the pigging ball inside the pig launcher at the wellhead position, and use the pressure difference of the oil-water mixture before and after the pigging ball to push the pigging ball forward in the pipeline, scrape the wax deposits from the inner wall of the oil-water mixed transportation pipeline. After the pigging ball enters the pig receiver, the pigging operation is completed. Weigh the scraped wax deposits using an electronic balance, and calculate the wax deposition thickness based on the size of the wax deposits and the pipeline size.

[0017] In the above solution, step three is more specifically as follows:

[0018] Before the pigging operation starts, check the pig launching device and the pig receiving device to ensure that the valves of the pig launcher operate flexibly and are well-sealed. Close the branch valves that have nothing to do with the pigging operation to prevent the pigging device from entering the wrong branch; Place the pigging ball inside the pig launching device at the wellhead, and use the pressure difference of the oil-water mixture before and after to push the pigging ball forward in the oil-water mixed transportation pipeline;

[0019] When the pigging ball reaches the pig receiver, close the valve connecting the pig receiver and the oil-water mixed transportation pipeline, open the blowdown valve, and discharge the wax deposits carried by the pigging ball from the pig receiver;

[0020] After the pigging operation is completed, weigh the wax deposits scraped from the inner wall of the oil-water mixed transportation pipeline by the pigging device, and calculate the average thickness of the wax deposits in the oil-water mixed transportation pipeline.

[0021] In the above solution, step four is specifically as follows:

[0022] First, the multi-physical quantity operating parameters include the water content k1, the inlet velocity k2, the inlet temperature k3, and the soil temperature k4, and each physical parameter has 3 values. Among them, the values of k1 are: k 11 、k 12 、k 13 ; The values of k2 are: k 21 、k 22 、k 23 ; The values of k3 are: k 31 、k 32 、k33 ; The value range of k4 is: k 41 , k 42 , k 43 ; Control the water injection rate by controlling the size of the water injection valve, select the soil temperature in different seasons, and at the same time control the inlet temperature and inlet velocity of the oil-water mixture by controlling the size of the water injection valve;

[0023] Secondly, select a suitable orthogonal array S according to the number of parameters and the number of value ranges i (n t ), where S represents the orthogonal array, the subscript i represents the number of experiments, n represents the number of value ranges of the parameters, and t represents the number of physical parameters arranged; for four physical quantity parameters with three value ranges for each parameter, select the orthogonal array S9(3 4 ).

[0024] Advantageous effects:

[0025] The present invention breaks through the study of the wax deposition law of oil-water two-phase flow in the oil-water mixed transportation pipeline by using a loop experimental device, takes part of the horizontal pipeline as the research object, ignores the comprehensive influence of local elbows, vertical pipes and long-distance horizontal pipelines from the wellhead to the metering room on the crude oil flow and wax deposition, cannot truthfully reflect the fluid flow and heat transfer characteristics in the actual mixed transportation pipeline, and will cause certain errors. It realizes the accurate and convenient prediction of the wax deposition amount during the transportation process of the oil-water mixed transportation pipeline, and provides technical support for the normal temperature gathering and transportation production operation of oil enterprises. Description of the drawings:

[0026] Figure 1 are the measured and predicted values of the wax deposition thickness of the oil-water mixed transportation pipeline under each working condition. Specific implementation manners:

[0027] This method for predicting the wax deposition amount during the transportation process of the oil-water mixed transportation pipeline includes the following contents:

[0028] Step 1: Take the oil-water mixed transportation pipeline as the research object, measure the soil temperature near the buried pipeline through the thermocouple thermometer arranged in the soil near the buried depth of the pipeline on site, and measure the temperature and velocity of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions through the thermocouple thermometer at the pipeline temperature measurement interface and the volumetric flowmeter on the straight section of the pipeline in the metering room.

[0029] Arrange the thermocouple thermometer probe in the soil around the oil-water mixed transportation pipeline. The insertion position should be close to the pipeline but 0.2 - 0.3 m away from the pipeline to avoid damaging the probe due to contact with the pipeline. Select a thermocouple thermometer wire with certain moisture-proof and anti-damage performance, read the temperature reading through the on-site connected instrument and record it. Consider the representativeness of the measurement position when analyzing the data, and take the average value of multiple measurements to reduce errors.

[0030] By observing the flowmeter and thermometer in the metering station, read and record the flow rate and temperature data of the oil-water mixture in the oil-water mixed transportation pipeline. When reading the temperature, it should be read when the thermometer reaches the thermal equilibrium state, and multiple measurements can be taken within a period of time and the average value can be obtained. When reading the flow rate, it is necessary to observe the stability of the flow rate of the oil-water mixture. If there are abnormal fluctuations, check whether there are blockages, leaks or flowmeter failures in the pipeline.

[0031] Step 2: Obtain an oil-water mixture sample at the wellhead sampling point, use the static separation method to separate the oil and water, and calculate the water cut of the oil-water mixture inside the oil-water mixed transportation pipeline through a formula.

[0032] By changing the opening and closing size of the water injection valve, control the water cut of the oil-water mixture in the pipeline. Prepare a clean, dry and well-sealed sampler and sample near the pipeline wellhead. When sampling, slowly open the sampling valve on the pipeline to let the fluid flush the sampling port for a period of time to remove possible impurities remaining at the sampling port, and then align the sampling container with the sampling port to let the oil-water mixture flow into the container.

[0033] Bring the obtained sample back to the laboratory, use the static separation method, place the sample in a transparent graduated cylinder, let it stand for a period of time to completely separate the oil and water, and calculate the water cut by measuring the volumes of the oil layer and the water layer. The calculation formula is: Water cut = (Volume of water layer / (Volume of oil layer + Volume of water layer)) × 100%.

[0034] Step 3: During the operation of the oil-water mixed transportation pipeline, place the pigging ball inside the pig launcher at the wellhead position, use the pressure difference of the oil-water mixture before and after the pigging ball to push the pigging ball forward in the pipeline, scrape the wax deposits from the pipe wall, and complete the pigging operation after the pigging ball enters the pig receiver. Weigh the scraped wax deposits using an electronic balance and calculate the wax deposition thickness based on the size of the wax deposits and the size of the pipeline.

[0035] Before the pigging operation starts, check the pigging and receiving devices to ensure that the valves of the pig launcher operate flexibly and are well-sealed. Close the branch valves that have nothing to do with the pigging operation to prevent the pigging tool from entering the branch by mistake. Place the pigging ball inside the pigging device at the wellhead and push the pigging ball forward in the pipeline through the pressure difference of the oil-water mixture before and after.

[0036] When the pigging ball reaches the pig receiver, close the valve connecting the pig receiver and the pipeline, open the drain valve, and discharge the wax deposits and the like carried by the pigging ball from the pig receiver.

[0037] After the pigging is completed, weigh the wax deposits scraped from the pipe wall by the pigging tool. The calculation formula for the average thickness of the wax deposits in the oil-water mixed transportation pipeline is:

[0038]

[0039] Among them, h is the measured calculated value of the wax deposition thickness in the oil-water mixed transportation pipeline, in mm; m is the mass of the wax deposit, in kg; r is the radius of the pipeline, in m; L is the length of the pipeline, in m; ρ is the density of the wax deposit, in kg / m 3 .

[0040] Step 4: Since the wax deposition amount in the oil-water mixed transportation pipeline is mainly affected by the water content, inlet velocity, inlet temperature, and soil temperature comprehensively, considering the influence of the interaction among multiple physical quantity parameters such as the water content, inlet velocity, inlet temperature, and soil temperature in the oil-water mixed transportation pipeline, therefore, through orthogonal experiments, a scientific and reasonable combination form of multiple physical quantity operation parameters is formed to form an orthogonal table.

[0041] The orthogonal experimental design evaluates the influence of each parameter on the wax deposition amount in different value ranges by combining physical parameters in different value ranges, making the parameter combinations more scientific and reasonable. The specific steps are as follows:

[0042] First, based on the cumulative data of on-site actual operations, clarify the physical parameters to be studied and the value range of each physical parameter. In the study of the wax deposition amount during the transportation process of the oil-water mixed transportation pipeline, the physical parameters include the water content k1, inlet velocity k2, inlet temperature k3, and soil temperature k4, and each physical parameter has 3 values. Among them, the value of k1 is: k 11 , k 12 , k 13 ; the value of k2 is: k 21 , k 22 , k 23 ; the value of k3 is: k 31 , k 32 , k 33 ; the value of k4 is: k 41 , k 42 , k 43 . By controlling the size of the water injection valve, the water injection rate is controlled, and different soil temperatures are studied in different seasons. At the same time, the inlet temperature and flow rate of the oil-water mixture are controlled by controlling the size of the valve.

[0043] Secondly, select a suitable orthogonal table S i (n t ), where S represents the orthogonal table, the subscript i represents the number of experiments, n represents the number of values of the parameter, and t represents the number of physical parameters arranged. For four physical quantity parameters and each parameter having three values, the orthogonal table S9(3 4 ) can be selected, as shown below:

[0044]

[0045]

[0046] Step 5: Adopt the mathematical method of multiple nonlinear regression to establish a multi-parameter combined mathematical model for the operation process of the oil-water mixed transportation pipeline, and obtain the functional relationship between the water cut, inlet velocity, inlet temperature, and soil temperature and the wax deposition amount in the oil-water mixed transportation pipeline. Combine the use of the mean square error MSE and the goodness of fit M 2 Two indicators to comprehensively evaluate the performance of the model.

[0047] On the basis of obtaining the orthogonal table of the parameter combinations of each physical quantity, take the wax deposition thickness as the prediction index of the wax deposition amount in the oil-water mixed transportation pipeline, and obtain the on-site measured data as follows:

[0048]

[0049] Adopt the mathematical method of multiple linear regression to further establish a multi-parameter combined model for the transportation process of the oil-water mixture transportation pipeline, and obtain the functional relationship between parameters such as water cut, inlet velocity, inlet temperature, and soil temperature and the wax deposition thickness.

[0050]

[0051] Among them, h is the measured value of the wax deposition thickness in the oil-water mixed transportation pipeline, in mm; Represents the regression coefficient of the established model; z1, z2,... z w Is the power coefficient of the parameters in the regression model; d represents the degree of the polynomial.

[0052] After giving the initial value of the regression model, through iterative solution, obtain the corresponding regression coefficient And the power coefficients z1, z2,... z of the parameters w , on this basis, substitute the parameter values into the established multi-parameter combined model for the transportation process of the oil-water mixture transportation pipeline to obtain the calculated value of the wax deposition thickness, h s .

[0053] Use the mean square error (MSE) as the loss function to evaluate the gap between the calculated value of the wax deposition thickness and the experimental data. The closer the mean square error is to 0, the smaller the gap between the model calculation result and the experimental value, and the more accurate the model. The mean square error is defined as:

[0054]

[0055] Among them, h s Is the measured value of the wax deposition thickness of the s-th group of oil-water mixed transportation pipelines, in mm; h s Is the calculated value of the wax deposition thickness of the s-th group of oil-water mixed transportation pipelines, in mm.

[0056] At the same time, through the goodness of fit M 2 As the explanatory ability of the regression model for the overall fluctuation of the data, M2 The closer it is to 1, the better the model fits the data, that is, the higher the proportion of the fluctuating part of the data that the model can explain in the total fluctuation. It can be used to represent the functional relationship between parameters such as water content, inlet velocity, inlet temperature, soil temperature, etc. and the wax deposition amount in the oil-water mixed transportation pipeline, M 2 The calculation is as shown in the following formula:

[0057]

[0058] where SS t is the total error; SS r is the random error; is the experimental average value of the wax deposition thickness in the oil-water mixed transportation pipeline,

[0059]

[0060] Combining the use of the mean square error MSE and the goodness of fit M 2 The multi-parameter combination model of the oil-water mixed transportation pipeline with a smaller mean square error and a higher goodness of fit obtained by the two indicators is as shown in the following formula:

[0061]

[0062] To make the above content of the present invention more concise and understandable, the following takes a certain section of the oil-water mixed transportation pipeline in a certain oilfield as the research object, predicts the wax deposition situation on the fifteenth day of its operation, and makes the following detailed description:

[0063] A certain section of the oil-water mixed transportation pipeline in a certain oilfield, with a pipeline length of 500 m, a pipe diameter of φ89×5, and the insulation layer material is rigid polyurethane foam with a thickness of 30 mm. Based on mathematical methods such as orthogonal experiments and multiple nonlinear regressions, the present invention establishes a mathematical model of the wax deposition change during the transportation process of the oil-water mixed transportation pipeline, determines the functional relationship between the wax deposition amount in the oil-water mixed transportation pipeline and the inlet velocity, inlet temperature, water content, and soil temperature of the oil-water two-phase mixture. Thus, the prediction of the wax deposition during the transportation process of the oil-water mixed transportation pipeline is realized. The specific steps are as follows:

[0064] Step 1: Taking the oil-water mixed transportation pipeline as the research object, measure the soil temperature near the buried pipeline through the thermocouple thermometer arranged in the soil near the pipeline burial depth on site, and measure the temperature and velocity of the oil-water mixture in the oil-water mixed transportation pipeline under different working conditions through the thermocouple thermometer at the pipeline temperature measurement interface and the volumetric flowmeter in the straight section of the pipeline in the metering room. The specific values of the temperature, flow rate of the oil-water mixture in the oil-water mixed transportation pipeline and the soil temperature around the pipeline under each working condition are shown in the table:

[0065]

[0066] Step 2: Obtain the oil-water mixture sample at the wellhead sampling point, separate the oil and water by the static separation method, and calculate the water cut of the oil-water mixture inside the oil-water mixed transportation pipeline during the transportation process through a formula. The specific values are shown in the table:

[0067]

[0068] Step 3: During the operation of the oil-water mixed transportation pipeline, place the pig in the pig launcher inside the wellhead position. Use the pressure difference of the oil-water mixture before and after the pig to push the pig forward in the pipeline, scrape the wax deposits from the pipe wall. After the pig enters the pig receiver, the pigging operation is completed. Weigh the scraped wax deposits using an electronic balance, and calculate the wax deposition thickness based on the size of the wax deposits and the pipe size. The wax deposition thickness after the 15th day of operation of the oil-water mixed transportation pipeline under different parameter combinations is shown in the following table:

[0069]

[0070] Step 4: Since the wax deposition amount in the oil-water mixed transportation pipeline is mainly affected by the comprehensive influence of water cut, inlet velocity, inlet temperature, and soil temperature, considering the interaction effects among multiple physical quantity parameters such as water cut, inlet velocity, inlet temperature, and soil temperature in the oil-water mixed transportation pipeline, therefore, through orthogonal experiments, a scientific and reasonable combination form of multiple physical quantity operating parameters is formed to create an orthogonal table.

[0071] In the study of predicting the wax deposition amount in the oil-water mixed transportation pipeline, the physical parameters include water cut k1, inlet velocity k2, inlet temperature k3, and soil temperature k4. Among them, the values of k1 are: 70%, 40%, 10%; the values of k2 are: 1.5, 1.2, 1.0; the values of k3 are: 317K, 316K, 315K; the values of k4 are: 293K, 283K, 273K; generate an S9(3 4 ) orthogonal table as follows:

[0072]

[0073] Step 5: Adopt the mathematical method of multiple nonlinear regression to establish a multi-parameter combination mathematical model for the operation process of the oil-water mixed transportation pipeline, and obtain the functional relationship between water cut, inlet velocity, inlet temperature, and soil temperature and the wax deposition amount in the oil-water mixed transportation pipeline. Combine the use of two indicators, the mean square error MSE and the goodness of fit M 2 to comprehensively evaluate the performance of the model.

[0074] Based on the obtained orthogonal table of each physical quantity parameter combination, take the wax deposition thickness as the prediction index of the wax deposition amount in the oil-water mixed transportation pipeline, and obtain the wax deposition thickness of the oil-water mixed transportation pipeline under each parameter combination measured on site as shown in the following table:

[0075]

[0076] Multi - physical quantity combined mathematical model for the transportation process of oil - water mixed transportation pipelines:

[0077]

[0078] After multiple non - linear regression, the polynomial form obtained is:

[0079] y = a 0000 + a 1100 y1y2 + a 1010 y1y3 + a 1001 y1y4 + a 0110 y2y3 + a 0101 y2y4 + a 0011 y3y4 + a 1000 y1 + a 0100 y2 + a 0010 y3

[0080] Among them, the coefficients and power coefficients of each term are respectively:

[0081] a 0000 =-0.30787, a 1100 =0.08916, a 1010 =-0.03466, a 1001 =-0.00567, a 0110 =1.80757, a 0101 =-0.07747, a 0011 =0.00096, a 1000 =12.46239, a 0100 =-549.64428, a 0010 =-0.26836

[0082] Substitute the multi - parameter numerical values back into the multi - physical quantity combined mathematical regression model for the transportation process of the oil - water mixed transportation pipeline to obtain the calculated value h of the wax deposition thickness. As shown in the following table:

[0083]

[0084] Use the mean square error (MSE) as the loss function to evaluate the gap between the calculated value of the wax deposition thickness and the measured data. The closer the mean square error is to 0, the smaller the gap between the model calculation result and the measured value, and the more accurate the model. The mean square error is defined as:

[0085]

[0086] The mean square error MSE value approaches 0, indicating that the gap between the predicted value of the wax deposition amount in the oil - water mixed transportation pipeline and the on - site measured data is small.

[0087] Through the goodness of fit M 2 As the explanatory power of the regression model for the overall fluctuation of the data, M 2 The closer it is to 1, the better the model fits the data, that is, the higher the proportion of the data fluctuation part that the model can explain in the total fluctuation.

[0088] Random error SS r Calculation:

[0089]

[0090] SS r =(0.83 - 0.82) 2 +(1.17 - 1.13) 2 +(1.39 - 1.42) 2 +(0.50 - 0.52) 2 +(0.21 - 0.29) 2 +(0.30 - 0.25) 2 +(0.25 - 0.22) 2 +(0.34 - 0.36) 2 +(0.18 - 0.17) 2 =0.0133

[0091] Calculation of the average wax deposition thickness of the oil - water mixed transportation pipeline:

[0092]

[0093] Calculation of the total error:

[0094]

[0095] SS t =(0.83 - 0.574444) 2 +(1.17 - 0.574444) 2 +(1.397 - 0.574444) 2 +(0.50 - 0.574444) 2 +(0.21 - 0.574444) 2 +(0.30 - 0.574444) 2 +(0.25 - 0.574444) 2 +(0.34 - 0.574444) 2 +(0.18 - 0.574444) 2 =3.960909

[0096] Therefore, the goodness of fit M 2 is:

[0097]

[0098] After calculation, the goodness of fit M 2 is close to 1, indicating that the model has a good fitting degree for the data, that is, the proportion of the data fluctuation part that the model can explain in the total fluctuation is relatively high.

[0099] By combining the mean square error MSE and the goodness of fit M 2 Two indicators are used to comprehensively evaluate the performance of the established model, and a multi-parameter combined regression mathematical model for the oil-water mixed transportation pipeline transportation process with a mean square error of 0.001478 and a goodness of fit of 0.99 and good fitting performance is obtained.

[0100] The multi-physical quantity combined regression mathematical model for the oil-water mixed transportation pipeline transportation process is:

[0101] h = -0.30787 + 0.08916y1y2 - 0.03466y1y3 - 0.00567y1y4 + 1.80757y2y3 - 0.07747y2y4 + 0.00096y3y4 + 12.46239y1 - 549.64428y2 - 0.26836y3

[0102] On the basis of obtaining the multi-physical quantity combined regression mathematical model for the oil-water mixed transportation pipeline transportation process, by changing the size of the water injection valve, the water content of the oil-water mixture at the site is controlled to be 60%, and the temperature and velocity of the oil-water mixture are adjusted to 316K and 1.2m / s respectively. When operating in spring, the soil temperature near the oil-water mixed transportation pipeline is 283K, and the wax content is measured during 15 days of operation under this combination.

[0103] The wax deposition thickness measured on site is h = 1.03mm

[0104] After calculation, when the multi-physical parameter operation combination of the oil-water mixed transportation pipeline is: k1 = 60, k2 = 1.2, k3 = 316, k4 = 283, the wax deposition thickness:

[0105] h = -0.30787 + 0.08916×60×1.2 - 0.03466×60×316 - 0.00567×60×283 + 1.80757×1.2×316 - 0.07747×1.2×283 + 0.00096×316×283 + 12.46239×60 - 549.64428×1.2 - 0.26836×316 = 1.02

[0106] The relative error ε between the on-site measured data h and the calculated data h is:

[0107]

[0108] The reliability of the model was verified.

[0109] Generally speaking, the prediction method for the wax deposition amount during the operation of the oil-water mixed transportation pipeline breaks through the conventional research on the wax deposition law of oil-water two-phase by using a loop experimental device, ignoring the influence of local elbows, vertical pipes, and long-distance horizontal pipelines from the wellhead to the metering room on the crude oil flow and wax deposition, and cannot truthfully reflect the fluid flow and heat transfer characteristics in the actual mixed transportation pipeline, which will cause certain errors. It fully considers the influence of multiple physical parameters such as water cut, inlet temperature, inlet velocity, and soil temperature on the wax deposition amount, and realizes accurate and convenient calculation of the wax deposition amount prediction during the transportation process of the oil-water mixed transportation pipeline.

Claims

1. A method for predicting wax deposition in a mixed oil-water pipeline transportation process, characterized in that The steps include: Step 1: Arrange a thermocouple thermometer in the soil near the buried depth of the oil-water mixed pipeline on site to measure the soil temperature near the buried pipeline; use the thermocouple thermometer of the pipeline temperature measurement interface in the metering room to measure the temperature of the oil-water mixture in the oil-water mixed pipeline under different working conditions; use the volumetric flowmeter of the straight section of the pipeline in the metering room to measure the velocity of the oil-water mixture in the oil-water mixed pipeline under different working conditions; Step 2: Obtain oil-water mixture samples at the on-site wellhead sampling point and calculate the water content of the oil-water mixture during the oil-water mixed pipeline transportation process; Step 3: Scrape wax deposits from the pipeline wall during the operation of the oil-water mixed pipeline, weigh the scraped wax deposits, and calculate the wax deposit thickness based on the wax deposit size and pipeline size; Step 4: The wax deposition amount of the oil-water mixed pipeline is comprehensively affected by the multi-physical operation parameters, which include the water content, inlet velocity, inlet temperature and soil temperature in the oil-water mixed pipeline. The multi-physical operation parameters are combined to form an orthogonal table in the form of multi-parameter combination; Step 5: Establish a multi-parameter combined mathematical model for the operation process of the oil-water mixed pipeline to predict wax deposition during the transportation process of the oil-water mixed pipeline: Where: h s is the calculated value of wax deposition thickness, mm; Represents the regression coefficient of the constructed model; z1, z2, …z w is the power coefficient of the parameter in the regression model; d represents the degree of the polynomial.

2. The method for predicting wax deposition in the oil-water mixed pipeline transportation process according to claim 1 is characterized by: The step 2 specifically comprises: controlling the water content of the oil-water mixture in the pipeline by changing the opening and closing size of the water injection valve of the oil-water mixed pipeline; preparing a clean, dry and well-sealed sampler, sampling near the wellhead of the oil-water mixed pipeline, slowly opening the sampling valve on the pipeline during sampling, allowing the fluid to flush the sampling port for a period of time to remove the impurities remaining in the sampling port, and then aligning the sampler with the sampling port to allow the oil-water mixture to flow into the container; The obtained oil-water mixture is brought back to the laboratory, and the static separation method is used. The oil-water mixture is placed in a transparent measuring cylinder and allowed to stand for a period of time to allow the oil and water to completely separate. The water content is calculated by measuring the volume of the oil layer and the water layer.

3. The method for predicting wax deposition in the oil-water mixed pipeline transportation process according to claim 2 is characterized in that: The step three is specifically as follows: during the operation of the oil-water mixed pipeline, a cleaning ball is placed inside a ball-serving barrel at the wellhead position, and the pressure difference of the oil-water mixture before and after the cleaning ball is used to push the cleaning ball forward in the pipeline, so as to scrape the wax deposits from the wall of the oil-water mixed pipeline. After the cleaning ball enters the ball-receiving barrel, the cleaning operation is completed, and the scraped wax deposits are weighed using an electronic balance, and the wax deposit thickness is calculated according to the wax deposit size and the pipeline size.

4. The method for predicting wax deposition in the oil-water mixed pipeline transportation process according to claim 3 is characterized by: The step three is more specifically: Before the start of the pigging operation, check the ball launcher and ball receiver to ensure that the valve of the ball launcher is flexible and well sealed, close the branch valves not related to the pigging operation to prevent the pig from entering the branch by mistake; put the pig into the ball launcher at the wellhead, and push the pig forward in the oil-water mixed pipeline through the pressure difference between the front and rear of the oil-water mixture; When the cleaning ball reaches the ball receiving bucket, close the valve connecting the ball receiving bucket and the oil-water mixed transmission pipeline, open the drain valve, and discharge the wax sediment carried by the cleaning ball into the ball receiving bucket; After the cleaning is completed, the wax deposits scraped from the wall of the oil-water mixed pipeline by the pig are weighed, and the average thickness of the wax deposits in the oil-water mixed pipeline is calculated.

5. The method for predicting wax deposition in the oil-water mixed pipeline transportation process according to claim 4 is characterized in that: The step 4 is specifically as follows: First, the multi-physical operation parameters include moisture content k1, inlet velocity k2, inlet temperature k3, and soil temperature k4, and each physical parameter has three values, among which k1 has the value: k 11 , k 12 , k 13 ; k2 value: k 21 , k 22 , k 23 ; k3 value: k 31 , k 32 , k 33 ; k4 value: k 41 , k 42 , k 43 ; The water mixing rate is controlled by controlling the size of the water mixing valve, and the soil temperature in different seasons is selected. At the same time, the inlet temperature and inlet speed of the oil-water mixture are controlled by controlling the size of the water mixing valve; Secondly, select the appropriate orthogonal table S according to the number of parameters and the number of values. i (n t ), where S represents the orthogonal table, the subscript i represents the number of experiments, n represents the number of parameter values, and t represents the number of arranged physical parameters; for four physical quantity parameters and each parameter has three values, select S9(3 4 )Orthogonal array.

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