CN112304998A - Shale pore structure fluid flow channel tracer, preparation method and tracing method - Google Patents
Shale pore structure fluid flow channel tracer, preparation method and tracing method Download PDFInfo
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Abstract
The invention relates to a tracer agent, a preparation method and a tracing method for a fluid flow channel with a shale pore structure, relating to the technical field of shale gas development; wherein the tracer comprises gold nanoparticles or ferroferric oxide nanoparticles and composite nanoparticles containing any one of the components; the tracing method comprises the steps of introducing a nano tracer with a proper concentration into a shale fluid spontaneous imbibition experiment or utilizing an external magnetic field to absorb a fluid containing a magnetic nano tracer into a shale micro-nano pore structure, drying the fluid and then carrying out electron microscope scanning on a shale sample, and revealing a flow channel of the fluid in the shale micro-nano pore structure by utilizing position information of the nano tracer. The invention discloses a shale micro-nano pore structure fluid channel tracer and a tracing method, which solve the problem that the existing tracer and tracing method can not intuitively obtain the migration information of fluid in shale micro-nano pores, and have higher resolution compared with the traditional CT and micro optical microscopic imaging.
Description
The invention relates to the technical field of shale gas development, in particular to a tracer agent for a fluid flow channel with a shale pore structure, a preparation method and a tracing method.
Background
At present, hydraulic fracturing is a core technology for shale gas development. The research on the flow characteristics of water in the pore structure of the shale has very important research significance for revealing the fluid transportation and water erosion characteristics of the shale in the hydraulic fracturing process. A number of water spontaneous dialysis experimental studies have been used to characterize the flow characteristics of water in the pore structure of shale. Although the methods can qualitatively analyze the flow characteristics of water by utilizing the fluid self-absorption rate in the spontaneous imbibition process and further judge the connectivity characteristics of micro-nano pores of the shale, the micro migration path of the water cannot be obtained. Hukinhong et al (2018) use polar (e.g. brine) and non-polar (e.g. n-decane) tracers for self-priming and diffusion experiments in rock capillary, and trace element imaging by laser ablation-inductively coupled-plasma mass spectrometry (LA-ICP-MS) gives an approximate profile of the water flow path. However, due to the development of a large number of micro-nano pore structures in the shale gas reservoir, the resolution of the imaging method and the commonly used microscopic characterization methods such as CT and optical microscopy cannot meet the experimental observation and characterization of the shale micro-nano pore structures, especially the water flow channels in a large number of nano pore structures. Although the pore types can be intuitively identified under a high-resolution scanning electron microscope, the high-resolution observation under the scanning electron microscope is limited by the requirement of high vacuum degree, and the fluid cannot be imaged.
Disclosure of Invention
In order to solve the technical problems, the invention provides a tracer agent for a fluid flow channel in micro-nano pores of shale, introduces metal elements which are easy to identify under a scanning electron microscope, and solves the problem of intuitively judging the hydrophilic pores of the shale in the prior art.
The invention also provides a preparation method for preparing the tracer for the fluid flow channel in the shale micro-nano pores.
The invention also provides a tracing method of the fluid flow channel with the shale pore structure, which traces the flow channel of the fluid entering the shale sample by adopting a tracer agent which can be easily identified under a scanning electron microscope and can realize spontaneous imbibition with the shale pores, thereby solving the technical problem that the migration information of the fluid in the shale micro-nano pores is difficult to directly obtain in the prior art.
The technical scheme for solving the technical problems in the embodiment of the application is as follows: the tracer for the shale pore structure fluid channel comprises at least one of gold nanoparticles or gold/ferroferric oxide composite nanoparticles.
In the tracer, the gold nanoparticles are used for self-priming injection of fluid into shale pores; the gold/ferroferric oxide composite nanoparticles are used for magnetically attracting and injecting fluid into shale pores; in the gold/ferroferric oxide composite nano tracer, the average particle size of the ferroferric oxide nano particles is smaller than that of the gold nano particles, so that the ferroferric oxide nano particles are uniformly distributed around the gold nano particles to form the composite nano tracer with the dual attributes of magnetism and precious metal materials.
In the tracer, gold is a precious metal and is very rare in minerals contained in shale. Therefore, when shale containing the tracer is subjected to scanning electron microscope imaging, the position and the content of gold obtained by scanning electron microscope energy spectrum analysis can represent the position and the content of the tracer so as to be distinguished from other minerals of the shale. Meanwhile, gold has a high atomic number and extremely high brightness under a scanning electron microscope, and the matrix and pores in the shale are dark under the scanning electron microscope, so that the position of the tracer can be easily identified under the scanning electron microscope.
Further, the particle size D50 of the gold nanoparticles is 10-15 nm; the particle size D50 of the gold/ferroferric oxide composite nano particles is 20-40 nm. The gold nanoparticles and the ferroferric oxide nanoparticles are both spherical nanoparticles or quasi-spherical nanoparticles.
Further, the gold nanoparticles and the gold/ferroferric oxide composite nanoparticles are modified by a polymer, wherein the polymer is any one of polyethylene glycol, polyvinylpyrrolidone, polymethacrylate, polystyrene and polydopamine.
The application also discloses a preparation method of the gold nanoparticle tracer, which specifically comprises the following steps:
s1) 0.4g of polyvinylpyrrolidone was uniformly dispersed in ultrapure water.
S2) adding an aqueous solution of chloroauric acid and a reducing agent into the dispersion liquid of the step S1).
The concentration of the chloroauric acid solution is 2.44 multiplied by 10-3mol/L～5.0×10-3mol/L; the reducing agent is preferably trisodium citrate, or hydroxylamine hydrochloride or trisodium citrate and hydroxylamine hydrochloride.
S3) heating the reaction solution obtained in the step S2) to 75 ℃, and stirring for 30-60 min to complete the reaction.
S4) cooling the system after the reaction is completed to room temperature, dispersing the system in ultra-pure water added with polyethylene glycol, and stirring for 1-2 h to obtain gold nanoparticles.
The invention also discloses a preparation method of the gold/ferroferric oxide composite nanoparticle tracer, which comprises the following steps:
A1) preparing ferroferric oxide nano particles;
A2) uniformly dispersing the ferroferric oxide nanoparticles prepared in the step A1), adding aqueous solution of chloroauric acid and a reducing agent, and reacting to generate a sol system of gold nanoparticles and ferroferric oxide nanoparticles;
A3) and D) carrying out suction filtration and washing on the sol system prepared in the step A2) to obtain a product.
In the technical scheme, the ferroferric oxide nano-particles are reduced into the ferroferric oxide nano-particles by a reducing agent in an oxygen removal solvent by using a trivalent ferric salt and a divalent ferrous salt; then adding the ferroferric oxide nano particles into a system of water-soluble gold chemicals, and uniformly distributing the ferroferric oxide nano particles around the gold nano particles in the process of reducing gold ions into the gold nano particles, so that the reduced gold nano particles are not easy to agglomerate, and the uniformly distributed ferroferric oxide nano particles and the gold nano particles are formed.
Preferably, after the reaction of the sol system is completed, suction filtration is carried out, and precipitates after suction filtration are alternately cleaned by ultrapure water and ethanol for at least 3 times.
Further, in the step a1), the raw materials for preparing the ferroferric oxide nanoparticles include water-soluble ferric salt or water-soluble ferric salt hydrate, water-soluble ferrous salt or water-soluble ferrous salt hydrate, and a reducing agent; the molar mass ratio of the iron element in the water-soluble ferric salt or the water-soluble ferric salt hydrate to the iron element in the water-soluble ferrous salt or the water-soluble ferrous salt hydrate is 2: 1.
The water-soluble ferric salt or the water-soluble ferric salt hydrate is preferably ferric chloride or ferric sulfate and ferric chloride hexahydrate or ferric sulfate hexahydrate; the water-soluble ferrous salt or the water-soluble ferrous salt hydrate is ferrous chloride or ferrous sulfate and ferrous chloride tetrahydrate or ferrous sulfate tetrahydrate; the reducing agent is preferably trisodium citrate. Wherein the reducing agent is selected from hydrazine hydrate, chitosan, polyvinylpyrrolidone (PVP), polyethylene terephthalate (PET), stearic acid, gum arabic, hydroxypropylmethylcellulose, sodium alginate, cetyltrimethylammonium bromide (CTAB), Sodium Dodecylsulfate (SDS), Sodium Dodecylbenzenesulfonate (SDBS), polyvinyl alcohol (PVA), long chain fatty acid, starch and dodecanethiol.
Further, the step a1) specifically includes the following steps:
A11) weighing water-soluble ferric salt or water-soluble ferric salt hydrate and water-soluble ferrous salt or water-soluble ferrous salt hydrate according to the molar mass ratio of the iron element of 2:1, and dissolving into a mixed solution by using deoxidized ultrapure water;
A12) heating the mixed solution at 70-100 ℃ in a water bath, and introducing nitrogen into the solution to remove oxygen;
A13) slowly dropwise adding an alkali solution into the mixed solution under the stirring condition, and adjusting the pH value of the reaction system to 9-10; after the dropwise addition of the alkali solution is finished, adding a reducing agent solution into the mixed system under the stirring condition, and stirring for reacting for 20-60 min to complete the reaction;
A14) and cooling the system after the reaction is completed to room temperature, separating particles in the system by using a magnet, and cleaning for at least 3 times by using deoxidized ultrapure water to obtain the ferroferric oxide nano particles.
The alkali solution is preferably an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution or aqueous ammonia.
The reducing agent may be trisodium citrate or hydroxylamine hydrochloride or trisodium citrate and hydroxylamine hydrochloride.
Further, in step a2), the reducing agent includes trisodium citrate and hydroxylamine hydrochloride; the molar mass ratio of trisodium citrate to hydroxylamine hydrochloride for reducing the chloroauric acid into the gold simple substance is 1: 4.5-5.5.
Further, the step a2) specifically includes the following steps:
A21) adding the ferroferric oxide nanoparticles prepared in the step A1) into deoxygenated ultrapure water, and performing ultrasonic dispersion to obtain uniformly dispersed ferroferric oxide nanoparticle dispersion liquid;
A22) respectively adding chloroauric acid aqueous solution and trisodium citrate aqueous solution with the same volume into ferroferric oxide nanoparticle dispersion liquid, and carrying out ultrasonic dispersion reaction; the molar concentration of the chloroauric acid aqueous solution is the same as that of the trisodium citrate aqueous solution;
A23) and (3) carrying out constant-temperature water bath on the system subjected to the ultrasonic treatment at 55-70 ℃, quickly adding hydroxylamine hydrochloride under the stirring condition, and continuously stirring for 20-60 min to finish the reaction.
In the step A2), trisodium citrate is added for a preliminary reduction reaction, the particle size of the generated gold nanoparticles is controlled, and hydroxylamine hydrochloride with strong reducibility is added for reducing gold ions, so that the obtained gold nanoparticles have narrow particle size distribution and meet the particle size ratio of the gold nanoparticles to ferroferric oxide nanoparticles.
The application also discloses a tracing method of the shale pore structure fluid channel, wherein the tracer disclosed or prepared in the application document is retained on the surface of the shale pore when fluid enters the shale pore, so that the marking of the shale pore structure fluid channel is realized; and identifying the fluid channel in the shale pore by an electronic scanning electron microscope.
The fluid may be water or other aqueous solution with water as a carrier.
Further, the tracing method specifically comprises the following steps:
step 1, grinding, polishing and cleaning stratum shale to be detected to form a shale sample, and drying the shale sample for later use;
and 3, intercepting a fresh section of the shale sample, cleaning the surface, and then performing imaging analysis by using a scanning electron microscope to obtain the distribution characteristics of the tracer in the pore microstructure in the shale sample for tracing and representing the fluid flow channel.
In the technical scheme, the tracer enters the pores of the shale sample along with the fluid and is adsorbed on the surfaces of the pores in the shale sample along with the flow of the fluid, and then electron scanning electron microscope scanning is carried out to obtain the distribution diagram of the tracer in the shale sample, so that the pore structure in the shale sample can be obtained. Due to the fact that the performance of the adsorption retention tracer in the clay mineral and the performance of the adsorption retention tracer in the organic matter are different, the organic matter and the clay mineral in a pore structure in the shale sample can be distinguished through the adsorption retention tracer in the obtained scanning electron microscope image, and a reference material is provided for distribution analysis of the organic matter and the clay mineral in the shale sample.
Further, the shale sample is cubic in shape; and the shale sample is polished by adopting an argon ion polisher. And bombarding the surface of the shale sample by using an argon ion beam to obtain the shale sample with higher surface flatness, and more favorably observing the size, the shape and the distribution of the nano-aperture in the shale sample under the imaging of back scattering electrons. After the shale sample is imbibed, the tracer on the surface of the shale sample needs to be cleaned, so that the condition that the tracer adsorbed on the surface of the shale sample influences the observation of a scanning electron microscope on the tracer in the pores in the shale sample is avoided.
Further, analyzing the element composition of the fluid channel by utilizing X-ray energy spectrum analysis to obtain the matrix composition and the type of the pores in the shale sample.
The invention has the beneficial effects that: the application discloses a tracer for fluid channel in micro-nano hole of shale adopts the gold nanoparticle that has high resolution under electron microscope as the tracer, has obvious difference with the adsorption efficiency of clay mineral and organic matter, makes it also can be used to refer to the inside clay mineral of sign shale and organic matter and distributes.
The tracer for the fluid channel in the shale micro-nano pore adopts a mixture formed by magnetic ferroferric oxide nanoparticles and precious metal gold nanoparticles, so that the tracer has the dual attributes of a magnetic material and a precious metal material, the pore structure inside a shale sample can be clearly shown under a scanning electron microscope, and the migration information of fluid in the shale micro-nano pore can be visually obtained; meanwhile, the gold nanoparticles have higher resolution ratio under a scanning electron microscope and are obviously different from the adsorption capacity of clay minerals and organic matters, so that the gold nanoparticles can also be used for reference identification of the clay mineral and organic matter distribution in the shale.
The preparation method of the gold nanoparticle tracer agent disclosed by the application is simple in steps, narrow in particle size distribution of the gold nanoparticles and obvious in tracing. ,
according to the preparation method of the tracer, the ferroferric oxide nano particles are prepared firstly, and the dispersed ferroferric oxide nano particles are added into a system for preparing gold nano particles, so that a tracer product is directly obtained, and the defects that the gold nano particles are not completely dispersed and the particle size distribution is increased due to the fact that the ferroferric oxide nano particles and the gold nano particles are prepared separately and then are dispersed and mixed are overcome; meanwhile, trisodium citrate with weak reducibility is added in the preparation process of the gold nanoparticles to control the particle size of the gold nanoparticles, and hydroxylamine hydrochloride with strong reducibility is added to reduce the gold nanoparticles to obtain the gold nanoparticles with narrow particle size distribution, so that the gold nanoparticles in the obtained tracer are uniformly distributed and have narrow particle size distribution range.
According to the tracing method disclosed by the application, obvious tracer agent is identified under a scanning electron microscope and is absorbed into a shale sample along with fluid seepage, so that the migration information of the fluid in the micro-nano pores of the shale is visually obtained; meanwhile, the tracer has high resolution, and can qualitatively analyze the influence of the shale micro-pore structure on the fluid migration path.
Drawings
FIG. 1 is a TEM image of a gold nanopaclor as disclosed in the present invention;
FIG. 2 is a TEM image of the gold/ferroferric oxide composite nano tracer disclosed by the invention;
FIG. 3 is a hysteresis loop of the gold/ferroferric oxide composite nano tracer disclosed by the invention;
FIG. 4 is an SEM image of a disclosed tracer after adsorption on organic matter;
FIG. 5 is an SEM image of a tracer disclosed in the present invention after adsorption on clay;
FIG. 6 is an SEM image of a disclosed tracer after adsorption on different types of pores, wherein FIG. 6(A) is pyrite; FIG. 6(B) shows the interparticle pores; FIG. 6(C) is a crack;
FIG. 7 is an SEM image of gold/ferroferric oxide composite nano tracer flowing through the pores of shale disclosed by the invention;
FIG. 8 is a photograph of a spectral surface scan of a gold/ferroferric oxide composite nano tracer disclosed by the present invention flowing through the pores of shale;
Detailed Description
The principles and features of the present application are described below in conjunction with the following examples, which are set forth merely to illustrate the present invention and are not intended to limit the scope of the present application.
The method for analyzing the connectivity of the micro-nano pores is a key point and a difficult point in the research of the shale micro-nano pore structure. Although the spontaneous imbibition method can simply and conveniently obtain a part of qualitative information of conventional pore connectivity, the method is immature in theory and experimental research applied to research on the pore connectivity of the shale micro-nano pores. The existing tracer fluid self-imbibition method mainly detects the information of the tracer by a laser ablation-inductively coupled plasma-mass spectrometer method (LA-ICP-MS) to determine the distribution and migration characteristics of the tracer in pores; the method has low resolution and cannot acquire the migration condition of the fluid in the micro-nano pores.
Based on the technical problems, the inventor discloses a tracer for a shale pore structure fluid channel, which comprises at least one of gold nanoparticles or gold/ferroferric oxide composite nanoparticles; the mass ratio of the gold nanoparticles to the ferroferric oxide nanoparticles in the gold/ferroferric oxide composite nanoparticles is 0.1-0.25: 1.
In some embodiments, the gold nanoparticles have a particle size D50 of 10-15 nm; the particle size D50 of the gold/ferroferric oxide composite nano particles is 20-40 nm. The gold nanoparticles and the ferroferric oxide nanoparticles are both spherical nanoparticles or quasi-spherical nanoparticles.
The preparation method of the gold nanoparticle tracer specifically comprises the following steps:
s1) 0.4g of polyvinylpyrrolidone was uniformly dispersed in ultrapure water.
S2) adding an aqueous solution of chloroauric acid and a reducing agent into the dispersion liquid of the step S1).
The concentration of the chloroauric acid solution is 2.44 multiplied by 10-3mol/L～5.0×10-3mol/L; the reducing agent is preferably trisodium citrate, or hydroxylamine hydrochloride or trisodium citrate and hydroxylamine hydrochloride.
S3) heating the reaction solution obtained in the step S2) to 75 ℃, and stirring for 30-60 min to complete the reaction.
S4) cooling the system after the reaction is completed to room temperature, dispersing the system in ultra-pure water added with polyethylene glycol, and stirring for 1-2 h to obtain gold nanoparticles.
The preparation method of the gold/ferroferric oxide composite nanoparticle tracer specifically comprises the following steps:
A1) preparing ferroferric oxide nano particles;
A11) weighing water-soluble ferric salt or water-soluble ferric salt hydrate and water-soluble ferrous salt or water-soluble ferrous salt hydrate according to the molar mass ratio of the iron element of 2:1, and dissolving into a mixed solution by using deoxidized ultrapure water;
A12) heating the mixed solution at 70-100 ℃ in a water bath, and introducing nitrogen into the solution to remove oxygen;
A13) slowly dropwise adding an alkali solution into the mixed solution under the stirring condition, and adjusting the pH value of the reaction system to 9-10; after the dropwise addition of the alkali solution is finished, adding a reducing agent solution into the mixed system under the stirring condition, and stirring for reacting for 20-60 min to complete the reaction;
A14) cooling the system after the reaction is completed to room temperature, separating particles in the system by using a magnet, and cleaning for at least 3 times by using deoxidized ultrapure water to obtain ferroferric oxide nano particles;
A2) preparing a sol system of gold nanoparticles and ferroferric oxide nanoparticles;
A21) adding the ferroferric oxide nanoparticles prepared in the step A1) into deoxygenated ultrapure water, and performing ultrasonic dispersion to obtain uniformly dispersed ferroferric oxide nanoparticle dispersion liquid;
A22) respectively adding chloroauric acid aqueous solution and trisodium citrate aqueous solution with the same volume into ferroferric oxide nanoparticle dispersion liquid, and carrying out ultrasonic dispersion reaction; the molar concentration of the chloroauric acid aqueous solution is the same as that of the trisodium citrate aqueous solution;
A23) and (3) carrying out constant-temperature water bath on the system subjected to the ultrasonic treatment at 55-70 ℃, quickly adding hydroxylamine hydrochloride under the stirring condition, and continuously stirring for 20-60 min to finish the reaction.
A3) And D) carrying out suction filtration and washing on the sol system prepared in the step A2) to obtain a product.
In the technical scheme, the ferroferric oxide nano-particles are reduced into the ferroferric oxide nano-particles by a reducing agent in an oxygen removal solvent by using a trivalent ferric salt and a divalent ferrous salt; then adding the ferroferric oxide nano particles into a system of water-soluble gold chemicals, and uniformly distributing the ferroferric oxide nano particles around the gold nano particles in the process of reducing gold ions into the gold nano particles, so that the reduced gold nano particles are not easy to agglomerate, and the uniformly distributed ferroferric oxide nano particles and the gold nano particles are formed.
After the reaction is completed, the sol system is subjected to suction filtration, and precipitates after the suction filtration are alternately cleaned by ultrapure water and alcohol for at least 3 times.
In some embodiments, in the step a1), the raw materials for preparing the ferroferric oxide nanoparticles include water-soluble ferric salt or water-soluble ferric salt hydrate, water-soluble ferrous salt or water-soluble ferrous salt hydrate, and a reducing agent; the molar mass ratio of the iron element in the water-soluble ferric salt or the water-soluble ferric salt hydrate to the iron element in the water-soluble ferrous salt or the water-soluble ferrous salt hydrate is 2: 1.
The water-soluble ferric salt or the water-soluble ferric salt hydrate is preferably ferric chloride or ferric sulfate and ferric chloride hexahydrate or ferric sulfate hexahydrate; the water-soluble ferrous salt or the water-soluble ferrous salt hydrate is ferrous chloride or ferrous sulfate and ferrous chloride tetrahydrate or ferrous sulfate tetrahydrate; the reducing agent is preferably trisodium citrate.
The alkali solution is preferably an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution or aqueous ammonia.
The reducing agent may be trisodium citrate or hydroxylamine hydrochloride or trisodium citrate and hydroxylamine hydrochloride.
In some embodiments, in step a2), the reducing agent comprises trisodium citrate and hydroxylamine hydrochloride; the molar mass ratio of trisodium citrate to hydroxylamine hydrochloride for reducing the chloroauric acid into the gold simple substance is 1: 4.5-5.5.
In the step A2), trisodium citrate is added for a preliminary reduction reaction, the particle size of the generated gold nanoparticles is controlled, and hydroxylamine hydrochloride with strong reducibility is added for reducing gold ions, so that the obtained gold nanoparticles have narrow particle size distribution and meet the particle size ratio of the gold nanoparticles to ferroferric oxide nanoparticles.
The above tracers are prepared by the following specific examples.
Example 1
In a 250mL flask, 0.4g of polyvinylpyrrolidone and 80mL of ultrapure water were mixed, and then 2.44X 10 was added- 310ml of chloroauric acid solution in mol/L, heating the flask to 75 ℃ in a constant-temperature water bath, and adding 3.43X 10 to the mixture-23ml of mol/L sodium citrate solution, continuously stirring for 30min, returning to room temperature, addingAnd adding 5mg of polyethylene glycol under the stirring state, and continuously stirring for 1h to obtain the gold nano tracer.
Example 2
Weighing 2.34g FeCl3·6H2O (ferric chloride hexahydrate) and 0.96g FeCl2·4H2O (ferrous chloride tetrahydrate) in a flask (250mL), 100mL of deoxidized ultrapure water was added, and the flask was placed in a constant-temperature water bath at 80 ℃ to start nitrogen gas filling in the flask to remove oxygen. Under mechanical stirring (stirring speed of 800r/min), 40mL of NaOH solution with the concentration of 1.15mol/L is slowly dripped into the flask by using a dropping funnel, after the dripping is finished, 40mL of trisodium citrate with the concentration of 0.1mol/L is added, and the reaction is continued for 30 min. And cooling to room temperature, performing magnetic separation on the obtained particles by using a magnet, and cleaning for 3 times by using ultrapure oxygen to obtain the ferroferric oxide nano-particles.
And adding 50mg of prepared ferroferric oxide nano particles into a beaker, adding 150mL of deoxidized ultrapure water, and performing ultrasonic treatment for 30min to uniformly disperse the ferroferric oxide nano particles. 6mL of chloroauric acid and trisodium citrate with a concentration of 0.00934mol/L were added to the beaker, respectively. And after ultrasonic treatment for 15min, putting the beaker in a constant-temperature water bath kettle at 60 ℃, quickly adding 8mL of hydroxylamine hydrochloride with the concentration of 0.035mol/L under mechanical stirring, continuously stirring for 30min, cooling to room temperature after the reaction is finished, washing for 3 times by using ultrapure water and alcohol respectively, and dispersing in the ultrapure water to obtain the gold/ferroferric oxide composite nano tracer.
The tracers prepared in examples 1 and 2 above were topographically characterized using a HitachiHU-11B Microscope (japan) operating at 200kV, which yielded Transmission Electron Microscope (TEM) images as shown in fig. 1 and 2. As shown in FIG. 1, the gold nanoparticles in the tracer prepared in example 1 have a particle size mainly distributed in the range of 10-15 nm, and the average particle size is about 13 nm; the gold/ferroferric oxide composite particles prepared in the embodiment 2 mainly have the particle size of 20-40 nm, and the average particle size of the gold/ferroferric oxide composite particles is about 30 nm.
The magnetic performance of the tracer prepared in example 2 was tested using a vibrating sample magnetometer, before the test, the tracer was dried in a 60 ℃ oven at constant temperature for 4 hours, after complete drying, the solid nanoparticles were ground into powder or used as a sample to be tested, and the hysteresis loop measured is shown in fig. 3. As shown in fig. 3, the hysteresis loop of the tracer is "S" type, and when the magnetic field strength is 0, the magnetic induction is also 0 and the coercive force is 0, which indicates that the sample has superparamagnetism. The nano particles with superparamagnetism do not show magnetism when no external magnetic field exists; and when an external magnetic field is applied, the particles are magnetized to show magnetism.
The application also discloses a tracing method of the shale pore structure fluid channel, wherein the tracer disclosed or prepared in the application document is retained on the surface of the shale pore when fluid enters the shale pore, so that the marking of the shale pore structure fluid channel is realized; and identifying the fluid channel in the shale pore by an electronic scanning electron microscope.
The fluid can be water or oil or other organic matter with good fluidity; the fluid is preferably water.
Further, the tracing method specifically comprises the following steps:
step 1: taking stratum shale to be detected, and grinding, polishing and cleaning the stratum shale to be detected to obtain a shale sample;
step 2: preparing the tracer or the prepared tracer disclosed by the application into a tracer water solution with the concentration of 0.01-1.0 mg/mL; then placing the shale sample prepared in the step 1 into a gold nano tracer aqueous solution for spontaneous imbibition; or the composite nano tracer aqueous solution is uniformly dispersed on the surface of the shale sample, and the magnet is placed below the shale sample for magnetic absorption injection.
And step 3: and cleaning the surface of the shale sample after imbibition, and then performing imaging analysis by using a scanning electron microscope to obtain the internal pore microstructure of the shale sample.
The specific implementation is as follows:
taking a stratum shale raw material to be detected, polishing the stratum shale raw material into a cube with the side length of 5mm and the thickness of 2mm, polishing the surface of the cube by using abrasive paper, sticking the cube on a mould, placing the mould in an argon ion polishing instrument, and bombarding the surface of the cube by using an argon ion beam to flatten the surface of the cube to obtain a pretreated shale sample. And wiping the surface of the polished shale sample, and putting the shale sample into deionized water added with 1mg/mL of tracer for spontaneous imbibition experiment. After the experiment, the polished surface was cleaned with alcohol cotton and analyzed by SEM imaging, and SEM images thereof are shown in fig. 4 to 6. Wherein, fig. 4 is an SEM image of the adsorption of the tracer on the organic matter; fig. 5 is an SEM image of tracer adsorption on clay minerals, fig. 6 is an SEM image of the disclosed tracer after adsorption on different types of pores, wherein fig. 6(a) is pyrite; FIG. 6(B) shows the interparticle pores; FIG. 6(C) shows a crack, where it can be seen that a large number of bright spots appear in each of the different types of pore structures, demonstrating the flow of fluid through these locations.
As shown in fig. 6, after the tracer-containing water contacts the shale surface, a significant amount of the tracer is retained on the mineral surface, demonstrating that the water does flow through these locations. Comparing fig. 4(a) and fig. 5(a), it can be clearly seen that the tracer particles remained in the organic matter are significantly less than those remained in the clay mineral. And calculating the face porosity occupied by the tracer particles by using Photoshop software to quantitatively analyze the residual degree of the tracer on the surface, wherein the calculated face porosity is 0.53%, 0.81%, 1.32% and 3.20%, and the tracer particles remained in the organic matter are actually less than the tracer particles remained on the clay surface by more than 2 times.
Because the injected nano tracer contains gold element, the nano tracer is high-brightness under the scanning electron microscope, and can be directly observed under the scanning electron microscope, as shown in fig. 7, because the content of the gold element in the rock is extremely small, if the enrichment of the gold element is found in a certain area, the area is determined as a pore channel area through which the nano tracer flows, and thus the characteristics of the shale pore channel can be obtained by analyzing the distribution of the gold element in the area.
The elemental composition of the fluid channel is analyzed by X-ray energy spectroscopy (EDS) analysis, the EDS obtained is shown in fig. 8, and the matrix composition of each portion in the fluid channel in the shale sample can be obtained according to the EDS, and the type of the matrix can be obtained according to the matrix composition.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. The shale pore structure fluid flow channel tracer agent is characterized by comprising at least one of gold nanoparticles or gold/ferroferric oxide composite nanoparticles.
2. The shale pore structure fluid channel tracer agent as claimed in claim 1, wherein the gold nanoparticles have a particle size D50 of 10-15 nm; the particle size D50 of the gold/ferroferric oxide composite nano particles is 20-40 nm.
3. The tracer of claim 1, wherein the gold nanoparticles or gold/ferroferric oxide composite nanoparticles are modified by a polymer, wherein the polymer is any one of polyethylene glycol, polyvinylpyrrolidone, polymethacrylate, polystyrene and polydopamine.
4. The method for preparing gold nanoparticles according to claim 1 or 2, wherein a compound containing a gold element is reacted with a reducing agent system in an aqueous solvent to obtain gold nanoparticles.
5. The method of claim 5, wherein the elemental gold-containing compound is chloroaurate; the molar ratio of the gold-containing compound to the reducing agent is 1: 4.5-5.5; the concentration of the compound containing the gold element is 2 x 10-4～2×10-3mol/L; the molar ratio of the gold-containing compound to the reducing agent is 1: 4.5-5.5; the reducing agent is any one of trisodium citrate, sodium borohydride, hydroxylamine hydrochloride and tartaric acid.
6. The preparation method of gold/ferroferric oxide composite nanoparticles according to claim 1 or 2, characterized by reacting a ferric salt hydrate with a ferrous salt compound in a mixed system of an aqueous solvent, an alkaline compound and a reducing agent to obtain a ferroferric oxide nanoparticle dispersion liquid;
adding a compound containing a gold element into a dispersion liquid of the ferroferric oxide nano particles in a water solvent and reducing agent system, and reacting to obtain the gold/ferroferric oxide composite nano particles.
7. The method according to claim 6, wherein the alkaline compound is any one of sodium hydroxide, potassium hydroxide and ammonium hydroxide; the molar ratio of the ferric salt compound to the ferrous salt compound is 2: 1.
8. A tracing method for a fluid flow channel in a shale micro-nano pore structure is characterized in that the tracer according to any one of claims 1 to 3 or the tracer prepared according to any one of claims 4 to 7 is adopted to be left on the surface of a shale pore when a fluid passes through the shale pore to mark the fluid channel in the shale pore structure, and SEM or FIB-SEM analysis is carried out on the shale microfluidic channel by utilizing the high brightness of gold nanoparticles or ferroferric oxide nanoparticles during SEM observation.
9. The tracing method according to claim 8, characterized by comprising the following steps:
step 1, grinding, polishing and cleaning stratum shale to be detected to form a shale sample, and drying the shale sample for later use;
step 2, placing the prepared shale sample into a tracer fluid solution, and selecting spontaneous imbibition or magnetic attraction according to the type of the tracer;
and 3, intercepting a fresh section of the shale sample, cleaning the surface, and then performing imaging analysis by using a scanning electron microscope to obtain the distribution characteristics of the tracer in the pore microstructure in the shale sample for tracing and representing the fluid flow channel.
10. The tracing method of claim 8, wherein the elemental composition of the fluid channel is analyzed by X-ray spectroscopy to obtain the matrix composition and type of the pores in the shale sample.
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