Tracer agent for oil field and method for evaluating oil production contribution of each section of horizontal well by tracer agent

Abstract

The invention provides a tracer agent for an oil field and a method for evaluating oil production contribution of each section of a horizontal well, and belongs to the technical field of oil field development. The tracer agent for the oil field, provided by the invention, is prepared from white oil, a nonionic surfactant, 3-allyloxy-2-hydroxy propanesulfonic acid sodium salt and alcohols; wherein the rare earth metal salt, the complexing agent and the sodium 3-allyloxy-2-hydroxy propanesulfonate form a complex; the complexing agent is a mixture of glycolic acid, triethylene tetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10: (3-5): (1-2). The tracer agent for the oil field can stably exist under complex stratum conditions and can resist hypersalinity; in the process of evaluating the oil production contribution of each section of the horizontal well by using the tracer agent for the oil field, different types and different dosages of tracer agents are selected for different layer sections, so that the evaluation of the oil production contribution of each section of the horizontal well can be realized, and an effective basis is provided for subsequent refracturing.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield development, and in particular relates to an oilfield tracer and a method for evaluating the oil production contribution of each section of a horizontal well. Background Art

[0002] Horizontal wells have greatly increased the single-well production of oil wells due to their unique advantage of large contact area with the oil layer, and have been widely used in various oil fields. Horizontal well staged fracturing technology is the main technology for tight oil development. Tracer monitoring technology is currently widely used to monitor the fracturing effect. With the widespread application of tracer monitoring technology, some problems have gradually emerged, such as in the selection of tracers: how can the tracer be effectively and evenly injected into the formation, and can it distinguish the oil and water production contributions of each section of the horizontal well. In addition, due to the limitations of the reservoir environment, the tracer must also meet good temperature resistance, mineralization resistance, chemical stability, physical stability and biological stability.

[0003] At present, the tracers commonly used in oilfield development mainly include chemical tracers, isotope tracers, trace element tracers, etc. Although these tracer technologies are widely used in various oilfields, there are also many problems. For example, chemical tracers have less adsorption on the surface of the formation, small consumption, many types, and are easily detected by spectrophotometer. However, due to the large amount of such tracers used on site, they are costly, have poor adaptability and selectivity, and low precision. For example, radioactive isotope tracers are radioactive, which is unfavorable to the safety of personnel and the environment, and their application is limited; although stable isotope tracers have no radioactive hazards, their analysis and testing methods are complicated and expensive. As the fourth generation of tracer technology, trace element tracers have the advantages of no radioactivity, no pollution, corrosion resistance, good safety and stability, small dosage, direct addition from the wellhead, low price, low cost, high analysis accuracy, and many optional methods. It has become the development direction of tracer technology.

[0004] However, due to the presence of clay minerals in the formation, the active component cations in the tracer are strongly adsorbed, and there are also a large number of anions such as hydroxide ions, carbonate ions or bicarbonate ions in the formation water. The single added metal cations are easy to react chemically with them in the formation, resulting in a large loss of metal cations in the tracer. In addition, the mineralization of formation water in the western region is high, and the mineralization resistance of the current trace element tracer needs to be further improved.

[0005] Therefore, it is necessary to provide a new type of tracer and a method for evaluating the oil production contribution of each section of a horizontal well that can distinguish the oil production and water production contributions of each section of the horizontal well, so as to screen and obtain tracers with a wider range of applications. Summary of the invention

[0006] In view of the shortcomings of the prior art, the first object of the present invention is to provide a tracer for oil fields, which can stably exist under complex formation conditions, can withstand high mineralization, and has wide adaptability.

[0007] The second object of the present invention is to provide a method for evaluating the oil production contribution of each section of a horizontal well using the above oil field tracer.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In one aspect, a tracer for oil fields comprises 50 to 60 parts of white oil, 2 to 5 parts of nonionic surfactant, 1 to 2.5 parts of sodium 3-allyloxy-2-hydroxypropanesulfonate, and 5 to 10 parts of alcohols; wherein: The rare earth metal salt forms a complex with the complexing agent and sodium 3-allyloxy-2-hydroxypropanesulfonate; The complexing agent is a mixture of glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:(3-5):(1-2).

[0009] In a further embodiment, the oil field tracer comprises the following raw materials by weight: 12 parts of rare earth metal salt, 12 parts of complexing agent, 55 parts of white oil, 3 parts of nonionic surfactant, 1.5 parts of sodium 3-allyloxy-2-hydroxypropane sulfonate, and 8 parts of alcohol.

[0010] In a further embodiment, the rare earth metal salt is selected from at least one of rare earth nitrates, rare earth sulfates and rare earth hydrochlorides.

[0011] In a further embodiment, the rare earth metal element in the rare earth metal salt is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

[0012] Preferably, the mass ratio of glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in the complexing agent is 10:4:1.5.

[0013] In a further embodiment, the nonionic surfactant is selected from at least one of Tween 20, Tween 40, Tween 60 and Tween 80.

[0014] In a further embodiment, the alcohol is at least one of ethanol, isopropanol, glycerol, and n-butanol.

[0015] As a further preferred solution, phenylsuccinic anhydride acylated chitosan with a mass percentage of 8 to 10% of rare earth metal salt is added to the raw material of the oil field tracer, and the phenylsuccinic anhydride acylated chitosan is prepared by modifying chitosan with phenylsuccinic anhydride.

[0016] Preferably, the molecular weight of the chitosan is 5-10 kDa; the mass ratio of the phenylsuccinic anhydride to the chitosan is (0.2-0.35):1; more preferably, the mass ratio of the phenylsuccinic anhydride to the chitosan is 0.28:1.

[0017] Preferably, the phenylsuccinic anhydride acylated chitosan is prepared by the following method: The chitosan is dispersed in an acetic acid solution, sodium carbonate is added, and the mixture is stirred for reaction for 30 minutes, followed by adding phenylsuccinic anhydride. The mixture is reacted at room temperature for 5 to 6 hours, the pH value is adjusted to 9 to 10, and the unreacted chitosan is removed by centrifugation. The remaining product is dialyzed, and then the pH value is adjusted to 3 to 4 with concentrated hydrochloric acid to obtain a white flocculent precipitate. The precipitate is centrifuged again and dried to obtain the phenylsuccinic anhydride acylated chitosan.

[0018] In the preparation process of phenylsuccinic anhydride acylated chitosan, the mass ratio of the added amount of sodium carbonate to chitosan is 1:(0.2-0.3); the mass fraction of the acetic acid solution is 1-2%.

[0019] In a further embodiment, the method for preparing the complex comprises the following steps: (1) dissolving a rare earth metal salt in water to prepare a rare earth metal salt solution; (2) Add a complexing agent to a rare earth metal salt solution and mix well, then add sodium 3-allyloxy-2-hydroxypropanesulfonate to react to obtain a rare earth metal complex.

[0020] Preferably, in step (1), the mass fraction of the rare earth metal salt solution is 8-10%.

[0021] Preferably, in step (2), the reaction time is 0.5 to 1.5 h.

[0022] In a further embodiment, in step S2, after adding sodium 3-allyloxy-2-hydroxypropanesulfonate, phenyl succinic anhydride is added to acylate the chitosan.

[0023] In a further embodiment, the method for preparing the oil field tracer comprises the following steps: A nonionic surfactant is added to the rare earth metal complex, stirred for reaction, and then white oil and alcohol are added, and the temperature is raised to 50-60° C. and stirred for reaction to obtain a tracer for oil fields.

[0024] Preferably, the stirring reaction time is 45 to 70 minutes; the continued stirring reaction time is 1 to 2 hours.

[0025] On the other hand, a method for evaluating the oil production contribution of each section of a horizontal well includes using the above-mentioned oil field tracer for evaluation.

[0026] The method for evaluating the oil production contribution of each section of a horizontal well comprises the following steps: (1) Extract background samples from each section of the horizontal well for analysis and select the tracer for that section; select the tracer made from rare earth elements that are not contained or have a low content in the samples of that section as the tracer for that section; (2) Based on the fracture volume in the fracturing design, the oil saturation of the reservoir, and the minimum detection limit of the effective tracer material, the amount of tracer is calculated by magnifying it 20 times; (3) Pumping the tracer into the fracturing pre-fluid of different well sections and starting fracturing; (4) During the fracturing fluid flowback and production process, samples are taken for analysis and testing to determine the concentration of chemical tracers in the samples and calculate the contribution rate of oil and water production in each section.

[0027] In a further embodiment, in step (2), the calculation formula for the amount Q of the tracer is: ; Wherein, Q is the amount of tracer, kg; A is the fracture affected area, m2; H is the average fracture thickness; φ is the reservoir porosity, %; So is the reservoir oil saturation, %; MDL is the minimum detection limit, dimensionless.

[0028] In a further embodiment, in step (4), the sampling is performed once every 12 hours on the wellhead produced fluid for 30 consecutive days.

[0029] In a further embodiment, in step (4), the analysis is performed using a mass spectrometer.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1. The oil field tracer of the present invention can stably exist under complex formation conditions, can withstand high mineralization, and has wide adaptability.

[0031] 2. The oil field tracer of the present invention uses glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate as complexing agents, which are complexed with rare earth metal elements to form a complex. The complexing agent is wrapped on the surface of the rare earth metal, which can effectively prevent anions in water from directly combining with rare earth metal ions, thereby reducing product performance, and is helpful to improve the dispersion stability of the tracer in complex formations and improve mineralization resistance. The three complexing agents cooperate with each other, which can not only further improve the mineralization resistance, but also when the ratio of the three complexing agents is within a specific range, the obtained tracer has higher heat resistance and salt resistance.

[0032] 3. The addition of sodium 3-allyloxy-2-hydroxypropanesulfonate to the oil field tracer of the present invention makes the complex structure formed on the surface of the rare earth ions more compact, which helps to improve the mineralization resistance and salt resistance of the tracer.

[0033] 4. Adding phenylsuccinic anhydride acylated chitosan to the oil field tracer of the present invention and controlling the ratio of phenylsuccinic anhydride to chitosan are helpful for rapid diffusion of the tracer in the well, improving the dispersion stability of the tracer, preventing agglomeration in the water in the formation, and helping to further improve the mineralization resistance, temperature resistance and salt resistance of the tracer.

[0034] 5. The present invention utilizes the oilfield tracer to evaluate the oil production contribution of each section of the horizontal well. By selecting different types and amounts of tracers for different layers, the oil production contribution rate of each section of the horizontal well can be determined, which can effectively guide the optimization design of volume fracturing. DETAILED DESCRIPTION

[0035] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of the present invention.

[0036] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0037] Example 1 A tracer for oil fields is prepared by the following method: S1. Dissolve 10 g of ytterbium chloride in water to prepare a rare earth metal salt solution with a mass fraction of 10%; S2, add 8g of complexing agent (hydroxyacetic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:3:1) to the rare earth metal salt solution, mix well, add 1g of sodium 3-allyloxy-2-hydroxypropanesulfonate and react for 0.5h to obtain a rare earth metal complex; S3. Add 2 g of Tween 60 to the rare earth metal complex, stir and react for 45 min, then add 50 g of white oil and 5 g of isopropanol, raise the temperature to 50° C. and continue stirring and reacting for 2 h to obtain a tracer for oil fields.

[0038] Example 2 A tracer for oil fields is prepared by the following method: S1. Dissolve 12 g of ytterbium chloride in water to prepare a rare earth metal salt solution with a mass fraction of 10%; S2, add 12g of complexing agent (hydroxyacetic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:4:1.5) to the rare earth metal salt solution, mix well, add 2.5g of sodium 3-allyloxy-2-hydroxypropanesulfonate and react for 0.5h to obtain a rare earth metal complex; S3. Add 3 g of Tween 60 to the rare earth metal complex, stir and react for 60 min, then add 55 g of white oil and 8 g of isopropanol, raise the temperature to 60° C. and continue stirring and reacting for 2 h to obtain a tracer for oil fields.

[0039] Example 3 A tracer for oil fields is prepared by the following method: S1. Dissolve 15 g of ytterbium chloride in water to prepare a rare earth metal salt solution with a mass fraction of 12%; S2, add 15g of complexing agent (hydroxyacetic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:5:2) to the rare earth metal salt solution, mix well, add 2.5g of sodium 3-allyloxy-2-hydroxypropanesulfonate and react for 1.5h to obtain a rare earth metal complex; S3. Add 5 g of Tween 60 to the rare earth metal complex, stir and react for 70 min, then add 60 g of white oil and 10 g of isopropanol, raise the temperature to 60° C. and continue stirring and reacting for 2 h to obtain a tracer for oil fields.

[0040] Example 4 The difference between this embodiment and embodiment 2 is that the complexing agent is glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:2:0.5, and the total amount of the complexing agent remains unchanged.

[0041] Example 5 The difference between this embodiment and embodiment 2 is that the complexing agent is glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:6:3, and the total amount of the complexing agent remains unchanged.

[0042] Example 6 The difference between this embodiment and embodiment 2 is that phenylsuccinic anhydride acylated chitosan (i.e., 0.96 g) with a mass percentage of 8% of the rare earth metal salt is further added to the oil field tracer, and the phenylsuccinic anhydride acylated chitosan is added immediately after the addition of sodium 3-allyloxy-2-hydroxypropanesulfonate.

[0043] Wherein, phenylsuccinic anhydride acylated chitosan is prepared by the following method: 10g chitosan (molecular weight 10kDa) was dispersed in 50g acetic acid solution with a mass fraction of 1%, 2g sodium carbonate was added, and the mixture was stirred for reaction for 30min, then 2g phenylsuccinic anhydride was added, and the mixture was reacted at room temperature for 5h. The pH was adjusted to 10, and the mixture was centrifuged. The remaining product was dialyzed, and the pH was adjusted to 4 with concentrated hydrochloric acid to obtain a white flocculent precipitate. The mixture was centrifuged again and dried to obtain the phenylsuccinic anhydride acylated chitosan.

[0044] Example 7 The difference between this embodiment and embodiment 6 is that the addition amount of phenylsuccinic anhydride acylated chitosan is 10% of the mass of the rare earth metal salt, and the phenylsuccinic anhydride acylated chitosan is prepared by the following method: 10g chitosan (molecular weight of 10kDa) was dispersed in 50g acetic acid solution with a mass fraction of 1%, 3g sodium carbonate was added, and 3.5g phenylsuccinic anhydride was added after stirring for 30min, and the reaction was carried out at room temperature for 5h. The pH was adjusted to 10, centrifuged, and the remaining product was dialyzed. Then, the pH was adjusted to 4 with concentrated hydrochloric acid to obtain a white flocculent precipitate, which was centrifuged again and dried to obtain the phenylsuccinic anhydride acylated chitosan.

[0045] Example 8 The difference between this embodiment and embodiment 6 is that, in the preparation process of phenylsuccinic anhydride acylated chitosan, the amount of phenylsuccinic anhydride used is 1 g, that is, the mass ratio of phenylsuccinic anhydride to chitosan is 0.1:1.

[0046] Example 9 The difference between this embodiment and embodiment 6 is that, in the preparation process of acylation of chitosan with phenylsuccinic anhydride, the amount of phenylsuccinic anhydride used is 4 g, that is, the mass ratio of phenylsuccinic anhydride to chitosan is 0.4:1.

[0047] Example 10 The difference between this example and example 6 is that the phenylsuccinic anhydride acylated chitosan is replaced by an equal amount of maleic anhydride acylated chitosan, and the maleic anhydride acylated chitosan is prepared by the following method: 10g chitosan (molecular weight 10kDa) was dispersed in 50g water, 2.5g sodium carbonate was added, and 2.8g maleic anhydride was added after stirring for 30min, and the reaction was carried out at room temperature for 5h. The pH was adjusted to 10, centrifuged, and the remaining product was dialyzed. Then, the pH was adjusted to 4 with concentrated hydrochloric acid to obtain a white flocculent precipitate, which was centrifuged again and dried to obtain the maleic anhydride acylated chitosan.

[0048] Comparative Example 1 The difference between this comparative example and Example 2 is that the sodium dithiopropanesulfonate in the complexing agent is replaced by an equal amount of sodium sulfosalicylate. Comparative Example 2 The difference between this comparative example and Example 2 is that the complexing agent is glycolic acid and triethylenetetramine in a mass ratio of 10:6, and the total amount of the complexing agent remains unchanged.

[0049] Comparative Example 3 The difference between this comparative example and Example 2 is that the complexing agent is glycolic acid and sodium dimercaptopropane sulfonate in a mass ratio of 10:3, and the total amount of the complexing agent remains unchanged.

[0050] Comparative Example 4 The difference between this comparative example and Example 2 is that the complexing agent is replaced by an equal amount of glycolic acid.

[0051] Comparative Example 5 The difference between this comparative example and Example 2 is that sodium 3-allyloxy-2-hydroxypropanesulfonate is not added.

[0052] Comparative Example 6 The difference between this comparative example and Example 2 is that sodium 3-allyloxy-2-hydroxypropanesulfonate is replaced by an equal amount of sodium allyl sulfonate.

[0053] Test Example 1 Mineralization resistance The tracers of the embodiment and the comparative example were respectively prepared into tracer solutions with a concentration of 0.0996 μg / L using simulated formation water with a mineralization of 250,000 mg / L, and placed at 200°C for 360 days. The tracer mass concentration was detected by a mass spectrometer, and the concentration retention rate was calculated using the ratio of the concentration after aging to the initial concentration, which was used to evaluate the mineralization resistance.

[0054] The test results are shown in Table 1.

[0055] Table 1

[0056] As shown in the table, the tracers obtained in Examples 1-3 of the present invention can still maintain a concentration of more than 90% after 360 days in simulated formation water with a mineralization of 250000 mg / L, with good mineralization resistance and good dispersion stability. Compared with Example 2, the concentration retention rate of the tracers obtained in Examples 6 and 7 is higher than that of Example 2 after being placed for 120 days and 360 days, while the preparation conditions of phenyl succinic anhydride acylated chitosan in Examples 8-10 are changed, and the concentration retention rate is slightly different from that of Example 2, which shows that adding specific phenyl succinic anhydride acylated chitosan to the tracer helps to improve the mineralization resistance of the tracer. In Comparative Examples 1-3, the concentration retention rate is significantly reduced by changing the complexing agent component, which shows that the selection of the complexing agent has a greater impact on the mineralization resistance of the tracer, and the selection of a specific complexing agent helps to significantly improve the mineralization resistance of the tracer.

[0057] Test Example 2 Salt tolerance Take the mineralization degree of 250000mg / L, Na + Concentration 50000mg / L, Ca 2+ The tracers of the embodiment and the comparative example were added to the simulated formation water with a concentration of 50000 mg / L to prepare a mixed solution containing 50000 mg / L, and the solution was oscillated at the formation temperature for 120 days. The mass concentration of the tracer was detected by a mass spectrometer, and the loss rate of the tracer concentration was calculated by the ratio of the change in concentration to the initial concentration, which was used to evaluate the salt tolerance.

[0058] The test results are shown in Table 2 below.

[0059] Table 2

[0060] As shown in the table, after the tracers prepared in the embodiments and comparative examples of the present invention were placed under high salt concentration for 30 days, the concentration change range was small and the stability was good. As the placement time increased to 90 days, the concentration change range of the tracers in the embodiments and comparative examples showed obvious differences; it can be seen that the concentration loss rate of the tracers obtained in the embodiments is less than 4%, especially in embodiments 1-3 and embodiments 6 and 7, the concentration loss rate is below 2%, while the concentration loss rate of the tracer in the comparative example is higher than 5.5%, which is significantly higher than that in embodiment 2, and the salt tolerance is relatively low. As the placement time increases to 120 days, the difference in the concentration loss rate of the tracers in the embodiments and comparative examples becomes larger. The concentration loss rate of the comparative example increases to more than 9%, even to more than 15%, and the concentration loss rate of embodiment 2 is 4.25%, which is significantly lower than that of the comparative example. It can be seen that the selection of the complexing agent and the addition of sodium 3-allyloxy-2-hydroxypropanesulfonate help to improve the salt tolerance of the tracer. It can also be seen that when chitosan acylated with phenylsuccinic anhydride is added to the tracers of Examples 6 and 7, the concentration loss rate is further reduced, indicating that the addition of chitosan acylated with phenylsuccinic anhydride can further improve the salt tolerance of the tracer.

[0061] Test Example 3 Heat resistance Tracers were added to simulated formation water with a mineralization of 250,000 mg / L to prepare a mixed solution with a concentration of 10 ug / L. The mixed solution was placed at 350°C for 90 days. The mass concentration of the tracer was detected by a mass spectrometer, and the concentration loss rate was calculated to evaluate the heat resistance.

[0062] The test results are shown in Table 3 below.

[0063] Table 3

[0064] As shown in the table, the tracers prepared in the examples and comparative examples of the present invention have a small concentration loss rate after aging at 350°C for 30 days. As the aging time increases to 60 days, the concentration loss rates of the tracers in Examples 4, 5 and the comparative example are significantly higher than that in Example 2, and the heat resistance decreases. As the aging time increases to 90 days, the concentration loss rate of Example 2 is about 5%, and the concentration loss rates of the tracers in Examples 4, 5 and the comparative example are significantly higher than that in Example 2, and the heat resistance is significantly worse than that in Example 2. It can be seen that the tracer provided by the present invention has good heat resistance, and the specific proportion of complexing agent helps to improve the heat resistance of the tracer.

[0065] Test Example 4 Tracer static adsorption test The tracers of the examples and comparative examples were prepared into 500 mg / L tracer solutions. 300 mL of the tracer solution was mixed with 100 g of the crushed rock sample, sealed, and oscillated at the formation temperature for 60 days. The tracer concentration was measured and the loss rate was calculated.

[0066] The test results are shown in Table 4 below.

[0067] Table 4

[0068] As shown in the table, the concentration loss rate of the mixed solution of the tracer and the rock sample obtained in Examples 1-3 was less than 5.5% after oscillating at the formation temperature for 60 days, and the concentration loss rate of the tracer in Comparative Examples 1-4 was 11-16%. It can be seen that the selection of a specific complexing agent for the tracer can reduce the adsorption amount of the tracer in the rock formation and improve the stability.

[0069] Application Example 1 A method for evaluating the oil production contribution of each section of a horizontal well using an oil field tracer comprises the following steps: (1) There are 5 test sections in the horizontal well to be tested. Background samples of each section of the horizontal well are extracted for analysis. A tracer made from a rare earth element that is not contained or contained in a small amount in the sample of the section is selected as the tracer of the section. Three types of tracers X1 to X3 are determined, X1: a tracer prepared in the above-mentioned Example 2; X2: a tracer prepared by the method described in the above-mentioned Example 2 using samarium chloride as a rare earth metal salt; X3: a tracer prepared by the method described in the above-mentioned Example 2 using praseodymium chloride as a rare earth metal salt; wherein, X1 is noted for the 1st and 4th sections, X2 is noted for the 2nd and 3rd sections, and X3 is noted for the 3rd section; (2) Based on the fracture volume in the fracturing design, the oil saturation of the reservoir, and the minimum detection limit of the effective tracer material, the amount of tracer is calculated by magnifying it 20 times using the following formula; ; (1) In formula (1), Q is the amount of tracer, kg; A is the fracture affected area, m2; H is the average fracture thickness; φ is the reservoir porosity, %; So is the reservoir oil saturation, %; MDL is the minimum detection limit, dimensionless.

[0070] (3) Pump the tracer into the fracturing pre-fluid of different well sections and start fracturing.

[0071] (4) During the fracturing fluid flowback and production process, samples are taken for analysis and testing. The wellhead production fluid is sampled once every 12 hours for 30 consecutive days. The concentration of chemical tracers in the samples is measured by mass spectrometry. The change in chemical tracer concentration over time is plotted to obtain a tracer production curve. The measured tracer production concentration values ​​are fitted and calculated, and the contribution of each section to oil production can be calculated based on the total production of the field test.

[0072] After testing and analysis, it was found that the middle section of the horizontal well made a significant contribution to oil production. Among them, sections 2 and 3 were the main oil-producing sections, with oil production contribution rates of 38% and 31% respectively. The oil production contribution rates of sections 1, 4 and 5 of the horizontal well were 14%, 12% and 5% respectively.

[0073] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A tracer for oil fields, characterized in that: It contains 50-60 parts of white oil, 2-5 parts of nonionic surfactant, 1-2.5 parts of sodium 3-allyloxy-2-hydroxypropanesulfonate, and 5-10 parts of alcohols; wherein, The rare earth metal salt forms a complex with the complexing agent and sodium 3-allyloxy-2-hydroxypropanesulfonate; The complexing agent is a mixture of glycolic acid, triethylenetetramine and sodium dimercaptopropanesulfonate in a mass ratio of 10:(3-5):(1-2).

2. The oil field tracer according to claim 1, characterized in that: The rare earth metal salt is selected from at least one of rare earth nitrates, rare earth sulfates and rare earth hydrochlorides; the rare earth metal element in the rare earth metal salt is selected from at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

3. The oil field tracer according to claim 1, characterized in that: The nonionic surfactant is selected from at least one of Tween 20, Tween 40, Tween 60 and Tween 80.

4. The oil field tracer according to claim 1, characterized in that: The alcohol is at least one of ethanol, isopropanol, glycerol and n-butanol.

5. The oil field tracer according to claim 4, characterized in that: Phenyl succinic anhydride acylated chitosan is also added into the raw materials of the oil field tracer, and the phenyl succinic anhydride acylated chitosan is prepared by modifying chitosan with phenyl succinic anhydride.

6. The oil field tracer according to any one of claims 1 to 5, characterized in that: The preparation method of the complexing agent comprises the following steps: (1) dissolving a rare earth metal salt in water to prepare a rare earth metal salt solution; (2) Add a complexing agent to a rare earth metal salt solution and mix well, then add sodium 3-allyloxy-2-hydroxypropanesulfonate to react to obtain a rare earth metal complex.

7. The oil field tracer according to claim 6, characterized in that: In step (2), after adding sodium 3-allyloxy-2-hydroxypropanesulfonate, the method further includes adding phenylsuccinic anhydride to acylate the chitosan.

8. A method for evaluating the oil production contribution of each section of a horizontal well, characterized in that: The method comprises using the oil field tracer according to any one of claims 1 to 7 for evaluation.

9. The method for evaluating the oil production contribution of each section of a horizontal well according to claim 8, characterized in that: The steps include: (1) extracting background samples from each section of the horizontal well for analysis, and selecting an oilfield tracer for the section; the oilfield tracer is the oilfield tracer according to any one of claims 1 to 7; (2) Based on the fracture volume in the fracturing design, the oil saturation of the reservoir, and the minimum detection limit of the effective tracer material, the amount of tracer is calculated by magnifying it 20 times; (3) Pumping the tracer into the fracturing pre-fluid of different well sections and starting fracturing; (4) During the fracturing fluid flowback and production process, samples are taken for analysis and testing to determine the concentration of chemical tracers in the samples and calculate the contribution rate of oil and water production in each section.

10. The method for evaluating the oil production contribution of each section of a horizontal well according to claim 9, characterized in that: In step (2), the calculation formula of the amount Q of the tracer is as follows (I): （I） Wherein, Q is the amount of tracer, kg; A is the fracture affected area, m2; H is the average fracture thickness; φ is the reservoir porosity, %; So is the reservoir oil saturation, %; MDL is the minimum detection limit, dimensionless.

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