Tracing method for fluid channeling between oil-water wells

Abstract

The invention discloses an oil-water interwell fluid channeling tracing method, which relates to the technical field of petroleum engineering, and comprises the following steps: selecting a fluorescent dye as a tracer agent, and preparing a tracer agent aqueous solution; a tracer agent aqueous solution is adopted for well washing, judgment is carried out according to the time T < return > when the color of the wellhead return liquid appears and the theoretical time T < theory >, if the two are close, it is judged that the integrity of the underground pipe column is good, and if the two are different, the underground pipe column needs to be replaced; the tracer agent aqueous solution is injected into a water injection well, sampling detection is conducted on a corresponding oil producing well from the second day, during detection, if color is observed through naked eyes, a channeling channel exists between oil-water wells, if the color cannot be judged through naked eyes, light absorption spectrophotometry is adopted for detection, and when the concentration of the tracer agent in a sample is lower than the lower detection limit of an instrument, the tracer agent aqueous solution is detected. The sample is detected again after being distilled; the tracing method provided by the invention has the characteristics of high accuracy and reliability, visual detection, short detection period, less tracer dosage, environmental friendliness and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum engineering, and in particular to a method for tracing oil-water crossflow between wells. Background Art

[0002] Oil-water interwell tracing is an important tool for reservoir characterization. Tracer technology commonly used in the oil industry involves injecting tracers into the formation from injection wells. The tracers collected from the oil wells are then analyzed to provide qualitative and quantitative information on the connectivity between the injection and production wells, the presence of dissolved fluids in the porous medium, the flow direction and seepage velocity, and whether there is connectivity in the formation between the oil and water wells. At present, there are generally four types of tracers used in aqueous solution systems at home and abroad: radioactive isotope tritium water (3H2O), fluorescent dyes, water-soluble salts and water-soluble alcohols; among them, radioactive isotopes can be detected at low concentrations, but their application is limited due to their radioactive hazards; the main advantage of fluorescent dyes is that they can be detected at extremely low concentrations, but the prominent disadvantage is that they have strong adsorption in reservoirs and are rarely used in China; water-soluble salts and alcohols are the most commonly used tracers, mainly including ammonium thiocyanate, ammonium nitrate, potassium bromide or sodium bromide, potassium iodide or sodium iodide, sodium chloride, isopropyl alcohol, methanol, ethanol, etc. This type of chemical tracer is diverse and easy to detect, but the main disadvantage is that it is impossible to perform multi-layer simultaneous detection, the amount used is large, there are environmental protection risks, and it is difficult to transport overseas.

[0003] In practice, ammonium thiocyanate and ammonium nitrate are commonly used in oilfields. Their tracing principle involves identifying the characteristic absorption peak of the reduction reaction product of a sample collected under acidic conditions, and then using a spectrophotometer to perform colorimetric analysis to quantitatively detect NO₃ in the produced fluid. However, the disadvantages of using ammonium nitrate as a tracer include: ferric iron in the water can bias the results upward; large amounts of chloride ions can bias the results downward; barium ions in the water make colorimetric analysis difficult; colored substances in the water hinder the use of colorimetric materials; nitrate in groundwater can affect the results; zinc reduction methods have poor reproducibility and complex analytical procedures; and the nitrite generated during the experiment is carcinogenic. Disadvantages of using ammonium thiocyanate as a tracer include: interference with the complexation method caused by copper, lead, and zinc ions in the water; high mineralization reduces test sensitivity; high cost; potential pollution to environmental water bodies; and irritation. In summary, both of these tracers commonly used in oil fields require large tracer dosages, have long detection cycles (up to several weeks), are expensive (requiring the use of construction equipment and laboratory analysis equipment for long-term preparation, injection, large-scale sampling, and experimental testing), pose significant environmental pollution, and are not suitable for rapid detection of interwell crossflow channels (thief layers).

[0004] Therefore, how to quickly detect whether there are high-speed crossflow channels between oil and water wells in a short period of time and develop a tracing method that uses less tracer, has low cost, short detection time, simple detection method, and accurate results is of great significance for realizing the rapid detection of crossflow channels between oil and water wells without moving the tubing in the wellbore and using complicated ground equipment. Summary of the Invention

[0005] The present invention aims to solve the technical problems of the prior art in detecting high-speed crossflow channels between oil and water wells, such as long detection time, complex detection methods, errors in detection results, large tracer usage, and high cost. The present invention aims to provide a method for tracing crossflow between oil and water wells, which realizes visual observation and low-cost oil casing leak detection, and realizes leak detection of wellbore integrity without operating or moving the pipe string. At the same time, through visual observation, detection instruments, and combined with low-concentration sample distillation and concentration, even low-concentration tracers can be effectively detected, thereby improving the credibility and accuracy of crossflow tracing diagnosis between oil and water wells. The method has the characteristics of visual detection, short detection cycle, small tracer usage, environmental friendliness, and low cost.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a method for tracing oil-water crossflow between wells, comprising the following steps: S1. Select fluorescent dye as tracer and prepare tracer aqueous solution; S2, use tracer aqueous solution to wash the well, according to the time T when the liquid returned from the wellhead appears color 返 With the theoretical time T 理论 Make a judgment, if (T 返 -T 理论 ) / T 理论 ≤5%, then the downhole string integrity is judged to be good and the next step can be carried out. 返 -T 理论 ) / T 理论 >6%, the downhole tubing needs to be replaced; S3. Inject the tracer aqueous solution into the water injection well. Starting from the second day, sample and test the corresponding oil production well. During the test, if color is observed by the naked eye, it means that a crossflow channel exists between the oil and water wells. If the naked eye cannot determine, use spectrophotometry to detect. When the tracer concentration in the sample is lower than the detection limit of the instrument, distill the sample and test it again.

[0008] Currently, traditional chemical tracers (such as ammonium thiocyanate and ammonium nitrate) used in oilfields suffer from high dosage, long detection cycles (weeks), and high costs (requiring the use of construction equipment and laboratory analysis equipment for lengthy preparation, injection, extensive sampling, and laboratory testing). These tracers are unsuitable for rapid detection of interwell crossflow channels (thief layers). Tracers must also meet high precision, low dosage, and be safe and environmentally friendly. Fluorescent dye tracers are rarely used in oilfields due to their high adsorption capacity in rock formations. However, due to the short duration of high-speed crossflow between injection and production wells, even with high adsorption, they can be detected with extreme sensitivity as long as their residence time in the reservoir is not too long. This is the basis of the present invention. While no reports have been found using fluorescent dyes as tracers to detect crossflow channels between oil and water wells, fluorescent dye tracers are simple to use. Spectrophotometry and fluorescence spectrophotometry can be used to monitor the output fluid of adjacent production wells. The shortest crossflow channel (macropore) distance can be determined by detecting the data point at which the first occurrence of the crossflow channel occurs in the production well.

[0009] The present invention uses fluorescent dye as a tracer. The material is a low-toxic chemical, can directly contact the skin, is environmentally friendly and pollution-free, and meets the oilfield wastewater discharge standard.

[0010] Before conducting crossflow channel tracing diagnosis, the present invention first conducts a downhole tubular integrity test. The downhole tubular integrity test determines whether the downhole tubular (oil pipe, casing) has a leak point, thereby preventing the tracer from causing crossflow and affecting the subsequent tracing diagnosis of crossflow channels between oil and water wells. Existing technologies mainly use methods such as X-ray, ultrasound, magnetic powder, penetration, and eddy current to perform non-destructive testing on tubulars. The tubulars need to be lifted from the operating well to the ground and then tested using instruments. The operation is complicated and the cost is high. In order to achieve low-cost visual leak detection of downhole tubulars, the present invention innovatively uses fluorescent dyes as wellbore integrity detection tracers (casing and tubing leak detection). The principle is: by dissolving the tracer in the well washing water, the downhole tubular is leak-checked by using the ground circulation well washing method, and the time required for a certain amount of tracer aqueous solution to wash the well at a specific displacement is calculated as the theoretical time T. 理论 Then, during the well washing process, observe the time T for the colored tracer solution to return from the wellhead. 返 (Because the tracer solution is colored, it can be visually distinguished from the well-flushing fluid.) The two times are then compared. If the difference is within a certain range, the tubing string is considered leak-free. A significant difference indicates a leak point in the tubing string, requiring replacement or repair before further operations can proceed. This method for detecting downhole tubing leaks does not require the tubing to be brought to the surface, offering advantages such as simplicity, high operability, and visual inspection.

[0011] The present invention conducts tracer diagnosis of crossflow channels between oil and water wells based on the following principle: after a tracer plug is injected from an injection well, it will always first penetrate the corresponding production well along the high-permeability layer. The shorter the breakthrough time of the tracer from the injection well to the corresponding oil production well, the more it indicates the presence of a crossflow channel between the wells. Based on this principle, the present invention uses a fluorescent dye as a tracer to sample and test the output fluid of the oil production well. Because the fluorescent dye tracer has color, it will show a corresponding color at high concentrations, allowing the presence of a crossflow channel to be directly determined by the naked eye. If the color is not visible to the naked eye, absorption photometry is used for detection using an instrument such as a spectrophotometer. Because a spectrophotometer has a detectable range, the instrument's detection data is reliable only when the sample concentration is within the detectable range. If the detection result exceeds the instrument's reliable measurement range, the sample solution must be distilled to increase the tracer concentration, and then the concentration must be measured using a spectrophotometer. Therefore, the detection method of the present invention can cover any concentration of the tracer. Even if the tracer concentration is very low, it can be further detected and judged after distillation and concentration, thereby improving the credibility of the detection results. The detection method is simple and easy to operate.

[0012] In summary, the tracing method of the present invention realizes visually observable, low-cost leak detection of oil casing and tubing, and realizes leak detection of wellbore integrity without operating or moving the tubing string. At the same time, through visual observation, detection instruments, and combined with low-concentration sample distillation and concentration, even low-concentration tracers can be effectively detected, thereby improving the reliability and accuracy of oil-water crossflow tracing diagnosis between wells. The method has the characteristics of visual detection, short detection cycle, small tracer usage, environmental friendliness, and low cost.

[0013] Furthermore, the calculation method of the tracer dosage is: First calculate the maximum dilution volume V of the tracer for a certain injection well p =S×H×φ×S w ×a; Where, V p : Maximum dilution volume of tracer, m 3 ; S: water flooding monitoring area (π•R 2 ), m 2 ; H: oil layer thickness, m; φ: porosity; R: average distance between water injection wells and oil production wells, m; a: Scanning efficiency, %; S w : Water saturation, %; Then calculate the amount of tracer used for a certain injection well: A=B×V p ×μ; Where, A: injection amount of tracer, kg; B: tracer detection sensitivity, ppb, ranging from 6 to 10; μ: Usage coefficient, ranging from 1 to 3.

[0014] The present invention uses the above formula to determine the dosage of dye tracer based on parameters such as the injection-production well spacing, porosity, and reservoir thickness. This dosage ensures that the tracer can be detected under the condition of this minimum dosage. In addition, individual wells in the water-injected oil wells have a strong response relationship with the water injection wells. By intermittently changing the injection rate of the water injection wells while observing the changes in the water content and liquid production of the oil wells and the formation pressure, the main crossflow direction of the injected water can be roughly determined. Therefore, it can be assumed that after the tracer is injected, it will mainly diffuse rapidly in the local formation area along the crossflow direction. Based on the calculation of directional rapid diffusion, which assumes that the fan-shaped diffusion volume occupies 1 / 3–1 / 4 of the formation diffusion volume, the tracer dosage will be equivalent to 1 / 3–1 / 4 of the simplified method commonly used in actual field operations. This will significantly reduce the actual tracer usage and cost.

[0015] Furthermore, the tracer aqueous solution is prepared at a concentration of 3 Add 1-20kg of tracer to clean water. The calculated minimum tracer dosage ensures that the tracer can be detected. However, when preparing the solution on site, a concentration limit should be set to avoid the tracer concentration being too low in the solution, which would increase the difficulty of detection.

[0016] Furthermore, the fluorescent dye is any one of rhodamine B, fluorescein sodium, calcein disodium salt, and fluorescent nanoparticles.

[0017] Furthermore, the theoretical time T 理 Set as the time for wellbore flushing N weeks, N ≥ 1. T 理 The calculation method is the volume of tracer solution used to wash the well / the volume of well washing. For example, taking N=1 as an example, T 理 =The amount of tracer solution required for one week of wellbore flushing / well flushing discharge volume.

[0018] Furthermore, the well should be washed with clean water for at least one week before using the tracer aqueous solution. Washing the well with clean water for at least one week before using the tracer aqueous solution can reduce the interference of well materials on the tracer, thereby improving the sensitivity and accuracy of the detection.

[0019] Furthermore, in step S2, the method for checking the integrity of the downhole tubular string is specifically as follows: (T 返 -T 理论 ) / T 理论 ≤5%, it is judged that there is no leakage point in casing and tubing; (T返 -T 理论 ) / T 理论 >5%, and T 返 <T 理论 , determine if there is a leak in the oil pipeline; (T 返 -T 理论 ) / T 理论 >5%, and T 返 >T 理论 , determine whether there is a leakage point in the casing.

[0020] Furthermore, the sampling in step S3 needs to be continued for 2-10 days.

[0021] Furthermore, the absorbance photometric detection is performed using a spectrophotometer, and the detection concentration of the spectrophotometer is 0.1 mg / L-5 mg / L.

[0022] Furthermore, when the sample is distilled, after the volume of the sample solution is reduced by 1 / 4, the instrument can be used for detection again until the sample concentration enters the detection range of the instrument.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0024] 1. The tracing method of the present invention realizes visual observation and low-cost leak detection of oil casing, and realizes leak detection of wellbore integrity without operating or moving the pipe string. At the same time, through visual observation, detection instruments, and combined with low-concentration sample distillation and concentration, even low-concentration tracers can be effectively detected, thereby improving the reliability and accuracy of oil-water crossflow tracing diagnosis between wells. It has the characteristics of visual detection, short detection cycle, small tracer usage, environmental friendliness, and low cost.

[0025] 2. The present invention uses fluorescent dye as a tracer. This material is a low-toxic chemical that can directly contact the skin, is environmentally friendly and pollution-free, and meets oilfield wastewater discharge standards.

[0026] 3. Before conducting crossflow channel tracing diagnosis, the present invention first conducts a downhole tubular integrity test. This test determines whether there are leaks in the downhole tubular (tubing, casing), preventing tracer crossflow from affecting subsequent tracing diagnosis of crossflow channels between oil and water wells. Furthermore, the downhole tubular leak detection method does not require the tubular to be lifted from the well to the surface, offering advantages such as simplicity, high operability, and visual inspection.

[0027] 4. When sampling and testing the produced fluid from the oil production well, the present invention first observes it with the naked eye. If no color is visible to the naked eye, absorption photometry is used for detection. If the detection result exceeds the reliable range of the instrument measurement, the sample solution is distilled to increase the tracer concentration, and then the concentration is measured with a spectrophotometer. This detection method can cover any tracer concentration. Even if the tracer concentration is very low, it can be further detected and judged after distillation and concentration, thereby improving the reliability of the detection results. The detection method is simple and easy to operate. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the embodiments. Obviously, the schematic implementation modes of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0029] The following describes, in detail, an embodiment of a method for tracing oil-water crossflow between wells according to the present invention. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions may be omitted. This is done to avoid unnecessary redundancy and to facilitate understanding by those skilled in the art.

[0030] The "ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other substances not listed may also be included or that only the listed substances are included.

[0034] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] The technical solution of the present invention is further described in detail below with reference to the embodiments.

[0036] It should be noted that the experimental methods used in the examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art, unless otherwise specified, and can be obtained from commercial channels by those skilled in the art.

[0037] Example 1 The present invention provides a method for tracing oil-water crossflow between wells, comprising the following steps: S1. Tracer selection, dosage and concentration determination This example uses rhodamine B as a tracer. Rhodamine B is an organic dyeing material widely used in industries such as inks, pigments, printing and dyeing, and coatings. It is used for coloring paper and cosmetics, and is also used to make lakes and dye silk. Its performance indicators are shown in Table 1.

[0038] Table 1. Performance indexes of basic rose essence dye

[0039] The calculation method for tracer dosage is: First calculate the maximum dilution volume V of the tracer for a certain injection well p =S×H×φ×S w ×a; Where, V p : Maximum dilution volume of tracer, m 3 ; S: water flooding monitoring area (π•R 2 ), m 2 ; H: oil layer thickness, m; φ: porosity; R: average distance between water injection wells and oil production wells, m; a: Scanning efficiency, %; S w : Water saturation, %; Taking a certain well as an example, the calculation results are shown in Table 2.

[0040] Table 2. Parameters for calculating the maximum dilution volume of XX-XX well

[0041] Then calculate the amount of tracer used for a certain injection well: A=B×V p ×μ; Where, A: injection amount of tracer, kg; B: tracer detection sensitivity, ppb, ranging from 6 to 10; (1 ppb = 10 -3 ppm=10 -9 g / L) μ: dosage coefficient, ranging from 1 to 3; The calculation results are shown in Table 3.

[0042] Table 3. Calculation and application parameters of tracer dosage for Well XX-XX

[0043] The tracer aqueous solution was prepared on site with a concentration of 100 m 3 Clean water, add 1-20kg tracer, in this example the concentration is 2.5kg / 100m 3 .

[0044] When preparing the liquid, a simple construction mode of directly taking water and preparing the liquid on site using a liquid preparation tank truck, a pump truck, and a water injection wellhead process is used to reduce the construction cost to an extremely low level. The tracer particles are very fine. In order to prevent dust from flying and facilitate on-site preparation, the tracer is packaged in water-soluble plastic bags at 0.5kg / bag. 20m 3 Take the tank truck transporting tracer aqueous solution as an example: after removing the outer packaging of the oil pipeline leak detection tracer, put it together with the water-soluble packaging bag into the tank truck, and add 20m 3 After the water is clean, the preparation is completed.

[0045] It should be noted that the tracer solution can also be prepared using the injected wastewater released from the wellhead process of the injection well. If the prepared water is turbid, the concentration can be appropriately increased. The goal is to ensure that the color is bright and visually clear.

[0046] S2. Downhole tubing leak detection The flushing fluid flows downward through the wellhead test gate into the tubing, circulates upward through the annular space between the tubing and casing, and exits the wellbore, passing through the casing outlet gate and the sewage gate. One complete cycle is called a well flush, meaning one wellbore volume is flushed. Before injecting the tracer solution, at least one wellbore volume must be flushed until flushing water returns from the wellhead casing outlet gate.

[0047] The pump truck is turned on and the prepared tracer solution is used for positive circulation to wash the well. The amount of water required for washing the wellbore for one week is 10.82 cubic meters. The time required for washing the wellbore for one week is calculated based on the displacement of the pump truck. If the wellbore displacement is 15m 3 When the flow rate is 500 rpm / h, the time for the red tracer liquid to return from the wellhead is about 0.72 hours, or 43 minutes. Therefore, we only need to observe the time for the red tracer liquid to return from the wellhead during well washing. At this time, we may encounter three situations: (T 返 -T 理论 ) / T 理论 ≤5%, it is judged that there is no leakage point in casing and tubing; (T 返 -T 理论 ) / T 理论 >5%, and T 返 <T 理论 , it is judged that there is a leak in the oil pipe. The well must be inspected and the unqualified oil pipe must be replaced before the next step of construction. This can be further divided into the following situations: 1. The time for the tracer solution to return T 返 Closer to T 理论 , indicating that the depth of the oil pipe leakage point is close to the bottom of the oil pipe; 2. The time for returning the tracer solution T 返 Much smaller than T 理论 , indicating that the depth of the tubing leakage point is close to the wellhead device at the top; (T 返 -T 理论 ) / T 理论 >5%, and T 返 >T 理论 Even if there is no return, it is judged that there is a leakage point in the casing, and it is also necessary to operate the casing and then take the next step.

[0048] S3. Tracer solution injection and sampling After the leak test in step S2 passes, the tracer aqueous solution is injected into the injection well. The sampling and analysis interval is determined based on the estimated breakthrough time of 3-5 days. Starting from the second day, production fluid samples are collected twice a day at the corresponding oil production well sampling gate. Two barrels of samples are collected each time using a 25-liter sampling cylinder. The collected production fluid samples are sent to the oilfield on-site laboratory for oil-water separation. The tracer concentration in the remaining collected water samples is measured using a 752 spectrophotometer. Sampling and testing are continued for 2-10 days.

[0049] S3. Sample testing During the test, if color is observed with the naked eye, there is a crossflow channel between the oil and water wells. If it cannot be determined with the naked eye, the absorption photometry method is used for detection.

[0050] Absorbance photometry was used for detection, specifically using a 752 spectrophotometer. The detection principle is as follows: basic rose bengal dye with a characteristic absorption wavelength of 520 nm was prepared with clean water in multiple concentration ranges from 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, 0.5 mg / L, 1.0 mg / L, 1.5 mg / L, 2.0 mg / L to 5 mg / L, and the corresponding absorbance value at each concentration was measured. The linear regression method was used to draw a curve of the absorbance and concentration relationship as a standard template, and the linear relationship coefficient K value between absorbance and concentration was calculated. Experiments showed that basic rose bengal dye has good detectability and stability within the concentration range of 0.1 mg / L~5 mg / L.

[0051] Use a 752 spectrophotometer to measure the absorbance of the sample, and then use the K value to calculate the sample concentration. There are two situations: 1. When the calculated concentration value is between 0.1mg / L and 5mg / L, it is considered to be within the instrument's measurable range. At this time, it can be determined that the tracer has broken through. If the tracer is first detected in the produced fluid of the corresponding production well, it is considered that there is a crossflow channel between the tracer and the injection well where the tracer was injected. 2. When the calculated concentration value is lower than 0.1 mg / L, it exceeds the reliable range of the instrument measurement and the reliability of the detection concentration is low. In this case, it is necessary to increase the tracer concentration by distilling the tracer solution and then measure its concentration with a spectrophotometer: Tracer solution samples with low detection reliability and inaccuracy are heated and distilled in the laboratory. By reducing the volume of water in the test sample, the concentration of basic rose bengal dye in the sample is artificially increased until it reaches the lower limit of detection by the spectrophotometer. This ensures that the tracer in the concentrated sample is within the instrument's detection range. During the distillation process, when the sample solution volume is reduced by 1 / 4, the instrument can be used to detect it again. If it is still undetectable, distillation and testing are continued until the sample concentration enters the instrument's detection range, thus achieving tracer identification at lower concentrations. It should be noted that the distillation operation can also directly concentrate the sample solution to a highly concentrated red color that can be directly observed by the naked eye. At this time, the detection method can be directly judged by visual observation, but it requires a longer distillation time and consumes more energy.

[0052] Application Example 1 The use of alkaline rhodamine dye tracer for downhole tubing leak detection has been successfully applied in eight wells in the BEKTAS reservoir of the K&B oil field in Kazakhstan. The implementation is described using the profile control water injection well B-25 in the BEKTAS reservoir as an example: (1) Well washing method and requirements: Generally speaking, water is injected in a forward injection method without a return water process. The well is washed by a pump truck + tank truck forward washing method, and the water is recovered by a tank truck. It is necessary to equip one pump truck, two water tank trucks, and one set of three-way water guide device. When washing the well, a three-way + high-pressure well washing pipeline is used at the wellhead to guide the well washing return water into the tank truck to ensure the continuity of the well washing process. The well washing water is injected into the wellbore by the pump truck to establish a well washing cycle. The well washing water and the return water are both transported by tank trucks; (2) Flushing volume requirement: To prevent sand from flowing out of the well due to flushing, the volume should be controlled at 15m 3 / h, the return water volume is not more than 18m 3 / h, and at the same time, steadily control the wellhead vent valve to keep the oil pressure within the normal well-washing pressure range of 5MPa-6.5MPa. (The starting pressure of the well is about 6MPa); (3) Downhole tubing leak detection process: Well washing: positive circulation well washing, requiring the outlet return water displacement to be equal to the pump truck pump displacement; Preparation of leak detection tracer: wait until the leak detection tracer aqueous solution is prepared (the water in the tank truck tank is completely dyed red); (4) Leak detection method: Calculate the time required for wellbore flushing for one week based on the displacement of the pump truck, and observe the time it takes for red water to return from the wellhead during well flushing. Compare the two to determine whether there are leaks in the oil pipe or casing.

[0053] Application Example 2 The L13-9 injection-production unit in the XX small block sandstone reservoir in the XX Oilfield features numerous oil-bearing layers with severe heterogeneity. Injected water primarily flows through high-permeability zones, accelerating the rise in water content. To address this issue, a basic rose bengal dye tracer was used to identify the oil-water interwell crossflow channels and conduct plugging tests. Prior to the experiment, the downhole tubing string had passed integrity testing.

[0054] The test used 200m 3 A 25ppm dye tracer (prepared as a base fluid using wellhead injection water) was pumped into the L13-9 unit L41-437 injection wellhead using a fixed tubing string. Daily sampling was conducted for seven consecutive days, with the corresponding water sample from the L13-29 production wellhead monitoring. The results revealed a crossflow channel between the two wells. After profile control and water shutoff, the injection pressure of the L41-437 injection well increased from 8.6MPa to 15MPa, corresponding to an average daily precipitation of 22.2m in the production well. 3 The test successfully verified the presence of crossflow channels between the water injection well and the oil well, demonstrating that dye tracers can be used to identify crossflow channels between oil and water wells for early diagnosis and profile control by plugging large pores. The test results are shown in Table 4.

[0055] Table 4. Dye tracer test results

[0056] Table 4 shows that Well L41-437 is 330 m away from its corresponding production well, Well L13-29. A peak tracer concentration was detected 70 h after tracer injection. The peak tracer concentration was 10.6 times the background concentration of produced water at the wellhead of Well L13-29 before tracer injection, indicating that the tracer had broken through in Well L13-29. The injected water is estimated to advance 133 m / day through the channel. Therefore, a crossflow channel is believed to exist between the injection well L41-437 and its corresponding production well, Well L13-29.

[0057] Finally, it should be noted that the above specific embodiments are only used to explain in detail the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above is only a specific implementation method of the present invention and is not used to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above specific embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions described in the above embodiments, or to replace or improve some or all of the technical features therein. These modifications, equivalent replacements, and improvements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and description of the present invention.

Claims

1. A method for tracing oil-water crossflow between wells, characterized in that: The following steps are involved: S1. Select fluorescent dye as tracer and prepare tracer aqueous solution; S2, use tracer aqueous solution to wash the well, according to the time T when the liquid returned from the wellhead appears color 返 With the theoretical time T 理论 Make a judgment, if (T 返 -T 理论 ) / T 理论 ≤5%, then the downhole string integrity is judged to be good and the next step can be carried out. 返 -T 理论 ) / T 理论 >6%, the downhole tubing needs to be replaced; S3. Inject the tracer aqueous solution into the water injection well. Starting from the second day, sample and test the corresponding oil production well. During the test, if color is observed by the naked eye, it means that a crossflow channel exists between the oil and water wells. If the naked eye cannot determine, use spectrophotometry to detect. When the tracer concentration in the sample is lower than the detection limit of the instrument, distill the sample and test it again.

2. The oil-water crossflow tracing method according to claim 1, characterized in that: The calculation method of the tracer dosage is: First calculate the maximum dilution volume V of the tracer for a certain injection well p =S×H×φ×S w ×a; Where, V p : Maximum dilution volume of tracer, m 3 ; S: water flooding monitoring area (π•R 2 ), m 2 ; H: oil layer thickness, m; φ: porosity; R: average distance between water injection wells and oil production wells, m; a: Scanning efficiency, %; S w : Water saturation, %; Then calculate the amount of tracer used for a certain injection well: A=B×V p ×μ; Where, A: injection amount of tracer, kg; B: tracer detection sensitivity, ppb, ranging from 6 to 10; μ: Usage coefficient, ranging from 1 to 3.

3. The oil-water cross-flow tracing method according to claim 1, characterized in that: The tracer aqueous solution is prepared at a concentration of 3 Clean water, add 1-20kg tracer.

4. The oil-water crossflow tracing method according to claim 1, characterized in that: The fluorescent dye is any one of rhodamine B, fluorescein sodium, calcein disodium salt, and fluorescent nanoparticles.

5. The oil-water crossflow tracing method according to claim 1, characterized in that: The theoretical time T 理 Set to the time for N weeks of wellbore flushing, where N ≥ 1.

6. The oil-water cross-flow tracing method according to claim 1, characterized in that: The well should be flushed with clean water for at least one week before using the tracer aqueous solution.

7. The oil-water cross-flow tracing method according to claim 1, characterized in that: In step S2, the method for checking the integrity of the downhole tubular string is as follows: (T 返 -T 理论 ) / T 理论 ≤5%, it is judged that there is no leakage point in casing and tubing; (T 返 -T 理论 ) / T 理论 >5%, and T 返 <T 理论 , determine if there is a leak in the oil pipeline; (T 返 -T 理论 ) / T 理论 >5%, and T 返 >T 理论 , determine whether there is a leakage point in the casing.

8. The oil-water cross-flow tracing method according to claim 1, characterized in that: The sampling in step S3 needs to be continued for 2-10 days.

9. The oil-water crossflow tracing method according to any one of claims 1 to 8, characterized in that: Absorbance photometry is performed using a spectrophotometer, and the detection concentration of the spectrophotometer is 0.1 mg / L-5 mg / L.

10. The oil-water interwell crossflow tracing method according to any one of claims 1 to 8, characterized in that: During sample distillation, when the volume of the sample solution is reduced by 1 / 4, the instrument can be used for detection again until the sample concentration falls within the instrument detection range.

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