Gas well shaft sulfur blockage diagnosis method

Abstract

The invention belongs to the technical field of high-sulfur-content gas field exploitation, and particularly relates to a gas well shaft sulfur blockage diagnosis method. The sulfur blockage condition of the gas well shaft is judged mainly through a chart diagnosis method and a simulation calculation method. According to the plate diagnosis method, a shaft node analysis model of a gas well is used, gas well parameters under different blockage conditions are set, a gas well blockage condition judgment plate is drawn according to the calculated result, the actually measured parameters are compared with the plate, and the blockage degree of the gas well is judged. And the model calculation method is used for comparing the calculated sulfur solubility with the original sulfur solubility by iteratively calculating the temperature and pressure parameters of the shaft to judge the blockage condition of the gas well. And performing weighted calculation on the two calculation results by using a fuzzy mathematics theory to obtain the comprehensive blockage degree evaluation of the gas well shaft. According to the method, multi-parameter and multi-angle model calculation is utilized, the actual condition of gas well blockage is comprehensively judged, and the problems that a traditional diagnosis method is inaccurate in diagnosis result and low in credibility when the gas well condition is complex and changeable are successfully solved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-sulfur gas field exploitation, and in particular relates to a method for diagnosing sulfur plugging in a gas wellbore. Background Art

[0002] As high-sulfur gas fields enter the middle and late stages of development, the formation pressure of the gas reservoir gradually decreases, the sulfur saturation in the natural gas decreases, and elemental sulfur is continuously precipitated. When the gas production of the gas well is insufficient to carry elemental sulfur, it is attached and deposited on the wellhead and the inner wall of the oil pipe, causing sulfur deposition blockage, which has a serious impact on the development of the gas field. The production dynamics of high-sulfur gas fields show that once sulfur blockage occurs in the wellbore of a gas well, it will affect the gas well production capacity to varying degrees. In severe cases, the gas well may be forced to shut down, affecting the safe and efficient development of the gas field. Therefore, the diagnosis technology of sulfur blockage in the wellbore of a gas well is particularly important. Accurately analyze and determine the location and degree of sulfur blockage, and promptly implement corresponding sulfur blockage relief measures to minimize the impact of sulfur blockage on production.

[0003] After investigating relevant patents and documents, the invention patent "A method and device for evaluating the degree of wellbore blockage" with the application publication number CN112115573A was applied. By selecting a reference well, counting its data, and using computer programs and hardware training to obtain the corresponding model, the data of the well to be evaluated was input on this basis to obtain the model of the well to be evaluated for analysis and judgment. Dr. Hyne (1968) investigated more than 100 sulfur-containing gas wells and proposed a sulfur deposition statistical model for wellbore sulfur deposition prediction, but it was largely based on statistics, lacking rigorous theoretical analysis and proof, and lacking practical application value. In 2009, Jin Zhirong considered the changes in the flow state of fluids in the wellbore and established a prediction model for the wellbore pressure and temperature distribution of high-sulfur gas wells with and without elemental sulfur precipitation. The sulfur solubility model was combined to predict the sulfur precipitation location, and the actual gas flow rate and the critical suspension flow rate of sulfur were compared to determine the sulfur deposition in the wellbore. "Prediction of sulfur deposition law in high-sulfur inclined wellbore" (authors: Guo Xiao, Chen Yali, Shi Jianjun, Yang Hongbo, Jia Haowei, published in the journal "Daqing Petroleum Geology and Development" 2021.40(01) pages 74-80), based on mechanical theory and sulfur solubility model, considering the influence of well inclination on the critical suspension velocity of sulfur particles in high-sulfur gas reservoirs, a critical suspension velocity model of sulfur particles in inclined wells was established, and the conditions for sulfur precipitation and deposition were determined to obtain a sulfur deposition law prediction model. The above method requires complex calculations based on certain theoretical knowledge in application, cannot achieve rapid diagnosis of sulfur plugging, and is not widely applicable.

[0004] The location of sulfur deposition blockage is different, and the characterization of gas well production dynamics is also different. The changes in parameters such as oil pressure, gas volume, and oil temperature are different. Faced with the complex and complicated data of the production site and the complex and changeable sulfur blockage of the wellbore, simple data analysis and experience judgment will be biased, and the unblocking measures are not targeted, and the on-site unblocking effect is not ideal. The survey found that there is currently no mature, feasible, and systematic patented technology for wellbore sulfur blockage diagnosis. There is no systematic and effective diagnostic analysis method specifically for wellbore sulfur deposition blockage at home and abroad, and the location and degree of sulfur blockage cannot be accurately analyzed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for diagnosing sulfur plugging in a gas wellbore, so as to solve the problem that the current diagnostic method cannot cope with the complex and changeable sulfur plugging situation in the wellbore and cannot accurately analyze the location and degree of sulfur plugging.

[0006] In order to solve the above technical problems, the present invention provides a method for diagnosing sulfur plugging in a gas wellbore, comprising the following steps:

[0007] 1) Establishing a wellbore node analysis model for a gas well, calculating gas well parameters under different blockage conditions based on the wellbore node analysis model, drawing the calculated parameters into a discriminant chart of the gas well blockage condition, and comparing the gas well parameters actually measured with the discriminant chart to determine the blockage condition of the gas well;

[0008] 2) Establishing a gas wellbore temperature and pressure distribution model, iteratively calculating the temperature and pressure parameters at a certain depth through the wellbore temperature and pressure distribution model, using the iteratively calculated temperature and pressure parameters to calculate the calculated sulfur solubility at the certain depth through the sulfur solubility prediction model, and comparing and analyzing the calculated sulfur solubility with the original sulfur solubility to determine the blockage of the gas well; the original sulfur solubility represents the solubility of sulfur element at different temperatures and pressures obtained through test data;

[0009] 3) Performing a weighted summation on the two blockage judgment results obtained in step 1) and step 2), and performing a comprehensive sulfur blockage diagnosis on the gas well based on the weighted summation result.

[0010] The beneficial effects are as follows: using two different methods, judging from the chart and iterative calculation of the model, two different groups of gas well blockage results are obtained from different angles, and the gas well blockage situation is comprehensively evaluated by fuzzy mathematics theory through the weighted summation calculation method. Using multi-parameter and multi-angle model calculation, the actual situation of the gas well is comprehensively judged, which successfully solves the problem of inaccurate diagnosis results and low credibility of traditional diagnostic methods when the gas well conditions are complex and changeable.

[0011] Furthermore, the method of obtaining the blockage situation by the method of step 1) is called the plate diagnosis method, and the method of obtaining the blockage situation by the method of step 2) is called the model calculation method, and the blockage situation includes the blockage position and the blockage degree; the weighted summation method based on multi-factor fuzzy mathematical diagnosis in step 3) is: according to the actual blockage position of the gas well, the difference between the results of the plate diagnosis method and the model calculation method is calculated respectively, and the weights of the two methods are determined; on the basis of the weight determination, the final blockage degree and blockage position are obtained by weighted summation, and the weighted summation formula is:

[0012]

[0013]

[0014] A=w1a1+w2a2

[0015] B=w1b1+w2b2

[0016] Wherein: w1 is the weight of the blockage degree calculated by the plate diagnosis method, w2 is the weight of the blockage degree calculated by the model calculation method, a1 is the blockage position calculated by the plate diagnosis method, a2 is the blockage position calculated by the model calculation method, a0 is the actual blockage position of the gas well, b1 is the blockage degree calculated by the plate diagnosis method, b2 is the blockage degree calculated by the model calculation method, A is the weighted summation result of the blockage position, and B is the weighted summation result of the blockage degree.

[0017] The beneficial effect is: ensuring the accuracy of weight calculation.

[0018] Furthermore, the wellbore node analysis model described in step 1) is obtained in the following manner: first, an initial wellbore node analysis model is established using the basic parameters of the gas well, and then the initial wellbore node analysis model is corrected based on the measured parameters during actual production to obtain a wellbore node analysis model that conforms to reality.

[0019] The beneficial effect is that the model is corrected by using the parameters of the actual wellbore production, which can ensure the applicability of the model in actual production and improve the credibility of the calculation results.

[0020] Furthermore, the blockage condition described in step 2) includes the blockage degree. The weight of the sulfur element precipitated within the time dt is calculated based on the difference between the calculated sulfur solubility and the sulfur solubility under the original conditions to determine the degree of sulfur deposition blockage. The calculation formula is as follows:

[0021] dM s =q g B g ΔCdt

[0022] Where: dM s q is the weight of sulfur precipitated in time dt;g B is the volume of mixed gas under standard conditions; g is the volume coefficient of the mixed gas; ΔC is the solubility change of elemental sulfur.

[0023] Furthermore, the calculation formula of the sulfur solubility prediction model established in step 2) is:

[0024]

[0025] Where: C is sulfur solubility; γ g is the relative density of natural gas; p is the natural gas pressure; T is the absolute temperature of natural gas; Z is the natural gas deviation coefficient; R is the molar volume gas constant.

[0026] Furthermore, the iterative calculation process described in step 2) is as follows: in the temperature and pressure distribution model of the wellbore initially established, the initial temperature and pressure data are set at a certain depth, a set of new temperatures and pressures at the measuring depth are calculated by an iterative formula, and the iterative calculation results are compared with the actual measured values ​​to determine whether the accuracy is met. If the accuracy meets the requirements, the iterative calculation is considered to be completed; if the accuracy does not meet the requirements, the newly calculated pressure and temperature are used as the initial pressure and temperature, and the iterative calculation is continued until the accuracy requirements are met.

[0027] Furthermore, the basic parameters required to establish the initial wellbore node analysis model in step 1) include: well depth of the target layer of the gas well, geothermal gradient, surface temperature, natural gas production, gas specific heat, gas specific gravity, gas composition, liquid-gas ratio, produced water specific gravity, formation heat transfer coefficient, comprehensive heat transfer coefficient from the oil pipe to the outer wall of the casing, and the inner diameter size of the oil pipe and the roughness of the insertion depth.

[0028] Furthermore, the measured parameters used in step 1) for correcting the initial wellbore node analysis model include: production logging pressure and temperature, and oil pressure, gas volume and oil temperature during normal production.

[0029] The beneficial effects are: a large number of gas well parameters are combined to establish a model, and the model is corrected by actual production measurement data, so that the model can obtain highly reliable calculation results even in a complex gas well environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention uses PIPESIM software to calculate the temperature and pressure profile of the gas well;

[0031] Figure 2 This is a blockage position and blockage degree diagnosis chart of Well No. 1 of the present invention;

[0032] Figure 3 It is the coupled gas-solid two-phase wellbore temperature, pressure-well depth variation model of the present invention;

[0033] Figure 4 It is the sulfur precipitation prediction chart of the present invention;

[0034] Figure 5 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to specific examples.

[0036] Method Example:

[0037] Combine the following Figure 5 , the implementation process of the whole method is introduced.

[0038] Step 1: Use the plate diagnosis method to determine the blockage of the gas well.

[0039] The overall idea is as follows: First, determine the depth of the target layer of the gas well, geothermal gradient, surface temperature, natural gas production, gas specific heat, gas specific gravity, gas components, liquid-gas ratio, produced water specific gravity, formation heat transfer coefficient, comprehensive heat transfer coefficient from the oil pipe to the outer wall of the casing, the inner diameter of the oil pipe, the roughness of the insertion depth and other basic parameters, and use PIPESIM software to establish a gas wellbore node analysis model; secondly, based on the established wellbore node analysis model, use the production logging pressure and temperature data and the oil pressure, gas volume, and oil temperature during normal production to fit and adjust the model to obtain a wellbore node analysis model that conforms to actual production; then, based on the fitted wellbore node analysis model, carry out a sensitivity analysis of sulfur deposition blockage conditions, calculate the oil pressure, oil temperature, and gas volume parameters of the gas well under different blockage positions and blockage degrees, and draw the calculation results to obtain a gas well blockage condition discrimination chart; finally, based on the drawn gas well blockage condition discrimination chart, compare it with the current gas well oil pressure, gas volume, and oil temperature parameters to obtain the gas well blockage position and blockage degree. Specifically:

[0040] 1) Use PIPESIM software to establish a wellbore node analysis model.

[0041] Using PIPESIM software, the first step is to select the gas well type as a production well and the production method as tubing gas production. According to the completion method, open hole completion or casing completion is selected. The second step is to input the bathymetric, vertical depth, inner diameter, wall thickness, roughness and other parameters of the tubing and casing, set the perforation layer section, and input the depth of special equipment such as the packer and downhole safety valve. The third step is to input the gas reservoir parameters (gas reservoir static pressure, gas reservoir temperature and other parameters, vertical depth of the middle gas layer and test depth), fluid physical properties (each component and its proportion), and production data to establish a wellbore node analysis model.

[0042] 2) Modify the wellbore node analysis model.

[0043] Based on the gas well bore node analysis model established in step 1), the pipe flow calculation model is optimized and fitted using parameters such as oil pressure, gas volume, oil temperature, and production logging pressure measured during normal production of the gas well, to obtain a revised bore node analysis model that conforms to the actual situation of the gas well site.

[0044] 3) Calculate the wellbore pressure and temperature profiles at different blockage locations and blockage degrees.

[0045] The blockage position is the distance between the wellhead and the blockage point; the remaining inner diameter of the blockage degree oil pipe is the equivalent diameter of the remaining airflow channel after the blockage. Using the wellbore node analysis model that conforms to the actual site established in step 2), a sensitivity analysis of the blockage position and blockage degree is performed. Multiple combinations of different blockage positions and blockage degrees are set to simulate and calculate the wellbore pressure and temperature profile data under different blockage conditions.

[0046] 4) Draw a wellbore blockage identification chart.

[0047] The changes in the gas volume, oil pressure, and oil temperature parameters of the gas well under different sulfur plugging schemes calculated in step 3) are plotted on the same graph to obtain a wellbore plugging condition identification chart, which is convenient for the production site to quickly diagnose the blockage position and blockage degree of sulfur plugging in the gas wellbore.

[0048] 5) Determine the actual location and degree of sulfur deposition blockage in the gas wellbore.

[0049] Record the actual production parameters of the gas well such as gas volume, oil pressure, oil temperature, etc. under the condition of wellbore blockage, and find the corresponding curve in the chart of step 4). The blockage position and blockage degree corresponding to this curve are the actual blockage position and blockage degree of sulfur deposition in the wellbore of the gas well.

[0050] Step 2: Use the model calculation method to determine the blockage status of the gas well.

[0051] The overall idea is: based on the experimental measurement data of the saturated content of elemental sulfur in the sour natural gas of a gas field, a sulfur solubility prediction model for a gas field is established. According to the initial temperature, pressure and other data, iterative calculations are performed according to the wellbore temperature and pressure distribution model to obtain the pressure and temperature values ​​at the current depth of the wellbore. Using the temperature and pressure data as intermediate parameters, coupled with the solubility model in the current state, the calculated sulfur solubility is compared and analyzed with the original sulfur solubility to determine the blockage location of sulfur deposition, and the degree of sulfur deposition blockage is determined according to the weight of the precipitated sulfur. Specifically:

[0052] 1) Establish a sulfur solubility model for a gas field. Based on the sulfur solubility data obtained experimentally under different temperature and pressure conditions, a sulfur solubility prediction model for the Puguang gas field was established through data fitting:

[0053]

[0054] Where: C is sulfur solubility; γ g is the relative density of natural gas; p is the natural gas pressure; T is the absolute temperature of natural gas; Z is the natural gas deviation coefficient; R is the molar volume gas constant.

[0055] 2) Establish a wellbore temperature and pressure distribution model for gas-solid two-phase flow in high-sulfur gas wells. Set the initial wellbore temperature and pressure of the gas well at a certain depth, calculate a new set of pressure and temperature values ​​through the model, and compare the difference between the wellhead pressure and temperature and the calculated pressure and temperature to see if they meet the accuracy requirements. If the accuracy meets the requirements, the iterative calculation is considered complete. If it does not meet the accuracy requirements, the newly calculated pressure and temperature are used as the initial pressure and temperature, and the iterative calculation continues.

[0056] 3) Compare the original sulfur solubility with the calculated sulfur solubility. The temperature and pressure distribution in the wellbore of a high-sulfur gas well affects the solubility of elemental sulfur. The temperature and pressure parameters are coupled to the temperature and pressure distribution model and the sulfur solubility model to calculate the sulfur solubility at the pressure and temperature corresponding to the current well depth, and compare it with the original sulfur solubility. If the original sulfur solubility is greater than the calculated sulfur solubility, sulfur is precipitated at this depth, and this depth is the sulfur deposition blockage location; if the original sulfur solubility is less than the calculated sulfur solubility, sulfur is not precipitated at this depth.

[0057] 4) Determination of the degree of sulfur deposition blockage: According to the change of sulfur solubility and original sulfur solubility, the weight of sulfur element precipitated within the time dt can be calculated to determine the degree of sulfur deposition blockage.

[0058] dM s =q g B g ΔCdt

[0059] Where: dM s q is the weight of sulfur precipitated in time dt; g B is the volume of mixed gas under standard conditions; g is the volume coefficient of the mixed gas; ΔC is the solubility change of elemental sulfur.

[0060] Step three: Use multi-factor fuzzy mathematics diagnosis method to make a comprehensive judgment on the congestion situation.

[0061] The diagnosis of sulfur plugging position and degree in high-sulfur gas field wellbore mainly adopts the plate diagnosis method and model calculation method. In order to verify and organically combine these two methods, a comprehensive multi-factor fuzzy diagnosis method is established. Specifically:

[0062] 1) Determine the set of evaluation factors according to the evaluation purpose. Based on the theoretical research and calculations in the previous article, the plate diagnosis method and the model calculation method are determined as two relevant influencing factors. The set of evaluation factors for determining the location of the blockage is determined to be A1 = {a1, a2} = {plate diagnosis method, model calculation method}; the set of evaluation factors for determining the degree of blockage is determined to be B1 = {b1, b2} = {plate diagnosis method, model calculation method}.

[0063] 2) Provide an evaluation level set: The evaluation level set is C = {c1, c2, c3, c4} = {severe congestion, relatively heavy congestion, moderate congestion, slight congestion}.

[0064] 3) Determine the weight of each evaluation factor. Based on the statistical analysis of the field gas well blockage big data, the weights of the plate diagnosis method and the model calculation method are determined to be w1 and w2 respectively, and the same weight coefficient matrix W = {w1, w2} is used to determine the blockage location and blockage degree; that is, regardless of the blockage location or blockage degree, the weight corresponding to the same method is the same. Moreover, when calculating the weight coefficient, the measured blockage location is used, that is, the weights of the two methods (plate method and model method) are inferred using the measured data.

[0065]

[0066]

[0067] Wherein, w1 is the weight of the blockage degree calculated by the plate diagnosis method, w2 is the weight of the blockage degree calculated by the model calculation method, a1 is the blockage position calculated by the plate diagnosis method, a2 is the blockage position calculated by the model calculation method, a0 is the actual blockage position of the gas well, b1 is the blockage degree calculated by the plate diagnosis method, and b2 is the blockage degree calculated by the model calculation method.

[0068] 4) Evaluation model. The weighted sum model is used for evaluation: A is the weighted sum of the congestion locations, and B is the weighted sum of the congestion degrees.

[0069] According to the corresponding weight coefficients and blockage score values ​​of the blockage positions and blockage degrees of each method, the comprehensive diagnosis of sulfur blockage degree status evaluation set is obtained through fuzzy mathematics theory: mild blockage ≤30; moderate blockage between 30-60; heavier blockage between 60-90; severe blockage ≥90.

[0070] The following takes Well No. 1 of a gas field as an example gas well:

[0071] Step 1: Use the plate diagnosis method to calculate the sulfur plugging situation of Well 1.

[0072] The basic data of Well No. 1 are statistically compiled, including gas reservoir parameters (gas reservoir static pressure, gas reservoir temperature and other parameters), tubing parameters (vertical depth in the middle of the gas layer and test depth in the middle of the gas layer, ambient temperature, tubing inner diameter and depth, casing inner diameter and depth, and measured depth at the bottom of the completion string), fluid physical parameters (various components and their proportions), and production data (gas volume, oil pressure, and oil temperature during normal production and other parameters).

[0073] PIPESIM software was used to establish the wellbore node analysis model of Well No. 1: the gas well type was selected as a production well, and fluid parameters such as natural gas composition, specific gravity and produced water salinity were input; well inclination data and wellbore parameters (including the depth, inner diameter, wall thickness, roughness and other parameters of the tubing and casing) were input; perforation intervals were set, and the depth of special equipment such as packers and downhole safety valves was input.

[0074] The established gas well bore node analysis model is used to fit the parameters such as oil pressure, gas volume, oil temperature, and measured pressure of the production well during normal production of the gas well, optimize the pipe flow calculation model, and correct the bore node analysis model.

[0075] The No. 1 wellbore node analysis model established with PIPESIM software was used to conduct sensitivity analysis of wellbore blockage location and blockage degree. Figure 1 As shown in the figure, the cross-sectional diagram of the change of pressure and temperature in the wellbore with the depth of the wellbore when sulfur plugging occurs at a distance of 1390m from the wellhead is simulated. The horizontal axis is the depth (True vertical depth), the left vertical axis is the pressure (Pressure), and the right vertical axis is the temperature (Temperature). The seven different schemes of blockage positions are set to be 100, 300, 500, 700, 900, 1100, and 1300 meters, and the three different schemes of blockage degrees are 40mm, 50mm, and 60mm. There are a total of 21 schemes with different blockage positions and different blockage degrees. The oil pressure, gas volume, and oil temperature parameter change curves corresponding to all schemes are plotted on a chart to form the No. 1 wellbore blockage status judgment chart ( Figure 2 ), the location and degree of gas well blockage can be diagnosed based on production parameters.

[0076] When the gas volume of Well No. 1 is 480,000 cubic meters per day and the oil pressure is 12.1 MPa, there are two different situations corresponding to the blockage position and blockage degree in the figure. The first situation is sulfur blockage at 1,300 meters from the wellhead. After blockage, the equivalent diameter of the remaining gas volume channel of the tubing is 40 mm. The second situation is sulfur blockage at 1,300 meters from the wellhead. After blockage, the equivalent diameter of the remaining gas volume channel of the tubing is 60 mm. In order to solve the problem of multiple solutions, the actual production parameters of the oil temperature of 52°C on site are compared with the results of multiple solutions. Finally, it is determined that the first blockage situation, that is, sulfur blockage at 1,300 meters from the wellhead, and the equivalent diameter of the remaining gas volume channel of the tubing after blockage is 60 mm, is in line with the actual blockage situation on site.

[0077] The degree of wellbore blockage was evaluated according to the empirical formula and the inner diameter of the tubing after wellbore blockage (Table 1). An equivalent diameter of 60 mm was considered moderate blockage.

[0078] Table 1 Parameter changes and corresponding blockage scores for different degrees of sulfur blockage in gas wellbore

[0079] Degree of blockage Oil pipe inner diameter (mm) Congestion Score Severe blockage ≤40 100 Severe blockage 55-40 80 Moderate congestion 65-55 60 Mild blockage 76-65 40

[0080] Step 2: Calculate the sulfur plugging situation of Well 1 using the model calculation method.

[0081] Based on the experimental solubility data of elemental sulfur under different temperature and pressure conditions, a sulfur solubility prediction model was established through data fitting.

[0082] Establish the initial wellbore temperature and pressure distribution model of Well No. 1, set the gas well temperature and pressure at a certain depth as the initial temperature and pressure, use the above model to calculate the wellhead temperature and pressure, and compare the calculated wellhead temperature and pressure with the actually measured wellhead temperature and pressure to determine whether the accuracy is met. If the accuracy is not met, use the calculated temperature and pressure as the new initial temperature and pressure, and continue to iteratively calculate the wellhead temperature and pressure from a certain depth until the iterative result meets the accuracy, then the iterative calculation is determined to be completed. Get the gas-solid two-phase wellbore temperature and pressure-well depth change model of Well No. 1 ( Figure 3 ). Using temperature and pressure as intermediate parameters, coupled with the sulfur solubility prediction model, the sulfur precipitation prediction chart is obtained ( Figure 4 ). The current formation pressure of Well No. 1 is 28.2MPa. By coupling the temperature and pressure parameters with the gas-solid two-phase wellbore temperature, pressure-well depth variation model and sulfur solubility prediction model, the calculated sulfur solubility at the corresponding temperature and pressure of each well depth is calculated and compared with the original sulfur solubility. It is found that the calculated sulfur solubility at a well depth of 1390m is less than the original sulfur solubility, and it is judged that sulfur is precipitated at a well depth of 1390m.

[0083] According to the change of sulfur solubility and original sulfur solubility, the weight of sulfur precipitated per unit time is calculated. At present, it is judged that sulfur deposition blockage occurs at 1390m in Well No. 1, and the weight of sulfur precipitation is calculated to be 26.2kg. According to the classification evaluation of sulfur precipitation weight under different formation pressures and precipitation positions, the blockage degree is moderate (Table 2).

[0084] Table 2 Parameter changes and corresponding blockage scores for different degrees of sulfur plugging in gas wellbore

[0085] Degree of blockage Sulfur precipitation weight (kg) Congestion Score Severe blockage >45 100 Severe blockage 35-45 80 Moderate congestion 25-35 60 Mild blockage ＜25 40

[0086] Step three, use fuzzy mathematics theory to conduct a comprehensive evaluation of the blockage degree of Well No. 1.

[0087] According to the plate diagnosis method analysis: sulfur blockage occurred 1300m away from the wellhead. After the blockage, the equivalent diameter of the remaining gas volume channel in the oil pipe was 60mm, which was defined as the inner diameter of the medium-blocked gas well, and the corresponding blockage degree score was 60 points.

[0088] According to the model calculation method: sulfur blockage occurred at 1390m away from the wellhead. After blockage, the equivalent diameter of the remaining gas volume channel in the oil pipe was 65mm, which was defined as the inner diameter of the medium-blocked gas well, and the corresponding blockage degree score was 60 points.

[0089] According to the analysis of the actual on-site detection data, it can be obtained that the gas well blockage position of Well No. 1 in a certain quarter is 1200m away from the wellhead. According to the difference between the measured blockage position and the blockage position diagnosed by the two methods, the weight of the plate diagnosis method is determined to be (1300-1200) / [(1300-1200)+(1390-1200)]=34.5%;

[0090] The weight of the model calculation method is (1390-1200) / [(1300-1200)+(1390-1200)]=65.5%

[0091] The comprehensive blockage location is 1200m according to fuzzy mathematical analysis; the comprehensive blockage degree is 0.345*60+0.655*60=60 according to fuzzy mathematical analysis, and the blockage degree is comprehensively determined to be a moderately blocked gas well.

[0092] In summary, this embodiment calculates two different blockage results through the plate diagnosis method and the model calculation method, and uses fuzzy mathematical analysis and actual data to assign weights to the two calculation results to comprehensively judge the blockage of the gas well. It can change the parameters of the model by inputting data of different gas wells, and can deal with gas wells in different situations. It can also greatly improve the credibility of the calculation results through the support of a large number of gas well parameters, and solve the problem that the existing diagnostic method cannot deal with the complex and changeable sulfur blockage of the wellbore and cannot accurately analyze the sulfur blockage of the gas well.

Claims

1. A method for diagnosing sulfur plugging in a gas wellbore, characterized in that: The following steps are involved: 1) Establishing a wellbore node analysis model for a gas well, calculating gas well parameters under different blockage conditions based on the wellbore node analysis model, drawing the calculated parameters into a discriminant chart of the gas well blockage condition, and comparing the gas well parameters actually measured with the discriminant chart to determine the blockage condition of the gas well; 2) Establishing a gas wellbore temperature and pressure distribution model, iteratively calculating the temperature and pressure parameters at a certain depth through the wellbore temperature and pressure distribution model, using the iteratively calculated temperature and pressure parameters to calculate the calculated sulfur solubility at the certain depth through the sulfur solubility prediction model, and comparing and analyzing the calculated sulfur solubility with the original sulfur solubility to determine the blockage of the gas well; the original sulfur solubility represents the solubility of sulfur element at different temperatures and pressures obtained through test data; 3) Performing a weighted summation on the two blockage judgment results obtained in step 1) and step 2), and performing a comprehensive sulfur blockage diagnosis on the gas well based on the weighted summation result.

2. The method for diagnosing sulfur plugging in a gas wellbore according to claim 1, characterized in that: The method of obtaining the blockage condition by the method of step 1) is called the plate diagnosis method, and the method of obtaining the blockage condition by the method of step 2) is called the model calculation method, and the blockage condition includes the blockage position and the blockage degree; The weighted summation method based on multi-factor fuzzy mathematical diagnosis in step 3) is: according to the actual blockage position of the gas well, the difference between the results of the plate diagnosis method and the model calculation method is calculated, and the weights of the two methods are determined; on the basis of the weight determination, the final blockage degree and blockage position are obtained by weighted summation, and the formula for weighted summation is: A=w1a1+w2a2 B=w1b1+w2b2 Wherein: w1 is the weight of the blockage degree calculated by the plate diagnosis method, w2 is the weight of the blockage degree calculated by the model calculation method, a1 is the blockage position calculated by the plate diagnosis method, a2 is the blockage position calculated by the model calculation method, a0 is the actual blockage position of the gas well, b1 is the blockage degree calculated by the plate diagnosis method, b2 is the blockage degree calculated by the model calculation method, A is the weighted summation result of the blockage position, and B is the weighted summation result of the blockage degree.

3. The method for diagnosing sulfur plugging in a gas wellbore according to claim 1, characterized in that: The wellbore node analysis model described in step 1) is obtained in the following manner: first, an initial wellbore node analysis model is established based on the basic parameters of the gas well, and then the initial wellbore node analysis model is corrected according to the measured parameters during actual production to obtain a wellbore node analysis model that conforms to reality.

4. The method for diagnosing sulfur plugging in a gas wellbore according to claim 1, characterized in that: The blockage condition described in step 2) includes the blockage degree. The weight of the sulfur element precipitated during the dt time is calculated based on the calculated sulfur solubility and the change of the sulfur solubility under the original conditions to determine the blockage degree of sulfur deposition. The calculation formula is as follows: dM s =q g B g ΔCdt Where: dM s q is the weight of sulfur precipitated in time dt; g B is the volume of mixed gas under standard conditions; g is the volume coefficient of the mixed gas; ΔC is the solubility change of elemental sulfur.

5. The method for diagnosing sulfur plugging in a gas wellbore according to claim 1, characterized in that: The calculation formula of the sulfur solubility prediction model established in step 2) is: Where: C is sulfur solubility; γ g is the relative density of natural gas; p is the natural gas pressure; T is the absolute temperature of natural gas; Z is the natural gas deviation coefficient; R is the molar volume gas constant.

6. The method for diagnosing sulfur plugging in a gas wellbore according to claim 1, characterized in that: The iterative calculation process described in step 2) is as follows: in the initially established wellbore temperature and pressure distribution model, initial temperature and pressure data are set at a certain depth, a new set of temperatures and pressures at the measurement depth are calculated by an iterative formula, and the iterative calculation results are compared with the actual measured values ​​to determine whether the accuracy is met. If the accuracy meets the requirements, the iterative calculation is considered to be completed; if the accuracy does not meet the requirements, the newly calculated pressure and temperature are used as the initial pressure and temperature, and the iterative calculation is continued until the accuracy requirements are met.

7. The method for diagnosing sulfur plugging in a gas wellbore according to claim 3, characterized in that: The basic parameters required to establish the initial wellbore node analysis model include: well depth of the target layer of the gas well, geothermal gradient, surface temperature, natural gas production, gas specific heat, gas specific gravity, gas composition, liquid-gas ratio, produced water specific gravity, formation heat transfer coefficient, comprehensive heat transfer coefficient from the tubing to the outer wall of the casing, and the inner diameter size and running depth roughness of the tubing.

8. The method for diagnosing sulfur plugging in a gas wellbore according to claim 3, characterized in that: The measured parameters used in the correction of the initial wellbore node analysis model include: production logging pressure, temperature, and oil pressure, gas volume and oil temperature during normal production.

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