Fracturing tracing monitoring method based on nano colloidal gold particles

Abstract

The invention discloses a fracturing tracing monitoring method based on nano colloidal gold particles, and relates to the technical field of fracturing tracing. The nano colloidal gold particles prepared through special design serve as a tracer agent to be injected into a stratum along with fracturing fluid, a flowback signal is tested, and the fracturing tracing monitoring task which cannot be achieved by a common tracer agent at present is completed. The method comprises the implementation steps of tracer agent injection, flowback fluid sampling, tracer agent signal detection, curve drawing, fracture development degree evaluation and the like, and data support can be provided for fracture volume inversion, fracture complexity and fracture effect evaluation through implementation of the method. The method has the characteristics of rapid detection, accurate quantitative analysis, high detection sensitivity, accurate data, no background interference and the like, and has unique advantages in the field of fracturing tracing monitoring.

Description

Technical Field

[0001] This invention relates to the field of fracturing tracing technology, specifically to a fracturing tracing and monitoring method based on nano-colloidal gold particles. Background Technology

[0002] In oil and gas extraction, hydraulic fracturing technology is widely used to improve reservoir permeability and oil and gas recovery. To evaluate well connectivity and fracturing effectiveness, tracers need to be introduced into the fracturing fluid or proppant for fracturing tracer monitoring. Current technologies typically inject tracers during fracturing to monitor inter-section and inter-well connectivity, fluid production in different sections of horizontal wells, and gas production profiles. Commonly used tracers include radioactive isotopes (such as tritium water), chemical dyes (such as fluorescent dyes), trace elements (such as rare earth elements and specific transition metals), and quantum tracers. However, each tracer has certain limitations: radioactive tracers pose potential safety risks and environmental impacts, and are complex and costly to process; chemical dyes are easily affected by formation conditions (such as pH and temperature), have poor stability, and low detection sensitivity; trace elements are easily affected by background interference, which may mask the tracer signal; quantum tracers also pose certain biosafety risks, have strict detection requirements, and are costly to apply. From the perspective of fracturing tracer monitoring methods, it is difficult to achieve real-time, high-precision monitoring using these tracers, leading to inaccurate fracturing assessments. Furthermore, most methods are only used for inter-well monitoring and horizontal well oil, gas, and water production profile analysis, with limited expansion into other functions, thus restricting the application scope of fracturing tracer monitoring technology. For example, invention patent CN109138989A discloses a tracer monitoring technology method for analyzing reservoir heterogeneity and determining injection-production connectivity; invention patent CN117662126A discloses a method for monitoring fracture closure pressure and production profile based on quantum tracers. Most published patents are only used for determining inter-well connectivity and monitoring horizontal well production profiles, with relatively simple application methods, lacking deeper tracer monitoring capabilities for fracturing fractures and fracture network modification effects.

[0003] In recent years, nanomaterials have shown potential in the field of tracer applications due to their unique physicochemical properties. Colloidal gold nanoparticles, with their advantages of high stability, tunable optical properties (such as surface plasmon resonance), and ease of functionalization, have been widely used in biomedical tracer applications. Invention patent CN118455540 B discloses a method for preparing nanoscale, highly stable colloidal gold, which is used as a marker in immunochromatography. Invention patent CN116678875 B discloses an alcohol content detection method and device based on a gold nanoparticle self-assembly system. Currently, a systematic method for combining colloidal gold nanoparticles with fracturing tracer monitoring is still lacking. Summary of the Invention

[0004] To address at least one of the aforementioned problems, this invention provides a fracturing tracer monitoring method based on nano-colloidal gold particles.

[0005] The technical solution of this invention to solve the above problems is as follows: a fracturing tracer monitoring method based on nano-colloidal gold particles, comprising the following steps: S1. Take positively charged colloidal gold particles and negatively charged colloidal gold particles with a mass ratio of 1:1 as composite tracers and add them to the fracturing fluid, which is then injected into the reservoir along with the fracturing fluid. S2. During the flowback stage, samples of the fracturing flowback fluid are taken at a preset frequency, and the concentrations of positively charged colloidal gold particles and negatively charged colloidal gold particles are detected to obtain the detection values. S3. Based on the detected values, plot the detected values ​​with respect to time. C 0 (t)-t Curve, based on the aforementioned C 0 (t)-t The curves yielded the areas A_m and A_s covered by different colloidal gold particle signal curves. The development of hydraulic fracturing fractures was assessed based on these two area values. In the formula, W represents the degree of development of secondary / microcracks; A_m represents the negative potential colloidal gold particles in... C 0 (t)- t The coverage area on the curve; A_s represents the positive potential colloidal gold particles in C 0 (t)-t The area covered by the curve.

[0006] In one embodiment of the present invention, in S1, the positively charged colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a silver shell, and a surface loaded with quaternary ammonium groups or amino groups; the negatively charged colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a lead shell, and a surface loaded with one of carboxyl groups, phosphate groups, or thiol groups.

[0007] In one embodiment of the present invention, in S1, the positively charged colloidal gold particles have a zeta potential of +20mV and a particle size of 50nm, and the negatively charged colloidal gold particles have a zeta potential of -35mV and a particle size of 50nm; or, the positively charged colloidal gold particles have a zeta potential of +10mV and a particle size of 30nm, and the negatively charged colloidal gold particles have a zeta potential of -30mV and a particle size of 30nm.

[0008] In one embodiment of the present invention, in S1, the concentration of the composite tracer in the fracturing fluid is at least 5 times the lower detection limit of the composite tracer.

[0009] In one embodiment of the present invention, in S2, the preset frequency is as follows: when the fracturing flowback fluid exceeds the volume of two wellbore fluids, samples are taken every 15-30 minutes for the first 2 hours; from the 2nd to the 12th hour, samples are taken every 1-2 hours; from the 12th to the 48th hour, samples are taken at logarithmic intervals, wherein the logarithmic intervals are set to: 12h, 15h, 19h, 24h, 30h, 36h, 42h, and 48h; after the 48th hour, samples are taken every 6 hours.

[0010] In one embodiment of the present invention, in step S2, the concentrations of positively charged colloidal gold particles and negatively charged colloidal gold particles are detected using one of ultraviolet-visible spectroscopy, enhanced Raman scattering, or inductively coupled plasma mass spectrometry.

[0011] In one embodiment of the present invention, in S3, the evaluation criterion is: W <0.3, fracturing is mainly characterized by the main fracture; 0.3 < W <0.5, indicating moderate formation of primary joints and secondary / micro-cracks; W >0.5 indicates the formation of numerous secondary / microcracks and a complex fracture network.

[0012] The beneficial effects of this invention are as follows: 1. This invention introduces highly stable and functionally designable colloidal gold nanoparticles as a fracturing tracer, overcoming the bottlenecks of traditional tracers that are prone to degradation, have weak signals, and suffer from significant interference in high-temperature and high-salt environments, thus significantly improving the accuracy, sensitivity, and adaptability of tracer monitoring. Compared with conventional chemical tracers and quantum dot tracers, colloidal gold nanoparticles are non-radioactive, non-biotoxic, and environmentally friendly.

[0013] 2. This invention employs a dual-potential (positive and negative) colloidal gold particle combination strategy, combined with backflow curve difference analysis, to achieve quantitative estimation of the development degree of secondary / micro-fractures in fracturing. This provides a new physical index and calculation model for fracturing effect evaluation, and can be used to optimize fracturing fluid, construction parameters, etc., which is not addressed in the fracture structure identification of existing tracing technologies.

[0014] 3. The method of this invention is applicable to unconventional reservoirs such as shale oil and gas, tight oil and gas, and coalbed methane. It is compatible with various fracturing systems such as slickwater, gel, foam, and CO2 enhancement, and has broad reservoir adaptability and process compatibility. It provides a new and unique fracturing tracer monitoring technology option for the efficient development of unconventional oil and gas resources. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the method of an embodiment of the present invention.

[0016] Figure 2 Embodiments of the present invention C 0 (t)-t Line graph.

[0017] Figure 3 This is a demonstration of area calculation performed in an embodiment of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be clearly and completely described below with reference to examples. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments.

[0019] Unless otherwise specified, all pharmaceutical agents used in the following examples are conventional commercial products.

[0020] Unless otherwise specified, all operations used in the following embodiments are conventional operations in the art.

[0021] like Figure 1 As shown, a fracturing tracer monitoring method based on colloidal gold nanoparticles includes the following steps: S1. Take positively charged colloidal gold particles and negatively charged colloidal gold particles with a mass ratio of 1:1 as composite tracers and add them to the fracturing fluid, which is then injected into the reservoir along with the fracturing fluid. In this step, the positively charged colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a silver shell, and a surface loaded with quaternary ammonium groups or amino groups. Preferably, this is a combination of a quaternizing agent and PEG-thiol (molecular weight 2000-5000). Specifically, the quaternary ammonium group can be selected from one of (3-mercaptopropyl)trimethoxysilane-N,N,N-trimethylammonium chloride, hexadecyltrimethylammonium bromide, or (3-mercaptopropyl)-N,N,N-trimethylammonium chloride. The negatively charged colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a lead shell, and a surface loaded with one of carboxyl, phosphate, or thiol groups. Preferably, this is a combination of a carboxylating agent and PEG-thiol (molecular weight 2000-5000). Specifically, the carboxylating agent is one of 11-mercaptoundecanoic acid, 16-mercaptohexadecanoic acid, 3-mercaptopropionic acid, or N-hydroxysuccinimide.

[0022] For core-shell colloidal gold particles, a size of 10-100 nm and a zeta potential maintained between -35 mV and +20 mV are sufficient. Under these conditions, the obtained core-shell colloidal gold particles can be used in this invention. In particular, after extensive experimentation, the inventors discovered that using the following two combinations of positively and negatively potentiated colloidal gold particles yields better results: the positively potentiated colloidal gold particles have a zeta potential of +20 mV and a particle size of 50 nm, while the negatively potentiated colloidal gold particles have a zeta potential of -35 mV and a particle size of 50 nm; or, the positively potentiated colloidal gold particles have a zeta potential of +10 mV and a particle size of 30 nm, while the negatively potentiated colloidal gold particles have a zeta potential of -30 mV and a particle size of 30 nm.

[0023] The core-shell colloidal gold particles described above can be prepared using existing conventional methods, and as long as the above requirements are met, they can be applied to this invention. However, to facilitate further understanding of this invention by those skilled in the art, a preparation method is given below. It should be understood by those skilled in the art that this preparation method should not be considered a limitation of this invention.

[0024] Preparation of colloidal gold: By mass, add 2-3 parts tetrachloroauric acid tetrahydrate and 57-68 parts deionized water to the reaction vessel, heat to boiling, then add 30-40 parts of 10wt% sodium citrate solution, stir, and continue to react for 15-30 minutes to obtain colloidal gold seed crystals.

[0025] Preparation of negative potential colloidal gold particles: By mass, take 59-65 parts of the above colloidal gold seed solution, add 12-14 parts of silver nitrate (85 mg / L) and 10-12 parts of sodium citrate solution (25 mg / L) at room temperature, and react in the dark for 30-60 min to obtain Au-Ag particle solution; add 10-12 parts of PEG-thiol (2-5 g / L) to the above solution, stir continuously for 1.5-2 h, then add 2.5-3 parts of carboxylating agent (2 g / L), and continue stirring for 60-80 min; after the reaction is complete, filter out large particles with a 0.22 μm filter membrane, and then centrifuge at 12000 rpm for 20-30 min to obtain the final product.

[0026] Preparation of positively potentiated colloidal gold particles: Take 59-65 parts by mass of the above colloidal gold seed solution, add 10-12 parts of Na2PdCl4 with a concentration of 147 mg / L and 10-13 parts of sodium citrate solution with a concentration of 25 mg / L at room temperature, and react in the dark for 50-70 min to obtain Au-Pb particle solution; add 12-15 parts of PEG-thiol with a concentration of 2-5 g / L to the above solution, stir continuously for 1.5-2 h, then add 2-3 parts of quaternizing agent with a concentration of 3 g / L, and continue stirring for 60-90 min; after the reaction is completed, filter out large particles with a 0.22 μm filter membrane, and then centrifuge at 12000 rpm for 20-30 min to obtain the final product.

[0027] The reason for choosing this combination in this invention is based on the easy detection of colloidal gold and the special properties of the composite tracer: the composite tracer is not easily adsorbed by the fracture in large-sized primary fractures; while in secondary fractures or micro-fractures generated by fracturing, negatively charged colloidal gold particles are basically not adsorbed due to charge repulsion, and can therefore be smoothly discharged; while positively charged colloidal gold particles are adsorbed due to charge attraction, resulting in a large difference in the concentration of the two types of colloidal gold particles in the fracturing flowback fluid. Based on this, the area ratio of secondary fractures or micro-fractures can be obtained.

[0028] Meanwhile, to facilitate subsequent detection, the concentration of the composite tracer should not be too low. Its concentration in the fracturing fluid should be at least 5 times the lower limit of detection of the composite tracer, such as 5 times or 10 times. Of course, it should not be too high either, as this will lead to a rapid increase in costs.

[0029] S2. During the flowback stage, samples of the fracturing flowback fluid are taken at a preset frequency, and the concentrations of positively charged colloidal gold particles and negatively charged colloidal gold particles are detected to obtain the detection values. Once the fracturing flowback fluid exceeds the volume of two wellbore fluids, samples are taken every 15-30 minutes for the first 2 hours; every 1-2 hours for the 2nd-12th hours; and at logarithmic intervals for the 12th-48th hours, with the logarithmic intervals set as follows: 12h, 15h, 19h, 24h, 30h, 36h, 42h, and 48h. After the 48th hour, samples are taken every 6 hours.

[0030] In this embodiment of the invention, the reason for sampling according to the above method is to take into account the component changes of the fracturing flowback fluid at different flowback stages: the fracturing flowback fluid has the characteristics of rapid information changes in the early stage and relatively stable tail fluid in the later stage. By using a logarithmic-step mixed sampling frequency of "dense at the beginning and sparse at the end", more than 90% of the change information can be compressed into 10% of the sample quantity, so as not to miss key data or waste analysis resources.

[0031] When detecting their concentration, the appropriate detection method can be selected according to the reagents: when testing on-site, the relatively low-requirement ultraviolet-visible spectroscopy detection method can be selected, which can quickly measure the concentration of the two tracers in the fracturing flowback fluid; in the laboratory, the more accurate enhanced Raman scattering method or inductively coupled plasma method can be selected, which has higher accuracy.

[0032] S3. Based on the detected values, plot the detected values ​​with respect to time. C 0 (t)-t Curve, based on the aforementioned C 0 (t)-t The curves yielded the areas A_m and A_s covered by different colloidal gold particle signal curves. The development of hydraulic fracturing fractures was assessed based on these two area values. In the formula, W represents the degree of development of secondary / microcracks; A_m represents the negative potential colloidal gold particles in... C 0 (t)- t The coverage area on the curve; A_s represents the positive potential colloidal gold particles in C 0 (t)-t The area covered by the curve.

[0033] After sampling and testing S2, a plot is first drawn based on the test results and the sampling time of the sample. C 0 (t)-t curve, C 0 (t) This represents the concentration of the tracer at time t. Subsequently, the coverage area of ​​negatively charged colloidal gold particles and positively charged colloidal gold particles on the curve was measured respectively. Based on the above formula, the fracturing fracture was evaluated. During the evaluation process, based on the inventors' extensive experimental findings, the evaluation criteria were set as follows: W <0.3, fracturing is mainly characterized by the main fracture; 0.3 < W <0.5, indicating moderate formation of primary joints and secondary / micro-cracks; W >0.5 indicates the formation of numerous secondary / microcracks and a complex fracture network.

[0034] To further illustrate the effects of the embodiments of the present invention, specific test examples are given below.

[0035] First, a composite tracer is prepared, and the preparation method is shown below: Preparation of colloidal gold: By mass, 2.5 parts tetrachloroauric acid tetrahydrate and 62.5 parts deionized water were added to the reaction vessel, heated to boiling, and then 35 parts of 10wt% sodium citrate solution were added. After stirring, the reaction was continued for 25 minutes to obtain colloidal gold seed crystals.

[0036] Preparation of negatively potentiated colloidal gold particles: 60 parts by mass of the above colloidal gold seed solution were added to 13 parts of 85 mg / L silver nitrate solution and 12 parts of 25 mg / L sodium citrate solution at room temperature. The mixture was reacted in the dark for 60 min to obtain the Au-Ag particle solution. 12 parts of 2 g / L PEG-thiol were added to the aforementioned solution, and the mixture was stirred continuously for 2 h. Then, 3 parts of 2 g / L 11-mercaptoundecanoic acid were added, and the mixture was stirred for another 60 min. After the reaction was complete, large particles were filtered out using a 0.22 μm filter membrane, and the particles were then centrifuged at 12000 rpm for 20 min to obtain the final product. These negatively potentiated colloidal gold particles were stored in a 0.06 g / L sodium chloride solution at 4 °C. The measured particle size was 30 nm, and the zeta potential was -30 mV.

[0037] Preparation of positively potentiated colloidal gold particles: 64 parts by mass of the above colloidal gold seed solution were added to 10 parts of 147 mg / L Na₂PdCl₄ and 11 parts of 25 mg / L sodium citrate solution at room temperature. The reaction was carried out in the dark for 70 min to obtain Au-Pb particle solution. 12 parts of 2 g / L PEG-thiol were added to the above solution, and the mixture was stirred continuously for 2 h. Then, 3 parts of 3 g / L quaternizing reagent were added, and the mixture was stirred for another 90 min. After the reaction was complete, large particles were filtered out using a 0.22 μm filter membrane, and the particles were then centrifuged at 12000 rpm for 20 min to obtain the final product. These positively potentiated colloidal gold particles were stored in a 0.06 g / L sodium chloride solution at 4 °C. The measured particle size was 30 nm, and the zeta potential was +20 mV.

[0038] Taking a deep coal and rock vertical well in the Ordos Basin as an example, its well depth is 2850m, reservoir temperature is 85℃, and formation water salinity is 16.3×10⁻⁶. 4 mg·L -1 The zeta potential on the rock surface is -30 mV. It is proposed to use nano-colloidal gold particles as a tracer for fracturing monitoring in this well.

[0039] According to the fracturing operation design, the fluid volume required for the operation is 2500m³. 3 The detection limit of the equipment for colloidal gold is 0.5 μg / L. During on-site injection, 12.5 g of the above-mentioned negative potential colloidal gold particles and 12.5 g of positive potential colloidal gold particles are added to the fracturing fluid. The injection timing is during the entire sand-carrying fluid stage of fracturing construction.

[0040] During the fracturing flowback process, the fracturing flowback fluid was sampled and tested according to the method of this embodiment of the invention, and the final results are shown in Table 1.

[0041] Table 1. Sampling Time and Test Results In Table 1, G1 represents the detection concentration of negatively charged colloidal gold particles in the fracturing flowback fluid, and G2 represents the detection concentration of positively charged colloidal gold particles in the fracturing flowback fluid.

[0042] Subsequently, according to the method of the embodiments of the present invention, a system is established. C 0 (t)-t Curves, such as Figure 2 As shown in the figure, the peak occurrence time is 10 h for G1 and 9.5 h for G2; the peak concentration C_max is 4.913 μg / L for G1 and 3.68 μg / L for G2.

[0043] Subsequently according to C 0 (t)-t Calculate the areas of curves G1 and G2, such as... Figure 3 As shown, the final values ​​are: A_m = 5.3 × 10³ (dimensionless) and A_s = 3.1 × 10³ (dimensionless). Based on the formula, W = 41.51%, indicating a moderate level of primary fracture and secondary / microfracture formation. According to the reservoir microseismic-CT inversion, the calculation results of this invention are the same as the measured inversion results, demonstrating that the method of this embodiment has high accuracy.

[0044] The present invention has been disclosed above with preferred embodiments. However, those skilled in the art should understand that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Further improvements can be made without departing from the principles of the invention, and these improvements should also be considered as protections of the present invention.

Claims

1. A fracturing tracer monitoring method based on nanocolloidal gold particles, characterized in that, The method comprises the following steps: S1, taking positive potential colloidal gold particles and negative potential colloidal gold particles with a mass ratio of 1:1 as a composite tracer and adding them to the fracturing fluid, and injecting them into the reservoir with the fracturing fluid; S2, during the flowback stage, sampling the fracturing flowback fluid at a preset frequency, and detecting the concentrations of the positive potential colloidal gold particles and the negative potential colloidal gold particles to obtain detection values; S3, based on the detection value, drawing the detection value about time C 0 (t)-t curve, based on the foregoing C 0 (t)-t The area A_m, A_s covered by different colloidal gold particle signal curves is obtained based on the foregoing, and the fracture development condition is evaluated based on the two area values: , wherein W represents the secondary / micro-fracture development degree value; A_m represents the covered area of the negative potential colloidal gold particles on the C 0 (t)-t curve; and A_s represents the covered area of the positive potential colloidal gold particles on the C 0 (t)-t curve.

2. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1, characterized in that, In S1, the positive potential colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a silver shell, and a surface loaded with quaternary ammonium groups or amino groups; and the negative potential colloidal gold particles refer to core-shell colloidal gold particles with a gold core, a lead shell, and a surface loaded with one of carboxyl groups, phosphoric acid groups, and mercapto groups.

3. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1 or 2, characterized in that, In S1, the Zeta potential of the positive potential colloidal gold particles is +20 mV, and the particle size is 50 nm; the Zeta potential of the negative potential colloidal gold particles is -35 mV, and the particle size is 50 nm; or, the Zeta potential of the positive potential colloidal gold particles is +10 mV, and the particle size is 30 nm; the Zeta potential of the negative potential colloidal gold particles is -30 mV, and the particle size is 30 nm.

4. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1, characterized in that, In S1, the concentration of the composite tracer in the fracturing fluid is at least 5 times the lower limit of composite tracer detection.

5. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1, characterized in that, In S2, the preset frequency is as follows: when the fracturing flowback fluid exceeds 2 wellbore fluid volumes, sample every 15-30 min in the first 2 h; sample every 1-2 h in the 2nd-12th hour; in the 12th-48th hour, sample at logarithmic intervals, and the logarithmic intervals are set to be 12 h, 15 h, 19 h, 24 h, 30 h, 36 h, 42 h, and 48 h; and after the 48th hour, sample every 6 h.

6. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1, characterized in that, In S2, one of ultraviolet-visible spectroscopy detection, enhanced Raman scattering, and inductively coupled plasma mass spectrometry is used to detect the concentrations of the positive potential colloidal gold particles and the negative potential colloidal gold particles.

7. The nanocolloidal gold particle-based fracturing tracer monitoring method according to claim 1, characterized in that, In S3, the evaluation criteria are: W <0.3, fracturing is mainly in the main fracture; 0.3 W <0.5, main fracture, secondary / micro-fracture formation is moderate; W > 0.5, secondary / micro-fracture formation is multiple, and the fracture network is complex.

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