CN113429959B - Preparation method of trace substance tracing proppant and application of trace substance tracing proppant in fracture monitoring - Google Patents

Abstract

The invention discloses a preparation method of trace substance tracer propping agent and application thereof in crack monitoring, wherein trace substance tracer is embedded on traditional propping agent-quartz sand to obtain a novel trace substance tracer functionalized propping agent, and controllable release of the tracer in practical application is realized, the method for estimating the position of the propping agent by using the tracer flowback curve is established by controlling the controllable release of the tracer from the propping agent and the influence of the position and the flow rate of the propping agent on the tracer flowback curve, the defects of small amount of tracer, large dosage, low sensitivity, large environmental toxicity and the like in the prior art are overcome, the obtained propping agent has the advantages of high detection sensitivity, no pollution, low adsorption, high chemical biological stability, capability of realizing the control of releasing a long-term monitoring output profile, wide use temperature range, no influence on the body health of well site workers and the like, is beneficial to the practical application and popularization of the well site.

Description

A kind of preparation method of trace substance tracer proppant and its application in fracture monitoring

technical field

The invention relates to the field of preparation of functionalized proppant, in particular to a preparation method of tracer proppant for trace substances and its application in fracture monitoring.

Background technique

Fracturing technology is currently the core technology for stimulation and stimulation of unconventional oil and gas reservoirs. Fracturing is the artificial formation of cracks in the formation, which increases the production of oil wells, plays an important role in improving the flow of oil layers, and is an important technical means for stabilizing and increasing production in oil and gas fields. Fracturing technology can be divided into several development stages, such as explosive fracturing, high-energy nuclear explosion fracturing, acid fracturing, hydraulic fracturing, and anhydrous fracturing. Based on considerations of safety, economy and environmental protection, hydraulic fracturing technology is currently the most widely used.

Proppants play a very important role in hydraulic fracturing, which is related to the diversion effect of propped fractures and even the success or failure of the entire hydraulic fracturing construction. Only fractures that are effectively supported are important fluid channels in the process of oil and gas production. With the improvement of fracturing process requirements and the continuous emergence of complex construction problems in the field, a large number of different functional proppants have been researched continuously. Engineering problems provide new ideas and new solutions, and become a hot research content in the current petrochemical field.

A proppant is a fine particulate solid material whose primary function is to maintain an established fracture after fracturing. Unsupported fractures close easily, limiting the potential flow of oil and gas. The proppant is usually divided into natural quartz sand, ceramsite and film-coated proppant.

Due to the diversity of geological conditions, simple proppants cannot meet the diverse needs of the emerging fracturing construction. In order to overcome the technical challenges inside the reservoir and meet the production needs under various geological conditions, a series of more characteristic functional proppants are derived from common proppants.

The detection of propped fractures is the key to the effect of fracturing, and the tracer-functionalized proppant has the advantage of distinguishing propped and unsupported fractures. Tracer-functionalized proppants are divided into two categories. One is to add radioactive substances, stable isotopes, magnetic substances, conductive substances, etc. as markers to the proppant. And the marker loaded in it as a whole, it needs to be used with logging equipment in the formation; the other type does not need logging equipment, the tracer is loaded on the surface of the proppant through the polymer film, and the tracer is used in use. It is released from the polymer and flows back to the surface with the fracturing fluid. The content of the tracer in the fracturing fluid is monitored, the flowback curve is drawn, and then the fracture information can be obtained by simulating and analyzing the flowback curve.

The monitoring of fracturing fractures is the key content of evaluating the construction effect and adjusting the construction plan. The monitoring of the location of propped fractures is particularly important in fracturing monitoring. The location of propped fractures can be indicated by the location of proppant. The tracer-functionalized proppant provides an effective technical means for indicating the position of the proppant in the fracture. At present, the most common staged fracturing interval in horizontal wells is 20 to 30 intervals. During fracturing construction, it is hoped that each interval has a unique tracer to achieve layered and segmented fracturing. fine-tuned monitoring requirements. However, the current research in this area is still in its infancy and trial stage, and there are shortcomings such as a small number of tracers, a large amount of tracers, low sensitivity and high environmental toxicity, which are not conducive to the practical application and promotion of well sites.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings of the prior art, and discloses a method for preparing a trace substance tracer proppant and its application in fracture monitoring. The trace substance tracer is embedded in the traditional proppant-quartz sand, and the A new type of tracer-functionalized proppant, which realizes the controllable release of the tracer in practical applications, by controlling the controllable release of the tracer from the proppant and the relationship between the position and flow rate of the proppant. The influence of the tracer flowback curve was established, and a method for estimating the proppant position using the tracer flowback curve was established, which solved the shortcomings of the prior art such as a small number of tracers, a large amount of tracers, low sensitivity and high environmental toxicity. The proppant has the advantages of high detection sensitivity, no pollution, low adsorption, high chemical and biological stability, long-term controlled release monitoring of the production profile, a wide range of operating temperatures, and no impact on the health of well site workers. , which is beneficial to the practical application and promotion of the well site.

To achieve the above purpose, the technical scheme adopted in this application is:

A method for preparing trace substance tracer proppant, comprising the following steps:

Step S1: prepare HCl solution, add an appropriate amount of HCl solution to rare earth oxide powder, and react while stirring; when the powder solid completely disappears, heat and evaporate the solution to remove excess HCl, then add deionized water, and continue to add if there is precipitation. HCl is dissolved; repeated several times until the addition of deionized water no longer produces precipitation, and an intermediate solution is obtained;

Step S2: prepare a concentrated solution of EDTA-Na ₄ in proportion, then add it to the intermediate solution of step S1, evaporate and crystallize, filter with suction, and wash the filter cake with ethanol solution for many times, then put the filter cake into an oven to dry, and the obtained product is Add water to dissolve, recrystallize and purify to obtain trace substance tracer;

Step S3: prepare a solvent, add the tracer tracer obtained in step S2 and mix thoroughly; then add the coating polymer to the acetone solution, and continue stirring until the polymer solid is completely dissolved; put the proppant into the polymer solution And fully mixed, and then drained the polymer solution, the acetone was completely evaporated, and after dispersion and sieving, the tracer functionalized proppant was obtained.

Further, when the rare earth oxide powder in the step S1 is replaced with a rare earth salt, the step S1 is: weighing the rare earth salt, adding deionized water to completely dissolve the solution, and filtering the solution with a filter membrane to obtain an intermediate solution.

Further, in the step S1, the concentration of the HCl solution is 1 mol/L.

Further, the method of adding an appropriate amount of HCl solution to the rare earth oxide powder in the step S1 is to wet the rare earth oxide with a small amount of deionized water before adding the HCl solution, so as to prevent it from reacting with the acid solution and causing a large amount of exothermic heat to cause liquid. splash.

Further, in the step S2, the concentration of the solvent solution is 95%.

Further, in the step S3, the concentration of the acetone solution is 95%; the mesh number of the tracer functionalized proppant obtained in the step S3 is 20-40 meshes.

Further, in the step S3, the coating polymer is ammonium polymethacrylate, and the coating polymer concentration is 2.5%-15.0%.

Further, in the step S3, the solvent is one or more of methanol, ethanol, acetone, and isopropanol.

Further, in the step S2, the tracer of trace substances is one of LaEDTA-Na, SmEDTA-Na, and NdEDTA-Na.

Further, the application of the tracer-functionalized proppant according to any one of claims 1 to 9 in fracturing fracture monitoring.

The beneficial effects of the present invention are:

The invention discloses a preparation method of a trace substance tracer proppant and its application in fracture monitoring. The trace substance tracer is embedded on a traditional proppant-quartz sand to obtain a new type of trace substance tracer function. By controlling the controllable release of the tracer from the proppant and the influence of the position and flow rate of the proppant on the tracer flowback curve, the established The method of using the tracer flowback curve to estimate the position of the proppant solves the shortcomings of the prior art, such as a small amount of tracers, a large amount of tracers, low sensitivity and high environmental toxicity, and the obtained proppant has high detection sensitivity and no pollution. , low adsorption, high chemical and biological stability, can realize controlled release, long-term monitoring of production profile, wide operating temperature range, and will not affect the health of wellsite staff, etc., which is beneficial to the practical application and promotion of wellsites .

The functional tracer proppant developed with trace tracer as the core can be easily used for fracturing fracture monitoring in oil and gas wells. Combined with the advantages of various tracer technologies, it can optimize the current core technology of fracture monitoring and evaluation, and has a high sensitivity It has the advantages of high efficiency, small impact on the environment, good compatibility with existing logging equipment, and easy promotion in well sites and construction sites. After forming a series of products, there are various types, which can meet the actual needs of multiple tracer substances for staged fracturing.

Description of drawings

Fig. 1 is a schematic diagram of the structure of tracer proppant in the application;

Fig. 2 is the infrared image of trace material tracer in the embodiment of the application;

Wherein A, EDTA; B, LaEDTA-Na; C:, SmEDTA-Na; D, NdEDTA-Na; E, EDTA-Na4;

Fig. 3 is the XRD pattern of NdEDTA-Na in the embodiment of the application;

FIG. 4 is a comparison of the surface morphology of the proppant functionalized with quartz sand and trace tracer in the embodiment of the application;

Among them, a1 quartz sand; a2 local enlarged view of quartz sand; b1 tracer-functionalized proppant; b2 tracer-functionalized proppant;

Fig. 5 is the infrared analysis spectrum of quartz sand and sample in the embodiment of the application;

Fig. 6 is the sample EDS analysis (La element distribution) in the embodiment of the application;

FIG. 7 is an experimental flow chart for simulating the release of the tracer in the crack in the embodiment of the application;

FIG. 8 is a graph showing the variation of the concentration of the tracer with the outflow volume of the liquid in the embodiment of the application;

FIG. 9 is a flowback curve diagram of simulated staged fracturing monitoring in an embodiment of the present application.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings, and the protection scope of the present invention is not limited to the following:

Example 1: Synthesis

Using La ₂ O ₃ , Nd ₂ O ₃ , Sm(NO ₃ ) ₃ · 6H ₂ O as raw materials and EDTA-Na ₄ to prepare trace tracers, LaEDTA-Na, NdEDTA-Na, SmEDTA-Na were obtained. Three trace substance tracers.

1. Synthesis steps of tracer tracer:

(1) Prepare 1 mol/L HCl solution (9 ml of 36% HCl solution in a 100 ml volumetric flask, and dilute to 100 ml with deionized water). Add an appropriate amount of HCl solution to the rare earth oxide (La ₂ O ₃ , Nd ₂ O ₃ ) powder, and react while stirring (before adding the HCl solution, use a small amount of deionized water to remove the rare earth oxide (La ₂ O ₃ , Nd ₂ O 3 ) ₃ ) Wetting to prevent it from reacting with the acid solution and causing a large amount of exothermic liquid splashing);

(2) When the powder solid disappears completely, heat and evaporate the solution to dryness, remove excess HCl, then add 100 ml of deionized water, and continue to add HCl to dissolve if there is precipitation. Repeat several times until the addition of deionized water no longer produces precipitation;

(3) Weigh EDTA-Na ₄ in proportion and prepare it into a concentrated solution (dissolve with a small amount of deionized water), and then add it into the above-treated solution. Evaporate and crystallize, filter with suction, and wash the filter cake with 95% ethanol solution for many times, and then put the filter cake into an oven for drying. The obtained product was dissolved in water, and the product (LaEDTA-Na, NdEDTA-Na) was obtained after recrystallization and purification.

In addition to oxides of rare earth elements, rare earth salts (Sm(NO ₃ ) ₃ ·6H ₂ O) can also be used as raw materials for synthesizing complexes.

(1) Weigh the rare earth salt, add deionized water to dissolve it completely, and filter the solution with a 0.45 μm water filter. Weigh EDTA-Na ₄ in proportion, dissolve in deionized water, mix with rare earth salt solution, evaporate and crystallize.

(2) vacuum filtration after the crystal is separated out completely, rinse the filter cake with 95% ethanol solution, dry to obtain the crude product of the tracer, add deionized water to the obtained product to dissolve, and recrystallize to obtain the tracer tracer after purification ( SmEDTA-Na).

2. Tracer functionalized proppant synthesis

Using quartz sand as the proppant base material, ammonium polymethacrylate as the coating polymer, tracer tracers (LaEDTA-Na, NdEDTA-Na, SmEDTA-Na) as the marker, the solvent evaporation method was used to synthesize tracer tracers Agent-functionalized proppant.

First prepare 95% acetone solution (95% acetone, 5% deionized water), add trace tracers (LaEDTA-Na, NdEDTA-Na, SmEDTA-Na) and mix well, and then stir the polymer solid Add to the acetone solution and continue stirring until the polymer solids are completely dissolved; place the proppant in the polymer solution and mix well, drain the polymer solution, leaving the proppant and liquid trapped around the proppant, and finally The proppant was placed in a well-ventilated fume hood and waited for the acetone to evaporate; after the acetone evaporated completely, the polymer formed a film on the surface of the quartz sand, and some trace tracers were captured in the coating; After fractionation, 20/40 mesh tracer functionalized proppants (LaEDTA-Na, NdEDTA-Na, SmEDTA-Na) were obtained. The schematic diagram of the tracer functionalized proppant is shown in Figure 1.

Example 2: Tracer Characterization of Trace Substances

The product was analyzed by infrared spectroscopy with KBr tablet method. The FT-IR of three trace tracers and main raw materials are shown in Figure 2. The figure shows the infrared spectrum of EDTA in the presence of acid, complex and tetrasodium salt in sequence.

In the figure, A is the IR curve of EDTA, the vibration absorption at 1693 cm ^-1 can be assigned to the vibration absorption peak of the uncoordinated carboxyl group, and the vibration absorption peak of 3016 cm ^-1 can be assigned to the NH vibration absorption peak. B, C and D are the infrared spectra of the complexes of La, Nd, Sm and EDTA respectively, wherein the vibrational absorption of the free carboxyl group absorption peak of EDTA at 1693 cm- ¹ disappears completely, and at 1571 cm ^-1 , 1596 cm- ¹ , 1594 cm-1 respectively The antisymmetric stretching vibration absorption peak of -COO ^- appeared in ^-1 ; the absorption peaks at 1398cm ^-1 , 1409cm ^-1 , and 1412cm ^-1 were the symmetric stretching vibration absorption peaks of -COO ^- in the three trace tracers, respectively; The broad absorption peak between 3200 and 3400 cm ^-1 is the absorption peak of water, which proves that all products contain crystal water. E is the infrared spectrum of EDTA-Na ₄ , 1588cm ^{- 1} is the antisymmetric stretching vibration peak of -COO-, 1420cm ^{- 1} is the symmetric stretching vibration absorption peak of -COO-; 1670cm ^-1 is the EDTA-Na ₄ in the Carbonyl absorption peak of impurity H ₂ EDTA-Na ₂ . Compared with the raw material EDTA-Na ₄ , the anti ^- symmetric vibration absorption peaks and the symmetrical vibration absorption peaks of -COO- in the tracer molecules of the three trace substances are all shifted, which indicates that rare earth elements successfully form complexes with EDTA.

In the coordination reaction, the formation and dissociation of complexes are in dynamic equilibrium, and the equilibrium constant of this reaction is represented by the stability constant (or formation constant). The stability constant of LaEDTA-Na is 15.5, the stability constant of NdEDTA-Na is 16.61, and the stability constant of SmEDTA-Na is 17.14. The larger the stability constant, the more stable the complex is. The stability of the three tracer tracers showed that the smaller the ionic radius of the central element, the higher the antisymmetric stretching vibration absorption peak frequency of its complex -COO- ^, and with the decrease of the ionic radius, the metal-ligand bond became stronger. The increased covalent nature minimizes the carboxylic acid resonance, resulting in an increase in the frequency of the antisymmetric carboxyl stretch band.

Further, X-ray powder diffraction (X-Ray Diffraction, XRD) was used to confirm the structures of the three trace tracers (the radiation source Cu target Kα, the step width was 0.02°, the scanning speed was 2°/min, and the current was 30mA).

The 2θ angles of the main diffraction peaks of NdEDTA-Na are 8.95°, 10.00°, 11.36°, 13.44°, 28.68°, 44.41°; the 2θ angles of the main diffraction peaks of SmEDTA-N are 8.83°, 9.83°, 11.27°, 13.34°, 28.78° The 2θ angles of the main diffraction peaks of LaEDTA-Na are 9.63°, 10.24° and 12.10°. The XRD pattern of NdEDTA-Na is in good agreement with the diffraction peaks of standard card PDF 00-010-0767, C ₁₀ H ₁₂ N ₂ O ₈ Nd-Na (ICDD, 1957), as shown in Figure 3, which proves the synthesis of The product is that Nd forms a complex with EDTA.

Example 3: Tracer functionalized proppant characterization

(1) Scanning Electron Microscope (SEM)

SEM analysis of the proppant functionalized with quartz sand aggregate and tracer tracer was performed to observe the change of the surface morphology of the proppant after being coated with polymer. The results obtained are shown in Figure 4.

Among them, a1 and a2 are respectively the quartz sand aggregate particles and their partial enlarged images; b1 and b2 are respectively the trace substances marked proppant and its partial enlarged images. From Figure 4, it can be observed that the surface of quartz sand particles is relatively uniform, while the surface of the tracer functionalized proppant has some protrusions; if the surface of the two particles continues to be enlarged, it can be observed that the surface of quartz sand is uneven, while The surface of the polymer-coated proppant is relatively smooth. The SEM results show that the surface of the proppant sample is smoother after coating treatment.

(2) Infrared spectroscopy analysis

The quartz sand and the tracer functionalized proppant were ground into powder, and the samples were analyzed by KBr pellet method. Figure 5 is an infrared analysis diagram of the quartz sand and polymer-coated samples.

As shown in Fig. 5, the infrared spectra of the tracer-functionalized proppant and the quartz sand proppant are very similar. The infrared spectra of the tracer-functionalized proppant and the quartz sand have an absorption peak at 1430cm ^-1 . Si-O transverse and longitudinal symmetric shrinkage vibration peaks, the absorption peak at 880cm ^-1 is the symmetric shrinkage vibration peak of Si-O. The infrared spectrum of the tracer-functionalized proppant has a weaker intensity at the position of 1724cm ^-1 The absorption peak, which can be assigned to the absorption peak generated by the stretching vibration of the ester carbonyl group. The polymer used in synthesizing tracer tracers is polyammonium methacrylate, so the increased ester carbonyl absorption peak in the infrared spectrum of the synthesized proppant sample comes from the polymer coated on its surface. The results showed that the surface of the proppant sample was successfully coated with ammonium polymethacrylate.

(3) Energy Dispersive Spectroscopy (EDS)

The synthetic tracer-functionalized proppant samples were analyzed by EDS, and the distribution of tracer tracers on the sample surface was detected. The element content of a single sample was analyzed by energy spectrum analysis, and the central element La of the tracer tracer LaEDTA-Na was used as the detection target. The test results are shown in Figure 6.

The trace element tracer LaEDTA ^- is distributed in most positions on the proppant surface, and the La element is sparsely distributed in a few positions on the proppant particle surface. However, there is no obvious difference in the surface state of the part with tracer and the part without tracer distribution in the bright field image, indicating that the polymer forms a relatively complete coating layer on the surface of the quartz sand. The absence of La element distribution in some positions should be the reason why LaEDTA-Na is not uniformly distributed in the polymer solution. Because the tracer tracer LaEDTA-Na is a water-soluble substance, and the polymer solution is prepared with acetone as the solvent, the tracer tracer cannot be mixed evenly in the organic solvent, so there is no trace substance in some positions of the functionalized proppant. tracer distribution.

Example 4: Introduction to the application of tracer functionalized proppant----fracture location monitoring

The tracer-functionalized proppant used in this example is NdEDTA-Na.

1. Study tracer release of trace substances

A small sand column filled with tracer-functionalized proppant was fabricated and injected alternately with NaCl and deionized water. The solution flowing out from the sand column was taken, and the outflow sample was digested and then used to test the tracer content with a UV-Vis spectrophotometer. .

2. Fitting the release kinetic model

Kinetic model fitting was performed on the release profiles from the salinity and temperature experiments. By fitting different kinetic models, analyzing variance, and comparing, the most consistent release kinetic equation was obtained.

3. Simulated crack release experiment

As shown in Fig. 7, the flowback test of tracer tracer in the fracture system is simulated. The fracture system was simulated by a chromatographic column with a diameter of 1 cm and a length of 20 cm. The column is packed with quartz sand as proppant, and the total void volume between proppants is the fracture volume (Fv), which can be determined from the mass or volume of fluid driven into the column. According to the mass estimation, first fill the predetermined positions with quartz sand and the sample respectively, then weigh the mass of the chromatography column filled with quartz sand, drive in the fluid until the sand column is filled with liquid, and then weigh the mass of the chromatography column again. The difference is that the mass of the driven fluid can be obtained from the corresponding volume according to the density of the fluid. According to the fluid volume estimation, it is also necessary to fill the sand column first, prepare a known volume of liquid, and drive it into the chromatography column until it is filled with liquid. According to the change of the prepared liquid volume, the fracture volume in the chromatography column can be obtained. In the experiment, the above two methods are used to estimate the fracture volume, and the obtained results are basically the same. The fracture volumes of experiments 1, 2, and 3 were 7.99 mL, 7.68 mL, and 8.44 mL, respectively.

In the simulated fracture flowback test, a certain amount of tracer-functionalized proppant was placed in a specific location of the fracture, and the rest was covered with quartz sand. A section of 0.1% NaCl (determined by the size of the fracture space) was injected to trigger the release of the tracer in the tracer; after injection, the brine flow was stopped for 12 hours to simulate on-site well shut-in, allowing enough time to complete the tracer Finally, deionized water was injected from the opposite direction to simulate the fracturing fluid flowback process. The experimental process is shown in Figure 7. The effluent solution was analyzed for tracer concentration and a flowback curve was drawn.

Specifically:

The 0.1% NaCl solution was injected into the fracture system at 5.0 mL/min, and the 0.1% NaCl solution injected into it was driven out by different displacement flow rates in the flowback stage, and the outflow curve was optimized to obtain the best displacement rate.

In the experiment, the tracer-functionalized proppant was spread on the front, middle and back of the fracture, respectively. When injecting 0.1% NaCl solution into the fracture, the flow rate of the solution is 5mL/min; in the three groups of experiments in the reflux stage, the flow rate of the fluid is 1mL/min. Take 0.5mL as a unit of measure when receiving the solution flowing back from the fracture.

The collected solution samples were digested first, and then the tracer content of trace substances in the solution was detected by ultraviolet spectrophotometry. The specific experimental settings and experimental results are shown in Table 1, and the curves of the three experiments are drawn in Figure 8. The abscissa was normalized when drawing, and the outflow volume was converted into the fracture volume corresponding to each group of experiments. Based on the outflow time corresponding to the peak of the flowback curve, the method for calculating the position of the tracer-functionalized proppant in the fracture system is as follows:

in:

L: the placement position of the tracer functionalized proppant, cm;

ν: reflux rate, mL/min;

t: the time corresponding to the peak value of the tracer flowback curve, min;

L ₀ : the length of the simulated fracture system, cm;

V: total volume of the fracture system, cm ³ .

Table 1 Simulated release experimental parameters

In Experiment 1, Experiment 2 and Experiment 3, the peaks of the tracer concentration appeared at 0.31FV, 0.58FV, and 1.00FV, which corresponded to the position of the tracer-functionalized proppant in the fracture, and the deviation value They are 1 cm, 0.85 cm, and 0.25 cm, respectively. Compared with the placement position of the tracer functionalized proppant, the positions calculated from the peaks of the tracer flowback curve have a certain deviation. However, for the entire length of the fracture system, the maximum deviation of the test value is only 5%, which indicates that the peak information of the tracer in the flowback curve can be used to judge the position of the proppant in the fracture.

Example 4: Introduction to the application of tracer functionalized proppant ---- monitoring of fracture location in staged fracturing

The tracer-functionalized proppants used in this example are LaEDTA-Na, NdEDTA-Na, and SmEDTA-Na.

In shale gas development, staged fracturing technology is usually used in horizontal wells. At present, the most common horizontal well staged fracturing interval is 20 to 30 intervals. As shale gas enters the infill development stage, the number of layers fractured by layers is still increasing. If the same tracer is used in each interval, it is difficult to distinguish the tracer contribution from which fracturing interval is the peak tracer concentration on the flowback curve, and if there are multiple tracers on the flowback curve When tracer peaks overlap, it is difficult to obtain a single intact tracer peak. Therefore, during the fracturing construction, it is hoped that each interval has a unique tracer to meet the fine monitoring requirements of the fracturing fracture layered and segmented.

The synthetic tracer-functionalized proppant of the present invention can also be used in the monitoring of staged fracturing fractures in horizontal wells. In the conventional proppant injection process, a section of tracer-functionalized proppant is injected, and each section contains proppants with different labeled tracers. Each tracer carries the information of the fracturing fractures in the corresponding interval, and by monitoring various markers in the flowback fluid, the reconstruction status of each fracturing interval can be obtained, providing more information for the subsequent mining work. Precise guidance.

Simulation experiments were designed in the laboratory to explore the feasibility of the tracer-functionalized proppant synthesized in this study for fracture monitoring of staged fracturing. A section of tracer-functionalized proppant is laid at the front, middle and rear of the column, and each section of proppant carries different markers, and the rest of the column is filled with ordinary quartz sand proppant. A 20 cm long, 1 cm diameter column was used, with Nd tracer-carrying proppant at 4.9 cm from the outlet, Sm tracer-carrying proppant at 10.8 cm from the outlet, and La tracer-carrying proppant at 10.8 cm from the outlet. The position of the exit 14.9cm. The subsequent experimental steps are the same as in the previous section. Since the spectrophotometric detection of the solution cannot distinguish the specific concentrations of the three trace substances in the solution, ICP-MS is used to detect the content of the three markers in the reflux liquid.

In the simulated staged fracturing experiment, the flowback curves of the three trace tracers are shown in Figure 9. It can be seen from the experimental results that the outflow order of several tracers is consistent with the placement order of the proppants functionalized with each tracer tracer in the experimental design. The sample placed in the middle section is closer to the sample placed in the rear section, and the flowback curve of the sample placed in the middle section is also shown to be closer to that of the sample placed in the rear section. The relative positions of the peaks of the three flowback curves are consistent with the relative positions of the three trace material-labeled proppants.

Under the condition that the permeability of each fracture is the same, the peak shape of each flowback curve is similar. Under the condition of different fracture permeability in each section, the peak shape of the tracer outflow curve is mainly affected by the permeability of each section, and the fracturing condition of each section is also reflected in the peak shape of the flowback curve. Using multiple tracer-functionalized proppants in the fracture system at the same time, multiple tracer information can be obtained simultaneously from the backflow fluid. After separate analysis of each flowback curve, the fracture information of the interval corresponding to the proppant functionalized with the tracer tracer can be obtained.

In summary, the present invention discloses a preparation method of tracer proppant for trace substances and its application in fracture monitoring. The tracer tracer is embedded in traditional proppant-quartz sand to obtain a new type of tracer proppant. Substance tracer functionalized proppant, and the controlled release of the tracer in practical application is realized, by controlling the controllable release of the tracer from the proppant and the position and flow rate of the proppant on the tracer flowback curve Therefore, a method for estimating the proppant position using the tracer flowback curve was established, which solved the shortcomings of the prior art, such as a small number of tracers, a large amount of tracers, low sensitivity and high environmental toxicity, and the obtained proppant had the ability to detect High sensitivity, no pollution, low adsorption, high chemical and biological stability, can realize controlled release, long-term monitoring of production profile, wide operating temperature range, and will not affect the health of well site staff, etc., which is beneficial to the well site Practical application and promotion of

So far, those skilled in the art realize that although the embodiments of the present invention have been shown and described in detail herein, without departing from the spirit and scope of the present invention, it is still possible to directly determine or deduce the following Numerous other variations or modifications of the principles of the present invention. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims (9)

1. a preparation method of trace material tracer proppant, is characterized in that, described preparation method comprises the following steps: Step S1: prepare HCl solution, add an appropriate amount of HCl solution to rare earth oxide powder, and react while stirring; when the powder solid completely disappears, heat and evaporate the solution to remove excess HCl, then add deionized water, and continue to add if there is precipitation. HCl is dissolved; repeated several times until the addition of deionized water no longer produces precipitation, and an intermediate solution is obtained; Step S2: prepare a concentrated solution of EDTA-Na ₄ in proportion, then add it to the intermediate solution of step S1, evaporate and crystallize, filter with suction, and wash the filter cake with ethanol solution for many times, then put the filter cake into an oven to dry, and the obtained product is Add water to dissolve, recrystallize and purify to obtain a trace substance tracer, and the trace substance tracer is one of LaEDTA-Na, SmEDTA-Na, and NdEDTA-Na; Step S3: prepare a solvent, add the tracer tracer obtained in step S2 and mix thoroughly; then add the coated polymer ammonium polymethacrylate into the acetone solution, and continue to stir until the polymer solid is completely dissolved; put the proppant into the solution. The polymer solution is poured into the polymer solution and fully mixed, the polymer solution is drained, the acetone is completely evaporated, and the tracer functionalized proppant is obtained after dispersion and sieving. 2. The method for preparing a trace substance tracer proppant according to claim 1, wherein when the rare earth oxide powder in the step S1 is replaced with a rare earth salt, the step S1 is: weighing the rare earth salt, After adding deionized water to dissolve completely, the solution was filtered through a filter membrane to obtain an intermediate solution. 3 . The method for preparing a trace substance tracer proppant according to claim 1 , wherein the concentration of the HCl solution in the step S1 is 1 mol/L. 4 . 4. The method for preparing a trace substance tracer proppant according to claim 1, wherein the method for adding an appropriate amount of HCl solution to the rare earth oxide powder in the step S1 is to use a small amount of HCl solution before adding the HCl solution. The rare earth oxide is wetted with deionized water to prevent it from reacting with the acid solution with a large exothermic splash. 5 . The method for preparing a trace substance tracer proppant according to claim 1 , wherein the concentration of the solvent solution in the step S2 is 95%. 6 . 6. The method for preparing a trace substance tracer proppant according to claim 1, wherein the concentration of the acetone solution in the step S3 is 95%; the trace substance tracer obtained in the step S3 has a function of The mesh of chemical proppant is 20-40 mesh. 7 . The method for preparing a trace substance tracer proppant according to claim 1 , wherein the concentration of ammonium polymethacrylate in the step S3 is 2.5%-15.0%. 8 . 8 . The method for preparing a trace substance tracer proppant according to claim 1 , wherein the solvent in the step S3 is one or more of methanol, ethanol, acetone, and isopropanol. 9 . 9. Application of a tracer-functionalized proppant in fracture monitoring, characterized in that the tracer-functionalized proppant prepared by the method for preparing a tracer-functionalized proppant according to any one of claims 1 to 8 Application of tracer-functionalized proppant in fracturing fracture monitoring.

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