Tracer agent and application thereof in shale oil and gas exploration and development

Abstract

The invention provides a tracer agent and application thereof in shale oil and gas exploration and development, the tracer agent comprises a rare earth element compound, a composite complexing agent and a compatible additive, and the composite complexing agent comprises a phenanthroline compound and ethylenediamine tetraacetic acid. The tracer agent has high rare earth element retention rate, good compatibility with fracturing fluid, good high temperature performance, safety and environmental protection performance, is more suitable for shale stratums, can still continuously and effectively play a monitoring role in the environment with the dual dilution effect of the fracturing fluid and stratum fluid, and has the advantages of being capable of improving the sedimentation stability of the propping agent in the fracturing fluid, good in high temperature performance and good in safety and environmental protection performance. The current shale oil-gas exploration and development technical requirements are met.

Description

[0001] Related Applications

[0002] This application claims the priority of Chinese patent application CN 202310855402.9, filed on July 12, 2023, entitled “A tracer and an integrated device and method for preparation, pumping and monitoring thereof”, and the entire contents of CN202310855402.9 are incorporated herein by reference. Technical Field

[0003] The invention relates to a tracer and application thereof in shale oil and gas exploration and development, belonging to the technical field of shale oil and gas exploration and development. Background Art

[0004] Chemical tracers, radioactive isotope tracers, non-radioactive isotope tracers and rare earth element tracers are widely used in inter-well tracing technology of oil and gas fields. Among them, chemical tracers are mainly represented by various inorganic salts, dyes, halogenated hydrocarbons and alcohols, but they have been gradually eliminated due to large dosage, high cost, poor adaptability and low test accuracy. Radioactive isotope tracers are used in small quantities and have high accuracy, but the placement and detection of radioactive isotope tracers require professionals and departments and there are potential radioactive hazards, so their application is limited. Non-radioactive isotope tracers have the advantages of radioactive isotope tracers and do not have potential radioactive hazards, but non-radioactive isotope tracers require reactor activation, so their detection still requires professionals. Rare earth element tracer technology is the latest tracer technology, which mainly uses non-existent or trace elements in the formation as test tracers. It has a series of advantages such as safety and stability, a wide variety, small dosage, high accuracy, etc., and has broad application prospects. However, the existing rare earth element tracer technology is not applicable to the fluid tracing technology required in the current unconventional oil and gas exploration and development process due to differences in geological characteristics and exploration and development technology. The specific reasons are: (1) Compared with the geological characteristics of conventional oil and gas reservoirs, shale oil and gas reservoirs have the characteristics of low porosity, low permeability, high organic matter content and high clay mineral content, which greatly increases the adsorption capacity of the formation for fluids and tracers, so that trace amounts of rare earth element tracers may be adsorbed by the underground rock formation and cannot be detected; (2) Compared with conventional oil and gas reservoir development technology, shale oil and gas reservoir development also requires horizontal well drilling and supporting hydraulic fracturing technology. On the one hand, it is necessary to avoid the reaction between the tracer and the components of the fracturing fluid, and on the other hand, it is also necessary to consider the dilution effect of the fracturing fluid itself on the tracer concentration.

[0005] Using complexing agents to form complexes with rare earth elements to protect rare earth elements is an effective method to prevent rare earth elements from being adsorbed by formations. However, existing rare earth element complexing agents still have problems such as poor solubility, insufficient complexing ability, and easy adsorption by formations when used as tracers in oil and gas exploration, which affects the accuracy of tracer applications.

[0006] In view of the above, the existing tracers fail to effectively consider the low porosity and low permeability of the dense formations of shale oil and gas reservoirs and the complexity and particularity of the fracturing fluid components. In actual application, they are easily adsorbed by the formation and cannot monitor and affect the performance of the original fracturing fluid, which greatly affects the implementation effect. Therefore, it is necessary to develop new tracers based on the characteristics of shale oil and gas exploration and development. Summary of the invention

[0007] In view of the above technical problems existing in the prior art, the present invention proposes a tracer and its application in shale oil and gas exploration and development. The tracer provided by the present invention has the characteristics of high rare earth element retention rate, good compatibility with fracturing fluid, ability to improve the sedimentation stability of proppant in fracturing fluid, good high temperature performance and high safety and environmental protection. It can still continuously and effectively play a monitoring role in the environment of dual dilution of fracturing fluid and formation fluid, meets the current technical requirements of shale oil and gas exploration and development, and is more suitable for shale oil and gas exploration and development.

[0008] According to a first aspect of the present invention, a tracer is provided, comprising a rare earth element compound, a composite complexing agent and a compatible additive, wherein the composite complexing agent comprises a phenanthroline compound and ethylenediaminetetraacetic acid.

[0009] A further improvement of the present invention is that the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.5-1):(0.01-0.1); and / or

[0010] The mass ratio of the ethylenediaminetetraacetic acid to the phenanthroline compound is 1:(0.01-0.5).

[0011] A further improvement of the present invention is that the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.8-1):(0.01-0.05).

[0012] A further improvement of the present invention is that the phenanthroline compound has a structure as shown in Formula I:

[0013]

[0014] Wherein, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, halogen, CN, NO2, C1-C8 alkyl, halogenated C1-C8 alkyl, C1-C8 alkoxy, halogenated C1-C8 alkoxy, C1-C8 alkylthio, halogenated C1-C8 alkylthio, C1-C8 alkylsulfinyl, halogenated C1-C8 alkylsulfinyl, C1-C8 alkylsulfonyl, halogenated C1-C8 alkylsulfonyl, aryl, halogenated sulfoaryl, carboxyl, C1-C8 alkylcarboxyl, halogenated C1-C8 alkylcarboxyl, C1-C8 alkyl substituted C1-C8 alkylcarboxyl substituted amino.

[0015] A further improvement of the present invention is that in formula I, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, phenyl, chlorosulfonylphenyl, carboxyl and -CH2N(CH2COOH)2.

[0016] A further improvement of the present invention is that the phenanthroline compound is selected from at least one of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline), 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline and 4,7-dichlorosulfonylbenzene-2,9-dicarboxylic acid-1,10-phenanthroline.

[0017] A further improvement of the present invention is that the rare earth element in the rare earth element compound is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

[0018] A further improvement of the present invention is that the rare earth element compound is a soluble salt of the rare earth element, preferably at least one of a nitrate, a chloride and a sulfate.

[0019] A further improvement of the present invention is that the compatibility additive is selected from at least one of gum arabic, xanthan gum, natural rubber, casein, casein, casein and sodium alginate.

[0020] A first aspect of the present invention provides the use of the tracer in shale oil and gas exploration and development.

[0021] Beneficial effects of the present invention:

[0022] In the tracer of the present invention, the phenanthroline compound and ethylenediaminetetraacetic acid in the composite complexing agent are synergistically enhanced under a specific quantitative relationship, and the composite complexing agent and the compatible additive are synergistically enhanced under a specific quantitative relationship, so that the rare earth elements in the tracer can be very effectively protected, and the adsorption amount in the shale formation is significantly reduced, thereby being able to maintain a relatively high rare earth element retention rate (at room temperature, in a fracturing fluid with a shale content of 20 weight percent, the retention rate of the rare earth elements contained in the tracer is higher than 70%, and can reach up to 92.5%), and the tracer has good compatibility with the fracturing fluid, the stability of the tracer in the fracturing fluid is less affected by the components of the fracturing fluid, and the addition of the tracer has little effect on the viscosity of the fracturing fluid, and the tracer can also significantly improve the sedimentation stability of the proppant in the fracturing fluid.

[0023] The tracer has good high temperature performance (under 95°C use conditions, the retention rate of the rare earth elements contained in the tracer is higher than 65%, and can reach up to 92.8%). Compared with existing tracers, the tracer provided by the present invention is more suitable for shale formations, and can continue to and effectively play a monitoring role in an environment of dual dilution of fracturing fluid and formation fluid, meeting the current technical requirements of shale oil and gas exploration and development.

[0024] The tracer provided by the present invention is highly safe and environmentally friendly, and its usage concentration in the fracturing fluid is below 10 ppm, reaching the food-grade industrial dosage standard of rare earth elements, and hardly causes pollution to the underground. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It reflects the relative position information of the 10-1HF well and the 10HF well in a shale gas field in Example 15.

[0026] Figure 2 It reflects the monitoring of rare earth element concentrations in the return fluid of well 10-1HF within 55 days.

[0027] Figure 3 It reflects the monitoring of rare earth element concentrations in the return fluid of well 10HF within 67 days. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with examples, but the examples of the present invention are only exemplary descriptions, and the implementation methods do not constitute limitations of the present invention under any circumstances.

[0029] According to one aspect of the present invention, a tracer is provided, comprising a rare earth element compound, a composite complexing agent and a compatible additive, wherein the composite complexing agent comprises a phenanthroline compound and ethylenediaminetetraacetic acid.

[0030] The inventors found that there is a synergistic effect between the phenanthroline compound and ethylenediaminetetraacetic acid in the composite complexing agent. Compared with using ethylenediaminetetraacetic acid alone or a phenanthroline compound alone as a complexing agent, the composite complexing agent can better complex rare earth elements and improve the element retention rate of rare earth elements in low-concentration solutions. At the same time, the oil-water amphiphilicity of the tracer is enhanced, making it more suitable for shale formations and significantly reducing the adsorption of the tracer by the shale formation.

[0031] The inventors also found that there is a synergistic effect between the compatible additive and the composite complexing agent in the tracer, which can enhance the solubility of the rare earth element compound in the fracturing fluid, and play a buffering protection and stabilizing role when the tracer contacts the fracturing fluid, thereby preventing the anionic and cationic drag reducers in the fracturing fluid from reacting in large quantities with the tracer and causing complex failure, further improving the element retention rate of the rare earth element in the low concentration solution, and at the same time improving the high temperature performance of the tracer, and enabling the tracer to have the function of enhancing the sand carrying capacity of the fracturing fluid.

[0032] According to the present invention, the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.5-1):(0.01-0.1), for example, 1:0.5:0.01, 1:0.8:0.01, 1:0.9:0.1, 1:0.9:0.03, 1:1:0.01, 1:1:0.05; and / or

[0033] The mass ratio of the ethylenediaminetetraacetic acid to the phenanthroline compound is 1:(0.01-0.5), for example, 1:0.01, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5.

[0034] According to the present invention, on the basis of satisfying the above-mentioned quantitative relationship, in order to enable the tracer to obtain better rare earth element retention rate, compatibility with fracturing fluid, high temperature stability and improved comprehensive performance of sand carrying capacity of fracturing fluid, preferably, the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.8-1):(0.01-0.05), for example, 1:0.8:0.01, 1:0.9:0.03, 1:1:0.01, 1:1:0.05.

[0035] According to the present invention, the phenanthroline compound has a structure as shown in Formula I:

[0036]

[0037]

[0038] Wherein, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, halogen, CN, NO2, C1-C8 alkyl, halogenated C1-C8 alkyl, C1-C8 alkoxy, halogenated C1-C8 alkoxy, C1-C8 alkylthio, halogenated C1-C8 alkylthio, C1-C8 alkylsulfinyl, halogenated C1-C8 alkylsulfinyl, C1-C8 alkylsulfonyl, halogenated C1-C8 alkylsulfonyl, aryl, halogenated sulfoaryl, carboxyl, C1-C8 alkylcarboxyl, halogenated C1-C8 alkylcarboxyl, C1-C8 alkyl substituted C1-C8 alkylcarboxyl substituted amino.

[0039] According to a preferred embodiment of the present invention, in Formula I, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, phenyl, chlorosulfonylphenyl, carboxyl and -CH2N(CH2COOH)2.

[0040] According to a further preferred embodiment of the present invention, the phenanthroline compound is selected from at least one of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline), 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline and 4,7-dichlorosulfonylbenzene-2,9-dicarboxylic acid-1,10-phenanthroline, which can better cooperate with ethylenediaminetetraacetic acid, and make the composite complexing agent and the compatible additive better cooperate, bring better rare earth element complexing, so that the tracer has better rare earth element retention rate, compatibility with fracturing fluid, high temperature performance and comprehensive performance of improving the sand carrying capacity of fracturing fluid.

[0041] According to the present invention, the rare earth element in the rare earth element compound is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

[0042] According to the present invention, the rare earth element compound is a soluble salt of the rare earth element, preferably at least one of a nitrate, a chloride and a sulfate.

[0043] According to the present invention, the compatibility additive is selected from at least one of gum arabic, xanthan gum, natural rubber, casein, casein, casein and sodium alginate. Preferably, the compatibility additive is gum arabic and / or sodium alginate.

[0044] According to the present invention, the tracer can be prepared by the following method:

[0045] The tracer is prepared by mixing the rare earth element compound, the composite complexing agent and the compatible additive that satisfy the above-defined quantitative relationship with water until the precipitation completely disappears.

[0046] Application of the tracer according to the present invention in shale oil and gas exploration and development.

[0047] According to the present invention, preferably, the application includes: using the tracer described in the first aspect above to: determine the connectivity between the shale gas development well and the adjacent wells, calculate the fracturing fluid return rate of the tracer injection section, and determine the migration direction of the fracturing fluid in the formation and calculate the migration rate.

[0048] According to the present invention, in the application, by understanding the connectivity relationship between the development well and the adjacent production wells during the fracturing process, the effect of the fracturing construction can be effectively evaluated (generally, connectivity will lead to poor fracturing effect). Further, the rationality of the well spacing setting can be evaluated (for example, if it is determined to be connected, it is necessary to consider increasing the spacing setting of other wells in the area to avoid connectivity between other wells), which is beneficial to the optimization of the development plan.

[0049] According to the present invention, in the application, by calculating the flowback rate of a single fracturing stage, it is possible to judge the fracturing effect (it is generally believed that a fracturing stage with a high flowback rate has a poorer fracturing effect). In addition, the water production, estimated gas production and remaining recoverable volume of a single fracturing stage can be calculated by the flowback rate, and these parameters are helpful to more reasonably regulate the later shale gas production and development cycle.

[0050] According to the present invention, in the application, the migration direction of the fracturing fluid in the formation is determined and the migration rate is calculated, so that the migration of the fracturing fluid in the formation can be obtained, and key evidence is provided for the high flowback characteristics of nearby development wells during production (the characteristic that the flowback volume of the well is higher than the fracturing fluid volume during shale gas production), and whether the high flowback rate is caused by the migration of the fracturing fluid. In addition, it also has a certain indicative significance for correctly understanding the stress effect of the formation and the migration law of the formation fluid.

[0051] According to the present invention, in the application, the actual usage of the tracer is determined by detecting the concentration of rare earth elements in the initial flowback fluid of the formation and combining the concentration of rare earth elements in the initial flowback fluid of the formation and the amount of fracturing fluid in the shale gas development well.

[0052] Preferably, the concentration of rare earth elements in the initial flowback fluid from the formation is detected by an inductively coupled plasma mass spectrometer.

[0053] In the present invention, when the provided tracer contains the above-mentioned specific content of rare earth element compounds, composite complexing agents and compatible additives, and adopts a specific composite complexing agent composition and a specific type of compatible additives, the phenanthroline compound in the composite complexing agent and ethylenediaminetetraacetic acid can produce a synergistic effect, and the composite complexing agent and the compatible additive can also produce a synergistic effect; this dual synergistic effect enables the tracer to have the characteristics of low adsorption in the shale environment, good compatibility with water-based fracturing fluid, good high-temperature performance, and the ability to improve the sand carrying capacity of the fracturing fluid. Compared with the existing tracers, the tracer provided by the present invention has better adaptability to shale oil and gas reservoirs with low porosity, low permeability, high organic matter content, and high clay mineral content, and can continuously and effectively play a monitoring role, meeting the requirements of shale oil and gas exploration and development technology. Outside the above-mentioned limited range, the obtained tracer cannot have the comprehensive performance of the tracer provided by the present invention in terms of rare earth element retention rate, compatibility with fracturing fluid, high-temperature performance, and improving the sand carrying capacity of the fracturing fluid. The use of the tracer provided by the present invention in shale oil and gas exploration and development can more continuously and effectively monitor the connectivity between layers or horizontal sections in real time, quantitatively analyze the return rate of single-stage fracturing fluid, determine the migration direction of fracturing fluid in the formation and calculate the migration rate, and can be well used for qualitatively evaluating the implementation effect of horizontal well fracturing and optimizing the fracturing construction deployment in the target area.

[0054] The present invention will be described in detail below by way of examples. In the following examples and comparative examples, unless otherwise specified, all materials used are common commercially available products.

[0055] Complex complexing agent and tracer

[0056] Example 1

[0057] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.3;

[0058] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (praseodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S1);

[0059] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.03.

[0060] Comparative Example 1

[0061] The composite complexing agent provided in this comparative example is the same as that in Example 1;

[0062] The tracer provided in this comparative example is as follows: the method of Example 1 is followed, except that no compatibility additive is used. Other conditions are the same as those of Example 1. Specifically, a certain amount of complexing agent and rare earth element compound (praseodymium nitrate) are slowly added into water and stirred evenly until the precipitate completely disappears, thereby obtaining a uniform and transparent tracer solution (denoted as D1);

[0063] Among them, the weight ratio of rare earth element compound:composite complexing agent is 1:0.9.

[0064] Comparative Example 2

[0065] The tracer provided in this comparative example is as follows: the method of Example 1 is followed, except that no complexing agent is used. Other conditions are the same as those of Example 1. Specifically, a certain amount of a compatibility additive (gum arabic) and a rare earth element compound (praseodymium nitrate) are slowly added to water and stirred evenly, and the precipitate is not completely dissolved to obtain a tracer solution (denoted as D2);

[0066] Among them, the weight ratio of rare earth element compound:compatible additive is 1:0.03.

[0067] Comparative Example 3

[0068] The complexing agent provided in this comparative example is as follows: the ethylenediaminetetraacetic acid in the composite complexing agent provided in Example 1 is replaced with an equal weight of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline);

[0069] The tracer provided in this comparative example: the composite complexing agent in Example 1 is replaced by the complexing agent provided in this comparative example. Other conditions are the same as those in Example 1. A uniform and transparent tracer solution (denoted as D3) is obtained.

[0070] Comparative Example 4

[0071] The composite complexing agent provided in this comparative example is as follows: the ethylenediaminetetraacetic acid in the composite complexing agent provided in Example 1 is replaced with an equal weight of dipyridinecarboxylic acid;

[0072] The tracer provided in this comparative example: the composite complexing agent in Example 1 is replaced by the composite complexing agent provided in this comparative example. Other conditions are the same as those in Example 1. A uniform and transparent tracer solution (denoted as D4) is obtained.

[0073] Comparative Example 5

[0074] The complexing agent provided in this comparative example is: 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in the composite complexing agent provided in Example 1 is replaced with an equal weight of ethylenediaminetetraacetic acid;

[0075] The tracer provided in this comparative example: the composite complexing agent in Example 1 is replaced by the complexing agent provided in this comparative example. Other conditions are the same as those in Example 1. A uniform and transparent tracer solution (denoted as D5) is obtained.

[0076] Comparative Example 6

[0077] The composite complexing agent provided in this comparative example is the same as that in Example 1;

[0078] The tracer provided in this comparative example: the method of Example 1 is followed, except that the ratio of the complexing agent is changed, and the other conditions are the same as those of Example 1. Specifically, a certain amount of the complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatibility additive (gum arabic), and a rare earth element compound (praseodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears, to obtain a uniform and transparent tracer solution (denoted as D6);

[0079] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.1:0.03.

[0080] Comparative Example 7

[0081] The composite complexing agent provided in this comparative example is the same as that in Example 1;

[0082] The tracer provided in this comparative example: the method of Example 1 is followed, except that the ratio of the compatibility additive is changed. The other conditions are the same as those of Example 1. Specifically: weigh a certain amount of complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatibility additive (gum arabic), and a rare earth element compound (praseodymium nitrate), slowly add them into water and stir evenly until the precipitate completely disappears, to obtain a uniform and transparent tracer solution (denoted as D7);

[0083] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.005.

[0084] Comparative Example 8

[0085] The tracer provided in this comparative example is as follows: the method of Example 1 is followed, except that no complexing agent and compatibility additive are added. Other conditions are the same as those of Example 1. Specifically, a certain amount of rare earth element compound (praseodymium nitrate) is weighed and slowly added into water and stirred evenly until the precipitate completely disappears, thereby obtaining a uniform and transparent tracer solution (denoted as D8);

[0086] The concentration of the rare earth element (measured by weight of the rare earth element) in the tracer is equal to that in Example 1.

[0087] Comparative Example 9

[0088] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.6;

[0089] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (praseodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as D9);

[0090] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.03.

[0091] Comparative Example 10

[0092] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.001;

[0093] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (praseodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as D10);

[0094] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.03.

[0095] Example 2

[0096] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.2;

[0097] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (ytterbium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S2);

[0098] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:1:0.01.

[0099] Example 3

[0100] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 4,7-dichlorosulfonylbenzene-2,9-dicarboxylic acid-1,10-phenanthroline at a weight ratio of 1:0.3;

[0101] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 4,7-dichlorosulfonylbenzene-2,9-dicarboxylic acid-1,10-phenanthroline), a compatible additive (sodium alginate), and a rare earth element compound (samarium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S3);

[0102] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:1:0.05.

[0103] Example 4

[0104] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0105] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (yttrium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S4);

[0106] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.5:0.01.

[0107] Example 5

[0108] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0109] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (casein), and a rare earth element compound (lanthanum nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S5);

[0110] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.5:0.01.

[0111] Example 6

[0112] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0113] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (natural rubber), and a rare earth element compound (cerium nitrate) are slowly added into water and stirred evenly until the precipitate completely disappears, thereby obtaining a uniform and transparent tracer solution (denoted as S6);

[0114] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.5:0.01.

[0115] Example 7

[0116] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0117] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (sodium alginate), and a rare earth element compound (neodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears, thereby obtaining a uniform and transparent tracer solution (denoted as S7);

[0118] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.5:0.01.

[0119] Example 8

[0120] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0121] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (terbium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S8);

[0122] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.8:0.01.

[0123] Example 9

[0124] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0125] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (xanthan gum), and a rare earth element compound (erbium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S9);

[0126] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.8:0.01.

[0127] Example 10

[0128] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1;

[0129] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (casein), and a rare earth element compound (lutetium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S10);

[0130] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.8:0.01.

[0131] Embodiment 11

[0132] The composite complexing agent provided in this embodiment is as follows: 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in the composite complexing agent in Example 10 is replaced by 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline, and the rest are the same as the composite complexing agent in Example 10;

[0133] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline), a compatible additive (casein), and a rare earth element compound (lutetium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears, thereby obtaining a uniform and transparent tracer solution (denoted as S11);

[0134] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.8:0.01.

[0135] Example 12

[0136] The composite complexing agent provided in this embodiment is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline at a weight ratio of 1:0.01;

[0137] The tracer provided in this embodiment: the method of embodiment 11 is followed, except that the composite complexing agent is the composite complexing agent provided in this embodiment, and the other conditions are the same as those in embodiment 11. A uniform and transparent tracer solution (denoted as S12) is obtained;

[0138] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.8:0.01.

[0139] Embodiment 13

[0140] The composite complexing agent provided in this embodiment is the same as that in embodiment 1;

[0141] The tracer provided in this embodiment is as follows: the method of embodiment 1, except that gum arabic is replaced by an equal weight of casein. Other conditions are the same as those of embodiment 1. A uniform and transparent tracer solution (denoted as S13) is obtained;

[0142] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.03.

[0143] Embodiment 14

[0144] The composite complexing agent provided in this embodiment is the same as that in embodiment 1;

[0145] The tracer provided in this embodiment: a certain amount of a complex complexing agent (ethylenediaminetetraacetic acid, 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline)), a compatible additive (gum arabic), and a rare earth element compound (praseodymium nitrate) are weighed and slowly added into water and stirred evenly until the precipitate completely disappears to obtain a uniform and transparent tracer solution (denoted as S14);

[0146] Among them, the weight ratio of rare earth element compound:complex complexing agent:compatible additive is 1:0.9:0.1.

[0147] The technical effect of the tracer provided by the present invention in improving the retention rate of rare earth elements is described in detail below through Test Examples 1 and 2; it should be noted that the "contributed rare earth element retention rate" referred to in Test Examples 1 and 2 specifically refers to "the amount of rare earth element retention rate increased after adding phenanthroline compounds and / or ethylenediaminetetraacetic acid to the tracers S1, tracer D3, and tracer D5 provided in Example 1, Comparative Example 3, and Comparative Example 5, compared with the rare earth element retention rate of the tracer D2 provided in Comparative Example 2 in the fracturing fluid A" or "the amount of rare earth element retention rate increased after adding composite complexing agents and / or compatible additives to the tracers S1, tracer D1, and tracer D2 provided in Example 1, Comparative Example 1, and Comparative Example 2, compared with the rare earth element retention rate of the tracer D8 provided in Comparative Example 8 in the fracturing fluid A".

[0148] Test Example 1 - Element Retention Test of Tracer in Shale-Containing Fracturing Fluid

[0149] ⅰ Preparation of fracturing fluid A:

[0150] Fracturing fluid A is prepared according to the formula: "98% water + 1% potassium chloride + 0.5% dilute hydrochloric acid + 0.5% carboxymethyl cellulose", wherein the content of each component is based on the total weight of fracturing fluid A;

[0151] ⅱThe tracers S1-S14 and D1-D10 prepared in the above Examples 1 to 14 and Comparative Examples 1 to 10 were respectively added to the fracturing fluid A so that the concentration of rare earth elements (based on the weight of rare earth elements) in the fracturing fluid A was 1 mg / L, and then shale powder was added (the amount of shale powder added was 20% by weight of the fracturing fluid A, and the shale powder was black shale powder collected from the Longmaxi Formation in Qijiang area of ​​Sichuan Basin, with a particle size of 50-100 mesh). After stirring evenly for 24 hours, the element retention rate was tested using an inductively coupled plasma mass spectrometer at room temperature and pressure. The results are shown in Table 1.

[0152] Table 1. Element retention of tracers S1-S14, D1-D10

[0153] Test subjects Rare earth element retention rate / % Fracturing fluid A+shale powder+tracer S1 92.5 Fracturing fluid A+shale powder+tracer S2 91.7 Fracturing fluid A+shale powder+tracer S3 90.3 Fracturing fluid A+shale powder+tracer S4 79.6 Fracturing fluid A+shale powder+tracer S5 78.5 Fracturing fluid A+shale powder+tracer S6 76.4 Fracturing fluid A+shale powder+tracer S7 80.5 Fracturing fluid A+shale powder+tracer S8 73.8 Fracturing fluid A+shale powder+tracer S9 75.6 Fracturing fluid A+shale powder+tracer S10 71.8 Fracturing fluid A+shale powder+tracer S11 70.5 Fracturing fluid A+shale powder+tracer S12 71.7 Fracturing fluid A+shale powder+tracer S13 81.5 Fracturing fluid A+shale powder+tracer S14 78.3 Fracturing fluid A+shale powder+tracer D1 65.2 Fracturing fluid A+shale powder+tracer D2 47.2 Fracturing fluid A+shale powder+tracer D3 62.8 Fracturing fluid A+shale powder+tracer D4 59.3 Fracturing fluid A+shale powder+tracer D5 57.6 Fracturing fluid A+shale powder+tracer D6 51.1 Fracturing fluid A+shale powder+tracer D7 54.2 Fracturing fluid A+shale powder+tracer D8 42.6 Fracturing fluid A+shale powder+tracer D9 68.1 Fracturing fluid A+shale powder+tracer D10 58.3

[0154] As can be seen from Table 1, the tracers S1-S14 provided by the present invention have the advantage of low adsorption in a shale environment. Specifically, when used at room temperature in a fracturing fluid with a shale content of 20 wt%, the rare earth element retention rates are all higher than 70%, and can reach up to 92.5%, which are higher than those of the tracers D1-D10. Therefore, they are more suitable for shale formations. A higher rare earth element retention rate enables the tracer to perform a monitoring function more continuously and effectively.

[0155] Furthermore, by combining the formulas of tracers S1, D2, D3 and D5 and analyzing the retention rates of rare earth elements of the four, it can be seen that: compared with tracer D2, tracer D3 adds 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) as a single-component complexing agent, tracer D5 adds ethylenediaminetetraacetic acid as a single-component complexing agent, and tracer S1 adds 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) and ethylenediaminetetraacetic acid as a composite complexing agent. In terms of rare earth element retention rate, compared with tracer D2, the rare earth element retention rate contributed by the single-component complexing agent in D3 was 15.6%, the rare earth element retention rate contributed by the single-component complexing agent in tracer D5 was 10.4%, and the rare earth element retention rate contributed by the composite complexing agent in tracer S1 was 45.3%, which was higher than the sum of the rare earth retention rates contributed by the two single-component complexing agents in tracers D3 and D5. It can be seen that there is a synergistic effect between the phenanthroline compounds and ethylenediaminetetraacetic acid in the composite complexing agent, which can achieve a better complexing effect on rare earth elements and improve the retention rate of rare earth elements.

[0156] Furthermore, by combining the formulas of tracer S1 and tracers D1, D2 and D8, the rare earth element retention rates of the four tracers were analyzed, and it was found that: compared with tracer D8, tracer D1 added a composite chelating agent, tracer D2 added a compatible additive, and tracer S1 added a composite chelating agent of medium mass to tracer D1 and a compatible additive of medium mass to tracer D2, as shown in the following: compared with tracer D8, the rare earth element retention rate contributed by the composite chelating agent in tracer D1 was 22.6%, the rare earth element retention rate contributed by the compatible additive in tracer D2 was 4.6%, and the rare earth element retention rate of the composite chelating agent and the compatible additive used simultaneously in tracer S1 was 49.9%, which was higher than the sum of the rare earth element retention rates contributed by the composite chelating agent in tracer D1 and the compatible additive in tracer D2, proving that in the fracturing fluid A with shale powder added, there is an obvious synergistic effect between the composite chelating agent and the compatible additive.

[0157] Tracer D4 uses raw materials outside the scope of the present invention, and the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive in tracers D6, D7, D9 and D10 or the mass ratio of ethylenediaminetetraacetic acid and the phenanthroline compound in the composite complexing agent is outside the scope of the present invention, resulting in that at room temperature and pressure, the rare earth element retention rate of tracers D4, D6, D7, D9 and D10 in the fracturing fluid A added with shale powder is significantly lower than that of tracer S1, and the complexing and protection capabilities of the rare earth elements are poor.

[0158] Test Example 2 - Test on element retention rate of tracer in fracturing fluid at different temperatures

[0159] ⅰ Preparation of fracturing fluid A: same as test example 1;

[0160] ii. adding the tracers S1-S14 and D1-D10 prepared in the above Examples 1 to 14 and Comparative Examples 1 to 10 to the fracturing fluid A respectively, so that the concentration of the rare earth element (based on the weight of the rare earth element) in the fracturing fluid A is 1 mg / L;

[0161] ⅲ The temperature of the fracturing fluid with tracer added was controlled by a water bath device to maintain the temperature at 25°C, 60°C and 95°C respectively. After stirring evenly for 24 hours, the element retention rate was tested by inductively coupled plasma mass spectrometry. The results are shown in Table 2.

[0162] Table 2. Element retention rates of tracers S1-S14, D1-D10 at different temperatures

[0163]

[0164] As can be seen from Table 2, with the increase of temperature, the retention rate of rare earth elements of each tracer in the fracturing fluid decreases to varying degrees. At 25°C, 60°C and 95°C, the retention rates of rare earth elements of the tracers S1-S14 provided by the present invention are all higher than those of the tracers D1-D10. Among them, at 95°C, the retention rates of rare earth elements of the tracers S1-S14 provided by the present invention are still higher than 65%, and can reach up to 92.8%, showing good use effect and thermal stability at high temperature. Comparing the effects of S1 with those of S13 and S14, it can be seen that the material selection and proportion of the compatible additives have a significant effect on the use effect and thermal stability of the tracer at high temperature.

[0165] The following is an analysis of the synergistic effect between phenanthroline compounds and ethylenediaminetetraacetic acid in the composite complexing agent at different temperatures and the synergistic effect between the composite complexing agent and the compatible additives, based on the formulas of tracer S1, tracer D1, D2, D3, D5, and D8 and the rare earth retention rate data in Table 2.

[0166] On the one hand, compared with tracer D2, tracer D3 with the addition of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) as a single-component complexing agent, tracer D5 with the addition of ethylenediaminetetraacetic acid as a single-component complexing agent, and tracer S1 with the addition of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) and ethylenediaminetetraacetic acid as a composite complexing agent showed similar results to tracer D2 at 25 °C without the addition of shale powder. Compared with the single-component complexing agent in D3, the rare earth element retention rate contributed by the single-component complexing agent in tracer D5 was 15.6%, the rare earth element retention rate contributed by the composite complexing agent in tracer S1 was 11.3%, and the rare earth element retention rate contributed by the composite complexing agent was 47.6%. The rare earth element retention rate contributed by the composite complexing agent was 20.7% higher than the sum of the rare earth element retention rates contributed by the two single-component complexing agents. Under the condition of 60℃ and without adding shale powder, compared with tracer D2, the rare earth element retention rates contributed by the single-component complexing agent in D3 and the tracer S1 were 16.7%, 11.3%, and 47.6%. The rare earth element retention rate contributed by the single-component complexing agent in tracer D5 was 11.6%, and the rare earth element retention rate contributed by the composite complexing agent in tracer S1 was 48.9%. The rare earth element retention rate contributed by the composite complexing agent was 20.6% higher than the sum of the rare earth element retention rates contributed by the two single-component complexing agents. Under the condition of 95℃ and without adding shale powder, compared with tracer D2, the rare earth element retention rate contributed by the single-component complexing agent in D3 was 17.1%, the rare earth element retention rate contributed by the single-component complexing agent in tracer D5 was 13.2%, and the rare earth element retention rate contributed by the composite complexing agent was 48.9%. The rare earth retention rate contributed by the composite complexing agent in agent S1 is 52.6%, and the rare earth element retention rate contributed by the composite complexing agent is 22.3% higher than the sum of the rare earth element retention rates contributed by the two single-component complexing agents. It can be seen that there is a synergistic effect between the phenanthroline compounds and ethylenediaminetetraacetic acid in the composite complexing agent, and this synergistic effect of the two has good high-temperature stability, is less affected by temperature, and will not weaken with the increase of temperature. Better complexing effect can be achieved for rare earth elements at room temperature to 95°C, so that the rare earth element retention rate is maintained at a high level.

[0167] On the other hand, compared with tracer D8, tracer D1 added a complex complexing agent, tracer D2 added a compatible additive, and tracer S1 added a complex complexing agent of medium mass with tracer D1 and a compatible additive of medium mass with tracer D2. At 25°C and without adding shale powder, compared with tracer D8, the rare earth element retention rate contributed by the complex complexing agent in tracer D1 was 19.3%, and the rare earth element retention rate contributed by the compatible additive in tracer D2 was 2.3%. -0.4%, the rare earth element retention rate contributed by the composite complexing agent and the compatibility additive used in tracer S1 was 47.2%, and the rare earth element retention rate contributed by the composite complexing agent and the compatibility additive in tracer S1 was increased by 28.3% compared with the sum of the rare earth element retention rates contributed by the single composite complexing agent and the single compatibility additive; at 60℃ and without adding shale powder, the rare earth element retention rate contributed by the composite complexing agent in tracer D1 was 10 .6%, the retention rate of rare earth elements contributed by the compatible additives in tracer D2 was 1.5%, the retention rate of rare earth elements contributed by the composite complexing agent and the compatible additives used simultaneously in tracer S1 was 50.4%, and the retention rate of rare earth elements contributed by the composite complexing agent and the compatible additives in tracer S1 increased by 38.3% compared with the sum of the retention rates of rare earth elements contributed by the single composite complexing agent and the single compatible additive; under the condition of 95℃ and without adding shale powder, compared with tracer D8, the retention rate of rare earth elements contributed by the composite complexing agent in tracer D1 was 5.2%, the retention rate of rare earth elements contributed by the compatible additives in tracer D2 was 2.9%, and the retention rate of rare earth elements contributed by the composite complexing agent and the compatible additives used simultaneously in tracer S1 was 55.5%, and the retention rate of rare earth elements contributed by the composite complexing agent and the compatible additives in tracer S1 increased by 47.4% compared with the sum of the retention rates of rare earth elements contributed by the single composite complexing agent and the single compatible additive. From the above analysis, it can be seen that there is a synergistic effect between the composite complexing agent and the compatible additive, and it has good high-temperature stability. This synergistic effect between the two will increase with the increase of temperature.

[0168] In addition, tracer D4 uses raw materials outside the scope of the present invention, and the mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive in tracers D6, D7, D9 and D10 or the mass ratio of ethylenediaminetetraacetic acid and the phenanthroline compound in the composite complexing agent is outside the scope of the present invention, resulting in that at a temperature of 25 to 95°C, the rare earth element retention rate of tracers D4, D6, D7, D9 and D10 in fracturing fluid A is significantly lower than that of tracer S1, the high temperature stability is poor, and the complexing and protection ability for rare earth elements is poor.

[0169] The following describes in detail the technical effects of the tracer provided by the present invention on maintaining the viscosity of the fracturing fluid A and improving the sand carrying performance through test examples 3 and 4.

[0170] Test Example 3 - Test on the effect of tracer on the viscosity of fracturing fluid

[0171] ⅰ Preparation of fracturing fluid A: same as test example 1;

[0172] ii. adding the tracers S1-S14 and D1-D10 prepared in the above Examples 1 to 14 and Comparative Examples 1 to 10 to the fracturing fluid A respectively, so that the concentration of the rare earth element (based on the weight of the rare earth element) in the fracturing fluid A is 1 mg / L;

[0173] ⅲ Under normal temperature and pressure conditions, the viscosity of the fracturing fluid with added tracer was tested using a viscosity meter at a shear rate of 75 r / min. The results are shown in Table 3.

[0174] Table 3. Viscosity of fracturing fluid A and fracturing fluid A with added tracer

[0175]

[0176]

[0177] As can be seen from Table 3, compared with the fracturing fluid A without adding tracers, the viscosity maintenance rate of the fracturing fluid A after adding tracers S1-S14 is above 83%, and the viscosity is even occasionally increased. It can be seen that the tracers S1-S14 provided by the present invention have a very limited effect on the viscosity reduction of the water-based fracturing fluid and are well compatible with the water-based fracturing fluid.

[0178] Test Example 4 - Test on the effect of tracer on the sand carrying performance of fracturing fluid

[0179] ⅰ Preparation of fracturing fluid A: same as test example 1;

[0180] ii. The tracers S1-S14 and D1-D10 prepared in the above Examples 1 to 14 and Comparative Examples 1 to 10 were respectively added to the fracturing fluid A, so that the concentration of the rare earth element (based on the weight of the rare earth element) in the fracturing fluid A was 1 mg / L, and then the proppant (specifically quartz sand particles with a particle size of 50 mesh) was added and stirred evenly, so that the content of the proppant in the fracturing fluid A was 0.5 g / mL;

[0181] ⅲ Test the sedimentation rate of the proppant particles under normal temperature and pressure conditions. Specifically, record the time it takes for most of the proppant particles in Test Example ⅱ to settle to the bottom of the fracturing fluid A with added tracer. Combined with the liquid level height of the fracturing fluid A with added tracer, calculate the sedimentation rate of the proppant particles in the fracturing fluid A. The lower the sedimentation rate of the proppant particles, the better the sand carrying performance of the fracturing fluid. The results are shown in Table 4.

[0182] Table 4. Settling rate of proppant in fracturing fluid A with added tracer

[0183] Test subjects <![CDATA[Proppant settlement rate / cm·s -1 > Fracturing Fluid A 2.5 Fracturing fluid A+tracer S1 1.4 Fracturing fluid A+tracer S2 1.6 Fracturing fluid A+tracer S3 1.2 Fracturing fluid A+tracer S4 1.6 Fracturing fluid A+tracer S5 1.7 Fracturing fluid A+tracer S6 1.8 Fracturing fluid A+tracer S7 1.6 Fracturing fluid A+tracer S8 1.6 Fracturing fluid A+ tracer S9 1.8 Fracturing fluid A+ tracer S10 1.7 Fracturing fluid A+tracer S11 1.6 Fracturing fluid A+tracer S12 1.6 Fracturing fluid A+tracer S13 1.8 Fracturing fluid A+tracer S14 1.5 Fracturing fluid A+tracer D1 3.5 Fracturing fluid A+tracer D2 1.6 Fracturing fluid A+tracer D3 1.7 Fracturing fluid A+tracer D4 1.6 Fracturing fluid A+tracer D5 1.6 Fracturing fluid A+tracer D6 1.6 Fracturing fluid A+tracer D7 2.3 Fracturing fluid A+tracer D8 3.6 Fracturing fluid A+tracer D9 2.0 Fracturing fluid A + tracer D10 1.5

[0184] As can be seen from Table 4, compared with the sedimentation rate of the proppant in the simple fracturing fluid A, the addition of the tracers S1-S14 provided by the present invention reduces the sedimentation rate of the proppant by 28% to 52%, which has a significant effect on improving the sand carrying capacity of the water-based drilling fluid. In addition, by comparing the effects of tracer S1 with tracers S13 and S14, it can be seen that the material selection and proportion of the compatible additives in the tracer have an impact on the sand carrying capacity of the fracturing fluid.

[0185] Based on the results of the above test examples, in the tracer provided by the present invention, there is synergistic enhancement between the phenanthroline compound and ethylenediaminetetraacetic acid in the composite complexing agent, and there is also synergistic enhancement between the composite complexing agent and the compatible additive. This double synergistic enhancement makes the tracer provided by the present invention have the comprehensive performance advantages of low adsorption in the shale environment, good high temperature performance, good compatibility with water-based fracturing fluid, and improved sand carrying capacity of the fracturing fluid. It can continuously and effectively play a monitoring role in the shale layer with the characteristics of "dense formation characteristics of low porosity and low permeability and complexity and particularity of fracturing fluid components", meeting the current needs of shale oil and gas exploration and development technology. Tracers outside the scope of the present invention cannot have the comprehensive performance of the tracer provided by the present invention in terms of rare earth element retention rate, compatibility with fracturing fluid, high temperature performance, and improved sand carrying capacity of fracturing fluid, and cannot meet the current needs of shale oil and gas exploration and development technology.

[0186] In order to further illustrate the practical application effect of the tracer provided by the present invention in shale oil and gas exploration and development, a field application example of the tracer is provided here for the purpose of determining the connectivity relationship between shale oil and gas development wells and adjacent wells and calculating the fracturing fluid return rate of the tracer injection section.

[0187] Embodiment 15

[0188] The 10-1HF well in a shale gas field was used as the tracer injection well, and the 10HF well was used as the monitoring well. The horizontal sections of the two wells were arranged in parallel with a spacing of about 300 meters (see Figure 1). By comprehensively analyzing the well leakage position, the well section with developed bedding fractures interpreted by dipole acoustic logging, and the well section with abnormal development predicted by seismic curvature, the fracturing sections (sections 14, 19, 21, and 22) with poor cementing quality and corresponding to the fracture development area in the formation were selected as the tracer injection sections in the whole well fracturing sections. Then, the concentration of rare earth elements in the initial flowback fluid of well 10HF was detected by inductively coupled plasma mass spectrometry. The actual usage of rare earth element compounds, composite complexing agents, and compatible additives were calculated based on the concentration of rare earth elements in the initial flowback fluid of the formation and the amount of fracturing fluid in shale gas development wells, as shown in Table 5. Among them, the composite complexing agent is obtained by mixing ethylenediaminetetraacetic acid and 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline) in a weight ratio of 1:0.1, and the compatible additive is gum arabic.

[0189] Table 5. Practical application of tracers in a shale gas field

[0190]

[0191]

[0192] The tracer was prepared into an aqueous solution before fracturing the shale gas development well. The prepared tracer was uniformly pumped in during the pre-fracturing stage of the 10-1HF well, with a pumping rate of 20L / min. After the tracer was placed, the return fluid was collected as soon as the 10-1HF well and the 10HF well were opened, and the concentration of rare earth elements was continuously monitored using an inductively coupled plasma mass spectrometer. The specific detection results are as follows:

[0193] (1) The concentration of rare earth elements in the return fluid of the 10-1HF well was monitored for 55 days. Figure 2 As shown, the concentrations of the four rare earth elements Ce, La, Yb, and Sm in the original formation were 0.45ng / g, 0.25ng / g, 0.02ng / g, and 0.05ng / g, respectively. The concentrations of the four rare earth elements increased significantly when the well was just opened, and slowly decreased during the monitoring process. Finally, the concentrations of the four rare earth elements in the return fluid were 0.10ng / g, 0.32ng / g, 0.41ng / g, and 0.06ng / g, respectively. Since the instrument monitoring accuracy is about 0.01-0.1ng / g, it is believed that the return fluid is basically consistent with the initial formation fluid element concentration, which indicates that the tracer fluid in the horizontal section of the 10-1HF well is basically completely discharged.

[0194] (2) The concentration of rare earth elements in the return fluid of the 10HF well was monitored for 67 days. Figure 3As shown in the figure, the concentrations of Ce, La, Yb and Sm in the original formation were 0.27ng / g, 2.16ng / g, 0.12ng / g and 0.91ng / g respectively. When the well was just opened, the concentration of Yb element increased significantly, and then decreased steadily and slowly, while the concentrations of the other three elements remained basically unchanged. Finally, the concentrations of the four rare earth elements in the return fluid were 0.06ng / g, 0.44ng / g, 10.31ng / g and 0.14ng / g respectively, which indicated that the horizontal section of the 10-1HF well was continuously connected with the 10HF well at the 21st section.

[0195] The above field application examples show that the tracer provided by the present invention has good applicability and effectiveness in the actual field application process of shale oil and gas exploration and development.

[0196] Although the present invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art that various changes may be made without departing from the true spirit and scope of the present invention. In addition, the subject matter, spirit and scope of the present invention may be varied to accommodate specific situations, materials, material combinations and methods. All of these changes are included within the scope of the claims of the present invention.

Claims

1. A tracer comprising a rare earth element compound, a complexing agent and a compatible additive, wherein: The composite complexing agent comprises a phenanthroline compound and ethylenediaminetetraacetic acid.

2. The tracer according to claim 1, characterized in that The mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.5-1):(0.01-0.1); and / or The mass ratio of the ethylenediaminetetraacetic acid to the phenanthroline compound is 1:(0.01-0.5).

3. The tracer according to claim 2, characterized in that The mass ratio of the rare earth element compound, the composite complexing agent and the compatible additive is 1:(0.8-1):(0.01-0.05).

4. The tracer according to any one of claims 1 to 3, characterized in that The phenanthroline compound has a structure as shown in Formula I: Wherein, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, halogen, CN, NO2, C1-C8 alkyl, halogenated C1-C8 alkyl, C1-C8 alkoxy, halogenated C1-C8 alkoxy, C1-C8 alkylthio, halogenated C1-C8 alkylthio, C1-C8 alkylsulfinyl, halogenated C1-C8 alkylsulfinyl, C1-C8 alkylsulfonyl, halogenated C1-C8 alkylsulfonyl, aryl, halogenated sulfoaryl, carboxyl, C1-C8 alkylcarboxyl, halogenated C1-C8 alkylcarboxyl, C1-C8 alkyl substituted C1-C8 alkylcarboxyl substituted amino.

5. The tracer according to claim 4, characterized in that In Formula I, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, phenyl, chlorosulfonylphenyl, carboxyl and -CH2N(CH2COOH)2.

6. The tracer according to claim 5, characterized in that The phenanthroline compound is selected from at least one of 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-4,7-(phenyl)-1,10-(phenanthroline), 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline and 4,7-dichlorosulfonylbenzene-2,9-dicarboxylic acid-1,10-phenanthroline.

7. The tracer according to claim 6, characterized in that The rare earth element in the rare earth element compound is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

8. The tracer according to claim 7, characterized in that The rare earth element compound is a soluble salt of the rare earth element, preferably at least one of a nitrate, a chloride and a sulfate.

9. The tracer according to any one of claims 1 to 8, characterized in that The compatibility additive is selected from at least one of gum arabic, xanthan gum, natural rubber, casein, casein, casein and sodium alginate.

10. Use of the tracer according to any one of claims 1 to 9 in shale oil and gas exploration and development.

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